Method for manufacturing a record disc by injection molding

Abstract

A method for producing vinyl records by injection molding comprises the steps of heating a polymer material to liquefy it, and feeding the liquid polymer material (2) under pressure from a feed zone (33) through a nozzle (11) into a space (7) between two mold sections (3, 5). The liquid polymer material (2) passes through a single passage located in one of the mold sections and is forced under pressure through the nozzle (7) into the space (7). A polyethylene terephthalate isophthalic acid-modified copolymer is used as the polymer material (2).

Description

Technical Field

[0001] The present invention relates to a method for manufacturing gramophone records by injection molding, the method including heating a polymer material to liquefy the material and supplying the liquid polymer material under pressure from a supply region through a nozzle into a space between two mold part, wherein in the method, the liquid polymer material passes through a single passage located in one of the mold parts, and the polymer material is introduced into the space under pressure through the nozzle.

Background Art

[0002] A gramophone record is an audio carrier that is played on a phonograph. It is a flat disc having spiral grooves extending from an end on at least one side towards near the center, and the spiral grooves have music information recorded therein in the form of small horizontal and / or vertical displacements from the spiral shape. These displacements are present on the left and right and at the bottom and can be scanned and listened to using a needle on the rotating disc.

[0003] Such a gramophone record is known in the form of a long-playing record, which is a vinyl record made of vinyl with a diameter of 30 cm (12 inches) and having spiral grooves on both sides. Known gramophone records are made by pressing a roll of PVC into a disc-shaped grooved plate. PVC as a material for long-playing records poses a health risk when frequently contacted in relation to carcinogenic PVC. Furthermore, pressing a roll of PVC into a plate for long-playing requires relatively a lot of energy and results in a relatively long cycle time.

[0004] A method for manufacturing a record disc using polyethylene terephthalate (PET) as a material for injection molding is known from Patent Document 1. PET is a homopolymer that can be modified by copolymerization to modify material characteristics such as mechanical and dimensional stability, melting point, and transparency. For example, it is well known that glycol-modified PET can be injection molded. Records manufactured according to this known process appear to have inferior characteristics regarding appearance, wear, and sound quality.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Means for Solving the Problems

[0006] An object of the present invention is to provide a method for manufacturing a record disc having better characteristics than a record disc manufactured by a known method. For this purpose, the method according to the present invention is characterized by using a polyethylene terephthalate isophthalic acid modified copolymer (PET-IPA modified copolymer) as a material for injection molding.

[0007] The PET-IPA modified copolymer in which the modifier is isophthalic acid is known to be advantageous for specific molding applications such as thermoforming used to make trays or blister packs. This known copolymer is also used for the manufacture of bottles by stretch blow molding. In the latter application, only a small amount of isophthalic acid is used in the copolymer. When only a small amount of comonomer is used, crystallization is retarded but not completely prevented.

[0008] During injection molding, the liquid material is pressed under high pressure through different channels and thus encounters friction (shear). This improves the flow of the plastic (reduces its viscosity). Therefore, for example, if the injection speed is high, the melt flows more easily. However, PET-IPA modified copolymers have a low "shear" dependent viscosity. PET-IPA modified copolymers have few of these advantages (which other thermoplastics have). This is why it is difficult to process PET-IPA modified copolymers by injection molding, especially for products with long / thin channels such as record discs.

[0009] PET-IPA modified copolymers are not common materials for injection molding and are difficult to inject into long and thin channels. However, as a result of testing more than 45 different plastic materials, it was found that they have good properties for application as record discs. Due to their high mechanical stability and dimensional stability, they have high wear resistance, a transparent appearance, and good sound quality.

[0010] After comprehensive testing, the characteristics of PET-IPA modified copolymers seem to be optimal for application in the injection molding process for manufacturing record discs when the amount of monomer isophthalic acid in the polyethylene terephthalate isophthalic acid modified copolymer is between 1.5% and 2.5%, preferably when this amount is about 1.8%.

[0011] Also, since polyethylene terephthalate isophthalic acid modified copolymers are easy to recycle, record discs manufactured by this method are more sustainable than other known record discs.

[0012] To optimize the injection molding manufacturing process, the material to be injected is heated to a temperature of 250 - 300 °C, preferably 270 - 290 °C, before being injected into the space between the two mold parts of the polymer material.

[0013] In order to further optimize the injection molding manufacturing process, while injecting material into the space between two mold parts, the mold parts are maintained at a temperature of 40 to 60 °C.

[0014] In one embodiment of the method according to the present invention, while injecting a polymer material into the space between two mold parts, the mold parts are maintained at a distance of 1 to 5 mm from each other, and immediately after injection, these mold parts are moved relative to each other to form a cavity having the shape of a record disc (so-called injection compression). This method has less friction during injection because the dimensions of the flow space between the mold parts are larger, so significantly less energy (temperature, pressure) is required. When injecting material into a closed cavity between these two mold parts and the mold parts are in contact with each other, similar to the method described in Patent Document 1, it is more difficult to fill the grooves of the mold parts, so the material becomes more liquid (lower viscosity), so a higher temperature, and thus more energy material is required or a material of a different composition is required, and the sound quality of the record disc becomes lower.

[0015] Compared with the prior art knowledge of Patent Document 1 in which a polyethylene terephthalate material is injected with a nozzle having a passage at least partially directed in the circumferential direction, in the method according to the present invention, the polymer material is injected into the space between two mold parts through a single nozzle having a straight injection channel. By injecting in this way, visible and during use audible transitions between parts of the record are avoided.

