Release films and functional films

Abstract

To provide a release film that allows a functional layer to be applied onto a rugged adherend such as an electronic component-mounted substrate with high accuracy of coating, and provide a functional film having the release film and the functional layer.SOLUTION: A release film has a cushion layer, and a release layer laminated on one side of the cushion layer. When the release film is subjected to viscoelasticity measurement at a temperature of 120°C, a frequency of 1 Hz, and in a torsional mode, the value of I, defined by the formula I=(G' / 100000) / tanδ, is 3.5 or more, where G'[Pa] is a storage elastic modulus measured 300 seconds after the start of measurement and tanδ is a loss tangent.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a release film and a functional film.

Background Art

[0002] In electronic devices such as mobile phones, smartphones, calculators, electronic newspapers, tablet terminals, videophones, and personal computers, an electronic component mounting substrate on which electronic components such as semiconductor elements, capacitors, and coils are mounted on a substrate is mounted. Such an electronic component mounting substrate may be sealed with a resin layer having functionality in order to prevent contact with external factors such as moisture and dust.

[0003] Such sealing with resin is known, for example, in addition to a potting method in which a thermosetting resin such as a highly fluid urethane resin is injected and sealed after placing the electronic component mounting substrate in a metal cavity, and a coating method in which a thermoplastic resin is melted and applied to the electronic component mounting substrate and then solidified to coat (seal) the applied area.

[0004] However, in the potting method, it takes time for the thermosetting resin to cure, and furthermore, usually a metal cavity is required for sealing, which causes a problem of increasing the weight of the resulting electronic device. In addition, in the coating method, there are problems of viscosity control of the thermoplastic resin in the molten state and time and labor for painting the coated area of the thermoplastic resin. [[ID=2,2]]

[0005] For the purpose of solving the above problems, it has been proposed to attach a hot-melt barrier film as a protective layer (functional layer) to an electronic component mounting substrate (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] In sealing electronic component substrates by attaching a film as described in Patent Document 1, the protective layer may not adequately conform to the irregularities caused by the presence of electronic components on the substrate. As a result, the barrier effect against external factors such as moisture and dust may not be sufficiently obtained.

[0008] In particular, in areas of an electronic component mounting substrate where multiple electronic components are arranged in a grid pattern, when applying a protective layer to the electronic component mounting substrate, the protective layer sometimes did not adequately conform to the sides of the electronic components that constituted the protrusions of the uneven surface, nor to the upper surface of the substrate that constituted the recesses.

[0009] The present invention has been made in view of these circumstances. The object of the present invention is to provide a release film for coating an adhesive, such as an electronic component mounting substrate, with excellent coating accuracy, and to provide a functional film having this release film and a functional layer. [Means for solving the problem]

[0010] The inventors have completed the invention described below and solved the above problems.

[0011] According to the present invention, the following release film is provided. A release film comprising a cushion layer and a release layer laminated on one side of the cushion layer, A release film in question is one in which, when the release film is subjected to viscoelasticity testing under the conditions of a temperature of 120°C, a frequency of 1 Hz, and torsion mode, the storage modulus measured 300 seconds after the start of the measurement is G'[Pa], and the loss tangent is tanδ, and the value of I, defined by the following formula, is 3.5 or greater. I = (G' / 100000) / tanδ

[0012] Also, according to the present invention, the above-described release film, and a functional layer laminated on the release layer of the release film, a functional film is provided.

Advantages of the Invention

[0013] According to the present invention, a release film capable of coating a functional layer with excellent coating accuracy on an electronic component mounting substrate having irregularities is provided. Also, according to the present invention, a functional film having this release film and a functional layer is provided.

Brief Description of the Drawings

[0014] [Figure 1] It is a longitudinal sectional view showing a part of an embodiment of a functional layer-coated electronic component mounting substrate manufactured using the functional film of the present embodiment. [Figure 2] It is a plan view showing an electronic component mounting substrate included in the functional layer-coated electronic component mounting substrate shown in FIG. 1. [Figure 3] It is a longitudinal sectional view for explaining a manufacturing method of manufacturing the functional layer-coated electronic component mounting substrate shown in FIG. 1 using the functional film of the present embodiment. [Figure 4] In FIG. 3(b), it is a plan view showing a state where the functional film of the present invention is arranged with respect to an electronic component mounting substrate. [Figure 5] It is a schematic sectional view of the functional film of the present embodiment. [Figure 6] It is a schematic sectional view of the release film of the present embodiment.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings, the same components are denoted by the same reference numerals, and the description will be omitted as appropriate. To avoid complexity, (i) when there are multiple identical components in the same drawing, only one of them is labeled with a reference numeral, and not all of them may be labeled, or (ii) particularly in Figures 2 and later, components similar to those in Figure 1 may not be relabeled. All the drawings are for illustrative purposes only. The shapes and dimensional ratios of the components in the drawings do not necessarily correspond to actual articles.

[0016] In this specification, the notation "X~Y" in the description of a numerical range represents X or more and Y or less, unless otherwise specified. For example, "1~5 mass%" means "1 mass% or more and 5 mass% or less".

[0017] In the notation of a group (atomic group) in this specification, a notation that does not indicate whether it is substituted or unsubstituted includes both those having no substituent and those having a substituent. For example, the term "alkyl group" includes not only an alkyl group having no substituent (unsubstituted alkyl group) but also an alkyl group having a substituent (substituted alkyl group).

[0018] The notation "(meth)acryl" in this specification represents a concept that includes both acryl and methacryl. The same applies to similar notations such as "(meth)acrylate".

[0019] As shown in Figure 6, the release film (release film 1) of this embodiment includes a cushion layer 13 and a release layer 11 provided on one surface of the cushion layer 13. The release film 1 may have a sub-release layer 12 on the surface opposite to the side where the release layer 11 of the cushion layer 13 is provided. When the release film 1 is used as a release film for a functional film, as shown in Figure 5, the functional film 100 may have a structure in which a functional layer 3 is laminated on the surface of the release layer 11 of the release film 1, that is, a structure in which the functional layer 3 / release layer 11 / cushion layer 13 / sub-release layer 12 are laminated in this order.

[0020] A method of using the functional film 100 provided with the release film 1 will be described with reference to Figures 2 to 4.

[0021] [Functional layer coated electronic component mounting board] The functional film of this embodiment is used to manufacture an electronic component mounting substrate coated with a functional layer (which may be referred to as a "functional layer coated component mounting substrate" in this specification). Figure 1 is a longitudinal cross-sectional view of a functional layer coated electronic component mounting substrate 50 manufactured using the functional film of this embodiment, and Figure 2 is a plan view showing the electronic component mounting substrate 45 provided in the functional layer coated electronic component mounting substrate 50 shown in Figure 1. In the following explanation, the upper part of Figure 1 and the front of the page in Figure 2 will be referred to as "top," and the lower part of Figure 1 and the back of the page in Figure 2 will be referred to as "bottom."

