resin pellets

Abstract

The objective is to provide resin pellets that are relatively easy to handle. [Solution] The resin pellet according to the first invention is a resin pellet containing a polyolefin resin, wherein the coefficient of variation of the center of gravity radius is 0.050 or more and 0.100 or less. The resin pellet according to the second invention is a resin pellet containing a polyolefin resin, wherein the projected area per unit mass is 5.05 cm². 2 / g or more 8.00cm 2 It is less than / g.

Description

Technical Field

[0001] The present invention relates to resin pellets.

Background Art

[0002] Conventionally, molded products containing polyolefin resins such as polyethylene and polypropylene have been used in industrial parts such as daily necessities, automotive parts, and electrical parts, as well as daily necessities and miscellaneous goods. For example, Patent Document 1 discloses a resin composition containing an ethylene-α-olefin copolymer and high-pressure radical polymerization method polyethylene, which is used for a lid used for sealing a container.

[0003] Such molded products containing polyolefin resins are obtained by using resin pellets as raw materials, supplying the resin pellets to an extrusion molding device or the like, melt-kneading them, and then performing extrusion molding.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, resin pellets are required to have excellent handling properties such as ease of discharge from a hopper, simplicity of conveyance from a feeder, and difficulty of bag breakage of a packaging bag for packaging the resin pellets. However, there is room for improvement in the handling properties of conventional resin pellets. By improving the handling properties of resin pellets, the energy required in each step when obtaining a molded product using the resin pellets as a raw material can be reduced. ]>

[0006] The present invention has been made in view of such problems, and an object thereof is to provide resin pellets having relatively excellent handling properties. [Means for solving the problem]

[0007] The resin pellet according to the first invention is a resin pellet containing a polyolefin resin, wherein the coefficient of variation of the center of gravity radius is 0.050 or more and 0.100 or less.

[0008] The resin pellet according to the second invention is a resin pellet containing a polyolefin resin, and has a projected area of ​​5.05 cm² per unit mass. 2 / g or more 8.00cm 2 It is less than / g. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide resin pellets that are relatively easy to handle. [Modes for carrying out the invention]

[0010] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0011] <First Embodiment> The following describes an embodiment of the first invention (first embodiment).

[0012] The resin pellets according to this embodiment are resin pellets containing a polyolefin resin.

[0013] The polyolefin resin may contain at least one selected from the group consisting of ethylene polymers and propylene polymers.

[0014] (Ethylene polymer) The ethylene-based polymer is a polymer containing more than 50% by mass of monomer units derived from ethylene. Examples of the ethylene-based polymer include ethylene homopolymers, ethylene-α-olefin copolymers, copolymers of α-olefins substituted with alicyclic compounds and ethylene, ethylene-vinyl acetate copolymers, and ethylene-methyl methacrylate copolymers. The ethylene-based copolymer may be used alone or in combination of two or more types.

[0015] In one embodiment, the polyolefin resin includes an ethylene-vinyl acetate copolymer or an ethylene-methyl methacrylate copolymer as the ethylene polymer. The density of the ethylene-vinyl acetate copolymer or ethylene-methyl methacrylate copolymer is 920 kg / m³. 3 More than 950kg / m 3 The following is also acceptable.

[0016] In other embodiments, the polyolefin resin includes low-density polyethylene as the ethylene polymer. The density of the low-density polyethylene is 900 kg / m³. 3 More than 930kg / m 3 The following is also acceptable.

[0017] The melting point of the low-density polyethylene may be between 100°C and 120°C. The melting point of the low-density polyethylene can be measured using a differential scanning calorimetry.

[0018] The glass transition temperature of the low-density polyethylene may be between -125°C and -100°C. The glass transition temperature of the low-density polyethylene is the softening temperature measured by thermomechanical analysis in accordance with JIS K7196.

[0019] In this specification, the density of ethylene polymers is measured using a sample that has undergone annealing as described in JIS K6760-1995, in accordance with Method A (water displacement method) as specified in JIS K7112-1980.

[0020] Examples of the ethylene homopolymer include, for example, high-pressure low-density polyethylene (LDPE) in which ethylene repeating units are randomly bonded with a branched structure by high-pressure radical polymerization using a radical initiator, having a density of 900 to 930 kg / m 3 3.

[0021] The ethylene homopolymer is produced, for example, by polymerizing ethylene at a polymerization pressure of 140 MPa or more and 300 MPa or less and a polymerization temperature of 200 °C or more and 300 °C or less in the presence of a radical generator using a tank reactor or a tubular reactor.

[0022] Examples of the ethylene-α-olefin copolymer include, for example, linear low-density polyethylene having crystallinity, an elastomer of a copolymer of ethylene and an α-olefin having low crystallinity and rubbery elastic properties, and the like.

[0023] The density of the linear low-density polyethylene may be 900 kg / m 3 or more and 930 kg / m 3 or less. The density of the elastomer of the copolymer of ethylene and an α-olefin may be 860 kg / m 3 or more and 900 kg / m 3 or less.

[0024] The α-olefin is preferably an α-olefin having 3 to 10 carbon atoms. Examples of the α-olefin having 3 to 10 carbon atoms include, for example, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 3-methyl-1-butene, and the like. The α-olefin having 3 to 10 carbon atoms is preferably an α-olefin having 4 to 10 carbon atoms, and more preferably 1-butene, 1-hexene or 1-octene.

[0025] An example of the α-olefin substituted with an alicyclic compound is vinylcyclohexane.

[0026] The content of monomer units derived from α-olefins in the ethylene polymer may be 3.5% by mass or more and 18% by mass or less.

[0027] Specific examples of the ethylene-α-olefin copolymer include ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-1-octene copolymer, ethylene-1-decene copolymer, and ethylene-(3-methyl-1-butene) copolymer. Note that the copolymer of ethylene and α-olefin may be used individually or in combination of two or more types.

[0028] As a method for producing the ethylene-α-olefin copolymer and the copolymer of α-olefin and ethylene substituted with an alicyclic compound, one method is to copolymerize ethylene with a monomer other than ethylene in the presence of a known complex catalyst such as a Ziegler-Natta catalyst, a metallocene complex, or a non-metallocene complex. Polymerization methods include slurry polymerization, solution polymerization, bulk polymerization, and gas-phase polymerization.

[0029] The content of monomer units derived from vinyl acetate in the ethylene-vinyl acetate copolymer may be 5% by mass or more and 40% by mass or less.

[0030] The content of monomer units derived from methyl methacrylate in the ethylene-methyl methacrylate copolymer may be 5% by mass or more and 30% by mass or less.

[0031] A method for producing ethylene-vinyl acetate copolymer and ethylene-methyl methacrylate copolymer includes, for example, a high-pressure radical polymerization method in which ethylene and vinyl acetate or methyl methacrylate are copolymerized in the presence of a radical generator at 50 to 400 MPa and 100 to 300°C, with or without a suitable solvent and chain transfer agent. By adjusting the polymerization conditions of high-pressure radical polymerization, the MFR or molecular weight distribution of the ethylene-vinyl acetate copolymer or ethylene-methyl methacrylate copolymer, or the content of monomer units based on vinyl acetate in the ethylene-vinyl acetate copolymer or the content of monomer units based on methyl methacrylate in the ethylene-methyl methacrylate copolymer, can be controlled.

