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(11) | EP 0 227 000 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Process for producing shielded wire |
| (57) A process for producing a shielded wire for use in electric/electronic equipment
comprises the steps of shielding a single stranded insulated wire prepared by covering
a stranded conductor with insulating material or a combination of such wires with
metal wires or a metal foil, coating the wire with insulating paint, and hardening
said paint to form an insulating film. |
BACKGROUND OF THE INVENTION
[0001] This invention relates to a process for producing a shelded wire for use in wiring of electric/electronic equipment, more particularly, to a process for producing a shelded wire by covering a stranded insulated wire with shield metal wires or a metal foil, coating the wires or foil with insulating paint and hardening the paint for sheathing and insulating purposes.
[0002] A shielded wire for use in wiring of electric/electronic equipment comprises a single stranded wire or a combination of plural stranded wires with weft-wound or knitted metal wires or a metal foil thereon and sheathed with an insulator. That is, the shielded wire is formed with the combination of a core conductor, an insulator for the core, shield metal wires or foil and a sheath insulator.
[0003] With the recent inclination to the miniaturization and improvement of performance of electric/electronic equipment, it has strongly been required that shielded wires for practical use should be.as thin and lightweight as possible. The present inventors have invented, in the process of manufacturing stranded insulated wires, a method for obtaining a thin-film stranded insulated wire through the formation of an insulating film by, instead of extrusion molding, applying and hardening insulating paint. Use of the thin-film stranded insulated wire, obtained by applying and hardening insulating point, as a core for a shielded wire has naturally made it possible to provide a thin lightweight shielded wire.
[0004] The present inventors has further made efforts to develop a shielded wire which is thinner and lighter in weight. One of the methods thus developed comprises applying and hardening insulating paint, in place of conventional extrusion molding for forming a sheath insulator. The shielded wire thus obtained has a thinner insulator and satisfies the demand for thin, lightweight wires. However, when solvent type insulating paint is employed, it is essential to heat the paint to evaporate the solvent after it is applied or to cause reaction to make the resin of a high polymer. During the process of heating the paint, the air confined around the shield metal wire or foil is expanded, whereby foam is often produced in the film of the paint.
SUMMARY OF THE INVENTION
[0005] An object of the present invention is to provide a process for producing a shielded wire having a sheath insulating film free from roughness and foam.
[0007] A feature of the process for producing a shielded wire for use in electric/electronic equipment comprises the steps of shielding a single stranded insulated wire or the combination of such wires prepared by covering a stranded conductor with insulating material with metal wires or a metal foil, coating the wires with non-solvent type paint being hardened by ultraviolet ray or electron beam irradiation, and hardening the paint by the ultraviolet ray or electron beam irradiation, thereby preventing thp generation of foam in thn film layer. The feature also includes the step of removing air bubbles left in the layer.
[0008] Another feature of the process for producing a shielded wire comprises the steps of providing shield metal wires or the like and, in forming at least the lowermost film layer, applying and hardening thermohardening insulating paint by using a felt or roller to prevent foam generation in the layer.
[0009] Still another feature of the process for producing a shielded wire comprises the steps of providing shield metal wires or the like, applying a solvent prior to applying insulating paint, applying and hardening thermohardening paint to prevent foam generation in the film layer.
[0010] A further feature of the process for producing a shielded wire comprises the steps of providing shield metal wires or the like and, when at least the lowermost film layer is formed, applying and hardening thermohardening insulating paint whose viscosity is 300 cps or less at 30°C to prevent foam generation in the film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011]
Fig. 1 is a sectional view showing a shielded wire according to a process of the present invention,
Fig. 2 is a sectional view of a shielded wire which includes air bubbles in a shieth isulating film,
Fig. 3 is a sectional view showing a paint tank provided with a reduced chamber according to the present invention, and
Figs. 4 and 5 are sectional views showing a shielded wire obtained by a precess of the present invention, respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The present invention comprising the above features will subsequently be described in detail.