[0022] The functional layer-coated electronic component mounting substrate 50 (electronic device) in Figure 1 comprises a substrate 5, electronic components 4 mounted (placed) on the substrate 5, an electronic component mounting substrate 45 composed of the substrate 5 and the electronic components 4, and a functional layer 3 that covers the electronic component mounting substrate 45 and the upper surface of the substrate 5.

[0023] The substrate 5 is a flat plate for supporting the electronic component 4, and its planar shape is usually a quadrilateral such as a square or rectangle. This substrate 5 is composed of a printed circuit board, for example, which comprises a sheet-like wiring (wiring board) and a resin layer covering the wiring above and below, and has exposed portions where the wiring is exposed at positions corresponding to the terminals of the electronic component 4.

[0024] Examples of electronic components 4 include semiconductor elements, capacitors, coils, connectors, and resistors. The electronic component 4 is mounted on the circuit board 5 with its terminals electrically connected to the wiring at the exposed portion described above. In this embodiment, multiple electronic components 4 of the same shape are arranged in a grid (matrix) pattern on the substrate 5 in the regions shown in Figures 1 and 2.

[0025] An electronic component mounting substrate 45 (adhesion substrate) is formed by a substrate 5 and electronic components 4. On this electronic component mounting substrate 45, when electronic components 4 are mounted on the substrate 5, a surface is formed on the substrate 5 consisting of protrusions 61 and recesses 62 (see Figures 1, 2, and 3(a)). In particular, in the regions shown in Figures 1 and 2, multiple electronic components 4 of the same shape are arranged in a grid pattern on the substrate 5, so that multiple recesses 62 formed along the X direction and multiple recesses 62 formed along the Y direction are arranged side by side in a state where they intersect at a right angle (90°) at the cross section 63 where they overlap.

[0026] The functional layer 3 is provided to cover the top surface and sides of the electronic component 4, as well as the top surface of the substrate 5 that is exposed from the electronic component 4. This covers the irregularities 6 formed on the substrate 5 by mounting the electronic component 4. Functional layer 3 functions as a protective layer that provides, for example, waterproofing, dustproofing, and stain resistance. Functional layer 3 functions to suppress or prevent contact between the electronic component mounting substrate 45, and in particular the electronic component 4, and external factors such as moisture and dust.

[0027] The electronic components 4 mounted on the substrate 5 are arranged in a grid pattern in the regions shown in Figures 1 and 2, with components having the same shape. However, the arrangement is not limited to this configuration; for example, the electronic components 4 may be randomly arranged with different shapes in the regions shown in Figures 1 and 2. Furthermore, outside the regions shown in Figures 1 and 2, components of the same shape may be arranged in a grid pattern, or components of different shapes may be randomly arranged.

[0028] [Manufacturing method for substrates with functional layer coated electronic components] The functional layer coated electronic component mounting substrate 50 can be manufactured using the functional film of this embodiment.

[0029] The functional layer-coated electronic component mounting substrate 50 is manufactured by covering the irregularities 6 on the electronic component mounting substrate 45 with the functional film of this embodiment. Specifically, the functional layer-coated electronic component mounting substrate 50 can be obtained as follows. First, the functional film 100, which consists of a release film 1 and a functional layer 3, is placed on the electronic component mounting substrate 45 such that the functional layer 3 faces the electronic component mounting substrate 45. Subsequently, the functional layer 3 is pressed into place by heat pressing from the cushion layer 13 or, if present, the secondary release layer 12, to conform to the shape of the uneven surface 6, thereby covering the uneven surface 6 with the functional layer 3. Details of the manufacturing method for the functional layer coated electronic component mounted substrate 50 are described below.

[0030] Figure 3 is a longitudinal cross-sectional view showing a method for manufacturing the functional layer coated electronic component mounting substrate 50 shown in Figure 1 using the functional film 100 of this embodiment. Figure 4 is a plan view showing the state in which the functional film 100 of this embodiment is placed on the electronic component mounting substrate 45 in Figure 3(b). Figure 5 is a longitudinal cross-sectional view of the functional film 100 of this embodiment. In the following explanation, the upper part of Figure 3 and the front of the page in Figure 4 will be referred to as "top," and the lower part of Figure 3 and the back of the page in Figure 4 will be referred to as "bottom."

[0031] [1] First, an electronic component mounting substrate 45 is prepared as a substrate for attachment, on which electronic components 4 are mounted on a substrate 5 (preparation step). The electronic component mounting substrate 45 can be obtained by mounting the electronic components 4 on the substrate 5 such that the terminals of the electronic components 4 are electrically connected to the wiring in the exposed portion where the wiring of the substrate 5 is exposed from the resin layer. On the substrate 5, the exposed areas where the wiring is exposed from the resin layer are typically formed in the same number as the number of terminals on the electronic component 4, corresponding to the positions where the electronic component 4 should be mounted. The electronic component 4 is mounted on the substrate 5 by electrical connection with the terminals on the electronic component 4 corresponding to the exposed areas.

[0032] When mounting the electronic components 4 onto the substrate 5, the electronic components 4 are arranged on the substrate 5 in a grid-like (matrix-like) pattern in the regions shown in Figures 1 and 2. Due to this arrangement of electronic components 4, recesses 62 are arranged side by side between adjacent electronic components 4, exposing the sides of the electronic components 4 along two mutually orthogonal directions: the X direction (short direction) and the Y direction (long direction). Specifically, the multiple recesses 62 formed along the X direction and the multiple recesses 62 formed along the Y direction are formed in a state where they intersect orthogonally (at 90°) at the cross section 63 where they overlap.

[0033] [2] Next, a functional layer 3 is formed using the functional film 100 of this embodiment to cover the top and side surfaces of the electronic component 4, and the top surface of the substrate 5 exposed from the electronic component 4 (functional layer formation step).

[0034] In this embodiment, we will describe a case where the functional film 100 is a laminate in which a functional layer 3 and a release film 1 are laminated, and the release film 1 is a laminate in which a release layer 11, a cushion layer 13, and a secondary release layer 12 are laminated in this order, and the functional film 100 is a laminate in which the functional layer 3, release layer 11, cushion layer 13, and secondary release layer 12 are laminated in this order.

