JP2023142503A - release film - Google Patents

Abstract

To provide a release film comprising a multilayer co-extruded polyolefin film with excellent peelability.SOLUTION: A release film comprises a multilayer co-extruded polyolefin film with at least a release layer and a support layer. The release layer contains linear ultra-low-density polyethylene. The value of normal peeling force is 0.05 N/50 mm or more and 0.6 N/50 mm or less.SELECTED DRAWING: None

Description

The present invention relates to a release film. In particular, it relates to a release film made of a multilayer coextruded film of polyolefin resin.

The release film can be used, for example, as a base film or protective film for adhesive sheets, as a carrier film for ceramic green sheets, photosensitive resin films (photoresist films), epoxy sealing resins for circuit boards, or for molding. It is used as a process film.

On the other hand, it is known to form a resin layer on one side of a polyester film (for example, Patent Documents 1 and 2).

JP2020-203384A Japanese Patent Application Publication No. 2015-199329

However, conventionally known release films made by forming a resin layer on the surface of a polyester film have high rigidity and do not have sufficient flexibility. On the other hand, release films made of polyolefin films did not have sufficient releasability from adherends such as adhesive sheets.

Therefore, an object of the present invention is to provide a release film made of a multilayer coextruded polyolefin film with good flexibility and peelability.

The above objects of the present invention have been achieved by the following invention.
[1] Consisting of a multilayer coextruded polyolefin film having at least a release layer and a support layer, the release layer contains linear ultra-low density polyethylene, and the normal peeling force value with the adherend is 0.05N. /50mm or more and 0.6N/50mm or less.
[2] The linear ultra-low density polyethylene has a density of 0.850 g/cm ³ or more and less than 0.900 g/cm ³ and an MFR of 0.5 g/10 min or more and less than 10.0 g/10 min as described in [1] release film.
[3] The release film according to [1] or [2], wherein the content of linear ultra-low density polyethylene is 10% by mass or more.

According to the present invention, it is possible to provide a release film made of a multilayer coextruded polyolefin film that is flexible and has good releasability from adherends such as adhesive sheets.

The release film of the present invention consists of a multilayer coextruded polyolefin film having at least a release layer and a support layer.

In the present invention, each layer constituting the multilayer coextruded polyolefin film preferably contains polyolefin as a main component. Here, containing polyolefin as a main component means that each layer contains 50% by mass or more of polyolefin based on 100% by mass of the total solid content of each layer.

The content of polyolefin in each layer is preferably 60% by mass or more, more preferably 75% by mass or more, and particularly preferably 90% by mass or more, based on 100% by mass of the total solid content of each layer. The upper limit is 100% by mass.

[Release layer]
In the present invention, the release layer constituting the multilayer coextruded polyolefin film contains linear ultra-low density polyethylene. By providing this release layer, releasability is improved. In other words, the peeling force with respect to an adherend such as an adhesive sheet is reduced.

Low-density polyethylene includes branched low-density polyethylene and linear low-density polyethylene. Generally speaking, low density polyethylene refers to branched low density polyethylene. Branched low-density polyethylene is also referred to as high-pressure low-density polyethylene, and is low-density polyethylene (hereinafter abbreviated as LDPE) having a large number of branches obtained by high-pressure radical polymerization. Even if the above LDPE is used in the release layer in the present invention, no improvement in releasability can be expected.

Conventionally, linear low density polyethylene (hereinafter abbreviated as LLDPE) has a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less, and in the present invention, the density is 0.850 g/cm ³ or more. Linear low density polyethylene with a weight of less than 0.900 g/cm ³ is referred to as linear very low density polyethylene (hereinafter abbreviated as VLLDPE).

The VLDPE has ethylene monomer as its main component, and is copolymerized with α-olefin. The term "main component" as used herein means a component that is contained in an amount of 50 mol% or more of the total monomer components constituting the VLDPE. Specifically, it is an ethylene/α-olefin copolymer that can be obtained by copolymerizing ethylene and an α-olefin having 3 to 18 carbon atoms using a catalytic polymerization method. As the above-mentioned catalyst, Ziegler-Natta catalyst and metallocene catalyst are generally known. Furthermore, as the content of α-olefin in the copolymer increases, the density tends to decrease.

