JP5528857B2 - Electromagnetic wave shielding film, flexible substrate using the same, and method for producing the same - Google Patents

Description

  The present invention relates to an electromagnetic wave shielding film, a flexible substrate using the same, and a method for producing the same, and more specifically, an electromagnetic wave shielding film capable of maintaining an electromagnetic wave shielding effect even after long-term sliding, and an electromagnetic wave shield using this film The present invention relates to a flexible substrate having a layer formed thereon and a method for manufacturing the same.

  2. Description of the Related Art Conventionally, electromagnetic wave shielding is performed by laminating an electromagnetic wave shielding film on a flexible substrate (FPC) disposed on a hinge portion or the like of a mobile phone. As the electromagnetic wave shielding film, a film having at least a conductive layer and a protective layer, and the conductive layer formed from a conductive adhesive (conductive paste) in which metal powder is dispersed in a binder resin is used.

  Such an electromagnetic wave shielding film is required to be thinner than ever in connection with the thinning of a mobile phone or the like, but if other conditions are the same, the shielding performance decreases as the thickness is reduced. It is a problem to suppress the decrease. In addition, flexible substrates that are subject to electromagnetic wave shielding are used in parts that are frequently bent and slid when used in mobile phones and the like, and the problem that the electromagnetic wave shielding effect decreases as the period of use increases. Therefore, the solution is also desired.

  In order to improve various performances of the electromagnetic wave shielding film, various ideas have been made on the shape and particle size of the metal particles. For example, Patent Document 1 discloses silver particles having an average particle size of 0.5 μm to 20 μm and granular silver particles having an average particle size of primary particles of 50 nm or less in order to improve conductivity, adhesion, and electromagnetic wave shielding properties. Is used at a certain rate. Further, in Patent Document 2, in order to obtain a conductive paste composition that can satisfy the bending characteristics required by a flexible substrate, scaly silver powder having an average particle size of 2.0 to 5.0 μm and an average particle size of 10 to 19 μm. The use of mixed powders with dendritic silver-plated copper powder is disclosed.

  However, at present, an electromagnetic wave shielding film that maintains sufficient electromagnetic wave shielding properties even after several hundred thousand times of bending and sliding has not yet been obtained.

JP 2005-294254 A JP 2009-230952 A

  The present invention has been made in view of the above, and has excellent electromagnetic shielding properties even when it is thinned, and is used for a part that is frequently bent and slid repeatedly like a hinge part of a mobile phone or the like. However, an object of the present invention is to provide an electromagnetic wave shielding film in which the initial electromagnetic wave shielding property is maintained for a long period of time. Moreover, it aims at providing the flexible substrate by which the electromagnetic wave shielding layer was formed using this film, and its manufacturing method.

That is, the electromagnetic wave shielding film of the present invention is an electromagnetic wave shielding film in which a protective layer is laminated on a conductive layer made of (A) metal powder and (B) a binder resin, in order to solve the above-described problems, The conductive layer as the metal powder includes (a) flaky metal powder having an average thickness of 50 to 300 nm and an average particle diameter of 3 to 10 μm, and (b) acicular or dendritic metal powder having an average particle diameter of 3 to 10 μm. The ratio of (A) metal powder and (B) binder resin in the conductive layer is in the range of A: B = 50: 50 to 80:20 by weight ratio. The ratio of the above (a) flaky metal powder and (b) acicular or dendritic metal powder is a: b = 20: 80 to 80:20 in weight ratio. Within the range and the thickness before the pressing process is 11-30 μm , And the thickness after the pressing process is 7~28μm der is, and it is assumed less than the thickness of the pre-press process.

  The method for producing a flexible substrate of the present invention comprises placing the electromagnetic wave shielding film of the present invention on a flexible substrate, and then heating the flexible substrate together with the electromagnetic wave shielding film while pressing in the thickness direction. In this method, an electromagnetic wave shielding layer is formed.

  Moreover, the flexible substrate of this invention shall have an electromagnetic wave shielding layer which consists of an electromagnetic wave shielding film of the said invention.

  The electromagnetic wave shielding film of the present invention has an excellent electromagnetic wave shielding effect. When an electromagnetic wave shielding layer is provided on a flexible substrate using this film, the electromagnetic wave shielding is high even after several hundred thousand times of bending or sliding. The effect of being maintained is obtained.

  Moreover, according to the manufacturing method of the board | substrate provided with the electromagnetic wave shielding layer of this invention, the flexible substrate provided with the electromagnetic wave shielding layer which the above-mentioned outstanding electromagnetic wave shielding effect lasts for a long period of time is obtained easily.

It is a model end view which shows the measuring method of sheet resistance. It is a model end view which shows the measuring method of connection resistance, (b) is the elements on larger scale of (a). It is a model end elevation which shows the method of a sliding test.

