JP7637400B2 - Abrasive grain - Google Patents

Description

The present invention relates to abrasive grains made of thermoplastic resin.

Molded products include various types of molded products, such as injection molding, in which a synthetic resin material is filled into a mold, resin molded products made by transfer molding, castings formed by pouring molten metal into a mold, and resin molded products created using a 3D printer. Since these molded products have unwanted burrs attached to them, a process to remove the burrs (known as deburring) is carried out. Abrasive grains are used for the deburring process, and the grains are sprayed onto the object, the grains are made to flow in contact with the object, or the object and grains are placed in a container and stirred together.

Abrasive grains for deburring are made of various materials such as glass, steel, alumina, and synthetic resins such as thermosetting resins and thermoplastic resins, and are selected appropriately depending on the material of the object, but there is a risk of scratching the surface of the object depending on the hardness and shape of the abrasive grains. Furthermore, if the abrasive grains are damaged by friction during deburring, the efficiency of the deburring work will decrease. Furthermore, if static electricity is generated by friction, the abrasive grains will stick to the object, making it difficult to deburr effectively. Patent Document 1 proposes addressing this problem by incorporating an antistatic agent into the deburring shot material.

JP2003-220559A

The objective of the present invention is to provide abrasive grains that do not damage the surface of the object, are durable and resistant to damage caused by friction during repeated work, and are also resistant to charging due to friction during work.

The present inventors have conducted research to solve the above problems and arrived at the present invention. That is, the present invention is a resin composition comprising a thermoplastic resin (A) as a base resin constituting the resin composition and a thermoplastic water-soluble polyethylene oxide resin having a weight average molecular weight of 50,000 to 9,000,000 blended therein,
the thermoplastic water-soluble polyethylene oxide resin is either a polymer consisting of ethylene oxide alone or a polyethylene oxide-propylene oxide random copolymer,
The gist of the invention is an abrasive grain characterized by being made of pellet-shaped material having a diameter of 50 μm to 3000 μm and a length of 0.05 mm to 10 mm.

The present invention will be described in detail below.
The abrasive grains of the present invention are used for removing burrs generated during the production of molded articles made of resin or the like, and for polishing the surfaces of molded articles, and are composed of a resin composition in which a thermoplastic resin (A) is blended with a thermoplastic water-soluble polyethylene oxide-based resin.

The thermoplastic resin (A) is the main resin that constitutes the resin composition, and polyester-based resin or polyamide-based resin is preferably used.

The polyester resin is not particularly limited as long as it has an ester bond in the molecule. For example, aromatic polyesters include polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, etc., and aliphatic polyesters include polylactic acid, polybutylene succinate, polycaprolactone, etc. In addition, the above-mentioned polyesters may be copolymerized with other dicarboxylic acid components, diol components, or oxycarboxylic acid components, etc., as long as the purpose of the present invention is not hindered. Alternatively, the above-mentioned polyesters may be blended with each other, or may be blends of polyesters copolymerized with the above-mentioned polyesters. Examples of other components that can be copolymerized include dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic anhydride, sebacic acid, adipic acid, and succinic acid, and diol components such as ethanediol, propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and cyclohexanedimethanol. Taking durability into consideration, the relative viscosity of the polyester resin is preferably 1.4 or more, and more preferably 1.5 or more.

The polyamide resin is not particularly limited as long as it has an amide group in the molecule, and examples thereof include nylon 6, nylon 66, nylon 69, nylon 46, nylon 610, nylon 1010, nylon 11, nylon 12, nylon 6T, nylon 9T, polymetaxylene adipamide, and copolymers or blends of these components. The relative viscosity of the polyamide resin is preferably 2.5 or more, more preferably 3.0 or more, taking durability into consideration.

The resin composition constituting the abrasive grains of the present invention is obtained by blending the thermoplastic water-soluble polyethylene oxide resin with the thermoplastic resin (A) described above. The blend amount of the thermoplastic water-soluble polyethylene oxide resin in the resin composition is preferably 1 to 15% by mass. More preferably, it is 1 to 12% by mass. By making the blend amount of the thermoplastic water-soluble polyethylene oxide 1% by mass or more, the triboelectric charging effect can be effectively exerted. On the other hand, by making the blend amount 15% by mass or less, the abrasive grains have good strength.

