JP4063993B2 - Thermoplastic elastomer material injection molding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for injection molding of a thermoplastic elastomer material, and more particularly, it has excellent sealing properties, good slidability of the surface of the molded body, and generation of volatile components is prevented even during long-term use. In particular, the present invention relates to an injection molding method of a thermoplastic elastomer material suitable for manufacturing a member for precision equipment.
[0002]
[Prior art]
In recent years, the development of electronic devices has been remarkable. These electronic devices use integrated circuits using semiconductors and are printed and wired on a substrate, and have been reduced in size and weight. These electronic devices dislike moisture, dust, and the like, and the sealing performance of the case that houses the electronic devices is an important factor for the performance and durability of the electronic devices.
A case for storing electronic equipment is composed of a box and a lid, and the box and the lid are integrated with a gasket made of vulcanized rubber, foamed urethane, thermoplastic material, etc. on the mating surfaces thereof. ing. Usually, the gasket takes the form of a gasket with a lid fixed to the lid, and is performed by, for example, a method of opening a hole in the lid and fixing the gasket material by sandwiching the hole from both sides of the lid. . In this case, since the gasket material is exposed at the upper part of the lid body, when the lid body is inserted into the space of the electronic device body that has become narrow due to the recent downsizing of electronic device parts, There is a problem that the gasket material exposed on the upper side may be rolled up, or the gasket material may be turned up due to contact with an external factor during work handling, which causes a problem of poor sealing performance. For this reason, attempts have been made to improve the slidability of the surface of the molded body by adding a silicone polymer to the thermoplastic material. In this case, too, the low molecular weight component of silicone volatilizes and forms a peripheral precision member. There is an inconvenience of adverse effects.
[0003]
On the other hand, when injection molding using a pellet-like thermoplastic elastomer material, as fine powder for preventing the adhesion of the pellets, inorganic fine powders such as calcium carbonate and talc, polytetrafluoroethylene, It is known that organic fine powders such as polystyrene and polyethylene are used. However, these conventionally used powders contain impurities in the production process, or contain halogen components and low molecular weight components due to adsorption of various volatile contaminants. After being processed, these components are released into the environment of use, and there is a concern that the performance of precision instruments may be adversely affected. In particular, when a molded product is used as a gasket material for a hard disk device, it is a serious problem in practical use.
In addition, since the conventional dusting components are incorporated almost uniformly into the thermoplastic elastomer material after molding, the surface of the molded body has the adhesiveness and stickiness that the original thermoplastic elastomer had. In a structure where the molding material is exposed on the front side (for example, a gasket material for a fitting type hard disk device), there is a problem that it is turned or pulled when it comes into contact with an external factor. there were.
[0004]
[Problems to be solved by the invention]
Under these circumstances, the present invention improves the surface slidability of the injection-molded product, thereby preventing the above-mentioned blistering phenomenon in the gasket material and the like, and in particular, contaminating volatile components for members for precision equipment. It is an object of the present invention to provide a method for injection molding a thermoplastic elastomer material for producing a molded body having a significantly reduced slag.
[0005]
As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the object can be achieved by using a specific powder for pelleting during injection molding. . The present invention has been completed based on such findings.
That is, in the present invention, when injection molding is performed using a pellet-like thermoplastic elastomer material, ultrahigh molecular weight polyethylene fine particles are used as a dusting powder for preventing adhesion between the pellets. A method for injection molding a thermoplastic elastomer material is provided.
Here, the thermoplastic elastomer material is (a) a block copolymer comprising at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound. 100 parts by weight of a hydrogenated block copolymer obtained by hydrogenation, (b) 50 to 1000 parts by weight of a non-aromatic softener having a kinematic viscosity at 40 ° C. of 100 mm ² / sec or more, and (c) polypropylene What consists of 1-100 weight part of propylene-type resin which is a main component is preferable.
Further, the injection molding method of the present invention is suitably applied to the manufacture of precision equipment members, particularly hard disk device gasket materials.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the method of the present invention, ultrahigh molecular weight polyethylene fine particles are used as a dusting powder for preventing adhesion between pellets when pellets are supplied. The molecular weight of ultra high molecular weight polyethylene is usually 1 million or more, and the particle diameter is preferably 50 μm or less.
When this polyethylene fine particle is used, it is an ultra-high polymer, so it has fewer low molecular weight components than ordinary polyethylene, so it is harmful to precision instrument parts compared to the case using conventional dusting. In addition, volatile components and contaminating components generated from the molded product can be significantly reduced. Furthermore, since the polyethylene used in the present invention has an ultra-high molecular weight, it is not melted and taken into the matrix during molding, and tends to segregate on the surface of the molded body. As a result, the slidability of the molded body surface is good Thus, even when formed outside the structure, it is less likely to get caught or stuck with an external factor, and there is no problem in handling the structure.