[0013] An attempt was made to produce a shielded wire for use in electric/electronic equipment in accordance with a process comprising the steps of winding shield metal wires or a metal foil on a single stranded insulated wire or a comination of plural wires, applying non-solvent type paint being hardened by ultraviolet ray or electron beam irradiation to the metal wires or metal foil at the room temperature, hardening the paint by irradiation of ultraviolet ray or electron beam, confining the air present in the gap 5 shown in Fig. 1, and further applying and hardening the same or different kind of insulating paint to obtain desired film thickness and the shielded insulated wire. According to the above process, foaming in the film due to the expansion of the air within the shielded wire did not occur and a shielded wire available for practical use was obtained.
[0014] The above manufacturing process includes the following features which will subsequently be described in detail.
[0015] A feature of the above process comprises the steps of, when paint being hardened by ultraviolet ray or electron beam irradiation is applied onto shield metal and hardened more than once, applying the paint thereto, passing the wire through a heating oven to remove small air bubbles present in the film before being hardened, and hardening the paint by ultraviolet ray or electron beam irradiation. When the paint being hardened by irradiation is applied to the shield metal wound on the stranded insulated wire by using dies or a felt, small air bubbles may still be present in the paint film even though it it squeezed by the dies or the like. If the ultraviolet ray or electron beam is irradiated in the above state, a problem arises that the film is hardened with the samll air bubbles contained. The small air bubbles thus contained are undesirable because they increase the electric charactaristic variation. Thus the problem should be solved. Fig. 2 is a transverse sectional view of a shielded insulated wire containing air bubbles. When the irradiation-hardened paint is supplied to a tank in continouse operation, air bubbles are gradually mixed into the paint.. The air bubble is produced since the air at the surface of an object being coated is surrounded by the paint while the object being coated is led to the paint. In the case of conventional thermohardening paint, since heat is added in an oven after the coating, air bubbles rises to surface and vanish due to the expansion of the air bubbles contained in the film before being hardened and the decrease in paint viscosity.
[0016] In the case of the irradiation-hardened paint, however, it is hardened instantly after being applied so that there is no time during which air bubbles rise to the surface. The present inventors'have therefore devised a method of reducing paint viscosity after an object to be painted is coated with irradiation-hardened paint, positively heating the object to the extent that air bubbles are caused to rise to surface and then hardening the paint by irradiation. The method was successful in obtaining a shielded insulated wire whose film contains no foam. Heating for the purpose of reducing paint viscosity and raising the air bubbles to surface must be varied with manufacturing conditions, e.g., the viscosity-temperature characteristics of the paint, film thickness, linear velocity of the object and the like. However, in general, the satisfactory temperatures inside the oven of about 1 m - 2 m long are within the range of 100°C - 250°C. The temperatures of the shielded insulated wire itself should preferably be within the range of 60°C ~ 150°C. In case the temperature is too high, the air confined in the gap between the shield metal wires or in the foil may be expanded and forced into the film. The number of times the irradiation-hardened paint is applied should be varied with the desired film thickness and, provided the thickness of the paint applied first is within the range of about 10 - 20 um, air bubbles will vanish even though they are contained therein while the paint viscosity is decreased by heating.
[0017] Another feature of the above process comprises the steps of installing a vacuum chamber under an irradiation-hardened paint tank into which an object being coated is led, removing the air on the periphery of the object by passing the object through the chamber so that air bubbles are prevented from being introduced in the irradiation-hardened paint in the tank, and coating the object with the irradiation-hardened paint free from the air bubbles by leading the object into the irradiation-hardened paint tank.