Here, examples of the α-olefin having 3 to 18 carbon atoms include propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 4,4-dimethyl-1 -pentene, 1-hexene, 4-methyl-1-hexene, 1-heptene, 1-octene, 1-decene, 1-octadecene and the like. These α-olefins can be used alone or in combination. Among the above α-olefins, those having 4 to 12 carbon atoms are preferred, and those having 4 to 10 carbon atoms are more preferred.

The content of α-olefin in VLLDPE is preferably 4 to 30 mol%, more preferably 7 to 25 mol%, particularly preferably 10 to 20 mol% of the total monomer components. If the content of α-olefin is less than 4 mol% of the total monomer components, sufficient mold releasability may not be obtained. Furthermore, if the content of α-olefin exceeds 30% of the total monomer components, film forming properties may deteriorate.

The density of the VLLDPE is preferably less than 0.900 g/cm ³ , more preferably less than 0.890 g/cm ³ , and particularly preferably less than 0.885 g/cm ³ . Further, the density is preferably 0.850 g/cm ³ or more, more preferably 0.860 g/cm ³ or more, and particularly preferably 0.865 g/cm ³ or more. If the density is less than 0.850 g/cm ³ , the normal peel force with the adherend may exceed 0.6 N/50 mm, and if the density exceeds 0.900 g/cm ³ , the normal peel force with the adherend may exceed 0.6 N/50 mm. may be less than 0.05N/50mm.

The MFR of VLLDPE is preferably less than 10.0 g/10 min, more preferably less than 8.0 g/10 min, and particularly preferably less than 6.0 g/10 min. Further, the MFR is preferably 0.5 g/10 min or more, more preferably 1.0 g/10 min or more, and particularly preferably 2.0 g/10 min or more. If the MFR is 10.0 g/10 min or more, it may become difficult to extrude the raw material when melt-extruding the film. On the other hand, when the MFR is less than 0.5 g/10 min, the furnace pressure of the extruder increases when melt-extruding the film, which may make film formation difficult.

From the viewpoint of improving releasability, the content of VLLDPE in the release layer is preferably 10% by mass or more, more preferably 15% by mass or more, and 20% by mass based on 100% by mass of the total solid content of the release layer. The above is especially more preferable, and the upper limit is 100% by mass.

It is preferable that the release layer contains LLDPE as a component other than VLLDPE.

From the viewpoint of improving releasability, the total content of VLLDPE and LLDPE in the release layer is preferably 70% by mass or more, more preferably 80% by mass or more, based on 100% by mass of the total solid content of the release layer. The upper limit is 90% by mass.

The release layer can contain polyolefins other than VLLDPE and LLDPE (hereinafter sometimes referred to as "other polyolefins"). Other polyolefins include, for example, branched low-density polyethylene (LDPE), high-density polyethylene (HDPE; density is 0.941 g/cm ³ or more), polypropylene, polybutene, poly(4-methyl-1-pentene), propylene -α-olefin copolymers, copolymers of ethylene and components other than α-olefins, and the like.

The α-olefin in the above propylene-α-olefin copolymer includes 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 3-methyl-1- Examples include butene, 4-methyl-1-pentene, and the like.

Examples of copolymers of ethylene and components other than α-olefins include ethylene-unsaturated carboxylic acid copolymers such as ethylene-acrylic acid copolymers (EAA) and ethylene-methacrylic acid copolymers (EMAA). Coalescence; Ionomer; Ethylene-(meth)acrylic acid ester copolymers such as ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer (EEA), and ethylene-methyl methacrylate copolymer (EMMA); Examples include ethylene-vinyl acetate copolymer (EVA); ethylene-vinyl alcohol copolymer.

The other polyolefins mentioned above can be used alone or in combination of two or more.

When the release layer contains other polyolefins, the content of the other polyolefins is preferably 0.1 to 20% by mass based on 100% by mass of the total solid content of the release layer.

[Support layer]
In the present invention, the support layer constituting the multilayer coextruded polyolefin film includes polypropylene (hereinafter sometimes abbreviated as PP) and high-density polyethylene (hereinafter referred to as HDPE) with a density of 0.941 g/cm ³ or more as polyolefins. It is preferable to contain at least one member selected from the group consisting of (sometimes abbreviated).

By providing such a support layer, the rigidity of the multilayer coextruded polyolefin film of the present invention is increased (stronger), and the handleability and peeling workability of the release film of the present invention are improved.

Examples of the polypropylene (PP) that can be contained in the support layer include propylene homopolymers, copolymers of propylene and other α-olefins, and mixtures thereof.

