JP2021014580A - Functional film, release film, and base film for adhesive sheet - Google Patents

Abstract

To provide a functional film comprising a polyolefin film having excellent release ability.SOLUTION: The present invention provides a functional film comprising a polyolefin film, at least one side of which has irregularities with a maximum height roughness Rz in a roughness curve of more than 30 μm. There are also provided a release film comprising the functional film and a base film for an adhesive sheet.SELECTED DRAWING: Figure 1a

Description

The present invention relates to a functional film in which irregularities are formed on a polyolefin film, and more particularly to a functional film suitable as a release film or a base film for an adhesive sheet.

Since the polyolefin film is excellent in transparency, mechanical properties, electrical properties, etc., it is used in various applications such as packaging applications, mold release applications, tape applications, and electrical applications such as cable wrapping and capacitors. In particular, since polypropylene film has relatively good releasability, it is used as a releasable film such as an adhesive sheet or a process film.

It has been proposed to roughen the surface of a release film made of a polyolefin film in order to transfer the unevenness of the release film to a molded product to impart design (for example, Patent Document 1).

JP-A-2018-204001

However, the release film made of the polyolefin film described in the above patent document does not fully satisfy the release property.

Therefore, an object of the present invention is to provide a functional film made of a polyolefin film having good releasability.

The above object of the present invention has been achieved by the following invention.
[1] A functional film made of a polyolefin film and having irregularities on at least one surface thereof having a maximum height roughness Rz of more than 30 μm in a roughness curve.
[2] The functional film according to [1], wherein the arithmetic average roughness Ra in the roughness curve of the surface having the unevenness is more than 6 μm.
[3] The functional film according to [1] or [2], wherein the average length RSm of the elements in the roughness curve of the surface having irregularities is more than 400 μm and 2000 μm or less.
[4] The functional film according to any one of [1] to [3], wherein the polyolefin film is an unstretched polyolefin film.
[5] The functional film according to any one of [1] to [4], wherein the Young's modulus in both the longitudinal direction and the width direction of the polyolefin film is less than 1,000 MPa.
[6] The normal peeling force (A) and the heat peeling force (B) of the surface having the uneven surface are both 1.0 N / 50 mm or less, and the heat peeling force (B) with respect to the normal peeling force (A) The functional film according to any one of [1] to [5], wherein the ratio (B / A) is 1.5 or less.
[7] The functional film according to any one of [1] to [6], wherein the polyolefin film is a polypropylene film.
[8] The functional film according to any one of [1] to [6], wherein the polyolefin film is a polyethylene film or a mixture film of polypropylene and polyethylene.
[9] A release film comprising the functional film according to any one of [1] to [8].
[10] A base film for an adhesive sheet, which comprises the functional film according to any one of [1] to [8].

According to the present invention, it is possible to provide a functional film made of a polyolefin film having good releasability. The functional film of the present invention is suitable as a release film or a base film for an adhesive sheet.

It is a schematic plan view of the silk-grained embossed roll. It is a schematic cross-sectional view seen along the line AA of FIG. 1a. It is a schematic plan view of the lattice-shaped embossed roll. It is a schematic cross-sectional view seen along the line AA of FIG. 2a.

Hereinafter, the present invention will be described in detail together with embodiments.
The functional film of the present invention comprises a polyolefin film. That is, the functional film of the present invention comprises only a polyolefin film, and other films other than the polyolefin film, for example, polyester film, acrylic film, cellulose film, polyimide film, fluorine film, polycarbonate film, polyurethane film. Resin film such as, and metal foil such as aluminum foil and copper foil are not included.

When another film is laminated or laminated on the polyolefin film, there are inconvenient problems such as poor adhesion between the polyolefin film and the other film, deterioration of moldability and punching processability, and reduction of productivity. May occur.

Further, the functional film of the present invention can obtain good releasability even if it is not surface-treated with a releasing agent such as a silicone compound, a long-chain alkyl compound, or a fluorine compound. Therefore, from the viewpoint of cost and productivity, it is preferable that the functional film of the present invention is not surface-treated with a release agent.

The functional film of the present invention is made of a polyolefin film, and has irregularities on at least one surface thereof having a maximum height roughness Rz of more than 30 μm in the roughness curve. Hereinafter, the maximum height roughness Rz in the roughness curve may be simply referred to as "Rz". Further, a surface having irregularities with an Rz of more than 30 μm may be referred to as an “uneven surface”.

