Porous particles and purging agents

Abstract

Provided is a purging agent capable of efficiently discharging a resin to be purged from inside a molding machine. Porous particles containing an ethylene-vinyl alcohol copolymer (A) and an alkali metal (B), the particles having a pore median diameter of 0.01 to 3µm, an average particle size of 2.5 to 8 mm, and an alkali metal (B) content of 1,000 to 100,000 ppm.

Description

[Technical Field]

[0001] The present invention relates to porous particles and purging agents. [Background technology]

[0002] Resins with excellent gas barrier properties, such as ethylene-vinyl alcohol copolymers (hereinafter sometimes referred to as EVOH), are widely used in products such as food packaging films and containers. When the resin is melt-extruded in a molding machine to produce these products, the resin can adhere to the flow path (e.g., the screw) of the molding machine. If this adhered resin is left for a long period of time, it can deteriorate through factors such as burning, gelation, and decomposition, resulting in defects such as streaks, bumps, and gels in the resulting products, or it can result in a significant amount of time and material loss in correcting the defects.

[0003] Various purging agents have been proposed for removing resin (hereinafter sometimes referred to as "resin to be purged") adhering to screws and other components in molding machines. For example, Patent Document 1 discloses a purging agent containing a hydrophobic thermoplastic resin such as a polyolefin resin, a hydrophilic thermoplastic resin such as a saponified ethylene-vinyl acetate copolymer, and water. Patent Document 2 discloses a purging agent containing a saponified ethylene-vinyl ester copolymer or the like and water in a predetermined ratio. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-16023 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-279623 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the purging agents described in Patent Documents 1 and 2 cannot be said to be able to sufficiently remove the resin to be purged from inside the molding machine, and there is a demand for an improvement in purging ability.

[0006] The present invention is intended to solve the above problems, and an object of the present invention is to provide a purging agent that can efficiently discharge the resin to be purged from inside a molding machine. [Means for solving the problem]

[0007] According to the present invention, the above object is to [1] Porous particles containing an ethylene-vinyl alcohol copolymer (A) and an alkali metal (B), the porous particles having a median pore size of 0.01 to 3 μm, an average particle size of 2.5 to 8 mm, and a content of the alkali metal (B) of 1,000 to 100,000 ppm; [2] Pore surface area is 25 to 60 m 2 / g, [1] porous particles; [3] The porous particles of [1] or [2], which are water-containing porous particles; [4] Porous particles according to [3], having a moisture content of 5 to 80 mass%; [5] The porous particles according to any one of [1] to [4], wherein the ethylene unit content of the ethylene-vinyl alcohol copolymer (A) is 18 to 52 mol%; [6] A purging agent containing porous particles according to any one of [1] to [5]; [7] The purging agent according to [6], further containing 50 mass% or more of a polyolefin resin (C); This is achieved by providing either [Effects of the Invention]

[0008] According to the present invention, the resin to be purged in the molding machine can be efficiently discharged from the molding machine, thereby reducing defective products obtained from the molding machine and the time and material loss required to correct the defective products. DETAILED DESCRIPTION OF THE INVENTION

[0009] In this specification, the use of "to" to indicate a range of values ​​means that the range includes the respective lower and upper limits. For example, A to B means that the range is A or more and B or less.

[0010] <Porous particles> The porous particles of the present invention contain EVOH (A) and an alkali metal (B), have a median pore size of 0.01 to 3 μm, an average particle size of 2.5 to 8 mm, and a content of the alkali metal (B) of 1,000 to 100,000 ppm.

[0011] (EVOH(A)) The EVOH (A) used in the present invention is typically obtained by saponifying an ethylene-vinyl ester copolymer. In the present invention, the EVOH preferably has an ethylene unit content of, for example, 18 mol% or more, 21 mol% or more, 24 mol% or more, or 30 mol% or more. The ethylene unit content of the EVOH is preferably, for example, 52 mol% or less, 49 mol% or less, or 46 mol% or less. When the ethylene unit content is 18 mol% or more, the risk of deterioration of the EVOH itself during purging is reduced, and the melting point is lowered, allowing the extrusion temperature to be set relatively low. When the ethylene unit content is 52 mol% or less, the viscosity of the molten resin (EVOH) increases, tending to facilitate removal of the resin to be purged. The ethylene unit content of the EVOH can be measured, for example, by nuclear magnetic resonance (NMR) spectroscopy.

