JP2022158895A - Protective film - Google Patents

Abstract

To provide a protective film which can accurately suppress or prevent an adhesive layer from remaining on a cut surface formed by punching when a resin substrate is punched and then the cut surface is peeled from the resin substrate.SOLUTION: A protective film 10 is stuck to a resin substrate 21 and used when the resin substrate 21 is thermally bent, and has a base material layer and an adhesive layer which is positioned between the base material layer and the resin substrate, and is bonded to the resin substrate, wherein the base material layer is composed of a laminate having a first layer positioned on a side opposite to the adhesive layer and a second layer positioned on the adhesive layer side, and the protective film 10 has a trouser breaking elongation strain in a direction inclined to both MD and TD of the protective film by 45°, which is measured according to JIS K 7128-1 (1998), of 300% or less.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a protective film used by being attached to a resin substrate when subjecting the resin substrate to thermal bending under heating.

A lens for sunglasses comprising a resin substrate in which both sides of a polarizer are coated with a coating layer made of polycarbonate resin, polyamide resin or cellulose resin is, for example, protected on both sides of the resin substrate which is flat in plan view. With the film attached, the resin substrate is punched into a predetermined shape such as a circular shape in plan view, and then the resin substrate is subjected to thermal bending under heating. After peeling off the protective film from the heat-bent resin substrate, the polycarbonate layer is injection-molded on the concave surface of the resin substrate.

As this protective film, for example, a base material whose main material is polyolefin resin is attached to the resin substrate via an adhesive layer whose main material is polyethylene, ethylene-propylene copolymer, or the like. has been proposed (see, for example, Patent Document 1).

However, although the protective film having such a configuration can be adhered to the resin substrate without being peeled off during punching and thermal bending of the resin substrate, it has the following problems. That is, when the resin substrate is punched, the adhesive layer extends to the resin substrate side on the cut surface formed by punching, so-called whiskers. As a result, the adhesive layer remains on the cut surface of the resin substrate. As a result, there is a problem that the yield of manufactured sunglasses lenses is lowered.

Such problems occur not only in the sunglasses lenses described above, but also in resin substrates such as the lenses of goggles and the visors of helmets.

JP-A-2003-145616

An object of the present invention is to provide a protective film that can accurately suppress or prevent an adhesive layer from remaining on a cut surface formed by punching when peeled from a resin substrate after punching the resin substrate. is to provide

Such objects are achieved by the present invention described in (1) to (10) below.
(1) A protective film that is used by being attached to a resin substrate when the resin substrate is subjected to thermal bending under heating,
a substrate layer;
an adhesive layer positioned between the base material layer and the resin substrate and adhering to the resin substrate;
The base 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 protective film has a trouser breaking elongation strain of 300% or less in a direction inclined by 45° with respect to both MD and TD of the protective film, measured in accordance with JIS K 7128-1 (1998). A protective film characterized by:

(2) The protective film is heated at 145 ° C. for 30 minutes, then cooled at 25 ° C. for 30 minutes, and then measured in accordance with JIS K 7128-1 (1998). The protective film according to (1) above, which has a trouser breaking elongation strain of 50% or more and 250% or less in a direction inclined at 45° to both MD and TD.

(3) According to JIS K 7127, the protective film is a test piece (No. 1 dumbbell) taken from the protective film in an atmosphere of 23 ° C. and 60% RH, Shimadzu Autograph (tensile speed: 500 mm / min). The protective film according to (1) or (2) above, which has a nominal strain at break measured at 400% or more and 650% or less.

(4) The protective film according to any one of (1) to (3) above, wherein the protective film has a crystallinity of 10% or less and 75% or less.

(5) The first layer contains a thermoplastic resin as a main material and has a melting point of 150°C or higher, and the second layer contains a thermoplastic resin as a main material and has a melting point of 120°C or higher. The protective film according to any one of (1) to (4) above, which is

(6) The protective film according to (5) above, wherein the thermoplastic resin contained in the first layer and the thermoplastic resin contained in the second layer are both polyolefins.

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

(8) The protective film according to any one of the above (1) to (7), wherein at least one side forming an edge of the resin substrate forms a curved convex curve in plan view.

(9) The resin substrate has a coating layer composed of a single layer or laminate having at least one layer selected from a polycarbonate resin layer, a polyamide resin layer and a cellulose resin layer on both sides, one side or the other side. The protective film according to any one of (1) to (8) above.

(10) The protective film according to any one of (1) to (9) above, wherein the resin substrate is subjected to the thermal bending process by press molding or vacuum molding.

According to the present invention, the protective film has a trouser breaking elongation strain of 300% in a direction inclined by 45° with respect to both MD and TD of the protective film, measured in accordance with JIS K 7128-1 (1998). Set to: In this way, by setting the trouser breaking elongation strain in the direction inclined by 45° to both the MD and TD of the protective film to be equal to or less than the upper limit value, the protective film is removed from the resin substrate after the resin substrate is punched. It is possible to accurately suppress or prevent the adhesive layer from remaining as so-called whiskers that extend to the resin substrate side on the cut surface formed by punching when the adhesive layer is peeled off. Therefore, when the resin substrate is applied to, for example, a resin substrate included in a lens for sunglasses, the lens for sunglasses can be manufactured with a high yield.

