JP2024068759A - Electromagnetic wave shielding sheet, printed circuit board, and electronic equipment - Google Patents

Abstract

To provide an electromagnetic wave shielding sheet, a printed circuit board, and electronic equipment, each having high blocking resistance, excellent scratch resistance and excellent dust resistance.SOLUTION: An electromagnetic wave shielding sheet of the present disclosure, is an electromagnetic wave shielding sheet in which a shield layer (B) is arranged only on one surface side of a protection layer (A), and in which the protection layer (A) after heated for 30 mins at 170°C satisfies that (1) a dynamic friction coefficient is 0.01 to 0.9, (2) a pencil hardness obtained in accordance with JIS K 5600 is HB to 9H, and (3) height of a protruded peak portion on a front surface opposite to the side in which the shield layer (B) of the protection layer (A) is arranged, is 0.001 or more and less than 10 μm, the height of the protruded peak portion being obtained in accordance with ISO 25178-2:2012.SELECTED DRAWING: Figure 1

Description

This disclosure relates to an electromagnetic wave shielding sheet. It also relates to a printed wiring board and an electronic device.

Various electronic devices, including mobile terminals, PCs, and servers, have built-in substrates such as printed wiring boards. These substrates are provided with an electromagnetic shielding structure to prevent malfunctions caused by external magnetic fields and radio waves, and to reduce unnecessary radiation from electrical signals (Patent Documents 1 and 2).

Patent Document 1 aims to provide a shielding film that appropriately controls the adhesive strength of a separate film to a protective layer to prevent problems caused by adhesion with excessively large or excessively small adhesive strength, and discloses a shielding film in which a protective layer is formed by coating a resin via a release agent on the side of a separate film having an uneven portion formed entirely on one side, the side on which the uneven portion is formed, and the surface roughness (Ra) of the protective layer when the separate film is peeled off from the protective layer is 0.2 μm to 1.0 μm.
Patent Document 2 discloses an electromagnetic wave shielding film that has an insulating layer and a shielding layer, and the insulating layer has a surface Sa of 0.8 μm or more, with the objective of realizing an electromagnetic wave shielding film that is less likely to discolor when fingerprints are wiped off.

JP 2014-112576 A JP 2018-41962 A

A printed wiring board with an electromagnetic shielding sheet, which is a bendable printed wiring board with an electromagnetic shielding sheet laminated thereon, is usually folded when incorporated into an electronic device. When a printed wiring board with an electromagnetic shielding sheet is folded with the surface on which the electromagnetic shielding sheet is laminated facing inward, the protective layers of the electromagnetic shielding sheet come into contact with each other, and the contacting protective layers often stick together, resulting in a problem of reduced yield. (Hereinafter referred to as "blocking")

In addition, printed wiring boards laminated with electromagnetic wave shielding sheets are sometimes laminated with stainless steel plates (SUS plates) to reinforce the connector area, and there is a problem that the hard SUS plate comes into contact with the protective layer of the electromagnetic wave shielding sheet during the folding process, damaging the protective layer. Therefore, there is a demand for an electromagnetic wave shielding sheet that does not cause the above-mentioned tears.

Furthermore, during the manufacturing process of printed wiring boards on which electromagnetic shielding sheets are laminated, fine dust and dirt can adhere to the surface of the protective layer of the electromagnetic shielding sheet, and this dust and dirt can become trapped in the unevenness of the protective layer, making it difficult to remove.

This disclosure has been made in view of the above background, and aims to provide an electromagnetic shielding sheet, a printed wiring board, and an electronic device that have high blocking resistance and excellent tear resistance and dust resistance.

As a result of extensive investigations, the present inventors have found that the problems of the present disclosure can be solved in the following aspect, and have thus completed the present disclosure.
[1]: An electromagnetic wave shielding sheet in which a shielding layer (B) is disposed only on one side of a protective layer (A), and the protective layer (A) satisfies the following (1) to (3) after heating at 170° C. for 30 minutes.
(1) The dynamic friction coefficient is 0.01 to 0.9.
(2) The pencil hardness measured in accordance with JIS K 5600 is HB to 9H.
(3) On the surface of the protective layer (A) opposite to the side on which the shield layer (B) is disposed,
The protruding peak height (Spk) determined in accordance with ISO 25178-2:2012 is 0.001 or more and less than 10 μm.
[2]: The electromagnetic wave shielding sheet according to [1], wherein the arithmetic mean height (Sa) of the other surface of the protective layer (A) measured in accordance with ISO 25178-2:2012 is 0.01 to 9 μm.
[3]: The electromagnetic wave shielding sheet according to [1], wherein the aspect ratio (Str) of the surface texture of the other surface of the protective layer (A) measured in accordance with ISO 25178-2:2012 is 0.3 to 1.0.
[4]: A printed wiring board having an electromagnetic shielding sheet, comprising the electromagnetic shielding sheet according to any one of [1] to [3].
[5]: An electronic device comprising a printed wiring board with an electromagnetic wave shielding sheet according to [4].

The present disclosure has the excellent effect of providing an electromagnetic wave shielding sheet, a printed wiring board, and an electronic device that have high blocking resistance and excellent tear resistance and dust resistance.

FIG. 2 is a schematic cross-sectional view showing an example of a precursor of the electromagnetic wave shielding sheet according to the embodiment. 1 is a conceptual diagram of a roughness curve including peak height (Spk). FIG. 2 is a schematic cross-sectional view showing an example of a main part of the printed wiring board according to the embodiment.

An example of an embodiment to which the present disclosure is applied will be described below. Other embodiments are also included in the scope of the present disclosure as long as they are consistent with the gist of the present disclosure. In addition, the numerical range specified using "~" in this specification includes the numerical values written before and after "~". In addition, in this specification, "film" and "sheet" are not distinguished by thickness. In addition, unless otherwise noted, the various components appearing in this specification may be used independently alone or in combination of two or more types. In addition, "β layer laminated on α layer" includes a laminate structure in which a β layer is laminated directly on an α layer, as well as a laminate structure in which a β layer is laminated on an α layer via another layer. In addition, the numerical values specified in this specification are values obtained by the method disclosed in the examples.

[Electromagnetic wave shielding sheet]
FIG. 1 shows an example of a precursor of an electromagnetic wave shielding sheet (hereinafter, also referred to as "this sheet") according to an embodiment of the present disclosure. As shown in FIG. 1, the electromagnetic wave shielding sheet precursor 1' includes a protective layer precursor (A') and a shielding layer (B) or a shielding layer precursor (B') only on one side of the protective layer precursor (A'), so that the other side of the protective layer precursor (A'), i.e., the side not in contact with the shielding layer (B) or the like, becomes the outermost layer. The electromagnetic wave shielding sheet precursor 1' is bonded to an adherend such as a printed wiring board by heating, and functions as an electromagnetic wave shielding member for the adherend. When the shielding layer precursor (B') has adhesive properties, the sheet is bonded to the adherend via the shielding layer (B), and when the shielding layer (B) does not have adhesive properties, the sheet may be bonded using a bonding layer precursor (C').

[Protective layer (A)], [Protective layer precursor (A')]
The protective layer (A) of this sheet has the function of protecting the shielding layer (B) and other layers when bonded to an adherend, and the function of preventing the shielding layer (B) from being electrically connected to an external conductor.

(1) (Kinematic Friction Coefficient of Protective Layer (A))
The dynamic friction coefficient of the other surface of the protective layer (A) of the present sheet, i.e., the surface not in contact with the shield layer (B) or the like, is 0.01 to 0.9. When the dynamic friction coefficient is 0.01 to 0.9, the protective layers (A) do not stick to each other even if they come into contact with each other when the printed wiring board with the present sheet is folded, and blocking resistance can be improved. The dynamic friction coefficient of the protective layer (A) after heating at 170°C for 30 minutes is preferably 0.05 to 0.8, more preferably 0.1 to 0.7.
The dynamic friction coefficient is a value when the electromagnetic shielding sheet precursor 1' having the protective layer precursor (A') is heated at 170° C. for 30 minutes.

