Polypropylene resin pellets

Abstract

Provided is a polypropylene resin pellet that solves problems caused by fine powder and enables stable production during molding processing. 【Solution means】A polypropylene resin pellet containing a propylene-based polymer as a main component and satisfying the following characteristics (A1) to (A4). (A1) The MFR measured at 230 °C and a load of 2.16 kg is more than 1500 g / 10 min and 20000 g / 10 min or less. (A2) The melting peak temperature is 100 °C or higher and 170 °C or lower. (A3) For 10 randomly extracted pellets, the average value of the major diameter is 3.0 mm or more and 8.0 mm or less, and the average value of the minor diameter is 2.0 mm or more and 8.0 mm or less. (A4) For 10 randomly extracted pellets, the average value L of the major diameter av and the standard deviation L σ satisfy formula (1), and the average value S of the minor diameter av and the standard deviation S σ satisfy formula (2). L σ / L av ×100 ≤ 20.0 Formula (1) S σ / S av ×100 ≤ 20.0 Formula (2)

Description

[Technical Field]

[0001] The present invention relates to polypropylene resin pellets, and more particularly to pellets of a polypropylene resin composition having properties suitable as a raw material for meltblown nonwoven fabrics. [Background technology]

[0002] Polypropylene resin is usually distributed in the market in pellet form due to handling considerations. However, polypropylene resin with a certain melting point and high fluidity, such as that used as a raw material for meltblown nonwoven fabrics, is difficult to produce in pellet form on an industrial scale. For this reason, it is distributed in the market in powder form, also known as powder or granule (hereinafter referred to as "powder").

[0003] The aforementioned polypropylene resin powder, due to its shape, caused deterioration of the working environment due to dust and increased equipment costs for measures such as dust explosion countermeasures.

[0004] Patent documents 1 and 2 disclose that pellets are obtained by melting and kneading a propylene resin with a melting point of 125°C and an MFR of 3600 in an extruder, while patent document 3 discloses that pellets are obtained by melting and kneading a propylene resin with a melting point of 125°C and an MFR of 17000 in an extruder. However, patent documents 1 to 3 do not disclose a method for producing pellets on an industrial scale, nor do they disclose the shape of the pellets. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2011-162636 [Patent Document 2] Japanese Patent Publication No. 2012-072514 [Patent Document 3] Japanese Patent Publication No. 2016-089317 [Overview of the project]

Problems to be Solved by the Invention

[0006] As described above, the powdered polypropylene resin has caused deterioration of the working environment due to dust and an increase in equipment costs for measures against dust explosion. Also, even when the size is such that dust does not fly, problems such as unstable discharge during molding processing or entering gaps when spilling outside the extruder have occurred with the powdered polypropylene resin. On the other hand, a polypropylene resin having a melting point and high fluidity suitable as a raw material for melt blown nonwoven fabric has been difficult to pelletize. Even when such a polypropylene resin is pelletized, individual pellets are likely to fuse during production, or it is likely to be difficult to cut the resin into the shape of pellets because the melt viscosity is too low, and it has been difficult to obtain pellets with a good shape. Depending on the shape of the pellets, problems such as unstable discharge during molding processing, inability to perform molding, or instability in the size of the molded product have occurred.

[0007] In view of such a prior art situation, an object of the present invention is to provide polypropylene resin pellets that solve problems caused by powdered polypropylene resin and enable stable production during molding processing.

Means for Solving the Problems

[0008] The inventor has found that by pelletizing a polypropylene resin having characteristics suitable as a raw material for melt blown nonwoven fabric but difficult to pelletize in a predetermined shape, problems such as deterioration of the working environment due to dust and an increase in equipment costs for countermeasures against dust explosion can be solved, and further, stable production can be achieved during molding processing. That is, the present invention relates to the following [1] to [2].

[0009] [1] Polypropylene resin pellets containing a propylene-based polymer as a main component and satisfying the following characteristics (A1) to (A4). (A1) It complies with JIS K7210-1:2014, and the melt flow rate (MFR) measured at 230°C under a load of 2.16 kg is more than 1500 g / 10 min and not more than 20000 g / 10 min. (A2) The melting peak temperature in differential scanning calorimetry measurement is 100°C or higher and 170°C or lower. (A3) For 10 randomly selected pellets, the average value of the major diameter is 3.0 mm or more and 8.0 mm or less, and the average value of the minor diameter is 2.0 mm or more and 8.0 mm or less. (A4) For 10 randomly selected pellets, the average value L of the major diameter av and the standard deviation L σ satisfy Formula (1), and the average value S of the minor diameter av and the standard deviation S σ satisfy Formula (2). L σ / L av ×100≦20.0 ‥‥ Formula (1) S σ / S av ×100≦20.0 ‥‥ Formula (2) [2] The polypropylene resin pellet according to [1], comprising a propylene-based polymer polymerized by a metallocene catalyst.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide a polypropylene resin pellet that solves the problems of powdery polypropylene resin and enables stable production during molding processing.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a diagram showing the pellet forms of Comparative Example 1 and Examples 1, 2 and 3. [Figure 2] FIG. 2 is a diagram showing the pellet forms of Examples 4, 5, 6 and 7 and Comparative Example 2.

Modes for Carrying Out the Invention

[0012] Hereinafter, the polypropylene resin pellets of the present invention will be described in detail for each item. In this specification, "~" indicating a numerical range is used to mean including the numerical values described before and after it as the lower limit value and the upper limit value.