It is a schematic diagram for demonstrating the manufacturing method of the lens for sunglasses using a protective film. 1 is a vertical cross-sectional view showing a preferred embodiment of a protective film of the present invention; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION The protective film of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings. In this specification, the main material refers to a constituent material contained in each layer in an amount of 50% by weight or more. For example, "the first layer 16 contains thermoplastic resin as its main material "The thermoplastic resin contained in the first layer 16 accounts for 50% by weight or more in the first layer 16 when the total weight of the first layer 16 is 100% by weight. point to

The protective film of the present invention is a protective film that is used by being attached to the resin substrate when the resin substrate is subjected to thermal bending under heating. and an adhesive layer positioned between and adhering to the resin substrate, wherein the base material layer includes a first layer positioned on the opposite side of the adhesive layer and a second layer positioned on the adhesive layer side and the protective film is measured in accordance with JIS K 7128-1 (1998), both MD and TD of the protective film are inclined at 45 ° Characterized by a trouser breaking elongation strain in the direction of 300% or less.

By setting the protective film to such a configuration, that is, by setting the trouser breaking elongation strain in the direction inclined by 45° with respect to both MD and TD of the protective film to the above upper limit value or less, the resin substrate After punching, when the protective film is peeled off from the resin substrate, the adhesive layer extends to the resin substrate side on the cut surface formed by punching. can be suppressed or prevented. Therefore, when the resin substrate is applied to, for example, a resin substrate included in a lens for sunglasses, the lens for sunglasses can be manufactured with a high yield.

Before describing the protective film of the present invention, a method for manufacturing a lens for sunglasses using the protective film of the present invention will be described below.

<Manufacturing method of lens for sunglasses>
FIG. 1 is a schematic diagram for explaining a method for manufacturing a sunglass lens using a protective film. For convenience of explanation, the upper side of FIG. 1 is hereinafter referred to as "upper", and the lower side thereof is referred to as "lower".

Each step of the method for manufacturing a lens for sunglasses will be described in detail below.
[1] First, a resin substrate 21 having a flat plate shape is prepared, and protective films 10 (masking tape) are attached to both surfaces of the resin substrate 21, so that the protective films 10 are attached to both surfaces of the resin substrate 21. A laminate 100 is obtained (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 plane of polarization in one predetermined direction from unpolarized natural light. will be prepared. In this resin substrate 21, the coating layer 24 is composed of a single layer or laminate having at least one layer selected from 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 surfaces (both surfaces) of the polarizer 23, or may be formed on either the upper surface (one surface) or the lower surface (the other surface). may

[2] Next, as shown in FIG. 1B, the prepared laminate 100, that is, the resin substrate 21 with the protective films 10 attached to both surfaces thereof, is punched out in the thickness direction. Thus, the laminated body 100 has a circular shape in plan view.

[3] Next, as shown in FIG. 1(c), the circular laminated body 100 is subjected to thermal bending under heating.

This thermal bending is usually performed by press molding using a mold or vacuum molding (rema molding).

At this time, the heating temperature (molding temperature) of the laminate 100 (resin substrate 21) is as described above. and at least one of the cellulose resin layers, the melting or softening temperature of the coating layer 24 is taken into account, and the temperature is preferably about 110° C. or higher and 160° C. or lower. , more preferably about 140° C. or higher and 150° C. or lower. By setting the heating temperature within such a range, the resin substrate 21 can be reliably thermally bent by softening or melting the resin substrate 21 while preventing alteration and deterioration of the resin substrate 21 .

[4] Next, as shown in FIG. 1(d), after peeling off the protective film 10 from the heat-bent resin substrate 21, that is, the laminate 100, the concave surface of the resin substrate 21 is made of polycarbonate resin. Injection molded polycarbonate layer 30 . A polyamide layer composed of a polyamide resin may be formed on the concave surface of the resin substrate 21 instead of the polycarbonate layer 30 .

As a result, the sunglasses lens 200 including the thermally bent resin substrate 21 is manufactured.

Here, in the method for manufacturing a lens for sunglasses as described above, a cut surface (end surface) of the resin substrate 21 formed by punching, particularly at the time of punching the resin substrate 21 in the step [2], is shown in FIG. 2 may extend to the resin substrate 21 side, that is, a so-called whisker may occur. When the protective film 10 is peeled off from the resin substrate 21 in step [4] with such whiskers, the adhesive layer 11 remains on the cut surface of the resin substrate 21 as whiskers. Therefore, there is a problem that the yield of the manufactured sunglasses lens 200 is lowered.

As a result of investigations by the inventors of the present invention regarding this problem, as described above, the occurrence of whiskers on the cut surface of the resin substrate 21 due to the extension of the adhesive layer 11 is caused by the circular shape of the laminate 100 in plan view. , that is, when the resin substrate 21 is punched so as to form a curve in which the sides forming the edge of the resin substrate 21 form a curved convex surface in a plan view, the resin substrate 21 is cut to form a curved convex surface. It has been found that this occurs frequently.

In addition, according to further studies by the present inventors, the generation of the whiskers on the cut surface (curved convex surface) of the resin substrate 21 is measured according to JIS K 7128-1 (1998), which is the trouser breaking elongation of the protective film 10. It has been found to be closely related to the magnitude of the strain and, moreover, to the angle of the protective film 10 at which the trouser breaking elongation strain is measured.

