KR100787562B1 - A method of preparing resin composition pellet for shielding electro-magnetic interference and molded articles using it - Google Patents

Abstract

A method for preparing an electromagnetic interference shielding resin composition, and a method for preparing an electromagnetic interference shielding resin molded product are provided to obtain excellent electromagnetic interference shielding property with using a minimized amount of stainless steel fiber. A method for preparing an electromagnetic interference shielding resin composition comprises the steps of sizing a plurality bundle of stainless steel fiber having a diameter of 1-20 micrometers with a thermoplastic polymer having a melt index of 13-26, and cutting it to obtain a stainless steel fiber pellet; injecting 60-93 wt% of a thermoplastic resin to the main hopper of a screw and injecting 7-40 wt% of the stainless steel fiber pellet into the screw just before the mixing zone or pulverization zone; mixing them with passing through a screw which comprises at least one mixing zone, at least one pulverization zone and at least one reverse zone and has a screw thread height of 7-15 mm; and extruding the mixed composition to obtain a pellet.

Description

A method of preparing Resin Composition Pellet for Shielding Electro-magnetic interference and molded articles using it}

1 is an embodiment of a screw used in the present invention.

2A and 2B show a conventional screw arrangement.

3 is a product production diagram.

<Description of Symbols for Major Parts of Drawings>

10: main hopper 11: stainless steel fiber inlet

20: outlet 30: flow zone

40: mixing zone 50: crushing zone

60: reverse zone 70: extrusion die (Die)

80: cooling device of the conveyor belt method 90: cutting device

The present invention relates to a pelletized electromagnetic wave shielding resin composition and a method for manufacturing the molded article thereof, and in particular to using a stainless steel fiber as a shielding material alone, to optimize the compounding conditions to lower the volume resistance to improve the electromagnetic shielding (EMI) and absorbent pellets It relates to a method for producing a phase resin composition and a thermoplastic resin molded article.

The development of information and communication technology in the modern society enabled the mass distribution of electronic and communication devices, and caused the harmful electromagnetic wave problem. Electromagnetic waves not only have a bad effect on the human body, but also cause serious damage by causing errors such as malfunctions in electronic communication or electronic devices themselves. For this reason, developed countries and domestic countries have established and regulated standards by associations and regulations. In particular, RS M 0015 was established in Korea to improve the reliability of electromagnetic shielding paint (hereinafter referred to as electromagnetic paint) for mobile phones.

Electromagnetic shielding (EMI) materials include metal powder, metal fibers, carbon nanotubes, carbon nanofibers, silver nano and the like. As an electromagnetic shielding (EMI) method, in addition to addition, there is a method of coating, plating, or depositing a layer with an electromagnetic shielding (EMI) material on the surface of the insulator. However, the method of coating, plating, and deposition, which occupy most of the EMI shielding resins, is subjected to several steps, making the manufacturing process complex and costly.

Electromagnetic shielding (EMI) imparting agent, if a metal, especially stainless steel fibers having various advantages can be added to the resin by kneading (compounding) to give the desired electromagnetic shielding ability, after kneading extruded to produce pellets By a simple process of injection molding directly to the mold can be produced a molded article having an electromagnetic shielding ability. In this case, the manufacturing process can be reduced compared to the existing coating, plating, and deposition methods, thereby reducing the cost, and the electromagnetic wave shielding material (stainless steel fiber) is present in a stable state inside the product. It can increase. However, in the known methods, it is difficult to obtain the desired electromagnetic shielding effect by a method in which stainless steel fibers are added to the resin alone and kneaded. Therefore, most conventional methods using stainless steel fibers have been used in combination with other electromagnetic shielding materials or other methods besides simple addition kneading.

In Korean Patent Laid-Open Publication No. 10-1990-0001500, a conductive nonwoven fabric composed mainly of conductive fibers such as stainless steel fibers, copper or copper alloy fibers and thermally meltable fibers is laminated on one side or both sides of a thermoplastic resin film, and the nonwoven fabric The electrically conductive thermoplastic resin sheet which contacted and superposed | superposed the thermoplastic resin film used as a protective layer, and heated and crimped at the temperature more than melting | fusing point of a heat meltable fiber is described. Patent Document 10-2003-53820 discloses a conductive polypropylene resin composition including polypropylene resin, stainless steel fiber, glass fiber, and the like. Patent Document 10-1997-027182 discloses an electrically conductive rubber composite resin in which fibrous carbon fibers and stainless steel fibers are added with SBS-based thermoplastic rubber as a base resin. Patent Document 10-1988-0011821 discloses a conductive resin composition containing 0.5 to 80% by weight of conductive fibers, such as copper fiber, stainless steel fiber, aluminum fiber, and molded articles thereof.

