JPH06215519A - Shutter - Google Patents

Abstract

PURPOSE:To provide the shutter of a cartridge having an excellent antistatic property by mixing a specific ratio of an antistatic agent into a polyacetal resin and molding the shutter which is specific or below in the thickness of a skin layer and max. spherulite size. CONSTITUTION:The disk or tape cartridge having <=15mum thickness of the skin layer and <=40mum max. spherulite size. is molded by using a material formed by compounding 0.01 to 5 pts.wt. antistatic agent with 100 pts.wt. polyacetal resin. The sufficient antistatic property is not obtainable if the compounding ratio of the antistatic agent is below this range. The thermal stability degrades if the compounding ratio exceeds this ratio. The change of the antistatic property with lapse of time increases if the thickness of the skin layer exceeds 15mum. The desired thickness, etc., of the skin layer are obtd. by a method of controlling the crystallization time of the resin, etc. As a result, the shutter which has the excellent antistatic property and lessens the change thereof with lapse of time is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shutter made of polyacetal resin, which has excellent antistatic properties and whose antistatic properties do not change over time.

[0002]

2. Description of the Related Art Polyacetal resins are plastics that are widely used as engineering resins in various fields, especially in the fields of automobiles and home appliances, because they have excellent mechanical properties and molding processability. However, in applications such as parts involving friction, static electricity is liable to be generated, which often causes various troubles. That is, problems such as easy dust formation, electric discharge and electrical noise are caused. Therefore, a material excellent in antistatic property with less of these problems has been desired.

The following methods are available as methods for improving the antistatic property. Japanese Patent Publication No. 56-22341 discloses a method of uniformly distributing a polyoxyalkylene-polysiloxane block copolymer in a polyacetal. Further, JP-B-56-52940 discloses a method of blending a polyhydric alcohol fatty acid ester having a hydroxyl group and polyethylene glycol with polyacetal.

Further, Japanese Patent Publication No. 57-16616 discloses a method of blending boric acid ester of glycerin monofatty acid ester with polyacetal. In addition, Japanese Patent Publication 2-57
No. 583, a composition comprising an acetal resin and a polyetheresteramide copolymer is added to an antistatic agent 0.00
There is a method of blending 5 to 5 parts by weight.

Japanese Patent Publication No. 14709/1992 discloses a method of blending 0.01 to 3% by weight of a hindered amine compound and an antistatic effective amount of an antistatic agent in a polyacetal resin. However, under the present circumstances, these conventionally known antistatic techniques do not always exhibit satisfactory antistatic properties and little improvement in antistatic properties over time.

Further, Japanese Patent Publication No. 3-80819 discloses a polyoxymethylene resin containing 0.5 to 0.5% of conductive carbon black.
There is a method for improving the antistatic property by blending 30% by weight, an epoxy compound of 0.05 to 10% by weight, and an organic phosphorus compound of 0.1 to 10% by weight. However, in this technique, since the conductive carbon black is blended, the color of the resin is limited to black, and there are drawbacks that the lubricity and thermal stability of the polyoxymethylene resin are greatly impaired. There is.

Further, Japanese Patent Laid-Open No. 61-41583 discloses a method of performing permeation printing on a polyacetal resin molded body having a depth up to a perfect spherulite layer of 200 μm or less in order to perform clear permeation printing on the polyacetal resin. Although disclosed, the polyacetal resin moldings in the above references all have a maximum spherulite diameter that is too large, and little change in the antistatic property over time has been improved.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a shutter made of a polyacetal resin which realizes a sufficient initial antistatic property and an antistatic property with little change over time.

[0009]

According to the present invention, a skin layer formed from a material obtained by mixing 0.01 to 5 parts by weight of an antistatic agent with 100 parts by weight of a polyacetal resin has a thickness of 15 μm or less, The present invention provides a disk or tape cartridge shutter having a maximum spherulite size of 40 μm or less.

