JPH04298875A - Polypropylene composition for disk cartridge and disk cartridge - Google Patents

Abstract

PURPOSE:To provide the disk cartridge having a shutter which does not generate worn powder in a cartridge case in spite of repetitive sliding of several tens thousand times and has excellent mechanical strength, etc. CONSTITUTION:The disk cartridge has the cartridge case 1 having a head insertion hole 3, a disk-shaped recording medium housed rotatably in the cartridge case 1 and the shutter 4 which opens and closes the head insertion hole 3 of the cartridge case 1. A compsn. contg. a polypropylene resin compsn. consisting of polypropylene and diorganopolysiloxane is used for the material of this shutter 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk cartridge, and more particularly to a disk cartridge and a polypropylene resin composition comprising polypropylene and diorganopolysiloxane used in a shutter for opening and closing a head insertion hole provided in the cartridge.

0002

BACKGROUND OF THE INVENTION Disc-shaped recording media such as magnetic discs and optical discs are easy to handle and protected from dust by being inserted into a recording/reproducing device while being housed in a disc cartridge to record desired information. I'm making it playable. For this reason, a head insertion hole is provided in the cartridge case forming the main body of the disc cartridge so that the head can access the disc-shaped recording medium when the disc cartridge is installed in a recording/reproducing apparatus.

However, when the head insertion hole is provided in this manner, when the disk cartridge is not in use, dust may enter the cartridge case through the head insertion hole and adhere to the recording surface of the disk-shaped recording medium, or the disk may When handling the cartridge, a finger or the like may touch the recording surface of the disk-shaped recording medium through the head insertion hole, causing dust or scratches on the recording surface, making it impossible to record and reproduce properly. For this reason, the disk cartridge is usually provided with a shutter that closes the head insertion hole when not in use.

Initially, a thin metal plate bent into a U-shape was used as this shutter, but when the metal shutter was frequently slid on the cartridge case, abrasion powder was generated, which could damage the recording medium. and the head, causing various problems. In order to prevent such problems,
The present inventors have proposed a shutter made of a resin material such as polyacetal resin or polypropylene resin mixed with a filler or a nucleating agent (JP-A-62-13318, JP-A-64-32479). , Japanese Patent Publication No. 6
4-70980).

[0005]Resin shutters have lower hardness than metal shutters, have superior lubricity, and are compatible with resin cartridge cases, so they can be slid repeatedly. Also, there was less generation of abrasion powder on the cartridge case, and various problems caused by adhesion of abrasion powder could be alleviated.

[0006]

[Problems to be Solved by the Invention] However, the polyacetal resin proposed here is deformed due to its hygroscopicity under high temperature and high humidity conditions, and the thin-walled closing portion that opens and closes the head insertion hole expands, resulting in disc failure. There were problems such as difficulty in attaching and detaching the drive device. On the other hand, polypropylene resin
In addition to surface modification by adding nucleating agents and fillers, improvements have been made to deformation caused by molecular orientation during molding, but these compositions do not eliminate the generation of wear particles due to repeated sliding. I couldn't do that.

[0007] In order to improve the sliding properties of polypropylene and apply it to disk cartridge shutters, it is necessary to select a polypropylene that has high properties such as dimensional stability against environmental changes, toughness, moldability, and scratch resistance. It is important to select a surface modifier that does not impair the properties of polypropylene and has a high effect on improving sliding properties. In view of this situation, the present inventors have earnestly searched for a polypropylene resin composition that has excellent printability by screen printing or the like in addition to the above-mentioned properties.

As a result, by blending diorganopolysiloxane with a viscosity of 100,000 cps or more at 25°C into a specific crystalline ethylene-propylene copolymer, hydrocarbon-based lubricants such as polyethylene wax, fatty acid-based For disk cartridges, it has significantly improved long-term sliding properties compared to general surface modifiers such as , fatty acid amide, and metal soaps, and has excellent moldability, toughness, scratch resistance, and printability. They discovered that a shutter can be obtained and arrived at the present invention. That is, the present invention combines a high-molecular-weight, highly lubricating surface modifier with crystalline polypropylene that has a specific fluidity, rigidity, and impact resistance, so that it can withstand repeated sliding tens of thousands of times. The object of the present invention is to provide a disk cartridge shutter that does not generate abrasion powder on the cartridge case and has excellent mechanical strength.