[0018] No heating oven is necessary after the painting process according to the present invention. To prevent air bubbles from penetrating into the liquid tank, the present inventors installed a chamber where the pressure is reducible, i.e., the vacuum chamber beneath the liquid tank to remove air accompanied with the object being coated and introduced the object without air on its surface into the liquid tank. With respect to the extent to which the pressure in the vacuum chamber is reduced, if the pressure is lower than one atmospheric pressure, the number of air bubbles allowed to enter the paint tank decreases to the extent. However, by reducing the pressure to 150 mmHg or less, the film is caused to contain almost nearly no air bubbles and a shielded insulated wire having stable electric characteristics becomes available. In case the reduced pressure is greater than 150 mmHg, the film may include small air bubbles. Elastic packing such as rubber must be held between the paint tank and the vacuum chamber because the paint tends to be readily dragged from the upper paint tank into the vacuum chamber as the pressure is further reduces, whereas a hole for passing the object being coated must be as small as possible to prevent the packing from deforming because of the suction froce generated by the pressure reduotion.'
Moreover, a counter measure should be taken to prevent air from penetrating into the vacuum chamber through a hole in the bottom thereof for passing the object being coated as the pressure is reduced. For example, elastic material such as rubber should be installed on the bottom of the vacuum chamber to minimize the size of the hole by making use of the elasticity thereof and to prevent the air from penetrating therethrough. The degree of pressure reduction can also be maintained effectively by attaching a reinforcing plate to the bottom of the elastic material to increase the resistance against the suction force while the pressure is reduced. A hole made in the reinforcing plate should naturally be as small as possible.
[0019] The longer the time during which the stranded conductor is passed through the vacuum chamber, the greater the amount of air removed from that carried by the stranded conductor becomes. From the results obtained from the experiments conducted by the present inventors, the vacuum chamber of 5 to 10 cm long has been proved satisfactory.
[0020] Fig. 3 shows a paint tank 7 equipped with a vacuum chamber 11 in the portion where a stranded conductor is introduced into the former, wherein an object being coated 10 is passed through the vacuum chamber 11 before being introduced into the paint tank 7. A vacuum pump 12 is such that it is capable of reduce the pressure to 150 mmHg or less. Numerals 13 and 14 show a packing and a reinforcing plate, respectively.
The installation of the vacuum chamber has contributed to greately reducing the amount of air bubbles contained in the paint tank and also preventing them from being contained in the film coated and hardened.
[0021] As the insulating paint that can be hardened by ultraviolet ray or electron beam irradiation, use can be made of polyester acrylate, polyol acrylate, urethane acrylate, epoxy acrylate, silicone acrylate, polybutadien acrylate, melamine acrylate, polyene/polythiol, unsaturated polyester, etc. in the form of a single substance or their.mixture.
[0022] A photosensitizer must be added to the above compound to be hardened by ultraviolet ray irradiation. As the photosensitizer, benzoin alkyl ethers such as benzoin ethyl ether, benzoin-n-butyle ether, acetophenone derivatives such as diethoxyacetophenone, amyl oxyme esters and many known photosensitizers are usable.
[0023] The present inventors have continued examination and established a method of preventing air bubbles from being produced because of the air among shield metal wires even if solvent type heat-hardened insulated paint is used. An description will subsequently be given of this case.
[0024] Shield insulating metal wires or a metal foil is wound on a stranded insulated wire and coated with solvent type insulating paint, which is then hardened to produce a shielded insulated wire. When dies are used to apply the insulating paint, the die having a diameter larger than the outer diameter of an object being coated must be used. In this case, the paint it thickly applied between the stranded wires. As a result, the air between the shield metals iz caused to readily produce air bubbles because of the expansion of the air and the vaporization of the solvent contained in the insulating paint. Actually, it may become impossible to continue production because of troubles resulting from disconnection or quality deterioration. If the die whose diameter is almost equal to the outer diameter of the object being coated is used to apply the insulating paint further thinly, it will quickly wear and the uneven frictional force between the object and the die due to variations in the outer diameter of the former makes uniform coating impossible.