[0012] In the present invention, the saponification degree of EVOH (i.e., the saponification degree of the vinyl ester component of EVOH) is, for example, preferably 95 mol% or more, more preferably 98% or more, and even more preferably 99 mol% or more. On the other hand, the saponification degree of EVOH is, for example, preferably 100% or less, and may be 99.99% or less. The saponification degree of EVOH is, 1 It can be calculated by measuring the peak area of ​​the hydrogen atoms contained in the vinyl ester structure and the peak area of ​​the hydrogen atoms contained in the vinyl alcohol structure by H-NMR measurement.

[0013] EVOH may also contain units derived from monomers other than ethylene, vinyl esters, and saponified products thereof, provided that the object of the present invention is not impaired. When EVOH contains units derived from other monomers, the upper limit of the content of the units derived from the other monomers relative to the total structural units of EVOH is, for example, 30 mol% or less, 20 mol% or less, 10 mol% or less, or 5 mol% or less. When EVOH contains units derived from the other monomers, the content is, for example, preferably 0.05 mol% or more, and more preferably 0.1 mol% or more.

[0014] Other monomers include alkenes such as propylene, butylene, pentene, and hexene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, and 3-acyloxy-4-methyl-1-butene. , 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy- Examples of suitable vinyl silane compounds include ester group-containing alkenes or saponified products thereof, such as 1-hexene and 1,3-diacetoxy-2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, and itaconic acid, or their anhydrides, salts, or mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, and methallylsulfonic acid, or their salts; vinyl silane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, and γ-methacryloxypropylmethoxysilane; and alkyl vinyl ethers, vinyl ketone, N-vinylpyrrolidone, vinyl chloride, and vinylidene chloride.

[0015] EVOH may be modified by urethanization, acetalization, cyanoethylation, oxyalkylenation, etc. When used as a purging agent, the modified EVOH has improved compatibility with the resin to be purged, such as a urethane-based, acetal-based, or acrylonitrile-based resin, and allows for more efficient purging.

[0016] As the EVOH, two or more kinds of EVOHs differing in ethylene unit content, degree of saponification, copolymer component, presence or absence of modification or type of modification may be used in combination.

[0017] EVOH can be obtained by known methods such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. In one embodiment, bulk polymerization or solution polymerization is used, in which polymerization can proceed without a solvent or in a solution such as an alcohol.

[0018] The solvent used in the solution polymerization method is not particularly limited, but is, for example, an alcohol, preferably a lower alcohol such as methanol, ethanol, propanol, etc. The amount of solvent used in the polymerization reaction solution may be selected taking into consideration the viscosity-average degree of polymerization of the target EVOH and chain transfer of the solvent, and the mass ratio of the solvent to the total monomers contained in the reaction solution (solvent / total monomers) is, for example, 0.01 to 10, preferably 0.05 to 3.

[0019] Examples of the catalyst used in the polymerization include azo initiators such as 2,2-azobisisobutyronitrile, 2,2-azobis-(2,4-dimethylvaleronitrile), 2,2-azobis-(4-methoxy-2,4-dimethylvaleronitrile), and 2,2-azobis-(2-cyclopropylpropionitrile); and organic peroxide initiators such as isobutyryl peroxide, cumyl peroxyneodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxyneodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide.

[0020] The polymerization temperature is preferably 20°C to 90°C, more preferably 40°C to 70°C. The polymerization time is preferably 2 hours to 15 hours, more preferably 3 hours to 11 hours. The polymerization rate is preferably 10% to 90% based on the amount of vinyl ester charged, more preferably 30% to 80%. The resin content in the solution after polymerization is preferably 5% to 85%, more preferably 20% to 70%.