[0009]

[Means for Solving the Problems] According to the present invention, there is provided a cartridge case having a head insertion hole, a disk-shaped recording medium rotatably housed in the cartridge case, and a head insertion hole for opening and closing the cartridge case. A composition for a disk cartridge is provided, in which the material of the shutter includes a polypropylene resin composition made of polypropylene and diorganopolysiloxane. Further, according to the present invention, a disk cartridge includes a cartridge case having a head insertion hole, a disk-shaped recording medium rotatably housed in the cartridge case, and a shutter for opening and closing the head insertion hole of the cartridge case. Provided is a disk cartridge in which the shutter is molded from a composition containing a polypropylene resin composition made of polypropylene and diorganopolysiloxane.

The polypropylene resin composition used in the present invention is composed of 90 to 99.5 parts by weight of crystalline polyprolene and 10.0 to 0.3 parts by weight of diorganopolysiloxane. Composition 3
The point support bending modulus is preferably 10,000 Kg/cm2 or more. Polyprolene has an ethylene content of 2
wt% or more, the MFR is 10 to 100 g/10 min, and the isotacticity of the propylene homopolymer portion of this crystalline ethylene-propylene copolymer is 94.0% or more. It is preferable that it is made of polypropylene.

The diorganopolysiloxane is preferably provided by a dialkylpolysiloxane having 1 to 4 carbon atoms, and the dialkylpolysiloxane is preferably provided by dimethylpolysiloxane having a viscosity of 100,000 cps or more at 25°C. As the diorganopolysiloxane, dialkylpolysiloxanes having 1 to 4 carbon atoms in each alkyl group, diphenylporosiloxanes, and methylphenylpolysiloxanes can be used as long as the viscosity is above a certain level, but dialkylpolysiloxanes, especially dialkylpolysiloxanes, Dimethylpolysiloxane is effective.

In order to improve the long-term repeated sliding properties of diorganopolysiloxanes, it is particularly preferred to use diorganopolysiloxanes having a viscosity of 100,000 cps or more at 25°C. If the viscosity of the diorganopolysiloxane at 25° C. is 100,000 cps or less, the diorganopolysiloxane will seep into the surface layer of the shutter molded product violently, resulting in poor screen printability and repeated sliding over a long period of time. Furthermore, if the content of diorganopolysiloxane is less than 0.3% by weight, the sliding properties will be insufficient for use as a shutter for a cartridge case, and if it is more than 10% by weight, screen printability will be significantly impaired.

[0013] If the three-point support bending modulus of the polypropylene resin composition is 10,000 Kg/cm2 or less, the bending force is low and there is a drawback that plastic deformation occurs when forced displacement is applied. The crystalline ethylene-propylene copolymer described above is produced by homopolymerizing propylene in the first step in the presence of a catalyst combination of titanium trichloride and an alkyl aluminum compound, which is usually called a Ziegler-Natta type catalyst. A block copolymer is obtained by copolymerizing ethylene and propylene in two steps. Further, in the second step, some α-olefin such as butene-1 may be copolymerized in addition to ethylene. The polymerization method uses butane, pentane,
Slurry polymerization in an inert hydrocarbon catalyst such as hexane, heptane, or octane; solvent polymerization in which the resulting polymer is polymerized while dissolved in the inert hydrocarbon solvent; bulk polymerization in liquefied monomers; Polymerization methods such as gas phase polymerization in gaseous monomers are possible.

If the ethylene content of the crystalline polypropylene is less than 2% by weight, or if the MFR is more than 100 g/10 minutes, the cartridge case is likely to be damaged by impact when dropped. If the MFR is less than 10 g/10 min, a thin-walled shutter will lack fluidity during molding, deformation of the molded product due to molecular orientation, and propylene homopolymerization of the crystalline ethylene-propylene copolymer. Isotacticity of the polymer part measured by infrared spectrophotometer is 9.
If it is less than 4.0%, the surface hardness will be significantly lowered, the scratch resistance will be significantly lowered, and the sliding property will also be lowered.

