JPS61100415A - Electrically-conductive molding material - Google Patents

Abstract

PURPOSE:To enable to unify an appearance without making mechanical strength of a molded article deteriorate, by a method wherein synthetic resin of a master pellet is made identical with that of a natural pellet and flowability of the synthetic resin of the master pellet is made larger than that of the synthetic resin of the natural pellet. CONSTITUTION:Synthetic resin of a master pellet is made identical with that of a natural pellet to improve dispersion of a filler. It is necessary that a ratio of a flowability (a) of the synthetic resin of the master pellet to a flowability (b) of the synthetic resin of the natural pellet if a/b=1.1X1.3. A bundled long fiberlike filler 10 is passed through a die 12 of an extruder 11, the filler 10 is formed 13 by coating the same with the synthetic resin and made into the master pellet by cutting off 14 the same further. Based on the above matter, a surpassing molded article wherein an electrically-conductive filler is dispersed evenly, molding can be performed at a low temperature and low back pressure of a screw, mechanical strength does not deteriorate and appearance is uniform is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a conductive molding material in which a conductive filler has good dispersibility and can shorten cycle time.

[Technical background of the invention and its problems 1 In recent years, the housings of electronic devices have been designed to protect electronic circuits from external interference radio waves and to prevent unnecessary radio waves generated from oscillation circuits from leaking to the outside. It is required to be made of electromagnetic shielding material. Such N11 wave shielding materials include metals and conductive synthetic resins, but while the former metals have excellent electromagnetic wave shielding effects, they have drawbacks such as being heavy, expensive, and having poor workability. Therefore, the use of the latter conductive synthetic resin is becoming mainstream. In order to obtain a high shielding effect using the latter, the conductive filler in the resin must be long! It is necessary that the fiber be formed as a single filament. As this method, long lI
The best method is to form a synthetic resin layer on the surface of bundles of fibrous If-type fillers, cut them into pellets, and make them into master pellets. ).

In this method, the length of the conductive filler is 2 to 3 av in the conventional method of kneading synthetic resin and conductive filler. The advantage is that the conductive filler can be dispersed and molded into the resin. However, the master pelletizing method requires a screw back pressure of 15 to 25 when measuring in injection molding! + / C1l' (gauge) If we don't raise it to
There is a drawback that the molding cycle is increased because the conductive fiber bundles in the master pellet are not dispersed. Furthermore, if the metering amount exceeds 40% of the maximum injection amount, the kneading time in the cylinder will be short and the bundle of conductive filler will be molded without being dispersed, which may cause the gate to become clogged or the mechanical strength of the molded product to deteriorate. There are drawbacks such as deterioration and uneven appearance.

[Object of the Invention] The object of the present invention was to solve the above-mentioned drawbacks, and it has excellent dispersibility of the conductive filler, can be molded with low screw back pressure, can shorten cycle time, and can produce molded products. The object of the present invention is to provide a conductive molding material that can have a uniform appearance without decreasing its external mechanical strength.

[Summary of the Invention] As a result of extensive research to achieve the above object, the present invention has found that the above object can be achieved by increasing the fluidity of the synthetic resin of the master pellet. This is what we have come to.

That is, the present invention combines a master pellet formed by integrally covering and integrating a synthetic resin layer on the surface of a bundle of conductive fillers in the form of long fibers and cutting into pellets, and a natural pellet made of a pellet-shaped synthetic resin. Conductive molding characterized in that the synthetic resin of the master pellet and the synthetic resin of the natural pellet are the same as the main ingredients, and the fluidity of the synthetic resin of the master pellet is greater than that of the synthetic resin of the natural pellet. It is the material.

The long fiber conductive filler used in the present invention includes copper,
Examples include metal fibers such as iron, stainless steel, nickel, aluminium, nickel, or alloys thereof, or inorganic fibers with a metal layer on the surface, and these can be used alone or in a mixture of two or more types. can. The thinner the I [, the better, and it is used in bundles of about 100 to 50,000 pieces.

