Method for manufacturing record discs by injection molding

Abstract

To provide a method for manufacturing a record disc with improved characteristics in appearance, wear resistance, and sound quality.SOLUTION: A method for manufacturing a record disc by injection molding comprises the steps of heating a polymer material to liquefy it, and supplying the liquid polymer material (2) under pressure from a supply 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 into the space (7) via the nozzle (11). A polyethylene terephthalate isophthalic acid modified copolymer is used as the polymer material (2).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing gramophone records by injection molding, the method comprising heating a polymeric material to liquefy it and supplying the liquid polymeric material under pressure from a supply region through a nozzle into a space between two mold parts, the liquid polymeric material passing through a single passage located in one of the mold parts and forcing the polymeric material into the space under pressure through the nozzle. [Background technology]

[0002] A record is an audio carrier played on a phonograph. It is a flat disk with a spiral groove extending from at least one edge near the center, in which musical information is recorded in the spiral groove in the form of small horizontal and / or vertical deviations from the spiral shape. These deviations, on the left, right, and bottom, can be scanned and heard with a needle on the rotating disk.

[0003] Such records are known in the embodiment of long-playing records, which are vinyl records 30 cm (12 inches) in diameter with spiral grooves on both sides. Known records are made by forcing a roll of PVC into a disc-shaped grooved plate. PVC as a material for long-playing records poses health risks in case of frequent contact, as PVC is a carcinogen. Furthermore, forcing a roll of PVC into a long-playing plate requires a relatively high amount of energy and results in a relatively long cycle time.

[0004] From patent document 1, a method for producing vinyl records is known, which uses polyethylene terephthalate (PET) as the material for injection molding. PET is a homopolymer that can be modified by copolymerization to modify material characteristics such as mechanical and dimensional stability, melting point, transparency, etc. For example, it is well known that glycol-modified PET can be injection molded. Records produced according to this known process appear to have inferior characteristics with regard to appearance, wear and sound quality. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 1,353,953 Summary of the Invention [Means for solving the problem]

[0006] The object of the present invention is to provide a method for producing phonograph records having better characteristics than those produced by known methods.To this end, the method according to the invention is characterized in that polyethylene terephthalate isophthalic acid modified copolymer (PET-IPA modified copolymer) is used as the injection molding material.

[0007] PET-IPA modified copolymers in which the modifier is isophthalic acid are known to be advantageous for certain molding applications, such as thermoforming, used to make trays or blister packs. This known copolymer is also used to manufacture bottles by stretch-blow molding. In the latter application, only small amounts of isophthalic acid are used in the copolymer. Using only small amounts of comonomer slows down crystallization, but does not completely prevent it.

[0008] During injection molding, the liquid material encounters friction (shear) as it is forced through different channels under high pressure. This makes the plastic flow better (reducing viscosity). So, for example, the faster the injection speed, the easier the melt will flow. However, PET-IPA modified copolymers have low "shear" dependent viscosity. PET-IPA modified copolymers have little of this advantage (which other thermoplastics have). This is why PET-IPA modified copolymers are difficult to process by injection molding, especially into products with long / thin channels, such as vinyl records.

[0009] PET-IPA modified copolymer is not a commonly used material for injection molding, and it is difficult to inject into long, thin channels. However, after testing over 45 different plastic materials, it was found to have good properties for use in vinyl records. Its high mechanical and dimensional stability makes it highly resistant to wear, gives it a clear appearance, and produces good sound quality.

[0010] After comprehensive testing, it appears that the characteristics of the PET-IPA modified copolymer are optimal for application in the injection molding process for producing vinyl records when the amount of monopolymer 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] Additionally, vinyl records made with this method are more sustainable than other known vinyl records because polyethylene terephthalate isophthalic acid modified copolymer is easily recyclable.

[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 injecting the polymer material into the space between the two mold parts.

[0013] To further optimize the injection molding manufacturing process, the mold sections are maintained at a temperature of 40-60° C. while the material is being injected into the space between the two mold sections.

[0014] In one embodiment of the method according to the present invention, the mold parts are kept at a distance of 1-5 mm from each other while the polymer material is injected into the space between them. Immediately after injection, the mold parts are moved relative to each other to form a mold cavity with the shape of a record (so-called injection compression). This method requires significantly less energy (temperature, pressure) due to the larger dimensions of the flow space between the mold parts, resulting in less friction during injection. If the mold parts were in contact with each other while the material was being injected into the closed cavity between the two mold parts, as in the method described in Patent Document 1, it would be more difficult to fill the grooves of the mold parts, and the material would become more liquid (less viscous), requiring higher temperatures and therefore more energy, or a material of a different composition, resulting in a lower sound quality of the record.

[0015] In comparison with the state of the art knowledge of US 5,649,669, in which polyethylene terephthalate material is injected through a nozzle with at least some circumferentially oriented passages, in the method according to the invention the polymer material is injected into the space between the two mould parts through a single nozzle with a straight injection channel, which avoids visible and during use audible transitions between parts of the record.