[0015] Crystalline polypropylene has its molecular weight adjusted in the polymerization tank using a polymerization terminator such as hydrogen, as well as its MFR adjusted by molecular chain scission using an organic peroxide or the like during melt-kneading in an extruder. can also be used as appropriate. In addition, a small amount of polypropylene homopolymer or ethylene-propylene random copolymer may be mixed with the crystalline polypropylene within the above-mentioned conditions. To obtain the polypropylene resin composition of the present invention,
(a) Crystalline polypropylene and (b) diorganopolysiloxane are mixed within the above range using various known methods, such as a Henschel mixer, a V-type blender, a ribbon blender, etc., and then mixed using a single-screw extruder, twin-screw extruder, It is possible to adopt a method in which the materials are melt-mixed using a twin-screw extruder, kneader, Banbury mixer, etc., which is equipped with a raw material supply port in the cylinder section in addition to the usual raw material supply port, and then pelletized.

The polypropylene resin composition of the present invention also contains additives such as antioxidants, nucleating agents, ultraviolet stabilizers, lubricants, antistatic agents, copper inhibitors, dyes, talc, calcium carbonate, mica, etc. inorganic fillers, fiber reinforcement materials such as carbon fiber and glass fiber, copolymer rubbers of ethylene and olefins, copolymer rubbers of monovinyl-substituted aromatic hydrocarbon polymer blocks and conjugated diene elastomeric polymer blocks, Impact modifiers such as hydrogenated derivatives of copolymer rubber can be used as appropriate.

[0017]

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but it will be clear that the present invention is not limited to these Examples. The measurement methods used in the Examples and Comparative Examples of the present invention are as follows. Fluidity melt flow rate (MFR) <g/10min>
JIS K7210 Mechanical properties Tensile depression point strength <kg/cm2>
JIS K7113 flexural modulus
<kg/cm2> JIS K7203 shutter performance The shutter was injection molded using an M100SJ injection molding machine manufactured by Meiki Seisakusho Co., Ltd. at a molding temperature of 230°C, a mold temperature of 40°C, an injection time of 10 seconds, and a cooling time of 20 seconds. Ta.

A method for evaluating shutter performance will be described below. A shutter was attached to a slidable cartridge case, and insertion and removal were repeated up to 40,000 times, and the degree of wear on the opening/closing part of the cartridge case was checked every 1,000 times, and the number of insertions and removals at which wear started was determined. Visually observe the smoothness of the flat part of the shutter molded product. If there is no warpage at the edge of the flat part, the deformability is good (symbol: ○), and if there is deformation due to warp, the deformability is poor (symbol: ×). And so.

Printability The surface of the flat part of the shutter molded product is pretreated by corona discharge treatment so that the wet tension is 40 dyne/cm or more, and screen printing is performed using a urethane-based two-component curing ink. Ta. The adhesion of the ink was examined by a peeling test using cellophane tape (CT-18 manufactured by Nichiban Co., Ltd.) (the cellophane tape was brought into close contact with the printed surface and instantly peeled off at an angle of 90° upwards). No peeling at all (symbol: ○), partial peeling (symbol: △), mostly peeling (
It was evaluated as a symbol: ×). Deformation recovery property As shown in Figure 6, one plane part of the shutter molded product was deformed by a specified amount and held for 10 seconds, and after weight removal, it was deformed for 60 seconds.
After the elapse of ec, the deformation recovery was evaluated as poor (symbol: ×) if the shutter tip was in a floating state compared to before the deformation, and as good (symbol: ◯) if it recovered to the original position.

[0020] Attach the shutter to the cartridge case,
The shutter was dropped from a height of 1 m to check for damage to the shutter. The test was conducted on 10 cartridge cases, and if even one cartridge case was damaged, the impact resistance was considered poor (symbol: ×), and if none were damaged, the impact resistance was evaluated as good (symbol: ◯). Scratch resistance A flat plate (injection molded) with a thickness of 2 mm and 100 mm x 100 mm was used as a test piece, and a load of 1 kg was applied to this test piece.
Rub it back and forth with sandpaper, and visually observe and evaluate the damaged area. Good if the scratches are not noticeable (symbol: ○)
, those that were conspicuous were marked as defective (symbol: ×).