[0021] In the above polymerization, after a predetermined period of polymerization or after a predetermined polymerization rate has been reached, a polymerization inhibitor is added as needed, and unreacted ethylene gas is evaporated and removed, thereby removing unreacted vinyl ester.

[0022] Next, an alkali catalyst is added to the copolymer solution to saponify the copolymer. The saponification method may be, for example, either a continuous method or a batch method. Examples of alkali catalysts that can be added include sodium hydroxide, potassium hydroxide, and alkali metal alcoholates.

[0023] Since EVOH after the saponification reaction usually contains impurities, it is preferable to remove these by neutralization or washing as necessary.

[0024] The lower limit of the content of EVOH (A) in the porous particles of the present invention in a dry state is preferably 80% by mass, and in some cases, 90%, 92%, or 95% by mass is more preferable. The upper limit of this content is preferably 99.9% by mass. The content in a dry state is equal to the content based on all components other than water.

[0025] (alkali metal (B)) The alkali metal (B) contained in the porous particles of the present invention is not particularly limited in form and may exist, for example, as a salt or a compound other than a salt, preferably in the form of a salt. When present in the form of a salt, the alkali metal (B) may be free as an alkali metal ion or may be bound to a counter ion. The porous particles of the present invention may contain the alkali metal (B) element in a range of 1,000 to 100,000 ppm. Examples of alkali metals include lithium, sodium, potassium, rubidium, and cesium, with sodium and potassium being preferred from the viewpoint of excellent reactivity with the resin to be purged in the molding machine. Examples of counter ions of the salt include carbonate ions, bicarbonate ions, carboxylate ions, and hydroxide ions. Among these, anions of weak acids such as carbonate ions, bicarbonate ions, and carboxylate ions are preferred. When the alkali metal (B) forms a salt with a weak acid (an alkali metal salt of a weak acid), an alkaline aqueous solution is easily generated in the presence of water in the extruder flow path, allowing for particularly efficient removal of the resin to be purged.

[0026] The content of the alkali metal (B), calculated as the alkali metal element, is 1,000 ppm or more, preferably 2,500 ppm or more, more preferably 5,000 ppm or more, even more preferably 10,000 ppm or more, and in some cases even more preferably 12,000 ppm, 14,000 ppm or more, or 15,000 ppm or more. If the content of the alkali metal (B) is less than 1,000 ppm, the reactivity as a purging agent decreases. In addition, the content of the alkali metal (B) is 100,000 ppm or less, preferably 75,000 ppm or less, more preferably 50,000 ppm or less, and even more preferably 25,000 ppm or less, or 20,000 ppm or less. If the content of the alkali metal (B) exceeds 100,000 ppm, there is a risk of corrosion of the resin flow path in the extruder.

[0027] (Other additives) The porous particles of the present invention may contain additives other than the EVOH (A) and the alkali metal (B) (a component containing an alkali metal element), provided that the effects of the present invention are not impaired. Examples of such additives include metal salts other than alkali metal salts, acids, boron compounds, lubricants, colorants, UV absorbers, desiccants, crosslinking agents, abrasives, fillers, heat stabilizers, processing aids, antiblocking agents, antistatic agents, coupling agents, antioxidants, lubricants, foaming agents, surfactants, plasticizers, and combinations thereof. In particular, abrasives are used to physically polish the resin to be purged from the molding machine and discharge it, and examples of such additives include inorganic compounds such as alumina, zirconia, silica, titanium dioxide, and calcium carbonate.

[0028] (shape, etc.) The median pore diameter of the porous particles of the present invention measured by mercury intrusion porosimetry is 0.01 to 3 μm. The median pore diameter of the porous particles is a value in the range of 0.005 to 100 μm, specifically, a value measured by the method described in the Examples below. If the median pore diameter is less than 0.01 μm, moisture absorption may be slowed, resulting in reduced productivity. The lower limit of this median pore diameter is preferably 0.03 μm, more preferably 0.05 μm, and even more preferably 0.06 μm. If the median pore diameter exceeds 3 μm, water may be released too quickly, resulting in the porous particles being unable to retain moisture. If the median pore diameter exceeds 3 μm, the strength of the porous particles may decrease, reducing handleability and making the final product more susceptible to fine powder or chipped pellets. The upper limit of the median pore diameter is preferably 2 μm, more preferably 1 μm, and even more preferably 0.5 μm, 0.3 μm, 0.2 μm or 0.15 μm.

