KR102259633B1 - Thermoplastic polyurethane particles and method for preparing the same - Google Patents

Abstract

The present invention provides thermoplastic polyurethane particles formed in a continuous matrix phase from a thermoplastic polyurethane resin and having a particle diameter of 200 to 500 μm. The thermoplastic polyurethane particles are cooled 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) A peak of the crystallization temperature (T _{cc ) appears.} The thermoplastic polyurethane particles have a compressibility of 10 to 20%.

Description

Thermoplastic polyurethane particles and manufacturing method thereof

The present invention relates to a thermoplastic polyurethane particle and a method for producing the same, and more particularly, to a thermoplastic polyurethane particle having a particle diameter of 200 to 500 μm and a method for producing the same.

Thermoplastic polyurethane particles are used in various industrial fields such as cosmetics, fillers for paints or coatings, hot melt adhesives, heat-molded products, and polymerized toners. In particular, the thermoplastic polyurethane particles may be applied to an instrument panel (IP) or a door trim skin among interior materials for automobiles. The instrument panel or door trim skin is manufactured through a Powder Slush Molding (PSM) process.

The powder slush molding process consists of the following four steps. In the first step, after filling the powder box with particles, the mold heated to 200 to 300° C. with the desired three-dimensional formation is fastened. In the second step, the powder box is rotated so that the particles adhere to the mold and then melt to form the skin. In the third step, the mold is demolded in the powder box and cooled. In the fourth step, the polyurethane skin formed from the mold is taken out.

In order to properly utilize the thermoplastic polyurethane particles in the powder slush molding process, particle properties such as a suitable particle size are basically required. In particular, the second step of the powder slush molding process is an important step in determining the quality of the molded article. The better the compression, the better the flowability in the particle state, the less pin-holes occur, and the quality of the molded product can be improved.

As a method for producing the thermoplastic polyurethane particles, a pulverization method typified 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 formed by mixing 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, there is a problem in that it is difficult to ensure particle uniformity of the manufactured thermoplastic polyurethane 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 raw material of the thermoplastic polyurethane resin, 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 is a problem that other components such as a solvent may be detected as impurities in addition to the thermoplastic resin particles. Due to the above-described problems, when the thermoplastic polyurethane particles are manufactured by the conventional method, it is impossible to prepare the thermoplastic polyurethane particles having suitable physical properties that can be used in a powder slush molding process and the like.

Therefore, there is a need in the art for thermoplastic polyurethane particles having improved particle properties to be suitable for a powder slush molding process.

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

The present invention is by extruding a thermoplastic polyurethane resin, atomizing the extruded resin by contacting it with air, and cooling it to produce thermoplastic polyurethane particles, thereby effectively preventing the incorporation of impurities except for the resin component in the particles, and An object of the present invention is to provide thermoplastic polyurethane particles having properties suitable for use in a powder slush molding process that could not be obtained by this method.

According to a first aspect of the present invention,

The present invention provides a thermoplastic polyurethane resin formed in a continuous matrix phase from a thermoplastic polyurethane resin and having a particle diameter of 200 to 500 μm.

_{In one embodiment of the present invention, the thermoplastic polyurethane particles have a glass transition temperature (T g} ) and a melting point in a DSC curve derived from a temperature rise analysis of 10 ° C / min by Differential Scanning Calorimetry (DSC) A peak of the cold crystallization temperature (T _cc ) appears at a temperature between (T _{m ).}

In one embodiment of the present invention, the thermoplastic polyurethane particles have an aspect ratio of 1.00 or more and less than 1.05, and a sphericity of 0.95 to 1.00.

In one embodiment of the present invention, the thermoplastic polyurethane particles have a compressibility of 10 to 20%.

According to a second aspect of the invention,

The present invention comprises the steps of supplying a thermoplastic polyurethane resin to the extruder and extruding; supplying the extruded thermoplastic polyurethane resin and air to the nozzle, contacting the thermoplastic polyurethane resin with air to make the thermoplastic polyurethane resin particles, and then discharging the granulated thermoplastic polyurethane resin; and supplying the discharged thermoplastic polyurethane particles to a cooler to cool the thermoplastic polyurethane particles, and then obtaining the cooled thermoplastic polyurethane particles.

