JPS63160814A - Method for molding resin containing metal fibers - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention uses a styrene-based thermoplastic resin containing metal fibers to form housings for electronic and electrical equipment that have electromagnetic shielding performance by injection molding. The present invention provides a means for obtaining a molded product with extremely excellent surface quality.

(Prior art) Styrene-based thermoplastic resins are often used for the housings of electronic and electrical equipment due to their various advantages such as appearance, design, light weight, productivity, and low price. Because it is transparent, many proposals have been made to add conductivity to it in order to prevent electromagnetic interference. Especially regarding compositions containing conductive materials in resin.

For example, JP-A-58-150203, JP-A-58-21
Various proposals have been made, such as Japanese Patent No. 5313. These are mainly proposed as compositions for obtaining molded products by injection molding, but when actually injection molding is performed,
For example, compositions containing metal fibers have defects such as silver streaks and protruding fibers on the surface of the molded product, and the current situation is that they cannot be put to practical use as they are.

However, the above-mentioned prior art does not propose any means to improve these problems.

In addition, in general, in injection molding, in order to obtain good surface quality, it is necessary to quickly fill the molten resin into the mold without causing a drop in temperature, and to cool it uniformly, and to control the pressure waveform inside the mold. However, it is difficult to obtain good surface quality in the case of styrenic thermoplastic resin containing metal fibers using only these means.

(Problems to be Solved by the Invention) As mentioned above, when a styrene-based thermoplastic resin composition containing metal fibers is molded by injection molding, problems occur due to the inclusion of fibers on the surface. There are silver streaks and protruding fibers, which seriously spoil the appearance. The present invention
The object of the present invention is to provide a molding method that can improve this problem and obtain injection molded products with excellent surface quality.

(Means for Solving the Problems) The present inventors conducted various injection molding experiments regarding injection molding conditions in order to reduce narrow surface defects in injection molded deaf products made of styrene thermoplastic resin containing these metal fibers. As a result,
It has been found that the resin temperature, mold temperature, and injection speed, that is, the filling time required to fill the mold with resin, have a close relationship with surface quality.

In other words, it is generally said that the faster the injection speed, the better in the injection molding process, but in the case of styrenic thermoplastic resin containing metal fibers, the lower the mold temperature, the faster the injection speed becomes. Although surface defects cannot be eliminated even if the filling time is shortened, it was found that good surface quality could be obtained by setting the mold temperature higher (than the temperature normally used). . At the same time, the resin temperature is also important; even if the resin temperature does not exceed the normal molding range, if the temperature difference between the resin temperature and the mold temperature is large, good surface quality can be obtained with the same filling time. Ta.

From these results, the present inventors discovered that a molded product with a good surface can be obtained by selecting the resin temperature, mold temperature, and filling time as molding conditions that satisfy the range defined by the following formula. Ta.

Here, T: resin temperature ('c) and filling time (sec)
) Tm: mold temperature (°C) k, To: constants. k
and T. is a constant determined by the physical properties of the resin to be subjected to injection molding, and is the case for a thermoplastic composite resin containing metal fibers that is used as an IJ sock using a styrene-based thermoplastic resin.

When applying this method, it is important to note that when the content of metal fibers in the thermoplastic composite resin increases, the fluidity of the resin deteriorates, making high-speed filling difficult; Since the thermal properties of thermoplastic resins containing fibers differ greatly, the content of metal fibers is 5 Va.
It is desirable that it be t% or less.

In this formula, the resin temperature refers to the temperature just before it flows into the mold, but if it is not significantly different from the cylinder temperature of an injection molding machine, it can be regarded as the cylinder temperature in practical terms. Also, the filling time is
The time required for the resin to fill the mold is 17, and does not include process time such as holding pressure.

The thermoplastic resin compound used in this invention contains metal fibers, but when compared with this as an electromagnetic wave resistance material, those containing fibrous metals are different from those containing conductive materials with other properties and forms. It is particularly limited to resin compounds containing metal fibers because it exhibits excellent effects with a small amount added compared to .

Furthermore, surface defects such as protruding wires and fibers that are seen when molding this into a steel part by injection molding are characteristic of such resin compounds containing metal fibers. This method was developed to address such surface defects. However, in the case of compounds with a matrix of so-called crystalline thermoplastic resins such as polyolefins and polyamides, a surface of fairly high quality can be obtained even under commonly used injection molding conditions.
It is not necessary to limit the injection molding conditions as described above. When using IJ socks with so-called non-crystalline styrenic thermoplastic resins such as polystyrene and ABS (acrylonitrile-butadiene-styrene resin), molded products with good surface quality can only be obtained by limiting the injection molding conditions. be able to. The styrenic resin, which is an amorphous thermoplastic resin serving as a matrix, is a polymer of an aromatic monovinyl compound, a copolymer containing this, or a mixture containing one or more of these, and is a copolymer or a mixture. In the case of 20 wt% or more of aromatic monovinyl compound,
Preferably, it contains 60 wt% or more. Aromatic monovinyl compounds include styrene, α-methylstyrene, nozoramethylstyrene, parachlorostyrene, etc. Copolymers or mixtures include AS, HI
, MS, ABS.

MBS, styrene-maleic anhydride resin, PC-P
S.

A mixture of PMMA-ABS, etc.

In addition, stabilizers, plasticizers, i-fuel agents, mold release agents, dyes and
There is no problem with adding additives such as overhead.