The components used in the Examples and Comparative Examples are as follows. Crystalline Polypropylene The crystalline polypropylene used is shown in Table 1 below.

[0022]

Ethylene content (wt%) Polypropylene was made into a film with a thickness of 50 μm, and the absorbance ratio between 720 cm −1 and 974 cm −1 was measured using an infrared spectrophotometer, and was determined from a calibration curve prepared in advance. Isotacticity (%) In the production process of ethylene-propylene block copolymer, the propylene homopolymer produced in the first step is
998cm using an infrared spectrophotometer.
It was determined from the absorbance ratio between −1 and 974 cm −1. Note that the measurement film was heat-treated in advance at 135° C. for 6 hours.

Dimethylpolysiloxane masterbatch DMPS-1: Dimethylpolysiloxane containing 50% by weight polypropylene block copolymer with MFR 15g/10min and a viscosity of 500,000 cps or more at 25°C (Toray Dow Corning Silicone Co., Ltd.) BY16-1
40) and 50% by weight of ditylpolysiloxane were mixed in a pressure kneader at 180° C. for 20 minutes, and then pelletized with a square pelletizer to obtain master pellets containing 50% by weight of ditylpolysiloxane. The viscosity of dimethylpolysiloxane is BROOKFIELD
It was measured according to ASTM D3236 using a viscometer (DV-2 type).

DMPS-2: Viscosity at 25°C is 100,000c
DMP using PS dimethylpolysiloxane (SH200 oil manufactured by Toray Dow Corning Silicone Co., Ltd.)
Master pellets were obtained in the same manner as S-1. DMPS-3: Dimethylpolysiloxane (Toray Dow Corning Silicone) with a viscosity of 10,000 cps at 25°C
Master pellets were obtained in the same manner as DMPS-1 using SH200 oil (manufactured by Co., Ltd.).

Ethylene-propylene copolymer rubber EPR
: Ethylene-propylene copolymer rubber lubricant with ethylene content of 73% by weight and Mooney viscosity of 1+420 O-A: Oleic acid amide

(Examples 1 to 3 and Comparative Examples 1 to 3) In Example 1, 96% by weight of PP-3 and DMPS
-1 4% by weight were uniformly pre-blended in a tumbler blender, and using a single screw extruder with a screw diameter of 65mmФ, the screw rotation speed was 60 rpm and the cylinder temperature was 23.
Pellets containing 2% by weight of dimethylpolysiloxane were prepared by melt-kneading at 0° C. and a discharge rate of 25 kg/hr. The pellets were molded using a JSW100SAII injection molding machine manufactured by Japan Steel Works, Ltd. at a molding temperature of 230°C, a mold temperature of 60°C, an injection time of 10 sec, and a cooling time of 30 sec. At the same time, a shutter was also prepared under the same conditions as above and subjected to performance evaluation. Also,

In Example 2, 98% by weight of PP-3, D
MPS-1 2% by weight In Example 3, PP-3 90% by weight, DMPS-1
10% by weight In Comparative Example 1, 99.6% by weight of PP-3, DMPS-
1 0.4% by weight In Comparative Example 2, 70% by weight of PP-3, DMPS-1
30% by weight Comparative Example 3 was carried out in the same manner as Example 1 except that 99% by weight of PP-3 and 1% by weight of OA were used. The results are shown in Table 2.

[0029]

[Table 2]

(Example 4, Example 5 and Comparative Examples 4 to 6) In Example 4, 96% by weight of PP-2, DMPS-1
4% by weight In Example 5, 96% by weight of PP-3, DMPS-2
4% by weight In Comparative Example 4, 96% by weight of PP-1, DMPS-1
4% by weight In Comparative Example 5, 96% by weight of PP-4, DMPS-1
4% by weight In Comparative Example 6, 96% by weight of PP-3, DMPS-3
The same procedure as in Example 1 was carried out except that 4% by weight was used. The results are shown in Table 3.

