JP7806502B2 - protective film - Google Patents

Description

The present invention relates to a protective film that is attached to a resin substrate when the resin substrate is subjected to thermal bending processing under heat.

Sunglasses lenses equipped with a resin substrate in which both sides of a polarizer are coated with coating layers made of polycarbonate resin, polyamide resin, or cellulose resin are manufactured, for example, by punching the resin substrate into a predetermined shape, such as a circle, in a planar view with protective films attached to both sides of the flat resin substrate when viewed from above, and then subjecting the resin substrate to a heat-bending process under heat. The protective films are then peeled off from the heat-bent resin substrate, and a polycarbonate layer is injection-molded onto the concave surface of the resin substrate.

Proposed protective films include, for example, a base material primarily made of polyolefin resin that is attached to the resin substrate via an adhesive layer primarily made of polyethylene, ethylene-propylene copolymer, or the like (see, for example, Patent Document 1).

As described above, protective films are applied to both sides of the resin substrate prior to punching the resin substrate. This application is typically performed by hand or using an arm provided on a machine tool. During application of the protective film, wrinkles may form in the protective film or air bubbles may remain between the protective film and the resin substrate. This may require at least a portion of the protective film to be peeled off from the resin substrate and then re-applied (re-adhered) to the resin substrate.

However, with protective films configured as described above, it is not possible to obtain sufficient re-adhesion properties when the protective film is peeled off from the resin substrate and then re-attached to the resin substrate. Therefore, there has been a demand for the development of such protective films with excellent re-adhesion properties.

This problem occurs not only with the sunglasses lenses mentioned above, but also with resin substrates such as lenses in goggles and visors in helmets.

Japanese Patent Application Laid-Open No. 2003-145616

The object of the present invention is to provide a protective film with excellent re-adhesion properties that can be applied to a resin substrate, then at least partially peeled off, and then re-applied to the resin substrate.

These objects can be achieved by the present invention as set forth in (1) to ( 8 ) below.
(1) A protective film to be attached to a resin substrate when the resin substrate is subjected to a heat bending process under heating,
a substrate layer;
an adhesive layer positioned between the base layer and the resin substrate and adhering to the resin substrate;
the base material layer is composed of a laminate having a first layer located on the opposite side of the adhesive layer and a second layer located on the adhesive layer side,
the adhesive layer has a surface roughness Ra of 0.20 μm or less on the surface facing the resin substrate, as measured in accordance with JIS B 0601;
A protective film characterized in that the modulus of elasticity is 300 MPa or more and 600 MPa or less when a test piece (No. 1 dumbbell) taken from the protective film is measured in accordance with JIS K 7127 under an atmosphere of 23°C and 60% RH using an autograph manufactured by Shimadzu Corporation at a tension rate of 500 mm/min .

( 2 ) The protective film according to (1) above, wherein the first layer contains a thermoplastic resin as a main material and has a melting point of 150°C or higher, the second layer contains a thermoplastic resin as a main material and has a melting point of 120°C or higher, and the adhesive layer contains a thermoplastic resin as a main material and has a melting point of 110 °C or lower.

( 3 ) The protective film according to ( 2 ) above, wherein the thermoplastic resin contained in the first layer and the thermoplastic resin contained in the second layer both contain polyolefin-based resins.

( 4 ) The protective film according to any one of (1) to ( 3 ) above, wherein the adhesive layer contains, as a main material, a polyolefin resin having adhesive properties.

( 5 ) A protective film according to any one of (1) to (4) above, in which a protective film having a width of 25 mm and a length of 200 mm is attached to a polycarbonate substrate, and then, in an environment of 25°C, one end of the protective film is held and peeled off in a 90° direction to a length of 100 mm, and then the end of the protective film is released to reattach the protective film to the polycarbonate substrate, and one minute after reattachment, the total area in a plan view of the area where the polycarbonate substrate and the protective film are not bonded is less than 1250 ^mm2 .

( 6 ) The protective film according to any one of (1) to ( 5 ) above, which is attached to both sides of the resin substrate.

( 7 ) The protective film according to any one of (1) to (6) above, wherein the resin substrate has a coating layer on both sides, one side or the other side, which is composed of a monolayer or laminate having at least one layer selected from the group consisting of a polycarbonate resin layer, a polyamide resin layer and a cellulose resin layer.

( 8 ) The protective film according to any one of (1) to ( 7 ) above, wherein the resin substrate is subjected to the heat bending process by press molding or vacuum molding.

According to the present invention, the adhesive layer of the protective film has a surface roughness Ra of 0.20 μm or less on the surface facing the resin substrate, measured in accordance with JIS B 0601. By setting the surface roughness Ra of the adhesive layer on the surface facing the resin substrate to the above-mentioned upper limit or less, the protective film can be made to have excellent re-adhesion properties when it is attached to a resin substrate, at least a portion of which is then peeled off, and then re-attached to the resin substrate.

1A to 1C are schematic diagrams illustrating a method for manufacturing a sunglass lens using a protective film. 10A and 10B are schematic diagrams illustrating a method of peeling off at least a portion of a protective film attached to a resin substrate and then attaching the protective film to the resin substrate again. 1 is a longitudinal sectional view showing a preferred embodiment of a protective film of the present invention.

The protective film of the present invention will now be described in detail based on preferred embodiments shown in the accompanying drawings. In this specification, the term "main material" refers to a constituent material that accounts for 50% or more by weight in each layer. For example, "The first layer 16 contains a thermoplastic resin as its main material." means that, when the total weight of the first layer 16 is 100% by weight, the thermoplastic resin contained in the first layer 16 accounts for 50% or more by weight in the first layer 16.

The protective film of the present invention is a protective film that is attached to a resin substrate when the resin substrate is subjected to thermal bending processing under heating. It has a base layer and an adhesive layer that is positioned between the base layer and the resin substrate and adheres to the resin substrate. The base layer is composed of a laminate having a first layer positioned on the opposite side of the adhesive layer and a second layer positioned on the adhesive layer side. The adhesive layer is characterized in that the surface roughness Ra of the surface facing the resin substrate, measured in accordance with JIS B 0601, is 0.20 μm or less.

By configuring the protective film in this way, i.e., by setting the surface roughness Ra of the surface of the adhesive layer of the protective film facing the resin substrate to be equal to or less than the above upper limit, the protective film can be made to have excellent re-adhesion properties when it is attached to a resin substrate, then at least a portion of it is peeled off, and then re-attached to the resin substrate.