As disclosed in the above patent documents, there have been many attempts to use stainless steel fibers to produce electromagnetic shielding (EMI) thermoplastic resins, but products having electromagnetic shielding (EMI) performance by using stainless steel fibers alone. It was not developed until. The reason is that the stainless steel fiber is difficult to obtain uniform dispersion such as the dispersion varies depending on the conditions, and the stainless steel fiber itself is broken and broken during the compounding process. This is because there are problems such as difficult. That is, when used alone, it is difficult to reproduce the EMI shielding rate of the resin reproducibly by adding it in an appropriate range that does not affect the properties of the resin, whereas a large amount is required to secure EMI shielding. In the case of addition, there is a problem in that the physical properties of the resin are affected, which adversely affects the molding processability of the resin.

In the present invention, the stainless steel fiber is added to the resin in an appropriate amount so as not to affect the molding processability of the resin and uniformly dispersed so as to have electromagnetic shielding performance, that is, the stainless steel fiber as an electromagnetic shielding (EMI) material It aims to reduce electromagnetic volumetric stability while using alone, so that electromagnetic shielding (EMI) can be reproduced. The inventors have found that the method of adding stainless steel fiber to the resin has been difficult to secure the electromagnetic shielding (EMI) effect with proper use because the stainless steel fiber breaks finely during kneading and there is no network formation between the fiber and the fiber. Focusing on the point, through many repeated experiments, the stainless steel fibers are added to the resin in an appropriate size and then the compounding conditions are adjusted to maintain this length, thereby making the intersection between the stainless steel fibers and the fibers in the resin and The present invention was completed by confirming that stable electromagnetic wave shielding (EMI) can be reproduced even by the addition of an appropriate amount so as not to affect the molding processability of the resin.

Other objects and advantages of the present invention will be described below and will be better understood by practice of the present invention.

In the present invention,

Bundle of stainless steel fibers having a diameter of 1 μm to 20 μm in multiple layers, sizing them with a low-melting thermoplastic polymer (Thermoplatic Polymer), and cutting them into 3 mm to 10 mm lengths to obtain pellet-like stainless steel fibers;

Adding 93 to 60% by weight of thermoplastic resin into the main hopper of the screw, and then adding 7 to 40% by weight of the pelletized stainless steel fiber obtained in the above step into the screw immediately before the mixing zone or the crushing zone where kneading is started;

The thermoplastic resin and the pelletized stainless steel fibers introduced in the step are passed through a screw including at least one mixing zone, at least one crushing zone, and at least one reverse zone in which the flow is reversed, and having an acid height of 7 to 15 mm. Kneading while mixing; And extruding the kneaded resin composition of the above step into pellets, thereby providing a method for producing a pelletized electromagnetic shielding (EMI) resin composition.

In addition, the present invention provides a method for producing an electromagnetic shielding (EMI) resin molded article further comprising the step of extruding or injection molding the pellet-shaped electromagnetic shielding (EMI) resin composition obtained as described above.

Hereinafter, the manufacturing method of the present invention will be described in detail for each step.

Sized Pellet  Obtaining Stainless Steel Fibers

Stainless steel is drawn into long fibers with a diameter of 1㎛-20㎛ with a drawer. Bundled long fibers are squeezed into multiple layers, extruded into a low melting point thermoplastic polymer, and cut into 3-10 mm lengths to obtain pelletized stainless steel fibers. It is known in the art to size and cut stainless steel fibers into pellets. In the present invention, the fiber sized in this process is cut to an appropriate size of 3 mm to 10 mm to increase the dispersion of stainless steel fibers.

The low melting point thermoplastic polymer may be a conventional low melting point polymer used for sizing stainless steel fibers. For example, polyethylene or polypropylene having a low Melting Index (MI) may be used, and preferably, polyethylene having a MI of about 13 to 26 may be used.