Other α-olefins in copolymers of propylene and other α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene. , 3-methyl-1-butene, 4-methyl-1-pentene and the like. As the copolymer of propylene and other α-olefin, either a random copolymer or a block copolymer can be used. The content of α-olefin in the copolymer of propylene and other α-olefin is preferably 20% by mass or less, more preferably 10% by mass or less. If the α-olefin content exceeds 20% by mass, the degree of crystallinity may decrease.

Polypropylene (PP) preferably has a high degree of crystallinity from the viewpoint of increasing the rigidity (strengthening the stiffness) of the release film of the present invention. Specifically, the crystallinity of polypropylene (PP) is preferably 40% or more, more preferably 50% or more, and particularly preferably 60% or more. The upper limit of crystallinity is 100%.

The crystallinity of polypropylene (PP) can be adjusted by controlling the cooling temperature and cooling rate after melt extrusion in the film forming process of the support layer by melt extrusion. For example, the crystallinity of polypropylene (PP) increases by slowing the cooling rate. Further, by using a crystal nucleating agent in combination, the degree of crystallinity can be increased.

The crystal nucleating agent is not particularly limited, and known compounds can be used. Examples include inorganic substances such as talc, metal carboxylates, metal phosphates, sorbitol derivatives, and metal salts of rosin.

As the high-density polyethylene (HDPE) that can be contained in the support layer, polyethylene with a density of 0.941 to 0.980 g/cm ³ is preferable, and polyethylene with a density of 0.945 to 0.975 g/cm ³ is more preferable. Preferably, polyethylene having a density of 0.950 to 0.970 g/cm ³ is particularly preferred.

For the support layer, polypropylene (PP) and high density polyethylene (HDPE) may be used alone or in combination. The content ratio (PP:HDPE) when polypropylene (PP) and high density polyethylene (HDPE) are used together is not particularly limited, but for example, the mass ratio is preferably 98:2 to 2:98, and 95:5 to 5:95 is more preferred.

From the viewpoint of increasing the rigidity of the release film of the present invention, the total content of polypropylene (PP) and high-density polyethylene (HDPE) in the support layer is 50% by mass based on 100% by mass of the total solid content of the support layer. The content is preferably at least 60% by mass, more preferably at least 70% by mass, and particularly preferably at least 70% by mass. Further, the content is preferably 97% by mass or less, more preferably 95% by mass or less.

In the multilayer coextruded polyolefin film of the present invention, the interlayer adhesion of each layer is relatively good, but from the viewpoint of further increasing the adhesion between the release layer and the support layer, the support layer has a density of 0.940 g/ It is preferable to contain a polyethylene resin of cm ³ or less.

From the viewpoint of adhesion, the polyethylene resin that can be contained in the support layer preferably has a density of 0.890 to 0.935 g/cm ³ , and a density of 0.900 to 0.930 g/cm ³ . Particularly preferred are those within this range.

The polyethylene resin may be linear very low density polyethylene (VLLDPE), linear low density polyethylene (LLDPE), or branched low density polyethylene (LDPE), but may be linear Preferred is low density polyethylene (LLDPE). This linear low density polyethylene (LLDPE) is preferably of the same type as the linear low density polyethylene (LLDPE) used for the release layer. Here, the same type means that the difference in density is within 0.005 g/cm ³ .

Further, it is preferable that the support layer contains self-recovered waste generated during the process of forming the multilayer coextruded polyolefin film of the present invention, since this reduces costs. In this case, the self-recovery rate is preferably less than 50% by mass based on 100% by mass of the total solid content of the support layer.

The content of the polyethylene resin in the support layer is preferably 3% by mass or more, and 5% by mass or more based on the total solid content of the support layer of 100% by mass, from the viewpoint of improving the adhesion between the mold release layer and the support layer. % or more is more preferable, and 7 mass % or more is particularly preferable. On the other hand, if the content of the polyethylene resin becomes too large, the rigidity of the multilayer coextruded polyolefin film in the present invention may decrease, so the content is preferably 40% by mass or less, more preferably 30% by mass or less, Particularly preferred is 25% by mass or less.

The support layer can contain additives such as colored pigments and antioxidants.

