WO2024185835A1

WO2024185835A1 - Laminate and electromagnetic wave shielding film

Info

Publication number: WO2024185835A1
Application number: PCT/JP2024/008646
Authority: WO
Inventors: 洋平芝田
Original assignee: タツタ電線株式会社
Priority date: 2023-03-08
Filing date: 2024-03-07
Publication date: 2024-09-12

Abstract

Provided is a laminate having a sufficiently high peelability of an adhesive layer and low manufacturing cost. A laminate according to the present invention is characterized by comprising: a protective layer having a first main surface that is not subjected to release treatment; and an adhesive layer that contains an adhesive component and a filler and is laminated so as to be in contact with the first main surface, wherein the filler has a bulk density of 7-23 mL/g, and when the weight of the adhesive component included in the adhesive layer is 100 parts by weight, the adhesive layer contains 2-75 parts by weight of the filler.

Description

Laminate and electromagnetic wave shielding film

The present invention relates to a laminate and an electromagnetic wave shielding film.

Flexible printed circuit boards are widely used to incorporate circuits into the complex mechanisms of electronic devices such as mobile phones, video cameras, and laptops, which are rapidly becoming smaller and more functional. Furthermore, taking advantage of their excellent flexibility, they are also used to connect moving parts such as printer heads to control units.

In such electronic devices, a bonding film made of an adhesive layer is used to bond components together.
Usually, a bonding film is manufactured as a laminate by laminating an adhesive layer on a protective layer (separator). The protective layer is used as a base for molding the adhesive layer, and after the laminate is manufactured, it functions as a layer that protects the adhesive layer during transportation.

Such a laminate is finally used after the adhesive layer is peeled off from the protective layer.
When peeling the adhesive layer from the protective layer, parts of the adhesive layer and the protective layer may adhere to each other, causing heavy peeling between the adhesive layer and the protective layer, making it impossible to peel them normally, and the adhesive layer may be destroyed if peeled off forcibly.
In order to eliminate such problems and improve the releasability of the adhesive layer, a release treatment is sometimes applied to the surface of the protective layer on which the adhesive layer is laminated.

As a method for producing a laminate in which a protective layer (substrate) has been subjected to a release treatment, Patent Document 1 discloses a method for producing an active energy ray-curable adhesive film or sheet in which a release-treated substrate, an active energy ray-curable adhesive layer, and a release-treated substrate are formed in this order.

JP 2020-097660 A

As disclosed in Patent Document 1, applying a release treatment to the protective layer (substrate) improves releasability, but there is a problem in that the release treatment is costly.

The present invention was made in consideration of the above problems, and the object of the present invention is to provide a laminate having sufficiently high peelability of the adhesive layer and low manufacturing costs.

The inventors discovered that by adding a predetermined amount of a filler having predetermined parameters to the adhesive layer, the adhesiveness of the adhesive layer can be appropriately reduced, thereby improving the peelability, and thus completed the present invention.
That is, the laminate of the present invention comprises a protective layer having a first main surface that is not release-treated, and an adhesive layer containing an adhesive component and a filler and laminated so as to contact the first main surface, wherein the bulk density of the filler is 7 to 23 mL/g, and the adhesive layer contains 2 to 75 parts by weight of the filler, assuming that the weight of the adhesive component contained in the adhesive layer is 100 parts by weight.

In the laminate of the present invention, the adhesive layer contains a filler, which increases the strength of the adhesive layer and makes it less susceptible to breakage.
In addition, a part of the filler is located on the surface of the adhesive layer. The adhesiveness of the adhesive layer depends on the adhesive component contained in the adhesive layer. When a part of the filler is located on the surface of the adhesive layer, the area of the adhesive component constituting the surface of the adhesive layer becomes small. Therefore, the adhesiveness of the adhesive layer becomes moderately low, and the adhesive layer and the protective layer become easily peeled off.