Then, the present inventors have investigated the occurrence of the whiskers on the cut surface of the resin substrate 21 which is a curved convex surface, the magnitude of the trouser breaking elongation strain of the protective film 10, and the protective film 10 for measuring the trouser breaking elongation strain. As a result of further examination of the angle and relationship, by setting the magnitude of the trouser breaking elongation strain in the direction inclined by 45 ° with respect to the MD and TD of the protective film 10 to 300% or less, the curved convex surface and The inventors have found that the generation of the whiskers on the cut surface of the resin substrate 21 can be accurately suppressed or prevented, and have completed the present invention.

In this way, by setting the magnitude of the trouser breaking elongation strain to 300% or less, at the time of punching the resin substrate 21 in the step [2], at the cut surface of the resin substrate 21 formed by punching, The generation of whiskers in the adhesive layer 11 extending toward the resin substrate 21 can be accurately suppressed or prevented. Therefore, in the step [4], when the protective film 10 is peeled off from the resin substrate 21, the protective film 10 (adhesive Layer 11) can be peeled off from resin substrate 21 . Therefore, the sunglasses lens 200 can be manufactured with a high yield. The protective film 10 (protective film of the present invention) will be described in detail below.

<Protective film 10>
FIG. 2 is a longitudinal sectional view showing a preferred embodiment of the protective film of the invention. For convenience of explanation, the upper side of FIG. 2 is hereinafter referred to as "upper", and the lower side thereof is referred to as "lower".

The protective film 10 has a substrate layer 15 and an adhesive layer 11 positioned between the substrate layer 15 and the resin substrate 21 to adhere (bond) to the resin substrate 21, as shown in FIG. The base material layer 15 comprises a first layer 16 located on the opposite side of 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. have.

Each of these layers will be described in detail below.
<<adhesive layer 11>>
The adhesive layer 11 is positioned (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 allows punching and thermal bending of the resin substrate 21 in the steps [2] and [3] without peeling the protective film 10 from the resin substrate 21, and also allows ] is preferably used to peel the protective film 10 from the resin substrate 21 .

The adhesive layer 11 has a configuration in which a polyolefin resin alone is contained in the adhesive layer 11 as a thermoplastic resin, or a configuration in which a polyolefin resin and an elastomer are combined in the adhesive layer 11. is preferred. The function of the adhesive layer 11 can be reliably exhibited by using the adhesive layer 11 having a structure containing such a thermoplastic resin.

The polyolefin-based resin having adhesiveness is not particularly limited, and examples thereof include homopolymers of polypropylene (homopolymers), homopolymers of polyethylene, and propylene-ethylene block copolymers having an EPR phase (rubber phase). , ethylene-vinyl acetate block copolymers, ethylene-ethyl acrylate block copolymers, ethylene-methyl methacrylate block copolymers, etc., and one or more of these may be used in combination, Among them, it is preferably a homopolymer of polyethylene. Polyethylene homopolymers are available at relatively low cost. Moreover, if it is a homopolymer of polyethylene, transparency can be imparted to the adhesive layer 11 . Therefore, when the substrate layer 15 also has transparency, the protective film 10 has transparency. Therefore, when attaching the protective film 10 to the resin substrate 21 in step [1], it is possible to visually check whether or not dust such as dust is interposed between the protective film 10 and the resin substrate 21. Since it is possible to reliably prevent the layered body 100 containing dust from moving after step [2], as a result, the yield of the obtained sunglasses lens 200 can be improved.

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

Further, the elastomer is not particularly limited, but examples thereof include α-polyolefin resin/polyethylene copolymer elastomer, α-polyolefin resin/polypropylene copolymer elastomer, styrene block elastomer, etc. Among them, styrene block elastomer is preferred, and a styrene-olefin-styrene block copolymer elastomer is particularly preferred. In this way, since the elastomer is included in addition to the polyolefin resin, the adhesive layer 11 remains on the resin substrate 21 when the protective film 10 is peeled off from the resin substrate 21 in step [4]. That is, it is possible to accurately suppress or prevent the occurrence of adhesive residue on the resin substrate 21, so that the protective film 10 can be peeled off from the resin substrate 21 more smoothly. By using the elastomer containing styrene as a monomer component, it is possible to more accurately suppress or prevent the occurrence of adhesive deposits on the resin substrate 21 in step [4].

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

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, more preferably 10% by weight or more and 18% by weight or less. preferable. As a result, it is possible to accurately suppress or prevent an increase in the hardness of the adhesive layer 11 due to an increase in the styrene content. Therefore, it is possible to reliably maintain the adhesion of the adhesive layer 11 to the resin substrate 21 (coating layer 24 ), and more accurately suppress or prevent the occurrence of adhesive residue 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), and styrene-butadiene-styrene block copolymer. Copolymers (SBS), styrene-isoprene-styrene copolymers (SIS), and the like can be mentioned, among which styrene-ethylene-butylene-styrene block copolymers (SEBS) are 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, and the effects described above can be reliably obtained.

In addition, when the adhesive layer 11 contains an elastomer, the content of the elastomer in the adhesive layer 11 is not particularly limited, but is preferably 2% by weight or more and 60% by weight or less, more preferably 4% by weight or more and 40% by weight or less. is set to As a result, the effects obtained by including the elastomer in the adhesive layer 11 can be exhibited more remarkably.

The average thickness of the adhesive layer 11 is preferably 5 μm or more and 40 μm or less, more preferably 10 μm or more and 20 μm or less. Thereby, the function as the adhesion layer 11 mentioned above can be exhibited reliably.