[Multilayer coextruded polyolefin film]
The multilayer coextruded polyolefin film in the present invention may have a two-layer structure of a release layer and a support layer, or may have a structure of three or more layers including other layers. Other layers include a back layer and an intermediate layer. The intermediate layer is a layer disposed between the release layer and the support layer or between the support layer and the back layer.

The multilayer coextruded polyolefin film in the present invention can be produced, for example, by a conventionally known extrusion method (T-die multilayer coextrusion method, round die multilayer coextrusion method, etc.) or an inflation method.

The multilayer coextruded polyolefin film in the present invention preferably has a back layer on the side opposite to the side of the support layer having the release layer. The back layer will be explained in detail below.

[Back layer]
A back layer may be provided to protect the support layer or to improve the slipperiness of the multilayer coextruded polyolefin film of the present invention.

Examples of the polyolefin contained in the back layer include homopolymers of ethylene, propylene, and α-olefins having 4 to 10 carbon atoms, and copolymers thereof. Examples of α-olefins having 4 to 10 carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, and 3-methyl-1-butene. , 4-methyl-1-pentene and the like.

Examples of the above copolymers include copolymers of ethylene and propylene, copolymers of ethylene and α-olefins having 4 to 10 carbon atoms, and copolymers of propylene and α-olefins having 4 to 10 carbon atoms. Examples include copolymers, and copolymers of ethylene, propylene, and α-olefins having 4 to 10 carbon atoms.

The above polyolefins may be used alone or in combination of two or more.

The back layer preferably contains at least one selected from the group consisting of polyethylene resins and polypropylene resins. As the polyethylene resin, the aforementioned linear low density polyethylene (LLDPE), branched low density polyethylene (LDPE), and high density polyethylene (HDPE) are preferably used. As the polypropylene resin, a propylene homopolymer (hereinafter sometimes abbreviated as HPP) is preferably used.

The content of polyolefin in the back layer is preferably 55% by mass or more, more preferably 60% by mass or more, and particularly preferably 75% by mass or more, based on 100% by mass of the total solid content of the back layer. The upper limit is 100% by mass.

The back layer may have the same composition as the release layer, or may have a different composition.

The back layer preferably has a relatively large surface roughness from the viewpoint of ensuring the slipperiness of the release film. Specifically, the maximum height roughness Rz of the surface of the back layer is preferably 1.5 μm or more, more preferably 2.5 μm or more. The upper limit is about 7.0 μm.

In order to roughen the surface of the back layer, the back layer preferably contains a propylene homopolymer and a polyolefin other than the propylene homopolymer. Polyolefins other than propylene homopolymers include polyethylene, homopolymers of α-olefins having 4 to 10 carbon atoms, copolymers of propylene and ethylene, and copolymers of ethylene and α-olefins having 4 to 10 carbon atoms. It is preferable to use at least one selected from the group consisting of copolymers. Among these, propylene-ethylene random copolymer is preferred.

[Thickness of each layer in multilayer coextruded polyolefin film]
The thickness of the release layer is preferably 5 to 30 μm, more preferably 8 to 25 μm, and particularly preferably 10 to 20 μm.

The thickness of the support layer is preferably 20 to 90 μm, more preferably 25 to 70 μm, and particularly preferably 30 to 50 μm.

From the viewpoint of peelability and rigidity of the multilayer coextruded polyolefin film, the ratio (Rt/St) of the thickness of the release layer (Rt) to the thickness of the support layer (St) is preferably 0.05 to 0.50. It is preferably from 0.10 to 0.45, more preferably from 0.15 to 0.40.

The thickness of the back layer is preferably 2 to 30 μm, more preferably 3 to 25 μm, particularly preferably 4 to 20 μm.

When the multilayer coextruded polyolefin film has a structure of a release layer/support layer/back layer, the total thickness of the release layer and back layer is determined from the viewpoint of ensuring the rigidity of the multilayer coextrusion polyolefin film and suppressing curling. The ratio of the thickness of the support layer to the thickness {(thickness of the support layer)/(total thickness of the release layer and back layer)} is preferably 1.0 or more and less than 4.0, preferably 1.2 or more and less than 3.5, and 1 Particularly preferred is .5 or more and less than 3.0.

The total thickness of the multilayer coextruded polyolefin film is preferably 30 to 100 μm, more preferably 35 to 80 μm, and particularly preferably 40 to 70 μm.