[0025] According to the present invention, when at least the lowermost insulating film is formed during the process of manufacturing shielded wires, solvent type heat-hardening insulating paint is thinly applied using a felt or roller and then heat-hardened to prevent the generation of air bubbles.
[0026] The heat-hardening insulating paint thus applied is urged to fill the gap between the shield metal wires or in the metal foil. If the quantity of paint applied between the shield metal wires by means of the felt or roller is so arranged as to conform to AC≦ 1/2AB (see Fig. 4), the expanded air confined between the shield metal wires is caused to readily escape from the structure. Under this condition, it was confirmed through experiments that no air bubbles were generated in the film.
[0027] When the insulating paint is applied to portions AB shown in Fig. 4, it should preferably be applied 2 ~ 5 times and then applied further using dies depending on the desired film thickness. After a film of about 2 ~ 4 µm thick is formed on the outer surface of the object being coated, the total number of times the paint is coated and heated can be minimized if the dies are effectively used for the coating. This process is of high practical value. If it is attempted to obtain a film of about 20 ~ 25 µm thick by employing only the felt or roller coating method, the number of times that the paint must be applied will become over 10 ~ 15. If the paint is applied thickly at one time in accordance with the felt or roller method, the film thickness in the longitudianl direction tends to become uneven and therefore it must be applied thinly. A number of times the paint must be applied means that the number of pieces allowed to be hooked in the oven is limited, so that a serious problem arises that productivity in actual production is lowered. After a thin film free from air bubbles is formed on the metal wires by means of a felt or roller, no air bubbles ara generated even though dies are used to apply the paint, so that the manufacturing process is superior'in productivity.
[0028] The material of the felt according to the present invention may be any one of wool, polyester, Teflon, polypropylene, polyvinylidene chloride, rayon, etc. whose density should preferably be about 0.20 ~ 0.60 g/cm3. With respect to the shape and material quality of the die, use can be made of what is capable of applying insulating paint for enamel wires in general. In other words, super-hard metal, super-hard diamond, sapphire, artificial diamond, natural diamond, etc. with a hole of a suitable shape may be used. As for the roller coating, a conventional method of manufacturing enamel wires is usable.
[0029] An additional feature of the present invention to provide a shielded insulated wire of good quality whose film is free from air bubbles, comprises applying a solvent to an object being coated before applying and heating heat-hardening insulating paint thereto after winding shield metal wires or a metal foil on stranded insulated wires. That is, by applying the solvent to the object to wet the surfaces of the shield metal wires, applying the solvent type heat-hardening insulating paint thereto and baking the paint, the generation of air bubbles is remarkably reduced. This method makes it possible to form a film free from air bubbles and has an important technical meaning to the industry. The reasons why the foaming decreases are considered as follows: The air present between the shield metal wires is partially replaced with the solvent when the shield metal wires or the metal foil is wetted with the solvent so that the air escapes from the structure or otherwise the insulating paint for use in the later process is caused to insert into the portion between the shield metal wires and thus replace itself with the remaining air. In consequence, the foaming resulting from the expansion of the air when heated, it considered as being suppressed. It is important, however, that the solvent and the insulating paint coated in the later process are soluble in each other.
[0030] More specifically, a mixture of various cresol acids, xylene, toluene, naphtha having different boiling points and the like are often used for insulating paint of polyvinyl formal,' polyurethane, polyester or polyester imide. On the other hand, for polyamide imide or polyimide paint for use in heat resistant winding, pyrrolidone as a main solvent with xylene, toluene or naphtha having different boiling points as a diluent can be selectively used.
[0031] The solvent precoated on the shield metal may be the above solvent in the form of a single substance or mixture of them but are preferable to be capable of being mixed with the resin and solvent contained in the paint. The solvent may be applied to the shield metal by using the felt soaked with the solvent, by the roller coating method, or by dipping the object being coated in the solvent tank and uniformly wiping it with the felt or the like.