[0032] The melt flow rate (MFR) of the ethylene polymer may be between 0.1 g / 10 min and 50 g / 10 min, or between 1.0 g / 10 min and 30 g / 10 min. The MFR is measured according to Method A specified in JIS K7210-1995, under conditions of a temperature of 190°C and a load of 2.16 kg.

[0033] (Propylene polymer) The propylene-based polymer is a polymer containing more than 50% by mass of monomer units derived from propylene. Examples of the propylene-based polymer include propylene homopolymers, random copolymers of propylene and monomers other than propylene, and heterophagic propylene polymerization materials.

[0034] In one embodiment, the polyolefin resin includes a propylene homopolymer or a propylene-ethylene random copolymer as the propylene polymer. The density of the propylene homopolymer or propylene-ethylene random copolymer is 900 kg / m³. 3 More than 920kg / m 3 The following is also acceptable.

[0035] In this specification, the density of propylene polymers is measured using a sample prepared by the method described in JIS K6758-1981, conditioned at a temperature of 23°C for 40 to 72 hours, and measured according to Method A (water displacement method) specified in JIS K7112-1980.

[0036] The aforementioned propylene homopolymer can be produced, for example, by carrying out a polymerization process in which propylene is polymerized using a polymerization catalyst.

[0037] Examples of polymerization catalysts include Ziegler-type catalysts; Ziegler-Natta-type catalysts; catalysts containing compounds of Group 4 transition metals having a cyclopentadienyl ring and alkylaluminoxanes; catalysts containing compounds of Group 4 transition metals having a cyclopentadienyl ring, compounds that react with the transition metal compound to form an ionic complex, and organoaluminum compounds; and catalysts modified by supporting catalyst components (compounds of Group 4 transition metals having a cyclopentadienyl ring, compounds that form ionic complexes, organoaluminum compounds, etc.) on inorganic particles (silica, clay minerals, etc.).

[0038] Examples of the polymerization catalyst include catalysts described in Japanese Patent Publication No. 61-218606, Japanese Patent Publication No. 5-194685, Japanese Patent Publication No. 7-216017, Japanese Patent Publication No. 9-316147, Japanese Patent Publication No. 10-212319, Japanese Patent Publication No. 2004-182981, Japanese Patent Publication No. 2010-168545, Japanese Patent Publication No. 2011-246699, and the like.

[0039] Furthermore, a polymer obtained by prepolymerizing propylene in the presence of the polymerization catalyst can also be used as the polymerization catalyst.

[0040] Polymerization methods include, for example, bulk polymerization, solution polymerization, and gas-phase polymerization. Here, bulk polymerization refers to a method in which polymerization is carried out using liquid olefins at the polymerization temperature as a medium. Solution polymerization refers to a method in which polymerization is carried out in an inert hydrocarbon solvent such as propane, butane, isobutane, pentane, hexane, heptane, and octane. Gas-phase polymerization refers to a method in which a monomer in a gaseous state is used as a medium to polymerize a monomer in a gaseous state within that medium.

[0041] Polymerization methods include, for example, batch, continuous, and combinations thereof. The polymerization method may also be a multi-stage system in which multiple polymerization reactors are connected in series.

[0042] From an industrial and economically superior viewpoint, the polymerization method is preferably a continuous gas-phase polymerization method, or a bulk-gas-phase polymerization method that continuously performs bulk polymerization and gas-phase polymerization.

[0043] The various conditions in the polymerization process (polymerization temperature, polymerization pressure, monomer concentration, catalyst input amount, polymerization time, etc.) should be determined appropriately according to the molecular structure of the target polymer.

[0044] In the above-mentioned method for producing the propylene homopolymer, other steps may be performed before or after the polymerization step. For example, after the polymerization step, the polymer may be dried at a temperature below the melting point of the polymer, if necessary, in order to remove residual solvent contained in the polymer, ultra-low molecular weight oligomers produced as by-products during manufacturing, etc. Examples of drying methods include those described in Japanese Patent Publication No. 55-75410 and Japanese Patent No. 2565753.

[0045] The random copolymer of propylene and a monomer other than propylene contains monomer units derived from propylene and monomer units derived from the monomer other than propylene. In the random copolymer, the content of monomer units derived from the monomer other than propylene may be 0.01% by mass or more and 30% by mass or 0.1% by mass or more and 20% by mass or less, based on 100% by mass of the total mass of the copolymer.

[0046] Examples of monomers other than propylene include ethylene and α-olefins having 4 to 12 carbon atoms. In this specification, α-olefins are aliphatic unsaturated hydrocarbons having a carbon-carbon unsaturated double bond at the α-position. Examples of α-olefins having 4 to 12 carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 4-methyl-1-pentene, and 4-methyl-1-hexene.

[0047] The monomer other than propylene is preferably one or more selected from the group consisting of ethylene and α-olefins having 4 to 10 carbon atoms, more preferably one or more selected from the group consisting of ethylene, 1-butene, 1-hexene and 1-octene, and even more preferably one or more selected from the group consisting of ethylene and 1-butene.

[0048] Examples of the random copolymers of propylene and monomers other than propylene include propylene-ethylene random copolymer, propylene-1-butene random copolymer, propylene-1-hexene random copolymer, propylene-1-octene random copolymer, propylene-ethylene-1-butene random copolymer, propylene-ethylene-1-hexene random copolymer, and propylene-ethylene-1-octene random copolymer.

[0049] The random copolymer of propylene and a monomer other than propylene can be produced, for example, by polymerizing propylene and the monomer other than propylene according to the polymerization catalyst, polymerization method, polymerization scheme, and polymerization conditions that can be used in the production of the propylene homopolymer described above.

[0050] The heterophagic propylene polymerization material is a mixture comprising polymer I containing monomer units derived from propylene, and polymer II containing monomer units derived from ethylene and one or more α-olefins selected from the group consisting of α-olefins having 4 to 12 carbon atoms, and monomer units derived from propylene.

[0051] The heterophagic propylene polymerization material can be produced, for example, by carrying out a first polymerization step of polymer I and a second polymerization step of polymer II. These polymerization steps can be carried out according to the polymerization catalyst, polymerization method, polymerization scheme, and polymerization conditions that can be used in the production of the propylene homopolymer described above.

[0052] The heterophagic propylene polymerization material may be such that the sum of polymer I and polymer II contained in the heterophagic propylene polymerization material is 100% by mass, relative to 100% by mass of the total mass of the heterophagic propylene polymerization material.

[0053] Polymer I may contain 70% by mass or more of monomer units derived from propylene (provided the total mass of Polymer I is 100% by mass). Polymer I may be, for example, a propylene homopolymer, or it may contain monomer units derived from monomers other than propylene. If Polymer I contains monomer units derived from monomers other than propylene, the content is usually 0.01% by mass or more and 30% by mass or less, relative to 100% by mass of the total mass of Polymer I.

[0054] Examples of monomers other than propylene include ethylene and α-olefins having four or more carbon atoms. Examples of α-olefins having four or more carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 4-methyl-1-pentene, and 4-methyl-1-hexene.

[0055] The monomer other than propylene is preferably one or more selected from the group consisting of ethylene and α-olefins having 4 to 10 carbon atoms, more preferably one or more selected from the group consisting of ethylene, 1-butene, 1-hexene and 1-octene, and even more preferably one or more selected from the group consisting of ethylene and 1-butene.