The thermoplastic polyurethane particles according to the present invention are produced by atomizing the thermoplastic polyurethane resin by contacting it with air after extrusion, so that impurities such as solvents do not exist in the particles. In addition, the particles of the present invention exhibit a uniform particle distribution while having a large diameter of 200 to 500 μm, and have a high degree of compression of 10 to 20%.

When the thermoplastic polyurethane particles having the above-described physical properties are used in a powder slush molding process, the occurrence of defective products can be minimized and the quality of the molded product can be improved.

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

The specific examples provided according to the present invention can all be achieved by the following description. The following description is to be understood as describing preferred embodiments of the present invention, and it is to be understood that 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 thermoplastic polyurethane particles having properties suitable for use in a powder slush molding process that could not be obtained by a conventional particle production method. Hereinafter, the thermoplastic polyurethane particles according to the present invention will be described in detail.

Thermoplastic polyurethane particles

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

The thermoplastic polyurethane particles according to the present invention have a particle diameter of 200 to 500㎛. In the case of the thermoplastic polyurethane particles having a particle diameter of less than 200 μm or more than 500 μm, it is generally not applicable in the powder slush molding process because it acts as a factor hindering the flowability of the particles during the powder slush molding sheet molding. The particle diameter of the above size corresponds to a large diameter compared to general fine particles. The larger the particle diameter, the more difficult it is to control the shape of the particle during the manufacturing process. However, in the present invention, it is easy to control the shape of the particles during the manufacturing process, so that they are large-diameter particles and have a high degree of sphericity, and the particle size distribution is also relatively uniform.

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 roundness to 1, the closer the shape of the particle is interpreted as spherical. The aspect ratio is calculated by Equation 1 below.

[Calculation 1]

Aspect ratio = major axis/minor axis

In addition, the sphericity is calculated by the following formula (2).

[Calculation 2]

Roundness=4×area/(π×long axis^2)

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

According to one embodiment of the present invention, the thermoplastic polyurethane 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, 0.95 to 1.00, more specifically 0.98 to 1.00. It may have a sphericity. When the shape of the thermoplastic polyurethane particles satisfies the above-mentioned aspect ratio and sphericity range, the flowability and uniformity of the thermoplastic polyurethane particles increase, so that handling of the particles is easy in applying the powder slush molding process, and the particles Products manufactured through the powder slush molding process using

Numerical values according to Equations 1 and 2 above can be measured by image processing the image of the thermoplastic polyurethane particles using ImageJ (National Institutes of Health (NIH)) - converting to a binary image and quantifying the degree of spheroidization of individual particles - It is possible.

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

The particles formed into a continuous matrix from the thermoplastic polyurethane resin have high purity because impurities are not incorporated in the process of manufacturing the particles. Here, "impurities" means components other than the thermoplastic polyurethane that may be incorporated during the manufacture of the particles. Exemplary impurities include a solvent for dispersing the thermoplastic polyurethane 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 thermoplastic polyurethane 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 thermoplastic polyurethane particles are 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). The peak of the cold crystallization temperature (T _cc ) appears at the temperature of . Thermoplastic polyurethane particles are spherical solid particles at room temperature. When the temperature rise analysis of these particles using a differential scanning calorimeter, the thermoplastic polyurethane particles at _{a temperature between the glass transition temperature (T g} ) and the melting point (T _m ) The peak of the cold crystallization temperature (T _{cc ) appears and} , which means that the thermoplastic polyurethane particles have the property of generating heat before melting. Peak of cold crystallization temperature (T _cc) used herein refers to only the peak of cold crystallization temperature (T _cc) appears when the first temperature elevation analysis of the thermoplastic polymer particles, and the internal structure of the particles by the subsequent repeated temperature rise modification As The peak of the cold crystallization temperature (T _cc ) that may occur accordingly is not included in the particle properties described herein. If it has a peak of the cold crystallization temperature (T _cc ) by repeated temperature increase, energy for repeated temperature increase is consumed, so it does not have an advantage in terms of energy during particle processing. 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 this section, 0% is the glass transition temperature (T _g ), and 100% is the melting point (T _m ). Further, according to the DSC curve, the difference (ΔH1-ΔH2) between the endothermic amount (ΔH1) and the heating value (ΔH2) of the thermoplastic polymer particles may be 3 to 100 J/g. Due to these characteristics, when the powder slush molding process is performed using the thermoplastic polyurethane particles, it is possible to obtain an advantage that can be processed at a low temperature compared to the processing temperature of the same type of thermoplastic polyurethane particles in the prior art.