The method for bringing the dynamic friction coefficient of the other surface of the protective layer (A) into the aforementioned range is not particularly limited and can be appropriately selected from conventionally known methods, but a method of selecting and adjusting the type and amount of filler contained in the protective layer precursor (A') as described below is preferred.

(2) (Pencil hardness of protective layer (A))
The pencil hardness of the other surface of the protective layer (A) of this sheet, determined in accordance with JIS K 5600, is HB to 9H. With a pencil hardness of HB to 9H, even when an object comes into contact with the protective layer (A) and slides thereon, the protective layer (A) is sufficiently hard and has an appropriate stress relaxation property, so that the protective layers (A) are not damaged and tear resistance can be improved. The pencil hardness of the other surface of the protective layer (A) is preferably F to 8H, more preferably H to 3H.
The pencil hardness is a value obtained when the electromagnetic shielding sheet precursor 1' having the protective layer precursor (A') is heated at 170° C. for 30 minutes, in the same manner as the dynamic friction coefficient.

The method for bringing the pencil hardness of the other surface of the protective layer (A) into the aforementioned range is not particularly limited and can be appropriately selected from conventionally known methods, but a method of selecting and adjusting the type and amount of the hardener in the binder contained in the protective layer precursor (A') is preferred, as described below.

(3) (Protruding peak height (Spk) of protective layer (A))
The protruding peak height (Spk) of the other surface of the protective layer (A) of this sheet, measured in accordance with ISO 25178-2:2012, is 0.001 or more and less than 10 μm.

As shown in Figure 2, the protruding peak height (Spk) is defined as the average height of the protruding peaks above the core portion when the secant line of the load curve for the roughness curve, drawn at the center of the load curve with the difference ΔSmr in the load area ratios Smr of 40%, is the straight line with the gentlest slope, and the core portion is between the two height positions where the equivalent line intersects with the vertical axis at the load area ratios of 0% and 100%. The value of the protruding peak height (Spk) can be determined by the method shown in the examples described later.

By setting the protruding peak height (Spk) of the other surface of the protective layer (A) to less than 10, it is possible to prevent the protruding portion from getting caught and becoming a starting point for a tear when an object comes into contact with the surface. Furthermore, by setting the Spk to 0.001 or more, it is possible to form appropriate unevenness on the surface, which can suppress adhesion of dust and improve dust resistance. The protruding peak height (Spk) of the other surface of the protective layer (A) is preferably 0.01 to 7, and more preferably 0.1 to 5.
The protruding peak height (Spk) is a value obtained when the electromagnetic shielding sheet precursor 1' having the protective layer precursor (A') is heated at 170° C. for 30 minutes, similarly to the dynamic friction coefficient and pencil hardness.

The method for making the protruding peak height (Spk) of the other surface of the protective layer (A) fall within the above range is not particularly limited, and various methods can be used. For example, (1) a method of polishing the surface of the protective layer (A) by various polishing methods such as buffing; (2) a method of forming a protective layer precursor (A') and a protective layer (A) on a peelable substrate having a predetermined unevenness, and transferring the unevenness to the surface of the protective layer (A). As one example of the method (2), a method of forming a surface having a protruding peak height (Spk) of 0.001 or more and less than 10 μm by applying a composition containing a filler to a peelable substrate (not having a predetermined unevenness) and drying it, forming a protective layer precursor (A') on the surface, and transferring the unevenness to the surface of the protective layer (A) can be mentioned.

The protective layer (A) may be made of any suitable material without any particular restrictions as long as it satisfies the above-mentioned dynamic friction coefficient, pencil hardness, and peak height (Spk), but it is preferable that the protective layer contains a binder and a filler.

(Arithmetic mean height (Sa) of protective layer (A))
Here, the arithmetic mean height Sa is defined in the ISO 25178-2:2012 standard and is a parameter that extends the arithmetic mean height (Ra) of a line to a surface, and is a value calculated by averaging the absolute values of the heights of each point with respect to the average plane of the surface to be measured.

The arithmetic mean height (Sa) of the protective layer (A) is preferably 0.01 to 9 μm. When the arithmetic mean height (Sa) is 0.01 μm or more, unevenness of appropriate height is formed, reducing the number of contacts between the protective layers (A), improving blocking resistance. In addition, unevenness of appropriate height can suppress adhesion of dust and dirt. On the other hand, when Sa is 9 μm or less, dust and dirt can be suppressed from entering the unevenness, improving dust resistance. The arithmetic mean height (Sa) of the protective layer (A) is more preferably 0.05 to 6 μm, and even more preferably 0.1 to 4 μm.

(Aspect ratio (Str) of surface properties of protective layer (A))
The aspect ratio (Str) of the surface texture is defined in the ISO 25178-2:2012 standard and indicates the isotropy or anisotropy of the surface texture. Str can take a value between 0 and 1, with a value closer to 0 indicating the presence of highly regular uneven shapes such as streaks, and a value closer to 1 indicating that the uneven shape of the surface is not dependent on direction.

The aspect ratio (Str) of the surface texture of the protective layer (A) is preferably 0.3 to 1.0. When the aspect ratio (Str) of the surface texture is 0.3 or more, it is possible to impart isotropy to the surface unevenness, and the stress generated when the SUS plate comes into contact with the protective layer (A) can be sufficiently diffused, improving tear resistance. The aspect ratio (Str) of the surface texture of the protective layer (A) is more preferably 0.4 to 1.0, and even more preferably 0.5 to 1.0.

[binder]
The binder serves as a base for the protective layer (A) and has the function of dispersing and supporting the filler. The binder is preferably an organic material. The binder is not particularly limited in composition as long as it has the above-mentioned function, but preferably contains a resin. The resin in this disclosure is defined as an organic material that is usually solid, semi-solid, or solidified, has a softening or melting range, and has a weight average molecular weight (Mw) of 5,000 or more.

[resin]
The resin is not particularly limited in composition, molecular structure, and the like, other than the above-mentioned weight average molecular weight (Mw). From the viewpoint of exhibiting the function of dispersing and supporting the filler, the resin is preferably a thermosetting resin, a thermoplastic resin, a photocurable resin, a natural resin, or an elastomer, and from the viewpoint of imparting excellent adhesiveness to the conductive composition, the resin is preferably a thermosetting resin.

[Thermosetting resin]
Thermosetting resins are resins that have thermosetting properties. Thermosetting is defined as "a polymerizing and/or crosslinking reaction caused by heat, resulting in an irreversible increase in elastic modulus."

When the thermosetting resin has reactive functional groups, the aforementioned thermosetting property may be exhibited by the reaction between the reactive functional groups, or may be exhibited by the reaction between reactive functional groups incorporated in the thermosetting resin and the curing agent described below.

Examples of thermosetting resins include epoxy resins, phenolic resins, polyacrylic resins, polyester resins, polyurethane resins, polyamide resins, polyimide resins, polyamideimide resins, urea resins, polyurethane urea resins, melamine resins, and polyolefin resins.