Before explaining the protective film of the present invention, we will explain the method for manufacturing sunglasses lenses using the protective film of the present invention.

<Sunglasses lens manufacturing method>
Fig. 1 is a schematic diagram illustrating a method for manufacturing a sunglass lens using a protective film, and Fig. 2 is a schematic diagram illustrating a method for peeling off at least a portion of a protective film attached to a resin substrate and then attaching the film back to the resin substrate. For convenience of explanation, the upper side of Fig. 1 and Fig. 2 will be referred to as "upper" and the lower side as "lower" below.

Each step in the manufacturing method for sunglasses lenses will be described in detail below.
[1] First, a flat resin substrate 21 is prepared, and protective films 10 (masking tape) are attached to both sides of the resin substrate 21 to obtain a laminate 100 in which the protective films 10 are attached to both sides of the resin substrate 21 (see FIG. 1(a)).

In this embodiment, the resin substrate 21 is a polarizer 23 that functions as an optical element that extracts linearly polarized light having a polarization plane in a predetermined direction from unpolarized natural light, and is coated on both sides with a coating layer 24. In this resin substrate 21, the coating layer 24 is composed of a single layer or laminate having at least one layer of a polycarbonate resin layer, a polyamide resin layer, and a cellulose resin layer such as triacetyl cellulose. Furthermore, the coating layer 24 may be formed on both sides (both sides) of the polarizer 23, or it may be formed on either the top surface (one side) or the bottom surface (the other side).

[2] Next, as shown in Figure 1(b), the prepared laminate 100, i.e., the resin substrate 21 with the protective films 10 attached to both sides thereof, is punched out in its thickness direction, so that the laminate 100 has a circular shape in plan view.

[3] Next, as shown in Figure 1(c), the circular laminate 100 is subjected to a heat bending process under heat.

This hot bending process is usually carried out by press molding using a mold or vacuum forming (rema forming).

As mentioned above, in this embodiment, the resin substrate 21 has a coating layer 24, which is composed of a single layer or a laminate having at least one of a polycarbonate resin layer, a polyamide resin layer, and a cellulose resin layer. Therefore, the heating temperature (molding temperature) of the laminate 100 (resin substrate 21) is set to approximately 110°C or higher and 160°C or lower, and more preferably 140°C or higher and 150°C or lower, taking into account the melting or softening temperature of the coating layer 24. By setting the heating temperature within this range, the resin substrate 21 can be brought into a softened or molten state, ensuring reliable thermal bending of the resin substrate 21, while preventing alteration or deterioration of the resin substrate 21.

[4] Next, as shown in FIG. 1(d), the protective film 10 is peeled off from the thermally bent resin substrate 21, i.e., the laminate 100, and then a polycarbonate layer 30 made of polycarbonate resin is injection molded onto the concave surface of the resin substrate 21. Note that instead of the polycarbonate layer 30, a polyamide layer made of polyamide resin may be formed on the concave surface of the resin substrate 21.

This produces a sunglass lens 200 equipped with a thermally bent resin substrate 21.

In the above-described method for manufacturing sunglasses lenses, protective films 10 are attached to both sides of the resin substrate 21 in step [1] prior to punching the resin substrate 21 in the thickness direction in step [2], thereby obtaining a laminate 100 in which protective films 10 are attached to both sides of the resin substrate 21.

The protective film 10 in this laminate 100 is typically attached by hand or using an arm on a machine tool, but this can sometimes result in wrinkles in the protective film 10 or air bubbles remaining between the protective film 10 and the resin substrate 21.

In this case, as shown in FIG. 2(a), one end of the protective film 10 in the laminate 100, in which the protective film 10 is attached to both sides of the resin substrate 21, is grasped, and then, as shown in FIG. 2(b), the protective film 10 is peeled off from this end to the middle, thereby partially peeling off the protective film 10. Then, by releasing the grip on the one end of the protective film 10 and re-attaching the peeled protective film 10 to the resin substrate 21, the protective film 10 is re-attached (re-adhered) to the resin substrate 21, as shown in FIG. 2(c). However, when the protective film 10 is re-attached to the resin substrate 21 in this manner, there is a problem in that the adhesion of the protective film 10 to the resin substrate 21 is not as sufficient as when the protective film 10 was first attached to the resin substrate 21.

As a result of the inventor's investigation into this issue, it was found that the re-adhesion of a protective film 10 to a resin substrate 21 after it has been peeled off is closely related to the surface properties of the adhesive layer 11 on the protective film 10 on the side opposite the base layer 15, i.e., the surface of the adhesive layer 11 on the resin substrate 21 side.

The inventors then conducted further research into the relationship between the re-adhesion of the protective film 10 and the surface properties of the surface of the adhesive layer 11 facing the resin substrate 21. As a result, they discovered that by setting the surface roughness Ra of the surface of the adhesive layer 11 facing the resin substrate 21 to 0.20 μm or less, the protective film 10, once peeled off, exhibits excellent re-adhesion to the resin substrate 21, leading to the completion of the present invention.

Therefore, by using the protective film of the present invention, in which the surface roughness Ra on the surface facing the resin substrate 21 is set to 0.20 μm or less, as the protective film 10 and re-attaching the protective film 10, it is possible to effectively suppress or prevent waste of the protective film 10 and, ultimately, the resin substrate 21. This makes it possible to manufacture sunglass lenses 200 with a high yield. This protective film 10 (protective film of the present invention) is described in detail below.

<Protective film 10>
3 is a longitudinal sectional view showing a preferred embodiment of the protective film of the present invention. For convenience of explanation, the upper side of FIG. 3 will be referred to as "upper" and the lower side as "lower."

The protective film 10 has a base layer 15 and an adhesive layer 11 located between the base layer 15 and the resin substrate 21 and adhering (bonding) to the resin substrate 21. As shown in Figure 3, the base layer 15 has a first layer 16 located on the side opposite the adhesive layer 11, i.e., on the mold side, and a second layer 17 located on the adhesive layer 11 side, i.e., on the resin substrate 21 side.

Each of these layers will be described in detail below.
<<Adhesive layer 11>>
The adhesive layer 11 is located (interposed) between the base material layer 15 and the resin substrate 21 and adheres to the resin substrate 21 to bond the base material layer 15 to the resin substrate 21 .

