JP2007323918A - Shielded flat cable and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shielded flat cable small in dielectric loss, and excelling in reliability of a signal. <P>SOLUTION: This shielded flat cable comprises at least one conductive wire, and a cavity-including thermoplastic resin film extended and oriented at least in one direction. The shielded flat cable is characterized in that the cavity-including thermoplastic resin film includes 3-45 vol.% of cavities in its inside; the number of laminated layers of the cavities present in the thickness direction of the film is not smaller than five; cavity lamination number density defined by an expression: cavity lamination number density (number/μm)=the number of laminated layers of cavities in the film thickness direction (number)/film thickness (μm) is in the range of 0.1-10/μm; and a metal thin film layer is provided for one surface of the cavity-including thermoplastic resin film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flat cable for connecting devices in computers, communication devices, printers, and the like, and more particularly to a shielded flat cable excellent in electromagnetic wave shielding suitable for transmitting high-frequency signals. Is.

  In recent years, the signal band of information communication devices such as PHS and mobile phones, and the CPU clock time of computers have reached the GHz band, and the frequency has been increasing. Since the dielectric loss of an electric signal is proportional to the product of the square root of the relative dielectric constant of the insulating layer forming the circuit, the dielectric loss tangent, and the frequency of the electric signal, the dielectric loss increases as the frequency of the signal used increases. On the other hand, the increase in dielectric loss attenuates the electrical signal and impairs the reliability of the signal. To suppress this, it is important to select a material with a low dielectric constant and dielectric loss tangent as the material for the insulating layer. .

  Removal of polar groups in the molecular structure of the material is effective in reducing the dielectric constant and tangent of the material, and various materials have been proposed. Among them, in particular, a fluororesin typified by polytetrafluoroethylene (PTFE) has a low dielectric constant and dielectric loss tangent, and is widely used as an insulating layer for various electrical components that handle high-frequency signals. However, PTFE has many limitations in terms of processability, adhesiveness, cost, etc., and a versatile material has been desired. In particular, in an electronic component such as a flexible flat cable, a thin insulating film is required in addition to the above dielectric characteristics.

  Flexible flat cable is a thin tape-shaped parallel multi-core electric wire in which both sides of flat conductors arranged in parallel are sandwiched between plastic films, and used to connect between printed circuit boards of electronic devices and between printed circuit boards and electronic components. It is an electronic component that is indispensable for downsizing and increasing the density of devices used as lead wires. And the dielectric loss in a flexible flat cable becomes a factor of deterioration of a transmission signal and generation | occurrence | production of an error, and will reduce the reliability of an electronic device by extension.

  However, with fluororesins, there are restrictions on the lower limit of the thickness that can be produced, and mechanical strength is insufficient when thinned. In fact, polyester films that can be made thinner are widely used. That is, in these electronic components, an insulating material having a low dielectric loss has not been put into practical use.

A method of dispersing voids (air) in an insulating material is also known for reducing the dielectric constant and the dielectric loss tangent of the material. If this method is employed, an insulating material having a low dielectric constant can be obtained at a relatively low cost. For example, what laminated | stacked the synthetic resin film with a hole between two synthetic resin films is disclosed (for example, refer patent document 1). In addition, electric / electronic devices containing micro hollow spheres (micro balloons made of glass, silica, alumina, etc.) so that the dielectric constant of the insulating material is 2.5 or less, and electric wires (magnets) using these insulating materials Wire), composite film, coil-impregnating varnish, adhesive tape, insulating sleeve, and prepreg material are disclosed (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 9-151851 JP-A-11-288621

  However, in these methods, the dielectric constant and the dielectric loss tangent are only reduced according to the porosity, and it has been considered impossible to achieve innovative low dielectric loss.

  As a result of an independent study on this problem, the number of cavities stacked in the thickness direction of the film containing 3 to 45% by volume of cavities is 5 or more, and the cavity stacking number density defined by the following formula It was found that the dielectric loss can be solved by using a void-containing thermoplastic resin film characterized by a range of 0.1 to 10 pieces / μm.

  However, in recent years, the processing speed of digital devices such as computers has been increased, and countermeasures against so-called electromagnetic interference have been demanded. For this reason, a shielded flat cable provided with an electromagnetic wave shielding layer that shields radiation noise and intrusion noise is also used for flat cables for connecting devices in computers, communication devices, printers and the like.