[0029] The pore surface area of ​​the porous particles of the present invention is 25 to 60 m 2 / g. It is preferable that the pore surface area of ​​the porous particles is in the above range, since the alkali metal (B) is appropriately adsorbed. The pore surface area of ​​the porous particles is measured by mercury intrusion porosimetry. The pore surface area of ​​the porous particles is a value in the range of pore diameters of 0.005 to 100 μm, and specifically, is a value measured by the method described in the examples below. It is preferable that the pore surface area of ​​the porous particles is 25 m 2 / g or more, the content of alkali metal (B) and the water content of the porous particles can be sufficiently increased. 2 When the pore surface area is less than 45 m / g, the strength of the porous particles increases, improving the handling properties, and the final product tends to be less prone to fine powder or chipped pellets. 2 / g is more preferred.

[0030] The median pore size and surface area of ​​the porous particles of the present invention can be adjusted, for example, by adjusting the water content, alcohol content, and extrusion temperature of the EVOH paste used to prepare the hydrous EVOH pellets. When the hydrous EVOH pellets are obtained by precipitation in the form of strands, the median pore size and surface area can also be adjusted by the concentration of the EVOH solution, the temperature and alcohol concentration of the precipitation bath, the washing temperature of the obtained hydrous EVOH pellets, etc.

[0031] The average particle size of the porous particles of the present invention is 2.5 to 8 mm. If the average particle size is less than 2.5 mm, there is a risk of separation with other resins when introduced into an extruder. The lower limit of this average particle size may preferably be 3.0 mm. If the average particle size exceeds 8 mm, there is a risk of reduced penetration into the hopper when introduced into the extruder. The upper limit of this average particle size may preferably be 7 mm, 6 mm, 5 mm, or 4.0 mm. The average particle size of the porous particles is the median size based on a volume-based cumulative particle size distribution, and is a value measured by the method described in the Examples.

[0032] The porous particles of the present invention are preferably hydrous porous particles. When the porous particles contain water, they become an alkaline solution in the extruder flow path, allowing the resin to be purged to be efficiently removed. The water content of the hydrous porous particles is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. When the water content is 5% by mass or more, a sufficient amount of alkaline solution can be generated in the extruder flow path. Furthermore, the water content of the hydrous porous particles is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. When the water content is 80% by mass or less, a decrease in the concentration of the alkaline solution is suppressed.

[0033] <Purging agent> The purging agent of the present invention contains the porous particles of the present invention. The content of the porous particles in the purging agent of the present invention may be, for example, 1% by mass or more and 100% by mass or less, 2% by mass or more and 50% by mass or less, or 3% by mass or more and 30% by mass or less.

[0034] The purging agent of the present invention may further contain a polyolefin resin (C) to improve worker safety and extrudability. Examples of the polyolefin resin (C) include polyethylene (high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), very low-density polyethylene (VLDPE), etc.), homopropylene, random polypropylene, block polypropylene, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid ester copolymer, etc., as well as copolymers and modified products thereof. Among these, polyethylene is preferred, and high-density polyethylene is particularly preferred. The polyolefin resin (C) is usually in particulate form. In other words, one form of the purging agent of the present invention is a mixture of porous particles and particles of the polyolefin resin (C).

[0035] The content of polyolefin resin (C) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the total mass of the purging agent. When the content of polyolefin resin (C) is 50% by mass or more based on the total mass of the purging agent, poor biting tends to be improved and discharge tends to be improved. The upper limit of the content of polyolefin resin (C) in the purging agent may be 99% by mass or 95% by mass. Furthermore, the total content of porous particles and polyolefin resin (C) in the purging agent is preferably 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more or 99% by mass or more.

