Paint substitute films, laminates, metal components, vehicle exterior parts, and methods for producing laminates.

Abstract

Provided is a coating substitute film that includes a laminated film containing an A layer and a B layer, wherein: the plane alignment coefficient of the B layer is 1.65-1.80 inclusive; a melting point TmB of the B layer is higher than a melting point TmA of the A layer; a melting point difference TmB - TmA is 25-35℃ inclusive; in either of the flow direction and the width direction of the laminated film, the residual rate of the inner stress in a tension test under the condition of 100℃ (specifically, the residual rate of the inner stress found by ｜１－（Ｕｂ／Ｕａ）｜×１００) is no greater than 25%.

Description

Technical Field

[0001] The present invention relates to a coating alternative film that covers, for example, a metal such as an outer panel of a vehicle like an automobile with a film instead of painting, and exhibits good adhesion to the metal and excellent appearance design.

Background Art

[0002] Conventionally, in order to improve the designability of metal exterior parts of vehicles, spray painting has generally been used. However, in recent years, in a painting process including such spray painting, a large amount of equipment and space are required because painting and drying are repeated, and productivity decreases. Therefore, for the purpose of rationalizing the painting process, etc., a method of improving the appearance of a product by laminating a decorative film (hereinafter referred to as a coating alternative film) on the exterior part has been studied.

[0003] In Patent Document 1, a heat-sealing film has been proposed as a film that is physically adhered to a metal foil or a metal plate. Specifically, by using a polyester B layer with a refractive index in the thickness direction of "1.500 or more" and having little orientation in the plane direction, and a heat-sealing layer with a thickness of 4 to 40 μm made of a polymer with a number average molecular weight of 15,000 or more and contacting this, delamination within the B layer is suppressed and a decrease in adhesive force is reduced.

[0004] In Patent Document 2, among two-layer polyester films composed of a B layer and an adhesive layer, it has been proposed that when the refractive index in the thickness direction of the B layer is less than 1.500 and the melting point difference between the B layer and the adhesive layer is 20°C or more, it has an excellent appearance design required for an outer panel of an automobile or the like and can exhibit good adhesion to a metal.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] When laminated metal sheets, obtained by laminating a paint substitute film onto metal sheets for vehicles, such as steel sheets or aluminum alloy sheets, are press-formed into exterior components for vehicles, if the adhesion between the metal sheet and the paint substitute film is insufficient, defects such as tearing or peeling of the film may occur immediately after forming due to a springback phenomenon. The object of the present invention is to provide a paint substitute film that exhibits excellent adhesion to metal sheets during press forming and shows excellent appearance, mainly for use in exterior components for vehicles. [Means for solving the problem]

[0007] As a result of diligent research conducted by the present inventors to achieve the above objectives, they discovered that in a laminated film comprising layer B (hereinafter sometimes referred to as the "molded layer") and layer A (hereinafter sometimes referred to as the "adhesive layer"), the laminated film exhibits stress-strain curve characteristics similar to those of a metal plate, and the adhesive layer exhibits a lower melting point than the molded layer. This allows the laminated film to maintain adhesion to metal while exhibiting excellent moldability. Based on this, the present inventors conducted further research and improvements, ultimately completing the inventions represented below.

[0008] [1] A laminated film comprising at least two layers, A layer and B layer, The aforementioned layer A is a layer that mainly contains crystalline polyester as its constituent component, The aforementioned layer B is a layer mainly composed of crystalline polyester, the surface orientation coefficient of the layer B is 0.165 or more and 0.180 or less, the melting point TmB of the layer B is higher than the melting point TmA of the layer A, and the melting point difference TmB-TmA is 25°C or more and 35°C or less. In both the flow direction and the width direction of the laminated film, the 20% elongation stress: F20 value in the tensile test under 100°C conditions is 60 MPa or more and 110 MPa or less. A paint substitute film wherein, in both the flow direction and the width direction of the laminated film, the residual rate of the internal stress shown in the following formula 1 in a tensile test under 100°C conditions is 25% or less. Equation 1: Percentage of remaining internal stress (%) = |1 - (Ub / Ua)| × 100 Here, the tensile test described above was performed using a sample with a width of 15 mm, with a chuck distance of 50 mm, pulling at a tensile speed of 1000 mm / min until 20% elongation was achieved, and then returning to a chuck distance of 50 mm at a speed of 2000 mm / min after 20% elongation. The above Ua refers to the elastic strain energy from the starting point 0 to the yield point in the stress-strain curve obtained from the above tensile test, and the above Ub refers to the elastic strain energy when the stress-strain curve obtained from the above tensile test is returned to the distance between the chucks from 20% elongation. [2] The paint substitute film according to [1], wherein the surface orientation coefficient of layer A is 0.03 or less than the surface orientation coefficient of layer B. [3] The coating substitute film according to [1] or [2], wherein the sum of the shrinkage rate in the flow direction and the shrinkage rate in the width direction of the laminated film is 1.0% or more and 5.0% or less. [4] A paint substitute film according to any one of [1] to [3], wherein the peel strength obtained by laminating the surface of layer A of the laminated film with a metal substrate at 230°C is 10 N / 20 mm or more. [5] A paint substitute film according to any one of [1] to [4], wherein an easy-adhesion layer having at least one functional group selected from the group consisting of epoxy groups, oxazoline groups, silanol groups, and isocyanate groups, and at least one functional layer selected from the group consisting of a surface protective layer and a coloring layer are laminated in this order on the surface of the B layer side of the laminated film. [6] The paint substitute film according to [5], wherein the colored layer contains 0.5% by mass or more and less than 40% by mass of a coloring agent based on 100% by mass of the resin composition constituting the colored layer. [7] The coating substitute film according to [5] or [6], wherein the surface protective layer comprises at least one selected from the group consisting of thermosetting resins and photocurable resins as its main component. [8] A paint substitute film according to any one of [5] to [7], wherein the thickness of the easy-adhesion layer is 10 nm to 200 nm. [9] A paint substitute film according to any one of [1] to [8], wherein an easy-adhesion layer having at least one functional group selected from the group consisting of epoxy groups, oxazoline groups, silanol groups, and isocyanate groups, a coloring layer, and a surface protection layer are laminated in this order on the B-layer side surface of the laminated film.

[10] The paint substitute film according to [9], wherein the colored layer contains 0.5% by mass or more and less than 40% by mass of a coloring agent based on 100% by mass of the resin composition constituting the colored layer.

[11] The coating substitute film according to [9] or

[10] , wherein the surface protective layer comprises at least one selected from the group consisting of thermosetting resins and photocurable resins as a main component.

[12] A paint substitute film according to any one of [9] to

[11] , wherein the thickness of the easy-adhesion layer is 10 nm to 200 nm.

[13] A film-coated metal laminate in which a metal plate is laminated onto a paint substitute film as described in any of [1] to

[12] .

[14] A metal component formed by press-molding the film-coated metal laminate described in

[13] .

[15] Vehicle exterior parts using the film-coated metal laminate described in

[13] .

[16] A method for producing a film-coated metal laminate using a paint substitute film described in any of [1] to

[12] , characterized in that a metal plate is heated to a temperature T of the paint substitute film that is above the melting point TmA of the A layer and below the melting point TmB of the B layer, and the A layer side surface of the paint substitute film and the metal plate are heat-pressed together.

[0009] The present invention can also be described as having the configuration shown in

[21] below.