The present invention will be described in detail below. The polyacetal resin in the present invention refers to an oxymethylene homopolymer substantially composed of oxymethylene units produced from a cyclic oligomer such as a formaldehyde monomer or its trimer (trioxane) or tetramer (tetraoxane), And the above raw materials and ethylene oxide, propylene oxide, epichlorohydrin, 1,
An oxymethylene copolymer containing 0.1 to 20% by weight of an oxyalkylene unit having 2 to 8 carbon atoms, which is produced from a cyclic ether such as 3-dioxolane, glycol formal, or diglycol formal. Also included are oxymethylene copolymers having branched molecular chains, and oxymethylene block copolymers containing 50% by weight or more of oxymethylene repeating units and less than 50% by weight of different polymer units. Further, in the present invention, two or more kinds selected from oxymethylene homopolymers, oxymethylene copolymers, branched polymers and oxymethylene block copolymers can be blended and used.

The FR (ASTM D1238-57E conditions) of the polyacetal resin used in the present invention is 20 to 20.
100 g / 10 min is preferred. When FR is less than 20 g / 10 minutes, it is difficult to obtain a shutter having a skin layer thickness of 15 μm or less. If FR exceeds 100 g / 10 minutes, the antistatic property decreases, which is not preferable. The antistatic agent used in the present invention is a high / low molecular weight compound having a water absorption of 0.3% or more, and is an ethylene oxide adduct of the amine compound represented by the general formula (I).

[0012]

[Chemical 1]

(Wherein R ₁ is an alkyl or alkenyl group having 10 to 22 carbon atoms, m ₁ and n ₁ are both integers of 1 to 10) and are represented by the general formula (II). Amide compound

[0014]

[Chemical 2]

(Wherein R ₂ represents a carboxylic acid residue, x and y each represent an integer of 0 or 1 or more, and n ₂ represents an integer of 1 or more), ethylene oxide-propylene represented by the general formula (III). Oxide copolymer

[0016]

[Chemical 3]

(Where m ₃ and n ₃ are integers from 1 to 99, and m 3
₃ + n ₃ is an integer of 10 to 100. ), The general formula (I
V) polyethylene glycol alkyl ether

[0018]

[Chemical 4]

(Wherein R ₄ is an integer having 10 to 32 carbon atoms and n ₄ is an integer of 6 to 30), polyoxyalkylene-polysiloxane block copolymer, polyhydric alcohol fatty acid ester having a hydroxyl group, Examples thereof include boric acid ester of glycerin monofatty acid ester, polyethylene glycol, and ethylenebisstearylamide. Among them, polyethyleneglycol stearyl ether, boric acid ester of glycerin monostearate, polyethylene glycol (molecular weight 1000 to 10,000), ethylenebisstearylamide. Is more preferable.

The above antistatic agents may be used alone or in combination of two or more kinds. The molecular weight of the antistatic agent is preferably 200 to 20,000,
0 to 10000 is more preferable. The compounding amount of the antistatic agent in the present invention is 0.01 to 5 parts by weight, preferably 0.03 to 100 parts by weight with respect to 100 parts by weight of the polyacetal resin.
It is selected in the range of 3.0 parts by weight. This compounding amount is 0.01
If it is less than part by weight, sufficient antistatic properties cannot be obtained.
Further, if it exceeds 5 parts by weight, the thermal stability is lowered, silver streaks (silver stripes) are generated due to decomposition gas at the time of molding, and the appearance of the shutter is remarkably deteriorated, which is not preferable.

As a material for molding the shutter of the present invention, an additive which is commonly used in polyacetal resins, for example, a β-alanine polymer whose production method is described in JP-A-3-234729, 6 -6,6-6,
10 Copolymer nylon, polyamides such as nylon-6,6, heat stabilizers such as melamine, 2,2'-methylene-bis (4-methyl-6-t-butylphenol), triethylene glycol-bis [3- ( 3-t-butyl-5-
Methyl-4-hydroxyphenyl) propionate],
Antioxidants such as pentaerythritol-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], lubricants, glass fibers, carbon fibers,
Reinforcing materials such as potassium titanate fibers and organic fibers, glass beads, talc, inorganic fillers such as calcium carbonate, nucleating agents, release agents, plasticizers, carbon black and pigments are used to the extent that the objects of the present invention are not impaired. It can be blended.