The gold fA (R fiber) contained in these matrix resins is
Considering the Shahei effect of electromagnetic waves, weather resistance, and other characteristics, it is most desirable to use austenitic stainless steel fibers, but other ferritic or martensitic stainless steel fibers, steel, copper, aluminum, nickel, brass, Fibers of metals such as metals and their alloys may be used. There are no particular restrictions on the shape or the amount added, but for example, the diameter is 2 to 50 mm.
μm range, and the two-fiber length before injection molding is 3 to 3 μm.
One with a rotation speed of about 20 rm is suitable. The amount added is adjusted according to the required electromagnetic wave strength.
Generally 5 VoL% or less, especially 0.5 VoL%
Approximately t% to 3Vot% is suitable.

The method of combining the metal fiber and the amorphous styrene thermoplastic resin is not specified in the present invention, and any commonly used method may be used. For example, gold pA can be prepared by a solvent method using a suitable resin.
The fiber bundles may be bundled, cut as appropriate, and tri-blended with natural pellets, or the blended composition may be melt-kneaded using an extruder, mixed wire roll, or other device to form pellets. Alternatively, coat the metal fiber bundle with a suitable resin, cut it and cut it as necessary.

A tri-blended composition with RAL pellets may be used, and the composition may be melt-kneaded to form pellets again.

In these cases, the resin used for the initial focusing or coating and the resin mixed later need not necessarily be of the same type.

In carrying out the present invention, the injection molding machine used is:
Any tool may be used as long as it can achieve the mold temperature and filling time set in the present invention, but in the present invention, it is desirable that the filling time is as short as possible.
It is necessary to use a molding machine that is as fast as possible (high injection rate). Since the issue here is the filling time, the required injection rate varies depending on the size of the part to be molded, but generally speaking, an ordinary injection molding machine is equipped with an aki emulator to increase the speed. Alternatively, a so-called high-speed injection molding machine, which is equipped with a high-capacity injection mechanism in advance, can be used. At this time, it is advantageous to provide a sensor inside the cylinder or inside the cylinder to monitor the molding situation, or to perform injection control using preset or feedback, for example, the pressure inside the mold, in order to stabilize the molding. In addition, it is necessary to set the mold as high as possible without causing other adverse effects, but it is also necessary to take other measures such as reducing the pressure or creating a vacuum inside Venus, and creating a structure that allows air to escape easily. Rubbing is effective in ensuring stable quality.

Examples of the present invention are shown below.

The present invention is not limited to the following examples unless it exceeds the gist thereof.

(Example) Two types of styrene-based thermoplastic electromagnetic shielding materials (A and B) shown in Table 1 were used, and three types of high-speed injection molding machines shown in Table 2 were used under various molding conditions shown in Table 3. A molding process was performed. In both compositions A and B, 5US304 stainless steel fiber bundles (diameter 15 μm) were coated with resin, cut into 6 cm lengths, and triblended with natural pellets to obtain a fiber content of 10% by weight ( 1.5 Vot%).

Table 1 Test Resin Next, the surface unevenness and volume resistivity of the obtained molded product were measured. The results are shown in Table 3.

For comparison, three types of molding machines and one type of general-purpose injection molding machine were used, and the same mold used for high-speed injection was used to produce molded products under molding conditions outside the conditions of the present invention. The surface roughness, volume resistivity, and electromagnetic shielding performance were measured. The results are also shown in Table 3.
It was shown to.

In Table 3, the surface evaluation was performed by measuring the maximum roughness Rmax using a surface roughness meter.

Figure 1 shows the limits of the filling time of the examples and comparative examples in Table 3.
The results summarized using the calculation formula of the present invention are shown.

Regarding each example and comparative example, if the actual value of the filling time is larger than the upper limit of the filling time determined by the molding conditions (the area above the straight line l in the figure), the surface condition is not good. It can be seen that when , is small (the area below the straight line l in the figure), the surface condition becomes poor.

In addition, the electromagnetic shielding performance for all examples and comparative examples was 50 d for an electric field of 100 MHz.
Since the value was B or more or the volume resistivity was 100.100 or less, all were judged to be good (○). As is clear from Table 3, parts molded according to the conditions of the present invention have sufficient electromagnetic shielding properties and at the same time have excellent surface quality, and can be put to practical use as is, and are easy to use. It is possible to easily obtain a beautiful appearance with a simple coating.

(Effects of the Invention) By injection molding an electromagnetic shielding material containing metal fibers with a styrene thermoplastic resin matrix under the injection molding conditions determined by the present invention, a resin with excellent surface quality can be obtained. Can mold parts.

[Brief explanation of the drawing]

FIG. 1 is a drawing showing the relationship between the actually measured filling time, the value determined by the calculation formula of the present invention, and the surface quality. FJI (cusp) at the time of filling (point 1 point) Procedural amendment document Showa February 2010 J Otsu 0

Claims (2)

[Claims] (1) When injection molding styrene-based resin containing metal fibers, when the mold temperature is T_m (°C) and the molten resin temperature is T_r (°C), the time t for filling the resin into the mold is
A method for molding resin containing metal fibers, characterized by injection molding under conditions such that (sec) is ▲There are mathematical formulas, chemical formulas, tables, etc.▼. (2) Styrene resin is polystyrene, styrene acrylonitrile copolymer, styrene-methyl methacrylate copolymer, rubber reinforced polystyrene, A
The method for molding a resin containing metal fibers according to claim 1, wherein the resin is one or more thermoplastic styrenic resins selected from the group consisting of BS resin and MBS resin.