Here, Rz is a physical property value based on a roughness curve measured in accordance with JIS-B0601 (2001).

The Rz of the functional film is preferably more than 40 μm, more preferably more than 50 μm, and particularly preferably more than 60 μm from the viewpoint of improving the releasability. The upper limit is about 150 μm.

Further, from the viewpoint of further improving the releasability, the functional film of the present invention preferably has an arithmetic average roughness Ra (hereinafter, may be referred to as “Ra”) on the roughness curve of the uneven surface of more than 6 μm. , 8 μm or more is more preferable, 10 μm or more is further preferable, and 13 μm or more is particularly preferable. Further, the Ra is preferably 50 μm or less, more preferably 40 μm or less, and particularly preferably 30 μm or less.

Further, in the functional film of the present invention, from the viewpoint of further improving the releasability, the average length RSm of the elements in the roughness curve of the uneven surface (hereinafter, may be referred to as “RSm”) is more than 400 μm. It is preferable, more than 500 μm is more preferable, and more than 700 μm is particularly preferable. The RSm is preferably 2000 μm or less, more preferably 1700 μm or less, and particularly preferably 1500 μm or less.

Here, Ra and RSm are physical property values based on the roughness curve measured in accordance with JIS-B0601 (2001).

When the Rz of the functional film is more than 30 μm, the releasability is improved. Here, the releasability can be expressed by, for example, the peeling force between the functional film and the adhesive tape. Specifically, the peeling force (normal peeling force) when the adhesive tape is attached to the uneven surface of the functional film and the adhesive tape side is peeled to 180 ° after 24 hours have passed at room temperature (23 ± 2 ° C). Can be represented.

The normal peeling force (A) is preferably 1.0 N / 50 mm or less, more preferably 0.7 N / 50 mm or less, and particularly preferably 0.5 N / 50 mm or less. The lower limit of the normal peeling force is about 0.01 N / 50 mm.

Further, although it may be required that the releasability after heating is good, the conventional general releasable film tends to have an increasing heat releasability with respect to the normal releasability. The functional film of the present invention has a feature that the rate of change of the heat peeling force with respect to the normal peeling force tends to be small. Here, the heat peeling force is the peeling force after the adhesive tape is attached to the uneven surface of the functional film and heated at 70 ° C. for 24 hours.

The heat peeling force (B) of the functional film of the present invention is preferably 1.0 N / 50 mm or less, more preferably 0.7 N / 50 mm or less, and particularly preferably 0.5 N / 50 mm or less. The lower limit of the heat peeling force is about 0.01 N / 50 mm.

In the functional film of the present invention, the ratio (B / A) of the heat peeling force (B) to the normal peeling force (A) is preferably 1.5 or less, more preferably 1.3 or less, and 1.2 or less. Especially preferable. The lower limit is about 0.3.

The functional film of the present invention can be obtained by forming irregularities on a polyolefin film. Examples of the method for forming the unevenness include embossing treatment, sandblasting treatment, and chemical treatment. Of these, embossing is preferred.

As the embossing treatment, for example, a method of pressing the heated embossed roll against the polyolefin film is preferable, and Rz can be controlled by adjusting the heating temperature and the pressing pressure of the embossed roll. The heating temperature of the embossed roll is preferably 80 ° C. to 150 ° C., more preferably 85 ° C. to 140 ° C., and particularly preferably 90 ° C. to 120 ° C.

The unevenness formed on the surface of the polyolefin film is not particularly limited as long as the Rz is more than 30 μm, and for example, silk-like, satin-like, dot-like, and lattice-like can be adopted. Among these, from the viewpoint of releasability, silk-like and lattice-like are preferable, and silk-like is particularly preferable.

An example of an embossed roll that can be used to form silk-like and lattice-like irregularities on the surface of a polyolefin film is shown below.

FIG. 1a is a schematic plan view of a silk-grained embossed roll, and FIG. 1b is a schematic cross-sectional view taken along the line AA of FIG. 1a. In this embossing roll, protrusions 11 of a quadrangular pyramid stand are provided at substantially the same pitch.

FIG. 2a is a schematic plan view of the grid-like embossed roll, and FIG. 2b is a schematic cross-sectional view taken along the line AA of FIG. 2a. The embossed roll is provided with grid-like protrusions 12 at substantially the same pitch.

Examples of the polyolefin constituting the polyolefin film of the present invention include polyethylene, polypropylene, or a mixture thereof.