[0036] The purging agent of the present invention can be used as a purging agent for various resins that are melt-molded. Purging can be carried out by introducing the purging agent into a molding machine with the resin to be purged attached to the flow path, and then melt-extruding the resin. The resin to be purged is not particularly limited as long as it is a thermoplastic resin, but thermoplastic resins having polar groups (PMMA, PLA, ABS, AS, PVC, PVDF, TPU, PC, PBT, POM, PA, EVOH, adhesive resins, etc.) are preferred, and mixtures thereof are also effective. Of these, EVOH is particularly preferred. [Example]

[0037] The present invention will be specifically described below with reference to examples, but is not limited to these examples. Measurement, calculation and evaluation methods were as follows.

[0038] [Evaluation method] (1) Measurement of ethylene unit content and degree of saponification The porous particles obtained in each example and comparative example were dissolved in DMSO-d6. 1 The ethylene unit content and the degree of saponification were determined by H-NMR (JNM-GX-500 model, manufactured by JEOL Ltd.).

[0039] (2) Measurement of pore surface area and pore median diameter The porous particles obtained in each example and comparative example were frozen at -80°C and then freeze-dried to prepare samples for pore size measurement. Approximately 0.5 g of the sample was placed in a standard 5 cc powder cell (stem volume 0.4 cc) and measured using a Micromeritics pore size distribution analyzer (Shimadzu Corporation, Autopore V9620) under an initial pressure of 2.6 kPa. Mercury parameters were set to a mercury contact angle of 130 degrees and a mercury surface tension of 485 dynes / cm. The pore surface area and pore median diameter were calculated within a pore size range of 0.005 to 100 μm.

[0040] (3) Measurement of average particle size 100 g of freeze-dried pore measurement sample (porous particles) was measured using Verder Scientific's "CAMSIZER XT" and dynamic image analysis in accordance with ISO 13322-2 (2006) to determine the particle size at which the cumulative particle size distribution from the small particle size side of the circular equivalent particle size is 50% (volume basis) (Q3 50.0%), which was used as the average particle size.

[0041] (4) Measurement of moisture content Using 3 g of the porous particles obtained in each example and comparative example, the moisture content of the porous particles was measured using a halogen moisture analyzer "HR73" manufactured by METTLER under conditions of a drying temperature of 180°C and a drying time of 15 minutes.

[0042] (5) Determination of alkali metals (B) 0.5 g of the porous particles obtained in each Example and Comparative Example was placed in a Teflon (registered trademark) pressure vessel, and 5 mL of concentrated nitric acid was added and decomposed at room temperature for 30 minutes. After 30 minutes, the vessel was capped and heated at 150°C for 10 minutes and then at 180°C for 5 minutes using a wet decomposition apparatus (Actac Corporation, "MWS-2"), followed by cooling to room temperature. This treated solution was transferred to a 50 mL volumetric flask (TPX (registered trademark)) and made up to the desired volume with pure water. The metal content of this solution was analyzed using an ICP atomic emission spectrometer (PerkinElmer, "OPTIMA4300DV"), and the amount of metal (element) was calculated. For quantification, a calibration curve prepared using commercially available standard solutions was used.

[0043] (6) Purge evaluation (screw adhesion amount) EVOH (F101, manufactured by Kuraray) was passed through a twin-screw extruder ("2D25W" manufactured by Toyo Seiki Co., Ltd.; L / D=25) as the resin to be purged for 10 minutes, and the resin to be purged was left in the extruder. After stopping the screw rotation and allowing the resin to remain for 30 minutes, high-density polyethylene ("HI-ZEX 7000F" manufactured by Prime Polymer Co., Ltd.) was passed through the extruder for 5 minutes, and the die was removed. The cylinder was then heated to 290°C, and the resin to be purged was heated at a screw rotation speed of 10 rpm for 3 hours while air was flowing in, causing oxidative degradation.