[0013] The polypropylene resin pellets of the present invention contain a propylene-based polymer as a main component and satisfy the following characteristics (A1) to (A4). (A1) The melt flow rate (MFR) measured at 230 °C and a load of 2.16 kg in accordance with JIS K7210-1:2014 is more than 1500 g / 10 min and not more than 20000 g / 10 min. (A2) The melting peak temperature in differential scanning calorimetry measurement is 100 °C or higher and 170 °C or lower. (A3) For 10 randomly extracted pellets, the average value of the major diameter is 3.0 mm or more and 8.0 mm or less, and the average value of the minor diameter is 2.0 mm or more and 8.0 mm or less. (A4) For 10 randomly extracted pellets, the average value L of the major diameter av and the standard deviation L σ satisfy Equation (1), and the average value S of the minor diameter av and the standard deviation S σ satisfy Equation (2). L σ / L av ×100 ≤ 20.0 ··· Equation (1) S σ / S av ×100 ≤ 20.0 ··· Equation (2)

[0014] The polypropylene resin pellets of the present invention have a specific high fluidity and a specific melting peak temperature, and have a predetermined shape with a specific size and standard deviation. As a result, it solves the deterioration of the working environment due to dust caused by powdered polypropylene resin and the increase in equipment costs for dust explosion countermeasures, and also enables stable discharge during molding processing, stable size of molded products, and stable production of molded products.

[0015] 1. Characteristics of Polypropylene Resin Pellets (1) Characteristic (A1) The polypropylene resin pellets of the present invention have a melt flow rate (MFR) of more than 1500 g / 10 min and 20000 g / 10 min or less, measured at 230°C and a 2.16 kg load in accordance with JIS K7210-1:2014. Since the polypropylene resin pellets of the present invention have an MFR exceeding 1500 g / 10 min, when used in a meltblown nonwoven fabric, the fiber diameter becomes sufficiently fine. Furthermore, since the MFR is 20000 g / 10 min or less, when used in a meltblown nonwoven fabric, the strength of the nonwoven fabric can be maintained. The aforementioned MFR may be 1550 g / 10 min or more, while it may be 15000 g / 10 min or less, 10000 g / 10 min or less, or 5000 g / 10 min or less.

[0016] The MFR of the polypropylene resin pellets of the present invention can be mainly adjusted by the MFR of the propylene polymer contained therein. The MFR may be adjusted by polymerizing a propylene polymer or by melt-kneading a resin composition for polypropylene resin pellet production using an organic peroxide. Examples of organic peroxides include, but are not limited to, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (trade name: Perhexa 25B, manufactured by NOF Corporation) and bis(tert-butyldioxyisopropyl)benzene (trade name: Percadox 14, manufactured by Kayaku Nurion Co., Ltd.). It is preferable to adjust the MFR using a method that does not use organic peroxides, as this reduces the likelihood of problems such as smoke generation during pellet molding.

[0017] (2) Characteristics (A2) The polypropylene resin pellets of the present invention have a melting peak temperature of 100°C or higher and 170°C or lower, as measured by differential scanning calorimeter. Since the polypropylene resin pellets of the present invention have a melting peak temperature of 100°C to 170°C, they are suitable for use in the production of polypropylene nonwoven fabrics. The melting peak temperature may be 120°C or higher, or 125°C or higher, from the viewpoint of heat resistance, and may be 166°C or lower, or 160°C or lower, from the viewpoint of thermal fusion properties. In this invention, the melting peak temperature is measured by differential scanning calorimetry (DSC). A 5.0 mg sample is taken, held at 200°C for 5 minutes, then cooled to 40°C at a rate of 10°C / min, and then heated again at a rate of 10°C / min. The peak temperature of the melting curve observed is defined as the melting peak temperature (Tm). The melting peak temperature of the polypropylene resin pellets of the present invention can be adjusted primarily by the melting peak temperature of the propylene polymer contained therein.

[0018] (3) Characteristics (A3) The polypropylene resin pellets of the present invention have an average major diameter of 3.0 mm to 8.0 mm and an average minor diameter of 2.0 mm to 8.0 mm for 10 randomly selected pellets. The polypropylene resin pellets of the present invention are easy to handle when fed into an extruder because the average length of the major axis is 3.0 mm or more and 8.0 mm or less, and the average length of the minor axis is 2.0 mm or more and 8.0 mm or less. Because the length of the major axis and minor axis are both above the lower limit, even if spilled outside the extruder, they are less likely to get into gaps, making them easier to handle. Furthermore, because the length of the major axis and minor axis are both below the upper limit, they are more likely to bite into the screw, resulting in more stable discharge. The average value of the major axis may be 7.0 mm or less, 6.0 mm or less, 5.0 mm or less, or 4.0 mm or less, and the average value of the minor axis may be 7.0 mm or less, 6.0 mm or less, 5.0 mm or less, or 4.0 mm or less. The major and minor axes are determined by placing the pellets on a horizontal surface, applying vibration to ensure stable contact with the surface, and then measuring the major and minor axes of 10 randomly selected pellets one by one using calipers. In this specification, the major axis refers to the length of the longest part of the pellet when viewed from the direction normal to the horizontal plane, and the minor axis refers to the length of the longest part of the length perpendicular to the major axis.

[0019] (4) Characteristics (A4) The polypropylene resin pellets of the present invention have an average length L of 10 randomly selected pellets. av and standard deviation L σ The equation (1) is satisfied, and the average S of the minor axis av and standard deviation S σ This satisfies equation (2). L σ / L av ×100≦20.0 ‥‥ Formula (1) S σ / S av ×100≦20.0 ‥‥ Formula (2) The satisfaction of equations (1) and (2) indicates that the pellets satisfy the uniformity of a predetermined size. Even if the polypropylene resin pellets have an average particle size that satisfies the characteristic (A3), the presence of large pellets, for example, may cause bridging in or below the hopper, or make it difficult for the pellets to engage with the screw, resulting in unstable discharge. Because the polypropylene resin pellets of the present invention satisfy formulas (1) and (2), the pellets satisfy a predetermined uniformity of size, thereby suppressing bridging in or below the hopper, making it easier for the pellets to bite into the screw, and resulting in stable discharge.