The binder may further contain a curing agent. The curing agent in the present invention is a substance that accelerates or regulates the curing reaction, and is defined as a substance having a molecular weight or weight average molecular weight (Mw) of less than 5,000. The curing reaction is defined as "polymerizing and/or crosslinking a prepolymer or polymer composition by heating or other means such as radiation, a catalyst, etc., and irreversibly increasing the elastic modulus." From the viewpoint of forming polymerization and/or crosslinking in the binder by a stimulus such as heat, and exhibiting strong adhesiveness to the conductive composition, it is preferable that the binder of the present invention contains a curing agent.
In addition, when a thermosetting resin or a curing agent is used, it is sufficient that the thermosetting resin or the curing agent is contained in the protective layer precursor (A'), and it is also acceptable for them to no longer be contained in the protective layer (A) after heating due to disappearance during a curing reaction, etc.

The curing agent may be appropriately selected from known compounds that exhibit curing properties when combined with the thermosetting resin. Examples of curing agents include epoxy compounds, oxetane compounds, episulfide compounds, aziridine compounds, isocyanate compounds, amine compounds, isocyanate compounds, imidazole compounds, and acid anhydrides.

Preferred epoxy compounds include, for example, glycidyl ether type epoxy compounds, glycidyl amine type epoxy compounds, glycidyl ester type epoxy compounds, cyclic aliphatic (alicyclic) epoxy compounds, etc.

Examples of the glycidyl ether type epoxy compounds include bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, bisphenol S type epoxy compounds, bisphenol AD type epoxy compounds, cresol novolac type epoxy compounds, phenol novolac type epoxy compounds, a-1-naphthol novolac type epoxy compounds, bisphenol A type novolac type epoxy compounds, dicyclopentadiene type epoxy compounds, tetrabromobisphenol A type epoxy compounds, brominated phenol novolac type epoxy compounds, tris(glycidyloxyphenyl)methane, tetrakis(glycidyloxyphenyl)ethane, etc.

Examples of the glycidylamine type epoxy compound include tetraglycidyldiaminodiphenylmethane, triglycidyl paraaminophenol, triglycidyl meta-aminophenol, and tetraglycidyl meta-xylylenediamine.

Examples of the glycidyl ester type epoxy compounds include diglycidyl phthalate, diglycidyl hexahydrophthalate, and diglycidyl tetrahydrophthalate.

Examples of the cyclic aliphatic (alicyclic) epoxy compounds include epoxycyclohexylmethyl-epoxycyclohexanecarboxylate, bis(epoxycyclohexyl)adipate, etc.

Examples of oxetane compounds include 1,4-bis{[(3-ethyloxetan-3-yl)methoxy]methyl}benzene, 3-ethyl-3-{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, 1,3-bis[(3-ethyloxetan-3-yl)methoxy]benzene, 4,4'-bis[(3-ethyl-3-oxetanyl)methoxymethyl]biphenyl, esters of (2-ethyl-2-oxetanyl)ethanol and terephthalic acid, ethers of (2-ethyl-2-oxetanyl)ethanol and phenol novolac resins, and esters of (2-ethyl-2-oxetanyl)ethanol and polycarboxylic acid compounds.

Episulfide compounds include, for example, bis(1,2-epithioethyl) sulfide, bis(1,2-epithioethyl) disulfide, bis(2,3-epithiopropyl) sulfide, bis(2,3-epithiopropylthio)methane, bis(2,3-epithiopropyl) disulfide, bis(2,3-epithiopropyldithio)methane, bis(2,3-epithiopropyldithio)ethane, bis(6,7-epithio-3,4-dithiaheptyl) sulfide, Examples include bis(6,7-epithio-3,4-dithiaheptyl) disulfide, 1,4-dithiane-2,5-bis(2,3-epithiopropyldithiomethyl), 1,3-bis(2,3-epithiopropyldithiomethyl)benzene, 1,6-bis(2,3-epithiopropyldithiomethyl)-2-(2,3-epithiopropyldithioethylthio)-4-thiahexane, and 1,2,3-tris(2,3-epithiopropyldithio)propane.

Examples of aziridine compounds include trimethylolpropane-tri-a-2-aziridinyl propionate, tetramethylolmethane-tri-a-2-aziridinyl propionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), and N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide).

Examples of amine compounds include diethylenetriamine, triethylenetetramine, methylenebis(2-chloroaniline), methylenebis(2-methyl-6-methylaniline), 1,5-naphthalene diisocyanate, and n-butylbenzylphthalic acid.

Examples of isocyanate compounds include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, dicyclohexylmethane diisocyanate, 1,5-naphthalene diisocyanate, tetramethylxylylene diisocyanate, and trimethylhexamethylene diisocyanate.

Examples of imidazole compounds include 2-methylimidazole, 2-heptadecylimidazole, 2-phenyl-4-methylimidazole, and 1-cyanoethyl-2-undecylimidazolium trimellitate.

Acid anhydrides include tetrahydrophthalic anhydride, dodecenyl succinic anhydride, methylnadic anhydride, trimellitic anhydride, and pyromellitic anhydride.

The content of the curing agent is preferably 1 to 70 parts by mass, more preferably 3 to 50 parts by mass, and even more preferably 3 to 30 parts by mass, based on 100 parts by mass of the thermosetting resin.
By making the content of the curing agent 1 part by mass or more, a strong crosslinked structure can be formed after heating the protective layer (A), and blocking resistance and tear resistance can be improved. Also, by making the content of the curing agent 70 parts by mass or less, the formation of an excessive crosslinked structure can be suppressed, and the occurrence of cracks in the protective layer (A) during the folding process can be suppressed.

[Filler]
The filler is dispersed in the protective layer (A) and contributes to improving the properties of the protective layer (A).

Examples of the filler include ceramics and pigments. Ceramics are preferred because they can improve the insulating properties of the protective layer (A). Among ceramics, those having a volume resistivity of 1.0×10 ¹⁰ Ω·cm or more are preferred. When the volume resistivity of the ceramic is 1.0×10 ¹⁰ Ω·cm or more, the insulating properties of the protective layer (A) can be further improved. The volume resistivity of the ceramic is more preferably 1.0×10 ¹² Ω·cm or more, and even more preferably 1.0×10 ¹⁴ Ω·cm or more. Examples of materials having a volume resistivity of 1.0×10 ¹⁰ Ω·cm or more include ceramics such as aluminum oxide or aluminum trioxide (alumina), zirconium dioxide (zirconia), silicon dioxide (silica), boron carbide, aluminum nitride, boron nitride, magnesium oxide (magnesia), and titanium oxide. Among these, a more preferred material is zirconium dioxide (ZrO ₂ ; volume resistivity 1.0×10 ¹² Ω·cm), and an even more preferred material is silica (SiO ₂ ; volume resistivity 1.0×10 ¹⁴ Ω·cm). The volume resistivity of ceramics can be measured in accordance with JIS C2141. Examples of pigments include carbon black, carbon graphite, carbon nanotubes, and graphene. Among these, carbon black is preferably used because it has excellent dispersibility and can efficiently modify the protective layer (A). The shape of the filler is not limited, and examples include blocky, irregular, approximately spherical, spherical, and true spherical.

The filler content is preferably 1 to 50% by weight based on the total amount of components of the protective layer (A). A filler content of 1% by weight makes it possible to set the dynamic friction coefficient in the range of 0.9 or less. Furthermore, a filler content of 50% by weight makes it possible to set the pencil hardness to H or higher. The filler content is more preferably 3 to 40% by weight.

The average particle diameter _D50 of the filler contained in the protective layer (A) is preferably 0.02 to 20 μm. When the average particle diameter _D50 of the filler is 0.02 or more and is sufficiently large, it is possible to impart a sufficient modifying effect to the protective layer (A) and make the above-mentioned (1) to (3) within the desired range. The average particle diameter _D50 of the filler is more preferably 0.02 to 10 μm.