<<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 when the resin substrate 21 is punched and thermally bent in the steps [2] and [3], the resin substrate As a protective layer (functional layer) for protecting (masking) 21 and peeling (separating) the resin substrate 21 (protective film 10) from the mold used for thermal bending after the thermal bending in the step [3] It works.

Further, in the step [4], when the protective film 10 is peeled off from the thermally bent resin substrate 21, peeling does not occur between the base material layer 15 and the adhesive layer 11, and the adhesive layer 11 is On the other hand, it is for exhibiting excellent adhesiveness.

In order to allow the base layer 15 to exhibit these functions, in the present invention, as shown in FIG. 16 and a second layer 17 positioned on the adhesive layer 11 side, that is, on 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 protects (masks) the resin substrate 21 during punching and thermal bending of the resin substrate 21 in the steps [2] and [3]. It functions as the outermost layer for

The first layer 16 should maintain excellent releasability from the mold after thermal bending in step [3], that is, the first layer 16 should not adhere to the mold (mold). For this purpose, the melting point of the first layer 16 is preferably 150° C. or higher, more preferably about 155° C. or higher and 170° C. or lower. Here, as described above, the heating temperature of the coating layer 24 (resin substrate 21) during the thermal bending in the step [3] is preferably set to approximately 110° C. or higher and 160° C. or lower. 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 being melted or softened during the thermal bending in the step [3]. Therefore, after the thermal bending in the step [3], the laminate 100 can be reliably removed from the mold.

The first layer 16 contains, as its main material, a thermoplastic resin whose melting point is preferably 150° C. or higher, more preferably about 155° C. or higher and 170° C. or lower. Thereby, the melting point of the first layer 16 can be relatively easily set to 150° C. or higher. Therefore, after the thermal bending in the above step [3], the laminate 100 can maintain excellent releasability from the mold.

In this specification, the melting point of each layer constituting the protective film 10 including the first layer 16 refers to the melting point (peak temperature by DSC measurement) of each constituent material contained in each layer. Let the melting point be the sum of the products multiplied by the contained ratios.

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

Furthermore, the first layer 16 preferably has a structure in which the first layer 16 contains only a polyolefin resin of 150° C. or higher as the thermoplastic resin of 150° C. or higher. A polyolefin resin having a temperature of 150° C. or higher can be obtained relatively easily and inexpensively as a thermoplastic resin having a temperature of 150° C. or higher.

Further, the polyolefin resin having a melting point of 150° C. or higher is not particularly limited. Copolymers, ethylene-ethyl acrylate copolymers, ethylene-methyl methacrylate copolymers, etc., which have a melting point of 150° C. or higher, may be used alone or in combination of two or more thereof. , a homopolymer of polypropylene having a melting point of 150° C. or higher. As a result, a polyolefin resin having a melting point of 150° C. or higher can be obtained easily and inexpensively. Moreover, transparency can be imparted to the first layer 16 . Therefore, when the second layer 17 and the adhesive layer 11 also have transparency, the protective film 10 has transparency. Therefore, when attaching the protective film 10 to the resin substrate 21 in step [1], it is possible to visually check whether or not dust such as dust is interposed between the protective film 10 and the resin substrate 21. Since it is possible to reliably prevent the layered body 100 containing dust from moving after step [2], as a result, the yield of the obtained sunglasses lens 200 can be improved.

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

The average thickness of the first layer 16 is preferably 2 μm or more and 40 μm or less, more preferably 5 μm or more and 25 μm or less. Thereby, the function as the first layer 16 described above can be reliably exhibited.

<<second layer 17>>
The second layer 17 is located on the side of the adhesive layer 11, that is, on the side of the resin substrate 21, so that it is located between the adhesive layer 11 and the first layer 16 and functions as an intermediate layer that joins them together. It is something to do.

The second layer 17 contains a thermoplastic resin having adhesiveness (adhesiveness) as a main material in order to exhibit the function described above, thereby separating the adhesive layer 11 and the first layer 16 from each other. , through the second layer 17, can be bonded with excellent adhesion. Therefore, in the step [4], when peeling the protective film 10 from the resin substrate 21, the adhesive layer 11 and the second layer 17 and the first layer 16 and the second layer 17 It is possible to precisely suppress or prevent the separation from occurring between them.

The thermoplastic resin having adhesiveness (adhesive resin) is not particularly limited, but includes, for example, polyolefin resins, elastomers, acrylic resins, polyurethane resins, etc. One or more of these may be used. can be used in combination, and among them, polyolefin-based resins and elastomers having adhesive properties are preferred. Moreover, when the adhesive layer 11 contains an elastomer, it is particularly preferable to use a combination of a polyolefin resin and an elastomer. As a result, the adhesion between the adhesive layer 11 and the second layer 17 can be improved, and the separation between the adhesive layer 11 and the second layer 17 can be suppressed or prevented accurately. .

Examples of polyolefin resins include ethylene-vinyl acetate copolymer (EVA), ethylene-maleic anhydride copolymer, ethylene-methyl methacrylate copolymer (EMMA), and ethylene-methyl acrylate copolymer. (EMA), ethylene-methacrylic acid copolymer (EMAA), ethylene-acrylic acid copolymer (EAA), ethylene-ethyl acrylic acid copolymer (EEA), ethylene-methacrylate-glycidyl acrylate terpolymer In addition, grafted products obtained by grafting 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 onto various polyolefin resins, Various polyolefin resins include functional group-introduced products in which functional groups such as carboxylic acid groups, hydroxyl groups, amino groups, acid anhydride groups, oxazoline groups, and epoxy groups are introduced, and one or two of these More than one species can be used in combination. Examples of the graft material include maleic acid-grafted EVA and maleic acid-grafted ethylene-α-polyolefin resin copolymer.