[21] A laminated film including layer A and layer B, The aforementioned layer A contains a first crystalline polyester as its main component, The aforementioned layer B contains a second crystalline polyester as its main component, The surface orientation coefficient of the aforementioned B layer is 0.165 or more and 0.180 or less. The melting point of layer B is higher than the melting point of layer A, and the difference between the melting point of layer B and the melting point of layer A is 25°C or more and 35°C or less. When the laminated film was subjected to a tensile test, the residual internal stress index was 25% or less in both the flow direction and the width direction of the laminated film. The aforementioned remaining index rate is expressed by |1-(Ub / Ua)|×100, The aforementioned tensile test was performed by gripping a 15 mm wide test specimen with a pair of chucks at a distance of 50 mm between the chucks, widening the distance between the chucks at a tensile speed of 1000 mm / min at 100°C until a 20% strain occurred, and then returning the distance between the chucks to 50 mm at a speed of 2000 mm / min at 100°C. The aforementioned Ua is a value obtained by integrating the stress-strain curve obtained from the tensile test from 0% strain to yield strain. The aforementioned Ub is a value obtained by integrating the stress-strain curve from 20% strain to the strain at which the stress is 0 MPa. Paint substitute film.

[0010] The present invention preferably further comprises the configurations described in

[22] and later below.

[22] The laminated film is a coating substitute film according to

[21] , wherein the 20% strain tensile stress of the tensile test is 60 MPa or more and 110 MPa or less in both the flow direction and the width direction.

[23] The paint substitute film according to

[21] or

[22] , wherein the surface orientation coefficient of the B layer is greater than the surface orientation coefficient of the A layer, and the difference between the surface orientation coefficient of the B layer and the surface orientation coefficient of the A layer is 0.03 or more.

[24] The laminated film is a coating substitute film according to any one of

[21] to

[23] , wherein when heat-treated at 150°C for 15 minutes, the sum of the thermal shrinkage rate in the flow direction and the thermal shrinkage rate in the width direction is 1.0% or more and 5.0% or less. 〔25〕The coating substitute film is laminated on the metal substrate at 230°C so that the A layer contacts the metal substrate, and the peel strength when the coating substitute film is peeled from the metal substrate at a peel rate of 50 mm / min and 180° is 10 N / 20 mm or more, and the coating substitute film according to any one of 〔21〕~〔24〕. 〔26〕An easy adhesion layer provided on the surface of the B layer of the laminated film, and a functional layer, further comprising: The A layer, the B layer, the easy adhesion layer and the functional layer are arranged in this order, The functional layer includes at least one of a coloring layer and a surface protection layer, The coating substitute film according to any one of 〔21〕~〔25〕. 〔27〕The easy adhesion layer contains a resin having at least one functional group selected from the group consisting of an epoxy group, an oxazoline group, a silanol group and an isocyanate group, The coating substitute film according to 〔26〕. 〔28〕The functional layer includes the coloring layer and the surface protection layer, The A layer, the B layer, the easy adhesion layer, the coloring layer and the surface protection layer are arranged in this order, The coating substitute film according to 〔26〕 or 〔27〕. 〔29〕The functional layer includes the coloring layer, The coloring layer contains a colorant of 0.5% by mass or more and less than 40% by mass with respect to 100% by mass of the resin composition constituting the coloring layer, The coating substitute film according to any one of 〔26〕~〔28〕. 〔30〕The functional layer includes the surface protection layer, The surface protection layer includes at least one of a thermosetting resin and a photocurable resin, The coating substitute film according to any one of 〔26〕~〔29〕. 〔31〕The thickness of the easy adhesion layer is 10 nm to 200 nm, and the coating substitute film according to any one of 〔26〕~〔30〕. 〔32〕A metal plate, The metal plate is laminated with a coating substitute film according to any one of

[21] to

[31] , Laminated structure.

[33] A metal member formed by press-molding the laminate described in

[32] .

[34] Vehicle exterior parts including the laminate described in

[32] .

[35] A step of heating a metal plate to a temperature above the melting point of layer A and below the melting point of layer B in the paint substitute film described in any of

[21] to

[31] , The process includes pressing the metal plate, heated to the temperature, against the coating substitute film so that the metal plate and the A layer are in contact, A method for producing a laminate.

[36] A coating substitute film according to any one of

[21] to

[31] , wherein the sum of the thermal shrinkage rate in the flow direction and the thermal shrinkage rate in the width direction is 4.8% or less.

[37] A paint substitute film according to any one of

[21] to

[31] , wherein the sum of the thermal shrinkage rate in the flow direction and the thermal shrinkage rate in the width direction is 4.5% or less.

[38] A paint substitute film according to any one of

[21] to

[31] , wherein the sum of the thermal shrinkage rate in the flow direction and the thermal shrinkage rate in the width direction is 4.2% or less.

[39] A paint substitute film according to any one of

[21] to

[31] , wherein the sum of the thermal shrinkage rate in the flow direction and the thermal shrinkage rate in the width direction is 4.0% or less. [Effects of the Invention]

[0011] The paint-alternative film of the present invention exhibits excellent adhesion to various metals and excellent moldability, providing metal components with superior appearance and design, free from defects such as tearing or peeling of the film after press molding. The paint-alternative film of the present invention offers the value of eliminating the painting process in the manufacturing of metal components. [Brief explanation of the drawing]

[0012] [Figure 1] This diagram illustrates the concept of the formula for calculating the residual rate of internal stress. [Modes for carrying out the invention]

[0013] A coating substitute film according to an embodiment of the present invention includes a laminated film comprising layer A and layer B, The aforementioned layer A contains a first crystalline polyester as its main component, The aforementioned layer B contains a second crystalline polyester as its main component, The surface orientation coefficient of the aforementioned B layer is 0.165 or more and 0.180 or less. The melting point of layer B is higher than the melting point of layer A, and the difference between the melting point of layer B and the melting point of layer A is 25°C or more and 35°C or less. When the laminated film was subjected to a tensile test, the residual internal stress index was 25% or less in both the flow direction and the width direction of the laminated film. The aforementioned remaining index rate is expressed by |1-(Ub / Ua)|×100, The aforementioned tensile test was performed by gripping a 15 mm wide test specimen with a pair of chucks at a distance of 50 mm between the chucks, widening the distance between the chucks at a tensile speed of 1000 mm / min at 100°C until a 20% strain occurred, and then returning the distance between the chucks to 50 mm at a speed of 2000 mm / min at 100°C. The aforementioned Ua is a value obtained by integrating the stress-strain curve obtained from the tensile test from 0% strain to yield strain. The aforementioned Ub is a value obtained by integrating the stress-strain curve from 20% strain to the strain at which the stress is 0 MPa.

[0014] In this embodiment, the difference between the melting point of layer B and the melting point of layer A of the paint substitute film is 25°C or more. This makes it possible to increase the fluidity of layer A when the paint substitute film of this embodiment is heat-pressed onto a metal plate, and therefore, the peel strength (specifically, the peel strength when peeling the paint substitute film from the metal plate) can be improved.