[0056] Examples of polymer I containing monomer units derived from monomers other than propylene include propylene-ethylene copolymer, propylene-1-butene copolymer, propylene-1-hexene copolymer, propylene-1-octene copolymer, propylene-ethylene-1-butene copolymer, propylene-ethylene-1-hexene copolymer, and propylene-ethylene-1-octene copolymer.

[0057] Polymer I is preferably a propylene homopolymer, a propylene-ethylene copolymer, a propylene-1-butene copolymer, or a propylene-1-hexene copolymer, and more preferably a propylene homopolymer.

[0058] The content of polymer I is usually 30% to 99% by mass, preferably 50% to 95% by mass, and more preferably 60% to 90% by mass, based on 100% by mass of the total mass of the heterophagic propylene polymerization material.

[0059] As described above, polymer II contains monomer units derived from ethylene and one or more α-olefins selected from the group consisting of α-olefins having 4 to 12 carbon atoms, and monomer units derived from propylene. Examples of α-olefins having 4 to 12 carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 4-methyl-1-pentene, and 4-methyl-1-hexene.

[0060] Polymer II preferably contains 30% by mass or more monomer units derived from ethylene and one or more α-olefins selected from the group consisting of 4 to 12 carbon atoms, and also contains monomer units derived from propylene (provided the total mass of Polymer II is 100% by mass).

[0061] In polymer II, the content of monomer units derived from ethylene and one or more α-olefins selected from the group consisting of 4 to 12 carbon atoms is usually 1% by mass or more and 80% by mass or less, preferably 20% by mass or more and 70% by mass or less, and more preferably 30% by mass or more and 60% by mass or less (provided that the total mass of polymer II is 100% by mass).

[0062] In polymer II, one or more α-olefins selected from the group consisting of ethylene and α-olefins having 4 to 12 carbon atoms are preferably one or more selected from the group consisting of ethylene and α-olefins having 4 to 10 carbon atoms, more preferably one or more selected from the group consisting of ethylene, 1-butene, 1-hexene, 1-octene and 1-decene, and even more preferably one or more selected from the group consisting of ethylene and 1-butene.

[0063] Examples of polymer II include propylene-ethylene copolymer, propylene-ethylene-1-butene copolymer, propylene-ethylene-1-hexene copolymer, propylene-ethylene-1-octene copolymer, propylene-ethylene-1-decene copolymer, propylene-1-butene copolymer, propylene-1-hexene copolymer, propylene-1-octene copolymer, and propylene-1-decene copolymer. Among these, polymer II is preferably propylene-ethylene copolymer, propylene-1-butene copolymer, or propylene-ethylene-1-butene copolymer, and more preferably propylene-ethylene copolymer.

[0064] The content of polymer II is usually 1% to 70% by mass, preferably 5% to 50% by mass, and more preferably 10% to 30% by mass, based on 100% by mass of the total mass of the heterophagic propylene polymerization material.

[0065] Examples of the heterophagic propylene polymerization materials include (propylene)-(propylene-ethylene) polymerization materials, (propylene)-(propylene-ethylene-1-butene) polymerization materials, (propylene)-(propylene-ethylene-1-hexene) polymerization materials, (propylene)-(propylene-ethylene-1-octene) polymerization materials, (propylene)-(propylene-1-butene) polymerization materials, (propylene)-(propylene-1-hexene) polymerization materials, (propylene)-(propylene-1-octene) polymerization materials, and (propylene)-(propylene (-1-decene) polymerization material, (propylene-ethylene)-(propylene-ethylene) polymerization material, (propylene-ethylene)-(propylene-ethylene-1-butene) polymerization material, (propylene-ethylene)-(propylene-ethylene-1-hexene) polymerization material, (propylene-ethylene)-(propylene-ethylene-1-octene) polymerization material, (propylene-ethylene)-(propylene-ethylene-1-decene) polymerization material, (propylene-ethylene)-(propylene-1-butene) polymerization material, (propylene-ethylene)-(propylene-1-hexene) polymerization material (Xene) polymerization material, (propylene-ethylene)-(propylene-1-octene) polymerization material, (propylene-ethylene)-(propylene-1-decene) polymerization material, (propylene-1-butene)-(propylene-ethylene) polymerization material, (propylene-1-butene)-(propylene-ethylene-1-butene) polymerization material, (propylene-1-butene)-(propylene-ethylene-1-hexene) polymerization material, (propylene-1-butene)-(propylene-ethylene-1-octene) polymerization material, (propylene-1-butene)-(propylene-ethylene- 1-decene) polymerization material, (propylene-1-butene)-(propylene-1-butene) polymerization material, (propylene-1-butene)-(propylene-1-hexene) polymerization material, (propylene-1-butene)-(propylene-1-octene) polymerization material, (propylene-1-butene)-(propylene-1-decene) polymerization material, (propylene-1-hexene)-(propylene-1-hexene) polymerization material, (propylene-1-hexene)-(propylene-1-octene) polymerization material, (propylene-1-hexene)-(propylene-1-decene) polymerization material,Examples include (propylene-1-octene)-(propylene-1-octene) polymerization materials and (propylene-1-octene)-(propylene-1-decene) polymerization materials.

[0066] Here, the description "(propylene)-(propylene-ethylene) polymerization material" means "a heterophagous propylene polymerization material in which polymer I is a propylene homopolymer and polymer II is a propylene-ethylene copolymer." The same applies to other similar expressions.

[0067] The heterophagic propylene polymerization material is preferably a (propylene)-(propylene-ethylene) polymerization material, a (propylene)-(propylene-ethylene-1-butene) polymerization material, a (propylene-ethylene)-(propylene-ethylene) polymerization material, a (propylene-ethylene)-(propylene-ethylene-1-butene) polymerization material, or a (propylene-1-butene)-(propylene-1-butene) polymerization material, and more preferably a (propylene)-(propylene-ethylene) polymerization material.

[0068] The melt flow rate (MFR) of the propylene polymer may be 0.1 g / 10 min or more and 50 g / 10 min or less, or 1.0 g / 10 min or more and 30 g / 10 min or less. The MFR is measured according to the method specified in Method A of JIS K7210-1995, under conditions of a temperature of 230°C and a load of 2.16 kg.

[0069] The ethylene polymer and the propylene polymer may contain carbon 14 (14C) as a constituent element, may be virgin material, or may be recycled material. Examples of recycled material include mechanically recycled (materially recycled) and chemically recycled material.

[0070] The concentration of carbon 14 (14C) contained in the ethylene polymer and the propylene polymer is determined as pMC (percentage of modern carbon: in %) by the AMS (Accelerator mass spectrometry) method specified in ISO 16620-2:2019.

[0071] Because atmospheric carbon dioxide contains a certain proportion of carbon-14 (14C), it is known that plants that grow by taking in atmospheric carbon dioxide, such as corn and trees, contain 14C. It is also known that fossil resources such as petroleum, which are thought to have been stored underground for long periods of time, contain almost no carbon-14 (14C). Therefore, by using plant-derived substances as raw materials for monomers used in the production of the ethylene-based polymer and the propylene-based polymer, it is possible to include carbon-14 (14C) in the constituent elements of the ethylene-based polymer and the propylene-based polymer.