This adhesive layer 11 is preferably one that allows the punching and heat bending of the resin substrate 21 in steps [2] and [3] to be carried out without peeling the protective film 10 from the resin substrate 21, and that allows the protective film 10 to be peeled from the resin substrate 21 in step [4].

Furthermore, in the present invention, a material that can exhibit excellent re-adhesion is used in the re-application of the protective film 10 to the resin substrate 21, which is carried out as necessary prior to step [2].

From this perspective, the adhesive layer 11 preferably contains a thermoplastic resin with adhesive properties as its primary material, and more preferably contains a thermoplastic resin with a melting point of 110°C or less. Using such a material for the adhesive layer 11 significantly enhances the effect achieved by setting the surface roughness Ra of the adhesive layer 11 on the resin substrate 21 side to 0.20 μm or less, i.e., the effect that a protective film 10, once peeled, can be reattached to the resin substrate 21 with excellent re-adhesion. Furthermore, by containing a thermoplastic resin with a melting point of 110°C or less in the adhesive layer 11, the melting point of the adhesive layer 11 can be easily set to 110°C or less. This allows the adhesive layer 11 to have excellent flexibility at low temperatures, such as room temperature, thereby more significantly enhancing the effect achieved by setting the surface roughness Ra to 0.20 μm or less. In other words, a protective film 10, once peeled, can be reattached to the resin substrate 21 with excellent re-adhesion. Furthermore, from the perspective of achieving this effect more significantly, the melting point of the adhesive layer 11 is preferably 110°C or less, more preferably 100°C or less, and even more preferably 70°C or more and 95°C or less.

In addition, it is preferable that the adhesive layer 11 contains a polyolefin-based resin alone as the thermoplastic resin, or a combination of a polyolefin-based resin and an elastomer. By using such a thermoplastic resin in the adhesive layer 11, the above-mentioned effects can be more reliably achieved.

The adhesive polyolefin resin is not particularly limited and may, for example, be a polypropylene homopolymer, a polyethylene homopolymer, a propylene-ethylene block copolymer with an EPR phase (rubber phase), an ethylene-vinyl acetate block copolymer, an ethylene-ethyl acrylate block copolymer, or an ethylene-methyl methacrylate block copolymer. One or a combination of two or more of these may be used, with polyethylene homopolymers being preferred. Polyethylene homopolymers are relatively inexpensive, and those with a melting point of 110°C or below are also readily available. Furthermore, polyethylene homopolymers can impart transparency to the adhesive layer 11. Therefore, if the base layer 15 is also transparent, the protective film 10 will also be transparent. Therefore, when the protective film 10 is attached to the resin substrate 21 in step [1], and when the protective film 10 is reattached to the resin substrate 21 prior to step [2], it is possible to visually determine whether or not dust or other debris is present between the protective film 10 and the resin substrate 21. This makes it possible to reliably prevent the transfer of the laminate 100 containing debris from step [2] onwards, thereby improving the yield of the sunglass lenses 200 obtained.

This polyethylene homopolymer is not particularly limited, but examples include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and very low-density polyethylene (VLDPE), and one or more of these can be used in combination.

The elastomer is not particularly limited, but examples include α-polyolefin resin/polyethylene copolymer elastomer, α-polyolefin resin/polypropylene copolymer elastomer, and styrene block elastomer. Among these, styrene block elastomer is preferred, and styrene-olefin-styrene block copolymer elastomer is particularly preferred. By including an elastomer in addition to a polyolefin resin, the adhesive layer 11 remains on the resin substrate 21 when the protective film 10 is peeled from the resin substrate 21 in step [4]. This effectively suppresses or prevents adhesive residue from forming on the resin substrate 21, allowing for smoother peeling of the protective film 10 from the resin substrate 21. Furthermore, by including styrene as a monomer component in the elastomer, the adhesive residue from forming on the resin substrate 21 in step [4] can be effectively suppressed or prevented.

Examples of α-polyolefin resins include 1-hexene, 4-methyl-1-pentene, 1-octene, 1-butene, 1-pentene, and 1-heptene.

Furthermore, when a styrene-olefin-styrene block copolymer elastomer is used as the elastomer, the styrene content in the elastomer is preferably 25% by weight or less, and more preferably 10% to 18% by weight. This effectively suppresses or prevents an increase in the hardness of the adhesive layer 11 caused by a high styrene content. Therefore, it is possible to reliably maintain the adhesion of the adhesive layer 11 to the resin substrate 21 (coating layer 24) while more effectively suppressing or preventing adhesive residue from occurring on the resin substrate 21.

Furthermore, examples of styrene-olefin-styrene block copolymers include styrene-isobutylene-styrene block copolymer (SIBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-butadiene-styrene block copolymer (SBS), and styrene-isoprene-styrene copolymer (SIS), with styrene-ethylene-butylene-styrene block copolymer (SEBS) being preferred. By selecting SEBS as the styrene-olefin-styrene block copolymer, the styrene content in the elastomer can be easily set to 25% by weight or less, ensuring the aforementioned effects.

Furthermore, when the adhesive layer 11 contains an elastomer, the amount of elastomer contained in the adhesive layer 11 is not particularly limited, but is preferably set to between 1% and 30% by weight, and more preferably between 5% and 15% by weight. This allows the effects obtained by including an elastomer in the adhesive layer 11 to be more pronounced.

As mentioned above, it is more preferable that the thermoplastic resin contains one with a melting point of 110°C or less. However, when the adhesive layer 11 contains both a polyolefin-based resin and an elastomer as thermoplastic resins, it is preferable that the melting point of the polyolefin-based resin is 110°C or less. Furthermore, in this case, it is more preferable that the melting point of the polyolefin-based resin is 70°C or more and less than 110°C. This particularly significantly enhances the effect obtained by setting the surface roughness Ra of the adhesive layer 11 surface facing the resin substrate 21 to 0.20 μm or less, i.e., the effect that a protective film 10 that has been peeled off can be reattached to the resin substrate 21 with excellent re-adhesion.

In this specification, the melting point of each layer constituting the protective film 10, including the adhesive layer 11, is defined as the sum of the melting points (peak temperatures measured by DSC) of the constituent materials contained in each layer that have a melting point, multiplied by the proportion of each constituent material contained therein.