  Hereinafter, the electromagnetic wave shielding film of the present invention and the method for producing a flexible substrate using the same will be described in detail.

  As described above, the electromagnetic wave shielding film of the present invention has at least a conductive layer made of metal powder and a binder resin and a protective layer. As the metal powder, flaky metal powder and needle-like or dendritic metal powder are used. It is characterized by using together.

  The “flaky metal powder” referred to in the present invention is usually referred to as a scaly shape or a flake shape, and may be a flat shape, and its planar shape is not particularly limited. A scaly metal powder formed by crushing or crushing particles of various shapes is advantageous because it is advantageous in terms of cost and productivity.

  The metal type of the flaky metal powder is gold, silver, silver-coated copper, copper, nickel, etc. Among them, silver and silver-coated copper are preferable. The size of the flaky metal powder is preferably in the range of an average thickness of 50 to 300 nm and an average particle diameter of 3 to 10 μm. When the average thickness is larger than 300 nm, the melting point of the flaky metal powder is hardly lowered, and when the average thickness is smaller than 50 nm, the production cost is significantly increased. Further, when the average particle size is larger than 10 μm, the dispersibility is lowered, and when the average particle size is smaller than 3 μm, the conductivity when the metal powder is low-filled tends to be lowered.

  On the other hand, the “acicular or dendritic metal powder” may be acicular, dendritic or a mixture thereof. Here, the dendritic shape is not limited to those having a portion that is clearly recognized as a branched shape, and includes those having protrusions such as confetti and those having convex portions of various sizes. The kind of metal of this acicular or dendritic metal powder is also gold, silver, silver-coated copper, copper, nickel, etc., as described above, and silver-coated copper is particularly preferable. The size is preferably in the range of 3 to 10 μm in average particle size. When the average particle size is larger than 10 μm, it is difficult to reduce the thickness of the shield film, and when the average particle size is smaller than 3 μm, it is difficult to form the protrusion shape of the metal powder.

  The average particle diameter and average thickness of the metal powder can be measured by a laser diffraction scattering method.

  When using any one of these by combining the flaky metal powder and the needle-like or dendritic metal powder as described above, or when combining other shapes (for example, flaky metal powder and It is recognized that the sustainability of the electromagnetic shielding effect against repeated bending / sliding is remarkably improved as compared with the case of using spherical metal powder in combination. In the prior art, the shielding effect decreases with time, because it is considered that the contact state between the metal particles of the conductive layer deteriorates due to repeated deformation of the film. When powder and needle-like or dendritic metal powder are used in combination, it is presumed that physical coupling occurs such that the needle-like or dendritic metal powder partially pierces the flaky metal powder. Furthermore, it is considered that the metal powders are bonded to each other through a heating process under pressure, which will be described later, or a strong bond equivalent thereto, and further, the bonding is performed through a solder reflow process described later. It will be stronger.

  The flaky metal powder (a) and the needle-like or dendritic metal powder (b) are preferably used in a weight ratio of a: b = 20: 80 to 80:20. When the ratio of the needle-like or dendritic metal powder to the flaky metal powder is out of the above range, the decrease in conductivity due to bending / sliding becomes large. That is, the shielding effect is greatly reduced.

  Next, as the binder resin, a thermosetting resin such as an epoxy resin, a urethane resin, an acrylic resin, a polyimide resin, a phenol resin, or a melamine resin can be used without any particular limitation. Among these, urethane resin is preferably used because of its excellent flexibility.

  The blending ratio of the (A) metal powder and the (B) binder resin is preferably in the range of A: B = 50: 50 to 80:20 (in terms of solid content) by weight ratio, and A: B = 55: The range of 45-70: 30 is more preferable. If the amount of the metal powder is less than 50% by weight, it will be difficult to develop the conductivity, and if it is more than 80% by weight, the flexibility and adhesion will be reduced.

  The method for producing an electromagnetic wave shielding film from the metal powder and the binder resin is not particularly limited. For example, a paste made of the metal powder and the binder resin is prepared and coated on a release paper to form a film serving as a conductive layer. To do. The thickness of the film is preferably 8 to 28 μm, and preferably 5 to 25 μm after the pressing step described later. If the thickness after the pressing step is less than 5 μm, it is difficult to obtain sufficient electromagnetic wave shielding properties, and if it exceeds 25 μm, it is not preferable because of a demand for thinning.

  If necessary, known additives can be added to the conductive layer within a range not departing from the object of the present invention. Examples of additives include flame retardants, leveling agents, viscosity modifiers and the like. As the flame retardant, an inorganic or organic flame retardant such as phosphorus can be used as appropriate.