[0072] Examples of monomers used in the production of the ethylene-based polymer and the propylene-based polymer include fossil resource-derived monomers (ethylene, propylene, 1-butene, 1-hexene, etc.), plant-derived monomers (ethylene, propylene, 1-butene, 1-hexene, etc.), and chemically recycled monomers (ethylene, propylene, 1-butene, 1-hexene, etc.). Two or more of these monomers may be used in combination.

[0073] Examples of monomer combinations used in the production of the ethylene polymer include (fossil resource-derived ethylene / plant-derived ethylene / chemically recycled ethylene), (fossil resource-derived ethylene / plant-derived ethylene / chemically recycled ethylene / fossil resource-derived 1-butene / plant-derived 1-butene / chemically recycled 1-butene), and (fossil resource-derived ethylene / plant-derived ethylene / chemically recycled ethylene / fossil resource-derived 1-hexene / plant-derived 1-hexene / chemically recycled 1-hexene).

[0074] Examples of monomer combinations used in the production of the aforementioned propylene polymer include (fossil resource-derived propylene / plant-derived propylene / chemically recycled propylene), (fossil resource-derived propylene / plant-derived propylene / chemically recycled propylene / fossil resource-derived ethylene / plant-derived ethylene / chemically recycled ethylene), and (fossil resource-derived propylene / plant-derived propylene / chemically recycled propylene / fossil resource-derived 1-butene / plant-derived 1-butene / chemically recycled 1-butene).

[0075] Monomers derived from fossil resources are derived from carbon in underground resources such as petroleum, coal, and natural gas, and generally contain very little carbon-14 (14C). Methods for producing monomers derived from fossil resources include known methods such as cracking of petroleum-derived naphtha and ethane, and dehydrogenation of ethane and propane to produce olefins.

[0076] Plant-derived monomers are derived from carbon that circulates on the Earth's surface as plants and animals, and generally contain a certain proportion of carbon-14 (14C). Methods for producing plant-derived monomers include known methods such as cracking of bionaphtha, vegetable oils, animal oils, etc., dehydrogenation of biopropanes, etc., separating alcohol from fermented products such as sugars extracted from plant raw materials such as sugarcane and corn, and then dehydrating them (JP 2010-511634, JP 2011-506628, JP 2013-503647, etc.), and a method of metathesis reaction between ethylene obtained from plant-derived ethanol and n-butene (WO2007 / 055361, etc.).

[0077] Chemical recycled monomers are derived from carbon generated by the decomposition and combustion of waste, and their carbon-14 (14C) content varies depending on the type of waste. Known methods for producing chemical recycled monomers include, for example, a method of thermal decomposition of waste plastics (JP 2017-512246, etc.), a method of cracking waste vegetable oil, waste animal oil, etc. (JP 2018-522087, etc.), and a method of gasification, alcohol conversion, and dehydration reaction of waste such as food waste, biomass waste, food waste, waste oil, waste wood, paper waste, and waste plastics (JP 2019-167424, WO2021 / 006245, etc.).

[0078] When using two or more types of monomers derived from fossil resources, monomers derived from plants, and chemically recycled monomers, the monomers may be mixtures of monomers manufactured individually, such as (fossil resource-derived monomer / plant-derived monomer), (fossil resource-derived monomer / chemically recycled monomer), (plant-derived monomer / chemically recycled monomer), or (fossil resource-derived monomer / plant-derived monomer / chemically recycled monomer). Alternatively, the monomers may be manufactured as mixtures of the above monomer combinations by using mixtures of combinations such as (fossil resource-derived compound / plant-derived compound), (fossil resource-derived compound / chemically recycled compound, plant-derived compound / chemically recycled compound), or (fossil resource-derived compound / plant-derived compound / chemically recycled compound) as raw materials or intermediates in the monomer manufacturing process.

[0079] As the ethylene polymer containing carbon 14 (14C), commercially available ethylene polymers such as the "I'M GREEN" (green polyethylene) series from Braskem, the "TRUCIRCLE" series from SABIC, and the "CirculenRenew" series from LyondellBasell can be used.

[0080] As the propylene polymer containing carbon 14 (14C), commercially available propylene polymers such as the "Bornewables" series from Borealis, the "TRUCIRCLE" series from SABIC, and the "CirculenRenew" series from LyondellBasell can be used.

[0081] From the viewpoint of reducing environmental impact, the total concentration of carbon 14 (14C) in the ethylene-based polymer and the propylene-based polymer is preferably 0.2 pMC(%) or more, more preferably 0.5 pMC(%) or more, even more preferably 1 pMC(%) or more, even more preferably 5 pMC(%) or more, and particularly preferably 10 pMC(%) or more. From the viewpoint of cost, the total concentration of carbon 14 (14C) in the ethylene-based polymer and the propylene-based polymer is preferably 99 pMC(%) or less, more preferably 95 pMC(%) or less, even more preferably 90 pMC(%) or less, even more preferably 70 pMC(%) or less, and particularly preferably 50 pMC(%) or less.

[0082] The total concentration of the ethylene polymer and the propylene polymer can be adjusted by changing the ratio of fossil resource-derived monomers, plant-derived monomers, and chemically recycled monomers used in the production of the ethylene polymer and the propylene polymer.

[0083] The polyolefin resin may optionally contain additives such as inorganic fillers, organic fillers, antioxidants, ultraviolet absorbers, light stabilizers, pigments, adsorbents, and lubricants.

[0084] Examples of the inorganic filler include talc, calcium carbonate, calcined kaolin, silica, and aluminum oxide.

[0085] Examples of the organic filler include fibers, wood flour, cellulose powder, starch, polyolefin powder, polyester fibers, and the like.

[0086] Examples of the aforementioned antioxidants include phenolic antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, lactone-based antioxidants, vitamin-based antioxidants, amine-based antioxidants, and the like.

[0087] Examples of the aforementioned ultraviolet absorbers include benzotriazole-based ultraviolet absorbers, tridiamine-based ultraviolet absorbers, anilide-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, and benzoquinone-based ultraviolet absorbers.

[0088] Examples of the aforementioned light stabilizers include hindered amine-based light stabilizers, benzoate-based light stabilizers, and oxamide-based light stabilizers.

[0089] Examples of the aforementioned pigments include titanium dioxide, carbon black, iron oxide, cadmium dye, phthalocyanine dye, and aluminum paste.

[0090] Examples of the adsorbent include metal oxides such as zinc oxide and magnesium oxide, activated carbon, zeolite, silica gel, and bentonite.

[0091] Examples of the lubricant include fatty acids, higher alcohols, aliphatic amides, aliphatic esters, carnauba wax, calcium stearate, and silicone oil.

[0092] The content of the polyolefin resin is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass, relative to the total amount of the resin pellets.

[0093] The coefficient of variation of the center of gravity radius in the resin pellet is, from the viewpoint of improving transportability from the feeder, 0.050 or more and 0.100 or less, preferably 0.050 or more and 0.095 or less, more preferably 0.055 or more and 0.095 or less, even more preferably 0.055 or more and 0.090 or less, and most preferably 0.060 or more and 0.090 or less.

[0094] The coefficient of variation of the center of gravity radius in the aforementioned resin pellet can be calculated by the following method.