The laminate of the present invention contains a filler, and the filler has a bulk density of 7 to 23 mL/g.
When the bulk density of the filler is within the above range, the filler has an appropriate size, and a part of the filler is likely to be located on the surface of the adhesive layer.
If the bulk density of the filler is less than 7 mL/g, it will be difficult for part of the filler to be located on the surface of the adhesive layer, the adhesiveness of the adhesive layer will not decrease sufficiently, and the adhesive layer will be difficult to peel off from the protective layer.
If the bulk density of the filler exceeds 23 mL/g, a portion of the filler is likely to be located on the surface of the adhesive layer, the adhesive layer will have too little adhesion, and will be prone to falling off from the protective layer.

In this specification, the "bulk density of the filler" refers to a method measured by the following method.
First, 5 g of the filler is prepared. Next, the prepared filler is poured into a measuring cylinder without applying compaction stress. Next, the top surface of the filler layer poured into the measuring cylinder is carefully smoothed without compaction, and the loosely packed volume is read. The value obtained by dividing the loosely packed volume by 5 g is the "bulk density of the filler."

In the laminate of the present invention, the adhesive layer contains 2 to 75 parts by weight of the filler, assuming that the weight of the adhesive component contained in the adhesive layer is 100 parts by weight.
When the content of the filler is within the above range, the content of the filler is appropriate, and the filler is likely to be located on a portion of the surface of the adhesive layer.
If the content of the filler is less than 2 parts by weight, a portion of the filler is unlikely to be located on the surface of the adhesive layer, the adhesiveness of the adhesive layer is not sufficiently reduced, and the adhesive layer is unlikely to peel off from the protective layer.
If the content of the filler exceeds 75 parts by weight, the proportion of the adhesive component decreases, making it difficult to form an adhesive layer.

In the laminate of the present invention, the first main surface of the protective layer is not subjected to a release treatment. If an adhesive layer is laminated on the first main surface of such a protective layer, the adhesive layer becomes difficult to peel off.
However, in the laminate of the present invention, since the adhesive layer contains the above-mentioned filler, the peelability of the adhesive layer is sufficiently improved.
Furthermore, since the first main surface of the protective layer is not subjected to a release treatment, the manufacturing cost of the laminate is reduced.

In the laminate of the present invention, the adhesive layer may further contain a conductive filler, and the adhesive layer may have electrical conductivity.
The adhesive layers of such laminates are useful for electrically connecting electronic components together.

In the laminate of the present invention, the particle size (D ₅₀ ) of the filler is preferably 0.014 to 20 μm.
If the particle size ( _D50 ) of the filler is less than 0.014 μm, the filler will be too small, making it difficult for a part of the adhesive layer to be located on the surface, and the adhesiveness of the adhesive layer will not decrease sufficiently, making it difficult for the adhesive layer to peel off from the protective layer.
If the particle size (D ₅₀ ) of the filler exceeds 20 μm, a part of the filler is likely to be located on the surface of the adhesive layer, and the adhesive layer will have too low adhesion, making it prone to falling off from the protective layer.
In this specification, the particle size (D ₅₀ ) of the filler can be measured by a laser diffraction particle size distribution measuring device.
The average diameter (D ₅₀ ) of the conductive filler, which will be described later, is measured in the same manner.

In the laminate of the present invention, the filler particles may have insulating properties.
The filler particles are preferably at least one type selected from the group consisting of silica, talc, mica, and organic fillers.
When the filler particles are made of these materials, the effect of improving the releasability of the adhesive layer can be suitably obtained.
Furthermore, these materials are low in cost, which allows for low manufacturing costs for the laminate.

The laminate of the present invention may be used as a bonding film.
In the laminate of the present invention, the adhesive layer can be easily peeled off from the protective layer, so that the laminate can be suitably used as a bonding film.

The electromagnetic wave shielding film of the present invention is characterized by comprising the laminate of the present invention and a shielding layer formed on the surface of the adhesive layer on the side of the laminate that is not in contact with the protective layer.

Since the electromagnetic wave shielding film of the present invention includes the laminate of the present invention, the adhesive layer can be easily peeled off from the protective layer, and therefore the electromagnetic wave shielding film of the present invention is easy to handle.
In addition, since the first main surface of the protective layer is not subjected to a release treatment, the production cost of the electromagnetic wave shielding film is reduced.