In addition to the protective layer (A), optional components that may be added include silane coupling agents, rust inhibitors, reducing agents, antioxidants, tackifier resins, plasticizers, UV absorbers, defoamers, leveling adjusters, fillers, flame retardants, dyes, etc.

[Shield layer (B)]
The shield layer (B) plays a role in preventing malfunction due to external magnetic fields or radio waves, and/or a role in reducing unnecessary radiation from electric signals. As described above, when the shield layer precursor (B') has adhesiveness, the shield layer (B) is bonded to the adherend, and when the shield layer (B) does not have adhesiveness, the shield layer (B) may be bonded to the adherend via the shield layer (B). When the shield layer (B) does not have adhesiveness, the shield layer (B) may be bonded to the adherend using the bonding layer precursor (C') described later.
The shield layer (B) having no adhesiveness can be exemplified by a metal layer (B-1) not containing a binder, and the shield layer precursor (B') having adhesiveness can be exemplified by a conductive resin layer (B-2) formed from a conductive resin layer precursor (B-2') containing a binder. The shield layer (B) can also be formed by further combining the metal layer (B-1) not containing a binder and the conductive resin layer precursor (B-2') containing a binder.
The shielding layer precursor (B') in the electromagnetic wave shielding sheet precursor 1', like the bonding layer precursor (C') described later, is required to have adhesion to the adherend during thermocompression bonding and to be bonded to the adherend after thermocompression bonding.

[Metal layer (B-1)]
[Components of Metal Layer (B-1)]
The metal layer (B-1) of the present disclosure may be, for example, a metal foil, a metal vapor deposition film, or a metal plating film.
The metal used for the metal foil is preferably a conductive metal such as aluminum, copper, silver, or gold, and either one kind of metal or an alloy of multiple metals can be used. From the viewpoint of high frequency shielding properties and cost, copper, silver, and aluminum are more preferable, and copper is even more preferable. For copper, for example, rolled copper foil or electrolytic copper foil is preferably used.
The metal used for the metal deposition film and metal plating film is preferably one type of conductive metal such as aluminum, copper, silver, gold, etc., or an alloy of multiple metals, and copper and silver are more preferable. One or both surfaces of the metal foil, metal deposition film, and metal plating film may be coated with a metal or an organic substance such as a rust inhibitor.

[Thickness of Metal Layer (B-1)]
The thickness of the metal layer (B-1) is preferably 0.05 to 5.0 μm. By making the thickness of the metal layer (B-1) 0.3 μm or more, it is possible to suppress the transmission of the wavelength of electromagnetic noise generated from the wiring circuit board, and it is possible to exhibit sufficient high frequency shielding properties. The lower limit of the thickness of the metal layer (B-1) is more preferably 0.5 μm. By making the thickness of the metal layer (B-1) 5.0 μm or less, the bending property of the electromagnetic wave shielding sheet is improved. The upper limit of the thickness of the metal layer is more preferably 3.5 μm.

[Aperture]
The metal layer (B-1) may have a plurality of openings, and the opening ratio is preferably 0.10 to 20%. The openings improve the solder reflow resistance. The openings allow volatile components contained in the polyimide film of the wiring circuit board and the coverlay adhesive to escape to the outside when a printed wiring board having the electromagnetic shielding sheet is subjected to solder reflow treatment, and the occurrence of poor appearance due to interfacial peeling between the coverlay adhesive and the electromagnetic shielding sheet can be suppressed.

The shape of the opening as viewed from the surface of the metal layer (B-1) can be, for example, a perfect circle, ellipse, rectangle, polygon, star, trapezoid, branch-like, or any other shape as required. From the standpoint of production costs and ensuring the toughness of the metal layer, it is preferable that the opening shape be a perfect circle or ellipse.

[Aperture ratio of metal layer (B-1)]
The aperture ratio of the metal layer (B-1) can be calculated by the following formula (1).
Formula (1)
(Opening ratio [%])=(area of openings per unit area)/(area of openings per unit area+area of non-openings per unit area)×100

The aperture ratio can be measured, for example, by dividing the openings and non-openings into two parts using images magnified 500 to 2000 times by a laser microscope and a scanning electron microscope (SEM) perpendicular to the surface direction of the metal layer (B-1), and calculating the number of pixels of the divided colors per unit area as the area of each part.

[Method for producing metal layer (B-1) having openings]
The metal layer (B-1) having openings can be produced by a conventional method, and examples of the method that can be used include (i) a method of forming a pattern resist layer on a metal foil and etching the metal foil to form openings, (ii) a method of printing a conductive paste in a predetermined pattern by screen printing, (iii) a method of screen printing an anchor agent in a predetermined pattern and metal plating only the anchor agent-printed surface, and (iv) a production method described in JP2015-63730A.
That is, a water-soluble or solvent-soluble ink is pattern-printed on a support, a metal vapor deposition film is formed on the surface, and the pattern is removed. A release layer is formed on the surface and electrolytic plating is performed to obtain a metal layer having an opening with a carrier. Among these, the opening formation method (i) of forming a pattern resist layer and etching a metal foil is preferred because it allows precise control of the shape of the opening. However, other methods may also be used as long as the shape of the opening can be controlled, and the manufacturing method of the metal layer (B-1) is not limited to the etching method (i).

[Conductive resin layer (B-2)], [Conductive resin layer precursor (B-2')]
The conductive resin layer (B-2) of the present disclosure mainly contains a binder and a conductive filler, and has isotropic conductivity, which means that the electromagnetic wave shielding sheet has conductivity in the vertical and horizontal directions when placed horizontally.
The binder serves as a base for the conductive resin layer (B-2) and has the function of dispersing and supporting the filler. The binder is preferably an organic substance. The binder used in the conductive resin layer (B-2) can be appropriately selected from the same materials as those used in the protective layer (A). When a thermosetting resin or a curing agent is used as the binder, the thermosetting resin or the curing agent only needs to be contained in the conductive resin layer precursor (B'), and may not be contained in the conductive resin layer (B) after heating.

[Conductive filler]
The conductive fine particles as the conductive filler are preferably fine particles of conductive metals such as gold, platinum, silver, copper, and nickel, alloys thereof, and conductive polymers. From the viewpoint of cost reduction, composite fine particles having a core of metal or resin and a coating layer covering the surface of the core made of a highly conductive material are preferable, instead of fine particles of a single composition.
The core is preferably selected from nickel, silica, copper and resin, more preferably a conductive metal and its alloy.
The coating layer may be made of any material having excellent electrical conductivity, and is preferably made of a conductive metal or conductive polymer. Examples of conductive metals include gold, platinum, silver, tin, manganese, and indium, as well as alloys thereof. Examples of conductive polymers include polyaniline and polyacetylene. Among these, silver is preferred in terms of electrical conductivity.
The conductive fine particles can be used alone or in combination of two or more kinds.

Composite microparticles preferably have a coating layer in a ratio of 1 to 40 parts by weight, more preferably 5 to 30 parts by weight, per 100 parts by weight of the core. Coating with 1 to 40 parts by weight allows for further cost reduction while maintaining conductivity. It is preferable for the coating layer of the composite microparticles to completely cover the core. However, in practice, there are cases where part of the core is exposed. Even in such cases, conductivity is easily maintained as long as 70% or more of the core's surface area is covered with a conductive material.

The shape of the conductive fine particles is not limited as long as the desired conductivity is obtained. Specifically, for example, spherical, flake, leaf, dendritic, plate, needle, rod, and grape shapes are preferable.

The average particle size of the conductive fine particles is the _D50 average particle size, and is preferably 1 to 100 μm, and more preferably 3 to 50 μm.
The _D50 average particle size is a value obtained by measuring conductive fine particles using a laser diffraction/scattering method particle size distribution analyzer LS13320 (manufactured by Beckman Coulter, Inc.) with a Tornado dry powder sample module, and is the particle size at which the cumulative value in the cumulative particle size distribution is 50%. The refractive index was set to 1.6.