The thermoplastic polyurethane particles of the present invention have a high degree of compression compared to conventional thermoplastic polyurethane particles. The degree of compressibility may be calculated by Equation 3 below. According to one embodiment of the present invention, the thermoplastic polyurethane particles have a degree of compression of 10 to 20%.

[Formula 3]

Compressibility = (P-A)/P×100

In Equation 3, P denotes compressed bulk density, and A denotes relaxed bulk density.

As described above, since the thermoplastic polyurethane particles according to the present invention have good flowability, the voids between the particles can be filled well, and accordingly, the degree of compression is higher than that of the thermoplastic polyurethane particles produced by other manufacturing methods. maintain. The degree of compression of the thermoplastic polyurethane particles can affect the quality of the molded article when manufacturing the molded article through the particles, and when using the thermoplastic polyurethane particles having a certain degree of compression as in the present invention, the occurrence of pinholes in the molded article is reduced and the molded article the quality is increased According to one embodiment of the present invention, the thermoplastic polyurethane particles have a compressed bulk density ^{of 0.45 to 0.5 g/cm 3 .} The compressed bulk density has a lower numerical value than the thermoplastic polyurethane particles produced by other manufacturing methods, which means that the thermoplastic polyurethane particles according to the present invention having a high sphericity and a uniform particle size distribution are constant between the particles even after compression. Because it can have a pore size.

The thermoplastic polyurethane particles according to the present invention have a flow time of 10 to 20 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. The thermoplastic polyurethane particles according to the present invention can maintain an excellent level in terms of flow time, so that it is easy to handle the particles when applying the particles.

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

Method for producing thermoplastic polyurethane particles

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

In order to manufacture the thermoplastic polyurethane particles according to the present invention, the thermoplastic polyurethane resin as a raw material is first supplied to an extruder and extruded. By extruding the thermoplastic polyurethane resin, the thermoplastic polyurethane resin has properties suitable for particle processing in the nozzle. The thermoplastic polyurethane 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 thermoplastic polyurethane resin is supplied controls physical properties such as viscosity of the thermoplastic polyurethane resin by heating and pressurizing the thermoplastic polyurethane 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 ℃, preferably 170 to 270 ℃, more preferably 200 to 250 ℃. When the internal temperature of the extruder is less than 150° C., the viscosity of the thermoplastic polyurethane resin is high, so that it is not suitable for granulation in the nozzle, and the flowability of the thermoplastic polyurethane 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 thermoplastic polyurethane resin is high, so that efficient extrusion is possible, but it is difficult to control fine physical properties when the thermoplastic polyurethane resin is granulated in the nozzle.

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

The extruded thermoplastic polyurethane resin in the extruder is fed to the nozzle. Along with the thermoplastic polyurethane resin, air is also supplied to the nozzle. The air contacts the thermoplastic polyurethane resin in the nozzle to granulate the thermoplastic polyurethane resin. In order to properly maintain the properties of the thermoplastic polyurethane 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 ℃. If the temperature of the air is less than 250 ° C. or more than 450 ° C., when the thermoplastic polyurethane particles are produced from the thermoplastic polyurethane 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 °C, excessive heat is supplied to the contact surface with the air, which may cause the decomposition of the thermoplastic polyurethane on the surface of the particles.

The thermoplastic polyurethane resin and air supplied to the nozzle are set so that the thermoplastic polyurethane particles can have an appropriate size and shape, and the formed particles can be evenly dispersed. Figure 3 shows a cross-sectional view of the nozzle discharge part, the supply position of the thermoplastic polyurethane 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 thermoplastic polyurethane resin and air is circular. The air is supplied through a first air stream 40 supplied to the center of the circle and a second air stream 20 supplied to the outer part of the circle, and the thermoplastic polyurethane resin is a first air stream 40 . and the second air stream 20 is supplied. Each supply stream (thermoplastic polyurethane resin stream 30, first air stream 40, and second air stream 20) from when the thermoplastic polyurethane resin and air are supplied to the inlet part of the nozzle to just before the outlet part of the nozzle. ) are separated by the structure inside the nozzle. Just before the discharge portion of the nozzle, the thermoplastic polyurethane resin flow and the second air flow are combined to bring the thermoplastic polyurethane resin into contact with the air, whereby the thermoplastic polyurethane resin is granulated. In contrast, the first air stream is separated from the thermoplastic polyurethane resin stream and the second air stream by the nozzle internal structure until the thermoplastic polyurethane resin and air are discharged from the nozzle. The first air flow prevents the particles of the thermoplastic polyurethane resin granulated by the second air flow from sticking at the discharge part of the nozzle, and the role of evenly dispersing the discharged particles before being supplied to the cooler after discharge from the nozzle is do.