[Release film]
The release film of the present invention consists of the multilayer coextruded polyolefin film described above. That is, the release film of the present invention includes a multilayer coextruded polyolefin film laminated with other base materials such as plastic films such as polyester films, polyolefin films, and polyimide films, paper, and metal foils. is not included.

The release film of the present invention has a release agent such as a silicone release agent, a long-chain alkyl release agent, an alkyd release agent, or a fluorine release agent on the surface of the release layer constituting the multilayer coextruded polyolefin film. The surface can be treated with a mold release agent such as. However, considering that the release film of the present invention has relatively good releasability from adherends such as adhesive sheets, and that the release agent migrates to adhesive sheets, It is preferable not to perform surface treatment.

That is, it is preferable that the release film of the present invention consists only of a multilayer coextruded polyolefin film.

When a release film is applied, the required release force may vary depending on the type of adherend and the intended use. The release force of the release film of the present invention can be adjusted depending on the type of adherend to which it is applied and its use.

Although the release film of the present invention already has good releasability, the releasability can be further improved by forming fine irregularities on the surface of the release layer or by heat treatment. These methods can be carried out alone or in combination.

In other words, the peeling force can be adjusted by controlling the degree of fine irregularities (depth and pitch) formed on the surface of the release layer, and the peeling force can be adjusted by controlling the heating conditions (temperature and time). Can be adjusted.

Examples of methods for forming fine irregularities on the surface of the release layer include embossing, sandblasting, chemical treatment, or pressing a molding roll with irregularities engraved on the molten release layer in the process of forming the release layer. There are ways to apply it. Among these, embossing is preferred.

As the embossing treatment, for example, a method of pressing a heated embossing roll against a multilayer coextruded polyolefin film is preferable, and the uneven shape formed on the release layer can be adjusted by controlling the heating temperature and pressing pressure of the embossing roll. I can do it. The heating temperature of the embossing roll is preferably 80°C to 160°C, more preferably 90°C to 140°C. The surface of the multilayer coextruded polyolefin film against which the embossing roll is pressed may be the release layer surface or the support layer surface (back layer surface), but the release layer surface is preferable.

The fine unevenness formed on the surface of the release layer is not particularly limited, and may include the same unevenness pattern arranged regularly or irregularly, or different unevenness patterns arranged regularly or irregularly. You can adopt things. Examples of the uneven pattern include a lattice pattern, a grain pattern, a satin pattern, a dot pattern, and the like.

When the multilayer coextruded polyolefin film of the present invention is heat-treated, additive components are precipitated on the surface layer of the release layer, further improving releasability.

The heating temperature during the heat treatment is preferably 70°C or higher, more preferably 75°C or higher, and particularly preferably 80°C or higher. The upper limit is about 130°C. The heating time is appropriately set depending on the heating temperature and the form of the multilayer coextruded polyolefin film.

When heating in a film transport process such as a film forming process of a multilayer coextruded polyolefin film, it is preferable to heat at a temperature of 75 to 130°C for 30 seconds or more, more preferably 60 seconds or more. It is particularly preferred to heat for more than a second. On the other hand, when the multilayer coextruded polyolefin film is in the form of a roll or laminated sheet, it is preferable to heat it at a temperature of 70 to 100°C for 30 minutes or more, more preferably 1 hour or more, It is particularly preferable to heat the mixture for a period of time or more.

The release film of the present invention has a normal peeling force value of 0.05 N/50 mm or more and 0.6 N/50 mm or less with respect to the adhesive tape on the surface of the release layer.

Here, the normal peeling force and heating peeling force on the surface of the release layer with respect to the adhesive tape are measured according to the measuring method described in Examples described later.

Conventionally known release films tend to have a higher thermal peeling force compared to normal peeling force, but with the mold release film of the present invention, the thermal peeling force increases less than normal peeling force, and in fact tends to decrease. It is in.

[Application example]
The release film of the present invention can be used, for example, as a base film or protective film for adhesive sheets, as a carrier film for ceramic green sheets, photosensitive resin films (photoresist films), epoxy sealing resins for circuit boards, etc. It can be applied as a process film for products or as a release film for adhesive protective films.

The release film of the present invention is suitable, for example, as a protective film for pressure-sensitive adhesive sheets. That is, the release layer of the release film of the present invention is laminated so as to be in contact with the adhesive layer of the adhesive sheet having the adhesive layer on the base film.

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

[Measurement method and evaluation method]
(1) Measurement of density of polyethylene It was measured by the density gradient tube method (23° C.) according to JIS K7112 (1999).