[0095] First, select 10 resin pellets from the center of the container where the resin pellets are stored, place them on a flat blackboard, adjust their orientation to minimize their height (thickness), and acquire images of the resin pellets using a stereomicroscope (Nikon SMZ1000-3 standard BD set).

[0096] Next, the acquired images are imported into a computer and image analysis is performed using image analysis software (Python, OpenCV, NumPy, matplotlib, etc.). Specifically, first, the images of the resin pellets are converted to grayscale, and then Gaussian blur and histogram equalization are performed. After that, the images are binarized to match the contours of the resin pellets, and the contour with the largest area is extracted from the contours of the resin pellets detected in the image. The centroid coordinates of the extracted contours of the resin pellets are calculated, and the distance from the centroid to the contour (centroid radius) is measured radially in 360 directions at 1-degree intervals. Then, the standard deviation and mean are calculated from the obtained centroid radius data, and the coefficient of variation (CV) is determined.

[0097] The coefficient of variation of the center of gravity radius in the aforementioned resin pellet can be increased by raising the extrusion temperature or the cooling temperature during the resin pellet manufacturing process described later, and can be decreased by lowering the extrusion temperature or the cooling temperature.

[0098] From the viewpoint of improving handling ease, the major axis obtained by approximating the resin pellets as elliptical is preferably 3.7 mm to 5.0 mm, and more preferably 3.7 mm to 4.5 mm. Furthermore, from the viewpoint of improving handling ease, the minor axis obtained by approximating the resin pellets as elliptical is preferably 3.0 mm to 4.1 mm, and more preferably 3.0 mm to 4.0 mm.

[0099] The ratio of the major axis to the minor axis (aspect ratio, major axis / minor axis) obtained by approximating the resin pellets as an ellipse is preferably 1.10 or more and 1.40 or less, and more preferably 1.10 or more and 1.30 or less, from the viewpoint of improving handling.

[0100] The major and minor axes obtained by approximating the resin pellet as an ellipse are obtained by applying ellipse fitting (OpenCV's fitEllipse function) to the contour of the resin pellet extracted when determining the coefficient of variation of the centroid radius, obtaining the lengths of the major and minor axes of the ellipse (in pixels), and then converting them from pixels to millimeters.

[0101] From the viewpoint of improving handling, the maximum value of the center of gravity radius in the resin pellet is preferably 2.00 mm or more and 2.60 mm or less, and more preferably 2.00 mm or more and 2.50 mm or less. The maximum value of the center of gravity radius in the resin pellet is the largest value among the 360 ​​center of gravity radius data obtained when determining the coefficient of variation of the center of gravity radius as described above.

[0102] The difference between the maximum value of the center of gravity radius in the aforementioned resin pellet and the center of gravity radius at a point shifted 30 degrees from the position of that maximum value is preferably 0.09 mm to 0.35 mm, and more preferably 0.13 mm to 0.34 mm, from the viewpoint of improving handling. The center of gravity radius at a point shifted 30 degrees from the position of the maximum value is determined by identifying the angle (in the direction of maximum distance) that results from the maximum value among the 360 ​​center of gravity radius data obtained when determining the coefficient of variation of the center of gravity radius mentioned above, and then shifting the center of gravity radius at a position shifted 30 degrees clockwise from the angle of the maximum value.

[0103] The projected area per unit mass of the resin pellets is preferably 5.05 cm², from the viewpoint of facilitating discharge from the hopper and improving the tear resistance of the packaging bag that wraps the resin pellets. 2 / g or more 8.00cm 2 It is less than or equal to / g, and more preferably 5.30cm 2 / g or more 7.70cm 2 It is less than or equal to / g, and more preferably 5.50cm 2 / g or more 7.50cm 2 It is less than or equal to / g, and is particularly preferably 5.70cm 2 / g or more 7.30cm 2 It is less than or equal to / g, and most preferably 5.80cm 2 / g or more 7.00cm 2 It is less than / g.

[0104] The projected area per unit mass of the aforementioned resin pellet can be calculated by the following method.

[0105] First, a white circular frame with an inner diameter of 24.5 cm is placed on a black board, and 40 g of resin pellets are placed inside it. After evenly dispersing the resin pellets so that they do not overlap, a photograph is taken from directly above the resin pellets at a height that captures the entire sample, and the image is obtained.

[0106] Next, the captured images are imported into a computer and analyzed using image analysis software (Python, OpenCV, NumPy, matplotlib, etc.). Specifically, four points are selected on the circumference of the circular frame using the software, and a circle is approximated from the selected four points using the least squares method to calculate the center coordinates and radius of the circle. Next, the region of the calculated circle is extracted, converted to grayscale, and then binarized using multiple thresholds. The area of ​​the resin pellet region is measured from the resulting binarized image, and the image in which the outline of the resin pellet is clear and the overlap between resin pellets is minimized is selected and used for analysis. Then, the area (number of pixels) of the resin pellet region and the background region is measured from the binarized image, and the projected area of ​​the resin pellet is calculated in cm² by correlating the actual size of the circular frame (inner diameter 24.5 cm) with the diameter (number of pixels) in the image. 2 Convert to units.

[0107] The projected area per unit mass of the resin pellet can be increased in the resin pellet manufacturing process described later by reducing the extrusion amount or increasing the rotation speed of the cutter box, and can be decreased in the resin pellet manufacturing process described later by increasing the extrusion amount or decreasing the rotation speed of the cutter box.

[0108] The average mass per 10 resin pellets is preferably 0.12g or more and 0.30g or less, more preferably 0.17g or more and 0.28g or less, even more preferably 0.18g or more and 0.26g or less, and most preferably 0.20g or more and 0.26g or less, from the viewpoint of improving handling. The average mass per 10 resin pellets is the average of the measured values ​​obtained by selecting 10 different resin pellets each time, measuring their mass, and repeating this 10 times.

[0109] The value obtained from the product of the projected area per unit mass and the aspect ratio is preferably 5.50 cm² from the viewpoint of improving handling. 2 / g or more 10.00cm 2 It is less than or equal to / g, and more preferably 5.70cm 2 / g or more 9.70cm 2 It is less than / g.

[0110] The value obtained by dividing the projected area per unit mass by the average mass per 10 grains is preferably 18.0 cm² from the viewpoint of improving handling. 2 / g 2 More than 70.0cm 2 / g 2 The following, and more preferably 18.3 cm 2 / g 2 More than 65.0cm 2 / g 2 The following applies:

[0111] The resin pellets according to this embodiment can be manufactured, for example, using known methods. Known manufacturing methods generally include the strand cutting method, in which a molten and kneaded polyolefin resin is extruded in strand form using an extruder and cut with a strand cutter; the die cutting method, in which a molten and kneaded polyolefin resin is extruded from the die of an extruder and cut on the die surface using a rotary cutter; and the sheet cutting method, in which a molten and kneaded polyethylene resin is extruded in sheet form and the resulting sheet is cut into pellets. Die cutting methods include the underwater cutting method, in which cutting is performed underwater, and the hot cutting method, in which cutting is performed while cooling with cooling air, water, etc. From the viewpoint of improving the ability to bite into the screw when molding with a single-screw extruder, the method for manufacturing the resin pellets is preferably the strand cutting method or the underwater cutting method.

[0112] The melt-mixing temperature of the polyolefin resin can be, for example, 150°C to 230°C. The extrusion temperature of the polyolefin resin can also be, for example, 150°C to 230°C. The melt-mixing temperature and extrusion temperature of the polyolefin resin can be the same. The cooling temperature of the polyolefin resin can be, for example, 20°C to 60°C.