Here, polyethylene includes homopolymers of ethylene and copolymers of ethylene with other olefins. In addition, polypropylene includes homopolymers of propylene and copolymers of propylene and other olefins.

Examples of the other olefins include ethylene, propylene, butene, pentene, hexene, heptene, octene, nonene, decene and the like. Among these, ethylene, propylene and butene are preferable.

The blending ratio of the other olefin in the above-mentioned copolymer of ethylene or propylene and the other olefin is preferably 40% by mass or less based on the total mass of ethylene or propylene as a monomer and the other olefin. It is more preferably 30% by mass or less, and particularly preferably 20% by mass or less.

Examples of the polyethylene include high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (L-LDPE).

The polyolefin film preferably contains at least polypropylene. Specifically, it preferably contains at least one selected from the group consisting of homopolymers of propylene and copolymers of propylene and other olefins.

Examples of the copolymer of propylene and other olefins include a copolymer of propylene and ethylene, a copolymer of propylene and butene, and a copolymer of propylene and ethylene and butene. These copolymers may be random copolymers or block copolymers. The blending ratio of other olefins in the above copolymer is preferably 40% by mass or less, more preferably 30% by mass or less, and 20% by mass or less, based on the total mass of propylene as a monomer and other olefins. Is particularly preferable.

In addition, the polyolefin film can contain a mixture of polypropylene and polyethylene. The content ratio of polypropylene in the mixture of polypropylene and polyethylene is preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more, based on the total mass of polypropylene and polyethylene. The content ratio is preferably 97% by mass or less.

The content ratio of polyethylene in the mixture of polypropylene and polyethylene is preferably 40% by mass or less, more preferably 30% by mass or less, and particularly preferably 20% by mass or less, based on the total mass of polypropylene and polyethylene. The content ratio is preferably 3% by mass or more.

The polyolefin film in the present invention may have a single-layer structure of polyolefin or a multi-layer structure of polyolefin.

Examples of the multi-layer laminated structure include a two-layer laminated structure of A layer / B layer and a three-layer laminated structure of A layer / B layer / A layer or A layer / B layer / C layer. Here, the A layer, the B layer, and the C layer have different compositions.

The polyolefin film may be an unstretched polyolefin film or a stretched polyolefin film. When the functional film of the present invention is used as a release film or a base film for an pressure-sensitive adhesive sheet, it is preferably a non-stretched polyolefin film. Details will be described later.

The polyolefin film is formed, for example, by cooling and solidifying a resin extruded into a sheet by a melt extruder with a casting roll. The unstretched polyolefin film is an unstretched film formed without stretching after cooling and solidification. The stretched polyolefin film is formed by being stretched in the uniaxial direction or the biaxial direction after being cooled and solidified.

The polyolefin film can contain particles, pigments, colorants, antistatic agents, UV absorbers, antioxidants, heat stabilizers, chlorine traps and the like. When the functional film of the present invention is applied as a release film, it is preferable to contain a pigment such as titanium oxide or a colorant in order to ensure distinctiveness for preventing forgetting to peel off.

The thickness of the polyolefin film is preferably 20 μm or more, more preferably 30 μm or more, and particularly preferably 40 μm or more. The thickness is preferably 150 μm or less, more preferably 100 μm or less, and particularly preferably 80 μm or less.

Polyolefin films are generally commercially available and they can be used. For example, from Toray Film Processing Co., Ltd., unstretched polypropylene film made of propylene homopolymer and unstretched polypropylene film made of copolymer polymer of propylene and other olefins are available as "Trefan (registered trademark)" NO (3301). , NO (3501), NO (9141), NO (3951), NO (9405S), NO (9407), NO (3701J), NO (3721), NO (ZK93KM), NO (ZK93FM), NO (ZK99S) , NO (ZK207), NO (ZK100), and stretched polypropylene films are commercially available as "Trefan (registered trademark)" BO (YT42), BO (YT62), BO (B128). Also, polyethylene films or mixed films of polypropylene and polyethylene are commercially available as "Tretec®" S500, 7932, 7332 and can be used. In addition, a mixture film of polypropylene and polyethylene is commercially available from Torei Tip Thin Film Co., Ltd. as "Tretec (registered trademark)" T001B, and can be used.

Further, the polyolefin film has a Young's modulus in both the longitudinal direction and the width direction preferably less than 1,000 MPa, more preferably less than 900 MPa, and particularly preferably less than 800 MPa. The lower limit of the Young's modulus is about 200 MPa.