Synthetic fiber and Pellet  Injecting stainless steel fiber into the screw

The screw is used by combining a commercially available screw for the purpose of the present invention. The screw must include at least one mixing zone, at least one crush zone and at least one reverse zone in which the flow is backflowed. Preferred examples of the screw used in the present invention are shown in FIG. First, thermoplastic resin is introduced into the main hopper 10 of the screw. The pellet-shaped stainless steel fiber prepared in the above step is placed in front of the mixing zone or the crushing zone where compounding is started by putting a separate inlet 11 instead of the main hopper together with the thermoplastic resin. When the thermoplastic resin and the stainless steel fiber are added to the main hopper at the same time as the conventional method, the fiber stays in the cylinder of the screw for a long time, so that the fiber may be broken by the tension generated between the resin and the screw. Contact can occur, which also causes the fiber to break down. Therefore, in the present invention, the stainless steel fiber is not added to the main hopper together with the synthetic resin, but is introduced just before the kneading is started to minimize the tension between the resins. The inlet of the stainless steel fibers is preferably just in front of the mixing zone when kneading starts from the mixing zone and just in front of the crushing zone when kneading starts from the crushing zone, which is from the outlet 20 from which the finished product comes out. It is about 50 ~ 150cm before.

In addition, in the present invention, the existing screw acid height was 5 to 7 mm, but the screw acid height was used to be deformed about 7 to 15 mm, which is about 1 to 10 mm higher than the acid height of the existing screw. Since the content of the stainless steel fiber reaches 7 to 40% by weight, if the existing screw is used as it is, the friction between the stainless steel fibers causes the fiber to be broken. Therefore, in the present invention, by increasing the acid height of the screw to secure a wide space for the fibers are kneaded to minimize the friction between the fibers to prevent the fracture of the fibers.

As the thermoplastic resin, all of the thermoplastic resin sheets which can be molded may be used without limitation. For example, polypropylene (PP), polystyrene (PS), polycarbonate (PC), ABS and the like can be used.

Synthetic resin Pellet  Stainless steel fiber Kneading  step

In this step, the thermoplastic resin and the pellet-like stainless steel fibers introduced into the screw are kneaded while passing through at least one mixing zone, at least one crushing zone, and at least one reverse zone in which the flow is reversed to form an electromagnetic shielding (EMI) resin composition. .

Existing screw arrangements are composed of several crushing zones and mixing zones, or only mixing zones, as shown in FIGS. 2A and 2B. In such a screw arrangement, the resin continues to flow in only one direction to generate tension between the resins, resulting in poor dispersibility of the mixed stainless steel fibers and crushing of the fibers. As a result, there was no crossover between fibers, distances, and networks were not formed, so the required volume resistivity value was not obtained.

In order to solve this problem, the present invention has a reverse zone in which the flow is reversed. In the reverse zone, since the resin does not flow in any direction but only rotates in a stagnant state, kneading may be performed without generating tension. Therefore, it is possible to prevent the crushing of the mixed stainless steel fibers as much as possible and to increase the dispersibility.

In one preferred embodiment of the present invention, a screw as shown in FIG. 1 is kneaded as follows. First, the stainless steel fiber and the thermoplastic resin injected are first broken in the crushing zone 50 and secondly kneaded well in the mixing zone 40. In this case, the dispersibility may be increased by further adding a mixing zone as necessary. Then, the reverse zone 60 stays without tension of the thermoplastic resin for 2 to 3 seconds so that the stainless steel fibers do not break and are well kneaded with the resin. As a result, the stainless steel fibers form a network as a whole. It is possible to have a shielding (EMI) rate.

Extrusion molding steps

The kneaded electromagnetic wave shielding resin composition is extruded into pellets. In one embodiment of the present invention, an electromagnetic shielding (EMI) resin composition kneaded in a screw is extruded while passing through a die hole of an extruder, cooled as it is passed through a conveyor belt type cooling device, and cut and pelletized. It becomes an electromagnetic wave shielding (EMI) resin composition. In this case, preferably, the diameter of the die hole of the extruder is at least 8-18 mm. The prepared pelletized electromagnetic shielding (EMI) resin composition of the present invention has an electromagnetic shielding (EMI) ratio of 30 to 90 dB.

Molded article manufacturing

When the pellet-shaped electromagnetic shielding (EMI) resin composition obtained through the above process is molded in a desired form according to a known plastic molding method, an electromagnetic shielding molded article is produced. Electromagnetic shielding (EMI) resin molded article of the present invention contains the size of pelletized stainless steel fibers in the ratio of 7 to 40% by weight to 60 to 93% by weight of the thermoplastic resin, while maintaining high dispersion and fiber length as a whole inter-fiber network It can form a has a stable volume resistance value. Electromagnetic shielding (EMI) resin molded articles produced according to the present invention include, in particular, cellular phone cases, communication equipment components and the like. Electromagnetic shielding (EMI) resin molded article according to the present invention is a electromagnetic wave shielding (EMI) material with a volume resistance of 10 ⁴ Ω to 10 ^-6 Ω or an electromagnetic shielding (EMI) ratio of 30 to 90dB or more, Can be used in the field.