[0007]
Next, the thermoplastic elastomer material used in the present invention comprises, as component (a), at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound. A hydrogenated block copolymer obtained by hydrogenating a block copolymer consisting of the above is used.
Examples of the hydrogenated block copolymer include a block copolymer of polybutadiene and polystyrene, a block copolymer of polyisoprene and polystyrene, or a block of polybutadiene or ethylene-butadiene random copolymer and polystyrene. Obtained by hydrogenating the copolymer, for example, diblock copolymer of crystalline polyethylene and polystyrene, styrene-ethylene / butylene-styrene triblock copolymer (SEBS), styrene-ethylene / propylene-styrene In particular, styrene-ethylene / butylene-styrene block copolymer or styrene-ethylene / propylene-styrene block copolymer can be used.
[0008]
The number average molecular weight of these hydrogenated block copolymers is preferably 60000 or more. When this number average molecular weight is less than 60000, the bleed of the softening agent increases, the compression set is large, and there may be a disadvantage that it cannot withstand actual use. The upper limit of the number average molecular weight is not particularly limited, but is usually about 400,000.
The content of the amorphous styrene block in the hydrogenated block copolymer is 10 to 70% by weight, preferably 15 to 60% by weight. The glass transition temperature (Tg) of the amorphous styrene block portion is 60 ° C. or higher, preferably 80 ° C. or higher. Also, the polymer at the portion connecting the amorphous styrene blocks at both ends is preferably amorphous, and examples thereof include an ethylene-butylene copolymer, a butadiene polymer, and an isoprene polymer. These blocks or random copolymers may be used.
In addition, although these hydrogenated block copolymers are mainly used independently, you may blend and use 2 or more types.
[0009]
In the thermoplastic elastomer material of the present invention, for the purpose of reducing the hardness of the thermoplastic elastomer of the component (a), the non-fragrance has a kinematic viscosity of 100 mm ² / sec or more at 40 ° C. as the component (b). It is necessary to add a family softener. If the softening agent has a kinematic viscosity at 40 ° C. of less than 100 mm ² / second, the weight loss and bleed of the composition due to volatilization are significant, and there is a disadvantage that it cannot withstand actual use. The kinematic viscosity, in terms of practical use and manufacturing, preferably from 100~10000mm ² / s at 40 ° C., in particular 200~5000mm ² / sec is preferred. Further, from the viewpoint of molecular weight, the number average molecular weight is preferably less than 20,000, particularly 10,000 or less, particularly 5000 or less. As such a softening agent, usually a liquid or liquid at room temperature is preferably used. Moreover, both hydrophilic and hydrophobic softeners can be used.
[0010]
The softener having such properties can be appropriately selected from various non-aromatic rubber softeners such as mineral oil, vegetable oil, and synthetic. Here, process oils such as naphthenic and paraffinic are exemplified as mineral oils, and as a vegetable oil, castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, Examples include wax, pine oil, and olive oil.
Especially, it is 1 type, or 2 or more types selected from mineral oil type paraffin type oil, naphthene type oil, or synthetic polyisobutylene type oil, and the number average molecular weights are 450-5000.
[0011]
In addition, these softeners may be used individually by 1 type, and may mix and use 2 or more types.
The blending amount of these softeners is 50 to 1000 parts by weight, preferably 55 to 300 parts by weight with respect to 100 parts by weight of the component (a). If this blending amount is less than 50 parts by weight, sufficient hardness reduction cannot be achieved and the flexibility of the thermoplastic elastomer composition may be insufficient, and if it exceeds 1000 parts by weight, the softening agent tends to bleed, In addition, the mechanical strength of the thermoplastic elastomer composition is reduced. The amount of the softening agent is appropriately selected within the above range depending on the molecular weight of the hydrogenated block copolymer (a) and the type of other components added to the hydrogenated block copolymer. It is preferable.
[0012]
In order to improve the processability and heat resistance of the thermoplastic emulsomer composition of the present invention, it is necessary to add a propylene-based resin mainly composed of polypropylene as the component (c). Examples of the resin include isotactic polypropylene, a copolymer of propylene and a small amount of other α-olefin (for example, propylene-ethylene copolymer, propylene / 4-methyl-1-pentene copolymer), and the like. be able to. When an isotactic polypropylene copolymer is used, those having an MFR (JIS K7210) in the range of 0.1 to 100 g / 10 minutes, particularly 0.5 to 50 g / 10 minutes can be preferably used.
The amount of component (c) is 1 to 100 parts by weight per 100 parts by weight of component (a), preferably 3 to 40 parts by weight, particularly preferably 5 to 30 parts by weight. If this blending amount exceeds 100 parts by weight, the hardness of the resulting thermoplastic elastomer material will be too high, resulting in poor sealing properties.