The present invention makes it possible to provide a laminate in which the adhesive layer has sufficiently high peelability and low manufacturing costs.

FIG. 1 is a cross-sectional view that illustrates an example of a laminate according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view that illustrates an example of an electromagnetic wave shielding film according to a second embodiment of the present invention.

The laminate and electromagnetic shielding film of the present invention are specifically described below. However, the present invention is not limited to the following embodiments, and can be modified as appropriate within the scope of the present invention.

First Embodiment
First, a laminate according to a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view that illustrates an example of a laminate according to a first embodiment of the present invention.
As shown in FIG. 1, the laminate 10 comprises a protective layer 20 having a first main surface 21 that has not been release treated, and an adhesive layer 30 that includes an adhesive component 31 and a filler 32 and is laminated so as to contact the first main surface 21.
As described below, the filler 32 has a predetermined bulk density and is contained in the adhesive layer 30 in a predetermined amount.

When the adhesive layer 30 contains the filler 32, the strength of the adhesive layer 30 increases and it becomes less susceptible to breakage.

As shown in FIG. 1 , in the adhesive layer 30 , a part of the filler 32 is located on the surface of the adhesive layer 30 .
Here, the adhesiveness of the adhesive layer 30 depends on the adhesive component 31 contained in the adhesive layer 30. When a part of the filler 32 is located on the surface of the adhesive layer 30, the area of the adhesive component 31 constituting the surface of the adhesive layer 30 becomes small. Therefore, the adhesiveness of the adhesive layer 30 becomes appropriately low, and the adhesive layer 30 and the protective layer 20 become easily peeled off from each other.

In the laminate 10, the bulk density of the filler 32 is 7 to 23 mL/g. The bulk density of the filler 32 is preferably 7.4 to 22 mL/g, and more preferably 12 to 22 mL/g.
When the bulk density of the filler 32 is within the above range, the filler 32 has an appropriate size, and a part of the filler 32 is likely to be located on the surface of the adhesive layer 30 .
If the bulk density of the filler is less than 7 mL/g, it will be difficult for part of the filler to be located on the surface of the adhesive layer, the adhesiveness of the adhesive layer will not decrease sufficiently, and the adhesive layer will be difficult to peel off from the protective layer.
If the bulk density of the filler exceeds 23 mL/g, a portion of the filler is likely to be located on the surface of the adhesive layer, the adhesive layer will have too little adhesion, and will be prone to falling off from the protective layer.

In the laminate 10, when the weight of the adhesive component 31 contained in the adhesive layer 30 is taken as 100 parts by weight, the adhesive layer 30 contains 2 to 75 parts by weight of the filler 32. The content of the filler 32 is preferably 5 to 50 parts by weight, and more preferably 10 to 50 parts by weight.
When the content of the filler 32 is within the above range, the content of the filler 32 is appropriate, and a part of the filler 32 is likely to be located on the surface of the adhesive layer 30 .
If the content of the filler is less than 2 parts by weight, a portion of the filler is unlikely to be located on the surface of the adhesive layer, the adhesiveness of the adhesive layer is not sufficiently reduced, and the adhesive layer is unlikely to peel off from the protective layer.
If the content of the filler exceeds 75 parts by weight, the proportion of the adhesive component decreases, making it difficult to form an adhesive layer.

In the laminate 10, the first main surface 21 of the protective layer 20 is not subjected to a release treatment. When the adhesive layer 30 is laminated on the first main surface 21 of such a protective layer 20, the adhesive layer 30 becomes difficult to peel off.
However, in the laminate 10, since the adhesive layer 30 contains the filler 32, the peelability of the adhesive layer 30 is sufficiently improved.

The components of the laminate of the present invention are described in detail below.