[0020] The polypropylene resin pellets of the present invention have an average length L of 10 randomly selected pellets. av and standard deviation L σ The equation (1') satisfies the mean S of the minor axis. av and standard deviation S σ It is acceptable for the expression to satisfy equation (2'). L σ / L av ×100≦15.0 ‥‥ Formula (1') S σ / S av ×100≦10.0 ‥‥ Formula (2')

[0021] 2. Composition of polypropylene resin pellets The polypropylene resin pellets of the present invention mainly contain a propylene polymer. Here, "containing a propylene polymer as the main component" means that, in addition to the propylene polymer, additives or other resins different from the propylene polymer may be included, as long as they do not impair the performance of the polypropylene resin pellets of the present invention, and that the polypropylene resin pellets contain 50% by mass or more of the propylene polymer. The polypropylene resin pellets of the present invention may contain 70% by mass or more of a propylene polymer, 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, 99% by mass or more, 99.5% by mass or more, 99.9% by mass or more, or 100% by mass.

[0022] (1) Propylene polymer The propylene-based polymer used in the polypropylene resin pellets of the present invention may be either a propylene homopolymer or a copolymer of propylene and another α-olefin. In the present invention, a copolymer of propylene and another α-olefin, particularly a propylene-α-olefin random copolymer, is preferred. Propylene-α-olefin random copolymer is a random copolymer of propylene, whose main component is a structural unit derived from propylene, and other α-olefins excluding propylene. The α-olefin used as the comonomer is preferably ethylene or an α-olefin having 4 to 18 carbon atoms. When α-olefins used as comonomers are included, their content may be 10.0% by mass or less, and preferably 6.0% by mass or less, relative to the total monomers (sum of propylene and α-olefins).

[0023] Other specific examples of α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methylpentene-1, 4-methylhexene-1, and 4,4-dimethylpentene-1. Furthermore, these other α-olefins may be used individually or in combination of two or more. Specific examples of such propylene-α-olefin random copolymers include propylene-ethylene random copolymer, propylene-1-butene random copolymer, propylene-1-hexene random copolymer, propylene-ethylene-1-octene random copolymer, and propylene-ethylene-1-butene random copolymer.

[0024] The propylene polymer used in the polypropylene resin pellets of the present invention may have a melt flow rate (MFR) measured at 230°C and a 2.16 kg load in accordance with JIS K7210-1:2014, which may be greater than 1 g / 10 min and 20,000 g / 10 min or less, 10 g / 10 min or more, 100 g / 10 min or more, 500 g / 10 min or more, 1500 g / 10 min or more, 1550 g / 10 min or more, 1600 g / 10 min or more, while also being 15,000 g / 10 min or less, 10,000 g / 10 min or less, or 5,000 g / 10 min or less. The MFR of the propylene polymer used in the polypropylene resin pellets of the present invention can be adjusted by (i) changing the catalyst system, polymerization temperature and / or polymerization pressure during polymerization of the propylene polymer, and / or (ii) adding hydrogen or other chain transfer agents to the monomer during polymerization of the propylene polymer.

[0025] Furthermore, the propylene polymer used in the polypropylene resin pellets of the present invention may have a melting peak temperature of 100°C to 170°C, 120°C or higher, 125°C or higher, while also being 166°C or lower, or 160°C or lower, as measured by differential scanning calorimeter. In the propylene-based polymer used in the polypropylene resin pellets of the present invention, the melting peak temperature of the propylene homopolymer can be adjusted, for example, by selecting the type of catalyst, or in the case of a metallocene catalyst, by selecting the complex. The melting peak temperature of the copolymer of propylene and other α-olefins can be easily adjusted, for example, by controlling the amount of α-olefin supplied to the polymerization reaction system.

[0026] Propylene polymers can typically be produced by polymerizing propylene or copolymerizing propylene with other α-olefins in the presence of a solid titanium catalyst and a Ziegler catalyst mainly composed of organometallic compounds, or a metallocene catalyst using a metallocene compound as one of the catalyst components. The propylene polymer used in the polypropylene resin pellets of the present invention is preferably a propylene polymer polymerized with a metallocene catalyst. With polymerization using a metallocene catalyst, a propylene polymer with an MFR exceeding 1500 g / 10 min can be polymerized without treatment with peroxides. In the case of polymerization using a Ziegler-Natta catalyst, for example, a propylene polymer with an MFR of less than 1500 g / 10 min can be obtained, and then treated with peroxides to obtain polypropylene resin pellets with an MFR exceeding 1500 g / 10 min. Pellets containing propylene polymers obtained by polymerization without peroxide treatment have the advantage of being less prone to problems such as smoke generation during molding. Polymerization methods for propylene polymers include slurry methods using an inert solvent in the presence of the above-mentioned catalyst, solution methods, gas-phase methods that use substantially no solvent, or bulk polymerization methods using the polymerization monomer as the solvent.

[0027] (2) Additives Various additives are blended to enhance the performance of the resin material or to add other properties, and known additives commonly used in polyolefins may be used. As additives, various additives such as antioxidants, neutralizing agents, light stabilizers, ultraviolet absorbers, lubricants, antistatic agents, and metal deactivators can be blended in a range that does not impair the objective of the present invention.