[0113] The resin pellet according to the embodiment of the first invention is a resin pellet containing a polyolefin resin, and because the coefficient of variation of the center of gravity radius is 0.050 or more and 0.100 or less, it has relatively good handling properties, and in particular, it can improve transportability from a feeder.

[0114] <Second Embodiment> The following describes an embodiment of the second invention (second embodiment). The second embodiment differs from the first embodiment described above in the following respects, but other configurations are common. Therefore, the description of common configurations will not be repeated.

[0115] The projected area per unit mass of the aforementioned resin pellets is set to 5.05 cm², from the viewpoint of facilitating discharge from the hopper and improving the tear resistance of the packaging bags that enclose the resin pellets. 2 / g or more 8.00cm 2 It is less than or equal to / g, preferably 5.30cm 2 / g or more 7.70cm 2 It is less than or equal to / g, and more preferably 5.50cm 2 / g or more 7.50cm 2 It is less than or equal to / g, and is particularly preferably 5.70cm 2 / g or more 7.30cm 2 It is less than or equal to / g, and most preferably 5.80cm 2 / g or more 7.00cm 2 It is less than / g.

[0116] The resin pellet according to the second embodiment of the invention is a resin pellet containing a polyolefin resin, and has a projected area of ​​5.05 cm² per unit mass. 2 / g or more 8.00cm 2 Being less than / g offers relatively good handling, particularly improving discharge from the hopper and enhancing the tear resistance of the packaging bags used to wrap the resin pellets.

[0117] Furthermore, the resin pellets according to the present invention are not limited to the configuration of the above embodiments, nor are they limited to the effects described above. Various modifications can be made to the resin pellets according to the present invention without departing from the spirit of the invention.

[0118] The present invention includes the following embodiments. [1] A resin pellet containing a polyolefin resin, A resin pellet having a coefficient of variation of the center of gravity radius of 0.050 or more and 0.100 or less. [2] The projected area per unit mass is 5.05 cm². 2 / g or more 8.00cm 2 The resin pellets described in [1] are less than or equal to / g. [3] A resin pellet containing a polyolefin resin, The projected area per unit mass is 5.05 cm². 2 / g or more 8.00cm 2 Resin pellets that are less than / g. [4] The resin pellet according to any one of [1] to [3], wherein the polyolefin resin comprises at least one selected from the group consisting of ethylene polymers and propylene polymers. [5] The polyolefin resin contains low-density polyethylene as the ethylene polymer, The density of the aforementioned low-density polyethylene is 900 kg / m³. 3 More than 930kg / m 3 The resin pellets described in [4] are as follows: [6] The polyolefin resin comprises an ethylene-vinyl acetate copolymer or an ethylene-methyl methacrylate copolymer as the ethylene polymer, The density of the ethylene-vinyl acetate copolymer or ethylene-methyl methacrylate copolymer is 920 kg / m³. 3 More than 950kg / m 3 The resin pellets described in [4] are as follows: [7] The polyolefin resin comprises a propylene homopolymer or a propylene-ethylene random copolymer as the propylene polymer, The density of the propylene homopolymer or the propylene-ethylene random copolymer is 900 kg / m³. 3 More than 920kg / m 3 The resin pellets described in [4] are as follows: [8] The resin pellet according to any one of [1] to [7], wherein the major axis obtained by approximating the resin pellet as an ellipse is 3.7 mm or more and 5.0 mm or less. [9] The resin pellet according to any one of [1] to [8], wherein the ratio of the major axis to the minor axis (aspect ratio) obtained by approximating the resin pellet as an ellipse is 1.10 or more and 1.40 or less.

[10] A resin pellet as described in any one of [1] to [9], wherein the maximum value of the center of gravity radius is 2.00 mm or more and 2.60 mm or less.

[11] The resin pellet described in

[10] , wherein the difference between the maximum value of the center of gravity radius and the center of gravity radius at a point shifted 30 degrees from the position of the maximum value is 0.09 mm or more and 0.35 mm or less.

[12] The resin pellet according to any one of [5], [8] to

[11] , wherein the melting point of the low-density polyethylene is 100°C or more and 120°C or less.

[13] The resin pellet according to any one of [5], [8] to

[12] , wherein the glass transition temperature of the low-density polyethylene is -125°C or higher and -100°C or lower.

[14] A resin pellet as described in any one of [1] to

[13] , wherein the average mass per 10 pellets is 0.12g or more and 0.30g or less.

[15] The value obtained from the product of the projected area per unit mass and the aspect ratio is 5.50 cm 2 / g or more 10.00cm 2 A resin pellet listed in any one of [9] to

[14] , which is less than or equal to / g.

[16] The value obtained by dividing the projected area per unit mass by the average mass per 10 grains is 18.0 cm². 2 / g 2 More than 70.0cm 2 / g 2 The resin pellets described in

[14] or

[15] below. [Examples]

[0119] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

[0120] The measured values ​​for each item in each test example were measured using the following method.

[0121] (Density (unit: kg / m³) 3 (Measurement method) (1) Density of ethylene polymers (unit: kg / m³) 3 ) After performing annealing as described in JIS K6760-1995, measurements were taken using Method A according to the method specified in JIS K7112-1980.

[0122] (2) Density of propylene polymer (unit: kg / m³) 3 ) Samples prepared using the method described in JIS K6758-1981 were annealed under conditioned conditions of 40 to 72 hours at a temperature of 23°C, and measured according to Method A (water displacement method) specified in JIS K7112-1980.

[0123] (Method for measuring melt flow rate (MFR, unit: g / 10 min)) (1) Melt flow rate (MFR, unit: g / 10 min) of ethylene copolymers The measurement was performed according to Method A, as specified in JIS K7210-1995, under conditions of a temperature of 190°C and a load of 2.16 kg.

[0124] (2) Melt flow rate (MFR, unit: g / 10 min) of propylene polymers The measurement was performed according to Method A, as specified in JIS K7210-1995, under conditions of a temperature of 230°C and a load of 2.16 kg.

[0125] (Method for measuring the content (mass %) of monomer units derived from vinyl acetate in ethylene-vinyl acetate copolymer) The content of monomer units derived from vinyl acetate in the ethylene-vinyl acetate copolymer was measured in accordance with JIS K7192:1999 (the content of monomer units derived from vinyl acetate is the sum of the content of monomer units derived from ethylene and the content of monomer units derived from vinyl acetate, with 100% by mass).

[0126] The materials used in each test example are as follows:

[0127] [PE-1] Linear low-density polyethylene ethylene-1-hexene copolymer was produced by high-pressure ionic polymerization using a tank reactor at a reaction temperature of 226°C, a reaction pressure of 73 MPa, and a gas flow rate of 33.9 tons / hour. The yield was 6.2 tons / hour. Sampling tests of the polymer properties revealed that the resulting linear low-density polyethylene had a molecular weight (MFR) of 0.8 g / 10 min and a density of 919 kg / m³. 3 That was the case.

[0128] [PE-2] Linear low-density polyethylene ethylene-1-hexene copolymer GZ802 (manufactured by Sumitomo Chemical Co., Ltd., MFR: 30g / 10min, density: 927kg / m³) 3 ) was used.

[0129] [PE-3] Metallocene linear low-density polyethylene ethylene-1-hexene copolymer FV201 (manufactured by Sumitomo Chemical Co., Ltd., MFR: 2.0 g / 10 min, density: 916 kg / m³) 3 ) was used.

[0130] [PE-4] Ethylene homopolymer F200 (manufactured by Sumitomo Chemical Co., Ltd., MFR: 2.0 g / 10 min, density: 924 kg / m³) 3 ) was used.

[0131] [PP-1] Propylene homopolymer D101 (manufactured by Sumitomo Chemical Co., Ltd., MFR: 0.5g / 10min, density: 900kg / m³) 3 ) was used.

[0132] [EVA-1] Ethylene-vinyl acetate copolymer KA-40 (manufactured by Sumitomo Chemical Co., Ltd., MFR: 22g / 10min, density: 950kg / m³) 3 The monomer unit content derived from vinyl acetate was 28% by mass.

[0133] The resin pellets for each test example were prepared using the following method.

[0134] <Test Example 1> 70% by mass of PE-1 and 30% by mass of PE-2 were mixed and kneaded using a 65mm single-screw extruder (manufacturer: CHAREON TUT CO.,LTD., model: SE-D65L15, L / D ratio 15) at a kneading temperature of 160°C and an extrusion rate of 8.1 kg / h. Next, using a 4-hole die with a hole diameter of 3.0 mm, the molten resin was cut in a cutter box equipped with two cutter blades (rotation speed 600 rpm, water temperature 40°C) using an underwater cut method in which the die outlet was directly submerged in water, to obtain the resin pellets of Test Example 1.

[0135] <Test Example 2> The resin pellets for Test Example 2 were obtained under the same conditions as in Test Example 1, except that the rotation speed of the cutter box was changed to 1000 rpm.

[0136] <Test Example 3> The resin pellets for Test Example 3 were obtained under the same conditions as in Test Example 1, except that 100% by mass of PE-3 was used as the material, the extrusion rate was set to 8.6 kg / h, and the rotation speed of the cutter box was changed to 700 rpm.

[0137] <Test Example 4> Except for using 100% by mass PP-1 as the material, setting the mixing temperature to 230°C, the extrusion rate to 6.6 kg / h, and changing the cutter box rotation speed to 1000 rpm, the resin pellets of Test Example 4 were obtained under the same conditions as Test Example 1. However, because the resin pellets of Test Example 4 were hard, the discharge volume of the resin pellets, as described later, could not be measured.

[0138] <Test Example 5> The resin pellets for Test Example 5 were obtained under the same conditions as in Test Example 3, except that the rotation speed of the cutter box was changed to 1500 rpm.

[0139] <Test Example 6> After obtaining resin pellets under the same conditions as in Test Example 1, 100g of the resin pellets were added to a 500mL beaker and shaken 100 times horizontally over a width of 10cm to perform particle size classification. Then, 40g of resin pellets were scooped out from the top of the resin pellets to obtain the larger particle size resin pellets of Test Example 6.

[0140] <Test Example 7> The resin pellets for Test Example 7 were obtained under the same conditions as in Test Example 1, except that the rotation speed of the cutter box was changed to 1500 rpm.

[0141] <Test Example 8> The resin pellets of Test Example 8 were obtained under the same conditions as in Test Example 1, except that 80% by mass of PE-4 and 20% by mass of EVA-1 were used as materials, the extrusion rate was set to 7.2 kg / h, and the water temperature was changed to 25°C.

[0142] (Evaluation of resin pellets) (i) Image taken from directly above the resin pellet A white circular frame with an inner diameter of 24.5 cm was placed on a black plate, and 40 g of resin pellets were placed inside. The resin pellets were spread out evenly using the bottom of a 50 mL beaker to prevent them from overlapping. Then, a photograph was taken from directly above the resin pellets at a height that captured the entire sample, and an image taken from directly above the pellets was obtained.

[0143] (ii) Projection area of ​​resin pellet (cm²) 2 Analysis of / g) The captured images obtained in (i) above were imported into a computer, and image analysis was performed using image analysis software (Python, OpenCV, NumPy, matplotlib, etc.) in the following procedure. 1. Four points were selected on the circumference of the circular frame using image viewing software. 2. A circle was approximated using the least squares method from the four selected points, and the coordinates of the circle's center and its radius were calculated. 3. The calculated circular region was extracted, converted to grayscale, and then binarized using multiple thresholds. The area of ​​the resin pellet region was measured for the resulting binarized image, and the image in which the outline of the resin pellet was clear and the overlap between resin pellets was minimized was selected and used for analysis. 4. The area (number of pixels) of the resin pellet region and the background region was measured from the binarized image. 5. By correlating the actual size of the circular frame (inner diameter 24.5 cm) with the diameter (number of pixels) in the image, the projected area of ​​the resin pellet can be measured in cm². 2 The units were converted. The results are shown in Table 1.

[0144] (iii) Pellet images obtained by stereomicroscope observation Ten resin pellets were selected from the center of the container where the resin pellets were stored, placed on a flat blackboard, and rotated by hand to adjust the orientation so that the height (thickness) of the resin pellets was minimized. Then, images of the resin pellets were acquired using a stereomicroscope under the following conditions (1) to (4).

[0145] (1) Stereomicroscope: Nikon SMZ1000-3 standard BD set (2) Light source: AS ONE LED illumination device for stereo microscopes 1-9227-02, with only one of the four independent incident light directions illuminated. (3) Objective lens: 0.5x (4) Zoom: 2x

[0146] (iv) Procedure for analyzing resin pellet images The images obtained in (iii) above were imported into a computer, and image analysis was performed using image analysis software (Python, OpenCV, NumPy, matplotlib, etc.). 1. After converting the acquired resin pellet images to grayscale, Gaussian blur and histogram equalization were applied. 2. The image was binarized to match the outline of the resin pellet, and the outline with the largest area was extracted from among the resin pellet outlines detected in the image. 3. The centroid coordinates of the outline of the extracted resin pellets were calculated, and the distance from the centroid to the outline (centroid radius) was measured radially in 360 directions at 1-degree intervals. 4. Ellipse fitting (OpenCV's fitEllipse function) was applied to the contour of the extracted resin pellet to obtain the lengths (in pixels) of the major and minor axes of the ellipse. 5. The acquired values ​​were converted from pixels to millimeters based on the scale bar in the image.

[0147] (v) Analysis of the center of gravity radius The standard deviation and mean value were calculated from 360 centroid radius data points obtained using the resin pellet image analysis procedure, and the coefficient of variation (CV) was determined. The calculation results are shown in Table 1.

[0148] (vi) Shape evaluation using elliptic approximation The aspect ratio (major axis / minor axis) was calculated using the major axis (mm) and minor axis (mm) of the ellipse obtained by the resin pellet image analysis procedure. The calculation results are shown in Table 1.

[0149] (vii) Calculation of the maximum value of the center of gravity radius (mm) and the difference (mm) from the maximum value to a position shifted 30 degrees. From the 360 ​​centroid radius data points obtained using the resin pellet image analysis procedure, the angle with the maximum value (in the direction of maximum distance) was identified. The centroid radius at a position shifted 30 degrees clockwise from the angle with the maximum value was then obtained, and the difference between this value and the maximum value was calculated. The calculation results are shown in Table 1.