As mentioned above, in the adhesive layer 11 having such a configuration, the surface roughness Ra of the surface on the resin substrate 21 side, measured in accordance with JIS B 0601, is set to 0.20 μm or less, preferably 0.16 μm or less, and more preferably 0.01 μm or more and 0.12 μm or less. This allows the peeled protective film 10 to exhibit excellent re-adhesion to the resin substrate 21 when the peeled protective film 10 is re-attached to the resin substrate 21 (see FIG. 3(c)), as shown in FIG. 2(b) .

Furthermore, the average thickness of the adhesive layer 11 is preferably 5 μm or more and 40 μm or less, and more preferably 10 μm or more and 20 μm or less. This ensures that the adhesive layer 11 can perform its functions as described above.

<<Base material layer 15>>
The base material layer 15 is bonded to the resin substrate 21 (coating layer 24) via the adhesive layer 11, and functions as a protective layer (functional layer) to protect (mask) the resin substrate 21 when punching and heat-bending the resin substrate 21 in the steps [2] and [3], and to peel (detach) the resin substrate 21 (protective film 10) from the mold used for heat-bending after heat-bending in the step [3].

Furthermore, in step [4], when the protective film 10 is peeled off from the thermally bent resin substrate 21, no peeling occurs between the base layer 15 and the adhesive layer 11, and the protective film 10 exhibits excellent adhesion to the adhesive layer 11.

In order for the base material layer 15 to exhibit these functions, in the present invention, as shown in Figure 3, the base material layer 15 is composed of a laminate having a first layer 16 located on the side opposite the adhesive layer 11, i.e., the mold side, and a second layer 17 located on the adhesive layer 11 side, i.e., the resin substrate 21 side.

The first layer 16 and the second layer 17 will be described below.
<<First Layer 16>>
The first layer 16 is located on the opposite side of the adhesive layer 11 and functions as the outermost layer for protecting (masking) the resin substrate 21 when punching and heat-bending the resin substrate 21 in the steps [2] and [3].

To ensure that the first layer 16 maintains excellent releasability from the molding die after the heat bending in step [3], i.e., to prevent the first layer 16 from adhering to the molding die (metal mold), the melting point of the first layer 16 is preferably 150°C or higher, and more preferably approximately 155°C to 170°C. As mentioned above, the heating temperature of the coating layer 24 (resin substrate 21) during heat bending in step [3] is preferably set to approximately 110°C to 160°C. Therefore, by setting the melting point of the first layer 16 as described above, it is possible to reliably prevent the first layer 16 from melting or softening during heat bending in step [3], and therefore the laminate 100 can be reliably released from the molding die after heat bending in step [3].

Such a first layer 16 preferably contains, as its main material, a thermoplastic resin with a melting point of 150°C or higher, and more preferably a thermoplastic resin with a melting point of approximately 155°C or higher and 170°C or lower. This makes it relatively easy to set the melting point of the first layer 16 to 150°C or higher. Therefore, excellent releasability of the laminate 100 from the molding die can be maintained after the heat bending in step [3].

Furthermore, when the second layer 17 (described below) also contains a thermoplastic resin with a temperature of 150°C or higher, the first layer 16 and the second layer 17 can have better adhesion. Therefore, when the protective film 10 is peeled off from the thermally bent resin substrate 21 in step [4], peeling between the first layer 16 and the second layer 17 can be effectively suppressed or prevented.

Furthermore, it is preferable that the first layer 16 contains only a polyolefin-based resin of 150°C or higher as the thermoplastic resin of 150°C or higher. Polyolefin-based resins of 150°C or higher are relatively easy and inexpensive to obtain as thermoplastic resins of 150°C or higher.

The polyolefin resin with a melting point of 150°C or higher is not particularly limited, and examples include polypropylene homopolymers, polyethylene homopolymers, propylene-ethylene copolymers, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and ethylene-methyl methacrylate copolymers, all of which have a melting point of 150°C or higher. One or more of these may be used in combination, and polypropylene homopolymers with a melting point of 150°C or higher are preferred. This allows polyolefin resins with a melting point of 150°C or higher to be easily and inexpensively obtained. Furthermore, transparency can be imparted to the first layer 16. Therefore, if the second layer 17 and adhesive layer 11 are also transparent, the protective film 10 will also be transparent. Therefore, when the protective film 10 is attached to the resin substrate 21 in step [1], and when the protective film 10 is reattached to the resin substrate 21 prior to step [2], it is possible to visually determine whether or not dust or other debris is present between the protective film 10 and the resin substrate 21. This makes it possible to reliably prevent the transfer of the laminate 100 containing debris from step [2] onwards, thereby improving the yield of the sunglass lenses 200 obtained.

The copolymer may be either a block copolymer or a random copolymer.

Furthermore, the average thickness of the first layer 16 is preferably 2 μm or more and 40 μm or less, and more preferably 5 μm or more and 25 μm or less. This ensures that the first layer 16 can perform its functions as described above.

<<Second Layer 17>>
The second layer 17 is located on the adhesive layer 11 side, i.e., on the resin substrate 21 side, and is therefore located between the adhesive layer 11 and the first layer 16, functioning as an intermediate layer that bonds them together.

To achieve this function, the second layer 17 contains an adhesive (sticky) thermoplastic resin as its main material, which allows the adhesive layer 11 and the first layer 16 to be bonded together with excellent adhesion via the second layer 17. Therefore, when peeling the protective film 10 from the resin substrate 21 in step [4], peeling between the adhesive layer 11 and the second layer 17 and between the first layer 16 and the second layer 17 is effectively suppressed or prevented. Therefore, even if whiskers of the adhesive layer 11 extending toward the resin substrate 21 are generated on the cut surface of the resin substrate 21 formed by punching during step [2], the protective film 10 (adhesive layer 11) can be peeled from the resin substrate 21 while effectively suppressing or preventing these whiskers from remaining on the cut surface of the resin substrate 21.

Adhesive thermoplastic resins (adhesive resins) are not particularly limited, but include, for example, polyolefin resins, elastomers, acrylic resins, polyurethane resins, etc., and one or more of these can be used in combination. Among these, adhesive polyolefin resins and elastomers are preferred. Furthermore, when the adhesive layer 11 contains an elastomer, a combination of a polyolefin resin and an elastomer is particularly preferred. This improves adhesion between the adhesive layer 11 and the second layer 17, and effectively suppresses or prevents peeling between the adhesive layer 11 and the second layer 17.