[0028] Examples of antioxidants include phenolic antioxidants, phosphite antioxidants, and thio-based antioxidants. Examples of neutralizing agents include higher fatty acid salts such as calcium stearate and zinc stearate, as well as hydrotalcites. Examples of light stabilizers and UV absorbers include hindered amines, nickel complex compounds, benzotriazoles, and benzophenones. Examples of lubricants include higher fatty acid amides such as stearate amide. Examples of antistatic agents include fatty acid partial esters such as glycerol fatty acid monoesters. Furthermore, examples of metal deactivators include phosphones, epoxynes, triazoles, hydrazides, and oxamides.

[0029] As an antioxidant to be incorporated into the polypropylene resin pellets of the present invention, a phenolic antioxidant that is less prone to hydrolysis is preferred, from the viewpoint of suitability for meltblown applications in which the pellets of the present invention are suitably used. Specific phenolic antioxidants include tris-(3,5-di-t-butyl-4-hydroxybenzyl)-isocyanurate, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1, Examples include 3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, 3,9-bis[2-{3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, and 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid.

[0030] In the polypropylene resin pellets of the present invention, the total content of additives is not particularly limited and can be appropriately selected according to the properties of the additives. The total content of additives, per 100 parts by mass of the propylene polymer, may have an upper limit of, for example, 10 parts by mass or less, 1,000 parts by mass or less, 0,500 parts by mass or less, 0,300 parts by mass or less, or 0,200 parts by mass or less, and a lower limit of 0 parts by mass, but may be 0.005 parts by mass or more, 0.010 parts by mass or more, or 0.100 parts by mass or more.

[0031] (3) Other resins Other resins that may be blended into the polypropylene resin pellets of the present invention include olefin polymers different from propylene polymers, and any other polymers. Specific examples of other resins include, but are not limited to, ethylene homopolymers, copolymers of ethylene and α-olefins having 3 to 10 carbon atoms, butene homopolymers, and copolymers of butene and α-olefins having 2 to 10 carbon atoms.

[0032] In the polypropylene resin pellets of the present invention, the total content of other resins may be selected from the viewpoint of desired performance in the application of the pellets, and may be 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 0% by mass in the polypropylene resin pellets.

[0033] 3. Method for manufacturing polypropylene resin pellets The polypropylene resin pellets of the present invention can be obtained by blending a powder of a propylene homopolymer obtained by polymerization in the presence of a catalyst, or a copolymer of propylene and another α-olefin, with other resins as needed, or with various additives, and then pelletizing it by a known method. Known pelletizing methods include melt extrusion, underwater cutting method, strand cutting method (open bath method), and underwater strand cutting method, with the underwater strand cutting method being preferred. Examples of underwater strand cutting systems include the APS-15H, APS-30H, APS-45H, APS-60H, APS-90H, APS-15V, APS-30V, APS-45V, APS-60V, and APS-90V models manufactured by Tokuki Co., Ltd. In order for the polypropylene resin pellets of the present invention to satisfy (A3) and (A4) above, the amount of polypropylene resin discharged during melt extrusion is adjusted by appropriately adjusting the set temperature and screw rotation speed of the extruder, as well as appropriately adjusting the take-up speed, cooling water temperature and cooling water volume.

[0034] 4. Applications of polypropylene resin pellets The polypropylene resin pellets of the present invention can be preferably used in nonwoven fabrics and injection molded articles, and are particularly preferably used in meltblown nonwoven fabrics. Meltblown molding, a well-known method for obtaining meltblown nonwoven fabrics, is widely used in the production of polyolefin resin nonwoven fabrics with fine fiber diameters. The molding process is outlined below. After the raw materials are melted in an extruder, the molten strands are extruded into a stream of heated air from a spinning nozzle head with a pore diameter of tens to hundreds of micrometers and a number of tens to thousands of pores. This air stream thins the molten strands, which are then gathered on a collection device such as a conveyor, and wound onto a roll to obtain a nonwoven fabric. [Examples]

[0035] The present invention will now be specifically described with reference to examples, but the present invention is not limited by these examples as long as it does not depart from its essence. The measurement method in these examples is as follows.

[0036] [Various physical property measurement methods] 1. MFR (Melt Flow Rate) MFR was measured in accordance with JIS K7210-1:2014, at a test temperature of 230°C and a load of 2.16 kgf. 2. Melting peak temperature (Tm) in DSC (Differential Scanning Calorimeter) measurements A 5.0 mg sample was taken and measured by differential scanning calorimetry (DSC). After holding it at 200°C for 5 minutes, it was cooled to 40°C at a rate of 10°C / min, and then heated again at a rate of 10°C / min. The peak temperature of the melting curve observed at this time was defined as the peak melting temperature (Tm). 3. Measuring pellet size After placing the pellets on a horizontal surface and applying vibration to ensure stable contact with the surface, the major and minor diameters of 10 randomly selected pellets were measured one by one using calipers. The major diameter was measured as the longest portion of the pellet when viewed from the direction normal to the horizontal plane, and the minor diameter was measured as the longest portion of the length perpendicular to the major diameter.