[0035] [2-1] First, a release film 1 is prepared, which is a laminate in which a release layer 11, a cushion layer 13, and a secondary release layer 12 are laminated in that order, and a functional film 100 is prepared, which has a functional layer 3 laminated on the release layer 11 of the release film 1 (see Figure 3(a)). On the electronic component mounting substrate 45, the functional film 100 is laminated (attached) to the electronic component 4 on the side (top side) where the electronic component 4 is mounted on the substrate 5, with the functional layer 3 facing the electronic component 4 (see Figure 3(c); attachment process).

[0036] The method for attaching the functional film 100 to the electronic component 4 is not particularly limited, but examples include vacuum pressure forming or press molding.

[0037] Vacuum pressure forming is a method of covering the top and side surfaces of an electronic component 4, as well as the top surface of a substrate 5 exposed from the electronic component 4, with a functional film 100, for example, using a vacuum pressure laminator. In vacuum pressure forming, first, as shown in Figure 3(b), an electronic component mounting substrate 45 and a functional film 00 are placed in a closed space that can be maintained under a vacuum atmosphere, with the side of the electronic component 4 opposite to the substrate 5 facing the side of the functional film 100 facing the functional layer 3. Then, under heating, the closed space is made under a vacuum atmosphere and subsequently pressurized so that the functional film 100 and the electronic component 4 on the electronic component mounting substrate 45 move closer to each other uniformly from the functional film 100 side.

[0038] As described above, by applying uniform pressure from the functional film 100 side while creating a vacuum in the enclosed space, the release film 1 pushes the functional layer 3 in accordance with the shape of the recess 62. In conjunction with this pushing, the functional layer 3 located on the electronic component 4 side of the release film 1 deforms to conform to the shape of the recess 62. As a result, as shown in Figure 3(c), with the functional layer 3 pushed in to conform to the shape of the recess 62, the top and side surfaces of the electronic component 4, as well as the top surface of the substrate 5 exposed from the electronic component 4, are covered by the functional layer 3.

[0039] On the other hand, the press molding method is a method in which, for example, a functional film 100 is placed on an electronic component 4 mounted on a substrate 5, a cushioning material is then placed on the functional film 100, and these are then sandwiched between two flat plates from the top and bottom sides, and then the two flat plates are brought close together and pressure is applied.

[0040] In the press molding method, first, a cushioning material is placed on the functional film 100, and the functional film 100 and the electronic component 4 are brought close together. This causes the release film 1 to press the functional layer 3 in accordance with the shape of the recess 62, and this pressing deforms the functional layer 3, which is located on the electronic component 4 side of the release film 1, to conform to the shape of the recess 62. As a result, as shown in Figure 3(c), with the functional layer 3 pressed in to conform to the shape of the recess 62, the top and side surfaces of the electronic component 4, as well as the top surface of the substrate 5 exposed from the electronic component 4, are covered by the functional layer 3.

[0041] In the bonding step [2-1] using vacuum pressure forming or press molding, the bonding temperature is preferably set to a relatively low temperature range when using the functional film 100 having the configuration described above. Specifically, the temperature is preferably set to 90°C or higher and 140°C or lower, more preferably to 100°C or higher and 130°C or lower, and even more preferably to 110°C or higher and 120°C or lower. By appropriately setting the heating temperature of the functional film 100 when using vacuum pressure forming or press molding, the functional layer 3 can be coated on the side surface of the electronic component 4 and the upper surface of the substrate 5 with excellent coating accuracy. The pressure applied is not particularly limited, but is preferably 0.1 MPa to 30.0 MPa, and more preferably 0.5 MPa to 25.0 MPa. The application time is not particularly limited, but is preferably 5 seconds to 90 minutes, and more preferably 30 seconds to 10 minutes. By setting the conditions in the application process within the above range, the functional layer 3 can be pressed into the recesses 62 between adjacent electronic components 4, and the top and side surfaces of the electronic components 4, as well as the top surface of the substrate 5 exposed from the electronic components 4, can be covered with excellent coverage accuracy by this functional layer 3.

[0042] In the functional film 100, as described above, the release film 1 conforms to the shape of the recess 62 and presses the functional layer 3 into place so that the top and side surfaces of the electronic component 4, and the top surface of the substrate 5 exposed from the electronic component 4, are covered by the functional layer 3 with excellent coverage accuracy, and also functions as a protective (cushioning) material that prevents the pressed functional layer 3 from breaking. Furthermore, the release film 1 is peeled off from the functional layer 3 in the next step [2-2].

[0043] [2-2] Next, as shown in Figure 3(d), the release film 1 is peeled off from the functional film 100 attached to the electronic component 4.

[0044] During the peeling of the release film 1, delamination occurs at the interface between the release film 1 and the functional layer 3 in the functional film 100, resulting in the release film 1 being peeled away from the functional layer 3. This allows for the creation of a functional layer-coated electronic component mounting substrate 50 in which the top and side surfaces of the electronic component 4, as well as the top surface of the substrate 5 exposed from the electronic component 4, are covered by the functional layer 3, with the release film 1 peeled away from the functional layer 3.

[0045] The method for peeling off the release film 1 is not particularly limited. For example, it can be peeled off by hand. In manual peeling, for example, one end of the release film 1 is first grasped, and the release film 1 is pulled away from the functional layer 3 from this grasped end, and then the release film 1 is sequentially pulled away from this end to the center and then to the other end, thereby peeling the release film 1 from the functional layer 3.

[0046] The peeling temperature is preferably 180°C or lower, more preferably 165°C or lower, and even more preferably 150°C or lower.

[0047] By going through steps [2-1] and [2-2], a functional layer-coated electronic component mounting substrate 50 can be obtained in which the top and side surfaces of the electronic component 4, as well as the top surface of the substrate 5 exposed from the electronic component 4, are covered with the functional layer 3, with the release film 1 peeled off from the functional layer 3.

[0048] [Release film] The release film (release film 1) of this embodiment will be described below. As described above, the release film 1 is preferably used as a release film in a functional film 100 used to manufacture a functional layer coated electronic component mounting substrate 50.

[0049] As shown in Figure 6, the release film 1 includes a cushion layer 13 and a release layer 11 provided on one side of the cushion layer 13. Preferably, the release film 1 has a secondary release layer 12 on the side of the cushion layer 13 opposite to the side on which the release layer 11 is provided. When the release film 1 is used as a functional film, as shown in Figure 5, the functional film 100 preferably has a structure in which a functional layer 3 is laminated on the surface of the release layer 11 of the release film 1, in other words, a structure in which the functional layer 3 / release layer 11 / cushion layer 13 / secondary release layer 12 are laminated in this order.