Considering the dispersibility in the thermoplastic resin (A) that is the base resin for constituting the resin composition, the thermoplastic water-soluble polyethylene oxide resin has a weight-average molecular weight of 50,000 to 9,000,000. The thermoplastic water-soluble polyethylene oxide resin with a weight-average molecular weight of 50,000 to 9,000,000 can be mixed well with the thermoplastic resin (A) in the melt extruder for producing the abrasive grains, and disperses well in the thermoplastic resin (A). When mixing a thermoplastic water-soluble polyethylene oxide resin with a weight-average molecular weight of more than 500,000, the temperature is set to 300°C or higher, and the thermoplastic water-soluble polyethylene oxide resin disperses well in the base polyester resin. When mixing a thermoplastic water-soluble polyethylene oxide resin with a weight-average molecular weight of 500,000 or less, the temperature is set to 300°C or lower, at which the thermoplastic resin (A) melts, and the thermoplastic resin disperses well in the base polyester resin at a temperature of 300°C or lower.

The thermoplastic water-soluble polyethylene oxide resin is a resin composed only of ethylene oxide , or an ethylene oxide-propylene oxide random copolymer obtained by random copolymerization of ethylene oxide and propylene oxide .

The thermoplastic water-soluble polyethylene oxide resin mixed into the thermoplastic resin (A) is a non-ionic polymer that is not easily affected by coexisting substances, and therefore has excellent compatibility with the thermoplastic resin (A) and disperses well, allowing the strength of the abrasive grains to be well maintained. In addition, since the thermoplastic water-soluble polyethylene oxide resin is uniformly dispersed in the parent thermoplastic resin (A), it is believed to function as a slip agent on the abrasive grain surface, resulting in an excellent balance between triboelectric charging properties and strength.

In the present invention, various additives such as heat stabilizers, crystallizing agents, pigments, antioxidants, antibacterial agents, fragrances, plasticizers, dyes, and surfactants can be added to the resin composition as needed, so long as the effects of the present invention are not impaired. In addition, fatty acid amides such as metaxylylene bisstearylamide, metaxylylene bisoleylamide, xylene bisstearic acid amide, ethylene bisstearylamide, and ethylene bisstearic acid amide may be added to increase strength.

The abrasive grains of the present invention are composed of a resin composition mainly composed of the above-mentioned thermoplastic resin (A) and a specific amount of thermoplastic water-soluble polyethylene oxide resin, but may be composited with a thermoplastic resin that does not contain a thermoplastic water-soluble polyethylene oxide resin.

The abrasive grains of the present invention are pellet-shaped objects made of the resin composition described above, and have a diameter of 50 μm to 3000 μm and a length of 0.05 mm to 10 mm. The diameter is the diameter in a direction perpendicular to the axial direction of the pellet-shaped object, and the cross-sectional shape in the direction perpendicular to the axial direction may be circular, irregular, or may have a hollow portion. If the shape of the surface perpendicular to the axial direction is irregular, the average diameter of the major axis and minor axis may be in the range of 50 to 3000 μm. If the surface perpendicular to the axial direction has a hollow portion, the outer diameter is regarded as the diameter. The length is the length in the axial direction of the pellet-shaped object. By setting the diameter and length of the abrasive grains in the above ranges, the abrasive grains have good handleability and appropriate strength. The preferred diameter of the abrasive grains is 100 μm to 1500 μm, and the preferred length is 0.1 mm to 10 mm.

The abrasive grains of the present invention are preferably used for deburring, and because they improve work efficiency without scratching the surface of the object, they can also be preferably used for polishing.

The abrasive grains of the present invention can be obtained, for example, by melt-spinning the resin composition described above into a monofilament thread and cutting the obtained monofilament to a predetermined length. When obtaining the monofilament, the thermoplastic resin (A), which is the main component, is oriented and crystallized, thereby making it possible to obtain abrasive grains having good strength and durability.

Specifically, a predetermined amount of thermoplastic water-soluble polyethylene oxide resin is blended with chips made of thermoplastic resin (A), melt-mixed, and then melt-spun. The filament obtained by melt spinning is then cooled, and an oil agent is applied or not applied, and the filament is wound up as an undrawn filament, and then drawn, either without being wound up or without being drawn. The filament after melt spinning may be cooled at room temperature, by blowing cooling air, or by passing through a water bath. The filament is hot-drawn at a draw ratio of 2 to 8 times. As a heating means for hot drawing, hot drawing is performed in a hot water bath or by using a heated roller. After hot drawing, a winding operation is continuously performed to obtain a monofilament, and the abrasive grain of the present invention can be obtained by cutting the obtained monofilament to a predetermined length in the filament axis direction.

The present invention provides abrasive grains that are less likely to scratch the surface of an object, are resistant to damage from repeated friction, are durable, and are less likely to become charged due to friction during work such as deburring or surface polishing, resulting in good work efficiency.

The present invention will be described based on examples. Note that the present invention is not limited to the examples.

Example 1
5% by mass of polyethylene oxide-propylene oxide random copolymer (manufactured by Meisei Chemical Industry Co., Ltd., trade name Alcox, product number EP-10) having a weight average molecular weight of 1,000,000 and 95% by mass of polyethylene terephthalate resin chips were mixed, and melt-spun at a melt spinning temperature of 295°C from a 1.0 mmφ×4H spinneret. The spun thread was cooled in a water bath at 50°C, and then stretched in a hot bath at 90°C at a speed of 20 m/min without winding, and then stretched and wound in a dry heat atmosphere at 120°C to a total stretch ratio of 5.3 times without winding. A monofilament having a fineness of 560 dtex (diameter 0.225 mm) was obtained. The obtained monofilament was cut to a length of 0.5 mm to 5 mm to obtain the abrasive grain of Example 1.

Example 2
2.5% by mass of polyethylene oxide (manufactured by Meisei Chemical Industry Co., Ltd., trade name Alcox, product number R-400) with a weight average molecular weight of 200,000 and 97.5% by mass of polyamide 6 resin chips were mixed, and melt-spun at a melt spinning temperature of 265°C from a 1.9mmφ×14H spinneret. The spun thread was cooled in a water bath at 25°C, and then stretched in a warm bath at 80°C at a speed of 30m/min without winding, and then stretched and wound in an atmosphere at 175°C to a total stretch ratio of 4.8 times without winding. A monofilament with a fineness of 1858dtex (diameter 0.45mm) was obtained. The obtained monofilament was cut to 0.5mm to 5mm to obtain the abrasive grains of Example 2.

Comparative Example 1
A monofilament having a fineness of 560 dtex (diameter 0.225 mm) was obtained in the same manner as in Example 1, except that only polyethylene terephthalate resin chips were used in Example 1. The obtained monofilament was cut to a length of 0.5 mm to 5 mm to obtain the abrasive grains of Comparative Example 1.

Comparative Example 2
A monofilament having a fineness of 1879 dtex (diameter 0.453 mm) was obtained in the same manner as in Example 2, except that only polyamide 6 resin chips were used in Example 2. The obtained monofilament was cut to 0.5 mm to 5 mm to obtain the abrasive grains of Comparative Example 2.

The obtained abrasive grains of Examples 1 and 2 and Comparative Examples 1 and 2 were used to conduct deburring tests and were evaluated.

<Deburring test>
A rod-shaped molded product with a length of 8 cm, a width of 1 cm, and a thickness of 2 mm was prepared using a 3D printer as the molded product to be deburred. The molded product was made using polylactic acid resin (Terramac 3D printer filament manufactured by Unitika Ltd.).

Next, the molded product created using the 3D printer was deburred. 20 g of abrasive grains were placed in a plastic container. The molded product was attached to the tip of a mixer (manufactured by Toyo Seiki Seisakusho), and the molded product attached to the mixer was rotated in the abrasive grains in the container at a rotation speed of 382 rpm for 4 hours to deburr the molded product.

After the burr removal test, the condition of the molded product was checked to see if the burrs had been successfully removed without damaging the surface of the molded product (burr removal effect). In addition, after the burr removal test, the abrasive grains were checked to see if static electricity had been generated (frictional charging property) and the surface condition of the abrasive grains was checked to see if there was any damage to the abrasive grains (abrasion resistance), and were then evaluated.

All molded products that underwent burr removal tests using the abrasive grains of Examples 1 and 2 had burrs removed successfully, and there were no scratches on the surfaces of the molded products. The abrasive grains also generated only a small amount of static electricity, and were evaluated as having good work efficiency. After the burr removal test, only a few areas of the abrasive grain surface were chipped, and the products were evaluated as being suitable for repeated use and having good durability.

On the other hand, in the case of the abrasives of Comparative Examples 1 and 2, the burrs of the molded products obtained in the deburring test were all well removed, and there were no scratches on the surfaces of the molded products, but the abrasive grains generated static electricity and stuck to some of the surfaces of the molded products. In addition, many chipped areas were observed on the surfaces of the abrasive grains after the deburring test.

Claims (4)

The resin composition is constituted by a resin composition in which a thermoplastic water-soluble polyethylene oxide resin having a weight average molecular weight of 50,000 to 9,000,000 is blended with a thermoplastic resin (A) that is a base resin constituting the resin composition,
the thermoplastic water-soluble polyethylene oxide resin is either a polymer consisting of ethylene oxide alone or a polyethylene oxide-propylene oxide random copolymer,
The abrasive grains are characterized in that they are pellet-shaped with a diameter of 50 μm to 3000 μm and a length of 0.05 mm to 10 mm. The abrasive grains according to claim 1, characterized in that the thermoplastic resin (A) is a polyester-based resin or a polyamide-based resin. The abrasive grains according to claim 1 or 2, characterized in that the thermoplastic water-soluble polyethylene oxide resin is blended in an amount of 1 to 15 mass % in the resin composition. 4. A deburring abrasive, comprising the abrasive according to claim 1, which is used for deburring.