[0044] Next, the purging agent obtained in each Example and Comparative Example was fed from the hopper of the extruder at a purge temperature of 190°C, a screw rotation speed of 100 rpm, and an extrusion rate of 3.2 kg / hour for 40 minutes. After that, low-density polyethylene ("LC-600A" manufactured by Japan Polyethylene Co., Ltd.) was passed through for 3 minutes, and then low-density polyethylene ("LC-600A" manufactured by Japan Polyethylene Co., Ltd.) was passed through for 10 minutes while the cylinder was heated to 220°C. Then, high-density polyethylene ("HI-ZEX 7000F" manufactured by Prime Polymer Co., Ltd.) was passed through for 5 minutes.

[0045] In each example and comparative example, after the purging, the die was disassembled, the twin screw was removed, and the resin to be purged that had adhered to the screw was recovered with a copper spatula. The mass of the recovered resin to be purged was measured.

[0046] Example 1 An EVOH solution containing 100 parts by weight of EVOH with an ethylene unit content of 32 mol% and a degree of saponification of 99.98 mol%, 60 parts by weight of methanol, and 40 parts by weight of water was continuously fed into a 0.3 m diameter, 10-plate tower through the top tray. Steam was blown into the bottom tray, resulting in countercurrent contact between the EVOH solution and the steam. The temperature inside the tower was 130°C, and the pressure inside the tower was 0.3 MPa. The resulting hydrous EVOH pellets were withdrawn from the bottom of the tower. The resulting hydrous EVOH pellets were fed into a twin-screw extruder at 42 kg / hr and extruded through a 30 mm diameter, 8-hole die attached to the tip of the extruder under the following conditions. The melt was cut 0.05 mm from the die using a two-blade hot cutter to obtain flattened spherical hydrous EVOH pellets. <Twin-screw extruder conditions> L / D: 14 Caliber: 30mm Screw: Full flight Rotation speed: 300 rpm Cylinder temperature: 90℃ Die temperature: 120℃ Number of dice holes: 8

[0047] The resulting 3 kg of hydrous EVOH pellets were washed twice in ion-exchanged water (bath ratio 20) with stirring at 50°C for 1 hour and then dewatered. The washed hydrous EVOH pellets were then placed in a 1 g / L aqueous acetic acid solution (bath ratio 20) and washed at 25°C for 2 hours with stirring and then dewatered. This process was repeated twice. The washed hydrous EVOH pellets were then placed in ion-exchanged water (bath ratio 20) with stirring at 25°C for 2 hours and then dewatered. This process was repeated twice. The electrical conductivity of the washing solution was measured using a CM-30ET electrical conductivity meter manufactured by Toa Denpa Kogyo Co., Ltd. The electrical conductivity of the washing solution was 10 μS / cm, so a third wash was performed in the same manner. The electrical conductivity of the washing solution after the third wash was measured and found to be below 3 μS / cm, so the wash was stopped.

[0048] The washed hydrous EVOH pellets were immersed in an alkaline aqueous solution with a potassium carbonate concentration of 1.0 mol / L for 2 hours with periodic stirring for chemical treatment. The hydrous EVOH pellets were then drained and dried under reduced pressure at 60°C for 5 hours to obtain porous particles with a moisture content of 24% by mass.

[0049] 5% by mass of the obtained porous particles and 90% by mass of high-density polyethylene particles ("HB111R" manufactured by Japan Polyethylene Corporation) were kneaded (dry blended) using a blender to obtain a purging agent composed of a mixture of the particles.

[0050] The obtained porous particles and purging agent were subjected to the measurements and evaluations (1) to (6) above. The results are shown in Table 1.

[0051] Example 2 Porous particles and a purging agent were produced, measured, and evaluated in the same manner as in Example 1, except that the moisture content was adjusted by changing the drying time of the dewatered EVOH pellets after the chemical treatment. The results are shown in Table 1.