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the scope of the present invention is not limited by the following examples, and those of ordinary skill in the art to which the present invention pertains should be within the equivalent scope of the technical concept of the present invention and the claims to be described below. Of course, various modifications and variations are possible.

Example  One

(1) The stainless steel is drawn into 8μm diameter long fiber with a drawer, and the fibers are bundled in multiple layers, extruded into polyethylene (MI 13), sized, cut into lengths of 6mm and pelletized. A sized stainless steel fiber was obtained.

(2) The screw was used by assembling the 65Φ Twin extruder of Daekwang Machinery. First, the thermoplastic resin (polypropylene) is introduced into the main hopper of the screw, and then the pelletized stainless steel fiber prepared in (1) is placed in front of the crushing zone where compounding starts at a rate of 10% by weight relative to the thermoplastic resin. Input via (11).

(3) The thermoplastic resin and pellet-like stainless steel fibers introduced into the screw in the above step were kneaded while passing the screw shown in FIG.

(4) The kneaded resin composition was extruded while passing through the die hole (12 mm in diameter) of the extruder, cooled and cut through a conveyor belt cooling device, and cut into a pelletized electromagnetic shielding (EMI) resin composition. Got it.

Example  2

The mobile phone case was manufactured from an electromagnetic wave shielding (EMI) resin molded article by injection molding the pelletized electromagnetic shielding (EMI) resin composition prepared in Example 1. The result of measuring the volume resistance value is shown in Table 1.

Comparative example  One

Except injecting stainless steel fibers into the main hopper simultaneously with the thermoplastic resin, the same procedure as in Example 1 was carried out to obtain an EMI shielding composition of pellets, and then injection molding was carried out in the same manner as in Example 2. Was prepared. The result of measuring the volume resistance value is shown in Table 2.

In the electromagnetic shielding molded article of Example 2 manufactured according to the present invention, the volume resistance was stably in the range of 10 ⁴ to 10 ² Ω, but in the comparative example, the volume resistance was 10 ⁸ to ^{10 10} Ω. appear. Through this, it can be seen that an important factor that greatly affects the electromagnetic shielding effect is in compounding conditions rather than the content of stainless steel fibers.

Example  3

(Electric amperage comparison according to the content of stainless steel fiber)

The diameter of stainless steel fiber was 8 micrometers, content was 15 weight%, and the length of fiber was 6 mm. The screw was used as a combination of 65Φ Twin extruder (Daekwang machine) as shown in Fig. 1, and was used by modifying the screw height of about 3mm (total height 10mm). RPM of the screw was 1200. The remaining conditions were performed similarly to Examples 1 and 2, and the electromagnetic wave shielding (EMI) resin molded article (cell phone case) was manufactured. The electrical ampere of the manufactured molded article was measured, and the results are shown in Table 3 below.

Exam conditions

1. Diameter of stainless steel fiber: 8㎛

2. Content of stainless steel fiber: 15% by weight

3. Screw model: 65Φ Twin extruder (manufacturer: Daekwang Machinery)

4. Screw RPM: 1200

Comparative example  2

The diameter of stainless steel fiber was 8 micrometers, content was 15 weight%, and the length of fiber was 6 mm. The screw was used as a combination combination of a model 65Φ Twin extruder (Daekwang machine) as shown in Figure 1, the height of the screw was used without modification. RPM of the screw was 1200. The remaining conditions were performed similarly to Examples 1 and 2, and the electromagnetic wave shielding (EMI) resin molded article (cell phone case) was manufactured. The electric ampere of the manufactured molded article was measured, and the results are shown in Table 4 below.

Exam conditions

1. Diameter of stainless steel fiber: 8㎛

2. Content of stainless steel fiber: 15% by weight

3. Screw model: 65Φ Twin extruder (manufacturer: Daekwang Machinery)

4. Screw RPM: 1200

In the case of Comparative Example 2, when the content of the stainless steel fiber was about 15%, the moldability was inferior and production was not possible. On the other hand, in Example 3, molding was possible by raising the acid height of the screw.

The electromagnetic wave shield (EMI) molded product produced according to Example 3 was prepared according to the reliability evaluation standard RS M 0015 to measure the volume resistance. As a result, it is shown in Table 5, which has a volume resistivity value of 10 ¹ ~ 10 ⁴ 나타나, the dispersibility is slightly reduced, but the electromagnetic shielding (EMI) ratio SE value is measured to be 50dB or more, and there is no problem in product application.