[0015] Furthermore, since the residual internal stress index is 25% or less (specifically, when a tensile test is performed on the laminated film, the residual internal stress index is 25% or less in both the flow direction and the width direction of the laminated film), it is possible to reduce or prevent the peeling of the paint substitute film from the metal sheet that may occur during or after press forming. Specifically, by heat-pressing the paint substitute film of this embodiment onto a metal sheet (for example, a steel sheet, an aluminum alloy sheet, etc.), it is possible to reduce or prevent the peeling of the paint substitute film that may occur when press forming the laminated metal sheet (hereinafter sometimes referred to as "film-coated metal laminate" or "laminated sheet") that includes the metal sheet and the paint substitute film laminated on the metal sheet, as well as the peeling of the paint substitute film that may occur after press forming. This will be explained below. The residual index of internal stress is expressed by the following formula: Internal stress retention index = |1 - (Ub / Ua)| × 100 =|(Ua-Ub) / Ua|×100 The Ua and Ub in this equation can be determined based on the stress-strain curve obtained from a tensile test (specifically, a tensile test in which a 15 mm wide specimen is gripped by a pair of chucks with a distance of 50 mm between the chucks, the distance between the chucks is increased at a tensile speed of 1000 mm / min and 100°C until a 20% strain occurs, and then the distance between the chucks is returned to 50 mm at a speed of 2000 mm / min and 100°C). Here, the stress-strain curve is a graph in which stress is plotted on the vertical axis and strain on the horizontal axis (see Figure 1). As shown in Figure 1, Ua is a value obtained by integrating the stress-strain curve from 0% strain to the yield strain, i.e., the strain indicating the yield point. If we consider the period from the start of tension to the occurrence of yield strain as elastic deformation, then Ua can be considered as the elastic strain energy stored in the laminated film due to tension. On the other hand, Ub is a value obtained by integrating from 20% strain down to the strain at which the stress is 0 MPa (hereinafter sometimes referred to as "rebound strain" or "rebound strain amount"). Ub is the energy released when the distance between the chucks returns from the distance at which 20% strain is applied back to the distance between the chucks at the start of tension (50 mm), that is, when the deformation of the laminated film (specifically, the deformation applied to the laminated film by tension) recovers, and therefore can be said to be elastic strain energy. If the balance between Ua and Ub is excessively poor, the springback that occurs when the laminated metal sheet is press-formed will not effectively release the elastic strain energy of the laminated film (specifically, the elastic strain energy stored in the laminated film by press-forming). In other words, the elastic strain energy will not effectively decrease, resulting in excessive internal stress remaining in the laminated film. In contrast, according to this embodiment, the value calculated by |(Ua-Ub) / Ua| × 100 (i.e., the residual internal stress index rate) is 25% or less. Therefore, the springback that occurs when the laminated metal sheet is press-formed effectively releases the elastic strain energy of the laminated film, and thus, excessive internal stress can be avoided in the laminated film. As a result, the occurrence of delamination of the paint substitute film that may occur during or after press-forming can be reduced or prevented. Furthermore, when the paint substitute film of this embodiment is heat-pressed onto a metal sheet for vehicles (for example, a steel sheet, an aluminum alloy sheet, etc.) to obtain a laminated metal sheet, and the laminated metal sheet is press-formed into a vehicle exterior part, the occurrence of peeling of the paint substitute film can be further reduced or prevented. This is because when the laminated metal sheet is press-formed, the paint substitute film stretches partially, and this stretch is generally considered to be at most about 20% in vehicle exterior parts. In addition, automobiles are preferred as the vehicle, and four-wheeled automobiles are more preferred. The residual internal stress index can be controlled by, for example, the surface orientation coefficient of layer B and the ratio of the thickness of layer B to the thickness of the laminated film. The higher the surface orientation coefficient of layer B, the lower the residual internal stress index tends to be. The larger the ratio (specifically, the ratio of the thickness of layer B to the thickness of the laminated film), the lower the residual internal stress index tends to be.

[0016] Furthermore, since the surface orientation coefficient of layer B is 0.165 or higher, the occurrence of wrinkles and bubbles that may occur when the paint substitute film of this embodiment is heat-pressed onto a metal plate can be reduced. In other words, the appearance of the laminated metal plate can be improved.

[0017] Therefore, the paint substitute film of this embodiment can reduce the occurrence of wrinkles and bubbles during heat bonding, and can also reduce or prevent peeling from the metal sheet that may occur during or after press molding. In other words, the paint substitute film of this embodiment can exhibit excellent adhesion to the metal sheet and can also show an excellent appearance when heat-bonded to the metal sheet.

[0018] Embodiments of the present invention will be described in more detail below. The flow direction may be referred to as the Machine Direction or MD direction. The width direction may be referred to as the Transverse Direction or TD direction. The stress at 20% elongation may be referred to as the F20 value or 20% strain tensile stress. Strain may be referred to as the amount of strain.

[0019] The paint-alternative film of this embodiment includes a laminated film comprising layers A and B. Layer A can primarily have the function of providing adhesion to the metal sheet. That is, layer A can function as an adhesive layer. On the other hand, layer B can primarily have the function of accompanying the deformation of the metal sheet during press forming. That is, layer B can function as a molding layer. In addition to layers A and B, the paint-alternative film of this embodiment may further include other layers. The other layers are preferably mainly made of polyester, and preferably mainly made of crystalline polyester. Crystalline polyester will be described later.

[0020] Layers A and B are mainly made of polyester. Here, "mainly" means that polyester makes up preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the total mass of the film.

[0021] The polyester constituting layer A is preferably a crystalline polyester. Here, a crystalline polyester refers to a polyester in which, when 10 mg of the polyester composition scraped from layer A is heated to 290°C at a rate of 20°C / min using a DSC-60 differential scanning calorimeter, is kept isothermal for 3 minutes, rapidly cooled at a rate of 200°C / min, and then heated again to 290°C at a rate of 10°C / min, a baseline shift corresponding to the glass transition point and an endothermic peak of 0.05 J / g or more associated with crystal melting are observed at a temperature higher than the baseline shift. The polyester constituting layer A can be a homopolyester or a copolymer polyester. Preferably, it is a copolymer polyester with a eutectic point of 160°C to 250°C, and more preferably a copolymer polyester with a melting point of 180°C to 250°C. The copolymer polyester is preferably mainly composed of ethylene terephthalate units. Here, "main component" means that in the copolymerized polyester, the ethylene terephthalate unit is preferably 60 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more.

[0022] The copolymer components of such copolymerized polyester may be either acidic or alcoholic components. Examples of acidic components include aromatic dicarboxylic acids other than the main acidic components such as isophthalic acid, phthalic acid, terephthalic acid, and 2,6-naphthalenedicarboxylic acid, as well as aliphatic dicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid. Examples of alcoholic components include ethylene glycol, trimethylene glycol, and tetramethylene glycol, as well as polyoxyalkylene glycols such as diethylene glycol. In addition, examples include aliphatic diols such as 1,6-hexanediol and alicyclic diols such as 1,4-cyclohexanedimethanol. These can be used individually or in combination of two or more. Among these, isophthalic acid and sebacic acid are preferred, and isophthalic acid is particularly preferred.

[0023] The crystalline polyester content in layer A is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on 100% by mass of layer A.

[0024] The polyester constituting layer B is preferably a crystalline polyester. Here, a crystalline polyester refers to a polyester in which, when 10 mg of the polyester composition scraped from layer B is heated to 290°C at a rate of 20°C / min using a DSC-60 differential scanning calorimeter, is kept isothermal for 3 minutes, rapidly cooled at a rate of 200°C / min, and then heated again to 290°C at a rate of 10°C / min, a baseline shift corresponding to the glass transition point and an endothermic peak of 0.05 J / g or more associated with crystal melting are observed at a temperature higher than the baseline shift.

[0025] The polyester constituting layer B can be a homopolyester or a copolymerized polyester. Preferably, it is a polyester with a melting point between 250°C and 260°C, and particularly preferably homopolyethylene terephthalate. Note that the term homopolyethylene terephthalate here does not exclude the inclusion of diethylene glycol components, which are inevitably present.

[0026] The crystalline polyester content in layer B is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on 100% by mass of layer B.

[0027] In order to ensure sufficient molten wetting with the metal during thermal lamination while maintaining good formability during cold press forming, the coating substitute film of the present invention preferably has a melting point TmB of layer B higher than the melting point TmA of layer A, and the melting point difference: TmB-TmA is preferably 25°C or higher and 35°C or lower. By having a melting point difference of 25°C or higher, sufficient molten wetting with the metal can be ensured even at low temperatures during lamination of the coating substitute film and the metal plate. On the other hand, by having a melting point difference of 35°C or lower, the refractive indices of layers A and B can be controlled within a predetermined range, enabling uniform forming by suppressing the effects of shear heat even during cold press forming, and contributing to improved adhesion and formability with the metal plate.

[0028] The intrinsic viscosity (i.e., IV) of the polyester used in layers A and B is preferably 0.60 or higher and less than 0.95. When the intrinsic viscosity is above the lower limit, the film manufacturing operation is good and the generation of thermally degraded products originating from low molecular weight materials can be suppressed. Furthermore, it is preferable because it is possible to prevent excessive internal stress generated during cold press forming of metals from remaining in the laminated film, and excellent adhesion to various metals and excellent formability can be achieved. On the other hand, when the viscosity is below the upper limit, adhesion is good and lamination with metal plates is improved.