Furthermore, as the elastomer, the same elastomer as described as the elastomer contained in the adhesive layer 11 can be used, and among them, the styrene block elastomer is preferable, and in particular, the styrene-olefin-styrene block copolymer elastomer. is preferably In this way, by including styrene as a monomer component in the elastomer, the adhesiveness of the second layer 17 to the adhesive layer 11 is improved. The occurrence can be more accurately suppressed or prevented.

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

Non-adhesive thermoplastic resins include, for example, polyolefin resins, polyesters, polyurethanes, silicone resins, polyamides, polyimides, polyvinyl chlorides, polycarbonates, and the like. Among them, polyolefin-based resins are preferable, and polyolefin-based resins having a melting point of 150° C. or higher are more preferable. Thereby, the said effect can be exhibited more notably.

The polyolefin-based resin is not particularly limited, and examples thereof include homopolymers of polypropylene (homopolymers), homopolymers of polyethylene, propylene-ethylene copolymers, ethylene-vinyl acetate copolymers, and ethylene-ethyl acrylate. Copolymers, ethylene-methyl methacrylate copolymers, etc., can be used alone or in combination of two or more of these, and among them, homopolymers of polypropylene are preferred. . As a result, the polyolefin resin can be obtained easily and inexpensively. Moreover, transparency can be imparted to the second layer 17 . Therefore, when the first layer 16 and the adhesive layer 11 also have transparency, the protective film 10 has transparency. Therefore, when attaching the protective film 10 to the resin substrate 21 in step [1], it is possible to visually check whether or not dust such as dust is interposed between the protective film 10 and the resin substrate 21. Since it is possible to reliably prevent the layered body 100 containing dust from moving after step [2], as a result, the yield of the obtained sunglasses lens 200 can be improved.

Further, the melting point of the polyolefin resin having a melting point of 150°C or higher is preferably 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 alone as non-adhesive thermoplastic resins because they do not have adhesive properties. : 151° C.) is used as a thermoplastic resin with adhesiveness because it has adhesiveness.

From the above, when the second layer 17 contains a non-adhesive thermoplastic resin, the adhesive thermoplastic resin and the non-adhesive thermoplastic resin are an elastomer and a melting point of 150 ° C. or higher. is a preferred combination. By such a combination, it is possible to accurately suppress or prevent peeling between the adhesive layer 11 and the second layer 17 and between the first layer 16 and the second layer 17. can.

The melting point of the second layer 17 having the above structure is preferably 120° C. or higher. Here, as described above, the heating temperature of the coating layer 24 (resin substrate 21) during the thermal bending in the 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 more and less than 150° C., the second layer 17 can be relatively easily melted or softened during the thermal bending in the step [3]. can do. Therefore, in the step [3], the second layer 17 is made to function as an intermediate layer in a molten or softened state, and the position of the first layer 16 is shifted with respect to the surface direction of the resin substrate 21. As a result, a gripping margin is formed by the first layer 16 at the edge of the laminate 100 . Therefore, since the peeling of the protective film 10 in the step [4] can be performed by gripping the gripping margin, this peeling can be easily performed. In the step [3], the second layer 17 can function as an intermediate layer in a molten or softened state to improve the cushioning property of the second layer 17 during molding with a mold. can. As a result, the unevenness of the mold or the unevenness of contaminants unintentionally mixed between the mold and the protective film 10 can be effectively absorbed. Substrate 21 can be obtained with excellent appearance.

Further, when the melting point of the second layer 17 is set to 150° C. or higher, the second layer 17 is suppressed or prevented from being melted or softened during the thermal bending in the step [3]. be able to. Therefore, it is possible to accurately suppress or prevent a decrease in adhesion between the first layer 16 and the second layer 17 . 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 is reliably prevented. prevented.

The average thickness of the second layer 17 is preferably 10 μm or more and 60 μm or less, more preferably 10 μm or more and 40 μm or less. Thereby, the function as the second layer 17 described above can be reliably exhibited.

The protective film 10 comprising the adhesive layer 11 and the base layer 15 having the above configuration has the magnitude A of the trouser breaking elongation strain in the direction inclined by 45° with respect to the MD and TD of the protective film 10. is 300% or less, but the magnitude A of the trouser breaking elongation strain is preferably 275% or less, more preferably 110% or more and 250% or less, and 130 % or more and 240% or less, and particularly preferably 130% or more and 220% or less. As a result, when the resin substrate 21 is punched in step [2], the adhesive layer 11 extends to the side of the resin substrate 21 on the cut surface of the resin substrate 21, which is a curved convex surface. can be precisely suppressed or prevented.

In addition, the trouser breaking elongation strain A is prepared as a test piece with a protective film 10 having a length of 100 mm, a width of 50 mm, a thickness of 50 μm, and a cut of 50 mm in accordance with JIS K 7128-1 (1998). It can be obtained by tearing the test piece at a 45° tilt with respect to the MD and TD at a grip distance of 50 mm and a tensile speed of 200 mm/min.