[0050] When the release film 1 is subjected to viscoelasticity testing under the conditions of a temperature of 120°C, a frequency of 1 Hz, and the torsion mode, the storage modulus measured 300 seconds after the start of the measurement is G'[Pa], and the loss tangent is tanδ. In this case, the value of I, defined by the following formula, is 3.5 or greater. I = (G' / 100000) / tanδ

[0051] Based on the inventors' studies and findings, the value of formula I correlates well with the conformability to the uneven surface when covering the uneven structure described above. The correlation between the value of formula I and conformability can be explained as follows.

[0052] A value of 3.5 or greater in formula I means that the storage modulus G' of release film 1 at 120°C is relatively large, and the loss tangent tanδ at 120°C is relatively small (120°C: roughly corresponds to the temperature during hot pressing). The relatively large G' at 120°C and the relatively small tanδ at 120°C (meaning that elasticity is more dominant than viscosity at 120°C) indicate that the release film 1 does not soften excessively during heating in the hot press process, but maintains appropriate rubber elasticity. Because the release film 1 maintains appropriate rubber elasticity at the temperature during hot pressing, the release film 1 can maintain its shape to some extent even when subjected to external force (flow is suppressed). As a result, it is thought that the force with which the release film 1 is "pressed" into the uneven surface when covering the uneven surface is less likely to dissipate. Consequently, it is thought that the ability to conform to the uneven surface when covering the uneven surface is improved.

[0053] Incidentally, the reason we used the G' and tanδ values ​​"300 seconds after the start of measurement" is to make the measurement conditions closer to the conditions under which release film 1 is actually applied (typical pressing conditions: around 115°C for about 2 minutes).

[0054] The value of Formula I should be 3.5 or higher, but from the viewpoint of better conformability to uneven surfaces, it is preferably 4 or higher, more preferably 5 or higher, particularly preferably 5.5 or higher, and especially preferably 6 or higher. There is no particular upper limit to the value of Formula I, but from the viewpoint of practical material design, the upper limit is, for example, 30.

[0055] The value of G' itself at 120°C is, for example, 1.0 × 10⁻⁶. 5 ~1.0×10 6 It is [Pa]. The value of tanδ itself at 120°C is, for example, 0.15 to 0.4. By designing the release film 1 so that G' and tanδ at 120°C fall within the specified numerical range, the aforementioned "dissipation of force when the release film 1 is pressed into the uneven surface" can be further suppressed, resulting in improved conformability to the uneven surface.

[0056] A release film 1 having a value of 3.5 or higher in formula I can be manufactured by selecting appropriate materials and manufacturing methods. While the materials and manufacturing methods of the release film 1 are not limited, it is preferable to manufacture a release film 1 having a value of 3.5 or higher in formula I by employing one or more of the following methods: (i) using polyethylene and / or polypropylene as the material for the cushion layer 13, (ii) including rubber particles in the cushion layer 13, (iii) crosslinking the resin in the cushion layer 13 by irradiation with radiation (e.g., electron beams), or (iv) making the cushion layer 13 a multilayer structure. Details of these methods will be described later.

[0057] The following is a continuation of the explanation regarding release film 1.

[0058] (Cushioning layer) The cushion layer 13 preferably contains a polyolefin resin. In the manufacturing process of the functional layer-coated electronic component mounting substrate 50 described above, the cushion layer 13 plays the role of pressing the functional layer 3 so as to conform to the shape of the irregularities 6 of the electronic component mounting substrate 45. In other words, the cushion layer 13 makes it possible to obtain a functional film 100 in which the conformability (embedding) of the functional layer 3 to the irregularities is improved.

[0059] The polyolefin resin used in the release film 1 is a polymer (including olefin-based elastomers) composed of olefins as essential monomer components; that is, a polymer containing at least one constituent unit derived from an olefin in its molecule (in one molecule). The type of olefin is not particularly limited. Examples include α-olefins such as ethylene, propylene, 1-butene, and 4-methyl-1-pentene.

[0060] Polypropylene resin and / or polyethylene resin are preferably used as the polyolefin resin.

[0061] Examples of polypropylene resins include propylene homopolymers (homopolypropylene) and propylene-α-olefin copolymers. Examples of α-olefins in propylene-α-olefin copolymers include ethylene and α-olefins having 2 to 20 carbon atoms (excluding propylene), such as 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene. One type of α-olefin may be used, or two or more types may be used. The propylene copolymer (propylene-α-olefin copolymer, etc.) may be a block copolymer, a random copolymer, or a graft copolymer.

[0062] Examples of polyethylene resins include ethylene homopolymers and ethylene-α-olefin copolymers. Examples of polyethylene-based resins include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). LDPE is a low-density polyethylene that primarily contains constituent units derived from ethylene, for example, and is manufactured using a high-pressure method. LLDPE is a low-density polyethylene with short-chain branching, manufactured by a medium-to-low pressure process, and primarily composed of structural units derived from ethylene, for example.

[0063] Examples of α-olefins in ethylene-α-olefin copolymers include α-olefins having 3 to 20 carbon atoms, such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene (preferably 1-butene, 1-pentene, 1-hexene, 1-octene, more preferably 1-pentene, 1-hexene, and 1-octene). One type of α-olefin may be used, or two or more types may be used.

[0064] In a preferred embodiment, the cushion layer 13 contains both polypropylene resin and polyethylene resin. This makes it easier for the value of formula I to be 3.5 or higher, and further moderate indentation and conformability to uneven surfaces can be achieved. When the cushion layer 13 contains both polypropylene resin and polyethylene resin, the blending ratio of polypropylene resin to polyethylene resin is, for example, 20:80 to 80:20 by mass ratio of polypropylene resin to polyethylene resin, preferably 30:70 to 70:30, and more preferably 40:60 to 60:40.

[0065] The cushion layer 13 may also contain polyolefin resins other than those described above. Examples of such resins include ethylene-propylene-rubber (EPR), ethylene-propylene-diene rubber (EPDM), thermoplastic olefin elastomer (TPO), ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-(meth)alkyl acrylate copolymer, or modified copolymers obtained by copolymerizing these with maleic anhydride.

[0066] In one embodiment, the cushion layer 13 preferably contains rubber particles. This makes it easier for the value of formula I to be 3.5 or higher, and further enhances appropriate indentation and conformability to uneven surfaces. The rubber particles maintain a high elastic modulus of the cushion layer 13 under heating conditions, and also have the function of imparting flexibility and toughness to the cushion layer 13.

[0067] The rubber particles preferably include (meth)acrylic rubber, butadiene rubber, or silicone-acrylic rubber. These may be used individually or in combination of two or more.

[0068] The rubber particles are preferably graft copolymers containing a rubber-like polymer (crosslinked polymer), that is, core-shell type rubber particles having a core made of a rubber-like polymer (crosslinked polymer) and a shell covering it.