[0031]

[Table 3]

(Example 6, Example 7 and Comparative Examples 7 to 9) In Example 6, 96% by weight of PP-7 and DMPS-1
4% by weight In Example 7, 96% by weight of PP-6, DMPS-1
4% by weight In Comparative Example 7, 96% by weight of PP-8, DMPS-1
4% by weight In Comparative Example 8, 96% by weight of PP-5, DMPS-1
4% by weight In Comparative Example 9, 96% by weight of PP-3, DMPS-1
The same procedure as in Example 1 was carried out except that 4% by weight of EPR and 4% by weight of EPR were used. The results are shown in Table 4.

[0033]

[Table 4]

Next, a specific example of the disk cartridge will be explained with reference to the drawings. 1 and 2 show a front view and a plan view, respectively, of a disk cartridge according to the present invention. FIG. 3 is a side view of the shutter according to the present invention, and FIG. 4 is a sectional view taken along line A in FIG.

1 is a cartridge case, upper case 1a
and a lower case 1b. The cartridge case 1 is injection molded from a hard resin such as ABS resin. A disk rotation area is formed inside the upper and lower cases 1a, 1b, and a recording medium 2 such as a flexible magnetic disk, optical disk, magneto-optical disk, or compact disk is rotatably housed therein. A cleaning sheet made of non-woven fabric, woven fabric, porous sheet, etc. is pasted on the inner surfaces of the upper and lower cases 1a and 1b, and is pressed against the disk surface by elastic pieces or ribs from the inner surfaces of the upper and lower cases to prevent rotation of the disk. The device is configured to clean the disk surface. Upper and lower cases 11a, 11b
are joined by ultrasonic welding. Cartridge case 1
A head insertion hole 3 is formed in the head insertion hole 3, and a shutter sliding area 5 with a lower surface is provided around the head insertion hole 3. A guide groove 6 is provided on the inner surface of the case at the front edge of the shutter sliding area 5 . Here, the cross-sectional shape of the guide groove portion is shown in FIG.

The shutter 4 has a U-shaped cross section and is composed of face plate portions 11a and 11b facing the shutter sliding area 5 and a connecting portion 12 that connects the double-sided plate portions. There are two engaging claws 13 and 14 on the inside of the connecting portion that fit into the guide groove 6.
Formed in several places. The shutter 4 is configured as described above,
The torsion coil spring 7 elastically biases the head insertion hole 3 in the closing direction.

[0037]

[Effects of the Invention] As explained above, the polypropylene composition of the present invention is made by blending diorganopolysiloxane having a viscosity higher than a specific level with crystalline polyprolene having a specific melt flow rate and rigidity in a specific ratio. In addition to having good long-term sliding properties, it also has excellent printability, moldability, and toughness, and is suitable for use in shutters that open and close head insertion holes provided in disk cartridges. .

[Brief explanation of drawings]

FIG. 1 shows a front view of a disc cartridge according to the present invention.

FIG. 2 shows a plan view of a disk cartridge according to the present invention.

FIG. 3 shows a side view of a shutter according to the invention.

FIG. 4 shows a sectional view of the section A--A in FIG. 3;

FIG. 5 shows a sectional view of the roller portion of FIG. 1;

FIG. 6 is an explanatory diagram showing a method for evaluating the deformation recovery property of a shutter.

[Explanation of symbols]

1 Cartridge case 1a Upper case 1b Lower case 2 Recording medium 3 Head insertion hole 4 Shutter 5 Shutter sliding area 6 Guide groove 7 Torsion coil spring 11a Face plate part 11b Face plate part 12 Connecting part 13 Engagement claw 14 Engagement claw

Claims (2)

[Claims] 1. A disk cartridge comprising: a cartridge case having a head insertion hole; a disk-shaped recording medium rotatably housed in the cartridge case; and a shutter for opening and closing the head insertion hole of the cartridge case. A polypropylene composition for a disk cartridge, characterized in that the material of the shutter includes a polypropylene resin composition composed of polypropylene and diorganopolysiloxane. 2. A disk cartridge comprising: a cartridge case having a head insertion hole; a disk-shaped recording medium rotatably housed in the cartridge case; and a shutter for opening and closing the head insertion hole of the cartridge case. A disk cartridge characterized in that the shutter is molded from a composition containing a polypropylene resin composition made of polypropylene and diorganopolysiloxane.