[0032] The present invention is further intended to provide a method for obtaining a shielded insulated wire of good quality which is free from air bubbles. When insulating paint is applied to an object being coated and hardened to form the lowermost layer, heat-hardening paint whose viscosity is less than 300 cps (measured by a B type viscometer under the measuring temperature of 30°C or lower) is applied thereto by a felt or roller and baked more than once and further the insulating paint is applied thereto and hardened more than once.
[0033] When the insulating paint is applied and baked, foaming is caused mainly by (1) the air present in the gap between the shield metals and (2) the vaporization of the solvent used for the insulating paint. The present inventors have already ascertained the fact that, in the case of the above reason (1), the air present in the gap between the shield metal and the stranded insulated wire is caused to escape and prevented from foaming, provided that the heat-hardening insulating paint is thinly'applied by using a felt or roller.
[0034] The present inventors have further made examinations and confirmed that the viscosity of the heat-hardening insulating paint is correlated to foaming in the film. In particular, the viscosity of the heat-hardening insulating paint to be applied . first is most closely related to foaming in the film. That is, it was found that considerations must be given to not only the thickness.of the paint applied first but also its viscosity.
[0035] The viscosity of the heat-hardening insulating paint applied to the object being coated is temporarily reduced while it is heated in the oven. Furthermore, the air present in the gap expands in volume and is forced to escape from the structure through the paint. The intensity of the viscosity at that time corresponds to that of the resistance against the air escaping from the structure.
[0036] When the viscosity is high, the air is hardly allowed to eacape therefrom and tends to generate air bubbles. Even though the air is allowed to escape therefrom, the drawback it that the surface is hardly smoothed despite the surface tension if the viscosity is high. The present inventors have further confirmed the fact through experiments that the viscosity(measured by B type viscometer, at 30°C) of the insulating paint should preferably be lower than 300 cps, more preferably 200 cps and further more preferably 100 cps to depress the occurrence of foaming.
[0037] The low viscosity of the heat-hardening insulating paint is further lowered in the oven and, in consequence, the expanded air is allowed to readily escape from the structure and the ruggedness on-the surface of the paint by the air escaping therefrom is smoothed because of the low viscosity and the action of surface tension. The above facts have also been confirmed through the experiments conducted by the present inventors. When heat-hardening insulating paint, whose viscosity is 300 cps or less, was used for forming the lowermost layer film between the shield metals as shown in Fig. 4, it was confirmed that no air bubbles were generated even if the insulating paint was applied up to the portions A and B at one time.
[0038] when the insulating paint is applied again after the first coating of the paint, it is possible to use heat-hardening insulating paint whose viscosity is higher than what is used for the first time. The reason is that most of the air present in the gap between the shield metal wires has already been allowed to escape from the structure. Even if the air is present in the film, it will be not allowed to escape from the film formed by the first coating and thus not attributable to foaming. However, during or after the insulating paint is applied and hardened twice, if the paint film is excessively thick or its viscosity is too high, undesirable foaming occurs in the film due to the vaporization of the solvent. When the felt is used to apply the insulating paint after the first coating, the viscosity thereof should preferably be less than about 700 cps and less than 5,000 cps when the dies are used therefor.
[0039] Fig. 5 is a transverse sectional view of the shielded insulated wire according to the present invention.
[0040] Any ordinary insulating paint may be used in the present invention by adjusting its viscosity. However, it is needless to say necessary to select the kind in accordance with required property.
[0041] If a sheath insulator for a shielded wire is formed by applying and hardening insulating paint, instead of extrusion molding, the sheath insulator can be made thinner and accordingly the total outer finished diameter of the shielded wire is made thinner and light in weight. When the sheath insulator is provided by extrusion molding, the film thickness generally exceeds 0.3 mm, whereas the use of the insulating paint makes it possible to provide such a film of 0.005 mm thick uniformly. However, when the insulating paint is applied and hardened to form such a sheath insulator, it is strongly adhesive to the shield metal wire or foil. Thus, when it is put to practical use, it tends to pose a problem that the separation of the film is difficult at its end. In that case, it is possible to improve the separation characteristics of the film at the end by applying lubricant to the surface of the shield metal wire or by coating the wound shield metal wires with a thin film.