[0069] Examples of rubbery polymers include butadiene-based crosslinked polymers, (meth)acrylic-based crosslinked polymers, and organosiloxane-based crosslinked polymers. Among these, (meth)acrylic-based crosslinked polymers are preferred, and acrylic-based crosslinked polymers (acrylic rubbery polymers) are more preferred, from the viewpoint of not impairing the transparency of the resulting cushion layer.

[0070] In other words, it is preferable that the acrylic graft copolymer contains an acrylic rubbery polymer. The acrylic graft copolymer containing an acrylic rubbery polymer is preferably a core-shell type particle having a core portion containing the acrylic rubbery polymer and a shell portion covering it. Such a core-shell type particle is a multi-stage polymer obtained by polymerizing a monomer mixture mainly composed of methacrylic acid ester in at least one stage in the presence of an acrylic rubbery polymer. Polymerization can be carried out by emulsion polymerization. The polymer of the monomer mixture constituting the shell portion is a graft component for the acrylic rubbery polymer. The monomer mixture preferably contains methacrylic acid ester as the main component.

[0071] The average particle diameter of the rubber particles is preferably 100 to 700 nm, and more preferably 300 to 600 nm. If the average particle diameter is 100 nm or more, the cushion layer 13 may have an elastic modulus appropriate for exhibiting indentation properties into the functional layer 3, and if it is 700 nm or less, the transparency of the cushion layer 13 is less likely to decrease.

[0072] The average particle size of rubber particles is determined as the average of the equivalent circle diameters of 100 particles obtained by SEM or TEM imaging of the film surface and sections. The equivalent circle diameter can be determined by converting the projected area of ​​the particles obtained by imaging to the diameter of a circle with the same area. In this case, rubber particles (acrylic graft copolymer) observed by SEM and / or TEM observation at a magnification of 5000x are used to calculate the average particle size. The average particle size of rubber particles (acrylic graft copolymer) in the dispersion can be measured using a zeta potential / particle size measurement system (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.).

[0073] The rubber particle content is, for example, 1 to 20% by mass, preferably 3 to 18% by mass, and more preferably 5 to 15% by mass, relative to the entire cushion layer 13. By using rubber particles within the above range, the resulting cushion layer 13 has an appropriate modulus of elasticity, relatively few irregularities caused by the rubber particles, and a certain degree of transparency.

[0074] In one embodiment, the cushion layer 13 preferably contains a crosslinked polyolefin resin. This is because the crosslinked polyolefin resin has a high crosslink density, which helps maintain a high modulus of elasticity at high temperatures.

[0075] Crosslinked polyolefin resins can be obtained by crosslinking an uncrosslinked polyolefin resin by known or conventional methods, such as (i) irradiation with radiation (e.g., electron beams), (ii) crosslinking by mixing with polyethylene organosilane compounds and permeating with water in the presence of a catalyst, or (iii) heating after mixing with a crosslinking agent (e.g., organic peroxides). In this embodiment, from the viewpoint of good workability, the crosslinked polyolefin resin is preferably (i) a polyolefin resin crosslinked by radiation (e.g., electron beams). Examples of "uncrosslinked polyolefin resins" here include the aforementioned polypropylene resin and polyethylene resin.

[0076] In one embodiment, the cushion layer 13 may be composed of two or more layers. Of course, the cushion layer 13 may be a single layer, as long as the value of formula I is 3.5 or greater.

[0077] From the viewpoint of further enhancing the ability to conform to uneven surfaces, it is preferable that the cushion layer 13 includes a first cushion layer that is in contact with the release layer 11, and a second cushion layer on the opposite side of the first cushion layer from the side facing the release layer 11. Furthermore, when p1 is the mass ratio of polyethylene in the total resin contained in the first cushion layer, and p2 is the mass ratio of polyethylene in the total resin contained in the second cushion layer, it is preferable that p1 > p2. Similarly, the cushion layer 13 preferably includes a first cushion layer in contact with the release layer 11, a second cushion layer on the opposite side of the first cushion layer from the side facing the release layer 11, and a third cushion layer on the opposite side of the second cushion layer from the side facing the first cushion layer. Furthermore, when p1 is the mass ratio of polyethylene in the total resin contained in the first cushion layer, p2 is the mass ratio of polyethylene in the total resin contained in the second cushion layer, and p3 is the mass ratio of polyethylene in the total resin contained in the third cushion layer, it is preferable that p1 > p2 > p3. Incidentally, if a portion of the resin in the first cushion layer is polyethylene, the remaining resin in the first cushion layer is, for example, polypropylene. The same applies to the second cushion layer.

[0078] The reason why it is preferable for p1 > p2 or p1 > p2 > p3, that is, for the mass ratio of polyethylene on the release layer 11 side of the cushion layer 13 to be large and the mass ratio of polyethylene on the secondary release layer 12 side of the cushion layer 13 to be small, can be explained as follows. As a general trend, a larger mass ratio of polyethylene resin in the cushion layer 13 results in a smaller G' at 120°C, while a smaller mass ratio of polyester resin in the cushion layer results in a larger G' at 120°C. For example, if the cushion layer 13 has a two-layer structure and p1 > p2, then it is considered that (storage modulus of the first cushion layer at 120°C) < (storage modulus of the second cushion layer at 120°C). When the release film 1 is used, pressure is applied from the side of the second cushion layer or the third cushion layer (or from the side of the secondary release layer 12, if present). Therefore, in terms of "suppressing the dissipation of force when the release film 1 is pressed into the uneven surface," as already mentioned, it is thought that the dissipation of force is further suppressed if the second cushion layer or the third cushion layer, to which the pressure is transmitted more directly, is harder. In addition, the fact that the second or third cushion layer has a relatively large G' at 120°C and is less prone to plastic deformation, while the first cushion layer has a relatively small G' at 120°C and is more prone to plastic deformation than the second or third cushion layer, is also thought to contribute to the further improvement in conformability to uneven surfaces.

[0079] When the cushion layer 13 comprises a first cushion layer and a second cushion layer, the value of p1-p2 is, for example, 5 to 30 mass%, preferably 5 to 25 mass%. Also, the value of p1 itself is, for example, 30 to 50 mass%, and the value of p2 itself is, for example, 10 to 40 mass%. When the cushion layer 13 comprises a first cushion layer, a second cushion layer, and a third cushion layer, the value of p1-p2 is, for example, 5-15 mass%, and the value of p2-p3 is, for example, 5-15 mass%. Furthermore, the value of p1 itself is, for example, 30-50 mass%, the value of p2 itself is, for example, 20-40 mass%, and the value of p3 itself is, for example, 10-30 mass%.

