JPH0225772B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a thermoplastic resin sheet (hereinafter simply referred to as a resin sheet) containing a low melting point metal layer.

With the rapid spread of digital electronic devices in recent years and the shift to plastic housings, noise generated by the operation of digital electronic devices or for other reasons can become a signal to other digital electronic devices, causing malfunctions. Electromagnetic interference has become a problem. For this reason, electromagnetic shielding materials for preventing noise leakage from digital electronic devices and protecting the circuits of digital electronic devices from noise are attracting attention, and as a method for manufacturing such materials, technology for making conductive plastics is attracting attention.

The resin sheet obtained by the present invention has a low melting point metal layer in its center layer, so it exhibits a high degree of conductivity, and can be used as a technology for imparting conductivity to plastic materials, including materials for electronic devices such as electromagnetic shielding materials. It can be applied in a wide range of fields.

[Conventional technology]

To date, the manufacturing technologies for plastic-based electromagnetic shielding materials that have been proposed or implemented include zinc spraying, conductive paint, metal vapor deposition,
surface treatment methods such as chemical plating, and fine fibers, particles, etc. of conductive materials such as plastics and metals.
There is a method of making a composite material by mixing it with flakes or the like.

Furthermore, conductive polymers are being developed in which the plastic itself exhibits conductivity due to its special chemical structure.

However, some problems remain in all methods, including those currently in practical use.

[Problem that the invention seeks to solve]

Generally, electromagnetic shielding materials are required to stably exhibit a high degree of conductivity.

Zinc thermal spraying has traditionally been the most common conductivity imparting technology for plastics, as it provides a good shielding effect at a relatively low cost. The deterioration of performance over time caused by zinc spraying has caused problems such as circuit damage in electronic equipment, and above all, the work environment has deteriorated significantly during zinc spraying, so it is desirable to use other methods as an alternative. ing.
The conductive paint is applied by spray painting in the same way as before.
Although electrical conductivity can be imparted to plastic molded objects, it is important to ensure that this spray painting is carried out smoothly and that the thin film of paint formed on the plastic surface exhibits a high degree of electrical conductivity so that performance does not deteriorate over time. In order to do this, a paint containing nickel, which is resistant to oxidation, is dispersed in a binder with a high additive rate of precious metals, or very fine fillers such as copper or aluminum that have undergone special oxidation prevention treatment.
Since the technology for supplying metal fillers with such performance at low cost and in large quantities has not yet been established, the conductive paint itself has not yet come into widespread use.

Metal evaporation requires expensive equipment and many processes, making it unsuitable for mass production.The situation with chemical plating is similar to that of metal evaporation, and the problem remains that the resins that can be used are limited. has been done.

All techniques for imparting conductivity to plastic molded bodies through surface treatment involve forming a conductive thin layer on the plastic surface through secondary processing. Composite materials obtained by mixing conductive materials have the conductive materials dispersed in the plastic, so compared to cases where the conductive layer appears on the surface of the plastic, there is less chance of performance degradation due to destruction or oxidation of the conductive layer. There is less worry about negative effects on electronic devices due to deterioration or peeling of the conductive layer.

However, in the case of composite materials, the conductive material is dispersed throughout the plastic, so in order to impart a high degree of conductivity, it is necessary to add a large amount of conductive material compared to when surface treatment is used. .

However, when conductive fine fibers, fillers, etc. are added to plasticized plastic, the apparent viscosity of the plastic composition increases rapidly as the amount added increases. This not only makes it difficult to uniformly disperse the conductive material into the plastic during processes such as kneading, but also increases the shear force acting on the conductive material when kneading is strengthened to achieve uniform dispersion. , the destruction of the conductive material becomes noticeable, and the aspect ratio of fine metal fibers and the like decreases significantly, so that in many cases, the expected effect of imparting conductivity cannot be obtained.

In addition, fine metal fibers and carbon fibers, which have a large effect on imparting conductivity, have low productivity and become expensive materials, so composite materials containing these conductive materials are also used for general purpose use, similar to conductive paints. It is quite expensive compared to plastic.

Furthermore, regarding conductive polymers, in which plastic itself exhibits electrical conductivity due to its special chemical structure, research is currently underway to find a material that exhibits high enough electrical conductivity to be used in electromagnetic shielding materials and is affordable enough for general use. It is.

The present invention provides a manufacturing method that can supply a plastic material exhibiting high conductivity at a low cost due to the special nature of the method.

[Means to solve the problem]

In the present invention, a slit for injecting a molten low melting point metal or alloy (hereinafter simply referred to as low melting point metal) is provided in front of the die slit of an extrusion die, and the thermoplastic material is heated to a temperature higher than the melting point of the low melting point metal to be used. While injecting the resin into the die, molten low melting point metal was continuously injected from the slit into the thermoplastic resin flux, and extruded while forming a molten low melting point metal layer in the thermoplastic resin flux. This is a method for manufacturing a resin sheet obtained by cooling the thermoplastic resin while taking it away to form a low melting point metal layer in the thermoplastic resin.

The thermoplastic resin used in the present invention may be any resin that can be used for ordinary extrusion molding and thermoforming.
There are no particular restrictions. Examples of such thermoplastic resins include polyolefins, polystyrenes, polyvinyl chloride, polyacrylic esters, polymethacrylic esters, polyacrylonitrile, polybutadiene, polyamides, polyesters, or modified products thereof,
Examples include copolymers and mixtures. These thermoplastic resins can be selected depending on their moldability and the physical properties of the molded product. Furthermore, in order to improve the affinity between the thermoplastic resin and the low melting point metal, an ionomer resin can be blended. Blending the ionomer resin in an amount of 5 parts by weight or more provides a great effect. Further, additive auxiliaries such as antioxidants, stabilizers, plasticizers, and lubricants may be added to these resin compositions as necessary.

The low melting point metal used in the present invention is one having a melting point below the temperature at which thermoplastic resin extrusion molding or heat molding is possible, that is, below 400°C, such as tin,
Examples include single substances or alloys of lead, zinc, bismuth, cadmium, antimony, etc.

[Effect]

The method for manufacturing a resin sheet according to the present invention will be further explained with reference to FIGS. 1 and 2.

A thermoplastic resin heated to a temperature equal to or higher than the melting point of the low melting point metal is injected into the die 1 using an extruder. At this time, the thermoplastic resin is injected in multiple fluxes 2 from multiple injection ports as in multilayer extrusion molding, as shown in Figure 1, or the thermoplastic resin is injected in an extrusion die as shown in Figure 2. After the resin flux 2 is once divided into a plurality of parts, in both the cases of FIGS. All you have to do is make them merge again. At the point where the fluxes of the thermoplastic resin merge, the molten low melting point metal 5 is continuously injected into the thermoplastic resin 6 through the molten low melting point metal injection slit 3 using a heat-resistant pump.

Due to the high viscosity of plasticized thermoplastics,
Molten low melting point metal 5 injected into thermoplastic resin 6
is supported in a thermoplastic resin and forms a molten low melting point metal layer without contacting the inner surface of the die.
By taking this heated thermoplastic resin composition and cooling it, the molten low melting point metal is
By cooling and solidifying, a resin sheet 7 containing a low melting point metal layer in a thermoplastic resin continuum is obtained.

〔Example〕

A resin composition having the following composition ABS resin (JSR ABS38) 95 parts by weight Ionomer resin (Himilan 1652) 5 parts by weight Lead stearate 0.1 part by weight was heated to a resin temperature of 200°C using a 40 mmφ extruder to plasticize it, and then Extrusion die kept at ℃ (Dice slit 0.4cm x 20
cm x 3 cm) while pumping a lead-tin alloy (melting point: 185°C) heated to 200°C from a molten metal injection device with a 0.1cm x 18cm slit in a stainless steel circular tube installed inside a die. After continuously injecting into the resin flux in the die and extruding it together with the resin, the resin sheet is taken off at 10 m/min while being cooled by two rolls to form a resin sheet containing a lead-tin alloy layer. Created.

The resin sheet after collection was a continuous sheet approximately 22 cm wide and 3 mm thick, and its center layer contained a nearly continuous layer of lead-tin alloy with a thickness of 0.7 mm.

A plate-shaped sample of 10 cm x 10 cm was cut from an arbitrary location on this continuous sheet, and the specific resistance of this sample was measured and was found to be 10 ^-1 Ω-cm or less.

〔Effect of the invention〕

The resin sheet according to the present invention can be manufactured without using special conductive materials such as metal fine fibers, which were conventionally necessary to impart conductivity to resin compositions.
It is possible to directly mold ordinary thermoplastic resins and low-melting metals. Therefore, the present invention can eliminate the steps of manufacturing conductive materials such as metal fine fibers and particles or carbon fibers, and kneading these conductive materials with thermoplastic resin, resulting in higher production efficiency compared to conventional methods. It can be said that this technology can provide a high-quality and economically practical conductive resin material.

[Brief explanation of drawings]

FIG. 1 shows an example of a resin sheet extrusion molding die used in the present invention, and is a schematic cross-sectional view of a structure in which a multilayer extrusion molding die is provided with a slit for injecting molten metal. FIG. 2 shows an extrusion molding die used in an embodiment of the present invention, and is a schematic cross-sectional view of a structure in which a molten metal injection device having a slit in a pipe is installed in the extrusion molding die. 1... Dice, 2... Flux of thermoplastic resin, 3
...Slit for injection of low melting point alloy, 4...Dice slit, 5...Low melting point metal, 6...Thermoplastic resin, 7...Resin sheet containing a low melting point metal layer.

Claims (1)

[Claims] 1. Continuously injecting a molten low melting point metal or alloy into a flux of thermoplastic resin heated to a temperature higher than the melting point of the metal or alloy through a molten metal or alloy injection slit provided in a die. A method for producing a thermoplastic resin sheet including a metal layer, characterized in that the thermoplastic resin is extruded.