Reference Example (1)
[0043] Seven stranded conductors/0.127 mm were covered with vinyl chloride resin to form a film of 0.27 mm thick by extrusion molding, weft-wound shield metal wires (0.05 mm x 35) and a sheath insulator of 0.40 mm thick by extrusion molding. The finished shielded wire was 1.83 mm in outer diameter.
Comprative Example (1)
[0044] The manufacturing process of this example is identical to that of Reference Example (1) except for the following:
[0045] Vinyl cholide resin paint (with solvent of methyl ketone, naphasa) was applied by using dies and hardened by baking to provide a sheath insulator whose thickness was 0.06 mm, so that the shield wire of finished outer diameter 1.15 mm was obtained. Air bubless were seen on the surface of the film.
Example (1-1)
[0046] The manufacturing process of this example is identical to that of comparative Example (1) except for the following:
For sheathing insulation, ultraviolet-hardend type paint (base polymer: polyester urethane acrylate origomer, reactive diluent: ethylene glycol diacrylate, vinyl pyrrolidine, light starting agents benzoin ethyle ether) was applied by using dies and hardened by ultraviolet ray irradiation to form a sheath insulator of 0.06 mm thick, so that the shielded wire of the finished outer diameter of 1.15 mm was obtained. Air bubbles were not seen on the surface of the film.
Example (1-2)
[0047] The manufacturing process of this example is identical to that of Reference Example (1) or Example (1-1) except for the following:
Stranded conductors were coated with the ultraviolet-hardened type paint used in Example (1-1), which was hardened by ultraviolet ray irradiation, to make a stranded insulated wire having a film of 0.05 mm thick. Shield wires were laterally wound on the stranded insulated wire and the same sheath insulator as that of Example (1-1) was formed, so that the shielded wire of the finished outer diameter of 0.72 mm was obtained.
Example (1-3)
[0048] The manufacturing process of this example is identical to that of Example (1-2) except for the following:
The shield metal wires were coated with ultraviolet hardened type paint and was passed through an oven of 1.5 m long whose temperature was held at 230°C. Thereafter the paint was hardened by ultraviolet ray irradiation. No air bubbles were contained in the sheath insulator.
Example (1-4)
[0049] The manufacturing process of this example is identical to that of Example (1-3) except for the following: An object being coated was passed through a vacuum chamber with the pressure reduced to 50 mmHg before forming of sheath insulator, coated with paint hardened by ultraviolet ray irradiation and then hardened thereby. No air bubbles were observed in the sheath insulator.
Comparative Example (2-1)
[0050] Seven stranded conductors /0.127 mm were coated with vinyl chloride resin by extrusion molding to form an insulating film of 0.27 mm thick and weft-wound shield metal wires (0.05 mm x 35) were added thereto and that combination was coated with polyester insulating paint (whose concentration is 40%) by using dies, which was baked. The number of paint application and baking was 7. There was obtained a shielded wire with a 0.05 mm thick sheath insulator, on the surface of which several grains due to foaming were observed.
Comparative Example ( 2 -2 )
[0051] The manufacturing process of this example is identical to that of Comparative Example (2-1) except for the following:
Polyester insulating paint (concentration being about 20%) was applied by using a wool felt and baked. The paint was applied 20 times to obtain a sheath insulating film of 0.05 mm thick. No grains due to foaming were observed on the surface thereof.