Here, the longitudinal direction of the polyolefin film is a direction generally called the MD direction, which is the direction in which the film advances during film production, and the width direction is a direction generally called the TD direction, which is longitudinal. A direction that is orthogonal to the direction.

When a functional film made of a polyolefin film having a Young's modulus in both the longitudinal direction and the width direction of less than 1,000 MPa is applied as a release film to, for example, an adhesive sheet, the uneven type of the functional film (release film) adheres. It is possible to suppress the problem of transferring to a sheet and deteriorating the appearance. In particular, since the functional film of the present invention has relatively large irregularities with an Rz of more than 30 μm, the above problem tends to be promoted, but the Young's modulus in both the longitudinal direction and the width direction is 1. It is effectively suppressed by using a polyolefin film having a modulus of less than 000 MPa.

Since the Young's modulus of the unstretched polyolefin film tends to be smaller than that of the stretched polyolefin film, it is preferable to use the unstretched polyolefin film as the polyolefin film from the viewpoint of the Young's modulus.

Further, the unstretched polyolefin film is easier to process by embossing than the stretched polyolefin film.

Release film of the present invention, from the viewpoint of improving the releasing property, it is preferable that the surface free energy is 21~35mJ / ^{m 2,} more preferably from 23~33mJ / ^{m 2,} 25~ It is particularly preferable that it is 31 mJ / m ² . When the surface free energy is smaller than 21 mJ / m ² , the coatability may be deteriorated when the adhesive layer is coated and formed on the surface of the release film, while when it is larger than 35 mJ / m ² , the peeling force is increased. Sometimes.

[Application example]
The functional film of the present invention is applied as, for example, a carrier film such as an adhesive sheet, a ceramic green sheet, a photosensitive resin film (photoresist film), an epoxy sealing resin for a circuit substrate, a base film, or a release film. Can be done. In particular, it is suitable as a release film for an adhesive sheet or a base film for an adhesive sheet.

When the functional film of the present invention is used as a release film for a pressure-sensitive adhesive sheet, it is preferable to use the functional film by laminating an uneven surface having an Rz of more than 30 μm on the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet. As a result, the peelability between the adhesive sheet and the functional film is improved.

The pressure-sensitive adhesive sheet to which the functional film of the present invention is applied as a release film is a base film on which an pressure-sensitive adhesive layer is laminated. The pressure-sensitive adhesive layer is not particularly limited, and examples thereof include non-silicone type pressure-sensitive adhesives such as acrylic pressure-sensitive adhesives, polyester-based pressure-sensitive adhesives, urethane-based pressure-sensitive adhesives, and rubber-based pressure-sensitive adhesives. In particular, when the functional film of the present invention is applied as a release film, good releasability can be obtained with respect to the acrylic pressure-sensitive adhesive layer.

When the functional film of the present invention is used as a base film for an pressure-sensitive adhesive sheet, it is preferable to laminate the pressure-sensitive adhesive layer on the surface of the functional film opposite to the uneven surface having an Rz of more than 30 μm. This pressure-sensitive adhesive sheet is usually manufactured by being wound into a roll on a production line, but this roll-shaped pressure-sensitive adhesive sheet has an Rz of more than 30 μm between the pressure-sensitive adhesive layer and the base film (functional film of the present invention). It is in close contact with a certain uneven surface. Since the functional film of the present invention has good releasability from the pressure-sensitive adhesive layer, the roll can be smoothly unwound.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

[Measurement method and evaluation method]
(1) Measurement of maximum height roughness Rz, arithmetic average roughness Ra and average length RSm of elements on the roughness curve of the functional film The functional film is cut into a rectangle of 150 mm in the longitudinal direction and 100 mm in the width direction for measurement. It was used as a sample. Measurement was performed using a surface roughness measuring machine (““ Surf Test (registered trademark) ”SJ-400” manufactured by Mitutoyo Co., Ltd.) in accordance with JIS B0601 (2001). The measurement direction was an inclination angle of 30 degrees with respect to the longitudinal direction. It was measured 5 times and averaged.