[0029] In the present invention, the surface orientation coefficient of layer B is preferably 0.165 or higher, more preferably 0.166 or higher, even more preferably 0.167 or higher, even more preferably 0.168 or higher, and even more preferably 0.170 or higher. By having a surface orientation coefficient of 0.165 or higher for layer B, it is possible to prevent excessive internal stress generated during cold press forming of metal from remaining in the laminated film. The surface orientation coefficient of layer B is preferably 0.180 or lower, and more preferably 0.178 or lower. It is preferable that the surface orientation coefficient of layer A is smaller than that of layer B, and it is preferable that the difference between the surface orientation coefficients of layer B and layer A is 0.030 or higher.

[0030] In the present invention, the coating substitute film preferably has a 20% elongation stress (F20) value of 60 MPa or more in both the flow direction and the width direction of the laminated film including layers A and B, under tensile conditions at 100°C. More preferably, it is 65 MPa or more, and even more preferably 70 MPa or more. By having a value of 60 MPa or more, the stress of the coating substitute film can be maintained even under heating due to shear heat generated during cold press forming of metal, thereby ensuring uniform formability. The upper limit of the F20 value is not particularly limited, but it is preferably 110 MPa or less, and more preferably 105 MPa or less.

[0031] In the present invention, it is preferable that the coating substitute film has a residual rate of internal stress (i.e., residual index rate) of 25% or less in a tensile test at 100°C, as shown in the following formula 1, in both the flow direction and the width direction of the laminated film including layers A and B. (Equation 1) Percentage of remaining internal stress (%) = |1 - (Ub / Ua)| × 100 Here, the above tensile test is performed using a sample with a specimen width of 15 mm, with a chuck distance of 50 mm, pulling at a tensile speed of 1000 mm / min until 20% elongation, and then returning to a chuck distance of 50 mm at a speed of 2000 mm / min after 20% elongation. Ua refers to the elastic strain energy from the starting point 0 to the yield point in the stress-strain curve obtained from the above tensile test, and Ub refers to the elastic strain energy when returning from 20% elongation to the chuck distance in the stress-strain curve obtained from the above tensile test.

[0032] In other words, when a tensile test is performed on a laminated film (specifically, a 15 mm wide test piece cut from the laminated film is gripped by a pair of chucks with a distance of 50 mm between the chucks, and the distance between the chucks is widened at a tensile speed of 1000 mm / min and 100°C until a 20% strain occurs, and then the distance between the chucks is returned to 50 mm at a speed of 2000 mm / min and 100°C), the residual index of internal stress shown in Equation 1 is 25% or less in both the flow direction and the width direction of the laminated film. Ua is a value obtained by integrating the stress-strain curve from a tensile test from 0% strain to the yield strain (i.e., the strain indicating the yield point). In other words, it is the area of ​​the region enclosed by the stress-strain curve and the portion of the horizontal axis from 0% strain to the yield strain. Ub is a value obtained by integrating the stress-strain curve from 20% strain to the strain where the stress is 0 MPa (i.e., "rebound strain"). In other words, it is the area of ​​the region between the stress-strain curve and the portion of the horizontal axis from 20% strain to rebound strain. Furthermore, considering that heat is generated by shear during the press forming of laminated metal sheets, the tensile test used to determine Ua and Ub is a 100°C tensile test.

[0033] In both the flow direction and the width direction of the laminated film, the residual index rate of internal stress, i.e., the residual rate, may be 23% or less, 20% or less, or 17% or less.

[0034] Furthermore, in the flow direction of the laminated film, Ub may be greater than or less than Ua. In the width direction of the laminated film, Ub may be greater than or less than Ua. In both the flow direction and the width direction of the laminated film, Ub may be greater than or less than Ua.

[0035] When cold-pressing a metal sheet laminated with a paint substitute film, a springback phenomenon occurs when a load is applied up to a certain deformation level and then removed, causing the sheet to return to its original shape along the slope of the elastic deformation region in the stress-strain curve. At this time, if the residual internal stress of the paint substitute film is high, the film may not be able to follow the springback, resulting in tearing or delamination. Since the residual internal stress of the paint substitute film is 25% or less, it is possible to prevent excessive internal stress generated during cold-pressing from remaining in the laminated film, and it is estimated that excellent adhesion to various metals and excellent formability can be achieved. The residual internal stress can be kept within the above range by controlling the intrinsic viscosity and surface orientation coefficient of layers A and B within a predetermined range.

[0036] The coating substitute film of the present invention preferably has a sum of the thermal shrinkage rate in the flow direction and the thermal shrinkage rate in the width direction after heat treatment at 150°C for 15 minutes of the laminated film including layers A and B, which is 5.0% or less. If it exceeds 5.0%, the adhesion force during heat lamination is low, requiring a high lamination temperature near or above the melting point, which is undesirable in practice and also undesirable from the viewpoint of dimensional stability during thermoforming. The sum of the thermal shrinkage rates is preferably 4.8% or less. The sum of the thermal shrinkage rates may be, for example, 4.5% or less, 4.2% or less, or 4.0% or less. Methods for achieving the above thermal shrinkage rates include appropriately setting the stretching conditions and heat fixing treatment conditions. The sum of the thermal shrinkage rate in the flow direction and the thermal shrinkage rate in the width direction may be 1.0% or more, 2.0% or more, or 3.0% or more. The thermal shrinkage rate can be calculated using the following formula. Thermal shrinkage rate (%) = {(L0 - L) / L0} × 100 Here, L is the gauge length after heat treatment (specifically, heat treatment at 150°C for 15 minutes), and L0 is the gauge length before heat treatment (specifically, heat treatment at 150°C for 15 minutes).

[0037] The paint substitute film of the present invention preferably has a peel strength of 10.0 N / 20 mm or more when the A layer and the metal substrate are laminated at 230°C. That is, it is preferable that the peel strength when the paint substitute film is laminated to the metal substrate at 230°C so that the A layer is in contact with the metal substrate, and then the paint substitute film is peeled from the metal substrate at a tensile speed of 50 mm / min and 180°, is 10.0 N / 20 mm or more. A peel strength of 10.0 N / 20 mm or more allows for the maintenance of adhesion and formability during cold press molding. The peel strength is more preferably 13.0 N / 20 mm or more, and even more preferably 15.0 N / 20 mm or more. There is no particular upper limit, but it is preferably 35.0 N / 20 mm or less, more preferably 30.0 N / 20 mm or less, and even more preferably 25.0 N / 20 mm or less.

[0038] The thickness of the laminated film of the present invention can be changed as needed, but a range of 15 to 200 μm is preferable for the overall thickness, with a range of 20 to 150 μm being particularly preferable, and especially 30 to 100 μm being preferable. A thickness of 15 μm or more provides good handling during film formation, functional layer lamination, and lamination processes. On the other hand, a thickness of 200 μm or less helps to prevent excessive load during molding.

[0039] The thickness of layer A is preferably 5 μm or more, and more preferably 8 μm or more. A thickness of 5 μm or more ensures sufficient molten wetting during lamination with the steel sheet, facilitating good adhesion between the film and the metal sheet. Furthermore, the thickness ratio of layer A to layer B (XB / XA: where XA is the total thickness of layer A and XB is the total thickness of layer B) is preferably 1.5 or more, and more preferably 2.0 or more, from the viewpoint of balancing improved adhesion between the film and the metal sheet with maintaining a good appearance. The ratio of the thickness of layer B to the thickness of the laminated film, i.e., the thickness of layer B / thickness of the laminated film, is preferably 0.50 or more, more preferably 0.60 or more, even more preferably 0.65 or more, and even more preferably 0.70 or more. On the other hand, this ratio is preferably 0.95 or less, and more preferably 0.90 or less.