(Protective Layer)
In the laminate of the present invention, the material constituting the protective layer is not particularly limited as long as it serves as a base when the adhesive layer is formed and can protect the adhesive layer. For example, thermoplastic resin compositions such as a styrene-based resin composition, a vinyl acetate-based resin composition, a polyester-based resin composition, a polyethylene-based resin composition, a polypropylene-based resin composition, an imide-based resin composition, an amide-based resin composition, and an acrylic-based resin composition, as well as resins such as a phenol-based resin composition, an epoxy-based resin composition, a urethane-based resin composition, a melamine-based resin composition, and an alkyd-based resin composition can be used.

The thickness of the protective layer is not particularly limited, but is preferably from 5 to 60 μm, and more preferably from 10 to 50 μm.
When the thickness of the protective layer is within the above range, the protective layer becomes easy to handle.
If the thickness of the protective layer is less than 5 μm, the strength of the protective layer will be weak, making it difficult to protect the adhesive layer.
If the thickness of the protective layer exceeds 60 μm, the protective layer becomes too thick and difficult to handle.

In the laminate of the present invention, the protective layer may further contain additives such as carbon black, silica, and organic fillers.

(Adhesive Layer)
In the laminate of the present invention, the thickness of the adhesive layer is preferably from 5 to 40 μm, and more preferably from 8 to 30 μm.
If the thickness of the adhesive layer is less than 5 μm, the strength of the adhesive layer will be low and the adhesive layer will be easily damaged when peeled off from the protective layer.
If the thickness of the adhesive layer exceeds 40 μm, the adhesive layer becomes too thick and difficult to handle, and the flexibility of the adhesive layer decreases.

In the laminate of the present invention, the surface roughness (Ra) of the surface of the adhesive layer which comes into contact with the protective layer is preferably 0.62 to 1.95 μm, and more preferably 0.7 to 1.7 μm.
When the surface roughness (Ra) of the surface of the adhesive layer that comes into contact with the protective layer is within the above range, the adhesion between the protective layer and the adhesive layer is at an appropriate level, and the protective layer and the adhesive layer are easily peeled off from each other.
The surface roughness (Ra) of the surface of the adhesive layer in contact with the protective layer can be measured by peeling the protective layer from the laminate and exposing the surface of the adhesive layer in contact with the protective layer.
The surface roughness (Ra) of the surface of the adhesive layer in contact with the protective layer refers to a value measured using a confocal microscope (OPTELICS HYBRID, manufactured by Lasertec) with an objective lens of 50x.

In the laminate of the present invention, examples of adhesive components contained in the adhesive layer include thermoplastic resin compositions such as styrene-based resin compositions, vinyl acetate-based resin compositions, polyester-based resin compositions, polyethylene-based resin compositions, polypropylene-based resin compositions, imide-based resin compositions, amide-based resin compositions, and acrylic-based resin compositions, and thermosetting resin compositions such as phenol-based resin compositions, epoxy-based resin compositions, urethane-based resin compositions, melamine-based resin compositions, and alkyd-based resin compositions.

As will be described in detail later, in the laminate of the present invention, the adhesive layer may contain a conductive filler and may have electrical conductivity.
In this case, the adhesive component preferably has a relative dielectric constant of 1-5, more preferably 2-4, at a frequency of 1 GHz and 23°C.
The adhesive component preferably has a dielectric loss tangent at a frequency of 1 GHz and at 23° C. of 0.0001 to 0.03, and more preferably 0.001 to 0.002.
Within such a range, when the laminate of the present invention is used as a bonding film for electrically connecting electronic components to each other, the transmission characteristics can be improved.

In the laminate of the present invention, the shape of the filler contained in the adhesive layer is not particularly limited, but can be appropriately selected from spherical, flat, scale-like, dendritic, rod-like, fibrous, etc.

In the laminate of the present invention, the particle size (D ₅₀ ) of the filler is preferably from 0.014 to 20 μm, more preferably from 1 to 9 μm, and even more preferably from 2 to 9 μm.
If the particle size ( _D50 ) of the filler is less than 0.014 μm, the filler will be small, making it difficult for a portion of the filler to be located on the surface of the adhesive layer, so that the adhesive property of the adhesive layer will not decrease sufficiently and the adhesive layer will not easily peel off from the protective layer.
If the particle size (D ₅₀ ) of the filler exceeds 20 μm, a part of the filler is likely to be located on the surface of the adhesive layer, the adhesive layer has too low adhesion, and is likely to fall off from the protective layer.