  The electromagnetic wave shielding film of the present invention is obtained by laminating the film constituting the protective layer on the film constituting the conductive layer. Or the film which comprises a protective layer previously can be formed, and the film which comprises a conductive layer can also be laminated | stacked on this film.

  The film constituting the protective layer can be formed of an epoxy resin, a urethane resin, or the like. Moreover, it is preferable that the surface hardness of a protective layer is H-4H in pencil hardness, For that purpose, it can also laminate | stack an acrylic hard coat layer on the layer which consists of the said epoxy resin and urethane resin as needed. If the surface hardness of the protective layer is less than H as the pencil hardness, the protective layer is likely to be damaged, whereas if it is greater than 4H, the flexibility is reduced and the sliding characteristics may be deteriorated.

  Moreover, it is preferable that the thickness of the film which comprises this protective layer is 3-15 micrometers, and it is preferable that it will be 2-12 micrometers after the press process mentioned later. When the thickness after the pressing step is less than 2 μm, the strength as the protective layer is insufficient, and when the thickness exceeds 12 μm, it is not preferable because of the demand for thinning.

  Furthermore, as a whole electromagnetic wave shielding film, it is preferable that the thickness before the press process mentioned later is 11-30 micrometers, and it is preferable that it will be 7-28 micrometers after a press process.

  Next, as a method for producing the flexible substrate of the present invention, the electromagnetic wave shielding film of the present invention is placed on the flexible substrate and subjected to a pressing step of heating while being pressurized at a pressure of 1 to 5 MPa, whereby an electromagnetic wave is formed on the flexible substrate. A shield layer can be formed. The heating temperature in the pressing step is preferably 140 to 200 ° C.

  Moreover, a sliding characteristic can be improved further drastically by using the flexible substrate in which the electromagnetic wave shielding layer was formed by the said press process for a solder reflow process. The conditions for performing solder reflow are not particularly limited as long as the conditions allow the solder to melt, but are usually about 260 ° C. for about 4 seconds. Since the melting point of the metal is lowered by thinning, the flaky metal powder used in the present invention is melted by the reflow process in this temperature range even with a high melting point metal such as silver having a melting point of 962 ° C. A metal bond or a strong bond equivalent thereto is generated.

  In addition, in order to ensure the adhesiveness with the flexible substrate used as coating | coated object, it is preferable that the electromagnetic wave shielding film of this invention has the adhesive force of 2N or more with a 180 degree peel strength with respect to a polyimide.

  Examples of the present invention are shown below, but the present invention is not limited to the following examples.

[Examples and Comparative Examples]
A two-layer structure consisting of an epoxy soft layer and an acrylic hard coat layer by coating an epoxy resin with a thickness of 6 μm on the release film and drying, and then applying and drying an acrylic hard coat solution on the release film. A protective layer (reference numeral 1 in FIGS. 1 and 2 described later) was formed. On this protective layer, a conductive paste prepared with the formulation shown in Tables 1 and 2 was coated and dried to form a conductive layer (reference numeral 2 in FIGS. 1 and 2), thereby obtaining an electromagnetic wave shielding film. The following evaluation was performed using the obtained electromagnetic wave shielding film. The details of the binder resin and metal powder used are as follows.

Binder resin: manufactured by Dainichi Seika Kogyo Co., Ltd., urethane resin UD1357
Metal powder: (a) scale-like silver powder: average thickness 100 nm, average particle diameter 5 μm, melting point about 250 ° C.
(B) Dendritic silver-coated copper powder: average particle size 5 μm

  However, in the comparative example 3, it replaced with (b) dendritic silver coat copper powder, and used the spherical silver coat copper powder (average particle diameter of 6-7 micrometers).

(1) Sheet resistance The cube-shaped electrodes A and B (electrode area: 1 cm ² (L1 = L2 = L3 = 1 cm), electrode interval d: 1 cm, electrode surface: gold plating treatment) shown in FIG. Then, a load of 4.9 N was applied to each electrode in the direction indicated by the arrow, the resistance value between the A and B electrodes was measured by the four-terminal method, and the value one minute after the start of measurement was taken as the sheet resistance. The measurement atmosphere temperature was normal temperature (18 to 28 ° C.), and a cut sample of 249 mm × 50 mm was used for the measurement. Table 1 shows the average value with n = 5.

(2) 180 ° peel strength The conductive layer side of the electromagnetic wave shielding film is attached to a test plate via a polyimide film (manufactured by Toray DuPont Co., Ltd., Kapton 100H (trade name)), and the adhesive is also applied to the protective layer side. A polyimide film (Kapton 100H) was pasted through the layers and peeled off from the polyimide film at 50 mm / min. Table 1 shows the average value with n = 5.