The thickness of the skin layer on the shutter surface of the present invention must be 15 μm or less. The thickness of the skin layer in the present invention means the thickness of a resin molding forming the shutter, which is sliced into 10 μm-thick slices in the thickness direction with a microtome and observed at 340 × with a transmission polarization microscope using crossed Nicols. , Refers to the thickness of the non-polarized layer on the outer surface of the molded body. If the thickness of this skin layer can be reduced, the change in antistatic property over time can be made extremely small. The thickness of the skin layer is 15 μm
When it exceeds, the change in antistatic property over time becomes large.

The thickness of the skin layer of the molded product constituting the shutter of the present invention can be obtained by (1) a method of controlling the crystallization time of the resin, (2) a method of selecting an appropriate molding method, or the like. These methods may be used alone or in combination. As a method of controlling the crystallization time of the resin, there is a method of setting the crystallization time to 20 to 100 seconds.

The crystallization time in the present invention means a sample of 5 mg of polyacetal resin at 320 ° C. by DSC.
When the temperature of the sample holder reaches 150 ° C, the temperature rises to 200 ° C at a temperature of 200 ° C / min., The temperature is held at 200 ° C for 2 minutes, and the temperature is lowered to 150 ° C at 80 ° C / min. It is the time (seconds) until the peak top is detected.

The method of controlling the crystallization time to 20 to 100 seconds is carried out by a generally known crystal nucleating agent, that is, silicate (inorganic filler) powder such as talc and wollastonite, hydrotalcite, calcium carbonate, etc. There is a method of adding an appropriate amount of an organic nucleating agent such as a carbonate and / or a branched polyacetal copolymer. Other additives that control crystallization time include melamine, amine compounds such as dicyandiamine, nitrides such as boron nitride, oxides such as zinc oxide, titanium oxide, calcium oxide and magnesium oxide, acetylene black, and conductivity. There are carbon powders such as water-soluble carbon black, powders of amide resins such as ionic polymers of nylon 6,6 and acrylamide, and powders of vinyl polymers such as radical polymers of acrylamide, but not particularly limited thereto. However, among them, preferred crystal nucleating agents are nitrides such as boron nitride, and amide resin powders such as ionic polymers of nylon 6,6 and acrylamide, and boron nitride is more preferable. Preferred boron nitride has an average particle size of 1 to 10 μm, preferably 2 to 7
The content of diboron trioxide is 0.05 to 0.7% by weight, preferably 0.1 to 0.6% by weight, and the addition amount thereof is 5 to 200 ppm, preferably 20 to 200%.
ppm is good. Strictly speaking, however, the shutter made of polyacetal resin has other properties (for example, heat aging property, hot water resistance, weather resistance, other than the shutter opening).
Antistatic properties, slidability, releasability, thermal stability and thermal decomposability at the time of molding, etc. are often required. It is necessary to select an appropriate crystal nucleating agent in consideration of compatibility.

As a method of controlling by selecting an appropriate molding method, there are the following methods. First,
Mold temperature is 100 ° C. or higher and 150 ° C. or lower, preferably 110
A method of molding by setting the temperature above 140 ° C and above 140 ° C. Next, the surface of a mold for injection molding (cavity) by induction heating with high frequency disclosed in Japanese Patent Publication No. 58-40804.
A method of selectively heating and injection molding. Next, a method of compression molding with a hot press and then slowly cooling. A method of cutting, polishing, and sandblasting extruded round bars. Next, it is a method of thermally annealing a molded body injection-molded at a mold temperature of 10 ° C. or higher and lower than 100 ° C. at a temperature of 150 ° C. or higher and lower than the melting point of the polyacetal resin. Of these molding methods, the method of or is preferable in view of productivity.