Examples of polyolefin resins include ethylene-vinyl acetate copolymer (EVA), ethylene-maleic anhydride copolymer, ethylene-methyl methacrylate copolymer (EMMA), ethylene-methyl acrylate copolymer (EMA), ethylene-methacrylic acid copolymer (EMAA), ethylene-acrylic acid copolymer (EAA), ethylene-ethyl acrylic acid copolymer (EEA), and ethylene-methacrylate-glycidyl acrylate terpolymers. These include grafted products obtained by grafting various polyolefin resins with monobasic unsaturated fatty acids such as acrylic acid and methacrylic acid, dibasic unsaturated fatty acids such as maleic acid, fumaric acid, and itaconic acid, or their anhydrides, and functional group-introduced products obtained by grafting various polyolefin resins with functional groups such as carboxylic acid groups, hydroxyl groups, amino groups, acid anhydride groups, oxazoline groups, and epoxy groups. These may be used singly or in combination of two or more. Examples of the grafted product include maleic acid grafted EVA and maleic acid grafted ethylene-α-polyolefin resin copolymer.

Furthermore, the elastomer may be the same as that described for the elastomer contained in the adhesive layer 11, with a styrene block elastomer being preferred, and a styrene-olefin-styrene block copolymer elastomer being particularly preferred. By using an elastomer containing styrene as a monomer component, the adhesion of the second layer 17 to the adhesive layer 11 is improved, thereby more effectively suppressing or preventing adhesive residue from being left on the resin substrate 21 in step [4].

The second layer 17 may contain, as its constituent material, a non-adhesive thermoplastic resin (non-adhesive resin) in addition to the adhesive thermoplastic resin. The non-adhesive thermoplastic resin exhibits excellent affinity with the polyolefin resin contained in the first layer 16 and having a melting point of 150°C or higher, thereby improving the adhesion between the first layer 16 and the second layer 17. Therefore, when peeling the protective film 10 from the resin substrate 21 in step [4], peeling between the first layer 16 and the second layer 17 can be effectively suppressed or prevented.

Examples of non-adhesive thermoplastic resins include polyolefin resins, polyesters, polyurethanes, silicone resins, polyamides, polyimides, polyvinyl chloride, and polycarbonates. One or more of these can be used in combination, but polyolefin resins are preferred, and polyolefin resins with a melting point of 150°C or higher are even more preferred. This allows the above-mentioned effects to be more pronounced.

The polyolefin resin is not particularly limited and may be, for example, a polypropylene homopolymer, a polyethylene homopolymer, a propylene-ethylene copolymer, an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, or an ethylene-methyl methacrylate copolymer. One or more of these may be used in combination, with a polypropylene homopolymer being preferred. This allows the polyolefin resin to be easily and inexpensively obtained. It also provides transparency to the second layer 17. Therefore, if the first layer 16 and the adhesive layer 11 are also transparent, the protective film 10 will also be transparent. Therefore, when the protective film 10 is attached to the resin substrate 21 in step [1], and when the protective film 10 is reattached to the resin substrate 21 prior to step [2], it is possible to visually determine whether or not dust or other debris is present between the protective film 10 and the resin substrate 21. This makes it possible to reliably prevent the transfer of the laminate 100 containing debris from step [2] onwards, thereby improving the yield of the sunglass lenses 200 obtained.

Furthermore, it is preferable that the melting point of polyolefin resins with a melting point of 150°C or higher be 155°C or higher and 170°C or lower.

The copolymer may be either a block copolymer or a random copolymer. However, polyolefin resins with a melting point of 150°C or higher are generally used as non-adhesive thermoplastic resins because they do not have adhesive properties on their own. However, for example, propylene-ethylene random copolymers (melting point: 151°C) have adhesive properties and are therefore used as adhesive thermoplastic resins.

For these reasons, when the second layer 17 contains a non-adhesive thermoplastic resin, a preferred combination of the adhesive thermoplastic resin and the non-adhesive thermoplastic resin is an elastomer and a polyolefin resin with a melting point of 150°C or higher. This combination effectively suppresses or prevents peeling between the adhesive layer 11 and the second layer 17, and between the first layer 16 and the second layer 17.

The second layer 17 configured as described above preferably has a melting point of 120°C or higher. As mentioned above, the heating temperature of the coating layer 24 (resin substrate 21) during the heat bending in step [3] is preferably set to approximately 110°C or higher and 160°C or lower. Therefore, when the melting point of the second layer 17 is set to 120°C or higher and lower than 150°C, the second layer 17 can be relatively easily melted or softened during the heat bending in step [3]. Therefore, in step [3], the second layer 17 functions as a molten or softened intermediate layer, allowing the first layer 16 to be displaced relative to the surface of the resin substrate 21, thereby forming a gripping area by the first layer 16 at the edge of the laminate 100. Therefore, peeling of the protective film 10 in step [4] can be performed easily by gripping the gripping area. Furthermore, in step [3], this second layer 17 can function as an intermediate layer in a molten or softened state, improving the cushioning properties of the second layer 17 during molding using a mold. As a result, irregularities on the mold or irregularities from contaminants that have unintentionally become mixed in between the mold and the protective film 10 can be effectively absorbed, allowing the thermally bent resin substrate 21 to have an excellent appearance.

Furthermore, when the melting point of the second layer 17 is set to 150°C or higher, the second layer 17 can be inhibited or prevented from melting or softening during the heat bending in step [3]. This effectively inhibits or prevents a decrease in the adhesion between the first layer 16 and the second layer 17. Therefore, when the protective film 10 is peeled off from the heat-bent resin substrate 21 in step [4], peeling between the first layer 16 and the second layer 17 is reliably prevented.

Furthermore, the average thickness of the second layer 17 is preferably 10 μm or more and 60 μm or less, and more preferably 10 μm or more and 40 μm or less. This allows the second layer 17 to reliably perform the functions described above.

The protective film 10 having the adhesive layer 11 and base layer 15 configured as described above preferably has a modulus of elasticity at 25°C of 300 MPa to 600 MPa, more preferably 300 MPa to 500 MPa, even more preferably 300 MPa to 450 MPa, and particularly preferably 300 MPa to 400 MPa. This allows the adhesive layer 11 to be said to have excellent flexibility in low temperature ranges such as room temperature, and therefore more significantly exhibits the effect obtained by setting the surface roughness Ra of the adhesive layer 11's surface facing the resin substrate 21 to 0.2 μm or less, i.e., the effect that a protective film 10 that has been peeled off can be reattached to the resin substrate 21 with excellent re-adhesion.