Example (2)
[0052] .The manufacturing process of this example is identical to that of Comparative Example (2-1) except for the following:
Stranded conductors were insulated by extrusion-molding and weft-wound shield metal wires were wound thereon. Thereafter, polyester insulating paint (concentration: 20%) were coated by using a wool felt and baked three times and then polyester insulating paint (40%) was applied thereto using dies and baked four times. The shielded wire obtained had a sheath insulator of 0.05 mm thick which was free from grains due to foaming.
Comparative Example (3)
[0053] Seven stranded conductors/0.127 mm were coated with vinyl chloride resin by extrusion molding to form a film of 0.27 mm and weft-wound metal wires (0.05 mm x 35) were added thereto. That combination was further coated with polyester insulating paint (solvent: m-cresole, naphtha) using dies and hardened by baking to form a film of 0.06 mm thick.
Example (3)
[0055] The process of this example is identical to that of Example (3) except for the following: The solvent composed of naphtha and butylcellosolve was applied to the surface of the shield metal wire by using a felt and then polyester insulating paint was applied and baked. No foaming was observed on the surface of the film.
Comparative Example (4)
[0056] Seven stranded conductors/0.127 mm were coated with vinyl chloride resin by extrusion molding to form a film of 0.27 mm and weft-wound metal wires (0.05 mm x 35) were added thereto. The combination was further coated with nylon 66 insulating paint (concentration 20%; viscosity 1,400 cps) using a wool felt and baked. The number of times the paint was applied and baked was 15 to form the shielded insulated wire having a film of 0.045 mm. Grains due to foaming were observed on the surface of the film.
Example (4)
[0057] The process of this example is identical to that of Comparative Example 4 except for the following: Nylon 66 insulating paint was adjusted to concentration 13% and 130 cps in viscosity and'applied and baked first. The same insulating paint as that in Comparative Example (4) was used secondly and thereafter. Grains due to foaming were not observed in the film.
1. A process for producing a shielded wire for use in electric/ electronic equipment,
comprising the steps of: shielding a single stranded insulated wire prepared by covering
a stranded conductor with insulating material or a combination of such wires with
metal wires or a metal foil; coating said metal wires or said metal foil with insulating
paint; and hardening said paint to form an insulating film.
2. A process for producing a shielded wire for use in electric/ electronic equipment
as claimed in claim 1, wherein said insulating paint is non-solvent type ultraviolet
ray or electron beam irradiation-hardened paint and is hardened by ultraviolet ray
or electron beam irradiation after the coating step.
3. A process for producing a shielded wire for use in electric/ electronic equipment
as claimed in claim 2, further comprising the step of passing the stranded insulated
wire through a heating oven to remove air.bubbles in said film after the coating step
and prior to the hardening step.
4. A process for producing a shielded wire for use in electric/ electronic equipment
as claimed in claim 2, further comprising the steps of: passing the stranded insulated
wire through a vacuum chamber to remove the air around said shield metal wires or
metal foil after the shielding step; and leading the stranded insulated wire to a
tank containing said ultraviolet ray or electron beam irradiation-hardened paint prior
to the coating step.
5. A process for producing a shielded wire for use in electric/ electronic equipment
as claimed in claim 4, wherein the pressure in said vacuum chamber is reduced to 150
mmHg or less.
6. A process for producing a shielded wire as claimed in claim 1, wherein, after the
shielding step, said insulating paint of heat-hardening type is coated on said metal
wires or said metal foil by using a felt or roller and is hardened when at least the
lowermost layer of said film is formed
7. A process for producing a shielded wire as claimed in claim 1, further comprising
the step of coating the metal wires or metal foil with a solvent after the shielding
step and prior to coating and hardening said paint of heat-hardening type.
8. A process for producing a shielded wire as claimed in claim 7, wherein said solvent
and said paint of heat-hardening type are soluble in each other.
9. A process for producing a shielded wire as claimed in claim 1, wherein a heat-hardening
insulating paint having viscosity of 300 cps or less is coated on said metal wires
or said metal foil after the shielding step and is hardened when at least the lowermost
layer of said film is formed.