[0040] Other additives, such as coloring pigments (i.e., colorants), fluorescent whitening agents, antioxidants, heat stabilizers, ultraviolet absorbers, and antistatic agents, may be added to layers A and B as needed, within a range that does not hinder the objectives of the present invention. When the laminated film is used as a metal concealing layer, the addition of coloring pigments is preferable, and either inorganic or organic pigments may be used, but inorganic pigments are preferred. Examples of inorganic pigments include alumina, titanium dioxide, calcium carbonate, and barium sulfate, with titanium dioxide being more preferred. The content of the coloring pigment is preferably more than 2% by mass and 50% by mass or less based on the mass of layer B, a more preferable content is in the range of 5 to 40% by mass, and even more preferably in the range of 10 to 35% by mass. Fluorescent whitening agents may be used to particularly improve whiteness. In addition, inert particles may be added to improve handling in the film-forming and molding processes. The inert particles to be included are not particularly limited as long as they can exist stably in the polymer, and known particles can be used. For example, polymers or copolymers of monomers selected from polystyrene, methyl polyacrylate, ethyl polyacrylate, methyl polymethacrylate, ethyl polymethacrylate, and divinylbenzene, or organic materials such as polytetrafluoroethylene, polyacrylonitrile, benzoguanamine, and silicone, or inorganic materials such as silica, kaolin, talc, and graphite are preferred. The preferred particle size of these inert particles is 0.1 to 10 μm. Layer B may contain inert particles, layer A may contain inert particles, or both may contain inert particles. The content of inert particles in the laminated film is preferably in the range of 0.002 to 0.5% by mass of 100% by mass of the laminated film. If layer B contains inert particles, the content of inert particles is preferably in the range of 0.002 to 0.5% by mass of 100% by mass of layer B. On the other hand, if layer A contains inert particles, it is preferable that the amount of inert particles is in the range of 0.002 to 0.5 mass% of 100 mass% of layer A. Furthermore, if the laminated film contains a coloring pigment, i.e., a coloring agent, then layer A may contain the coloring agent, layer B may contain it, or both layers A and B may contain the coloring agent. Of course, the laminated film does not have to contain colorants. That is, neither layer A nor layer B can contain colorants.

[0041] The manufacturing method for layers A and B in this invention is not particularly limited, and conventionally known film-forming methods can be applied. For example, when manufacturing a biaxially oriented laminated film, an unstretched laminated sheet is first prepared, and then stretched in two directions. Typical examples are shown below.

[0042] For example, a polyester composition is prepared for layer A by adding inert particles to polyester, and after being thoroughly dried, it is melted in an extruder at a temperature of ~(melting point + 50)°C. Here, the melting point is the melting point of the polyester used. Simultaneously, a polyester composition is prepared for layer B by adding inert particles to crystalline polyester, and after being thoroughly dried, it is supplied to another extruder and melted at a temperature of ~(melting point + 50)°C. Subsequently, a laminated unstretched laminated sheet is produced by a method of laminating both molten resins inside a die, for example, a simultaneous lamination extrusion method using a multi-manifold die. In this simultaneous lamination extrusion method, the molten resin forming one layer and the molten resin forming the other layer are laminated inside the die and formed into a sheet from the die while maintaining the laminated structure.

[0043] The unstretched laminated sheet can then be manufactured by sequential or simultaneous biaxial stretching and heat-fixing. When forming a film by sequential biaxial stretching, the unstretched laminated sheet is heated by roll heating, infrared heating, etc., and first stretched in the flow direction, and then stretched transversely with a tenter. At this time, the lower limit of the stretching temperature in the flow direction is preferably 70°C, and more preferably 80°C. If the temperature is below 70°C, not only is breakage more likely to occur, but the orientation in the flow direction becomes stronger due to stretching at low temperatures, so the shrinkage stress during the heat-fixing treatment becomes larger, which increases the strain of the molecular orientation in the width direction, and as a result the processability during molding may decrease. The upper limit of the stretching temperature in the flow direction is preferably 110°C, and more preferably 100°C. If the temperature exceeds 110°C, the orientation decreases, which may reduce the processability during molding.

[0044] The lower limit of the stretching ratio in the flow direction is preferably 3 times, and particularly preferably 3.5 times. If it is less than the above, the orientation will decrease, which will reduce processability during molding, and uneven thickness may cause sagging in the film roll. The upper limit of the stretching ratio in the flow direction is preferably 5.0 times, more preferably 4.5 times, and particularly preferably 4.0 times. If it exceeds the above, the effects of improving mechanical strength and thickness uniformity may saturate. Stretching in the flow direction can be performed, for example, by heating the unstretched film with heated rolls or infrared radiant heat in a roll stretching machine and stretching it using the speed difference between the rolls.

[0045] The lower limit of the stretching temperature in the width direction is preferably 90°C; below this temperature, fracture may be more likely to occur. The upper limit of the TD stretching temperature is preferably 130°C; exceeding this temperature may reduce the orientation and thus the processability during molding.

[0046] The lower limit of the stretching ratio in the width direction is preferably 3.0 times, and more preferably 3.5 times. If it is less than the above, the degree of orientation in the width direction will be small, which will reduce processability during molding and may cause sagging in the film roll due to thickness unevenness. The upper limit of the stretching ratio in the width direction is preferably 5.0 times, and more preferably 4.5 times. If it exceeds the above, the effects of processability during molding and improvement of thickness unevenness may saturate.

[0047] After the biaxial stretching described above, it is preferable to perform a heat-setting treatment. The heat-setting temperature is preferably selected in the range of 150 to 230°C according to the melting point of the polyester in order to adjust the film quality. At this time, if the temperature is too low, the adhesion to the metal deteriorates, and if it is too high, the surface orientation coefficient decreases, preventing the function of suppressing elastic strain energy from being exhibited, leading to deterioration of adhesion to the metal and moldability. Taking this into consideration, the heat-setting temperature is preferably 205°C or higher, more preferably 210°C or higher, and even more preferably 215°C or higher.

[0048] It is preferable to perform a thermal relaxation treatment in conjunction with or separately from the thermal setting treatment. In the thermal relaxation treatment, it is preferable to relax in at least one of the flow direction (i.e., MD direction) and the width direction (i.e., TD direction). In particular, relaxation in the width direction is preferable. When relaxing in the width direction, the relaxation rate in the width direction is preferably 3% or more, and more preferably 4% or more. If it is 3% or more, the thermal shrinkage rate can be effectively reduced. On the other hand, the relaxation rate in the width direction is preferably 8% or less, and more preferably 7% or less.

[0049] One preferred embodiment of the present invention is a coating substitute film in which an easy-adhesion layer is laminated on the B-layer side surface of a laminated film comprising at least two layers, A-layer and B-layer. The easy-adhesion layer has the function of improving the adhesion between the laminated film and the surface protection layer and coloring layer described later. The easy-adhesion layer preferably contains a resin having at least one functional group selected from the group consisting of epoxy groups, oxazoline groups, silanol groups, and isocyanate groups. Among these, it is preferable to contain an epoxy group or an oxazoline group from the viewpoint of obtaining excellent adhesion and vividness with the B-layer (see Patent Document 2, i.e., Japanese Patent Application Publication No. 2020-192787). The thickness of the easy-adhesion layer is preferably 10 nm or more, more preferably 15 nm or more, even more preferably 20 nm, and particularly preferably 40 nm or more from the viewpoint of adhesion. On the other hand, the upper limit of the thickness is preferably 200 nm or less, more preferably 180 nm, even more preferably 150 nm, and particularly preferably 120 nm or less from the viewpoint of reducing uneven coating thickness and adhesion.