The synthetic resin used in the present invention includes polystyrene resin,
ABS resin, polycarbonate resin, modified PPO resin,
Examples include PBT resin, which may be used alone or in combination of two or more. The important thing about the synthetic resins used is that first, the synthetic resin of the master pellet and the synthetic resin of the natural pellet must be the same.
This is to improve the dispersibility of the filler by using the same synthetic resin. Second, the fluidity of the synthetic resin in the master pellets is greater than that in the natural pellets. In order to increase the fluidity of a synthetic resin, the fluidity of the same synthetic resin can be increased by lowering the molecular weight, adding a lubricant (for example, phosphate ester), or increasing the amount of As in ABS resin. Furthermore, the same resins made by different synthetic resin manufacturers but with different fluidities may be selected, and the method is not limited, as long as the same resins have different fluidities. If the fluidity is increased, the impact strength and heat distortion temperature are lowered, so it is necessary to keep the amount of highly fluid resin used in the master pellets at 40% by weight or less. If the amount of highly fluid resin exceeds 40% by weight, the mechanical strength of the molded product will decrease, and the productivity of master pellets cannot be increased. The fluidity in the present invention is defined as L/l, which is obtained by dividing the flow length (shi) by the thickness (1) in a spiral flow test. Fluidity of synthetic resin of natural pellets L/l = (b)
Fluidity L/ of synthetic resin of master pellet
The ratio of l = (a) is (a)/(b) =
It is necessary that it is 1.1 to 1.3. This ratio is 1
．． If it is less than 1 or more than 1.3, the dispersibility will not be uniform, and the mechanical strength of the molded product will be impaired or cycle-up may occur, which is not preferable.

Next, the conductive molding material of the present invention will be further explained using the drawings. FIG. 1 is a cross-sectional view of the master pellet used in the present invention, with a synthetic resin layer 2 on the surface of the bundled long fiber filler 1.
is formed. Cut this into an appropriate size,
It is used as a master pellet. FIG. 2 is a perspective view of the master pellet 3. The master pellets produced usually have a circular cross section, but are not necessarily circular in cross section, and may be flat, and are not particularly limited in shape.

To explain the method for manufacturing master pellets using FIG.
2, the bundled long fiber filler 10 is coated 13 with a synthetic resin, and further cut 14 to form master pellets 15. Although this manufacturing process can be carried out batchwise, it is economically advantageous to carry it out continuously.

The conductive molding material of the present invention mainly consists of master pellets and natural pellets, but other components can be added as necessary. This conductive molding material is used as a housing for electronic devices that require electromagnetic shielding.

[Embodiments of the invention] Next, examples of the present invention will be described.

Examples 1-2 Copper mN300 with a diameter of 50 μm according to the composition shown in Table 1
The book is bundled and a synthetic resin layer is coated and integrated on the surface, 5 mm.
A conductive molding material was produced by mixing master pellets cut into lengths with natural pellets made of pellet-shaped synthetic resin. A molded article was molded using this molding material, and the screw back pressure, resin temperature, and cycle time at which the filler was completely dispersed were measured. The results are shown in Table 1.

Comparative Example A molding material was produced in the same manner as in the example using the composition shown in Table 1, and a molded article was molded using it. The characteristics were measured in the same manner as in the examples, and the results are shown in Table 1.

Table 1 *2: Engineering plastic N-12*
3: Engineering plastic I N-190J
*4: Manufactured by Japan Synthetic Rubber Co., Ltd. JSR-ABS-12*5
: Size of molded product 2oomm x 200mm x 3
t [Effect of the invention] As explained above, in the conductive molding material of the present invention, the conductive filler is uniformly dispersed by making the fluidity of the synthetic resin of the master pellet higher than that of the synthetic resin of the natural pellet. However, it can be molded at low temperatures and low screw back pressure, shortens cycle time, and has excellent electromagnetic shielding effects. By using this molding material, it is possible to produce an excellent molded product with uniform appearance and no deterioration in mechanical strength.

[Brief explanation of drawings]

FIG. 1 is an enlarged sectional view of a master pellet used in the present invention, FIG. 2 is an enlarged perspective view of the master pellet, and FIG. 3 is a diagram showing a method for manufacturing the master pellet. 1.10... Long fibrous filler, 2... Synthetic resin layer, 3.15... Master pellet, 11... Extruder, 12... Dice, 13... Synthetic resin coating,
14... Cutting.

Claims (1)

[Scope of Claims] 1. A master pellet formed by forming and integrating a synthetic resin layer on the surface of a bundle of conductive fillers in the form of long fibers and cutting it into pellets, and a natural pellet made of a synthetic resin in the form of pellets. is the main component, the synthetic resin of the master pellet and the synthetic resin of the natural pellet are the same, and
A conductive molding material characterized in that the fluidity of the synthetic resin of the master pellets is greater than that of the synthetic resin of the natural pellets. 2. The ratio ((a)/(b)) of the fluidity of the synthetic resin of the master pellet (a) to the fluidity of the synthetic resin of the natural pellet (b) is within the range of 1.1 to 1.3. The conductive molding material according to claim 1, characterized in that: