JPS61249713A - Manufacture of molding for electromagnetic wave shield - Google Patents

Abstract

PURPOSE:To obtain the titled molding ensuring sufficient electromagnetic shield by ring opening-polymerizing and molding the monomer containing norbornene unit simultaneously by reactive injection molding system under the existence of electric conductive filler. CONSTITUTION:The used monomer containing norbornene unit is shown by the general formula I or II. The mixture in which the monomer to be used is mixed and dispersed with electric conductive filler is divided into two parts. One of them is added with the first component of catalytic substance, and the other is added with the second component of catalytic substance, and the two obtained liquids are injected into a mold by RIM system, whereby polymerization and molding are simultaneously carried out. When injection is carried out, the two liquids are ordinarily mixed in a RIM machine and are injected into the mold. Reactive injection molding system has a characteristic in which two reactive liquids having lower viscosity rather than that of urethane RIM system may be used. The objective liquids may be injected into the mold at the pressure equal to or lower than 10kg/cm<2> and is rapidly polymerized in the mold, thereby producing the objective molding.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a novel method for producing an electromagnetic shielding material, and more specifically, to a reaction injection molding method in which a monomer containing rune units is molded in the presence of a conductive filler. The present invention relates to a method for producing an electromagnetic shielding composite consisting of a polymer and a conductive filler, characterized in that polymerization and molding are carried out simultaneously.

(Conventional technology) Conventionally, as a method of shielding electromagnetic waves emitted from electronic devices, secondary processing such as spraying metal such as zinc onto the housing or coating the housing with conductive paint has been used to cover the surface of the electronic device. Method for forming a conductive layer and molding to have conductivity by incorporating a conductive filler such as carbon black, carbon fiber, metal powder, metal flake, metal fiber, and metalized fiber when injection molding a thermoplastic resin Methods for obtaining the body are known.

However, the method of forming a conductive layer on the surface of a plastic casing requires secondary processing and has an essential drawback of being inferior in mass productivity.

Among these methods, when using conductive paint,
Since the shielding effect is affected by the coating thickness, it is necessary to ensure the uniformity of the coating when painting.1. In particular, it has the disadvantage that it is difficult to apply pottery coating to the corners. However, the metal spraying method still has disadvantages, such as a poor working environment and the need for bulky equipment, which increases costs.

On the other hand, when a composite body containing a conductive filler is injection molded to obtain a housing, the polymer does not flow uniformly through the mold, resulting in uneven distribution of the conductive filler, which reduces the shielding effect and reduces the conductivity. If the filler is fibrous, it must be cut into short pieces during injection molding, so a sufficient shielding effect cannot be obtained, and furthermore, it is expensive.

It has disadvantages such as requiring an injection molding machine and a mold. Also, a reaction injection molding method has been attempted, in which a mixture of polyol-free conductive filler (undiluted solution) and incyanate are mixed immediately before injection and injected into a mold, but this method has the disadvantage that the viscosity of the undiluted solution is too high and the piping is clogged. be. Furthermore, the filler cannot be used in large quantities, and improvements in molding machines are required.

(Problems to be Solved by the Invention and Means for Solving the Problems) The present invention aims to provide a method for producing a molded article for shielding electromagnetic waves without such drawbacks. This is achieved by simultaneously carrying out ring-opening polymerization and molding of a unit-containing monomer in the presence of a conductive filler using a reaction injection molding method.

The norbornene unit-containing monomer used in the present invention is represented by general formula (1) or (2).

(In the formula, R1 to R4 represent hydrogen or a substituent, and R1 and R
2. R3 and R4 may form a saturated or unsaturated ring) monomer.

Specifically, 2-norbornene, 5-mer-2-norgernene, 5.6-dimethyl-2-norbornene, 5-ethyl-2-nor is runene, dicyclopentadiene, methylcyclododecene, dihydrodicyclointadiene. , methyltetracyclododecene, and mixtures thereof. Furthermore, mono- and synchro-olefins such as cyclobutyne, cyclointene, cyclooctene, and cyclododecene, which can be copolymerized with 1s or more of these monomers, can be used in combination.

These monomers are converted into υ polymers by known ring-opening polymerization, and known metathesis polymerization catalysts are used as catalysts for ring-opening polymerization. A catalyst system consisting of a tungsten-containing compound such as tungsten hexachloride or tungsten oxytetrachloride and an alkyl aluminum halide such as diethylaluminum chloride or ethylaluminum dichloride disclosed in JP-A-58-127728; A transition metal compound and an organometallic compound or a Lewis acid, such as a catalyst system consisting of an alkyl aluminum chloride and an organoammonium molybdate such as tridodecyl ammonium molybdate, or a tungstate, as described above. Examples include metathesis polymerization catalysts consisting of cocatalysts such as. Also, activators such as oxygen-containing compounds such as alcohol enols can be used to speed up the polymerization rate. The amount of the catalyst containing these two components separately is usually in the range of 0.01 to 50 (r,) mm IJ mole per mole of the total monomer as molybdenum or tungsten. The amount of the alkylaluminium halide catalyst to be used is usually 200:1 to 1:1 to molybdenum or tungsten as aluminum.
The range is 10.

The reaction injection molding (referred to as RIM) method used in the present invention is a known method for producing polyurethane molded bodies from polyols and diisocyanates. The present invention is characterized by the use of a two-component reaction solution with a much lower viscosity than the urethane RIM method, and is only 10 kg/cm
It is a process in which a target material can be injected into a mold at a low pressure of rfL2 or less and rapidly polymerized within the mold to produce the desired molded product.

In the present invention, for example, a mixture of the monomers to be used and a conductive filler described later is mixed and dispersed, and the first component of the catalyst is added to one side, and the second component of the catalyst is added to the other side. The obtained two liquids are injected into a molding mold using the RIM method, and polymerization and molding are performed simultaneously. During injection, the two liquids are typically mixed in a RIM machine and injected into a mold. The temperature of the mold is usually in the range of 40 to 100°C, and the injection pressure is usually less than 10 kg/F2.

The conductive fillers used in the present invention include carbon fibers, glass fibers coated with aluminum or nickel on the surface, fibrous conductive fillers such as stainless steel fibers, copper fibers, and aluminum fibers, and fibrous conductive fillers such as copper and aluminum fibers. Examples include flakes and powder, such as woven fabrics, non-woven fabrics, and nets of the above-mentioned fibers, but fillers and flakes are preferably those whose specific gravity is close to that of the reaction liquid and which do not settle during initial curing.

When using a cloth-like or net-like material as a conductive filler, set these materials in the mold in advance,
A two-component mixed reaction solution is poured into the mold, and after the reaction hardens, it is removed from the mold to form a product cylinder. At this time, it is preferable to use a conductive net having a thread diameter of 1501 J/rrL or less and a mesh size of 15 mm or less. On the other hand, the fibrous conductive filler can be used by being mixed into one or both of the two reaction solutions.

The amount of the conductive filler etc. to be mixed is usually in the range of 5 to 70 parts by weight, preferably 20 to 40 parts by weight, per 100 parts by weight of the total reaction solution. If it is less than 5 parts by weight, the electromagnetic wave shielding effect will be weakened, and if it is more than 70 parts by weight, the strength of the molded product will be poor, which is not preferable.

Furthermore, in the present invention, plasticizers, impact-resistant agents, flame retardants, antioxidants, and the like can be mixed into the reaction liquid in order to increase the impact strength of the molded article.

(Effects of the Invention) When a conductive net is used in the molded article according to the present invention, stain magnetic shielding is performed by a thin net, which is different from applying conductive paint to the casing, so sufficient electromagnetic shielding is achieved. Unlike injection molding, products that contain fibrous conductive filler utilize a polymerization reaction, so the filler does not break and become short, and the fibrous shape is maintained as is. , good electromagnetic shielding is obtained,
Therefore, a molded product with less noise can be obtained.

Furthermore, since the low-pressure RIM method is used, it is possible to use inexpensive molding machines and simple molds such as resin molds and rubber molds, which is different from injection molding, so complex molded products can be obtained without increasing costs. I can do it.

The present invention will be explained in more detail with reference to Examples below. Note that parts and sections in the examples are based on weight unless otherwise specified.

Example 1 Desired amounts of dicyclo/tadiene were placed in two containers, and in one container, diethylaluminium chloride was adjusted to a concentration of 0.048 mol per mol of the monomer. WCt6 was similarly added to the other container to give a KO,007 molar concentration.

In addition, as a conductive net, the thread diameter is 50 μm, the mesh size is 1
A wire mesh made of 00 Metssie Monel Metal was used and set in the mold. After that, the above two reaction solutions were mixed into 1=
After mixing at a ratio of 1:1 and directly injecting into a mold heated to 50° C. and carrying out a polymerization reaction for 2 minutes, a molded article was obtained. These series of operations were performed under a dry nitrogen atmosphere. When the attenuation rate of the molded product obtained in this manner at a frequency of 10 kI (z to 1.00 MHz) was examined using a spectrum analyzer, a damping effect of 40 to 60 dB was observed.

Example 2 Aluminum-coated glass wool with an outer diameter of 40 μm was added to the same reaction solution as in Example 1, and 100 μm of the reaction solution was added.
A molded article was obtained in the same manner as in Example 1 by mixing 30 parts per part. The attenuation factor of this molded body was measured in the same manner as in Example 1, and as a result, a damping effect of 35 to 60 dB was confirmed.

Example 3 A molded article with a thickness of 3n+m was obtained in exactly the same manner as in Example 1, except that dicyclopentadiene was replaced with methyltetradodecene. As a result of measuring the damping rate of this molded body, a damping effect of 40 to 65 was confirmed.

Claims (1)

[Claims] A method for producing a molded article for shielding electromagnetic waves, characterized by simultaneously carrying out ring-opening polymerization and molding of a monomer containing norbornene units by a reaction injection molding method in the presence of a conductive filler.