In addition, the trouser breaking elongation strain (tensile elongation strain) is calculated by the following formula (1) by dividing the distance between the chucks at the breaking point by the distance between the grips of the test piece (50 mm).
Breaking point (mm) / distance between chucks (mm) = trouser breaking elongation strain (1)

In addition, this protective film 10 is heated at 145 ° C. for 30 minutes, then cooled at 25 ° C. for 30 minutes, and then measured in accordance with JIS K 7128-1 (1998). It is preferable that the trouser breaking elongation strain B in the direction inclined at 45 ° to both MD and TD is 100% or more and 250% or less, more preferably 110% or more and 160% or less, 110% or more and 130% More preferably: Thus, by setting the trouser breaking elongation strain B after heating at 145° C. for 30 minutes within the above range, the protective film 10 can be relatively easily cut. , the punching of the resin substrate 21 in the step [2] can be reliably performed while accurately suppressing or preventing the generation of whiskers on the cut surface of the resin substrate 21 which is a curved convex surface.

Furthermore, according to JIS K 7127, the protective film 10 is a test piece (No. 1 dumbbell) taken so that the MD direction of the protective film 10 is the longitudinal direction of the dumbbell, under an atmosphere of 23 ° C. and 60% RH. The nominal tensile strain at break measured by an autograph (tensile speed: 500 mm/min) is preferably 400% or more and 650% or less, more preferably 450% or more and 600% or less.

By setting the nominal tensile strain at break of the protective film 10 within the above range, the magnitude of the trouser breaking elongation strain A can be relatively easily reduced to the upper limit value or less, furthermore, the trouser breaking elongation strain B The size can be relatively easily set within the range.

The crystallinity of protective film 10 is preferably 10% or more and 75% or less, more preferably 17% or more and 60% or less, and even more preferably 20% or more and 55% or less. By setting the crystallinity of the protective film 10 within the range, the nominal tensile strain at break of the protective film 10 can be relatively easily set within the range. The magnitude of the elongation strain A can be set to be equal to or less than the upper limit, and the magnitude of the trouser breaking elongation strain B can be set within the above range.

The crystallinity of the protective film 10 can be obtained by calculating the crystal peak area ratio to the total area using a wide-angle X-ray diffractometer.
Crystallinity [%] = (Σ crystal peak area) ÷ (total area) × 100

In addition, the protective film 10 having the degree of crystallinity within such a range can be obtained by adjusting the degree of crystallinity as follows, for example.

That is, when the protective film 10 is manufactured using the co-extrusion method described later, the molten or softened adhesive layer 11, the first layer 16 and the second layer are laminated by being extruded from the co-extrusion T die. can be obtained by appropriately setting the cooling rate and cooling temperature during cooling. Further, in the step [1], when the laminate 100 is obtained by attaching the protective films 10 to both surfaces of the resin substrate 21, the conditions for attaching the protective films 10 can be adjusted as appropriate. . Furthermore, the adhesive layer 11, the first layer 16 and the second layer 17 included in the protective film 10 can be adjusted by appropriately setting the combination of the constituent materials. , it is also possible to adjust by including a crystal nucleating agent.

Examples of the crystal nucleating agent include sorbitol-based crystal nucleating agents, organic phosphoric acid-based crystal nucleating agents, rosin acid-based crystal nucleating agents, amide-based crystal nucleating agents, aromatic carboxylic acid-based crystal nucleating agents, and inorganic crystals. Nucleating agents and the like can be mentioned, and one or more of these can be used in combination.

Note that each layer of the adhesive layer 11 and the base material layer 15 (the first layer 16 and the second layer 17) provided in the protective film 10 described above contains, in addition to the constituent materials described above, an antiblocking agent, an oxidation Various additives such as inhibitors, light stabilizers and antistatic agents may be included. The content of the additive may be 10% by weight or less, 8% by weight or less, or 0.001% by weight or more, or 0.1% by weight or more. can also

In particular, the first layer 16 preferably contains an antiblocking agent. As a result, the function of the first layer 16, which is capable of maintaining excellent releasability from the mold, can be exhibited more reliably.

Also, 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. The inorganic particles are not particularly limited, but examples thereof include particles of silica, zeolite, smectite, mica, vermiculite and talc. Particles of resin, polyester-based resin, polyurethane-based resin, polystyrene-based resin, silicone-based resin, fluorine-based resin, and the like are included.

When the first layer 16 contains an antiblocking agent, the content of the antiblocking agent in the first layer 16 is not particularly limited, but is preferably 0.5% by weight or more and 10% by weight or less, more preferably It is set to 1% by weight or more and 9% by weight or less. Thereby, the function of the first layer 16 can be exhibited more remarkably.
Intermediate layers containing the above-mentioned additives and the like may be formed between these layers.

Furthermore, the protective film 10 described above may be manufactured by any method, and can be manufactured by using, for example, a co-extrusion method.

Specifically, three extruders are prepared, and the constituent materials of the adhesive layer 11, the first layer 16, and the second layer 17 are placed in these extruders, respectively, and then melted or softened. By extruding, a molten or softened laminate in which these are laminated in layers from the co-extrusion T die is supplied to a sheet forming unit composed of a plurality of cooling rolls, etc., and then this sheet supply unit The protective film 10 is manufactured by cooling the laminate at .

Although the protective film of the present invention has been described above, the present invention is not limited to this, and each layer constituting the protective film can be replaced with an arbitrary structure capable of exhibiting the same function. can.