[0050] As mentioned above, the easy-adhesion layer preferably contains at least one functional group selected from the group consisting of epoxy groups, oxazoline groups, silanol groups, and isocyanate groups. The resin forming the easy-adhesion layer can be any known resin that has excellent adhesion to the laminated film or functional layer. To adjust the adhesive strength, copolymerization of each resin or blending of different resins can be suitably used to improve the adhesive strength. For example, any of the following can be used, either alone or in combination of two or more: polyurethane resins, vinyl chloride / vinyl acetate copolymer resins, vinyl chloride / vinyl acetate / acrylic copolymer resins, chlorinated polypropylene resins, acrylic resins, polyester resins, polyamide resins, butyral resins, polystyrene resins, nitrocellulose resins, cellulose acetate resins, etc. In the cold pressing molding of the present invention, the molding temperature preferably reaches about 150°C, so it is preferable that the glass transition temperature is lower than this temperature, and acrylic resins and polyester resins can be preferably used.

[0051] The above-mentioned easy-adhesion layer may be applied by in-line coating, which is performed during the film formation of the laminated film, or the laminated film may be wound into a roll after film formation, and then unwound again for off-line coating.

[0052] The resulting easy-adhesion layer contributes to improved adhesion between the laminated film and each layer when laminating the surface protection layer and / or colored layer described later, through the effects of bond formation between functional groups, reduction of interlayer interface energy, and interlayer interface mixing.

[0053] Another preferred embodiment of the present invention is a paint substitute film having at least one functional layer selected from the group consisting of a surface protection layer and a coloring layer, via an easy-adhesion layer, on the B-layer side surface of a laminated film comprising at least two layers, A layer and B layer.

[0054] Another preferred embodiment of the present invention is a paint substitute film in which a coloring layer and a surface protection layer are laminated in this order on the B-layer side surface of a laminated film comprising at least two layers, A and B, via an easy-adhesion layer. Laminating each layer in this order is preferable because it ensures good adhesion between the laminated film and the functional layer, and furthermore, allows for the expression of an excellent appearance and design.

[0055] The above-mentioned colored layer preferably contains a binder resin and at least one coloring agent selected from the group consisting of pigments and dyes, and from the viewpoint of design, it is preferable that the coloring agent is contained in an amount of 0.5% by mass or more and less than 40% by mass, based on the mass of the composition used for the colored layer. A more preferable range is 2% by mass or more and less than 30% by mass, and a particularly preferable range is 5% by mass or more and less than 25% by mass. If a binder resin is not used, cracks may easily occur in the colored layer due to the elongation during molding, which may impair the aesthetic appearance. Furthermore, by using a pigment or dye, a beautiful and superior appearance can be formed. The pigment or dye used is preferably one or more selected from the group consisting of carbon black (ink), iron black, titanium white, antimony white, lead yellow, titanium yellow, iron oxide, cadmium red, ultramarine, cobalt blue, quinacridone red, isoindolinone yellow, phthalocyanine blue, aluminum, brass, titanium dioxide, and pearlescent pigments. The use of other pigments and additives for color matching is a preferred embodiment, as long as it does not impair the effects of the present invention.

[0056] The method for forming the above-mentioned colored layer is not particularly limited, but a method of lamination by coating is simple and preferred. The adhesion between the above-mentioned colored layer and the above-mentioned layer B can be appropriately adjusted depending on the type of layer B and the easy-adhesion layer C, and the binder resin used for the colored layer.

[0057] The thickness of the above-mentioned colored layer is preferably 2 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. The upper limit of the thickness is preferably 100 μm or less, more preferably 75 μm or less, even more preferably 50 μm or less, even more preferably 45 μm or less, and even more preferably 30 μm or less. When the above-mentioned colored layer is used on the exterior of a vehicle, it is also preferable to make it a multi-layered colored layer in order to produce a beautiful design. For example, it is preferable to make it a two-layered colored layer by providing a colored layer containing a glossy material pigment in a binder resin on top of a colored layer made of pigment. Furthermore, considering the reflective properties from the viewing side, it is also preferable to make it a three-layered colored layer with a colored reflective layer made of aluminum pigment, a colored pigment layer, and a glossy material pigment layer of a clear coating film on the side of the colored layer closest to the laminated film. Using the colored layer as a single layer or as a multi-layered layer in order to impart the desired design properties does not in any way negate the purpose of the present invention.

[0058] The resin used in the above-mentioned surface protection layer is preferably mainly composed of at least one type of resin selected from the group consisting of thermosetting resins or photocurable resins, based on its suitability for the manufacturing process from paint substitute film production to metal component molding. In other words, the surface protection layer is preferably thermosetting or photocurable, with thermosetting being preferred. The above-mentioned surface protection layer is required to have weather resistance, scratch resistance, and transparency, and as an example, an acrylic resin can be used.

[0059] The thickness of the surface protective layer described above is preferably 5 to 80 μm in film thickness after drying. If the thickness of the surface protective layer is greater than the lower limit, less resin material is used, resulting in good cost performance, but the inner colored layer, laminated film, and the protective performance against scratches and chemicals after the component is formed cannot be maintained at a high level. On the other hand, if the thickness is less than the upper limit, it is good in terms of gloss and protective performance as a hard coat coating, but it is not economically advantageous because more resin is used than necessary. The preferred thickness of the surface protective layer is a lower limit of 10 μm, more preferably 15 μm, and an upper limit of 60 μm, more preferably 50 μm.

[0060] The above surface protection layer may consist of a single layer or multiple layers. For example, when coating with multiple layers of the same resin twice, the degree of curing can be adjusted by varying the drying conditions, and adhesion can be improved when a functional layer such as an anti-fouling layer is added to the outside of the surface protection layer. Furthermore, a glossy surface can be produced by creating multiple layers within the above range.

[0061] The above surface protection layer is preferably laminated by coating onto an easy-adhesion layer or a colored layer. Any known coating method may be used, but it is preferable to roll it up in a state where the heat curing is not yet complete (hereinafter sometimes referred to as "semi-cured state"). When the hard coat paint is dried, the primary reaction proceeds due to heat, and the hard coat becomes a coating film in a semi-cured state, making it possible to roll it up. The semi-cured surface protection layer can then be designed so that the secondary reaction proceeds at a temperature higher than the aforementioned drying temperature, thereby allowing the degree of curing to progress from semi-cured to fully cured by the heat generated when laminating to a metal plate or forming a component.

[0062] In one preferred embodiment of the present invention, the paint substitute film of the present invention may have further lamination applied to the surface of the functional layer consisting of a colored layer and / or a surface protective layer, as needed. Examples include an anti-fouling layer to prevent soiling during outdoor use, and lamination of a protective film to improve handling in the manufacturing process. In particular, when laminating the surface protective layer in a semi-cured state, it is preferable to laminate a protective film to improve handling in subsequent processes. The protective film may be peeled off at any time, but from the viewpoint of scratch resistance, it is preferable to peel it off after heat-press lamination with a metal plate and cold press molding of the film-coated metal laminate. Examples of protective films include films made of polyethylene resin, polyester resin, copolymerized polyester resin, polypropylene resin, polyvinyl chloride resin, and mixtures thereof, but from the viewpoint of moldability, polyethylene resin, polyvinyl chloride resin, and copolymerized polyester resin are preferred. The thickness of the protective film is not particularly limited, but a thickness of 15 to 150 μm is preferred in order to fully exhibit its protective function.

[0063] The present invention further provides a film-coated metal laminate in which a metal plate is laminated to the above-mentioned paint substitute film. In the film-coated metal laminate of the present invention, the metal plate and the A-layer side of the laminated film may be laminated by heat-pressing, and no adhesive for lamination is particularly used. Since the metal plate is usually wound in a roll, and the paint substitute film can also be manufactured in a roll, roll-to-roll lamination is possible if they are used.