When adhesiveness is imparted to the conductive resin layer (B-2), the content of the conductive filler in the conductive resin layer (B-2) is preferably 20 to 80% by weight based on the total amount of the components of the conductive resin layer (B-2) from the viewpoint of good adhesion to the adherend, and when adhesiveness is not imparted to the conductive resin layer (B-2), the content of the conductive filler is preferably 50 to 90% by weight based on the total amount of the components of the conductive resin layer (B-2) from the viewpoint of electromagnetic wave shielding properties.

[Bonding layer (C)], [Bonding layer precursor (C')]
The bonding layer precursor (C') serves to bond this sheet to an adherend. The electromagnetic wave shielding sheet precursor 1' is usually bonded to an adherend by thermocompression bonding. The bonding layer precursor (C') in the electromagnetic wave shielding sheet precursor 1' only needs to have adhesion to the adherend during thermocompression bonding and be bonded to the adherend as the bonding layer (C) after thermocompression bonding.

The bonding layer (C) contains a binder. The binder serves as a base for the bonding layer (C) and, when the bonding layer (C) contains a filler, has the function of dispersing and supporting the filler. The binder is preferably an organic material. The binder used for the bonding layer (C) can be appropriately selected from the same materials as those for the protective layer (A). When a thermosetting resin or a curing agent is used as the binder, the thermosetting resin or the curing agent only needs to be contained in the bonding layer precursor (C'), and may not be contained in the bonding layer (C) after heating.

The bonding layer (C) may contain a conductive filler for the purpose of electrically connecting the shield layer (B) to the adherend. The conductive filler used in the bonding layer (C) can be appropriately selected from the same materials as those used in the shield layer (B).
In this case, the bonding layer (C) is preferably anisotropically conductive, which means that the electromagnetic wave shielding sheet has conductivity only in the vertical direction when placed horizontally.

The content of the conductive filler in the bonding layer (C) is preferably 10 to 50% by weight based on the total amount of the components of the bonding layer (C) from the viewpoint of providing a highly reliable electrical connection to the bonding layer (C) and imparting adhesiveness.

(Any other layer)
The sheet may further include other functional layers, such as layers having hard coat properties, water vapor barrier properties, oxygen barrier properties, thermal conductivity, low dielectric constant, high dielectric constant, or heat resistance.

This sheet is generally stored with release sheets attached to both main surfaces of the protective layer (A) and the bonding layer (C) to prevent the adhesion of foreign matter. The release sheets are sheets of substrates such as paper or plastic that have been subjected to a known release treatment.

[[Method of manufacturing electromagnetic shielding sheet]], [[Method of manufacturing precursor of electromagnetic shielding sheet]]
An example of a method for producing the present sheet will be described below. However, the manufacturing method of the present disclosure is not limited to the following manufacturing method. The precursor of the present sheet has a step of forming a protective layer precursor (A') and a step of forming a metal layer (B-1) or a conductive resin layer precursor (B-2') that functions as a shield layer (B). When the precursor of the present sheet has a bonding layer precursor (C'), it also has a step of forming the bonding layer precursor (C').

The order of stacking the precursors of this sheet is protective layer precursor (A')/shield layer (B) or shield layer precursor (B')/bonding layer precursor (C'). The order of steps for each layer is arbitrary. The method of stacking each layer can be arbitrarily performed by a known method. For example, a shield layer (B) is formed on a protective layer precursor (A'), a bonding layer precursor (C') is formed on the shield layer (B), and a bonding layer precursor (C') is formed on a peelable sheet. These are prepared, and then laminated in the order of protective layer precursor (A')/shield layer (B)/bonding layer precursor (C').
In addition, in the present disclosure, a film (a film formed from an insulating resin such as polyester, polycarbonate, polyimide, polyamideimide, polyamide, polyphenylene sulfide, or polyether ether ketone) that satisfies the dynamic friction coefficient, pencil hardness, and protruding peak height (Spk) of the present disclosure is used as the protective layer (A), a shield layer (B) is formed on the protective layer (A), and a bonding layer precursor (C') is formed on the shield layer (B), and a peelable sheet on which the bonding layer precursor (C') is formed is prepared. The precursor of this sheet can also be formed by laminating these in the order of protective layer precursor (A')/shield layer (B)/bonding layer precursor (C').

(Step of forming protective layer precursor (A') and protective layer (A))
A resin composition used to form the protective layer precursor (A') and the protective layer (A) is prepared. Specifically, the resin composition can be obtained by mixing and stirring the blending components. A known stirring device such as a dispermat or homogenizer can be used for stirring. After preparing the resin composition, the protective layer precursor (A') is formed by a known method. For example, the resin composition can be coated on a release sheet and dried to form the protective layer precursor (A'). Examples of the coating method include a gravure coating method, a kiss coating method, a die coating method, a lip coating method, a comma coating method, a blade method, a roll coating method, a knife coating method, a spray coating method, a bar coating method, a spin coating method, and a dip coating method. For the drying process, a known drying device such as a hot air dryer or an infrared heater can be used. In addition, a sheet-shaped protective layer precursor (A') may be formed using an extrusion molding machine such as a T-die. Depending on the drying conditions and extrusion molding conditions, the protective layer (A) can also be formed.

(Step of forming metal layer (B-1))
The metal layer (B-1) may be, for example, a metal foil, a metal vapor deposition film, a metal plating film, or the like. The metal layer (B-1) may also be formed by vacuum deposition, sputtering, CVD, or MO (metal organic). The metal layer (B-1) may be formed by accumulating one or more types of conductive fillers. Suitable examples of the conductive filler include flake particles, dendritic particles, and spherical particles. The conductive filler may be used alone or in combination of two or more types.

By making the thickness of the metal layer (B-1) about 0.05 to 2 μm, for example, gas-permeable micropores can be easily formed at the same time as the formation of the metal layer (B-1) without a separate pore-forming process, but a separate pore-forming process may also be provided. Conventionally known methods can be used for forming pores. Examples include a method of forming a pattern resist layer on the metal layer (B-1) and forming pores at desired positions, a method of screen-printing an anchor agent in a predetermined pattern and metal plating the anchor agent-printed surface, and the method described in JP 2015-63730 A.

(Step of forming conductive resin layer precursor (B-2') and conductive resin layer (B-2))
A conductive filler-containing composition used to form the conductive resin layer precursor (B-2') and the conductive resin layer (B-2) is prepared. Specifically, the conductive filler-containing composition can be obtained by mixing and stirring a predetermined amount of the blending components. Stirring can be performed, for example, by using a stirring device similar to that used in the case of the protective layer precursor (A'). After preparing the conductive filler-containing composition, the conductive resin layer precursor (B-2') is formed by a known method. For example, the conductive filler-containing composition can be coated on a release sheet and dried to form the conductive resin layer precursor (B-2'). When using the bonding layer precursor (C') described later for bonding to the adherend, the drying conditions and extrusion molding conditions can also be changed to form the conductive resin layer (B-2).
Alternatively, the conductive resin layer precursor (B-2') may be formed by applying a conductive filler-containing composition onto the bonding layer precursor (C') and drying the composition. Suitable examples of the application method and drying method include the application examples described in the case of the protective layer precursor (A').