Further, in the above embodiment, when the resin substrate is punched out to have a circular shape in plan view, that is, when the resin substrate 21 is seen in plan view, all the sides constituting the edge portion are curved and convex. Although the case of punching so as to form a curved line has been described, the present invention is not limited to this, and punching may be performed so as to form a curved line in which one side (part) of the sides constituting the edge portion forms a curved convex shape. good.

Furthermore, in the above-described embodiment, the case where the protective film of the present invention is attached to a resin substrate when thermally bending the resin substrate of a lens for sunglasses has been described, but the protective film of the present invention is In addition to being applicable to thermal bending of resin substrates of such sunglasses lenses, for example, it can also be used to thermally bend resin substrates of lenses of goggles, visors of helmets, and the like.

EXAMPLES The present invention will now be described more specifically based on examples. In addition, the present invention is not limited at all by these examples.

1. Preparation of raw materials First, the raw materials used for producing the protective films of each example and comparative example are as follows.

<<Thermoplastic resin having non-adhesiveness>>
<Polyolefin-based resin having 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 having a melting point of 120°C or more and less than 150°C>
Linear low-density polyethylene with a melting point of 121° C. (LLDPE, manufactured by Ube Maruzen Polyethylene Co., Ltd., “Umerit 2525F”, MFR=2.5 g/10 min)

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

<<Thermoplastic resin having adhesiveness>>
<Elastomer>
Styrene-ethylene-butylene-styrene block copolymer (SEBS, manufactured by Asahi Kasei Corporation, "Tuftec H1221")

<Polyolefin resin>
Block polypropylene (propylene-ethylene block copolymer) having a melting point of 165° C. (b-PP, manufactured by Sumitomo Chemical Co., Ltd., “Noblen KS23F8”, MFR=2.1 g/10 min)

<Crystal nucleating agent>
Sorbitol crystal nucleating agent (IRGACLEAR, manufactured by BASF, "XT 386")

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

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

[2] Next, in forming the second layer (intermediate layer) included in the base material layer, SEBS as a thermoplastic resin having adhesiveness and h having a melting point of 167 ° C. -PP was kneaded so that the content of SEBS was 20% by weight to prepare a second layer-forming material (resin composition).

[3] Next, as a polyolefin resin having a melting point of 150 ° C. or higher for forming the prepared adhesive layer forming material, the prepared second layer forming material, and the first layer (outermost layer), the melting point is 167° C. h-PP were each loaded into three extruders.

[4] Next, by extruding these in a molten state from three extruders, a molten laminate in which these are laminated in layers is obtained from a co-extrusion T die. is cooled with a cooling roll at 40 ° C. at a line speed of 40 m / min (cooling condition A), so that the average thicknesses of the first layer, the second layer and the adhesive layer are 10 μm, 30 μm and 10 μm, respectively. A protective film of Example 1 was obtained.

In addition, the trouser breaking elongation strain A in the direction inclined at 45 ° with respect to both MD and TD of the protective film is 100 mm long, 50 mm wide, 50 μm thick, incision in accordance with JIS K 7128-1 (1998). A 50 mm protective film was prepared as a test piece, and this test piece was tilted 45° with respect to its MD and TD using a precision universal testing machine (manufactured by Shimadzu Corporation, "AG-X plus"). It was 245% when the distance between grips of the test piece was 50 mm and the tensile speed was 200 mm/min.

In addition, the protective film is heated at 145 ° C. for 30 minutes, then cooled at 25 ° C. for 30 minutes, and then measured according to JIS K 7128-1 (1998), MD and TD of the protective film. The trouser breaking elongation strain B in the direction inclined 45 ° with respect to both was measured in the same manner as described above using a precision universal testing machine (manufactured by Shimadzu Corporation, "AG-X plus"), and was 132%. there were.

Furthermore, according to JIS K 7127, the tensile breaking nominal strain of the protective film at 25 ° C. was measured so that the MD direction of the protective film was the longitudinal direction of the dumbbell. Using Shimadzu Autograph (precision universal testing machine, "AG-X plus"), the tensile speed was 500 mm/min, and the result was 630%.

In addition, the degree of crystallinity [%] of the protective film was measured using a wide-angle X-ray diffractometer (manufactured by Rigaku Co., Ltd., "Ultima IV"), using a CuKα ray as a radiation source and a focusing method as an optical system. 10 mm. Then, the scanning speed was set to 0.5 degrees/minute for 2θ=5 to 35 degrees, and the sample rotation was set to 60 rpm, and the crystal peak area ratio to the total area was calculated.
Crystallinity [%] = (Σ crystal peak area) ÷ (total area) × 100

(Examples 2 to 12, Comparative Example 1)
Type of polyolefin resin used in step [1], presence or absence of elastomer, presence or absence of crystal nucleating agent, type of adhesive thermoplastic resin used in step [2], non-adhesiveness Table 1 shows the presence or absence of a thermoplastic resin having a Protective films of Examples 2 to 12 and Comparative Example 1 were obtained in the same manner as in Example 1, except for changing as follows.

The cooling conditions A to E for cooling the laminate in the step [4] listed in Table 1 were the conditions shown below.