(2) Measurement of normal peeling force Layer acrylic adhesive tape (No. 31B manufactured by Nitto Denko Corporation) on the surface of the release layer of the release film so that the adhesive side faces each other, and use a rubber roller with a weight of 5 kg to A sample was prepared by pasting the pieces together by moving them back and forth while pressing and leaving them at room temperature (23±2°C) for 24 hours. For the sample, the peeling force when the adhesive sheet side was peeled off at 180° at a speed of 300 mm/min using a tensile tester (product number "EZ-SX" manufactured by Shimadzu Corporation) was defined as the normal peeling force.

(3) Measurement of the maximum height roughness Rz of the surface of the release layer and back layer A surface roughness measuring device (“Surf Test SJ-400” manufactured by Mitutoyo Co., Ltd.) was used in accordance with JIS B0601 (2001). It was measured using
<Measurement conditions>
・Stylus tip radius: 2μm
・Measurement force: 0.75mN
・Cutoff value; λs=2.5μm, λc=0.8mm
(Cutoff value after embossing; λs=2.5 μm, λc=2.5 mm).

(4) Melt flow rate (MFR)
Using a melt indexer made by Toyo Seiki Seisakusho, in accordance with JIS K7210-1 (2014), for polypropylene resin, the temperature is 230°C and the load is 2.16kg, or for the polyethylene resin, the temperature is 190°C and the load is 2.16kg. The MFR of the raw materials used in Examples and Comparative Examples was measured.

[Example 1]
A release film having a three-layer laminated structure of release layer/support layer/back layer was produced by a three-layer melt coextrusion method using the following raw materials. The extrusion temperature of each layer was set to 200°C for the release layer, 210°C for the support layer, and 210°C for the back layer. A release film having a total thickness of 40 μm was produced by extruding the film to have a thickness of 28 μm and a back layer thickness of 4 μm. The maximum height roughness Rz of the surface of the back layer was 2.8 μm, and the maximum height roughness Rz of the surface of the release layer was 0.3 μm.

The produced release film was heat-treated. In the heat treatment, 500 sheets of A4-sized release films were stacked and heated in a hot air oven at 80° C. for 1 hour. The peeling force was measured using the 250th release film from the top of the stack of 500 films. The normal peeling force was 0.3N/50mm. It is possible that the heat treatment caused a small amount of low molecular weight components within the film to precipitate on the surface of the release layer, resulting in a decrease in the normal release force.

<Raw materials for each layer>
・Raw material for release layer: 90 parts by mass of LLDPE (“Evolue (registered trademark)” SP2540 manufactured by Prime Polymer Co., Ltd.; density 0.924 g/cm ³ , MFR 3.8 g/10 min) and VLDPE (manufactured by Sumitomo Chemical Co., Ltd.) A mixture with 10 parts by mass of Excellen (registered trademark) "FX201; density 0.898 g/cm ³ , MFR 2.0 g/10 min).
・Supporting layer raw materials: 80 parts by mass of HDPE (“Novatec (registered trademark)” HF562 manufactured by Japan Polyethylene Co., Ltd.; density = 0.961 g/cm ³ ) and LLDPE (“Evolu (registered trademark)” manufactured by Prime Polymer Co., Ltd.) SP2540; density 0.924 g/cm ³ ) A mixture with 20 parts by mass.
- Back layer raw material; a mixture of 80 parts by mass of polypropylene ("Noblen (registered trademark)" FLX80E4 manufactured by Sumitomo Chemical Co., Ltd.) and 20 parts by mass of propylene-ethylene random copolymer (ethylene content: 5% by mass).

[Example 2]
A release film having a three-layer laminated structure of release layer/support layer/back layer was produced in the same manner as in Example 1, except that the raw material for the release layer was changed as follows. The maximum height roughness Rz of the surface of the back layer was 2.8 μm, and the maximum height roughness Rz of the surface of the release layer was 0.3 μm.

The produced release film was heat-treated. In the heat treatment, one A4 size release film was heated in a hot air oven at 100° C. for 60 seconds. The normal peeling force was 0.3N/50mm. It is possible that the heat treatment caused a small amount of low molecular weight components within the film to precipitate on the surface of the release layer, resulting in a decrease in the normal release force.
・Raw material for release layer: 80 parts by mass of LLDPE (“Evolue (registered trademark)” SP2540 manufactured by Prime Polymer Co., Ltd.; density 0.924 g/cm ³ , MFR 3.8 g/10 min) and VLDPE (manufactured by Sumitomo Chemical Co., Ltd.) A mixture with 20 parts by mass of Excellen (registered trademark) "FX201; density 0.898 g/cm ³ , MFR 2.0 g/10 min).