(Step of forming bonding layer precursor (C') and bonding layer (C))
The adhesive composition used to form the bonding layer precursor (C') and the bonding layer (C) is prepared. Specifically, the adhesive composition can be obtained by mixing and stirring the blending components. Stirring can be performed, for example, by using a stirring device similar to that used in the case of the protective layer precursor (A'). After preparing the adhesive composition, the bonding layer precursor (C') is formed by a known method. For example, the bonding layer precursor (C') can be formed by coating the adhesive composition on a release sheet and drying it. As a suitable example of the coating method and drying method, the coating example described in the case of the protective layer precursor (A') can be exemplified. In the drying process, a known drying device such as a hot air dryer or an infrared heater can be used. In addition, a sheet-shaped bonding layer precursor (C') may be formed using an extrusion molding machine such as a T-die.

[Printed Wiring Board]
An example of a main part of a printed wiring board with an electromagnetic shielding sheet according to an embodiment of the present disclosure is shown in Fig. 3. As shown in Fig. 3, a printed wiring board 20 with an electromagnetic shielding sheet includes a printed wiring board 10 and an electromagnetic shielding sheet 2. The printed wiring board 10 includes an insulating substrate 11, a circuit pattern 12 formed on the insulating substrate 11, and a cover coat layer 13 formed on the insulating substrate 11 and the circuit pattern 12. The electromagnetic shielding sheet 2 is bonded to the insulating substrate 11 by a bonding layer (C) of this sheet.

The electromagnetic shielding sheet 2 only needs to be attached to the printed wiring board 10, and the bonding area can be designed as appropriate, but in the example of FIG. 3, it is bonded to the cover coat layer 13 using the bonding layer (C) of this sheet. In the example of FIG. 3, the electromagnetic shielding sheet 2 has a three-layer structure of bonding layer (C)/shielding layer (B)/protective layer (A). Any bonding method is used, but bonding is usually performed by thermocompression bonding. By thermocompression bonding, a part of the bonding layer precursor (C') is filled inside the via 14 provided in the cover coat layer 13, forming a bonding layer (C) that is bonded to the exposed surface of the ground wiring 12b.

The insulating substrate 11 functions as a support for the circuit pattern 12. The insulating substrate 11 is not particularly limited. Examples of suitable resins when flexibility is required include polyester, polycarbonate, polyimide, and polyphenylene sulfide. Considering the use of the wiring circuit board to transmit high-frequency signals, resins with low relative dielectric constant and dielectric loss tangent are preferred, and among the examples of suitable resins given above, those classified as liquid crystal polymers are even more preferred. Liquid crystal polymers refer to polymers that exhibit liquid crystallinity when heated and melted. For insulating substrates that require rigidity, glass epoxy, which has excellent heat resistance, is preferred.

The circuit pattern 12 has signal wiring 12a and ground wiring 12b. The circuit pattern 12 is formed of a copper layer having a thickness of, for example, several μm to several tens of μm. The signal wiring 12a can be applied to, for example, a single-ended transmission line consisting of one signal wiring, or a differential transmission line consisting of two signal wirings. A differential transmission line uses two signal wirings, passes currents of opposite phases to each other, and reads the potential difference between the signal wirings, thereby reducing the effects of electromagnetic noise added to the signal wiring, and can achieve even more stable signal transmission by combining it with the electromagnetic shielding sheet of the present disclosure, so it is preferable to use a differential transmission line for the signal wiring 12a.

The cover coat layer 13 is an insulating material that covers the circuit pattern 12 of the printed wiring board 10 and protects it from the external environment. A known insulating material can be appropriately selected for the cover coat layer 13. A resin having heat resistance and flexibility, such as polyimide, is suitable. Suitable examples include a polyimide film with a thermosetting adhesive, a thermosetting or ultraviolet-curing solder resist, and a photosensitive coverlay film. The thickness of the cover coat layer 13 is usually about 10 to 100 μm. The opening area of the via 14 is not particularly limited, but is preferably 0.8 mm ² or less from the viewpoint of miniaturization of the printed wiring board 20. The lower limit is not particularly limited, but is, for example, 0.008 mm ² or more.

The sheet is generally bonded to the printed wiring board 10 by heat pressing (also called thermocompression bonding) at a temperature of about 150 to 190°C, a pressure of about 1 to 3 MPa, and a time of about 1 to 60 minutes. The heat press brings the bonding layer precursor (C') and the cover coat layer 13 into close contact, and the bonding layer precursor (C') flows and fills the vias 14 formed in the cover coat layer 13, bonding the sheet to the cover coat layer 13 and the ground wiring 12b, thereby obtaining a printed wiring board 20 with an electromagnetic shielding sheet. If the bonding layer (C) is conductive, the ground wiring 12b and the electromagnetic shielding sheet 2 are electrically connected. If any or all of the bonding layer precursor (C'), shield layer precursor (B'), and protective layer precursor (A') contain a thermosetting resin in the binder component, the corresponding layer becomes a hardened layer by heat pressing and/or hardening. The curing process can be, for example, a method in which the material is post-cured at about 150 to 190°C for 30 to 90 minutes after heat pressing.

To more effectively suppress leakage of electromagnetic waves, electromagnetic shielding sheets 2 may be provided on both sides of the wiring circuit board 10. In the printed wiring board 20, the electromagnetic shielding sheet 2 can be used as a ground circuit in addition to its function of shielding electromagnetic waves. By using the electromagnetic shielding sheet 2 as a ground circuit, it is possible to reduce the area of the ground circuit region of the wiring circuit board 10, thereby achieving miniaturization and cost reduction.

The present disclosure will be explained in more detail, but the following examples are not intended to limit the scope of the present disclosure. In the examples, "parts" and "%" represent "parts by mass" and "% by mass", respectively, and Mw means weight average molecular weight. The blending amounts in the tables are in parts by mass. The acid value, weight average molecular weight (Mw), and glass transition temperature (Tg) of the resin, and the average particle size of the conductive filler were measured using the following methods.

<<Measurement of the acid value of the resin in the binder component>>
The acid value was calculated by converting the measured acid value (mgKOH/g) into solid content according to the neutralization titration method of JIS K 0070. Approximately 1 g of sample was precisely weighed and placed in a stoppered Erlenmeyer flask, and 100 mL of a tetrahydrofuran/ethanol (volume ratio: tetrahydrofuran/ethanol = 2/1) mixture was added and dissolved. Phenolphthalein test solution was added as an indicator, and titration was performed with 0.1N alcoholic potassium hydroxide solution, and the end point was when the indicator maintained a light pink color for 30 seconds. The acid value was calculated by the following formula (unit: mgKOH/g).
Acid value (mgKOH/g) = (5.611 x a x F) / S
however,
S: Amount of sample collected (g)
a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (mL)
F: Potency of 0.1N alcoholic potassium hydroxide solution

<<Measurement of weight average molecular weight (Mw) of binder component resin>>
The Mw was measured using a GPC (gel permeation chromatograph) "HPC-8020" (manufactured by Tosoh Corporation). GPC is a liquid chromatograph that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on the difference in their molecular size. This measurement was performed using two "LF-604" columns (manufactured by Showa Denko KK: GPC column for rapid analysis: 6 mm ID x 150 mm size) connected in series, at a flow rate of 0.6 mL/min and a column temperature of 40°C. The Mw was determined in terms of polystyrene.

<<Glass transition temperature (Tg) of binder resin>>
The Tg was measured by a differential scanning calorimeter "DSC-1" (manufactured by Mettler Toledo).

<<Measurement of _D50 average particle size of filler and conductive filler>>
The _D50 average particle size was measured using a laser diffraction/scattering particle size measuring device MT3000II (manufactured by Microtrack Bell, measurement range: 0.02 μm-2.8 mm). The _D50 average particle size is the particle size at which the cumulative value in the cumulative distribution is 50%. The refractive index was set to 1.6.