[0064] A preferred method for manufacturing the above-mentioned film-coated metal laminate is, for example, to heat a metal plate and press the A-layer side of the supplied coating substitute film against the metal plate using a nip roll, thereby bonding the coating substitute film to the metal plate. In other words, to obtain a laminate, a heated metal plate and a coating substitute film can be pressed together. At that time, by setting the temperature T of the metal plate during heat pressing to be above the melting point TmA of the A-layer of the laminated film and within the melting point TmB of the B-layer of the laminated film, it is possible to ensure molten wetting between the metal plate and the A-layer while suppressing the melting of the B-layer, thereby obtaining excellent adhesion to the metal plate and processability. The heat-pressed coating substitute film becomes partially molten due to the heat from the metal plate, but solidifies and recrystallizes during the cooling process, which reduces subsequent processability. To prevent this, it is preferable to rapidly cool the film-coated metal laminate after heat pressing. The method of rapid cooling is not particularly limited, but known methods such as immersion in a cold water bath or spraying cold water can be used. The time from heat sealing to rapid cooling should be as short as possible, preferably within 5 seconds, more preferably within 3 seconds, and most preferably within 1 second.

[0065] The metal sheet used for heat-compression bonding can be appropriately selected from known materials according to the intended use of the metal component. Examples include, but are not limited to, steel sheets, galvanized steel sheets, tin-free steel (chrome-plated steel sheets), tinplate, aluminum sheets, and stainless steel sheets. Generally, metal sheets with good formability and a thickness of about 0.3 to 1.0 mm are used, so it is preferable to use such grades. For example, for metal sheets used in the exterior of a vehicle, steel sheets with a thickness of 0.4 to 0.8 mm that have been treated with a zinc alloy plating for rust prevention, or aluminum sheets with a thickness of 0.6 to 1.2 mm are preferred embodiments.

[0066] The present invention further provides a metal member, i.e., a processed product, formed by press forming of the above-mentioned film-coated metal laminate. Cold press forming is preferred as the press forming method. When cold press forming is performed on the above-mentioned film-coated metal laminate, whether it is stretch forming in which the edges of the metal sheet are held under high pressure, or forming (drawing) in which the metal sheet is held under low pressure and drawn in during forming, by pre-applying a heat-pressure bond to the surface of the metal sheet as described above, it becomes possible to coat the surface of the metal member with a paint substitute film.

[0067] The above-mentioned metal components are preferably used as exterior parts for vehicles such as automobiles and motorcycles. Excellent appearance is required for vehicle exterior parts, and the present invention can be suitably used in such applications. Exterior panels are preferred as vehicle exterior parts. The present invention is not limited to these applications and may also be used in ships (motorboats, etc.), home appliances, audio products, construction materials, steel plate products, etc. [Examples]

[0068] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Each characteristic value is measured by the following method. Furthermore, unless otherwise specified, parts and % in the examples refer to parts by mass and mass%, respectively.

[0069] (A) Method for measuring intrinsic viscosity 0.2 g of polyester resin was dissolved in 50 ml of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 (mass ratio)) and measured using an Ostwald viscometer at 30°C. The unit is dl / g.

[0070] (B) Method for measuring the melting point (Tm) Measurements were taken using a DSC-60 differential scanning calorimeter (Shimadzu Corporation). Polyester resin was heated and melted at 300°C for 5 minutes, then rapidly cooled with liquid nitrogen. 10 mg of the rapidly cooled polyester resin was used as a sample, and the endothermic peak temperature (melting point) based on crystal melting that appeared when the temperature was increased at a rate of 20°C / min was measured. The melting points of layers A and B of the polyester film were measured in the same manner as above, using samples scraped from the respective surfaces of layers A and B of the polyester film. Here, the melting point peak was defined as an endothermic peak of 0.05 J / g or more associated with crystal melting, located at a temperature higher than the baseline shift corresponding to the glass transition point.

[0071] (C) Thickness of each layer of polyester film Polyester film was cut into strips 2 mm in the flow direction and 2 cm in the width direction, fixed in an embedding capsule, and then embedded in epoxy resin. The embedded sample was then cut perpendicular to the width direction using a microtome (Reichert-Jung Supercut) to obtain 50 μm thick thin film sections. Using a scanning electron microscope (Hitachi 4300SE / N), the sections were observed and photographed at an accelerating voltage of 20 kV, and the thickness of each layer was measured from the photographs. The average thickness of five points was then calculated.

[0072] (D) Surface orientation coefficient According to JIS K 7142-1996 Method A, the refractive index in the flow direction (Nx), the refractive index in the width direction (Ny), and the refractive index in the thickness direction (Nz) of the polyester film were measured using an Abbe refractometer with sodium D line as the light source, and the surface orientation coefficient ΔP was calculated using the formula in Equation 2 below. Equation 2: Planar orientation coefficient ΔP = (Nx + Ny) / 2 - Nz

[0073] (E) Thermal shrinkage rate Test specimens were prepared by cutting out five points each from the flow direction and width direction of a polyester film, with dimensions of 10 mm in width and 150 mm in length. Each test specimen was marked with gauge lines spaced 100 mm ± 2 mm apart, centered on the center of the specimen. The spacing of the gauge lines on the test specimens before heating was measured with an accuracy of 0.1 mm. The test specimens were suspended without load in a hot air dryer (ESPEC PHH-202) and heat-treated at 150°C for 15 minutes. After removing the test specimens from the constant temperature bath and cooling to room temperature, the length and width were measured at the same points as when they were first measured. The thermal shrinkage rate, i.e., the dimensional change rate, of each test specimen was calculated as a percentage of the initial dimensional change in both the flow direction and width direction. The dimensional change rate in each direction was the average of the measured values ​​in that direction. In other words, the thermal contraction rate in each direction was calculated using the following formula. Thermal shrinkage rate (%) = {(L0 - L) / L0} × 100 Here, L is the gauge length after heat treatment (i.e., the distance between a pair of gauge marks), and L0 is the gauge length before heat treatment. As mentioned above, the average values ​​of the five test specimens were substituted for L and L0.

[0074] (F) Elastic strain energy In accordance with JIS K 7127, test samples of polyester film were cut to a width of 15 mm and a length of 100 mm in both the flow direction and the width direction. Tensile tests were performed using a tensile testing machine (Shimadzu Corporation Autograph AG-I) under the following conditions: a chuck distance of 50 mm, a tensile speed of 1000 mm / min, and pulling until 20% elongation, followed by returning to a chuck distance of 50 mm at a speed of 2000 mm / min. The tensile tests were conducted in a constant temperature chamber at 100°C. From the obtained stress-strain curves, the stress at 20% elongation (F20 value) of the test sample, and the elastic strain energy Ua from the test start point (0) to the yield point, and the elastic strain energy Ub of the return strain from 20% elongation to a chuck distance of 50 mm were calculated using equations 3 and 4.

[0075] (Formula 3)

number

[0076] (Formula 4)

number

[0077] Here, as shown in Figure 1, a represents the strain (%) at the yield point, and P1 represents the stress (MPa) at the yield point. b represents the strain (%) at which the stress becomes 0 MPa after 20% elongation, i.e., the return strain (%). In other words, b represents the strain (%) at which the stress becomes 0 MPa when the chuck distance returns to 50 mm. P2 represents the stress (MPa) at 20% elongation. P represents stress. λ represents strain (%). Furthermore, the yield point was determined by finding the first stress at which the stress increase per 0.3% increase in strain was 0.010 MPa or less in the stress-strain curve. Specifically, the stress was first read from the stress-strain curve at each 0.3% increase in strain, starting from 1.0%. That is, the stress was calculated at strains of 1.0%, 1.3%, 1.6%, 1.9%, 2.2%, 2.5%, 2.8%, 3.1%, and so on. Then, the yield point was determined by finding the first stress at which the stress increase per 0.3% increase in strain was 0.010 MPa or less.

[0078] (G) Evaluation of the appearance of laminated film and metal plate (Lamination evaluation) A polyester film (layer A) and a zinc alloy plated steel plate with a thickness of 0.6 mm were heat-pressed together at 260°C, and the appearance was visually evaluated according to the following criteria. Result A: No wrinkles or bubbles can be clearly observed. Judgment C: At least one of the following can be clearly observed: wrinkles or bubbles.