Specifically, the re-adhesion of protective film 10 is such that, when protective film 10 measuring 25 mm wide and 200 mm long is applied to a polycarbonate substrate, one end of protective film 10 is held and peeled at a 90° angle to a length of 100 mm in an environment of 25° C., and then protective film 10 is re-applied to the polycarbonate substrate by releasing the one end of protective film 10, one minute after re-application, the total area in a plan view of the region where the polycarbonate substrate and the protective film are not bonded is preferably less than 1,250 mm ² , more preferably less than 750 mm ² , and even more preferably less than 125 mm ^2. By setting the total area to be equal to or less than the upper limit, protective film 10 can be said to have excellent re-adhesion, and protective film 10, once peeled, can be reliably re-applied to resin substrate 21. This effectively reduces or prevents the protective film 10 and, ultimately, the resin substrate 21 from being wasted. This allows the sunglasses lenses 200 to be manufactured with a high yield.

In addition, the number of areas where the polycarbonate substrate and the protective film are not bonded is preferably 20 or less, more preferably 10 or less, and even more preferably 3 or less. By setting the number to the upper limit or less, the protective film 10 can be said to have better re-adhesion properties.

In addition, each of the adhesive layer 11 and base layer 15 (first layer 16 and second layer 17) provided in the protective film 10 described above may contain various additives such as antiblocking agents, antioxidants, light stabilizers, and antistatic agents in addition to the above-mentioned constituent materials. The content of the additives may be 10% by weight or less, 8% by weight or less, 0.001% by weight or more, or 0.1% by weight or more.

In particular, it is preferable that the first layer 16 contains an antiblocking agent. This allows the first layer 16 to more reliably perform its function of maintaining excellent releasability from the molding die.

In addition, as the antiblocking agent, for example, inorganic particles and organic particles can be used, and one or more of these can be used in combination. Inorganic particles include, but are not limited to, particles of silica, zeolite, smectite, mica, vermiculite, and talc. Organic particles include, but are not limited to, particles of acrylic resins, polyolefin resins, polyester resins, polyurethane resins, polystyrene resins, silicone resins, and fluorine-based resins.

When an antiblocking agent is contained in the first layer 16, the content of the antiblocking agent in the first layer 16 is not particularly limited, but is preferably set to between 0.5% and 10% by weight, and more preferably between 1% and 9% by weight. This allows the first layer 16 to more significantly exhibit the above-mentioned functions.

Between these layers, an intermediate layer containing the above-mentioned additives may be formed.
Furthermore, the protective film 10 may be produced by any method, but may be produced by, for example, a co-extrusion method.

Specifically, three extruders are prepared, and the constituent materials of the adhesive layer 11, first layer 16, and second layer 17 are respectively loaded into these extruders. These are then extruded in a molten or softened state, and the molten or softened laminate, in which these layers are stacked in layers, is supplied from a co-extrusion T-die to a sheet forming section consisting of multiple cooling rolls, etc. The laminate is then cooled in this sheet supply section to produce the protective film 10.

The surface roughness Ra of the adhesive layer on the side opposite the second layer can be adjusted to the desired size, for example, by using a cooling roll with a different surface roughness (e.g., a metal mirror roll) in the sheet forming unit, or by equipping the sheet forming unit with an air chamber or air knife so that air can be blown onto the surface of the adhesive layer.

The protective film of the present invention has been described above, but the present invention is not limited to this, and each layer constituting the protective film can be replaced with any other layer that can perform the same function.

In the above embodiment, in Figure 2, the case where the protective film is reattached to the resin substrate after a portion of the protective film is peeled off from the resin substrate is described. However, this is not limited to this, and the protective film can also be reattached after the entire protective film is peeled off from the resin substrate.

Furthermore, in the above embodiment, the protective film of the present invention is described as being attached to a resin substrate of a sunglass lens when the resin substrate is subjected to a heat bending process. However, the protective film of the present invention can be applied to the heat bending of such resin substrates of sunglass lenses, and can also be used, for example, when heat bending resin substrates of lenses included in goggles, visors included in helmets, etc.

The present invention will be explained in more detail below based on examples. However, the present invention is not limited to these examples in any way.

1. Preparation of Raw Materials First, the raw materials used to prepare the protective films of the Examples and Comparative Examples are as follows.

<<Non-adhesive thermoplastic resin>>
<Polyolefin resin with a melting point of 150°C or higher>
Homopolypropylene with a melting point of 167°C (h-PP, manufactured by Japan Polypropylene Corporation, "Novatec EA9FTD", MFR = 0.4 g/10 min)

<Polyolefin resin with a melting point of 120°C or higher and lower than 150°C>
Linear low-density polyethylene (LLDPE, manufactured by Ube Maruzen Polyethylene Co., Ltd., "Yumerit 2525F", MFR = 2.5 g/10 min) with a melting point of 121°C

<Polyolefin resin with a melting point of less than 120°C>
Linear low-density polyethylene (LLDPE, manufactured by Ube Maruzen Polyethylene Co., Ltd., "Yumerit 1520F", MFR = 2.0 g/10 min) with a melting point of 114°C

<Polyolefin resin with a melting point of less than 110°C>
Linear low-density polyethylene (LLDPE, manufactured by Tosoh Corporation, "Niboron-Z HF212R", MFR = 2.0 g/10 min) with a melting point of 93°C

<<Thermoplastic resin with adhesive properties>>
<Elastomer>
Styrene-ethylene-butylene-styrene block copolymer (SEBS, manufactured by Asahi Kasei Corporation, "Tuftec H1221")
Hydrogenated styrene-butadiene random copolymer (HSBR, manufactured by JSR Corporation, "Dynaron 1320P")

<Polyolefin resin>
Ethylene-methyl acrylate copolymer with a melting point of 90°C (EMA, manufactured by Japan Polyethylene Corporation, "Rexpearl EB330H")
Block polypropylene (b-PP) with a melting point of 165°C (Sumitomo Chemical Co., Ltd., "Noblen KS23F8", MFR = 2.1 g/10 min)

<Polyolefin resin with a melting point of 120°C or higher and lower than 150°C>
Random polypropylene copolymer with a melting point of 131°C (r-PP, manufactured by Sumitomo Chemical Co., Ltd., "Noblen S131", MFR = 1.3 g/10 min)

<<Anti-blocking agent>>
Anti-blocking agent (Kinoplus FPP-AB05A, manufactured by Sumika Color Co., Ltd.)