All of the thermoplastic polyurethane 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 thermoplastic polyurethane 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, preferably 30 to 240 m ³ /hr, more preferably 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 thermoplastic polyurethane resin is granulated by the second air flow, and the ratio of the thermoplastic polyurethane resin and the second air flow as well as the temperature of the second air flow may determine the physical properties of the particles. According to an embodiment of the present invention, the cross-sectional area ratio of the thermoplastic polyurethane resin and the second air flow based on the cross-section of the discharge part of the nozzle may be 2:1 to 4:1, preferably 2.5:1 to 3.5:1. have. When the ratio of the thermoplastic polyurethane resin and the second air flow is adjusted within the above range, it is possible to manufacture thermoplastic polyurethane particles of an appropriate size and shape with high utility in the powder slush molding process.

Since the thermoplastic polyurethane resin is granulated in the nozzle, the inside of the nozzle is adjusted to a temperature suitable for the thermoplastic polyurethane resin to be granulated. Since the rapid increase in temperature may change the structure of the thermoplastic polyurethane, 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 to the thermoplastic polyurethane resin is not transmitted, and if the internal temperature of the nozzle is more than 350 ℃, excessive heat is supplied to the thermoplastic polyurethane resin, The structure of urethane can be changed.

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 thermoplastic polyurethane, and specifically, it may be determined according to Equation 4 below.

[Formula 4]

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

Here, A may be 0.5 to 1.5, preferably 0.65 to 1.35, more preferably 0.8 to 1.2. If A is less than 0.5, it is difficult to expect improvement of the external and internal physical properties of the particles according to the temperature increase of the distal end of the nozzle, and if A is greater than 1.5, the heat substantially transferred to the thermoplastic polyurethane at the distal end of the nozzle is excessively increased Thus, the structure of the thermoplastic polyurethane may be deformed. 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 thermoplastic polyurethane of the present invention has a glass transition temperature of -40 to -20 ℃, a thermoplastic polyurethane 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 thermoplastic polyurethane 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 thermoplastic polyurethane particles are primarily cooled by ambient air before being supplied to the cooler. In the nozzle, not only the thermoplastic polyurethane 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, preferably 150 to 400 mm, more preferably 200 to 300 mm spaced apart from the nozzle. 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. When the separation distance is longer than the distance, the amount of cooling by the surrounding air is large and rapid cooling by the cooling chamber This cannot be done. In addition, the injection angle when discharging the thermoplastic polyurethane particles from the nozzle may be 10 to 60 °, when discharging the thermoplastic polyurethane particles at the angle, the effect due to the separation of the nozzle and the cooler can be doubled.

The cooler may cool the thermoplastic polyurethane particles by supplying low-temperature air into the cooler and bringing the air into contact with the thermoplastic polyurethane particles. The low-temperature air forms a rotating airflow in the cooler, and the residence time of the thermoplastic polyurethane 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 supply amount of the thermoplastic polyurethane particles, 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 thermoplastic polyurethane particles supplied to the cooler, the thermoplastic polyurethane particles are rapidly cooled and the internal structure of the high-temperature thermoplastic polyurethane particles can be properly maintained when discharged. When the thermoplastic polyurethane particles are actually applied for the production of products, they are reheated again. At this time, the reheated thermoplastic polyurethane has properties advantageous for processing. The thermoplastic polyurethane particles cooled by low-temperature air are cooled to 40° C. or less and discharged, and the discharged particles are collected through a cyclone or a bag filter.