<Cooling conditions>
A: Cooled with a cooling roll at 40°C at a line speed of 40 m/min.
B: Cooled with a cooling roll at 40°C at a line speed of 20 m/min.
C: After cooling under cooling condition B, heat at 100°C for 30 minutes,
After that, it was slowly cooled in the atmosphere.
D: After cooling under cooling condition B, heat at 120° C. for 30 min,
After that, it was slowly cooled in the atmosphere.
E: Cooled with a cooling roll at 40°C at a line speed of 80 m/min.

3. Evaluation The protective films of Examples and Comparative Examples were evaluated by the following methods.

<1> Evaluation of the presence or absence of whiskers on the resin substrate First, for the protective films of each example and comparative example, a resin substrate (Sumitomo Bakelite (manufactured by Co., Ltd.) by pressing with a roll under the condition of a load of 0.5 kg/cm ² to affix a protective film to obtain a laminate.

Next, after being stored at a temperature of 50° C. for 12 hours, this laminate, that is, the resin substrate having protective films attached to both sides thereof, is punched out in the thickness direction to form a circular laminate in a plan view. It was assumed that

Next, after peeling off the two protective films from the laminate, the presence or absence of residual whiskers (adhesive layer) on the punched surface (cut surface) of the resin substrate 21 was visually observed, and residual whiskers were observed. A case where the beard was not observed was evaluated as ⊚, a case where the remaining beard was slightly observed as O, a case where the remaining beard was definitely observed as Δ, and a case where the remaining beard was clearly observed as ×.

<2> Evaluation of presence or absence of formation of orange peel on the surface of the resin substrate A laminated body was obtained by attaching a protective film to both surfaces of a substrate (manufactured by Sumitomo Bakelite Co., Ltd.) by pressure bonding using a roll under a condition of a load of 0.5 kg/cm ² .

Next, after being stored at a temperature of 50° C. for 12 hours, this laminate, that is, the resin substrate having protective films attached to both sides thereof, is punched out in the thickness direction to form a circular laminate in a plan view. It was assumed that

Next, the circular laminate was subjected to thermal bending under heating using a REMA molding machine ("CR-32 type" manufactured by REMA Co., Ltd.) equipped with a mold.

Next, after peeling off the two protective films from the laminate, the presence or absence of formation of orange peel (unevenness) on the adhered surface (release surface) of the resin substrate 21 was visually observed to determine whether orange peel was formed. The case where no orange peel was observed was evaluated as ◎, the case where orange peel formation was slightly observed as 〇, the case where orange peel formation was definitely observed as △, and the case where orange peel formation was more clearly observed was evaluated as ×. did.

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

As shown in Table 1, the protective film in each example satisfied that the trouser breaking elongation strain A was 300% or less, so that when the resin substrate was punched in the step [2] In addition, it was found that it is possible to accurately suppress or prevent the remaining of whiskers caused by the extension of the adhesive layer on the cut surface of the resin substrate which is a curved convex surface.

On the other hand, in the protective film in the comparative example, the trouser breaking elongation strain A cannot be set to 300% or less, and as a result, in the punching of the resin substrate in the step [2], the resin substrate having a curved convex surface The results showed that the whiskers remained on the cut surface of the .

REFERENCE SIGNS LIST 10 protective film 11 adhesive layer 15 base layer 16 first layer 17 second layer 21 resin substrate 23 polarizer 24 coating layer 30 polycarbonate layer 100 laminate 200 lens for sunglasses

Claims (10)

A protective film that is used by being attached to a resin substrate when the resin substrate is subjected to thermal bending under heating,
a substrate layer;
an adhesive layer positioned between the base material layer and the resin substrate and adhering to the resin substrate;
The base 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 protective film has a trouser breaking elongation strain of 300% or less in a direction inclined by 45° with respect to both MD and TD of the protective film, measured in accordance with JIS K 7128-1 (1998). A protective film characterized by: The protective film is heated at 145 ° C. for 30 minutes, then cooled at 25 ° C. for 30 minutes, and then measured according to JIS K 7128-1 (1998), MD and TD of the protective film 2. The protective film according to claim 1, wherein the trouser breaking elongation strain in a direction inclined by 45° with respect to both is 50% or more and 250% or less. According to JIS K 7127, the protective film is measured by Shimadzu Autograph (tensile speed: 500 mm / min) in an atmosphere of 23 ° C. and 60% RH with a test piece (No. 1 dumbbell) taken from the protective film. 3. The protective film according to claim 1 or 2, which has a nominal tensile strain at break of 400% or more and 650% or less. The protective film according to any one of claims 1 to 3, wherein the protective film has a crystallinity of 10% or less and 75% or less. The first layer contains a thermoplastic resin as a main material and has a melting point of 150° C. or higher, and the second layer contains a thermoplastic resin as a main material and has a melting point of 120° C. or higher. A protective film according to any one of claims 1 to 4. The protective film according to claim 5, wherein both the thermoplastic resin contained in the first layer and the thermoplastic resin contained in the second layer are polyolefins. The protective film according to any one of claims 1 to 6, which is attached to both sides of the resin substrate. 8. The protective film according to any one of claims 1 to 7, wherein at least one side forming an edge of the resin substrate forms a curved convex curve in plan view. The resin substrate is provided with a coating layer composed of a single layer or laminate having at least one of a polycarbonate resin layer, a polyamide resin layer and a cellulose resin layer on both sides, one side or the other side. Item 9. The protective film according to any one of Items 1 to 8. The protective film according to any one of claims 1 to 9, wherein the resin substrate is subjected to the thermal bending process by press molding or vacuum molding.

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