2. Production of protective film (Example 1)
[1] First, to form the adhesive layer (innermost layer), an adhesive layer-forming material (resin composition) was prepared by kneading LLDPE having a melting point of 121°C as a polyolefin resin and SEBS as an elastomer so that the SEBS content was 10% by weight.

[2] Next, to form the second layer (intermediate layer) of the base layer, SEBS was used as an adhesive thermoplastic resin, and h-PP with a melting point of 167°C was used as a non-adhesive thermoplastic resin. The SEBS content was 20% by weight, and a second layer-forming material (resin composition) was prepared by kneading the mixture.

[3] Next, the prepared adhesive layer-forming material, the prepared second layer-forming material, and h-PP with a melting point of 167°C as a polyolefin resin with a melting point of 150°C or higher to form the first layer (outermost layer) were placed in three extruders, respectively.

[4] Next, these molten materials were extruded from the three extruders, and a molten laminate in which these materials were layered was obtained from a co-extrusion T-die.A metal mirror roll was then pressed against the adhesive layer to form a mirror finish on the surface of the adhesive layer, and the laminate was then cooled to obtain the protective film of Example 1, in which the average thicknesses of the first layer, second layer, and adhesive layer were 10 μm, 30 μm, and 10 μm, respectively.

The surface roughness Ra of the adhesive layer on the side opposite the second layer was measured in accordance with JIS B 0601 using a laser microscope (Keyence Corporation, "VK9700") and was found to be 0.05 μm.

Furthermore, in accordance with JIS K 7127 for protective films, a test piece (No. 1 dumbbell) taken from the film was measured in an atmosphere of 23°C and 60% RH using a Shimadzu autograph (tensile speed: 500 mm/min), and the result was 475 MPa.

(Examples 2 and 3)
The protective films of Examples 2 and 3 were obtained in the same manner as in Example 1, except that the formation of the adhesive layer in the step [4] was carried out by blowing air onto the surface of the adhesive layer using an air chamber or an air knife.

(Comparative Example 1)
The protective film of Comparative Example 1 was obtained in the same manner as in Example 1, except that in the step [4], the adhesive layer was formed by pressing a metal roll without mirror surface formation against the adhesive layer.

(Comparative Example 2 and Comparative Example 3)
Protective films of Comparative Examples 2 and 3 were obtained in the same manner as Comparative Example 1, except that the type of polyolefin resin used in the step [1] was changed as shown in Table 1.

Example 4
The protective film of Example 4 was obtained in the same manner as in Example 1, except that the type of polyolefin resin and the type of elastomer used in the step [1] were changed as shown in Table 1.

(Examples 5 and 6)
The protective films of Examples 5 and 6 were obtained in the same manner as in Example 4, except that the formation of the adhesive layer in the step [4] was carried out by blowing air onto the surface of the adhesive layer using an air chamber or an air knife.

Example 7
A protective film of Example 7 was obtained in the same manner as in Example 1, except that the type of polyolefin resin used in the step [1] was changed as shown in Table 1.

(Examples 8 to 9)
The protective films of Examples 8 and 9 were obtained in the same manner as in Example 7, except that the formation of the adhesive layer in the step [4] was carried out by blowing air onto the surface of the adhesive layer using an air chamber or an air knife.

Example 10
A protective film of Example 10 was obtained in the same manner as in Example 1, except that the type of polyolefin resin used in the step [1] was changed as shown in Table 1.

(Examples 11 and 12)
The protective films of Examples 11 and 12 were obtained in the same manner as in Example 10, except that the formation of the adhesive layer in the step [4] was carried out by blowing air onto the surface of the adhesive layer using an air chamber or an air knife.

Example 13
[1] First, to form the adhesive layer (innermost layer), LLDPE having a melting point of 93°C was prepared as a polyolefin resin for forming the adhesive layer.

[2] Next, to form the second layer (intermediate layer) of the base material layer, b-PP with a melting point of 158°C was prepared as an adhesive thermoplastic resin.

[3] Next, the adhesive layer-forming material, the second layer-forming material, and h-PP with a melting point of 167°C as a polyolefin resin with a melting point of 150°C or higher to form the first layer (outermost layer) were placed in three extruders, respectively.

[4] Next, these molten materials were extruded from the three extruders, and a molten laminate in which these materials were layered was obtained from a co-extrusion T-die. A metal mirror-finish roll was then pressed against the adhesive layer to form a mirror-finish on the surface of the adhesive layer, and the laminate was then cooled to obtain the protective film of Example 13, in which the average thicknesses of the first layer, second layer, and adhesive layer were 10 μm, 30 μm, and 10 μm, respectively. The surface roughness Ra of the adhesive layer on the side opposite the second layer was measured and found to be 0.06 μm.

Example 14
The protective film of Example 14 was obtained in the same manner as in Example 13, except that in the step [4], the adhesive layer was formed by blowing air onto the surface of the adhesive layer using an air knife. The surface roughness Ra of the adhesive layer on the side opposite to the second layer was measured and found to be 0.16 μm.

Example 15
A protective film of Example 15 was obtained in the same manner as in Example 13, except that in the step [3], a polyolefin resin having a melting point of 150°C or higher was used as the first layer (outermost layer) forming material, and an antiblocking agent (Kinoplus FPP-AB05A) was prepared as shown in Table 1.

3. Evaluation The protective films of the examples and comparative examples were evaluated by the following methods.
<1> Re-adhesion of protective film to attached substrate First, the protective film of each example and comparative example, measuring 25 mm wide x 200 mm long, was sandwiched between two polycarbonate substrates (manufactured by Sumitomo Bakelite Co., Ltd., "ECK100UU"), with the mirror surface facing the protective film side, and pressed using a roll under a load of 1 kg/ ^cm2 , to attach the protective film to the polycarbonate substrate located on the adhesive layer side.

The polycarbonate that makes up the polycarbonate substrate is an aromatic polycarbonate resin obtained by the interfacial polycondensation reaction of bisphenol A and phosgene. After being sheeted by extrusion molding, a mirror finish is imparted by mold transfer.

The protective film was then sandwiched between the polycarbonate substrates and held at 25°C for 30 minutes. Then, in a 25°C environment, one end of the protective film was held and peeled off the polycarbonate substrate at a 90° angle to a length of 100 mm. The protective film was then reattached to the polycarbonate substrate by releasing the end of the protective film.