In the laminate of the present invention, the filler may have insulating properties.
The filler is preferably at least one selected from the group consisting of silica, talc, mica and organic fillers, with silica being preferred among these.
When the filler is made of these materials, the effect of improving the releasability of the adhesive layer can be suitably obtained.
Furthermore, these materials are low in cost, which allows for low manufacturing costs for the laminate.

The conductive filler is not particularly limited, but may be metal particles, carbon nanotubes, carbon fibers, metal fibers, or the like.
Of these, metal particles are preferred.
The metal particles are not particularly limited, but may be silver powder, copper powder, nickel powder, solder powder, aluminum powder, silver-coated copper powder obtained by plating copper powder with silver, or particles of polymer microparticles or glass beads coated with metal.
Among these, from the viewpoint of economy, copper powder or silver-coated copper powder, which is inexpensively available, is preferable.

The shape of the conductive filler is not particularly limited, but can be appropriately selected from spherical, flat, scale-like, dendritic, rod-like, fibrous, etc.

When the adhesive layer contains a conductive filler, the adhesive layer preferably contains 1 to 100 parts by weight of the conductive filler, more preferably 5 to 70 parts by weight, and even more preferably 20 to 40 parts by weight, based on 100 parts by weight of the adhesive component.
If the content of the conductive filler is less than 1 part by weight, the amount of the conductive filler that imparts electrical conductivity to the adhesive layer is reduced, resulting in a decrease in the electrical conductivity of the entire adhesive layer.
If the content of the conductive filler exceeds 100 parts by weight, the proportion of the adhesive component decreases, so that the flexibility and adhesive strength of the adhesive layer decrease.

The particle size (D ₅₀ ) of the conductive filler is preferably from 9 to 30 μm, and more preferably from 12 to 20 μm.
If the particle size (D ₅₀ ) of the conductive filler is less than 9 μm, the conductive filler is likely to be displaced, and the connection reliability is likely to decrease.
If the particle size (D ₅₀ ) of the conductive filler exceeds 30 μm, the adhesive layer becomes too thick.

When the adhesive layer contains a conductive filler and has electrical conductivity, the adhesive layer may have isotropic electrical conductivity or anisotropic electrical conductivity.
Whether the adhesive layer has isotropic conductivity or anisotropic conductivity can be adjusted by adjusting the content and size of the conductive filler.

The adhesive layer may contain, as necessary, a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, an antifoaming agent, a leveling agent, a filler, a flame retardant, a viscosity adjuster, an antiblocking agent, etc.

Second Embodiment
Next, an electromagnetic wave shielding film according to a second embodiment of the present invention will be described with reference to the drawings.
FIG. 2 is a cross-sectional view that illustrates an example of an electromagnetic wave shielding film according to a second embodiment of the present invention.

The electromagnetic wave shielding film 11 shown in FIG. 2 is characterized by comprising a laminate 10 according to the first embodiment of the present invention described above, and a shielding layer 40 formed on the surface of the adhesive layer 30 on the side of the laminate 10 that is not in contact with the protective layer 20.

Since the electromagnetic wave shielding film 11 includes the laminate 10, the adhesive layer 30 can be easily peeled off from the protective layer 20. Therefore, the electromagnetic wave shielding film 11 is easy to handle.
In addition, since the first main surface 21 of the protective layer 20 is not subjected to a release treatment, the manufacturing cost of the electromagnetic wave shielding film 11 is reduced.

When the electromagnetic wave shielding film 11 is used, the protective layer 20 is peeled off and the film 11 is attached to an adherend such as a printed wiring board so that the adhesive layer 30 comes into contact with the adherend.
Since the electromagnetic wave shielding film 11 has the shielding layer 40, it can protect an adherend from electromagnetic waves.

In the electromagnetic wave shielding film 11, the preferred configuration of the laminate 10 is the same as the preferred configuration of the laminate according to the first embodiment of the present invention described above, so a description thereof will be omitted here.