[0037] [Production of propylene polymers] (Polymerization Example 1: Polymerization of Propylene-based Polymer 1 (PP-1)) (i) Preparation of prepolymerization catalyst (Chemical treatment of silicates) 3.75 liters of distilled water were added to a 10-liter glass separable flask equipped with a stirring blade, followed by 2.5 kg of concentrated sulfuric acid (96%). At 50°C, 1 kg of montmorillonite (product name "Benclay SL" manufactured by Mizusawa Chemical Co., Ltd.) was dispersed, and the temperature was raised to 90°C and maintained for 6.5 hours. After cooling to 50°C, the slurry was filtered under reduced pressure to recover the cake. Seven liters of distilled water were added to this cake to re-slurry it, and then filtered. This washing operation was repeated until the pH of the washing solution (filtrate) exceeded 3.5. The recovered cake was dried overnight at 110°C under a nitrogen atmosphere. The weight after drying was 707g. The chemically treated silicate thus obtained was further dried in a kiln dryer to obtain dried silicate. (Preparation of catalyst) 200 g of the dried silicate obtained above was introduced into a glass reactor with a stirring blade and an internal volume of 3 liters. 1,160 ml of mixed heptane and 840 ml of triethylaluminum heptane solution (0.60 M) were added, and the mixture was stirred at room temperature. After 1 hour, the mixture was washed with mixed heptane to prepare a silicate slurry to 2.0 liters. Next, 9.6 ml of a heptane solution of triisobutylaluminum (0.71 M / L) was added to the prepared silicate slurry and reacted at 25°C for 1 hour. In parallel, 2,180 mg (3 mmol) of [(r)-dichloro[1,1'-dimethylsilylenebis{2-methyl-4-(4-chlorophenyl)-4H-azlenyl}]zirconium] (synthesis carried out according to the examples in Japanese Patent Publication No. 10-226712) was mixed with 870 ml of heptane, and 33.1 ml of a heptane solution of triisobutylaluminum (0.71 M) was added and reacted at room temperature for 1 hour. This mixture was then added to the silicate slurry and stirred for 1 hour. (Pre-polymerization / cleaning) Next, 2.1 liters of n-heptane were introduced into a 10-liter stirred autoclave, which had been thoroughly purged with nitrogen, and the temperature was maintained at 40°C. The previously prepared catalyst slurry was then introduced. Once the temperature stabilized at 40°C, propylene was supplied at a rate of 100 g / hour, and the temperature was maintained. After 4 hours, the supply of propylene was stopped, and the temperature was maintained for another 2 hours. After the preliminary polymerization was complete, the remaining monomer was purged, stirring was stopped, and the mixture was allowed to stand for about 10 minutes, after which approximately 3 liters of the supernatant was decanted. Next, 9.5 ml of heptane solution of triisobutylaluminum (0.71 M / L) and then 5.6 liters of mixed heptane were added, the mixture was stirred at 40°C for 30 minutes, and after standing for 10 minutes, 5.6 liters of the supernatant was removed. This procedure was repeated three more times. A component analysis of the final supernatant revealed that the concentration of organoaluminum components was 1.23 mmol / L, and the Zr concentration was 8.6 × 10⁻⁶. -6 The concentration was g / L, and the amount present in the supernatant relative to the initial charge was 0.016%. Subsequently, 170 ml of heptane solution of triisobutylaluminum (0.71 M / L) was added, and the mixture was dried under reduced pressure at 45°C. This procedure yielded a prepolymerization catalyst containing 2.2 g of polypropylene per gram of catalyst.

[0038] (ii) First polymerization step A horizontal reactor (L / D=4.3, internal volume 100 liters) with stirring blades was thoroughly dried and the interior was placed under a nitrogen gas atmosphere. In the presence of a polypropylene powder bed, the prepolymerization catalyst prepared by the above method (as solid catalyst amount excluding prepolymerization powder) was continuously supplied to the upstream side of the reactor at a rotation speed of 30 rpm while stirring. Triisobutylaluminum was continuously supplied at a rate of 31 mmol / hr. The temperature was set to 57°C on the upstream side and 58°C on the downstream side of the reactor, the pressure was maintained at 2.1 MPaG, and a monomer mixed gas was continuously circulated into the reactor so that the ethylene / propylene molar ratio in the gas phase of the reactor was 0.03 and the hydrogen concentration was 0.16 mol%, and gas-phase polymerization was carried out. The polymer powder produced by the reaction was continuously withdrawn from the downstream side of the reactor so that the amount of powder bed in the reactor remained constant. At this time, the amount of polymer withdrawn when the steady state was reached was 7.1 kg / hr. Analysis of the propylene-ethylene random copolymer obtained in the first polymerization step revealed an MFR of 4,000 g / 10 min and an ethylene content of 1.1% by mass.

[0039] (iii) Second polymerization step The propylene-ethylene copolymer extracted from the first step was continuously supplied to a horizontal reactor (L / D = 4.3, internal volume 100 liters) equipped with stirring blades. While stirring at a rotation speed of 25 rpm, the reactor temperature was maintained at 65°C and the pressure at 1.9 MPaG. A monomer mixed gas was continuously circulated into the reactor to maintain an ethylene / propylene molar ratio of 0.03 and a hydrogen concentration of 0.16 mol% in the gas phase of the reactor, and gas-phase polymerization was carried out. The polymer powder produced by the reaction was continuously withdrawn from the downstream part of the reactor to maintain a constant amount of powder bed in the reactor. At this time, the polymer withdrawal rate was 8.9 kg / hr, and the activity was 47 kg / g-catalyst. The obtained propylene polymer 1 (PP-1) had a melting temperature of 140°C, an ethylene content of 1.1% by mass, and a melting peak temperature of 4000 g / 10 min.

[0040] (Polymerization Example 2: Polymerization of Propylene-based Polymer 2 (PP-2)) Polymerization was carried out under the same conditions as in Polymerization Example 1 of PP-1, except that the hydrogen concentration in the first and second polymerization steps was set to 0.135 mol%. The obtained propylene polymer 2 (PP-2) had an MFR of 1800 g / 10 min, an ethylene content of 1.1 mass%, and a melting peak temperature of 140°C.