[0080] If the cushion layer 13 comprises a first cushion layer and a second cushion layer, the ratio of their thicknesses is, for example, first cushion layer:second cushion layer = 10:90 to 90:10, specifically, first cushion layer:second cushion layer = 15:85 to 85:15. When the cushion layer 13 comprises a first cushion layer, a second cushion layer, and a third cushion layer, the thickness ratio is, for example, first cushion layer:second cushion layer:third cushion layer = 10:45:45 to 96:2:2, specifically, first cushion layer:second cushion layer:third cushion layer = 30:35:35 to 90:5:5.

[0081] (Release layer) As shown in Figure 5, the release layer 11 is laminated on one side of the cushion layer 13. When the release film 1 is used as a material for the functional film 100, the functional layer 3 is laminated on the surface of the release layer 11. The release layer 11 is a layer that has release properties for the functional layer 3.

[0082] The release layer 11 preferably contains a polyolefin resin. Examples of polyolefin resins used in the release layer 11 include linear high-density polyethylene, linear low-density polyethylene, high-pressure low-density polyethylene, isotactic polypropylene, syndiotactic polypropylene, block polypropylene, random polypropylene, polybutene, 1,2-polybutadiene, 4-methylpentene, cyclic polyolefins, and copolymers thereof (e.g., ethylene-methyl methacrylate copolymer).

[0083] The release layer 11 may contain additives as needed, such as antistatic agents, process oils, plasticizers, release agents, pigments, etc. Furthermore, the outer surface of the release layer 11 (the surface on which the functional layer 3 is laminated) may be subjected to a release treatment, such as coating with a release agent or heat treatment, to improve release properties.

[0084] (Sub-release layer) As shown in Figure 5, the secondary release layer 12 is laminated as needed on the side of the cushion layer 13 opposite to the side on which the release layer 11 is laminated. When the release film 1 is used as the material for the functional film 100, in the application step of the functional film 100 using the press molding method described above [2-1], a cushioning material for press molding is placed on top of the secondary release layer 12.

[0085] The secondary release layer 12 preferably contains a polyolefin resin. Specific examples of polyolefins include those exemplified as materials constituting the release layer 11. The release layer 11 and the secondary release layer 12 may contain the same polyolefin resin or different polyolefin resins.

[0086] The secondary release layer 12 may optionally contain, for example, an antistatic agent, process oil, plasticizer, release agent, pigment, etc. Furthermore, the outer surface of the secondary release layer 12 (the surface opposite to the surface on which the cushion layer 13 is laminated) may be subjected to a release treatment such as coating with a release agent or heat treatment to improve release properties.

[0087] As an example, the secondary release layer 12 preferably contains inorganic particles such as silica and aluminosilicate (zeolite). The inorganic particles function, for example, as an antiblocking agent. When inorganic particles are used, their amount is, for example, 5 to 30% by mass, preferably 10 to 20% by mass, in the secondary release layer 12.

[0088] (Other layers) The release film (release film 1) of this embodiment may include layers other than the cushion layer, release layer, and secondary release layer. These layers can be placed at any position.

[0089] (Thickness of each layer) In the release film 1, the thickness of the cushion layer 13 is, for example, 50 to 400 μm, preferably 100 to 350 μm, and more preferably 150 to 300 μm. By having the thickness of the cushion layer 13 within the above range, when the release film 1 including this cushion layer 13 is used as a release film for the functional film 100, the pressability against the functional layer 3 is improved, and thus a functional film 100 with excellent conformability can be obtained.

[0090] The thickness of the release layer 11 is, for example, 5 to 100 μm, preferably 15 to 80 μm, and more preferably 30 to 60 μm. By having a release layer 11 thickness within the above range, when the release film 1 is used as a release film for the functional film 100, it is possible to achieve both the release properties of the release film 1 during demolding and the ability to conform to the unevenness of the functional film.

[0091] The thickness of the secondary release layer 12 is, for example, 5 to 100 μm, preferably 15 to 80 μm, and more preferably 30 to 60 μm. A secondary release layer 12 having a thickness within the above range has good release properties with respect to the cushioning material for press molding that is placed on the secondary release layer 12 in the application step of the functional film 100 using the press molding method described above [2-1].

[0092] The overall thickness of the release film 1 can be, for example, 100 to 500 μm.

[0093] (Relationships between each layer) In the release film 1, when P1 is the mass ratio of polyethylene in the total resin contained in the cushion layer 13, P2 is the mass ratio of polyethylene in the total resin contained in the release layer 11, and P3 is the mass ratio of polyethylene in the total resin contained in the secondary release layer 12, it is preferable that P1 > P2 and P1 > P3. When the release film 1 is used, pressure is applied from the side of the secondary release layer 12. Since P1 > P3, that is, the cushion layer 13 contains more polyethylene with a relatively lower melting point than the secondary release layer 12, it is thought that at 120°C, the secondary release layer 12 is "harder" and the cushion layer 13 is "softer". In terms of suppressing the dissipation of force when the release film 1 is pressed into the uneven surface, it is thought that the secondary release layer 12, to which the pressure is directly transmitted, is harder, which further suppresses the dissipation of force. Furthermore, because P1 > P2, the cushion layer 13 can deform sufficiently while suppressing the tackiness of the release layer 11 material, thereby improving the release properties after the release film 1 has been used.

[0094] The P1-P2 values ​​are, for example, 1-50% by mass, specifically 5-40% by mass. The values ​​of P1-P3 are, for example, 1-50 mass%, specifically 5-40 mass%. The value of P1 itself is, for example, 20-50% by mass, specifically 25-50% by mass. The value of P2 itself is, for example, 0 to 30 mass%, specifically 0 to 20 mass%. The value of P3 itself is, for example, 0 to 30 mass%, specifically 0 to 20 mass%.

[0095] [Method for manufacturing release film] The release film 1 can be manufactured, for example, by co-extrusion. Specifically, it is formed by a resin melt extrusion method such as the tubular method, inflation method, or T-die method. More specifically, the release film 1 is manufactured, for example, by feeding the raw materials for the release layer, cushion layer, and optionally secondary release layer into multiple extruders set to predetermined temperatures, and co-extruding a laminated structure containing the raw materials for the release layer, cushion layer, and secondary release layer in this order from the co-extruders.

[0096] Co-extruded laminated structures are typically cooled using a cooling drum or the like. While the cooling method is not limited, it is preferable to cool under rapid cooling or near-rapid cooling conditions (e.g., water cooling) because this suppresses resin crystallization and improves transparency. Therefore, the cooling temperature is preferably 0 to 70°C, and more preferably 10 to 60°C.

