JPH0568325B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a conductive molding material that has good dispersibility of conductive filler and can shorten cycle time. [Technical background of the invention and its problems] In recent years, electronic circuits have been protected from external interference radio waves,
In addition, in order to prevent unnecessary radio waves generated from the oscillation circuit from leaking to the outside, it is required that the housing of the electronic device be formed of an electromagnetic shielding material. Such electromagnetic shielding materials include:
Examples include metals and conductive synthetic resins, but while the former metals have excellent electromagnetic shielding effects,
Due to drawbacks such as being heavy, expensive, and poor processability, the latter type of conductive synthetic resin is becoming mainstream. In order to obtain a high shielding effect using the latter, it is necessary that the conductive filler in the resin be formed in the form of long fibers. The best method for this is to form a synthetic resin layer on the surface of a bundle of conductive fillers in the form of long fibers, and then cut the material into pellets to form master pellets. (Gan Sho 58-124734).
This method differs from the conventional method of kneading synthetic resin and conductive filler in that the length of the conductive filler is 2 to 2.
3 mm, but there is an advantage that a long fiber-like conductive filler with a length of 5 to 10 mm can be dispersed and molded in the resin. However, in the method of forming master pellets, the conductive fiber bundles in the master pellets cannot be dispersed unless the screw back pressure is increased to 15 to 25 kg/cm ² (gauge) during metering during injection molding. It has the disadvantage of increasing the molding cycle. Additionally, if the metering amount exceeds 40% of the maximum injection amount, the kneading time in the cylinder will be short and the conductive filler bundle will be molded without being dispersed, which may clog the gate or reduce the mechanical strength of the molded product. There are drawbacks such as deterioration and uneven appearance. [Object of the invention] The object of the present invention has been made to eliminate the above-mentioned drawbacks, and has an excellent dispersibility of the conductive filler.
The object of the present invention is to provide a conductive molding material that can be molded with low screw back pressure, shorten cycle time, and provide a uniform appearance without reducing the mechanical strength of the molded product. [Summary of the Invention] As a result of intensive 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 led to the present invention. That is, the present invention comprises a master pellet formed by integrally forming a synthetic resin layer on the surface of a bundle of conductive fillers in the form of long fibers and cutting the pellet into pellets, and a synthetic resin. The synthetic resin of the master pellet is the same as the synthetic resin of the natural pellet, and the fluidity of the synthetic resin of the master pellet is the same as that of the natural pellet. This is an electrically conductive molding material characterized by having greater fluidity than that of resin. Note that the term "natural pellets" as used in the present invention is used to mean pellets of synthetic resin that are not integrated with a conductive filler. Examples of the long fiber conductive filler used in the present invention include metal fibers such as copper, iron, stainless steel, nickel, aluminum, nickel, or alloys thereof, or inorganic fibers having a metal layer on the surface. These can be used alone or in a mixture of two or more. The thinner the fibers, the better, and the finer the fibers, the better.
Used as a bundle of about 50,000 pieces. Examples of the synthetic resin used in the present invention include polystyrene resin, ABS resin, polycarbonate resin, modified PPO resin, PBT resin, etc.
They may be used alone or in a mixture of two or more. The important thing about the synthetic resins used is that the synthetic resin of the master pellets and the synthetic resin of the natural pellets 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 AS in the case of 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. Since increasing the fluidity lowers the impact strength and heat distortion temperature, it is necessary to keep the amount of highly fluid resin used in the master pellets at 40% by weight or less. Highly fluid resin content is 40% by weight
If it exceeds this, the mechanical strength of the molded product will decrease, and the productivity of master pellets cannot be improved. Fluidity in the present invention is calculated by dividing the flow length L by the thickness t in a spiral flow test.
Use t as a guide. The ratio of the fluidity L/t=a of the synthetic resin of the master pellet to the fluidity L/t=b of the synthetic resin of the natural pellets is a/b=1.1
~1.3 is required. If this ratio is less than 1.1 or more than 1.3, the dispersibility will not be uniform, and the mechanical strength of the molded product will be impaired, and cycle-up will be increased, which is undesirable. Next, the conductive molding material of the present invention will be further explained using the drawings. FIG. 1 is a sectional view of a master pellet used in the present invention, in which a synthetic resin layer 2 is formed on the surface of a bundle of long fiber fillers 1. This is cut into appropriate sizes and used as master pellets. FIG. 2 is a perspective view of the master pellet 3. The master pellets produced usually have a circular cross section, but they do not necessarily have to be circular.
It may be flat and is not particularly limited in shape. To explain the method for manufacturing master pellets using FIG. 3, the bundled long fibrous filler 10 is passed through a die 12 of an extruder 11, and the bundled long fibrous filler 10 is coated with a synthetic resin 13. Then, the pellets are further cut 14 to form master pellets 15. Although this manufacturing process can be carried out in batches, 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 housings for electronic devices that require electromagnetic shielding. [Embodiments of the Invention] Next, embodiments of the present invention will be described. Examples 1-2 Copper fibers with a diameter of 50 μm according to the composition shown in Table 1
A conductive molding material was produced by bundling 300 pellets and integrally covering the surface with a synthetic resin layer, and mixing master pellets cut into 5 mm lengths with natural pellets made of pellet-shaped synthetic resin. A molded article was molded using this molding material, and the screw back pressure at which the filler was completely dispersed, resin temperature, and cycle time were measured. The results are shown in Table 1. Comparative Example A molding material was produced in the same manner as in the example with 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】

[Table] [Effects of the Invention] As explained above, the conductive molding material of the present invention has improved conductivity by making the fluidity of the synthetic resin of the master pellets higher than that of the synthetic resin of the natural pellets. The filler is uniformly dispersed, it can be molded at low temperatures and low screw back pressure, it can shorten cycle time, and it has an excellent electromagnetic shielding effect. 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 the drawing]

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. DESCRIPTION OF SYMBOLS 1, 10... Long fibrous filler, 2... Synthetic resin layer, 3, 15... Master pellet, 11... Extruder, 12... Dice, 13... Synthetic resin coating,
14...Disconnection.

Claims (1)

[Scope of Claims] 1. Consisting of a master pellet formed by integrally forming a synthetic resin layer on the surface of a bundle of conductive fillers in the form of long fibers and cutting the pellet into pellets, and a synthetic resin,
The above-mentioned master pellets and natural pellets mixed in pellet form are the main components, and the synthetic resin of the master pellets and the synthetic resin of the natural pellets are the same, and the fluidity of the synthetic resin of the master pellets is the same. A conductive molding material characterized by having greater fluidity than natural pellet synthetic resin. 2. Claim 1, characterized in that the ratio (a/b) of the fluidity a of the synthetic resin of the master pellets to the fluidity b of the synthetic resin of the natural pellets is within the range of 1.1 to 1.3. Conductive molding material as described in section.