[0150] (viii) Average mass (g) per 10 resin pellets Ten different resin pellets were selected from the resin pellets used in the projected area analysis of the resin pellets, and this process was repeated 10 times to measure the mass of the 10 pellets. The average of the 10 measurements obtained was defined as the "average mass per 10 pellets (g)". The measurement results are shown in Table 1.

[0151] (ix) Discharge time from PVC pipe (seconds) The pellet discharge time was evaluated using a circular PVC pipe with a shutter. The pipe used had an inner diameter of 5.2 cm, a length of 142 cm below the shutter, a thickness of 1 mm, and an inclination angle of 17.3°. 20 g of resin pellets were placed above the shutter of this pipe, and the time (in seconds) until the resin pellets were completely discharged from the pipe was measured, with the time when the shutter was opened being set as 0 seconds. This operation was repeated three times, with a different resin pellet used each time. The average of the obtained discharge times was defined as the discharge time from the PVC pipe (in seconds). The measurement results are shown in Table 1. Note that a shorter discharge time from the PVC pipe indicates better discharge performance from the hopper.

[0152] (x) Breakage rate of plastic bags (%) Five evaluation samples were prepared by placing 15g of resin pellets into Unipack A4 bags (0.04mm thick, polyethylene, dimensions (width x below zipper): 50 x 70mm) manufactured by Seisan Nippon Co., Ltd., and sealing them with as much air removed as possible. Under conditions of 23°C and 50% humidity, the evaluation samples were placed in a DuPont impact tester, and a 2kg weight was dropped onto the evaluation samples from a height of 200mm up to 20 times. The bags were visually checked each time to see if they had burst, and the number of drops until the bag burst was defined as "the number of drops immediately before the bag burst." For example, if the bag burst on the 9th drop, the number of drops until burst was set to 8. For each resin pellet, the number of drops until the bag burst for all five bags was recorded, and the average of these recorded values ​​was calculated. The unbursted bag rate (%) was calculated by dividing the obtained average value by the maximum number of drops (20), and the bag burst rate (%) for the resin bags was calculated as "100 - unbursted bag rate (%)". The calculation results are shown in Table 1.

[0153] (xi) Standard deviation of resin pellet discharge volume (g) Using a capacitive feeder mounted on a twin-screw extruder manufactured by Technovel Co., Ltd. (model: KZW20TW-45MG-NH), the discharge rate of solid resin pellets was evaluated based on the following conditions (21) to (25). 100g of resin pellets were placed in the pellet feeder hopper, and the feeder was rotated to discharge. The start of resin pellet discharge was defined as 0 seconds, and the discharge rate was measured every minute, continuing until the pellet discharge was complete. A decrease of 20% or more in the discharge rate of resin pellets compared to the previous minute was considered a raw material shortage, and the standard deviation was calculated using all the minute-by-minute discharge rate data obtained up to the point of the raw material shortage. The calculation results are shown in Table 1. Note that a smaller standard deviation in the discharge rate of resin pellets indicates better transportability from the feeder.

[0154] (21) Equipment: Capacitive feeder mounted on a twin-screw extruder manufactured by Technobel Co., Ltd. (Model: KZW20TW-45MG-NH) (22) Feeder type: Auger type (Screw outer diameter: 17 mm, coil cross-sectional diameter: 4 mm (circular), pitch: 15 mm) (23) Feeder drive: Motor manufactured by Oriental Motor Co., Ltd. (Model: 5IK90GU-SWT) (24) Hopper filling amount: 100g (25) Feeder screw rotation speed: 10 rpm

[0155] [Table 1]

[0156] As can be seen from the results in Table 1, the resin pellets of Test Examples 1-3 and 5-7, which satisfy all the constituent elements of the first invention, have a relatively small standard deviation in the discharge volume of the resin pellets and excellent transportability from the feeder, and therefore can be said to be relatively easy to handle. Furthermore, the resin pellets of Test Examples 1-5, which satisfy all the constituent elements of the second invention, have a relatively short discharge time from the polyvinyl chloride piping, resulting in excellent dischargeability from the hopper, and also have a relatively small bag breakage rate in the packaging bags that pack the resin pellets, resulting in excellent bag breakage resistance, and therefore can be said to be relatively easy to handle.

Claims

1. Resin pellets containing polyolefin resin, A resin pellet having a coefficient of variation of the center of gravity radius of 0.050 or more and 0.100 or less.

2. The projected area per unit mass is 5.05 cm². ２ / g or more 8.00cm ２ The resin pellets according to claim 1, wherein the amount is less than or equal to / g.

3. Resin pellets containing polyolefin resin, The projected area per unit mass is 5.05 cm². ２ / g or more 8.00cm ２ Resin pellets that are less than / g.

4. The resin pellet according to claim 1 or 3, wherein the polyolefin resin comprises at least one selected from the group consisting of ethylene polymers and propylene polymers.

5. The polyolefin resin contains low-density polyethylene as the ethylene polymer. The density of the aforementioned low-density polyethylene is 900 kg / m³. ３ More than 930kg / m ３ The resin pellet according to claim 4, which is as follows:

6. The polyolefin resin includes, as the ethylene polymer, ethylene-vinyl acetate copolymer or ethylene-methyl methacrylate copolymer. The density of the ethylene-vinyl acetate copolymer or ethylene-methyl methacrylate copolymer is 920 kg / m³. ３ More than 950kg / m ３ The resin pellet according to claim 4, which is as follows:

7. The polyolefin resin includes a propylene homopolymer or a propylene-ethylene random copolymer as the propylene polymer. The density of the propylene homopolymer or the propylene-ethylene random copolymer is 900 kg / m ３ or more and 920 kg / m ３ or less. The resin pellet according to claim 4.

8. The resin pellet according to claim 1 or 3, wherein the major axis obtained by approximating the resin pellet as an ellipse is 3.7 mm or more and 5.0 mm or less.

9. The resin pellet according to claim 1 or 3, wherein the ratio of the major axis to the minor axis (aspect ratio) obtained by approximating the resin pellet as an ellipse is 1.10 or more and 1.40 or less.

10. The resin pellet according to claim 1 or 3, wherein the maximum value of the center of gravity radius is 2.00 mm or more and 2.60 mm or less.

11. The resin pellet according to claim 10, wherein the difference between the maximum value of the center of gravity radius and the center of gravity radius at a point shifted 30 degrees from the position of the maximum value is 0.09 mm or more and 0.35 mm or less.

12. The resin pellet according to claim 5, wherein the melting point of the low-density polyethylene is 100°C or higher and 120°C or lower.

13. The resin pellet according to claim 5, wherein the glass transition temperature of the low-density polyethylene is -125°C or higher and -100°C or lower.

14. The resin pellets according to claim 1 or 3, wherein the average mass per 10 pellets is 0.12 g or more and 0.30 g or less.

15. The value obtained from the product of the projected area per unit mass and the aspect ratio is 5.50 cm². ２ / g or more 10.00cm ２ The resin pellets according to claim 9, wherein the amount is less than or equal to / g.

16. The value obtained by dividing the projected area per unit mass by the average mass per 10 grains is 18.0 cm². ２ / g ２ 70.0cm or more ２ / g ２ The resin pellet according to claim 14, which is as follows:

Images