[Example 3]
A release film having a three-layer laminated structure of release layer/support layer/back layer was produced by a three-layer melt coextrusion method using the following raw materials. The die temperature of each layer was set to 200°C for the release layer, 230°C for the support layer, and 210°C for the back layer. A release film having a total thickness of 50 μm was produced by extruding the film so that the thickness was 35 μm and the thickness of the back layer was 5 μm. The maximum height roughness Rz of the surface of the back layer was 2.8 μm, and the maximum height roughness Rz of the surface of the adhesive layer was 0.3 μm. The normal peeling force of the formed release film was 0.5 N/50 mm.

<Raw materials for each layer>
- Release layer raw materials: 50 parts by mass of LLDPE ("Sumikasen (registered trademark)" CW3006 manufactured by Sumitomo Chemical Co., Ltd.; density 0.922 g/cm ³ , MFR 5.0 g/10 min) and VLDPE (manufactured by Sumitomo Chemical Co., Ltd.) A mixture with 50 parts by mass of Excellen (registered trademark) "FX402; density 0.880 g/cm ³ , MFR 8.0 g/10 min).
- Supporting layer raw materials: 80 parts by mass of polypropylene (C) ("Novatec PP (registered trademark)" FL4 manufactured by Nippon Polypro Co., Ltd.) and LLDPE ("Sumikasen (registered trademark)" CW3006 manufactured by Sumitomo Chemical Co., Ltd.; density 0. 922g/cm ³ , MFR5.0g/10min) 20 parts by mass.
- Back layer raw material; a mixture of 80 parts by mass of polypropylene ("Noblen (registered trademark)" FLX80E4 manufactured by Sumitomo Chemical Co., Ltd.) and 20 parts by mass of propylene-ethylene random copolymer (ethylene content: 5% by mass).

[Example 4]
A release film having a three-layer laminated structure of release layer/support layer/back layer was produced in the same manner as in Example 3, except that the raw material for the release layer was changed as follows. The maximum height roughness Rz of the surface of the back layer was 2.8 μm, and the maximum height roughness Rz of the surface of the adhesive layer was 1.3 μm. The normal peeling force of the formed release film was 0.4 N/50 mm.
- Release layer raw material; VLDPE (ethylene-1-octene copolymer; “Affinity (registered trademark)” KC8852G manufactured by Dow Chemical; density 0.875 g/cm ³ , MFR 3.0 g/10 min).

[Example 5]
A release film having a three-layer laminated structure of release layer/support layer/back layer was produced in the same manner as in Example 3, except that the raw material for the release layer was changed as follows. Note that the maximum height roughness Rz of the surface of the back layer was 2.8 μm, and the maximum height roughness Rz of the surface of the adhesive layer was 0.3 μm.

The produced release film was heat-treated. In the heat treatment, 500 sheets of A4-sized release films were stacked and heated in a hot air oven at 80° C. for 1 hour. The peeling force was measured using the 250th release film from the top of the stack of 500 films. The normal peeling force was 0.3N/50mm.
・Raw material for release layer: 80 parts by mass of LLDPE ("Sumikasen (registered trademark)" CW3006 manufactured by Sumitomo Chemical Co., Ltd.; density 0.922 g/cm ³ , MFR 5.0 g/10 min) and VLDPE (manufactured by Sumitomo Chemical Co., Ltd.) A mixture with 20 parts by mass of Excellen (registered trademark) "FX307; density 0.890 g/cm ³ , MFR 3.2 g/10 min).

[Example 6]
A release film having a three-layer laminate structure of release layer/support layer/back layer was produced in the same manner as in Example 3, except that the raw materials for the release layer and back layer were changed as follows. Note that the maximum height roughness Rz of the surface of the back layer was 3.8 μm, and the maximum height roughness Rz of the surface of the adhesive layer was 0.3 μm.