<Measurement conditions>
・ Radius of stylus tip; 2 μm
-Measuring power: 0.75 mN
-Cutoff value; λs = 25 μm, λc = 8 mm

(2) Measurement of Young's modulus in the longitudinal direction and the width direction of the polyolefin film The polyolefin film was cut into rectangles having a length of 150 mm and a width of 10 mm with respect to the test direction, and used as measurement samples. Using a tensile tester (Tencilon AMF / RTA-100 manufactured by Orientec Co., Ltd.), measurement was performed 5 times in a 25 ° C. and 65% RH atmosphere according to the method specified in JIS-K7127 (1999), and the average value was obtained. Asked. However, the initial distance between the chucks was 50 mm, the tensile speed was 300 mm / min, and the point where the load passed 1 N after the start of the test was defined as the origin of elongation.

(3) Measurement of surface free energy of functional film Water, diiodomethane, and 1-bromonaphthalene are used as three kinds of liquids whose surface free energy and the values of each component (dispersion force, polarity force, and hydrogen bond force) are known. The contact angle of each liquid on the cured layer was measured with a contact angle meter DropMasterDM501 (manufactured by Kyowa Interface Science Co., Ltd.) at 23 ° C. and 65% RH. One measurement surface was measured 5 times, and the average value was taken as the contact angle (θ). Introduced from the Kitazaki-Hata formula from the values of this contact angle (θ) and the known values of each liquid (Method IV by Panzer (described in Vol. 15, No. 3, page 96 of the Journal of the Japan Adhesive Association)). The value of each component was calculated using the following formula.
(ΓSd / γLd) 1/2+ (γSp / γLp) 1/2+ (γSh / γLh) 1/2 = γL (1 + cosθ) / 2

Here, γLd, γLp, and γLh represent each component of the dispersion force, the polarity force, and the hydrogen bond force of the measurement liquid, respectively, θ represents the contact angle of the measurement liquid on the measurement surface, and γSd, γSp, γSh represents the value of each component of the dispersion force, the polarity force, and the hydrogen bond force on the surface of the cured layer, and γL represents the surface energy of each liquid. The values of the three components of the measurement surface (hardened layer surface) were obtained by solving the simultaneous equations obtained by substituting the known values and θ into the above equations.

As shown in the following formula, the sum of the obtained value of the dispersion force component, the value of the polar force component, and the value of the hydrogen bonding force component was taken as the value of the surface free energy (E).
E = γSd + γSp + γSh

(4) Measurement of normal peeling force (A) and heat peeling force (B) on the adhesive tape Adhesive surface of acrylic adhesive tape (“No. 31B” manufactured by Nitto Denko Corporation) is applied to the uneven surface of the functional film. While holding it with a rubber roller of its own weight of 5 kg, reciprocate it once and stick it together, leave it at room temperature (23 ± 2 ° C) for 24 hours, and then peel off the adhesive tape side to 180 ° at a speed of 300 mm / min with a tensile tester. The peeling force (normal peeling force A) was measured.
Similarly, an acrylic adhesive tape was attached to the uneven surface of the functional film, and the peeling force (heat peeling force B) after heating at 70 ° C. for 24 hours was measured.

[Polyolefin film]
The following non-stretched polypropylene films 1 to 5 and polyethylene films 6 to 9 or a mixed film of polypropylene and polyethylene were prepared.

<Film 1>
"Trefan (registered trademark)" NO3301 from Toray Film Processing Co., Ltd .; Thickness is 40 μm, Young's modulus in the longitudinal direction is 770 MPa, and Young's modulus in the width direction is 760 MPa.

<Film 2>
"Trefan (registered trademark)" NO3721 of Toray Film Processing Co., Ltd .; Thickness is 70 μm, Young's modulus in the longitudinal direction is 810 MPa, and Young's modulus in the width direction is 720 MPa.

<Film 3>
Toray Film Processing Co., Ltd. "Trefan (registered trademark)"NO3701J; thickness is 40 μm, Young's modulus in the longitudinal direction is 650 MPa, and Young's modulus in the width direction is 600 MPa.

<Film 4>
"Trefan (registered trademark)" NO3501 of Toray Film Processing Co., Ltd .; Thickness is 60 μm, Young's modulus in the longitudinal direction is 650 MPa, and Young's modulus in the width direction is 630 MPa.

<Film 5>
"Trefan (registered trademark)" NO3951 of Toray Film Processing Co., Ltd .; Thickness is 60 μm, Young's modulus in the longitudinal direction is 580 MPa, and Young's modulus in the width direction is 530 MPa.

<Film 6>
"Tretec (registered trademark)" T001B from Torei Tip Thin Film Co., Ltd .; Thickness is 45 μm, Young's modulus in the longitudinal direction is 600 MPa, and Young's modulus in the width direction is 550 MPa.