The maximum spherulite size of the resin crystals forming the shutter of the present invention must be 40 μm or less. The maximum spherulite size in the present invention means that the cross section of the compact is 10
When sliced into thin slices with a microtome to a thickness of μm and observed at 340x with a transmission polarization microscope using crossed Nicols, when the spherulite diameter can be clearly discerned, the largest spherulite among them When the spherulite diameter cannot be clearly discriminated, it means twice the value of the one with the maximum length among the particles confirmed to have the same polarized part (same color part) without being connected to other polarized parts (( The maximum length of the same polarization is regarded as 1/2 of the diameter of the spherulite).

If the maximum spherulite size of the resin crystals constituting the shutter exceeds 40 μm, the spherulite state of the molded product is likely to change, and the amount of the antistatic agent on the surface changes with time. The preferable maximum spherulite size is 6 to 30 μm, more preferably 10 to 20 μm from the viewpoint of dimensional stability and antistatic stability.
m. The application of the present invention is a disk or tape cartridge shutter having a thickness of 1 mm or less, and a floppy disk shutter is more preferable.

The shutter of the disk or tape cartridge according to the present invention relates to a disk or tape cartridge containing a magnetic disk or a magnetic tape, and is a shutter attached to the outer surface of the case to open and close the head insertion window.

[0030]

【Example】

[0031]

[Reference example]

<Production of polyacetal resin> Ethylene oxide 2.
Polyacetal copolymerized with 8% was prepared according to US Pat.
It was synthesized by a known method described in 352. The intrinsic viscosity of this product was 1.0. (The intrinsic viscosity was measured at 60 ° C. by dissolving 0.1% by weight of the polymer in a p-chlorophenol solution containing 2% by weight of alphapinene.)
The melt index in STM D1238-57T (E condition) was 30.0 g / 10 minutes. This polyacetal is designated as P-1.

Both ends acetylated polyacetal homopolymer powder were prepared by the known method of US Pat. No. 2,998,409. The intrinsic viscosity of this product was 1.2. (The intrinsic viscosity was measured at 60 ° C. by dissolving 0.1% by weight of the polymer in a p-chlorophenol solution containing 2% by weight of alphapinene.) Also, ASTM D1238
Melt index at -57T (E condition) is 40.0
It was g / 10 minutes. This polyacetal is designated as P-2.

[0033]

Examples 1 to 18 and Comparative Examples 1 to 14 Triethylene glycol-bis [3- (3-t-butyl-5-methyl-4]
-Hydroxyphenyl) propionate], 0.2 parts by weight, polyacetal, antistatic agent and nucleating agent shown in Tables 1 and 2 were blended in a nitrogen atmosphere at the compounding ratio shown in the table, and 2
L / D = 25 single-screw vented extruder set at 00 ° C (conditions: screw rotation speed; 100 rpm, discharge 6 kg /
The pellets obtained by melt-kneading in hr) were dried, and a 3.5-inch floppy disk shutter was molded with a 5-ounce molding machine (conditions: mold temperature 100 ° C., cooling time 10 seconds). This shutter was left in a constant temperature and humidity chamber at a temperature of 20 ° C. and a humidity of 50% for 1 hour and 500 hours to prepare a sample, and then a voltage of 10 KV was applied to the sample, and the electrified voltage half-life after the application was stopped ( Second) was measured by a static Honest meter.

The results are shown in Tables 1 and 2. The symbols in the table indicate the following. (T) Antistatic agent : T-1: Polyethylene glycol stearyl ether T-2: Boric acid ester of glycerin monostearate T-3: Polyethylene glycol (molecular weight 6000) (K) Nucleating agent : K-1: Boron nitride ( Average particle size 2 μm) K-2: Boron nitride (average particle size 5 μm) K-3: Talc (average particle size 5 μm)

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

According to the present invention, it is possible to provide a shutter which is excellent in antistatic property and whose antistatic property does not change with time.

Claims (1)

[Claims] 1. A skin layer formed by mixing 0.01 to 5 parts by weight of an antistatic agent with 100 parts by weight of a polyacetal resin, having a skin layer thickness of 15 μm or less and a maximum spherulite size of 40 μm or less. A shutter for a disc or tape cartridge.