[0016] Also, compared with the prior art knowledge of Patent Document 1 in which the polyethylene terephthalate material injected into the cavity has a velocity component that causes a rotational movement of the material, in the method according to the present invention, the polymer material is injected into the space between two mold parts in a direction perpendicular or substantially perpendicular to the mold surface of the mold parts. This also contributes to the avoidance of visible and during use audible transitions between parts of the record.

[0017] A further embodiment of the method according to the present invention is characterized in that a label is directly printed on a polyethylene terephthalate isophthalic acid modified copolymer material by a UV printer at the center of a record disc. Therefore, since there is no separate label pressed onto the record, the record according to the present invention can be completely recycled, and there is no need to cut off the label portion and handle it separately as in the case of recycling known records. Therefore, the record disc manufactured by the method according to the present invention is easy to recycle and thus highly sustainable.

[0018] The present invention also relates to a record disc manufactured by the method according to the present invention. Regarding the record disc, the present invention is characterized in that it is made of or substantially consists of a polyethylene terephthalate isophthalic acid modified copolymer.

[0019] The amount of the monomer isophthalic acid in the polyethylene terephthalate isophthalic acid modified copolymer is preferably 1.5 to 2.5%.

Brief Description of the Drawings

[0020] Based on the drawings, the present invention will be further described below. These drawings show an embodiment of an injection molding apparatus for injection molding a record disc according to the present invention.

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0021] The injection molding apparatus for injection molding a record disc has a mold 1. This mold is schematically shown in FIG. 1. The mold 1 consists of two mold parts 3 and 5 having a space 7 therebetween. When the mold parts contact each other, the space 7 defines a mold cavity 8 (see FIG. 2) having the shape of a record disc. In the mold part 5, there is an insertion part 9 for receiving the injection nozzle 11. Only the front part of the injection nozzle is shown. In the mold part 3, there is a central bush 15 in which an ejector 17 is displaceable for discharging the remaining central injection piece that is not part of the record disc. A further ejector 19 is slidable on the bush for discharging the record disc. There is a discharge ring 21 between the mold parts 3 and 5. The mold cavity 8 is surrounded by two mirror parts 23 and 25 each provided with a pusher 27, 29.

[0022] FIG. 3 shows the injection nozzle 11 in detail. The injection nozzle comprises a nozzle piece 31, and the inlet opening 33 is part of the supply area. Inside the injection nozzle 11, there is an injection flow path 35 between the inlet opening and the nozzle piece. The injection flow path 35 is completely straight and is closed by a rotatable valve 37. This valve is adjustable by an arm 39. In FIG. 4, the injection nozzle 11 is shown with the valve 37 in the open position.

[0023] When spraying the record disc, a molding material of PET with additives (usually in the form of granules) to give the molding material optimal properties is heated to a liquid state. The liquid material is injected under pressure into the space 7 between the mold parts 3 and 5 via a single passage 12, and the material stream of the molding material from the place where the molding material melts in this space is not split into sub-streams that come together again later. The liquid material flows into the space 7 through the injection nozzle 11. While injecting the polymer material into the space 7 between the two mold parts 3 and 5, the mold parts are about 3 mm apart from each other. See FIG. 1. Immediately after injection, these mold parts 3 and 5 are moved relative to each other to form the mold cavity 8 having the shape of a record disc. See FIG. 2.

[0024] The polymer material 2 used for injection molding is a polyethylene terephthalate isophthalic acid modified copolymer. Conventional additives for improvement can be added to this base polymer material.

[0025] Although the present invention has been described above based on the given drawings, the present invention is not limited to the embodiments shown in the drawings at all. The present invention extends to all embodiments departing from the embodiments shown in the drawings within the scope of the present invention defined by the appended claims.

Claims

1. A method for manufacturing a record disc by injection molding, comprising: heating a polymer material to liquefy the material; and supplying the liquid polymer material under pressure from a supply zone through an injection nozzle into a space between two mold parts, wherein the liquid polymer material passes through a single passage located in one of the mold parts, and the polymer material is pushed into the space under pressure through the injection nozzle, and a polyethylene terephthalate isophthalic acid modified copolymer is used as the polymer material, wherein the amount of monomer isophthalic acid in the polyethylene terephthalate isophthalic acid modified copolymer is 1.5 to 2.5% by mass.

2. The method for manufacturing a record disc according to claim 1, wherein the polymer material is heated to a temperature of 250 to 300 °C before being injected into the space between the two mold parts.

3. The method for manufacturing a record disc according to claim 1 or 2, wherein the mold parts are maintained at a temperature of 40 to 60 °C during injection.

4. During the injection of the polymer material into the space between the two mold parts, the mold parts are separated from each other by 1 to 5 mm, and immediately after injection, the mold parts are moved relative to each other to form a mold cavity having the shape of a record disc. The method for manufacturing a record disc according to any one of claims 1 to 3.

5. The method for manufacturing a record disc according to any one of claims 1 to 4, wherein the polymer material is injected into the space between the two mold parts through a single injection nozzle having a straight injection flow path.

6. The method for manufacturing a record disc according to any one of claims 1 to 5, wherein the polymer material is injected into the space between the two mold parts in a direction perpendicular or substantially perpendicular to the mold surface of the mold parts.

7. The method for manufacturing a record disc according to any one of claims 1 to 6, wherein a label is directly printed on the polyethylene terephthalate isophthalic acid modified copolymer material by a UV printer at the central portion of the record disc.

8. A record disc manufactured by the method according to any one of claims 1 to 7, wherein the record disc is made of or mainly made of a polyethylene terephthalate isophthalic acid modified copolymer.

Images