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

Example

Example 1: Preparation of thermoplastic polyurethane particles according to the manufacturing method of the present invention

100% by weight of a thermoplastic polyurethane resin (Lubrizol, Pearlthane ^TM _{D91M80, Mw: about 160,000 g} /mol, glass transition temperature (T g ): about -37°C, pyrolysis temperature (T _d ): about 290°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 thermoplastic polyurethane resin has a viscosity of about 5 Pa·s, and the extruded thermoplastic polyurethane resin is heated to an internal temperature of about 300° C. and an end temperature of about 350° C. (A value according to Equation 4 is about 1.18). It was supplied to the set nozzle. 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 thermoplastic polyurethane 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 portion and the extruded thermoplastic polyurethane supplied between the air-supplied central portion and the outer portion was about 2.9:1. The thermoplastic polyurethane 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 1: Preparation of thermoplastic polyurethane particles according to the freeze grinding method

The same thermoplastic polyurethane resin as in Example 1 was supplied to 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 grinder 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.

Experimental example 1: Evaluation of particle properties

The physical properties of the particles prepared according to Example 1 and Comparative Example 1 were measured and shown in Table 1 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 )}
(%) Downtime ^{7 )}
(s) Example
One 410.3 1.02±0.01 0.99±0.01 0.418 0.487 14 14 Comparative example
One 408.5 1.44±0.34 0.71±0.21 0.491 0.526 6.7 19

1) Using ImageJ (National Institutes of Health (NIH)) at room temperature to derive the average particle diameter of the powder, which is an aggregate of particles. The long axis of each particle was taken as the particle diameter, and the number average value of each particle diameter for the aggregate of particles was taken as the average particle diameter.

2), 3) Image processing using the same device - After converting to binary image, quantifying the degree of spheronization of individual particles - The particle formation was analyzed, and the aspect ratio and sphericity were derived by Equations 1 and 2.

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 value measured 5 times)

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

6) Compressibility (%)=(P-A)/P×100, P: particle compressed bulk density, A: 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 1, the particles of Example 1 have a larger diameter and uniform particle distribution compared to the particles of Comparative Example 1. In addition, the particles of Example 1 have a high degree of sphericity compared to the particles of Comparative Example 1, whereby a constant space can be secured during compression, thereby having a low compressed bulk density. The particles of Example 1 have a low compressive bulk density and a high degree of compression, so that pinhole generation can be minimized when the particles are applied to a product. In addition, as can be seen through the short flow time, the particles of Example 1 have high fluidity, making it easy to handle and process the particles.

Experimental example 2: DSC analysis

DSC analysis of the particles prepared according to Example 1 and Comparative Example 1 is shown in Table 2 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 the endothermic value (ΔH1) and the calorific value (ΔH2) were derived from each DSC curve.

T _g (℃) T _m (℃) T _cc (℃) ΔH1-ΔH2 (J/g) Example 1 -37 136 36 5.5 Comparative Example 1 -34 140 - 10

While the thermoplastic polyurethane particles of Example 1 showed a cold crystallization temperature peak at 36° C., it was confirmed that the thermoplastic polyurethane particles of Comparative Example 1 did not exhibit such a cold crystallization temperature peak. Furthermore, in the case of Example 1, the difference between the endothermic amount (ΔH1) and the calorific value (ΔH2) is about 5.5 J/g, whereas in Comparative Example 1, the endothermic amount (ΔH1) and the calorific value (ΔH2) ) was found to be about 10 J/g. This is understood to have a relatively high calorific value because the thermoplastic polyurethane particles of Example 1 have a property of generating heat before the particles are melted due to cold crystallization.

When the thermoplastic polyurethane particles have a cold crystallization temperature peak as in Example 1, when the powder slush molding process is performed using these particles, it is possible to process at a low temperature compared to the processing temperature of the thermoplastic polyurethane particles of Comparative Example 1 can have

Comparative example 2: Preparation of thermoplastic polyurethane particles according to solvent polymerization method

An ester or ether-based polyol was added to a dimethylformamide solvent, stirred, and then diisocyanate was added to synthesize a prepolymer. Thereafter, a reactive monomolecular diol or diamine-based chain extender was added at a temperature of 80° C. to finally prepare thermoplastic polyurethane particles having a size of 400 μm.