[0041] (Polymerization Example 3: Polymerization of Propylene Polymer 3 (PP-3)) Polymerization was carried out under the same conditions as in Polymerization Example 1 of PP-1, except that the hydrogen concentration in the first and second polymerization steps was set to 0.11 mol%. The obtained propylene polymer 3 (PP-3) had an MFR of 500 g / 10 min, an ethylene content of 1.1 mass%, and a melting peak temperature of 140°C.

[0042] [Production of powdered resin compositions] (Manufacturing Example 1: Manufacturing of powdered resin composition (Pow-1)) To 100 parts by mass of the powdered propylene polymer 1 (PP-1) obtained in Polymerization Example 1, 0.05 parts by mass of 3-(4'-hydroxy-3',5-di-tert-butylphenyl)propionic acid-n-octadecyl (BASF trade name Irganox 1076) was added as an antioxidant and placed in a Henschel mixer. The mixture was then rapidly mixed at 750 rpm for 1 minute at room temperature to obtain the powdered resin composition Pow-1. The MFR of Pow-1 was 4000 g / 10 min.

[0043] (Manufacturing Example 2: Manufacturing of Powdered Resin Composition (Pow-2)) Powdered resin composition Pow-2 was obtained by the same procedure as in Production Example 1, except that propylene polymer 2 (PP-2) obtained in Polymerization Example 2 was used instead of propylene polymer 1 (PP-1). The MFR of Pow-2 was 1800 g / 10 min.

[0044] (Manufacturing Example 3: Manufacturing of Powdered Resin Composition (Pow-3)) Powdered resin composition Pow-3 was obtained by the same procedure as in Production Example 1, except that propylene polymer 3 (PP-3) obtained in Polymerization Example 3 was used instead of propylene polymer 1 (PP-1). The MFR of Pow-3 was 500 g / 10 min.

[0045] [Pellet manufacturing] (Comparative Example 1) (1) Manufacturing of comparative polypropylene resin pellets (Pel-C1) Pow-1 obtained in Production Example 1 was fed into the hopper of a PMS65-32V single-screw extruder manufactured by IKG Corporation, which is equipped with a hopper for powder input. Under the conditions described in Table 1, it was melt-extruded through a die with one round hole of approximately 5 mm in diameter, pelletized using an APS-H30 underwater strand cutter manufactured by Tokuki Co., Ltd. with a chute length of 3 m, and moisture was removed using a ZD7-200 dewatering machine manufactured by Tokuki Co., Ltd. to obtain comparative polypropylene resin pellets (Pel-C1). In the extruder, the set temperatures were as follows, starting from the side closest to the hopper: cylinder 1 (C1) at 180°C, cylinder 2 (C2) at 200°C, cylinder 3 (C3) at 200°C, cylinder 4 (C4) at 200°C, cylinder 5 (C5) at 200°C, and the adapter and die at 200°C. The resin temperature measured at the die was 203°C. In the extruder, the screw rotation speed was 91.6 rpm and the discharge rate was 36 kg / h. In the underwater strand cutter, the cooling water temperature was 10°C and the cooling water flow rate was 8 m³. 3 The pickup speed was set to 120 m / min. In the obtained Pel-C1, many pellets were found to be linked together or fused together in groups of 2 to 5. The MFR of Pel-C1 was 3800 g / 10 min. For pellets linked together or fused together in groups of 2 to 5, the entire group was treated as a single pellet, and the size of the pellets was measured and recorded in Table 2. The morphology of the pellets is shown in Figure 1.

[0046] (2) Manufacturing of meltblown nonwoven fabrics In Example 1 described below, we attempted to form a nonwoven fabric by performing the same procedure as in Example 1, except that we replaced the polypropylene resin pellet Pel-1 used as the raw material with comparative polypropylene resin pellet Pel-C1. However, the properties of the pellets were outside the scope of the present invention, and the pellets did not bite into the screw of the extruder and could not be discharged, so we were unable to obtain a nonwoven fabric.

[0047] (Example 1) (1) Manufacturing of polypropylene resin pellets (Pel-1) Polypropylene resin pellets Pel-1 were obtained in the same manner as in Comparative Example 1, except that the pelletizing conditions were changed to those of Example 1 in Table 1. There were almost no pellets that were linked together or fused together in groups of 2 to 5. The MFR of Pel-1 was 3800 g / 10 min. The size of the pellets was measured and is listed in Table 2. The morphology of the pellets is shown in Figure 1.

[0048] (2) Manufacturing of meltblown nonwoven fabrics (2-1) Molding The obtained polypropylene resin pellets Pel-1 were melt-blown under the following conditions, resulting in a basis weight of 5 g / m². 2 We obtained a nonwoven fabric. Extruder; Single-screw extruder: 25mm bore, with gear pump. Die; Die size: Effective length 225mm; Nozzle holes: 451; Nozzle diameter: 0.1mm Spinning conditions: Spinning temperature: 280℃, Air temperature: 320℃, Air flow rate: 1800L / min Fiber collection conditions; Ejector-conveyor distance: 285 mm (2-2) Evaluation of spinnability The spinnability was evaluated based on the following criteria. [Work Environment] We evaluated whether or not dust was generated when raw materials were added. ○ indicates no dust generation, and × indicates dust generation. [Dischargeability] A circle (○) indicates stable dispensing, while a cross (×) indicates unstable dispensing or inability to dispense. Example 1 showed excellent working conditions and superior dispensing performance. (2-3) Physical property evaluation The physical properties of the obtained nonwoven fabric were evaluated based on the following items. [Fiber diameter] Five arbitrary locations on the nonwoven fabric were photographed at a magnification of 1000x using a scanning electron microscope (Hitachi High-Technologies Corporation, Field Emission Scanning Electron Microscope SU-8020). The diameter of 20 arbitrary fibers was measured for each photograph, and this process was repeated for all five photographs. The average fiber diameter was then calculated by averaging the diameters of a total of 100 fibers. The evaluation results are summarized in Table 3.