[0097] When crosslinking the cushion layer 13, the method can be known or conventional, such as the methods described in (i) to (iii) above. When crosslinking the cushion layer by radiation, radiation is irradiated to the release layer side, the sub-release layer side, or both sides of the resulting laminated structure. Examples of radiation include alpha rays, beta rays, electron beams, gamma rays, and X-rays. Among these, electron beams and gamma rays are preferred, and electron beams are more preferred, from the viewpoint of large crosslinking effects before and after irradiation.

[0098] When irradiating with an electron beam as radiation, the acceleration voltage is preferably 150 to 500 kV. The irradiation dose is preferably 50 to 200 kilogray (kGy). If the acceleration voltage and / or irradiation dose are above the lower limit, the crosslinking of the polyolefin resin in the cushion layer will proceed sufficiently. If the acceleration voltage and / or irradiation dose are below the upper limit, the decomposition of the resin contained in the release layer or sub-release layer can be further suppressed.

[0099] [Method for manufacturing functional films] The functional film 100 of this embodiment can be manufactured by laminating a pre-fabricated functional layer 3 onto a release film 1 using an extrusion lamination method, or by dry lamination of a pre-fabricated functional layer 3.

[0100] The thickness of functional layer 3 is, for example, 3 to 300 μm. By having a thickness within this range, functional layer 3 can fully perform its function.

[0101] The overall thickness of the functional film 100 can be, for example, 100 to 800 μm.

[0102] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention. [Examples]

[0103] Embodiments of the present invention will be described in detail based on examples and comparative examples. It should be noted that the present invention is not limited to these examples.

[0104] <Manufacturing of release film> (Manufacturing of release film containing rubber particles in the cushion layer) Examples 1-4 100% by mass of random polypropylene (Sumitomo Chemical Co., Ltd., S131) ​​was used as the raw material for the release layer. The cushioning layer is made up of 40% by mass of random polypropylene (manufactured by Nippon Polypropylene Co., Ltd., EG7FTB) and low-density polyethylene (density: 0.928 g / cm³). 3The following materials were used: 60% by mass of LF280H (manufactured by Nippon Polyethylene Co., Ltd.) and rubber particles (average particle size: 500 μm, manufactured by Mitsubishi Chemical Corporation, W-450A). The rubber particles were used in the amounts shown in Table 1 (mass %) relative to the total amount of random polypropylene and low-density polyethylene. As raw materials for the secondary release layer, 85% by mass of random polypropylene (Sumitomo Chemical Co., Ltd., S131) ​​and 15% by mass of silica (Nippon Steel Chemical & Material Co., Ltd., product name: SC10-32F) were used. Using the raw materials for each layer prepared as described above, a laminate was formed by co-extrusion using a feed block and a multi-manifold die to produce a release film as a co-extruded film with a total thickness of 350 μm (thickness ratio: release layer / cushion layer / secondary release layer = 1 / 5.5 / 1). The temperature of the multi-manifold die was 250°C and the temperature of the cooling drum was 40°C.

[0105] • Comparative Example 1 A release film was prepared in the same manner as in Example 1, except that rubber particles were not used.

[0106] (Manufacturing of release film containing a cross-linked polyolefin resin cushion layer) Examples 2-1 to 2-10 100% by mass of random polypropylene (Sumitomo Chemical Co., Ltd., S131) ​​was used as the raw material for the release layer. The cushioning layer is made up of 40% by mass of random polypropylene (manufactured by Nippon Polypropylene Co., Ltd., EG7FTB) and low-density polyethylene (density: 0.928 g / cm³). 3 60% by mass of LF280H (manufactured by Nippon Polyethylene Co., Ltd.) was used. As raw materials for the secondary release layer, 85% by mass of random polypropylene (Sumitomo Chemical Co., Ltd., S131) ​​and 15% by mass of silica (Nippon Steel Chemical & Material Co., Ltd., product name: SC10-32F) were used. Using the raw materials for each layer prepared as described above, laminates were formed by co-extrusion using a feed block and a multi-manifold die. Low-density polyethylene was crosslinked by electron beam irradiation from the release layer side, the secondary release layer side, or both sides, using the acceleration voltage and irradiation dose shown in Table 2 below. A release film was then produced as a co-extruded film with a laminated structure having a total thickness of 350 μm (thickness ratio: release layer / cushion layer / secondary release layer = 1 / 5.5 / 1). The temperature of the multi-manifold die was 250°C, and the temperature of the cooling drum was 40°C.

[0107] Comparison Example 2-1 A release film was prepared in the same manner as in Example 2-1, except that electron beam irradiation was not performed.

[0108] (Manufacturing of release film with a multi-layered cushioning layer) Example 3-1 First, we prepared the following materials for each layer. Release layer: Random polypropylene (Sumitomo Chemical Co., Ltd., S131) ​​100% by mass Cushioning layer: For the first cushioning layer, a mixture of (i) polypropylene and (ii) polyethylene was prepared in a mass ratio of 60:40. For the second cushioning layer, a mixture of (i) polypropylene and (ii) polyethylene was prepared in a mass ratio of 70:30. (i) Random polypropylene manufactured by Nippon Polypropylene Co., Ltd., product name: Novatec PP, grade EG7FTB (ii) Low-density polyethylene manufactured by Nippon Polyethylene Co., Ltd., product name: Novatec LD, grade: LF280H Secondary release layer: Random polypropylene (Sumitomo Chemical Co., Ltd., S131) ​​85% by mass, and silica (Nippon Steel Chemical & Material Co., Ltd., product name: SC10-32F) 15% by mass

[0109] Using the raw materials for each layer prepared as described above, a laminate was formed by co-extrusion using a feed block and a multi-manifold die. A release film was then produced as a co-extruded film with a total thickness of 350 μm (thickness ratio: release layer / cushion layer (total in the case of multilayer) / secondary release layer = 1 / 5.5 / 1). The temperature of the multi-manifold die was 250°C and the temperature of the cooling drum was 40°C.

[0110] Examples 3-2 to 3-7 and Comparative Example 3-1 A release film was prepared in the same manner as in Example 3-1, except that the composition of the cushion layer and secondary release layer was as shown in Table 3.