Experimental example 3: Analysis of impurities in particles

The impurity content of the particles prepared according to Example 1 and Comparative Example 2 was analyzed and shown in Table 3 below. Specifically, the residual solvent in the particles was measured through a GC/FID apparatus (manufacturer: Agilent, model name: 7890A), and heavy metals in the particles were measured through an ICP/MS apparatus (manufacturer: Perkinelmer, model name: Nexion300). The impurity content in Table 3 below is the sum of the residual solvent content and the heavy metal content in the particles.

Impurity content (ppm) Example 1 3 Comparative Example 2 53

According to Table 3, the particles of Comparative Example 2 had a significantly higher content of impurities compared to the particles of Example 1 due to the residual solvent in the particles because a solvent was used in the preparation of the particles. In contrast, the particles of Example 1 hardly contained impurities such as residual solvent except for trace impurities introduced from the device during the production of the particles.

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: thermoplastic polyurethane resin flow
40: first air flow

Claims (13)

A method for producing thermoplastic polyurethane particles, comprising:
The manufacturing method is
(1) supplying a thermoplastic polyurethane resin to the extruder and extruding;
(2) supplying the extruded thermoplastic polyurethane resin and air to the nozzle, contacting the thermoplastic polyurethane resin with air to make the thermoplastic polyurethane resin particles, and then discharging the granulated thermoplastic polyurethane resin; and
(3) supplying the discharged thermoplastic polyurethane particles to a cooler to cool the thermoplastic polyurethane particles, and then obtaining cooled thermoplastic polyurethane particles,
In step (2), based on the cross section of the nozzle, air is supplied to the center and the outer portion, and the extruded thermoplastic polyurethane resin is supplied between the center and the outer portion to which air is supplied,
Based on the cross-section at the discharge part of the nozzle in step (2), the cross-sectional area ratio of the air supplied to the outer part and the extruded thermoplastic polyurethane resin supplied between the central part and the outer part supplied with air is 2:1 4:1,
The thermoplastic polyurethane particles are formed in a continuous matrix phase from the thermoplastic polyurethane resin, have a particle diameter of 200 to 500 μm, and have a degree of compression of 10 to 20% calculated by Equation 3 below. A method for producing particles.

[Formula 3]
Compression degree = (compressed bulk density - relaxed bulk density) / compressed bulk density x 100
The method according to claim 1,
The method for producing thermoplastic polyurethane particles, characterized in that the extruded thermoplastic polyurethane 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,
The method for producing thermoplastic polyurethane particles, characterized in that the inside of the nozzle in step (2) is maintained at 250 to 350 ℃.
The method of claim 3,
The method for producing thermoplastic polyurethane particles, characterized in that the distal end of the nozzle in step (2) is maintained at a temperature calculated by the following formula (4).

[Formula 4]
End temperature = glass transition temperature (T _g ) + (decomposition temperature (T _d ) - glass transition temperature (T _g )) × A

In Equation 4, the glass transition temperature and the decomposition temperature are values for the thermoplastic polyurethane, and A is 0.5 to 1.5.
As a thermoplastic polyurethane particle prepared by the manufacturing method according to claim 1,
Formed in a continuous matrix phase from a thermoplastic polyurethane resin,
having a particle size of 200 to 500 μm,
Thermoplastic polyurethane particles having a degree of compression of 10 to 20% calculated by Formula 3 below.

[Formula 3]
Compression degree = (compressed bulk density - relaxed bulk density) / compressed bulk density x 100
The method of claim 5,
The thermoplastic polyurethane particles, characterized in that the impurity content of the thermoplastic polyurethane particles is 50ppm or less.
The method of claim 5,
The thermoplastic polyurethane particles are cooled 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) Thermoplastic polyurethane particles, characterized in that the peak of the crystallization temperature (T _{cc ) appears.}
The method of claim 5,
The thermoplastic polyurethane particles have an aspect ratio calculated by Formula 1 below 1.00 or more and less than 1.05,
Thermoplastic polyurethane particles having a sphericity of 0.95 to 1.00 calculated by the following formula 2.

[Formula 1]
Aspect ratio = major axis/minor axis

[Calculation 2]
Roundness=4×area/(π×long axis^2)
The method of claim 5,
The thermoplastic polyurethane particles are thermoplastic polyurethane particles, characterized in that having a compressed bulk density ^{of 0.45 to 0.5 g / cm 3 .}
The method of claim 5,
The thermoplastic polyurethane particles are thermoplastic polyurethane particles, characterized in that having a flow time of 10 to 20 seconds.
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