The produced release film was heat-treated. In the heat treatment, one A4 size release film was heated in a hot air oven at 100° C. for 60 seconds. The normal peeling force was 0.4 N/50 mm.
・Release layer raw material: 80 parts by mass of LLDPE (“Sumikasen (registered trademark)” CW3006 manufactured by Sumitomo Chemical Co., Ltd.; density 0.922 g/cm ³ , MFR 5.0 g/10 min) and VLDPE (ethylene-1-octene copolymer) Mixture with 20 parts by mass of "Affinity (registered trademark)" KC8852G manufactured by Dow Chemical Company; density 0.875 g/cm ³ , MFR 3.0 g/10 min).
- Back layer raw material: PP (“Topilene (registered trademark)” J640F manufactured by Hyosung Chemical).

[Example 7]
A release film having a two-layer laminate structure of release layer/support layer was produced by a two-layer melt coextrusion method using the following raw materials. The die temperature of each layer was set to 200°C for the release layer and 230°C for the support layer, and placed on a casting drum maintained at 60°C so that the release layer had a thickness of 10 μm and the support layer had a thickness of 35 μm. A release film having a total thickness of 45 μm was prepared by extruding the mixture. The maximum height roughness Rz of the surface of the supporting layer opposite to the release layer was 1.4 μm, and the maximum height roughness Rz of the surface of the adhesive layer was 0.3 μm.

The produced release film was heat-treated. In the heat treatment, 500 sheets of A4-sized release films were stacked and heated in a hot air oven at 80° C. for 1 hour. The peeling force was measured using the 250th release film from the top of the stack of 500 films. The normal peeling force was 0.3N/50mm.

<Raw materials for each layer>
・Raw material for release layer: 90 parts by mass of LLDPE (“Evolue (registered trademark)” SP2540 manufactured by Prime Polymer Co., Ltd.; density 0.924 g/cm ³ , MFR 3.8 g/10 min) and VLDPE (manufactured by Sumitomo Chemical Co., Ltd.) A mixture with 10 parts by mass of Excellen (registered trademark) "FX307; density 0.890 g/cm ³ , MFR 3.2 g/10 min).
- Supporting layer raw material: polypropylene (C) (Novatec PP (registered trademark) FL4 manufactured by Nippon Polypro Co., Ltd.).

[Comparative example 1]
In the same manner as in Example 1, a release film having a three-layer laminated structure of release layer/support layer/back layer was produced. The maximum height roughness Rz of the surface of the back layer was 2.8 μm, and the maximum height roughness Rz of the surface of the release layer was 0.3 μm. No heat treatment was performed, and the normal peeling force of the formed release film was 1.3 N/50 mm. No low molecular weight components are precipitated on the surface of the release layer immediately after film formation, and there is a possibility that the normal release force is high.

[Comparative example 2]
In the same manner as in Example 2, a release film having a three-layer laminate structure of release layer/support layer/back layer was produced. The maximum height roughness Rz of the back layer surface was 2.8 μm, and the maximum height roughness Rz of the releasable surface was 0.3 μm. No heat treatment was performed, and the normal peeling force of the formed release film was 1.0 N/50 mm. No low molecular weight components are precipitated on the surface of the release layer immediately after film formation, and there is a possibility that the normal release force is high.

[Comparative example 3]
A release film having a three-layer laminate structure of release layer/support layer/back layer was produced in the same manner as in Example 6, except that the raw material for the release layer was changed as follows. Note that the maximum height roughness Rz of the surface of the back layer was 3.8 μm, and the maximum height roughness Rz of the surface of the mold release layer was 0.3 μm. The normal peeling force of the formed release film was 5.0 N/50 mm.
- Release layer raw material; LLDPE ("Sumikasen (registered trademark)" CW3006 manufactured by Sumitomo Chemical Co., Ltd.; density 0.922 g/cm ³ , MFR 5.0 g/10 min).

Claims (3)

Consisting of a multilayer coextruded polyolefin film having at least a release layer and a support layer, the release layer containing linear ultra-low density polyethylene, and a normal peel force value of 0.05 N/50 mm or more and 0.6 N/50 mm. A release film characterized by the following: The mold release according to claim 1, wherein the linear ultra-low density polyethylene has a density of 0.850 g/cm ³ or more and less than 0.900 g/cm ³ and an MFR of 0.5 g/10 min or more and less than 10.0 g/10 min. film. The release film according to claim 1 or 2, wherein the content of linear ultra-low density polyethylene is 10% by mass or more based on 100% by mass of the total solid content of the release layer.