Example  4

(Extrusion Condition Test)

It was carried out in the same manner as in Example 1, except that the following conditions and the extruder shown in FIG. 1 were used, and the hole inner diameter of the extruder tail portion die was largely changed to 6 mm. The extrusion was smooth in all 22 holes.

Exam conditions

1. Diameter of stainless steel fiber: 8㎛

2. Content of stainless steel fiber: 15% by weight

3. Screw Type: 65Φ Twin Extruder (Manufacturer: Daekwang Machinery)-

4. Screw RPM: 1200

Comparative example  3

(Extrusion Condition Test)

It carried out similarly to Example 4 except using 3.9 mm as it is, without changing the hole inside diameter size of the extruder tail part die. Some of the 22 holes (6 holes) were clogged.

Exam conditions

1. Diameter of stainless steel fiber: 8㎛

2. Content of stainless steel fiber: 15% by weight

3. Screw Type: 65Φ Twin Extruder (Manufacturer: Daekwang Machinery)-

4. Screw RPM: 1200

In the present invention, the stainless steel fiber alone and in addition to the molding process of the resin by maintaining the length of the stainless steel fiber in the kneading process with the thermoplastic resin so that the network can be formed between the fiber and the fiber as a whole It is possible to give a sufficient electromagnetic shielding (EMI) rate to the resin while using in an appropriate amount of. Electromagnetic shielding (EMI) resin composition according to the present invention can be used in various fields, such as mobile phone case, communication equipment as the electromagnetic shielding (EMI) material having a volume resistance of 10 ⁴ Ω or less. In addition, in the present invention, since the electromagnetic wave shielding effect is achieved using only stainless steel fibers without using carbon black or the like which affects the color of the product, it is possible to manufacture the molded article in various colors. In addition, since the electromagnetic shielding (EMI) resin molded article of the present invention has a sufficient electromagnetic shielding (EMI) rate while using a minimum of stainless steel fiber, it may also have a price competitiveness compared to conventional electromagnetic shielding (EMI) resin molded articles.

Claims (6)

Bundling several layers of stainless steel fibers with a diameter of 1 μm to 20 μm and sizing them with a thermoplastic polymer having a melting index of 13 to 26, cutting them into 3 mm to 10 mm lengths to obtain pellet-like stainless steel fibers. ; Adding 93 to 60% by weight of thermoplastic resin into the main hopper of the screw, and then adding 7 to 40% by weight of the pelletized stainless steel fiber obtained in the above step into the screw immediately before the mixing zone or the crushing zone where kneading is started; The thermoplastic resin and the pelletized stainless steel fibers introduced in the step are passed through a screw including at least one mixing zone, at least one crushing zone, and at least one reverse zone in which the flow is reversed, and having an acid height of 7 to 15 mm. Kneading while mixing; And Method of producing an electromagnetic shielding (EMI) resin composition comprising the step of extruding the kneaded resin composition of the step to form a pellet. The method according to claim 1, wherein the pellet-shaped electromagnetic shielding (EMI) resin composition has an electromagnetic shielding (EMI) ratio of 30 to 90 dB. The method according to claim 1 or 2, wherein the extrusion is performed by extruding the die by adjusting the diameter of an extruder die hole to 8 to 18 mm. Bundling several layers of stainless steel fibers with a diameter of 1 μm to 20 μm and sizing them with a thermoplastic polymer having a melting index of 13 to 26, cutting them into 3 mm to 10 mm lengths to obtain pellet-like stainless steel fibers. ; Adding 93 to 60% by weight of thermoplastic resin into the main hopper of the screw, and then adding 7 to 40% by weight of the pelletized stainless steel fiber obtained in the above step into the screw immediately before the mixing zone or the crushing zone where kneading is started; The thermoplastic resin and pellet-like stainless steel fibers introduced in the step are passed through a screw including at least one mixing zone, at least one crushing zone, and at least one reverse zone in which the flow is reversed, and an acid height of the screw is 7-15 mm. Kneading while mixing; Extruding the kneaded resin composition of the above step into pellets; And Method of producing an electromagnetic shielding (EMI) resin molded article comprising the step of extruding or injection molding the pellet-shaped electromagnetic shielding (EMI) resin composition prepared in the step. The method of claim 4, wherein the molded article has a volume resistivity of 10 ⁴ Ω to 10 ^-6 Ω and an electromagnetic shielding (EMI) ratio of 30 dB to 90 dB. The method of claim 4, wherein the molded article is a cell phone case or a communication equipment component.

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