As a method of providing an electromagnetic shield layer, there is a method of laminating a metal foil on a flat cable. However, this method has a problem that the metal foil cannot be thinned. For this purpose, a method of creating an electromagnetic wave shielding transfer film and transferring a metal layer to a flat cable has been proposed. In this method, a release layer is formed on a film, a metal layer is formed thereon using a vacuum deposition method, etc., and a transfer film having an adhesive layer formed thereon is further used to form a metal thin film layer into a flat cable. (For example, refer to Patent Document 3). In addition, there is a method of pasting instead of transferring (see, for example, Patent Document 4).
JP 2005-56906 A JP-A-7-94036

However, in either method, the adhesive layer is laminated on the insulating layer of the flat cable. The adhesive layer needs to have a thickness of several μm in order to exhibit a sufficient adhesive force.
Laminating a resin layer with a large dielectric chamber loss on the void-containing thermoplastic film described above for the problem of reducing dielectric loss is a significant improvement compared to not using a void-containing thermoplastic film. However, it is insufficient for the problem of reducing dielectric loss.

  The present invention has been made against the background of such prior art problems. That is, an object of the present invention is to provide a shielded flat cable having a low dielectric loss and excellent signal reliability.

  As a result of intensive studies, the present inventors have found that the above problems can be solved by the following means, and have reached the present invention.

That is, this invention consists of the following structures.
In a shielded flat cable comprising at least one conductive wire and a void-containing thermoplastic resin film stretched and oriented in at least one direction, the void-containing thermoplastic resin film contains 3 to 45% by volume of voids inside. The number of cavities laminated in the thickness direction of the film is 5 or more and the density of the number of cavities defined by the following formula is in the range of 0.1 to 10 / μm. A shielded flat cable having a metal thin film layer on one side.
Cavity layer number density (pieces / μm)
= Number of stacked cavities in the film thickness direction (pieces) / film thickness (μm)

  In the shielded flat cable, the shielded flat cable is characterized in that an adhesive modified resin layer of 0.5 μm or less is provided between the metal thin film layer and the cavity-containing thermoplastic resin film. The shielded flat cable is characterized by having an antioxidant resin layer on the metal thin film layer.

  Further, two laminates are prepared in which a metal thin film layer is formed on one side of a cavity-containing thermoplastic resin film stretched and oriented in at least one direction, and two laminates are formed with the metal thin film layer of the laminate being outside. The method for producing a shielded flat cable according to the above, wherein a shielded flat cable is produced by laminating at least one conductor wire with a body through an adhesive.

  According to the present invention, it is possible to provide a highly reliable shielded flat cable with less dielectric loss and less influence on noise.

Hereinafter, the shield flat cable of this invention is shown in detail.
FIG. 4 shows an example of a shielded flat cable. FIG. 4 shows a cross section of the shielded flat cable. FIG. 6 shows the shielded flat cable in a state where it is partially folded as viewed from above.

  In the present invention, the conductive wire 5 can be a general conductive wire. Although it does not specifically limit, a flat square tinned annealed copper foil is preferable. The cross-sectional size of the conductor wiring is approximately in the range of 35 to 100 μm in thickness and 0.3 to 1.0 mm in width. Moreover, although this conducting wire is arranged at intervals of about 0.3-1.5 mm, it is not limited to this conducting wire.

  In order to insulate this conducting wire, the conducting wire is sandwiched between films and laminated. A general adhesive is used for laminating. For example, reactive curing type adhesives such as polyester, polyether, and epoxy, and adhesive adhesives such as rubber, acrylic, and vinyl ethers such as polyvinyl ether can be used. From the viewpoint of productivity, in particular, hot melt adhesives such as polystyrene, vinyl acetate, AVB resin, polypropylene, polyethylene, polyester, and PVC resin are preferable.

  In particular, it is preferable to incorporate a flame retardant into the adhesive to impart flame retardancy to the flat cable. Further, the thickness of the adhesive layer is preferably as thin as possible within the range in which the adhesive strength can be sufficiently secured and the conductive wire is embedded, in view of the purpose of the present invention to suppress the dielectric loss.

  In the present invention, the films used for insulation are those shown in FIGS. The cavity-containing plastic resin film 1 is used as a portion that exhibits insulation properties.

  In the present invention, it is very important for the void-containing thermoplastic resin film used as the insulating layer to be stretched and oriented in at least one direction in order to significantly reduce dielectric loss and increase dielectric breakdown voltage.

  The present inventors evaluated the high-frequency characteristics of various void-containing thermoplastic resin films stretched and oriented in at least one direction. As a result, a film that can significantly reduce the dielectric loss tangent in a high-frequency region of 100 MHz to 100 GHz is obtained. It was discovered that there was a trigger for the development of the present invention.

  For example, in a polyester film that does not substantially contain a cavity inside, the dielectric loss tangent at 1 GHz was 0.016. When a 20% by volume cavity is formed inside the polyester film (foaming degree P: 0.2), the estimated value of the dielectric loss tangent predicted from the conventional technical common sense is 0 when read from FIG. .014. On the other hand, in the present invention, when a biaxially stretched polyester film having a 20% by volume cavity was produced (foaming degree P: 0.2), the measured value of dielectric loss tangent was 0.004. Therefore, the effect of reducing the dielectric loss tangent due to the cavity inside the film in the present invention is so remarkable and excellent that it cannot be predicted from conventional common sense.

  In the present invention, the void-containing film used as the insulating layer of the flat cable preferably has an upper limit of dielectric loss tangent at 1 GHz of 0.010, particularly preferably 0.005. When the mechanical strength of the film is required, the lower limit of the dielectric loss tangent is preferably 0.0005, particularly preferably 0.001.

  When the dielectric loss tangent at 1 GHz exceeds 0.010, the effect of reducing the dielectric loss in the flat cable becomes insufficient. On the other hand, the dielectric loss tangent at 1 GHz is preferably as small as possible. However, if the content of voids inside the film is significantly increased in order to make the dielectric loss tangent at 1 GHz less than 0.0005, the mechanical strength of the film may be significantly impaired. is there. As a method for increasing the content of voids inside the film, a method for increasing the content of an incompatible thermoplastic resin that becomes a void developing agent in the matrix thermoplastic resin, as an incompatible thermoplastic resin Examples thereof include a method using a thermoplastic resin having a large difference in surface tension from the matrix thermoplastic resin, or a method of increasing the stretching stress during film stretching.

  In the present invention, the upper limit of the void content of the void-containing film is 45% by volume, preferably 40% by volume, particularly preferably 35% by volume. On the other hand, the lower limit of the void content of the void-containing film is 3% by volume, preferably 5% by volume, particularly preferably 10% by volume.

  Furthermore, the present inventors also evaluated the electrical insulation characteristics of the void-containing film, and its dielectric breakdown voltage was clearly higher than that of a film that does not substantially contain voids compared to the conventional technical common sense. We found the fact that the properties are also excellent.

  When this void-containing film is subjected to a dielectric breakdown test, theoretically, the void inside the film should start partial discharge before the matrix thermoplastic resin. However, the discharge start voltage of the void-containing film in the actual dielectric breakdown test is almost the same as the discharge start voltage of the film not containing the void. On the other hand, in the case of a film that does not contain cavities, the entire film often leads to complete dielectric breakdown by a single discharge. However, in the case of a film that contains cavities, the entire film does not cause dielectric breakdown by a single discharge. It has been found that many discharges are necessary for complete dielectric breakdown. Therefore, it is considered that the dielectric breakdown voltage is higher in the cavity-containing film than in the film that does not substantially contain the cavity.

  In the present invention, the reason why the void-containing film used as the insulating layer has excellent characteristics such as a low dielectric loss tangent and a high dielectric breakdown voltage compared to conventional technical common sense is not completely clear, It is thought that the dispersion state and shape of the cavities contributed to this. In particular, regarding the effect of improving the dielectric breakdown voltage, it is assumed that a large number of cavities exist in the film thickness direction in the film as independent dispersions.

  Probably, only the cavity that was first discharged in the thickness direction of the film is destroyed by one discharge, and even if this cavity breaks down, new cavities (interfaces) appear one after another, As a result, it is considered that the continuous progress of the tree (dendritic breakdown trace) is suppressed. And it is thought that it is necessary to apply a very high voltage in order to cause the dielectric breakdown to penetrate the whole film at a stretch. This idea is consistent with the experimental results. That is, by making many cavities exist in the film thickness direction, a high breakdown voltage can be obtained as compared with the breakdown voltage of a film that does not contain cavities.

  Specifically, it is preferable that the dielectric breakdown voltage at a thickness of 250 μm of the void-containing film used as an insulating layer in the high-frequency electronic component of the present invention exceeds 1.2 times that of a film substantially not containing voids. Here, the film containing substantially no cavities means a film having a cavity lamination number density of less than 0.0 pieces / μm.

The technical feature of such a void-containing film having a very small dielectric loss and a high dielectric breakdown voltage is that the film contains 3 to 45 volume% of voids inside the film, and the number of laminated voids existing in the thickness direction of the film. Is a number of cavities in the film thickness direction such that the number density of cavities defined by the following formula satisfies the range of 0.1 to 10 / μm.
Cavity layer number density (pieces / μm)
= Number of stacked cavities in the film thickness direction (pieces) / film thickness (μm)

  The density of the number of voids inside the void-containing film is preferably large from the viewpoint of dielectric breakdown voltage, but generally the film strength tends to decrease. In order to increase the number of cavities, the number of cavities in the film can be increased by increasing the number of cavities inside the film by physical or chemical methods. A method of increasing the area of the cavity with respect to the direction is preferable. In order to increase the dielectric breakdown voltage while maintaining the film strength necessary for practical use, the upper limit of the number of voids is preferably 5 / μm, more preferably 1 / μm.

  The method for finely dispersing the number of cavities inside the film by physical or chemical methods to increase the number is arbitrary, and is not particularly limited. For example, the thermoplastic resin a, the thermoplastic resin b1 that is incompatible with the thermoplastic resin a, and the thermoplastic resin b2 that is incompatible with the thermoplastic resins a and b1 and has a surface tension greater than that of the thermoplastic resin b1 are used in combination. Or a method of using polyalkylene glycol or a derivative thereof together, a chemical method for finely dispersing incompatible resin b, a static mixer is installed in the resin melt extrusion process, and the shear force Examples thereof include a physical method for finely dispersing the incompatible resin b.

  Further, in order to increase the dielectric breakdown voltage of the film even when the thickness of the void-containing film is reduced, it is important that the number of voids present in the thickness direction of the film is 5 or more. In the present invention, the thickness of the void-containing film serving as the insulating layer is preferably 10 to 500 μm, and may be appropriately selected within the above range depending on the application and required characteristics. The upper limit of the film thickness is more preferably 350 μm, and particularly preferably 250 μm. On the other hand, the lower limit of the film thickness is more preferably 20 μm and particularly preferably 30 μm from the viewpoint of securing a more stable dielectric breakdown voltage.

  Next, the suitable manufacturing method of the cavity containing thermoplastic resin film used as an insulating layer for the flat cable of this invention is demonstrated.

  In the present invention, the void-containing thermoplastic resin film used as the insulating layer is composed of (1) a matrix thermoplastic resin a and a dispersion of a thermoplastic resin b incompatible with the thermoplastic resin a. A method of forming a cavity (air) around the dispersion by extruding a resin composition having an island structure into a sheet and then stretching the unstretched sheet in at least one direction, or (2) thermoplasticity A resin composition containing inorganic particles or heat-resistant organic particles in the resin a is extruded into a sheet shape, and then the unstretched sheet is stretched in at least one direction, whereby cavities (air) are formed around the particles. Is used. The former method (1) is more preferable because an incompatible thermoplastic resin serving as a cavity-expressing material has a small density, and thus a larger number of cavities can be obtained.

The method (1) having the sea / island structure will be described in detail.
In the above method (1), the material to be the sea component of the void-containing film is not particularly limited as long as it is a thermoplastic resin that can be stretch-oriented, but from the viewpoint of heat resistance. Polyester is preferred.

  Here, the polyester means an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid or an ester thereof, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, etc. Polyester produced by polycondensation with a glycol. These polyesters are (1) a direct polymerization method in which an aromatic dicarboxylic acid and a glycol are directly esterified and then a polycondensation reaction, (2) an alkyl ester of an aromatic dicarboxylic acid and a glycol are transesterified, Subsequently, it can be produced by any one of a transesterification method in which polycondensation is carried out and a method in which (3) a polyglycol ester of an aromatic dicarboxylic acid is polycondensed.

  Typical examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. The polyester may be a homopolymer or a copolymer of a third component. Among these polyesters, a polyester having an ethylene terephthalate unit, a trimethylene terephthalate unit, or an ethylene-2,6-naphthalate unit of 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more is preferable.

  In addition, the island component material is not particularly limited as a thermoplastic resin incompatible with polyester, and may be a homopolymer or a polymer having a copolymer component. A material mainly composed of polystyrene is preferred. Polystyrene is not necessarily limited to a homopolymer, and may be a copolymer obtained by copolymerizing various components. However, when a copolymer is used, it is necessary that the copolymer component does not interfere with the effects of the present invention. In addition, it is preferable that the compounding quantity of the thermoplastic resin incompatible with polyester shall be 1-30 mass% with respect to all the raw materials used for manufacture of a film.

  Polyolefin refers to polyethylene, polypropylene, polymethylpentene, various cyclic olefin-based polymers, and copolymers thereof. Among these polyolefins, polymethylpentene is preferable because it is difficult to soften even at high temperatures and has excellent cavity development. When polymethylpentene is used as the main component of the polyolefin, it is not always necessary to use it alone, and another polyolefin may be added as a subcomponent. Examples of the resin used as the subcomponent include polyethylene, polypropylene, and those obtained by copolymerizing various components with these, but are not particularly limited. The viscosity of the polyolefin added as a subcomponent is not particularly limited, but it is important that the addition amount does not exceed the addition amount of the resin added as a main component.

  Polystyrene refers to a thermoplastic resin containing a polystyrene structure as a basic component, and is modified by grafting or block copolymerizing other components in addition to homopolymers such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene. Resins such as impact-resistant polystyrene resins and modified polyphenylene ether resins, and also thermoplastic resins having compatibility with these polystyrene resins such as polyphenylene ether are included.

  When a polyolefin and polystyrene are used in combination as a thermoplastic resin incompatible with polyester, the ratio (ηo / ηs) of the polyolefin melt viscosity ηo (poise) to the polystyrene melt viscosity ηs (poise) is 0.80 or less. It is preferable that The melt viscosity ratio (ηo / ηs) is more preferably 0.60 or less, and most preferably 0.50 or less. When the melt viscosity ratio exceeds 0.80, the distribution of the polystyrene resin phase in the dispersed particles becomes non-uniform and the phase structure of the dispersed particles becomes unstable. Therefore, the dispersion state of the dispersed particles is deteriorated, and it becomes difficult to satisfy the cavity stacking number density defined in the present invention.

In the present invention, the metal thin film layer 2 preferably has a high electrical conductivity. This is to exhibit the function of shielding electromagnetic waves by the metal thin film layer 2.
As an effect of shielding electromagnetic waves, there are a reflection effect on the surface and an internal absorption effect by the metal thin film layer. When a plane wave is assumed, the absorption effect is expressed by the following equation when the absorption loss A is expressed in dB.
A = 132√ (fμσ) × t
In the above formula, f is the frequency (MHz), μ is the relative permeability with respect to copper, σ is the relative conductivity with respect to copper, and t is the thickness of the metal thin film layer.

On the other hand, when the reflection effect is assumed to be a plane wave, the reflection loss R is expressed by the following equation.
R = 108.1-10 log (fμ / σ)

  The plane wave shielding effect is determined by the relative magnetic permeability, the specific electric conductivity, and the thickness, but it can be seen that one having a large electric conductivity is effective.

  The metal constituting the metal thin film layer 2 shown in FIG. 1 is selected from known metals in consideration of conductivity, cost, corrosion resistance, and productivity. A single element metal may be used, or an alloy may be used to improve the properties. As the metal, silver, copper, gold, aluminum, iron or the like is preferable in terms of conductivity. Among these, copper and aluminum are particularly preferable from the viewpoint of cost and effect.

As a method of creating the metal thin film layer 2, there is a method of attaching a metal foil. However, in order to obtain sufficient adhesiveness, it is necessary to increase the thickness of the adhesive layer.
The formation method suitable for the present invention is a method of forming the metal thin film stack 2 by vapor deposition, sputtering, CVD, or plating directly or through an extremely thin anchor coat layer. In particular, as a method of forming the metal thin film layer, vapor deposition using a vacuum, sputtering, and CVD are preferable. In view of quality, the sputtering method is preferable. Moreover, the vacuum evaporation method is suitable from the point of productivity.

  As for the thickness of the metal thin film layer, the thicker the shielding effect by absorption, the thinner the better from the viewpoint of production efficiency. The shielding effect by reflection does not depend on the thickness, but high conductivity is required. A preferable film thickness is 10 nm to 5 μm. More preferably, it is 20 nm-500 nm. A preferable reason is that when the thickness is 10 nm or less, the thin film is difficult to become a continuous layer and the conductivity is lowered. In consideration of productivity, the upper limit of the thickness further considered the repeated bending performance required for flat cables.

  As for the metal thin film layer 2, it is desirable to form the metal thin film layer 2 in advance on one surface of the cavity-containing thermoplastic resin film 1 which is an insulating layer before producing a flat cable. Further, before forming the metal thin film layer 2, the surface of the void-containing thermoplastic resin film 1 is subjected to corona discharge treatment, glow discharge treatment, and other surface treatments, and the metal thin film layer 2 and the void-containing thermoplastic resin film are subjected to the surface treatment. 1 may be improved.

  Further, in order to improve the adhesion between the metal thin film layer 2 and the cavity-containing thermoplastic resin film 1 within a range that does not hinder the reduction of dielectric loss, which is one of the purposes of the present application, FIG. Such an anchor coat layer 3 can be provided. As the base resin of the anchor coat layer 3, polyester, polyacryl, polyurethane, polyvinyl alcohol and copolymers thereof, ethylene vinyl alcohol copolymer, and the like can be used. Known coating methods can be used, and examples thereof include bar coating, gravure coating, micro gravure coating, reversal coating, reverse kiss coating, die coating, curtain coating, and spray coating. Also, the coating can be either off-line coating in which the film after stretching is finished with a coater or in-line coating in which coating is performed during film formation.

  In order to make the dielectric loss negligible, at least the thickness of the anchor coat layer 3 is preferably 0.5 μm or less. Usually, since the thickness of the cavity-containing thermoplastic resin film 1 is 20 μm or more, it is preferable that the thickness be negligible. In-line coating is suitable for thin coating. This is because if the anchor coat layer 3 is coated before the film is stretched, the coat layer can be further thinned in the subsequent stretching step.

  In order to protect the metal thin film layer 3, it is preferable to provide an antioxidant resin layer 4 as shown in FIG. As the base resin, polyethylene, polyester, polyacryl, polyurethane, polyvinyl alcohol and copolymers thereof, ethylene vinyl alcohol copolymer, and the like can be used.

  A known coating method can be used, but since it is necessary to form the coating layer after forming the metal thin film layer 2, the in-line coating method cannot be adopted. In addition, since the metal thin film layer is sandwiched when viewed from the conductive wire, there is little influence on the dielectric loss. For this reason, the thickness of the antioxidant resin layer 4 is not particularly limited, but is preferably 100 μm or less from the viewpoint of flexibility.

Since the coat thickness may be increased as compared with the anchor coat layer 3, it is possible to laminate a molten resin.
The antioxidant resin layer 4 has a function of preventing the metal thin film layer from being exposed to the atmosphere for a long time and being oxidized to lower the conductivity. In addition, there is also a function of preventing the flat cable from coming into contact with another and the metal thin film layer from being worn.

  A preferred procedure for producing the shielded flat cable of the present invention is to create a void-containing thermoplastic resin film 1 and form an anchor coat layer 3 by in-line or off-line coating as necessary to form a metal thin film layer 2. Create a laminate. A laminate in which the antioxidant resin layer 4 is formed on the metal thin film layer 2 of the laminate as necessary is created.

  That is, it is preferable to manufacture a laminated body as shown in FIGS. Two pieces of this laminated body are prepared by slitting into a flat cable width. It is preferable to produce a shielded flat cable as shown in FIGS. 4 and 5 by placing two laminates facing each other on the surface side of the cavity-containing thermoplastic resin film, placing a conducting wire between them, and bonding them together with an adhesive. Prior to the bonding of the two laminates, a known surface treatment can be performed to improve adhesion.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples. First, the evaluation method of the characteristic values used in the present invention is shown below.

[Evaluation methods]
(1) Intrinsic viscosity of polyester resin In accordance with JIS K 7367-5, a mixed solvent of phenol (60% by mass) and 1,1,2,2-tetrachloroethane (40% by mass) is used as a solvent at 30 ° C. It was measured.

(2) Polymethylpentene and polystyrene melt viscosity (ηo, ηs)
The melt viscosity at a resin temperature of 285 ° C. and a shear rate of 100 / second was measured using a flow tester (manufactured by Shimadzu Corporation, CFT-500). Note that measurement of melt viscosity at a shear rate of 100 / sec is difficult to perform with the shear rate fixed at 100 / sec. Therefore, using an appropriate load, any shear rate of less than 100 / sec and The melt viscosity was measured at an arbitrary shear rate greater than the rate, the melt viscosity was plotted on the vertical axis, and the shear rate was plotted on the horizontal axis, and plotted on a log-log graph. The two points were connected by a straight line, and the melt viscosity (η: poise) at a shear rate of 100 / sec was determined by interpolation.

(3) Film thickness Measured according to JIS K 7130 "Foamed plastic-film and sheet-thickness measuring method". An electronic micrometer (Milltron 1240 manufactured by Marl Co., Ltd.) was used as a measuring device, and 5 points (4 pieces) of each 5 cm square sample were measured (20 points in total), and this average value was taken as the thickness.

(4) Apparent density of film Measured according to JIS K 7222 “Foamed plastics and rubber—Measurement of apparent density”. However, in order to simplify the notation, the unit was converted to g / cm ³ .

(5) Cavity content of film The apparent density was calculated | required by the method of said (3) about the film piece to measure. Next, this film piece was sufficiently finely pulverized by a freeze pulverizer. The crushed sample was degassed in a vacuum, remelted and then solidified into a sheet. This was taken out from the vacuum, sufficiently cooled until it reached room temperature, and then the apparent density was determined again. The magnitude of the difference in apparent density before and after degassing was divided by the density after degassing to determine the void content (%).

(6) Dielectric constant and dielectric loss tangent of film Parallel plate method using dielectric material measurement electrode (manufactured by Agilent Technologies, HP16453A type) and impedance material analyzer (manufactured by Agilent Technologies, HP4291A type) Thus, the characteristics at 1.0 GHz were evaluated. Samples used for the measurement were prepared by overlapping a plurality of samples cut to a size of 25 mm × 25 mm, and the total thickness was in the range of 0.90 to 1.10 mm. Then, the superposed samples were inserted between the electrodes, and the relative dielectric constant and dielectric loss tangent were measured. And the same measurement was performed 5 times and the average value was calculated | required. These measurements were performed in a laboratory controlled at 25 ° C. and a relative humidity of 50%.

(7) The number of cavities stacked in the thickness direction of the film, and the density of the number of cavities stacked in the film The scanning electron microscope was used to observe the cavities in the cross section of the film. A fractured surface parallel to the direction and perpendicular to the film surface was observed. The observation was performed at an appropriate magnification of 300 to 3000 times, and a photograph was taken so that the dispersion state of the cavities in the entire thickness of the film could be confirmed. Next, a straight line was drawn perpendicularly to the film surface at any location on the photographic image, and the number of cavities intersecting the straight line was counted. The number of cavities is defined as the number of cavities (number of layers) in the thickness direction of the film. Further, the total thickness (μm) of the film was measured along this straight line, and the cavity lamination number density (pieces / μm) was obtained by dividing the number of laminations of the cavities by the total thickness of the film. In addition, measurement was performed at five locations for each photograph, and an average value of a total of 25 locations was obtained to obtain the number of cavities stacked as a sample.

(8) Measurement of thickness of metal thin film layer When the film thickness is relatively submicron, a part of the metal thin film layer is etched to expose the substrate, and the metal thin film layer and the substrate are Measure the step. If the metal thin film layer is thinner than that, the film thickness is calculated using fluorescent X-ray analysis.

Example 1
The raw material which was vacuum-dried under heating was continuously weighed and continuously stirred so that a / b / c = 8/87/5 (mass ratio) to obtain the raw material for the A layer. Next, this raw material is supplied to a barrier type single-screw extruder having a dalmage zone at the tip, melted and kneaded, and then passed through a gear pump, a filter, and a 12-element static mixer mounted inside a short pipe having a diameter of 50 mm. Then, it was immediately supplied to a feed block (co-extrusion joint).

  On the other hand, the raw material of the B layer is obtained by continuously weighing the raw material so that b / c = 70/30 (mass ratio), and is supplied to a vent type twin screw extruder and melt-kneaded, and a gear pump, a filter To the feed block.

  In the feed block, the B layer was bonded to both surfaces of the A layer. At this time, the rotational speeds of the extruder and the gear pump on the A layer side and the B layer side were controlled so that the thickness ratio of each layer before stretching was B / A / B = 10/80/10.

  Next, the molten polymer joined by the feed block is supplied to a coat hanger die connected immediately below the feed block, and cast on a cooling drum having a surface temperature of 30 ° C. so that the B surface becomes the drum surface. A 0.5 mm unstretched film was produced.

Next, the unstretched film obtained by the above method was heated to 65 ° C. using a heating roll, and then stretched 3.2 times between rolls having different peripheral speeds. At this time, a condensing IR heater was installed at an intermediate portion between the low-speed roll and the high-speed roll at a position opposed to each other with the film interposed therebetween, and a sufficient amount of heat necessary for uniformly stretching the film was applied equally from both sides of the film.

  Next, the obtained uniaxially stretched film was introduced into a tenter, and stretched 4.0 times in the width direction while heating from 120 ° C to 150 ° C. Further, heat treatment was performed by blowing hot air of 220 ° C. for 7 seconds in the tenter. Then, while gradually cooling to room temperature over 9 seconds, a relaxation treatment of 2% was applied in the width direction, and a void-containing laminated biaxially oriented polyester film having an apparent density of 1.10 g / cm 3 and a thickness of 50 μm (film a) was prepared. The characteristic values of the obtained film 1 are shown in Table 1.

  Before introducing the above uniaxially stretched film into a tenter, a water-dispersed polyester resin (byronal MD-1200, manufactured by Toyobo Co., Ltd.) is applied by a fountain bar coating method so that the resin solid content thickness before stretching is 0.1 μm, A void-containing laminated biaxially oriented polyester film (film b) having a thickness of 50 μm was introduced into a tenter and stretched in the same manner. The characteristic values of the obtained film 2 are shown in Table 1.

A metal thin film layer was formed on the prepared film a using a roll coater type vacuum vapor deposition apparatus. The film a is set on the winding roll 14 and passed through the center roll 13 and the winding roll 12 along the roll of the apparatus.
As a vapor deposition source, a carbon crucible 8 having a width of 150 mm × depth of 70 mm × height of 50 mm was used, and granular copper having a purity of 99.9% and about 3 mm was placed.

The inside of the vacuum chamber 9 was drawn in advance to a vacuum degree of 5.0 × 10 ⁻⁸ Pa and heated with a 90 ° deflection type electron gun 10 (JEBG-1000UB, manufactured by JEOL). The electron beam 11 was heated in a range of 30 mm × 100 mm while scanning over the material. The input power is 9 kw.

  The distance from the crucible 8 to the center roll 13 is 450 mm. The center roll 13 was cooled to −15 ° C. in order to prevent the film 15 from being damaged by heat from the crucible 8.

With the state of the crucible stabilized by visual observation, the film 15 was run at 4 m / min. When the crucible was stable, the shutter 16 was opened and copper was deposited on the film 15. The pressure during vapor deposition was 1.0 × 10 ⁻⁶ Pa. Thus, a laminate 1 as shown in FIG. 1 was obtained.

  Similarly, vapor deposition was performed on the film b, and the laminated body 2 shown in FIG. 2 was obtained.

The obtained laminate 2 was taken out, coated with a polyester urethane resin (byron UR-2300, manufactured by Toyobo Co., Ltd.) so as to have a dry weight of 4 g / m ² by an offline coater, dried, and wound up. A laminate 3 as shown was obtained.

In order to evaluate the characteristics of the flat cable, samples were prepared according to the following procedure.
A polyester resin (Byron GM-995, manufactured by Toyobo Co., Ltd.) was extrusion coated to a predetermined thickness on one side of the laminate 1 with a T-die extruder to obtain an insulating substrate. Next, 10 tin-plated flat annealed copper conductors (thickness 35 μm × width 0.3 mm) were sandwiched in parallel at a pitch of 0.5 mm between the laminates produced in the same manner. Next, they were integrated by passing through a heat roller and laminating to prepare a sample. A cross-sectional view of the obtained shielded flat cable is shown in FIG. In FIG. 4, 1 is an insulating film, 6 is an adhesive agent, and 5 is a conducting wire.

Example 2
Similarly, FIG. 5 shows a cross-sectional view in which a shield flat cable is created using the laminate 3.

Comparative Example 1
A flat cable is prepared in the same manner as in Example 1 except that the metal thin film layer is not formed on the void-containing laminated biaxially oriented polyester film.
A shielded flat cable was prepared by adhering and laminating a 9 μm thick copper foil on both sides of the formed flat cable using a polyester resin (Byron GM-995, manufactured by Toyobo Co., Ltd.). The thickness of the polyester resin is 10 μm.

  In order to evaluate the dielectric loss of the shielded flat cable, in Example 1, the film a which is an insulating layer before forming the metal thin film layer and the film b in Example 2 were measured. In Comparative Example 1, the film a between the conductive wire and the copper foil serving as the shield layer was coated with a polyester resin having a thickness of 10 μm. The results are shown in Table 1.

In the shielded flat cable of the present invention, the dielectric loss at a high frequency is remarkably small, and the influence of noise is reduced by the shield layer, so that the reliability of the transmitted signal is improved. For this reason, it is expected that the reliability of electronic equipment using a flat cable is improved and greatly contributes to the industry.

It is sectional drawing of the cavity containing thermoplastic resin film which has a metal thin film layer. It is sectional drawing of the cavity containing thermoplastic resin film which has an intermediate | middle layer (anchor coat layer) of the laminated body of FIG. It is sectional drawing of the cavity containing thermoplastic resin film which has an antioxidant resin layer on the surface of the metal thin film layer of the laminated body of FIG. It is sectional drawing of a shield flat cable. It is sectional drawing of a shield flat cable. It is a top view of a shield flat cable. It is a conceptual diagram of a vapor deposition apparatus.

Explanation of symbols

1: Cavity-containing thermoplastic resin film 2: Metal thin film layer 3: Anchor coat layer 4: Antioxidation resin layer 5: Conductor wiring 6: Adhesive layer 7: Laminated film 8: Crucible 9: Vacuum chamber 10: Electron gun 11: Electron Beam 12: Winding roll 13: Center roll 14: Winding roll 15: Film 16: Shutter

Claims (4)

In a shielded flat cable comprising at least one conductive wire and a void-containing thermoplastic resin film stretched and oriented in at least one direction, the void-containing thermoplastic resin film contains 3 to 45% by volume of voids inside. The number of cavities laminated in the thickness direction of the film is 5 or more and the density of the number of cavities defined by the following formula is in the range of 0.1 to 10 / μm. A shielded flat cable having a metal thin film layer on one side.
Cavity layer number density (pieces / μm)
= Number of stacked cavities in the film thickness direction (pieces) / film thickness (μm)   2. The shielded flat cable according to claim 1, further comprising an adhesion modifying resin layer having a thickness of 0.5 [mu] m or less between the metal thin film layer and the void-containing thermoplastic resin film.   3. The shield flat cable according to claim 1, further comprising an antioxidant resin layer on the metal thin film layer.   Two laminates in which a metal thin film layer is formed on one side of a cavity-containing thermoplastic resin film stretched and oriented in at least one direction are prepared, and the laminate is composed of two laminates with the metal thin film layer of the laminate on the outside. The method for producing a shielded flat cable according to any one of claims 1 to 3, wherein a shielded flat cable is produced by laminating at least one conductor wire through an adhesive.