(3) Connection resistance The electromagnetic wave shielding film is placed on a flexible printed circuit board (thickness 53.5 μm) and heated at 170 ° C. for 30 minutes while being pressurized at a pressure of 3 MPa, as shown in FIGS. 2 (a) and 2 (b). A sample for evaluation of a flexible printed circuit board (FPC) provided with an electromagnetic wave shielding film layer having a cross-sectional shape was prepared, and then solder reflow was performed 5 times. 2A and 2B, reference numeral 1 denotes a protective layer of the electromagnetic wave shielding film, and reference numeral 2 denotes the conductive layer. Reference numeral 3 is an FPC polyimide layer (thickness 12.5 μm), reference numeral 4 is a copper layer (Cu: 18 μm), reference numeral 5 is an electroless nickel-gold plating layer (Ni: 3 to 5 μm, Au: 0.05 to 0.1 μm), reference numeral 6 denotes an adhesive layer (thickness of 35 μm), and reference numeral 7 denotes a polyimide layer (thickness of 25 μm). a is the diameter of the ground portion. (B) is an enlarged view of the ground part in (a). The resistance value R (connection resistance) was measured in each case where the diameter of the ground portion (a) was 0.5 mmφ, 0.8 mmφ, and 1.0 mmφ. Tables 1 and 2 show average values where the number of tests is n = 5.

(4) Sliding properties FPC 13 having a four-layer structure in which a polyimide layer (12.5 μm), an adhesive layer (15 μm), a copper foil layer (12 μm), and a polyimide layer (12.5 μm) are laminated in this order from above. Electromagnetic wave shielding films 14 and 15 (length 100 mm, width 12 mm) were laminated on both the upper and lower surfaces of the film, and an evaluation sample was prepared. This evaluation sample is bent in the length direction so that the upper surface side of the FPC 13 is inside, and is sandwiched between the fixed plate 11 and the sliding plate 12 as shown in FIG. 3 (bending radius b: 1.0 mm), Terminals (not shown) are connected to both ends of the conductive layers of the electromagnetic shielding films 14 and 15 via copper foil (width 10 mm), and the resistance values of these films 14 and 15 are measured, respectively. The initial layer resistance was taken. Subsequently, the stroke (sliding width 50 mm (c = c ′ = 25 mm), 60 reciprocations / min) with the black circle as a base point is made a stroke (the number of strokes when the shield layer resistance reaches 100Ω (“1 in reciprocation” And “sliding characteristics”. Moreover, the test was similarly performed also about the sample which used the said sample for evaluation for the solder reflow process 3 times. The results are shown in Tables 1 and 2. In the table, “inner bending” indicates the resistance value of the electromagnetic shielding film 15 that is inside the FPC 13 when bent, and “outer bending” indicates the resistance value of the electromagnetic shielding film 15 that is outside the FPC 13.

  The electromagnetic wave shielding film of the present invention is suitably used for all flexible substrates incorporated in devices such as digital cameras having bent portions and sliding portions in addition to mobile phones.

DESCRIPTION OF SYMBOLS 1 ... Protective layer of electromagnetic shielding film, 2 ... Conductive layer, 3, 7 ... Polyimide layer,
4 ... copper layer, 5 ... nickel-gold plating layer, 6 ... adhesive layer,
DESCRIPTION OF SYMBOLS 11 ... Fixed plate, 12 ... Sliding plate, 13 ... FPC, 14, 15 ... Electromagnetic wave shielding film

Claims (3)

(A) An electromagnetic wave shielding film in which a protective layer is laminated on a conductive layer made of metal powder and (B) a binder resin,
As the metal powder, the conductive layer includes (a) flaky metal powder having an average thickness of 50 to 300 nm and an average particle diameter of 3 to 10 μm, and (b) acicular or dendritic metal powder having an average particle diameter of 3 to 10 μm. Formed from a conductive paste containing
The ratio of (A) metal powder and (B) binder resin in the conductive layer is within the range of A: B = 50: 50 to 80:20 (however, solid content conversion) by weight ratio,
The ratio of said (a) flaky metal powder and (b) acicular or dendritic metal powder is in the range of a: b = 20: 80-80: 20 by weight, and the thickness before the pressing step Saga is 11～30Myuemu, electromagnetic wave shielding film, wherein the thickness after the pressing process is 7~28μm der is, and less than the thickness of the pre-press process. The electromagnetic wave shielding film according to claim 1 is placed on a flexible substrate,
Next, an electromagnetic wave shielding layer is formed on the flexible substrate by heating the flexible substrate together with the electromagnetic wave shielding film while pressing in the thickness direction. A method for producing a flexible substrate, comprising:   The flexible substrate which has an electromagnetic wave shielding layer which consists of an electromagnetic wave shielding film of Claim 1.

Images