"material"
The raw materials used in the examples and comparative examples are shown below. P1 to P5 in Tables 1 to 3 correspond to the following thermosetting resins P1 to P5, respectively. The same applies to other hardeners, fillers, and conductive fillers.
Thermosetting resin P1: polyester resin with acid value of 10 mg KOH/g, Mw of 47,000, and Tg of 12°C (manufactured by Toyochem)
Thermosetting resin P2: polyamide resin with acid value of 13 mg KOH/g, Mw of 51,000, and Tg of 3°C (manufactured by Toyochem)
Thermosetting resin P3: polyurethane resin with acid value of 5 mg KOH/g, Mw of 61,000, and Tg of -5°C (manufactured by Toyochem)
Thermosetting resin P4: polyurethane resin with acid value of 26 mg KOH/g, Mw of 88,000, and Tg of 32°C (manufactured by Toyochem)
Thermosetting resin P5: polyolefin resin with acid value of 18 mg KOH/g, Mw of 38,000, and Tg of 32°C (manufactured by Toyochem)
Hardener H1: Epoxy compound, "JER828" (bisphenol A type epoxy resin, epoxy equivalent = 189 g/eq, manufactured by Mitsubishi Chemical)
Filler F1: Carbon black "MA100" (manufactured by Mitsubishi Chemical) (average particle size = 0.042 μm)
Filler F2: Silica "AEROSIL R974" (manufactured by Nippon Aerosil) (average particle size = 0.040 μm)
Filler F3: Aluminum phosphinate "Exolit OP935" (manufactured by Clariant Co., Ltd.) (average particle size = 0.25 μm)
Conductive filler M1: Silver-coated copper powder: _D50 = 5.7 μm, dendritic (manufactured by Mitsui Mining & Smelting)
Conductive filler M2: Silver-coated copper powder: _D50 = 11.3 μm, flake-shaped (manufactured by DOWA Holdings)
[Example 1]
Preparation of protective layer precursor (A')
100 parts of thermosetting resin P1, 10 parts of filler F1, 20 parts of F2, and 20 parts of hardener H1 were charged in a container in terms of solid content, and a mixed solvent (toluene: isopropyl alcohol = 2: 1 (mass ratio)) was added so that the non-volatile content concentration was 40%, and the mixture was stirred with a disperser for 10 minutes to obtain a resin composition. The obtained resin composition was coated on a release sheet with a bar coater so that the dry thickness was 5 μm, and the protective layer precursor (A') was obtained by drying for 2 minutes in an electric oven at 100 ° C. The dry thickness was measured with an ABS digital indicator ID-CX (manufactured by Mitutoyo Corporation).
<<Preparation of Shield Layer (B) (Metal Layer (B-1))>>
A copper plating layer (2.5 μm) was formed as the metal layer (B-1) on the exposed surface of the protective layer precursor (A′) of the obtained “peelable sheet/protective layer precursor (A′).” The copper plating layer was formed by electrolytic plating using copper sulfate as the electrolyte and applying a current at 25° C. for 7 minutes.
Preparation of Bonding Layer Precursor (C')
A container was charged with 100 parts of thermosetting resin P5, 80 parts of conductive filler M1, and 20 parts of curing agent H1 calculated as solid contents, and a mixed solvent (toluene:isopropyl alcohol=2:1 (mass ratio)) was added so that the non-volatile content concentration was 40%, and the mixture was stirred with a disper for 10 minutes to obtain an adhesive composition.
The obtained adhesive composition was applied to the metal (plating) layer of "peeling sheet/protective layer precursor (A')/metal (plating) layer" using a bar coater so as to have a dry thickness of 10 μm, and dried for 2 minutes in an electric oven at 100° C. to form a bonding layer precursor (C'), thereby obtaining an electromagnetic wave shielding sheet precursor. The dry thickness of the bonding layer precursor (C') was measured using the same method as for the protective layer precursor (A').

[Examples 2 to 34, Comparative Examples 1 to 4]
As shown in Tables 1 to 3, the electromagnetic wave shielding sheets of Examples 2 to 34 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that the types of protective layer precursor (A') and bonding layer precursor (C') were changed.
In addition, for Examples 20 to 34, the release sheet used for producing the protective layer (A) was previously buffed and Spk, Sa, and Str were adjusted.

[Example 35]
As shown in Table 3, a first intermediate laminate having a structure of "release sheet/protective layer precursor (A')" similar to that of Example 1 was prepared.
A copper foil with a carrier film, in which a copper foil with a thickness of 4 μm was formed on a carrier film with a thickness of 25 μm, was separately prepared and laminated so that the surface where the protective layer precursor (A′) of the above-mentioned “release sheet/protective layer precursor (A′)” was exposed was in contact with the copper foil surface, to prepare a second intermediate laminate having a configuration of “release sheet/protective layer precursor (A′)/copper foil/carrier film.” The lamination was performed at a temperature of 90° C. and a pressure of 3 kgf/cm ² using a thermal laminator.
As shown in Table 3, the same adhesive resin composition as in Example 1 was prepared.
The carrier film was peeled off from the second intermediate laminate, and the adhesive resin composition was applied onto the copper foil of the "peelable sheet/protective layer precursor (A')/copper foil" to a dry thickness of 10 μm, and dried in an electric oven at 100° C. for 2 minutes to form a bonding layer precursor (C'), thereby obtaining an electromagnetic wave shielding sheet precursor.

[Example 36]
An electromagnetic wave shielding sheet precursor was obtained in the same manner as in Example 1, except that a copper vapor deposition process was performed instead of electrolytic copper plating to form a copper vapor deposition layer (0.5 μm) as the metal layer (B-1) on the protective layer precursor (A').

[Example 37]
As shown in Table 3, a first intermediate laminate having a structure of "release sheet/protective layer precursor (A')" similar to that of Example 1 was prepared.
<<Preparation of Shield Layer (B) (Conductive Resin Layer Precursor (B-2′))>>
A container was charged with 100 parts of thermosetting resin P1, 490 parts of conductive filler M2, and 20 parts of curing agent H1 in terms of solid content, and a mixed solvent (toluene:isopropyl alcohol=2:1 (mass ratio)) was added so that the non-volatile content concentration was 40%, and the mixture was stirred with a disper for 10 minutes to obtain a conductive resin composition.
The obtained conductive resin composition was applied onto a release sheet using a bar coater so as to have a dry thickness of 3 μm, and then dried for 2 minutes in an electric oven at 100° C. to prepare a third intermediate laminate having a configuration of "release sheet/conductive resin layer precursor (B-2')". The dry thickness of the conductive resin layer precursor (B-2') was measured by the same method as for the protective layer precursor (A').
The conductive resin layer precursor (B-2') of the obtained third intermediate laminate "peelable sheet/conductive resin layer precursor (B-2')" was bonded to the surface of the first intermediate laminate on which the protective layer precursor (A') was exposed, and then the release sheet on the conductive resin layer precursor (B-2') side was removed to obtain a fourth intermediate laminate having a configuration of "peelable sheet/protective layer precursor (A') 37/conductive resin layer precursor (B-2')."
<<Preparation of bonding layer (C)>>
As shown in Table 5, an adhesive resin composition similar to that in Example 1 was prepared.
The adhesive resin composition was applied onto the conductive resin layer precursor (B-2') of the fourth intermediate laminate, and dried in an electric oven at 100°C for 2 minutes to form a bonding layer precursor (C'), thereby obtaining an electromagnetic wave shielding sheet precursor.