In the electromagnetic wave shielding film 11, the material of the shielding layer 40 is not particularly limited as long as it has the function of shielding electromagnetic waves.
For example, the shield layer 40 may be made of a metal layer, a conductive adhesive layer, or the like.

When the shield layer 40 is made of a metal layer, the metal layer is preferably made of gold, silver, copper, aluminum, nickel, tin, palladium, chromium, titanium, zinc, etc. Of these, copper is more preferable.
The metal layer may also be made of an alloy of these.

Such a metal layer may be formed by methods such as sputtering, electroless plating, or electrolytic plating, and may be made of rolled metal.

The thickness of the shield layer 40 is preferably 0.01 to 10 μm.
If the thickness of the shielding layer is less than 0.01 μm, it is difficult to obtain a sufficient shielding effect.
If the thickness of the shield layer exceeds 10 μm, the flexibility decreases.

In the electromagnetic wave shielding film of the present invention, an insulating protective layer may further be formed on the surface of the shielding layer opposite the adhesive layer.
If an insulating protective layer is formed, the shield layer can be protected.

The insulating protective layer is not particularly limited, but is preferably composed of a thermoplastic resin composition, a thermosetting resin composition, an active energy ray curable composition, or the like.

The above-mentioned thermoplastic resin composition is not particularly limited, but examples thereof include a styrene-based resin composition, a vinyl acetate-based resin composition, a polyester-based resin composition, a polyethylene-based resin composition, a polypropylene-based resin composition, an imide-based resin composition, and an acrylic-based resin composition.

The above-mentioned thermosetting resin composition is not particularly limited, but may be at least one resin composition selected from the group consisting of an epoxy-based resin composition, a urethane-based resin composition, a urethane urea-based resin composition, a styrene-based resin composition, a phenol-based resin composition, a melamine-based resin composition, an acrylic-based resin composition, and an alkyd-based resin composition.

The active energy ray-curable composition is not particularly limited, but examples thereof include polymerizable compounds having at least two (meth)acryloyloxy groups in the molecule.

The thickness of the insulating protective layer is preferably 1 to 12 μm.

The insulating protective layer may contain, as necessary, a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, an antifoaming agent, a leveling agent, a filler, a flame retardant, a viscosity adjuster, an antiblocking agent, etc.

This specification includes the following:

The present disclosure (1) is a laminate comprising a protective layer having a first main surface that is not release-treated, and an adhesive layer that contains an adhesive component and a filler and is laminated so as to contact the first main surface, the bulk density of the filler being 7 to 23 mL/g, and the adhesive layer containing 2 to 75 parts by weight of the filler when the weight of the adhesive component contained in the adhesive layer is 100 parts by weight.

The present disclosure (2) is a laminate according to the present disclosure (1), in which the adhesive layer further contains a conductive filler, and the adhesive layer has electrical conductivity.

The present disclosure (3) is the laminate according to the present disclosure (1) or (2), in which the particle diameter (D ₅₀ ) of the filler is 0.014 to 20 μm.

The present disclosure (4) is a laminate according to any one of the present disclosures (1) to (3), in which the filler has insulating properties.

The present disclosure (5) is a laminate according to any one of the present disclosures (1) to (4), in which the filler is at least one selected from the group consisting of silica, talc, mica, and organic fillers.

The present disclosure (6) is a laminate according to any one of the present disclosures (1) to (5) used as a bonding film.

The present disclosure (7) is an electromagnetic wave shielding film characterized by comprising a laminate according to any one of the present disclosures (1) to (5) and a shielding layer formed on the surface of the adhesive layer on the side of the laminate that is not in contact with the protective layer.

The following examples are provided to more specifically explain the present invention, but the present invention is not limited to these examples.

Example 1
First, a protective layer made of polypropylene resin and having a length x width x thickness of 300 mm x 200 mm x 40 μm was prepared.
The protective layer was not subjected to a release treatment.