Then, one minute after this re-application, the total area ( ^mm2 ) in a plan view of the areas where the polycarbonate substrate and the protective film were not bonded was measured, and the number of areas where the polycarbonate substrate and the protective film were not bonded was counted, and the obtained total area and number were evaluated based on the following evaluation criteria.

(Evaluation of total area)
The total area of the region where the polycarbonate substrate and the protective film are not bonded is as follows: ◎ ◎: Less than 125 mm ² ◎: 125 mm ² or more and less than 750 mm ² ◯: 750 mm ² or more and less than 1,250 mm ² ×: 1,250 mm ² or more

(Quantity evaluation)
The number of regions where the polycarbonate substrate and the protective film are not bonded is as follows: ⊚: 3 or less ⊚: more than 3 and 10 or less ◯: more than 10 and 20 or less ×: more than 20

<2> Evaluation of the Presence or Absence of Whisker Adhesion to Resin Substrate First, for each of the protective films of the Examples and Comparative Examples, a laminate was obtained by applying the protective film to both sides of a resin substrate (manufactured by Sumitomo Bakelite Co., Ltd.) having a structure in which a polarizer was sandwiched between two polycarbonate substrates (polycarbonate layers) using a roll under a load of 0.5 kg/ ^cm2 .

Then, after storing it at a temperature of 23°C for 12 hours, this laminate, i.e., the resin substrate with protective films attached to both sides, was punched out in the thickness direction to give the laminate a circular shape in plan view.

Next, the two protective films were peeled off from the laminate, and the punched surface (cut surface) of the resin substrate 21 was visually inspected for the presence or absence of remaining whiskers (adhesive layer). The evaluation was carried out with the following criteria: ◎ if no remaining whiskers were found, ○ if slight remaining whiskers were found, and × if remaining whiskers were clearly found.

<3> Evaluation of the Presence or Absence of Orange Peel Formation on the Surface of Resin Substrate First, for each of the protective films of each Example and Comparative Example, a laminate was obtained by applying pressure to both surfaces of a resin substrate (manufactured by Sumitomo Bakelite Co., Ltd.) having a structure in which a polarizer was sandwiched between two polycarbonate substrates (polycarbonate layers) using a roll under a load of 0.5 kg/ ^cm2 .

Then, after storing it at a temperature of 23°C for 12 hours, this laminate, i.e., the resin substrate with protective films attached to both sides, was punched out in the thickness direction to give the laminate a circular shape in plan view.

The circular laminate was then subjected to a hot bending process under heat using a Rema molding machine (manufactured by Rema, model CR-32) equipped with a mold.

Next, the two protective films were peeled off from the laminate, and the attached surface (peeling surface) of the resin substrate 21 was visually inspected for the presence or absence of orange peel (irregularities). Evaluation was performed with a circle (O) if no orange peel was observed, and an X if orange peel was observed.

The evaluation results for the protective films of each Example and Comparative Example obtained as described above are shown in Table 1 below.

As shown in Table 1, in the protective films of each example, the surface roughness Ra of the adhesive layer was set to 0.20 μm or less, so that the total area in a planar view of the areas where the polycarbonate substrate and the protective film are not bonded is less than 1250 ^mm2 , and the number of areas where the polycarbonate substrate and the protective film are not bonded is 20 or less. It was found that this enables the protective film to exhibit re-adhesion properties to the resin substrate.

In contrast, in the protective films of each comparative example, the surface roughness Ra of the adhesive layer surface was not set to 0.20 μm or less, and as a result, it was not possible to satisfy the requirements that the total area in plan view of the regions where the polycarbonate substrate and the protective film were not bonded was less than 1250 ^mm2 and the number of regions where the polycarbonate substrate and the protective film were not bonded was 20 or less. In other words, it was not possible to make the protective film exhibit re-adhesion to the resin substrate.

REFERENCE SIGNS LIST 10 Protective film 11 Adhesive layer 15 Base layer 16 First layer 17 Second layer 21 Resin substrate 23 Polarizer 24 Covering layer 30 Polycarbonate layer 100 Laminate 200 Sunglasses lens

Claims (8)

A protective film to be attached to a resin substrate when the resin substrate is subjected to a thermal bending process under heating,
a substrate layer;
an adhesive layer positioned between the base layer and the resin substrate and adhering to the resin substrate;
the base material layer is composed of a laminate having a first layer located on the opposite side of the adhesive layer and a second layer located on the adhesive layer side,
the adhesive layer has a surface roughness Ra of 0.20 μm or less on the surface facing the resin substrate, as measured in accordance with JIS B 0601;
A protective film characterized in that the modulus of elasticity is 300 MPa or more and 600 MPa or less when a test piece (No. 1 dumbbell) taken from the protective film is measured in accordance with JIS K 7127 under an atmosphere of 23°C and 60% RH using an autograph manufactured by Shimadzu Corporation at a tension rate of 500 mm/min . The protective film according to claim 1, wherein the first layer contains a thermoplastic resin as its main material and has a melting point of 150°C or higher, the second layer contains a thermoplastic resin as its main material and has a melting point of 120°C or higher, and the adhesive layer contains a thermoplastic resin as its main material and has a melting point of 110 °C or lower. The protective film according to claim 2 , wherein the thermoplastic resin contained in the first layer and the thermoplastic resin contained in the second layer both contain polyolefin-based resins. The protective film according to claim 1 , wherein the adhesive layer contains, as a main material, a polyolefin resin having adhesive properties. A protective film according to any one of claims 1 to 4, wherein when a protective film having a width of 25 mm and a length of 200 mm is attached to a polycarbonate substrate, and then, in an environment of 25°C, one end of the protective film is held and peeled off in a 90° direction to a length of 100 mm, and then the end of the protective film is released to re-attach the protective film to the polycarbonate substrate, one minute after re-attachment, the total area in a plan view of the area where the polycarbonate substrate and the protective film are not bonded is less than 1250 ^mm2 . The protective film according to claim 1 , which is attached to both sides of the resin substrate. The protective film according to any one of claims 1 to 6, wherein the resin substrate has a coating layer on both sides, one side or the other side, which is composed of a single layer or a laminate having at least one layer selected from the group consisting of a polycarbonate resin layer, a polyamide resin layer and a cellulose resin layer. The protective film according to claim 1 , wherein the resin substrate is subjected to the heat bending process by press molding or vacuum molding.