[0052] Example 3 Except for using a sodium carbonate aqueous solution instead of a potassium carbonate aqueous solution as the alkaline aqueous solution, porous particles and a purging agent were produced, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0053] Example 4 Except for changing the concentration of the alkaline aqueous solution from 1.0 mol / L to 0.8 mol / L, porous particles and a purging agent were produced, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0054] Example 5 Except for changing the concentration of the alkaline aqueous solution from 1.0 mol / L to 1.2 mol / L, porous particles and a purging agent were produced, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0055] Example 6 Except for changing the ethylene unit content of EVOH to 27 mol%, porous particles and a purging agent were produced, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0056] Example 7 Except for changing the ethylene unit content of EVOH to 44 mol%, porous particles and a purging agent were produced, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0057] Example 8 An EVOH solution containing 100 parts by mass of EVOH with an ethylene unit content of 32 mol% and a saponification degree of 99.98 mol%, 60 parts by mass of methanol, and 40 parts by mass of water at 60°C was extruded into a water and methanol mixed solution (mass ratio: water / methanol = 9 / 1) maintained at 2°C in the form of strands through a gold plate with a circular opening with a diameter of 3.5 mm. The strands precipitated and solidified, and then cut with a cutter to obtain EVOH pellets. The obtained EVOH pellets were placed in water at 10°C and stirred for 4 hours to obtain hydrous EVOH pellets. The obtained hydrous EVOH pellets were washed and chemically treated in the same manner as in Example 1 to obtain porous particles. The obtained porous particles were used to produce a purging agent in the same manner as in Example 1. The obtained porous particles and purging agent were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0058] (Comparative Example 1) Except for changing the concentration of the alkaline aqueous solution from 1.0 mol / L to 0.1 mol / L, porous particles and a purging agent were produced, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0059] (Comparative Example 2) An EVOH solution containing 100 parts by mass of EVOH with an ethylene unit content of 32 mol% and a saponification degree of 99.98 mol%, 60 parts by mass of methanol, and 40 parts by mass of water at 60°C was extruded into a water and methanol mixed solution (mass ratio: water / methanol = 9 / 1) maintained at 5°C in the form of strands through a gold plate with a circular opening with a diameter of 3.5 mm. The strands precipitated and solidified, and then cut with a cutter to obtain EVOH pellets. The obtained EVOH pellets were then placed in warm water at 30°C and stirred for 4 hours to obtain hydrous EVOH pellets. The obtained hydrous EVOH pellets were washed and chemically treated in the same manner as in Example 1 to obtain porous particles. The obtained porous particles were partially chipped, and fragments resulting from the chipping were floating in the washing solution. The obtained porous particles were used to produce a purging agent in the same manner as in Example 1. The obtained porous particles and purging agent were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0060] (Comparative Example 3) Instead of the produced flat spherical hydrous EVOH pellets, ready-made EVOH pellets (EVAL H171 (manufactured by Kuraray)) were used, and these EVOH pellets were washed and chemically treated in the same manner as in Example 1 to produce porous particles. Using the obtained porous particles, a purging agent was produced in the same manner as in Example 1. The obtained porous particles and purging agent were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0061] [Table 1]

[0062] As shown in Table 1, when purging was performed using each of the purging agents obtained in Examples 1 to 8, the amount of remaining resin to be purged adhering to the screw was small, and it was found that the resin to be purged in the molding machine could be efficiently discharged from the molding machine.

Claims

1. Porous particles containing an ethylene-vinyl alcohol copolymer (A) and an alkali metal (B), The pore median diameter is 0.01 to 3 μm, The average particle size is 2.5 to 8 mm, Porous particles having an alkali metal (B) content of 1,000 to 100,000 ppm.

2. Pore ​​surface area is 25 to 60 m ２ The porous particle of claim 1 , wherein the pore size is 1 / g.

3. The porous particles according to claim 1 or 2, which are hydrous porous particles.

4. The porous particles according to claim 3, which have a moisture content of 5 to 80% by mass.

5. 5. The porous particle according to claim 1, wherein the ethylene-vinyl alcohol copolymer (A) has an ethylene unit content of 18 to 52 mol %.

6. A purging agent comprising the porous particles according to any one of claims 1 to 5.

7. The purging agent according to claim 6, further comprising 50% by mass or more of a polyolefin resin (C).

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