Next, 100 parts by weight of a polyester resin, which is a thermoplastic resin, as an adhesive component, 10 parts by weight of silica particles (bulk density: 7.0 mL/g, particle size ( _D50 ): 2.7 μm) as a filler, and nickel particles (particle size ( _D50 ): 10.6 μm) as a conductive filler were mixed to prepare a conductive adhesive composition.

Then, a conductive adhesive composition was applied to the main surface of the protective layer to form an adhesive layer with a thickness of 20 μm.

Through the above steps, the laminate of Example 1 was manufactured.

(Example 2) to (Example 9) and (Comparative Example 1) to (Comparative Example 8)
Laminates according to Examples 2 to 9 and Comparative Examples 1 to 8 were produced in the same manner as in Example 1, except that the type and content of the filler were changed as shown in Table 1.

(Measurement of surface roughness (Ra) of the surface of the adhesive layer in contact with the protective layer)
In each of the laminates according to the examples and comparative examples, the protective layer was peeled off, and the surface roughness (Ra) of the adhesive layer in contact with the protective layer was measured using a confocal microscope (OPTELICS HYBRID, manufactured by Lasertec). The measurement was performed using a 50x objective lens. The results are shown in Table 1.

(Evaluation of peelability: Observation of zipping)
A portion of the adhesive layer at an end of the laminate of each Example and Comparative Example was peeled off with fingers, and then the peeled portion of the adhesive layer was pinched with the fingers to peel off the adhesive layer and the protective layer.
Thereafter, the peeled adhesive layer was visually observed to see whether or not zipping occurred. The results are shown in Table 1.
The evaluation criteria are as follows:
⊚: No zipping occurred.
◯: A small amount of zipping occurred, but it was not a problem for practical use.
×: Zipping occurred, and there was a problem in practical use.

(Removability evaluation: peeling force measurement)
The electromagnetic wave shielding film was pressed using a press under the following conditions: temperature: 170°C, time: 30 minutes, and pressure: 2 to 3 MPa. After the electromagnetic wave shielding film returned to room temperature, the peel strength of the transfer film was measured using a peel strength tester (PFT50S, manufactured by Palmec Co., Ltd.). The measurement was performed at room temperature, with a tensile speed of 1000 mm/min and a peel angle of 170°. The measurement was performed five times to determine the maximum value.

As shown in Table 1, in the laminates according to each Example, no zipping occurred and the peel force was sufficiently low.
It was also found that zipping occurs when the bulk density of the filler is less than 7 mL/g or when the content of the filler is less than 2 parts by weight per 100 parts by weight of the adhesive component. It was also found that the peel force is too high. This is believed to be due to the adhesion between the protective layer and the adhesive layer being too high.
It was also found that when the content of the filler exceeds 75 parts by weight per 100 parts by weight of the adhesive component, the adhesive strength of the adhesive layer decreases, making it impossible to form a laminate.

REFERENCE SIGNS LIST 10 Laminate 11 Electromagnetic wave shielding film 20 Protective layer 21 First main surface 30 Adhesive layer 31 Adhesive component 32 Filler 40 Shielding layer

Claims

a protective layer having a first main surface that is not release-treated;
an adhesive layer including an adhesive component and a filler and laminated so as to contact the first main surface;
The bulk density of the filler is 7 to 23 mL/g;
A laminate, characterized in that the adhesive layer contains 2 to 75 parts by weight of the filler, assuming that the weight of the adhesive component contained in the adhesive layer is 100 parts by weight.
The laminate of claim 1, wherein the adhesive layer further contains a conductive filler, and the adhesive layer is conductive.
3. The laminate according to claim 1, wherein the particle diameter (D 50 ) of the filler is 0.014 to 20 μm.
The laminate according to any one of claims 1 to 3, wherein the filler has insulating properties.
The laminate according to any one of claims 1 to 4, wherein the filler is at least one selected from the group consisting of silica, talc, mica, and organic fillers.
A laminate according to any one of claims 1 to 5, used as a bonding film.
A laminate according to any one of claims 1 to 5,
and a shielding layer formed on the surface of the adhesive layer on the side not in contact with the protective layer of the laminate.