JPH0957750A - Method of molding molded item having thin wall part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the metering stability and greatly decrease the fraction defective of molded items by using a mixed resin with a specific rate mixture of a fluorocarbon resin powder contained with respect to a pelletized aromatic polyester resin in a method of injection molding molded items having a thin wall part. SOLUTION: In a method of molding molded items having a thin wall part through injection molding by the use of an aromatic polyester resin, a mixed resin comprising 0.1-0.2wt.% fluorocarbon resin powder is used relative to a palletized aromatic polyester resin. In this manner, slippage of the resin becomes well between the material supply part 7 and the screw part 6 of an injection molding machine, resulting in the improvement of a metering stability and also a mold releasing property to the mold. Also, a blending amount of the fluorocarbon resin is usually 0.1-0.2wt.% with respect to the aromatic polyester resin, and the blending effects hardly appear at below 0.1wt.%. On the other hand, when it is beyond 2.0wt.%, the slippage becomes large, as a result, melt blending can lead to insufficiency in an injection molding machine for molding aromatic polyester.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a molded article having a thin portion in the thin portion without trouble.

[0002]

2. Description of the Related Art In a molded product such as a bobbin for a floppy disk drive (hereinafter referred to as a bobbin for an FDD) which is relatively small and requires heat resistance and dimensional accuracy, an aromatic polyester resin which is a kind of so-called liquid crystal polymer is used. Many are used. Aromatic polyester resin has relatively good fluidity during molding, but if the molded product has a thin portion,
If the injection molding pressure is increased and filling is performed on the contrary, the thin-walled part may adhere to the mold and a good molded product may not be obtained. is there.

[0003]

SUMMARY OF THE INVENTION As a result of various studies to solve problems such as poor filling which occur when injection molding a molded product having such a thin portion using an aromatic polyester resin, the following results are obtained. The invention has been completed.

[0004]

The present invention relates to a method for molding a molded article having a thin portion by injection molding using an aromatic polyester resin, wherein the pelletized aromatic polyester resin contains 0 parts of fluororesin powder. The molding method is characterized by using a mixed resin in which 1 to 2.0% by weight is mixed.

In the present invention, an FDD bobbin, which is a typical example of a molded product having a thin portion, has, for example, FIGS.
The shape is as shown in, and the resin portion 1, 11 and the metal fitting portion 2,
12 and. In the figure, the thin portions 3 and 13 are a part of the resin portion and have a thickness of 0.1 to 0.2 mm.

The aromatic polyester resin used in the present invention is usually in the form of pellets having a size of about 2 to 4 mm. On the other hand, the fluororesin powder mixed with this resin includes polytetrafluoroethylene (PTFE), polytrifluorochloroethylene and the like. Fluorine resin is used for various purposes as a resin having excellent heat resistance and chemical resistance. In the present invention, the slipperiness of this resin is utilized. That is, by mixing a small amount of fluororesin powder with an aromatic polyester resin and using it for injection molding, slippage of the resin between the material supply section 7 and the screw section 6 of the injection molding machine shown in FIG. Is improved. Also, the releasability from the mold is improved.

The amount of the fluorine resin compounded is usually 0.1 to 2.0% by weight, preferably 0.3 to 1.0% by weight, based on the aromatic polyester resin. If it is less than 0.1% by weight, the compounding effect hardly appears. On the other hand, when the content exceeds 2.0% by weight, the slipperiness of the fluororesin becomes large, the melt-kneading becomes insufficient in the injection molding machine for molding the aromatic polyester, and the measurement stability also deteriorates.
Mechanical problems will occur in supplying the material to the injection molding machine, making stable production difficult.

The particle size of the fluororesin is not particularly limited, but it is preferably in the range of 1 to 30 μm in order to bring out the above-mentioned action and effects better. It can be used even if it is larger than 30 μm, but as it becomes larger, the adhesion density on the surface of the resin pellet decreases, so the above-mentioned effect becomes smaller, and if it is smaller than 1 μm, the effect remains the same, but it becomes ultrafine powder. Therefore, it is not easy to handle,
Adhesion to other things (due to static electricity) easily occurs.

The melting point of the aromatic polyester resin is about 300 to 350 ° C., though it depends on the grade. The temperature inside the cylinder of the injection molding machine is 3 at the tip near the nozzle.
It is set to a predetermined temperature in the range of 50 to 400 ° C. The mold temperature is set to a predetermined temperature in the range of 80 to 120 ° C.

[0010]

EXAMPLES Examples of the present invention will be described below. The equipment, materials and molding conditions used are as follows. 1. Injection molding machine Mold clamping force 30 tons Maximum injection capacity 19g Screw diameter 20mm 2. 16 molds (cavities) 3. Materials used Aromatic polyester resin (melting point 330 ° C.) PTFE powder mixed amount (%) 0 (Comparative Example 1), 0.3
(Example 1), 1.0 (Example 2) 4. Molding conditions Resin temperature 360 ° C (nozzle temperature) Injection pressure 1200kg / cm ² Injection speed 130mm / s Screw rotation speed 100rpm Mold temperature 90 ° C Molding cycle 16 seconds

200 shots were molded under the above conditions, and the measurement time of each shot and its standard deviation, and the number of non-defective and defective molded articles were determined. This is shown in Table 1. Further, changes in the weighing time are graphed and shown in FIGS.

[0012]

[Table 1]

[0013]

As is apparent from the above examples, in the injection molding method of the present invention, since the aromatic polyester resin is mixed with a small amount of the fluororesin, the metering stability is improved and the molded product is defective. The rate is also greatly reduced.

[Brief description of drawings]

FIG. 1 is an example of the shape of a bobbin for FDD, (a)
Is a perspective view, (b) is a front view, and (c) is a side view.

FIG. 2 is another example of the shape of the FDD bobbin,
(A) is a perspective view, (b) is a front view, and (c) is a side view.

FIG. 3 is a schematic sectional view of an injection molding machine.

FIG. 4 is a graph showing the relationship between the number of moldings and the measuring time in Comparative Example 1.

FIG. 5 is a graph showing the relationship between the number of moldings and the measuring time in Example 1.

FIG. 6 is a graph showing the relationship between the number of moldings and the measuring time in Example 2.

[Explanation of symbols]

 1,11 Resin part 2,12 Metal fitting part 3,13 Thin part 4 Nozzle part 5 Cylinder part 6 Screw part 7 Material supply part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G11B 23/033 102 G11B 23/033 102Z 25/04 101 25/04 101G // (C08L 67/02 27:12) B29L 31:34

Claims (2)

[Claims] 1. A method for molding a molded article having a thin portion by injection molding using an aromatic polyester resin, wherein 0.1 to 2.0% by weight of fluororesin powder is added to the pelletized aromatic polyester resin. A molding method using a mixed resin mixture. 2. The molding method according to claim 1, wherein the molded product is a bobbin for a floppy disk drive.