[0013]
In the present invention, the thermoplastic elastomer material may contain an antioxidant (anti-aging agent), an ultraviolet absorber, a light stabilizer, and various fillers, as long as the object of the present invention is not impaired. Can be contained.
[0014]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
Example 1
The compounding components shown below were kneaded at 220 ° C. using a twin screw extruder, extruded into strands, and then cut into pellets.
Compounding component (1) Triblock copolymer of styrene-ethylene / propylene-styrene [manufactured by Kuraray Co., Ltd., trade name: Septon] (SEPS having a number average molecular weight of 120,000 and a styrene amount of 30% by weight) 100 parts by weight (2 ) Paraffinic oil having a kinematic viscosity at 40 ° C. of 380 mm ² / sec [manufactured by Idemitsu Kosan Co., Ltd., trade name: Diana Process Oil PW380] (number average molecular weight 750) 110 parts by weight (3) Polypropylene by metallocene catalyzed polymerization [ Exxon Chemical Co., Ltd., trade name: Achieve] (Mw / Mn = 2.0) 15 parts by weight Next, over 100 parts by weight of the pellets obtained above, more than 1.5 parts by weight as dust DC60E5A manufactured by Nissei Plastic Industry Co., Ltd. is used as an injection molding machine after the high molecular weight polyethylene (average particle size 26 μm) is coated so as to be almost uniform. With E machine to produce a 1mm thick sheet. The obtained sheet had good peelability from the mold, and there was no stickiness between sheets.
Further, in order to test the contamination by the gas generated from the sheet, a 5 cm square was cut from the sheet and left in a glass sealed container together with a copper piece at 100 ° C. for 300 hours. Thereafter, as a result of observing the copper piece, there was no abnormality such as clouding of the copper piece.
[0015]
Comparative Example 1
In Example 1, the same components and methods as in Example 1 were used except that 1.5 parts by weight of polyolefin-based mixed wax (average particle size 10 μm) was used as the dust for 100 parts by weight of pellets. A sheet was prepared by injection molding. The sheet thus obtained felt sticking between the sheets.
Moreover, 5 cm square was cut out from this sheet | seat, and as a result of testing the contamination property by the generated gas performed like Example 1, cloudiness generate | occur | produced on the copper surface. When this generated component was analyzed, it was confirmed that it was the same component as that generated from the polyolefin mixed wax used.
[0016]
Example 2
Injection molding was carried out in the same manner as in Example 1, and a gasket with a lid for housing a hard disk drive device as shown in FIG. 1 was produced (this figure shows the gasket material with lid as seen from the sealing surface side). It is a figure.) The gasket 1 is in close contact with the surface of an aluminum lid 2, and the lid 2 serves as a lid for a hard disk drive device storage case. Devices such as magnetic disks, magnetic heads, actuators, etc. are arranged on the box side of the hard disk drive storage case in the central gap of the lidded gasket, and these devices are made of a metal box (not shown). It is closed with a gasket with a lid and stored in a hard disk drive device storage case.
When the operation for fitting such a gasket with a lid with a hard disk drive device storage case set in advance was repeated, the slidability of the gasket material was good, and the exposed portion of the surface of the lid was There was no concern that even if it came into contact with other parts, it turned over and the sealing performance was impaired. Further, when the apparatus was used for a long period of time, no failure that could be caused by gas or volatile components generated from the gasket material occurred.
[0017]
【The invention's effect】
In the method of injection molding of the thermoplastic elastomer material of the present invention, since the ultra-high molecular polyethylene fine particles are used as the dust for preventing the adhesion between the pellets, the molding of the obtained thermoplastic elastomer is performed. The body is excellent in sealing properties, has good slidability on the surface of the molded body, and can prevent generation of various gas components during use. For this reason, the injection molding method according to the present invention can be suitably applied particularly to the injection molding of precision equipment members such as gasket materials for hard disk devices.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a gasket according to the present invention.
[Explanation of symbols]
1: Gasket 2: Hard disk drive case lid

Claims (3)

When injection molding a member for precision equipment using a pellet-shaped thermoplastic elastomer material, it has a molecular weight of 1 million or more and an average particle size of 50 μm or less as a dusting powder for preventing adhesion between pellets. injection molding a thermoplastic elastomeric material, characterized by using an ultra-high molecular weight polyethylene fine particles is. The thermoplastic elastomer material is obtained by hydrogenating a block copolymer comprising (a) at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound. 100 parts by weight of the resulting hydrogenated block copolymer, (b) 50 to 1000 parts by weight of a non-aromatic softener having a kinematic viscosity at 40 ° C. of 100 mm ² / sec or more, and (c) polypropylene as a main component. The injection molding method according to claim 1, comprising 1 to 100 parts by weight of a propylene-based resin. The injection molding method according to claim 1 or 2, wherein the member for precision equipment is a gasket material for a hard disk device.

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