[0016] Also, compared to the state of the art knowledge of US 5,949,639, in which the polyethylene terephthalate material injected into the holes has a velocity component that causes a rotational movement of the material, in the method according to the invention the polymer material is injected into the space between the two mould parts in a direction perpendicular or nearly perpendicular to the mould faces of the mould parts, which also contributes to avoiding transitions between parts of the record that are visible and audible during use.

[0017] A further embodiment of the method according to the invention is characterized in that a label is printed in the center of the record directly onto the polyethylene terephthalate isophthalic acid-modified copolymer material using a UV printer. As a result, since there is no separate label pressed onto the record, the record according to the invention can be fully recycled, without the need to cut out the label and handle it separately, as is the case when recycling known records. Therefore, the record produced by the method according to the invention is easily recycled and therefore more sustainable.

[0018] The present invention also relates to a record produced by the method according to the present invention, characterized in that the record consists of or consists essentially of a polyethylene terephthalate isophthalic acid modified copolymer.

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

[0020] The invention will be further explained below on the basis of the drawings, which show an embodiment of an injection molding device for injection molding records according to the invention. [Figure 1] FIG. 1 is a schematic view of a mold of an injection molding machine for manufacturing records according to the present invention, with the injection channel closed. [Figure 2] Figure 2 shows the injection molding machine with the injection channel open. [Figure 3] FIG. 3 shows the injection nozzle of an injection molding machine with the injection tube closed. [Figure 4] Figure 4 shows the injection nozzle of an injection molding machine with the injection tube open. DETAILED DESCRIPTION OF THE INVENTION

[0021] An injection molding apparatus for injection molding vinyl records has a mold 1, which is shown diagrammatically in FIG. 1. Mold 1 consists of two mold sections 3 and 5 with a space 7 between them. When the mold sections come into contact with each other, space 7 defines a mold cavity 8 (see FIG. 2) having the shape of a vinyl record. Mold section 5 has a bayonet 9 for receiving an injection nozzle 11. Only the front of the injection nozzle is shown. Mold section 3 has a central bush 15 on which an ejector 17 can be displaced to eject the remaining central injection piece that is not part of the vinyl record. A further ejector 19 can slide on the bush to eject the vinyl record. Between mold sections 3 and 5 is an ejection ring 21. Mold cavity 8 is surrounded by two mirror sections 23 and 25, each equipped with a pusher 27 and 29.

[0022] Figure 3 shows the injection nozzle 11 in detail. The injection nozzle comprises a nozzle piece 31, with an inlet opening 33 being part of the feed area. Within the injection nozzle 11, between the inlet opening and the nozzle piece, there is an injection channel 35. The injection channel 35 is completely straight and is closed by a rotatable valve 37, which is adjustable by an arm 39. In Figure 4, the injection nozzle 11 is shown with the valve 37 in the open position.

[0023] When spraying vinyl records, the PET molding compound (usually in granular form) with additives to give the molding compound optimal properties is heated to a liquid state. The liquid material is injected under pressure into the space 7 between mold sections 3 and 5 through a single passage 12; the material stream from where the molding material melts into this space does not split into substreams that later recombine. The liquid material flows into space 7 through injection nozzle 11. During the injection of the polymer material into space 7 between the two mold sections 3 and 5, the mold sections are spaced approximately 3 mm apart (see Figure 1). Immediately after injection, these mold sections 3 and 5 are moved relative to each other to form a mold cavity 8 having the shape of a vinyl record (see Figure 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] It should be noted that although the present invention has been described above with reference to given drawings, the present invention is in no way limited to the embodiments shown in the drawings, and the present invention extends to all embodiments that deviate from the embodiments shown in the drawings within the scope of the present invention as defined by the appended claims.

Claims

1. 1. A method for producing a record by injection molding, comprising:

1. A method for producing a vinyl record, 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 two mold parts, and the polymer material is forced under pressure through the injection nozzle into the space in a direction perpendicular to the mold faces of the two mold parts, wherein the polymer material is polyethylene terephthalate isophthalic acid-modified copolymer.

2. 2. The method for producing a record according to claim 1, wherein during the injection of the polymer material into the space between the two mould parts, the mould parts are spaced 1 to 5 mm apart from one another, and immediately after injection, the mould parts are moved relative to one another to form a mould cavity having the shape of the record.

3. 3. The method for manufacturing a phonograph record according to claim 1 or 2, wherein the polymer material is injected into the space between the two mould parts through a single injection nozzle with a straight injection channel.

4. 4. A method for manufacturing a phonograph record according to claim 1, wherein the liquid polymer material is supplied from the inlet opening of the injection nozzle to the nozzle piece of the injection nozzle via a completely straight injection channel.

5. 5. A method for producing phonograph records according to any one of claims 1 to 4, wherein the completely straight injection channel can be closed by a rotatable valve.

Images