[Example 38]
As shown in Table 3, a first intermediate laminate having a structure of "release sheet/protective layer precursor (A')" similar to that of Example 1 was prepared.
<<Preparation of Shield Layer (B) (Conductive Resin Layer Precursor (B-2′))>>
A container was charged with 100 parts of thermosetting resin P1, 220 parts of conductive filler M2, and 20 parts of curing agent H1 in terms of solid content, and a mixed solvent (toluene:isopropyl alcohol=2:1 (mass ratio)) was added so that the non-volatile content concentration was 40%, and the mixture was stirred with a disper for 10 minutes to obtain a conductive resin composition.
The obtained conductive resin composition was coated onto a release sheet using a bar coater to a dry thickness of 15 μm, and then dried in an electric oven at 100° C. for 2 minutes to prepare a third intermediate laminate having a configuration of “release sheet/conductive resin layer precursor (B-2′)”.
The dry thickness of the conductive resin layer precursor (B-2') was measured in the same manner as in the protective layer precursor (A').
The conductive resin layer precursor (B-2') of the obtained third intermediate laminate "peelable sheet/conductive resin layer precursor (B-2')" was bonded to the exposed surface of the protective layer precursor (A') of the first intermediate laminate to obtain an electromagnetic wave shielding sheet precursor.

Preparation of evaluation samples
A polyimide film (Kapton (registered trademark), 200H, 50 μm) was attached to the bonding layer precursor (C) side of the electromagnetic shielding sheet precursor obtained in Examples 1 to 38 and Comparative Examples 1 to 4, and hot-pressed for 30 minutes under conditions of 170° C. and 2 MPa. Thereafter, the release sheet on the protective layer (A) side was peeled off to obtain an evaluation sample for each Example and Comparative Example.

<Coefficient of kinetic friction>
The dynamic friction coefficient of the protective layer (A) of the evaluation sample was measured using HEIDON (manufactured by Shinto Scientific Co., Ltd.). A weight of 100 g supported by three steel balls was attached to the protective layer (A) of the test piece, and pulled over the protective layer (A) at a speed of 60 cm/min to measure the dynamic friction coefficient of the protective layer (A) surface. The average value of the measurements at five different points was taken as the dynamic friction coefficient.

"Pencil hardness"
The pencil hardness of the surface of the protective layer (A) of the evaluation sample was measured by a pencil hardness test at a load of 750 g in accordance with JIS K5600-5-4.

<<Protruding peak height (Spk), arithmetic mean height (Sa), aspect ratio of surface texture (Str)>>
The height (Spk) of the protruding peaks on the surface of the protective layer (A) of the evaluation sample, the arithmetic mean height (Sa), and the aspect ratio (Str) of the surface properties were determined by the following methods.
Using a confocal microscope (manufactured by Lasertec, OPTELICS HYBRID+, objective lens 20x, white confocal), any five points of the protective layer (A) of the evaluation sample were measured, and then the surface inclination was corrected using data analysis software (LMeye8), and the surface properties were measured in accordance with ISO 25178-6: 2010 to obtain the average value. The cutoff wavelength of the S filter was 0.0025 mm, and the cutoff wavelength of the L filter was 0.8 mm.

<Blocking resistance>
Two evaluation samples with a width of 10 cm and a length of 10 cm were prepared and overlapped with each other with the protective layer (A) surface facing each other. The top and bottom were sandwiched between glass plates with a width of 15 cm, a length of 15 cm, and a thickness of 2 mm, and a weight of 2 kg was placed on the samples and the samples were left in an atmosphere at 50° C. for 24 hours. The evaluation samples were then separated from each other from the overlapping surfaces, and the blocking resistance was evaluated according to the following criteria.
⊚: No defects in appearance occurred in either protective layer (A). Excellent.
Good: One of the protective layers (A) is partially lifted.
Δ: Part of both protective layers (A) is lifted.
×: One or both are torn. Not usable.

<Tear resistance>
A sample having a width of 10 cm and a length of 10 cm was prepared, a stainless steel plate (SUS304, hairline finish, width of 5 cm, length of 5 cm, thickness of 100 μm) was placed on the surface of the protective layer (A), and a weight of 100 g was placed on the stainless steel plate, and the stainless steel plate was moved back and forth 10 times at 3 cm per time. The stainless steel plate was then removed, and the number of scratches on the surface of the protective layer (A) was visually counted, and the tear resistance was evaluated according to the following criteria.
⊚: The number of scratches is 10 or less. Excellent.
A: The number of scratches is 11 or more and 20 or less. Good.
Δ: The number of scratches is 21 to 30. Usable.
×: The number of scratches is 31 or more. Not usable.

<Dust resistance>
The evaluation samples (10 cm wide x 10 cm long) of each Example and Comparative Example were divided into 5 x 5 array-shaped sections by cutting, and then placed in a dust tester (DT-1-CF, manufactured by Suga Test Instruments) and exposed to dust for 60 minutes. As the test powder, 11 types of test powder (Kanto loam) specified in JIS Z8901 were used.
After removing the evaluation sample for dust exposure, the accumulated dust was removed with an air duster, and each section in the 5 x 5 array was observed one by one to check for the presence or absence of remaining dust, and the evaluation was performed as follows.
⊚: No residual dust was observed in any of the sections. Excellent.
◯: The number of sections in which dust remained was 1 or more and less than 3 out of 25 sections. Good.
△: Dust residue was observed in 3 or more but less than 5 of the 25 sections. Usable.
×: Dust residue was found in 5 or more sections. Not suitable for practical use.

According to the present disclosure, as shown in the present embodiment, it is possible to provide an electromagnetic wave shielding sheet that has high blocking resistance and excellent tear resistance and dust resistance.

The electromagnetic wave shielding sheet of the present disclosure can be used not only for FPCs but also for rigid printed wiring boards, COF, TAB, flexible connectors, liquid crystal displays, touch panels, etc. It can also be widely used in various applications that require electromagnetic wave shielding, such as computer cases, building materials such as walls and window glass, and electromagnetic wave blocking materials for vehicles, ships, aircraft, etc. The printed wiring board of the present disclosure can be mounted and used in electronic devices such as liquid crystal displays, touch panels, etc., as well as notebook PCs, mobile phones, smartphones, tablet terminals, etc.

1': electromagnetic wave shielding sheet precursor 2: electromagnetic wave shielding sheet,
10: printed wiring board,
11: insulating substrate,
12: circuit pattern,
12a: signal wiring,
12b: ground wiring,
13: cover coat layer,
14: Via 20: Printed wiring board with electromagnetic shielding sheet

(3) (Protruding peak height (Spk) of protective layer (A))
The protruding peak height (Spk) of the other surface of the protective layer (A) of this sheet, measured in accordance with ISO 25178-2:2012 , is 0.001 or more and less than 10 μm.

Claims (5)

An electromagnetic wave shielding sheet having a shielding layer (B) disposed on one surface of a protective layer (A),
An electromagnetic wave shielding sheet, the other surface of the protective layer (A) satisfying the following (1) to (3).
(1) The dynamic friction coefficient is 0.01 to 0.9.
(2) The pencil hardness measured in accordance with JIS K 5600 is HB to 9H.
(3) The protruding peak height (Spk) determined in accordance with ISO 25178-2:2012 is 0.001 μm or more and less than 10 μm. The electromagnetic shielding sheet according to claim 1, wherein the arithmetic mean height (Sa) of the other surface of the protective layer (A) determined in accordance with ISO 25178-2:2012 is 0.01 to 9 μm. The electromagnetic shielding sheet according to claim 1, wherein the aspect ratio (Str) of the surface properties of the other surface of the protective layer (A) determined in accordance with ISO 25178-2:2012 is 0.3 to 1.0. A printed wiring board with an electromagnetic shielding sheet comprising the electromagnetic shielding sheet according to any one of claims 1 to 3. An electronic device comprising the printed wiring board with the electromagnetic shielding sheet according to claim 4.