[0049] (Example 2) (1) Manufacturing of polypropylene resin pellets (Pel-2) Polypropylene resin pellets Pel-2 were obtained by the same procedure as in Example 1, except that the pelletizing conditions were changed to those of Example 2 in Table 1. There were almost no pellets that were linked together or fused together in groups of 2 to 5. The MFR of Pel-2 was 3800 g / 10 min. The size of the pellets was measured and is listed in Table 2. The morphology of the pellets is shown in Figure 1.

[0050] (2) Manufacturing of meltblown nonwoven fabrics The procedure was the same as in Example 1, except that the raw material was changed from polypropylene resin pellets Pel-1 to polypropylene resin pellets Pel-2, resulting in a basis weight of 5 g / m². 2 A nonwoven fabric was obtained. The evaluation was carried out in the same manner as in Example 1, and the evaluation results are summarized in Table 3. The results showed excellent working environment and excellent dispensing properties.

[0051] (Example 3) (1) Manufacturing of polypropylene resin pellets (Pel-3) Polypropylene resin pellets Pel-3 were obtained by the same procedure as in Example 1, except that the pelletizing conditions were changed to those of Example 3 in Table 1. There were almost no pellets that were linked together or fused together in groups of 2 to 5. The MFR of Pel-3 was 3800 g / 10 min. The size of the pellets was measured and is listed in Table 2. The morphology of the pellets is shown in Figure 1.

[0052] (2) Manufacturing of meltblown nonwoven fabrics The procedure was the same as in Example 1, except that the raw material was changed from polypropylene resin pellets Pel-1 to polypropylene resin pellets Pel-3, resulting in a basis weight of 5 g / m². 2 A nonwoven fabric was obtained. The evaluation was carried out in the same manner as in Example 1, and the evaluation results are summarized in Table 3. The results showed excellent working environment and excellent dispensing properties.

[0053] (Example 4) (1) Manufacturing of polypropylene resin pellets (Pel-4) Polypropylene resin pellets Pel-4 were obtained by the same procedure as in Example 1, except that the pelletizing conditions were changed to those of Example 4 in Table 1. There were almost no pellets that were linked together or fused together in groups of 2 to 5. The MFR of Pel-4 was 3800 g / 10 min. The size of the pellets was measured and is listed in Table 2. The morphology of the pellets is shown in Figure 2.

[0054] (2) Manufacturing of meltblown nonwoven fabrics The procedure was the same as in Example 1, except that the raw material was changed from polypropylene resin pellets Pel-1 to polypropylene resin pellets Pel-4, resulting in a basis weight of 5 g / m². 2 A nonwoven fabric was obtained. The evaluation was carried out in the same manner as in Example 1, and the evaluation results are summarized in Table 3. The results showed excellent working environment and excellent dispensing properties.

[0055] (Example 5) (1) Manufacturing of polypropylene resin pellets (Pel-5) Polypropylene resin pellets Pel-5 were obtained by the same procedure as in Example 1, except that the pelletizing conditions were changed to those of Example 5 in Table 1. There were almost no pellets that were linked together or fused together in groups of 2 to 5. The MFR of Pel-5 was 3800 g / 10 min. The size of the pellets was measured and is listed in Table 2. The morphology of the pellets is shown in Figure 2.

[0056] (2) Manufacturing of meltblown nonwoven fabrics The procedure was the same as in Example 1, except that the raw material was changed from polypropylene resin pellets Pel-1 to polypropylene resin pellets Pel-5, resulting in a basis weight of 5 g / m². 2 A nonwoven fabric was obtained. The evaluation was carried out in the same manner as in Example 1, and the evaluation results are summarized in Table 3. The results showed excellent working environment and excellent dispensing properties.

[0057] (Example 6) (1) Manufacturing of polypropylene resin pellets (Pel-6) In Example 1, polypropylene resin pellets Pel-6 were obtained by the same procedure as in Example 1, except that Pow-2 obtained in Production Example 2 was used instead of Pow-1 obtained in Production Example 1, and the pelletizing conditions were changed to those of Example 6 in Table 1. There were almost no pellets that were linked together or fused together in groups of 2 to 5. The MFR of Pel-6 was 1600 g / 10 min. The size of the pellets was measured and is listed in Table 2. The morphology of the pellets is shown in Figure 2.

[0058] (2) Manufacturing of meltblown nonwoven fabrics The procedure was the same as in Example 1, except that the raw material was changed from polypropylene resin pellets Pel-1 to polypropylene resin pellets Pel-6, resulting in a basis weight of 5 g / m². 2 A nonwoven fabric was obtained. The evaluation was carried out in the same manner as in Example 1, and the evaluation results are summarized in Table 3. The results showed excellent working environment and excellent dispensing properties. The nonwoven fabric of Example 6 had slightly larger fiber diameters compared to Examples 1-5.