[0111] <Measurement of viscoelasticity of release film> Viscoelasticity measurements were performed using the Anton Paar MCR301 viscoelasticity analyzer with the following settings in torsional mode. The storage modulus G'[Pa] and loss tangent tanδ, measured 300 seconds after the start of the measurement, were then determined. • Gap distance: Film thickness minus 0.03~0.05mm (set so that the normal force is 0.5~1N) ·Temperature: 120℃ • Frequency: 1Hz • Sample: Use a piece of release film manufactured in the above example or comparative example, cut to approximately 4cm x 4cm. • γ (degree of twist): Initial 1%, Final 0.1%

[0112] <Production of functional films> As a resin material (liquid material) for forming the functional layer, a mixture was prepared containing 22 parts by weight of epoxy resin (DIC Corporation, product name: EPICRON N-670), 22 parts by weight of acrylic rubber (Nagase ChemteX Corporation, product name: SG-708-6), and 11 parts by weight of phenol novolac resin (Sumitomo Bakelite Corporation, product name: PR-HF-3), and further containing methyl ethyl ketone as a solvent. The functional layer (thickness: 50 μm) was fabricated by coating the resin material onto the release PET that was dispensed between the dispensing roller and the winding roller, and then drying it. A functional layer was dry-laminated to the release film of each example and comparative example obtained above, and then the release PET was peeled off to obtain a functional film having a structure in which the release film and the functional layer are laminated.

[0113] <Manufacturing of electronic component mounting substrates with recessed areas> To obtain an electronic component mounting substrate 45 provided with recesses 62, first, Si substrates (pseudo-electronic components) measuring 5 mm in length, 10 mm in width, and 0.8 mm in thickness were arranged in a grid pattern on an FR4 substrate (a pseudo-wiring substrate formed by sealing glass fiber cloth with a cured epoxy resin) such that the distance between adjacent Si substrates was 0.2 mm.

[0114] <Performance evaluation of functional films> (1. Mold releasability) The release properties of the release film in the functional films obtained in each example and comparative example were evaluated by the following method. A release film with a functional film is placed on an electronic component mounting substrate 45 provided with a recess 62, such that the longitudinal direction of the release film is parallel to the longitudinal direction of the electronic component mounting substrate 45, and the functional film is in contact with the electronic component mounting substrate 45. Next, using a vacuum press (Kitagawa Seiki Co., Ltd., KVHCIII), the functional film was pressed onto the electronic component mounting substrate 45 under the conditions of a pressure of 13 MPa (effective pressure on the electronic component mounting substrate 45), a temperature of 115°C, and a time of 180 seconds, thereby pressing the functional layer of the functional film into a shape corresponding to the recess 62 provided on the electronic component mounting substrate 45. Next, the release film was peeled off the functional film attached to the electronic component substrate 45 by holding one end of the release film. The appearance of the functional layer after the release film was removed was visually observed, and the results were evaluated based on the evaluation criteria shown below. The evaluation results are shown in each table. [Evaluation Criteria] ◎: No roughness is observed on the surface of the functional layer covering the electronic component mounting substrate. ○: Minute roughness is observed on the surface of the functional layer covering the substrate on which the electronic components are mounted. ×: Obvious roughness is observed on the appearance of the functional layer covering the circuit board with electronic components.

[0115] (2. Followability 1 (Followability to the bottom)) The conformability of the functional films obtained in each example and comparative example to the uneven surfaces of the electronic component mounting substrate was evaluated by measuring the defect height of the functional layer. The defect height was measured using the following method. In the same manner as described in the evaluation of "1. Release Properties" above, the release film was peeled off from the functional film attached to the electronic component mounting substrate 45 by holding one end of the release film. Subsequently, the accuracy of the coverage of the bottom of the recess 62 was visually observed for the functional layer that had been pressed to correspond to the shape of the recess 62, and the results were evaluated based on the evaluation criteria shown below. The evaluation results are shown in the respective tables. [Evaluation Criteria] ◎◎: The functional layer covers the bottom of the recess 62, and no protrusions caused by lifting of the functional layer from the bottom of the recess 62 are observed. ◎: The functional layer covers the bottom of the recess 62, but tiny protrusions of the functional layer are observed around the cross-shaped portion 63. ○: The functional layer covers the bottom of the recess 62, but small protrusions of the functional layer are observed around the cross-shaped portion 63. ×: Although the functional layer covers the bottom of the recess 62, a clear protrusion is observed around the cross-shaped portion 63, which is caused by the functional layer lifting away from the bottom of the recess 62.

[0116] (3. Followability 2 (Followability to walls)) In the same manner as described in "2. Followability 1" above, the release film was peeled off the functional film attached to the electronic component mounting substrate 45 by holding one end of the release film. Then, in order to evaluate the coating accuracy of the side surface (wall surface) of the protrusion 61, the film was cut and separated into individual pieces using a dicer along the recess 62. The coating defects on the side surface (wall surface) of the separated protrusion 61 were measured using a microscope. The measurement results are shown in the tables.

[0117] [Table 1]

[0118] [Table 2]

[0119] [Table 3]

[0120] The functional film in the example exhibited excellent release properties for the release film and superior conformability of the functional layer to the uneven surfaces of the electronic component mounting substrate. [Explanation of symbols]

[0121] 1. Release film 3 Functional Layers 4 Electronic Components 5 circuit boards 6 Unevenness 11 Release layer 12 Sub-release layer 13. Cushioning layer 45 Electronic component mounted circuit board 50 Functional layer coated electronic component mounting board 61 Convex part 62 recesses 63 Cross 100 Functional Films

Claims

1. A release film comprising a cushion layer and a release layer laminated on one side of the cushion layer, The cushion layer contains a polyolefin resin, and the polyolefin resin is uncrosslinked. A release film in which, when the release film is subjected to viscoelasticity testing under the conditions of a temperature of 120°C, a frequency of 1 Hz, and torsion mode, the storage modulus measured 300 seconds after the start of measurement is G' [Pa], and the loss tangent is tanδ, and the value of I, defined by the following formula, is 3.5 or greater. I=(G' / 100000) / tanδ

2. The release film according to claim 1, The polyolefin resin is a release film comprising one or more selected from the group consisting of polypropylene and polyethylene.

3. A release film according to claim 1 or 2, The cushion layer is a release film containing rubber particles.

4. A release film according to any one of claims 1 to 3, A release film further comprising a secondary release layer laminated on the side of the cushion layer opposite to the side on which the release layer is laminated.

5. The release film according to claim 4, The aforementioned secondary release layer is a release film containing a polyolefin resin.

6. A release film according to any one of claims 1 to 5, The aforementioned release layer is a release film containing a polyolefin resin.

7. A release film according to claim 4 or 5, Let P1 be the mass ratio of polyethylene in the total resin contained in the cushion layer. Let P2 be the mass ratio of polyethylene in the total resin contained in the release layer. When P3 is the mass ratio of polyethylene in the total resin contained in the aforementioned secondary release layer, A release film where P1 > P2 and P1 > P3.

8. A release film according to any one of claims 1 to 7, The cushion layer is a release film containing both polypropylene resin and polyethylene resin.

9. A release film according to any one of claims 1 to 8, A functional film comprising a functional layer laminated on the release layer of the release film.

Images