<Film 7>
Toray Film Processing Co., Ltd. "Tretec (registered trademark)"S500; thickness is 40 μm, Young's modulus in the longitudinal direction is 460 MPa, and Young's modulus in the width direction is 410 MPa.

<Film 8>
Toray Film Processing Co., Ltd. "Tretec (registered trademark)"7932; thickness 60 μm, Young's modulus in the longitudinal direction is 460 MPa, Young's modulus in the width direction is 410 MPa.

<Film 9>
"Tretec (registered trademark)" 7332 of Toray Film Processing Co., Ltd .; Thickness is 30 μm, Young's modulus in the longitudinal direction is 560 MPa, and Young's modulus in the width direction is 650 MPa.

[Embossed roll]
Silk-grained embossed roll with protrusion height of 250 μm (1), silk-grained embossed roll with protrusion height of 125 μm (2), lattice-shaped embossed roll with protrusion height of 200 μm (3), protrusion height of 100 μm A lattice-shaped embossed roll (4) and a satin-shaped embossed roll (5) were prepared.

[Example 1]
A silk-grained embossed roll 1 heated to 100 ° C. was pressed against the side of the film 1 not subjected to the corona treatment to be embossed to prepare a functional film.

[Example 2]
A functional film was produced in the same manner as in Example 1 except that it was changed to silk-grained embossed roll 2.

[Example 3]
A functional film was produced in the same manner as in Example 1 except that the embossed roll 3 was changed to a grid pattern.

[Example 4]
A functional film was produced in the same manner as in Example 1 except that the embossed roll 4 was changed to a grid pattern.

[Comparative Example 1]
A functional film was produced in the same manner as in Example 1 except that the embossed roll was changed to a lattice-shaped embossed roll 4 and the temperature of the embossed roll was changed to 70 ° C.

[Comparative Example 2]
A functional film was produced in the same manner as in Example 1 except that the embossed roll 5 was changed to a satin finish.

[Example 5]
A functional film was produced in the same manner as in Example 1 except that the film 1 was changed to the film 2.

[Example 6]
A functional film was produced in the same manner as in Example 1 except that the film 1 was changed to the film 3.

[Example 7]
A functional film was produced in the same manner as in Example 1 except that the film 1 was changed to the film 4.

[Example 8]
A functional film was produced in the same manner as in Example 1 except that the film 1 was changed to the film 5.

[Example 9]
A functional film was produced in the same manner as in Example 1 except that the film 1 was changed to the film 6.

[Example 10]
A functional film was produced in the same manner as in Example 1 except that the film 1 was changed to the film 7.

[Example 11]
A functional film was produced in the same manner as in Example 1 except that the film 1 was changed to the film 8.

[Example 12]
A functional film was produced in the same manner as in Example 1 except that the film 1 was changed to the film 9.

[Evaluation]
The functional films of Examples and Comparative Examples prepared above were evaluated according to the above-mentioned measuring method and evaluation method. The results are shown in Table 1.

11 Protrusions of the quadrangular pyramid of the silk-grained embossed roll 12 Lattice-shaped protrusions of the lattice-shaped embossed roll

Claims (10)

A functional film made of a polyolefin film and having irregularities on at least one surface thereof having a maximum height roughness Rz of more than 30 μm in a roughness curve. The functional film according to claim 1, wherein the arithmetic average roughness Ra in the roughness curve of the surface having irregularities is more than 6 μm. The functional film according to claim 1 or 2, wherein the average length RSm of the elements in the roughness curve of the surface having irregularities is more than 400 μm and 2000 μm or less. The functional film according to any one of claims 1 to 3, wherein the polyolefin film is an unstretched polyolefin film. The functional film according to any one of claims 1 to 4, wherein the Young's modulus in both the longitudinal direction and the width direction of the polyolefin film is less than 1,000 MPa. The normal peeling force (A) and the heat peeling force (B) of the surface having irregularities are both 1.0 N / 50 mm or less, and the ratio (B) of the heat peeling force (B) to the normal peeling force (A). The functional film according to any one of claims 1 to 5, wherein / A) is 1.5 or less. The functional film according to any one of claims 1 to 6, wherein the polyolefin film is a polypropylene film. The functional film according to any one of claims 1 to 6, wherein the polyolefin film is a polyethylene film or a mixture film of polypropylene and polyethylene. A release film comprising the functional film according to any one of claims 1 to 8. A base film for an adhesive sheet, which comprises the functional film according to any one of claims 1 to 8.

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