[0059] (Example 7) (1) Manufacturing of polypropylene resin pellets (Pel-7) In Example 1, polypropylene resin pellets Pel-7 were obtained by performing the same procedure as in Example 1, except that Pow-2 obtained in Production Example 2 was used instead of Pow-1 obtained in Production Example 1, and the pelletizing conditions were changed to those of Example 7 in Table 1. There were almost no pellets that were linked together or fused together in groups of 2 to 5. The MFR of Pel-7 was 1600 g / 10 min. The size of the pellets was measured and is listed in Table 2. The morphology of the pellets is shown in Figure 2.

[0060] (2) Manufacturing of meltblown nonwoven fabrics The procedure was the same as in Example 1, except that the raw material was changed from polypropylene resin pellets Pel-1 to polypropylene resin pellets Pel-7, resulting in a basis weight of 5 g / m². 2 A nonwoven fabric was obtained. The evaluation was carried out in the same manner as in Example 1, and the evaluation results are summarized in Table 3. The results showed excellent working environment and excellent dispensing properties. The nonwoven fabric of Example 7 had slightly larger fiber diameters compared to Examples 1-5.

[0061] (Comparative Example 2) (1) Manufacturing of comparative polypropylene resin pellets (Pel-C2) Pow-1 obtained in Production Example 1 was loaded into the hopper of a PMS50-32V single-screw extruder manufactured by I.K.G. Co., Ltd., which is equipped with a powder input hopper. Under the conditions described in Table 1, the molten resin was extruded through a die with five round holes approximately 4 mm in diameter and guided into a water tank 20 cm wide and 2.5 m long. An attempt was made to form strands by taking up the molten resin in the water tank according to the standard method of strand cutting, but strand formation was not possible due to the low molten viscosity. The extruder screw was stopped before the resin lumps floating on the surface of the water tank completely covered the surface, and the cooled resin lumps were collected. Comparative polypropylene resin pellets Pel-C2 were obtained by crushing the collected resin lumps with a hammer. The pellets had an irregular shape and uneven size. The MFR was 3800 g / 10 min. Pellet sizes were measured after visually removing pellets with a short diameter of 2 mm or less, and the results are listed in Table 2. The morphology of the pellets is shown in Figure 2.

[0062] (2) Manufacturing of meltblown nonwoven fabrics An attempt was made to form a nonwoven fabric by performing the same procedure as in Example 1, except that polypropylene resin pellets Pel-C2 were used as the raw material instead of polypropylene resin pellets Pel-1. However, the properties of the pellets were outside the scope of the present invention, and the pellets did not bite into the screw of the extruder and could not be discharged, so a nonwoven fabric could not be obtained.

[0063] (Comparative Example 3) In the production of the meltblown nonwoven fabric, the procedure was the same as in Example 1, except that the polypropylene resin pellets Pel-1 used as the raw material were replaced with the powdered resin composition Pow-1 obtained in Production Example 1, resulting in a basis weight of 5 g / m². 2 A nonwoven fabric was obtained. The evaluation results are summarized in Table 3. The physical properties of the nonwoven fabric were the same as in Example 1, but dust was generated when raw materials were added, resulting in a less favorable working environment.

[0064] (Comparative Example 4) In the production of the meltblown nonwoven fabric, the procedure was the same as in Example 1, except that the polypropylene resin pellets Pel-1 used as the raw material were replaced with the powdered resin composition Pow-2 obtained in Production Example 2, resulting in a basis weight of 5 g / m². 2 A nonwoven fabric was obtained. The evaluation results are summarized in Table 3. The physical properties of the nonwoven fabric were the same as in Example 6, but dust was generated when the raw materials were added, resulting in a less favorable working environment.

[0065] (Comparative Example 5) In the production of the meltblown nonwoven fabric, the procedure was the same as in Example 1, except that the polypropylene resin pellets Pel-1 used as a raw material were replaced with the powdered resin composition Pow-3 obtained in Production Example 3, resulting in a basis weight of 5 g / m². 2 A nonwoven fabric was obtained. The evaluation results are summarized in Table 3. Dust was generated when raw materials were added, resulting in a poor working environment. In addition, because the MFR was lower than the range of the pellets of the present invention, the fiber diameter of the obtained nonwoven fabric was significantly thicker compared to Examples 1-7.

[0066] [Table 1]

[0067] [Table 2]

[0068] [Table 3] [Industrial applicability]

[0069] According to the present invention, it is possible to provide polypropylene resin pellets having a specific high fluidity and a specific melting peak temperature, while having a predetermined shape with a specific size and standard deviation. This solves the problem of deterioration of the working environment due to dust caused by powdered polypropylene resin and the increase in equipment costs for dust explosion countermeasures, and also enables stable discharge during molding, stable size of molded products, and stable production of molded products, making it highly applicable to industry.

Claims

1. Polypropylene resin pellets containing a propylene polymer as the main component and satisfying the following characteristics (A1) to (A4). (A1) The melt flow rate (MFR), measured at 230°C and a 2.16 kg load in accordance with JIS K7210-1:2014, is greater than 1500 g / 10 min and less than or equal to 20000 g / 10 min. (A2) The melting peak temperature measured by differential scanning calorimeter is between 100°C and 170°C. (A3) For 10 randomly selected pellets, the average length is between 3.0 mm and 8.0 mm, and the average width is between 2.0 mm and 8.0 mm. (A4) For 10 randomly selected pellets, the average value of the longest diameter L ａｖ and standard deviation L σ The equation (1) is satisfied, and the average S of the minor axis ａｖ and standard deviation S σ This satisfies equation (2). L σ / L ａｖ ×100≦20.0 ‥‥ Equation (1) S σ / S ａｖ ×100≦20.0 ‥‥ Equation (2)

2. The polypropylene resin pellets according to claim 1, comprising a propylene polymer polymerized with a metallocene catalyst.

Images