[0079] (H) Peel strength between film and metal plate When heat-pressing the A-layer side of a polyester film with an aluminum metal plate with a thickness of 0.9 mm at 230°C, a heat-resistant paper was inserted to create a peel edge. The resulting film-coated metal laminate with a peel edge was cut to a size of 20 mm in width and 150 mm in length. Using a tensile testing machine, one chuck gripped the aluminum metal plate and the other chuck gripped the film peel edge, and a tensile test was performed three times in a 180° direction. The average of the maximum loads was defined as the peel strength. The distance between the chucks was 50 mm, and the tensile speed was 50 mm / min.

[0080] (I) Evaluation of adhesion after cold press forming A polyester film (layer A) was heat-pressed onto a 0.6 mm thick zinc alloy plated steel sheet. The resulting film-coated metal laminate was cut to a size of 180 mm in width and 180 mm in length, and then cold-press-formed. Using a die with a drawing ratio of 1.3, the periphery of the steel sheet was held with a load of 15 tons, and the center of the steel sheet was pressed at room temperature with a load of 100 tons to perform deep drawing. An X-shaped cut was made in the middle of the resulting metal molded product (i.e., the deep-drawn film-coated metal laminate). Specifically, an X-shaped cut was made using a utility knife, reaching not only the polyester film but also the steel sheet (specifically, the zinc alloy plated steel sheet). Then, it was treated in a retort at 120°C, 0.2 MPa, for 2 hours. The adhesive strength of the bonded portion to the film attached to this molded product was determined as follows. Judgment A: No peeling Assessment B: Partial peeling present (some whitening observed) Assessment C: Peeling present (overall whitening observed)

[0081] In the examples and comparative examples, the following resins were used as the resin constituting the B layer of the laminated film.

[0082] (Resin composition A) A mixture of resins B and C was used as resin composition A. Resin B: PET resin, IV = 0.75 dl / g, melting point 255°C, 97.0 parts by mass Resin C: PET resin containing 0.036% by mass of silica particles (average particle size 1.7 μm) per 100% by mass of resin, IV = 0.75 dl / g, melting point 255°C, 3.0 parts by mass

[0083] (Resin composition D) A mixture of the following resins E and F was used as resin composition D. Resin E: PET resin, IV = 0.62 dl / g, melting point 255°C, 90.0 parts by mass Resin F: PET resin containing 0.72% by mass of silica particles (average particle size 2.7 μm) per 100% by mass of resin, IV = 0.62 dl / g, melting point 255°C, 10.0 parts by mass

[0084] (Resin composition G) PET resin, IV = 0.69 dl / g, melting point 225°C, 100.0 parts by mass

[0085] (Resin composition H) A mixture of the following resins I and J was used as the resin composition H. Resin I: Copolymer polyester resin containing 89.2 mol% ethylene terephthalate units and 10.8 mol% ethylene isophthalate units, IV = 0.71 dl / g, melting point 225°C, 55.0 parts by mass Resin J: PBT resin, IV = 0.67 dl / g, melting point 225°C, 45.0 parts by mass

[0086] In the examples and comparative examples, the following resins were used as the resin constituting layer A of the laminated film. (Resin K) Copolymer polyester resin containing 89.2 mol% ethylene terephthalate units and 10.8 mol% ethylene isophthalate units, IV = 0.63 dl / g, melting point 225°C (Resin L) Copolymer polyester resin containing 86.0 mol% ethylene terephthalate units and 14.0 mol% ethylene isophthalate units, IV = 0.70 dl / g, melting point 217°C (Resin M) Copolymer polyester resin containing 80.0 mol% ethylene terephthalate units and 20.0 mol% ethylene isophthalate units, IV = 0.63 dl / g, melting point 198°C (Resin N) Copolymer polyester resin containing 92.1 mol% ethylene terephthalate units and 7.9 mol% ethylene isophthalate units, IV = 0.62 dl / g, melting point 233°C

[0087] [Example 1] Resin composition A for layer B and resin K for layer A were supplied to separate hoppers. Both layers A and B were melted at 280°C, then merged into two layers in a die, and extruded into a cooling drum to form an unstretched sheet. Subsequently, the unstretched sheet was stretched 3.2 times in the flow direction at 80°C, and then stretched 3.0 times in the width direction at 130°C. After heat setting at 215°C, a 5% relaxation process was performed in the width direction. In this way, a polyester film consisting of two layers, layer A and layer B, was produced with a thickness of 10 μm for layer A, a thickness of 40 μm for layer B, and a total thickness of 50 μm.

[0088] [Example 2] A polyester film consisting of two layers, layer A and layer B, was prepared using the same method as in Example 1, except that it was stretched 3.9 times in the flow direction and 3.5 times in the width direction.

[0089] [Example 3] A polyester film consisting of two layers, A and B, was prepared in the same manner as in Example 1, except that resin composition D was used as the resin for layer B, and the film was stretched 3.5 times in the flow direction and 3.3 times in the width direction.

[0090] [Comparative Example 1] A polyester film consisting of two layers, A and B, was prepared using the same method as in Example 1, except that resin L was used as the resin for layer A, and it was stretched 3.0 times in the flow direction and 3.5 times in the width direction.

[0091] [Comparative Example 2] A polyester film consisting of two layers, A and B, was prepared in the same manner as in Example 1, except that resin composition D was used as the resin for layer B, and the film was stretched 3.5 times in the flow direction and 3.3 times in the width direction, with a heat-fixing temperature of 235°C.

[0092] [Comparative Example 3] A polyester film consisting of two layers, A and B, was prepared in the same manner as in Example 1, except that resin composition D was used as the resin for layer B and resin L was used as the resin for layer A, and the film was stretched 3.8 times in the flow direction and 3.3 times in the width direction.

[0093] [Comparative Example 4] A polyester film consisting of two layers, A and B, was prepared in the same manner as in Example 1, except that resin composition D was used as the resin for layer B and resin M was used as the resin for layer A, and the film was stretched 3.5 times in the flow direction and 3.3 times in the width direction.

[0094] [Comparative Example 5] A polyester film consisting of two layers, A and B, was prepared using the same method as in Example 1, except that resin N was used as the resin for layer A, and the film was stretched 3.0 times in the flow direction and 3.5 times in the width direction.

[0095] [Comparative Example 6] A polyester film consisting of single layers of the same raw materials for both layers A and B was prepared in the same manner as in Example 1, except that resin composition H was used as the resin for layers B and A, and the film was stretched 3.0 times in the flow direction and 3.0 times in the width direction, with a heat-fixing temperature of 205°C.

[0096] [Comparative Example 7] A polyester film consisting of single layers of the same raw materials for both layers A and B was prepared in the same manner as in Example 1, except that resin composition G was used as the resin for layers B and A, and the film was stretched 3.1 times in the flow direction and 3.5 times in the width direction, with a heat-fixing temperature of 180°C.

[0097] [Comparative Example 8] A polyester film was prepared using the method described in Example 7 of Patent Document 2 (i.e., Japanese Patent Application Publication No. 2020-192787). The resin used for layer A and the manufacturing conditions such as the stretching ratio are as shown in Table 1C below.

[0098] Table 1 shows the evaluation results of the polyester films prepared in Examples 1-3 and Comparative Examples 1-8. For the adhesion evaluation after cold press forming, the heat-press bonding of the film to the zinc alloy plated steel sheet was performed by heating the metal sheet to the temperatures shown in Table 1.

[0099] [Table 1A]

[0100] [Table 1B]

[0101] [Table 1C]

[0102] As shown in Table 1, the polyester films prepared in the examples showed good lamination to metal plates and good adhesion to metal molded products. On the other hand, the polyester films prepared in the comparative examples showed inferior lamination to metal plates and / or adhesion to metal molded products, making them unsuitable as alternative films for coatings. In particular, the residual internal stress index rates in Comparative Examples 1-4, 6, and 7 were considerably higher than those in Examples 1-3, and the adhesion evaluation results in these comparative examples were inferior to those in Examples 1-3. Meanwhile, although the residual internal stress index rate in Comparative Example 5 was similar to that of Example 2, the polyester film did not adhere firmly to the metal plate when heat-pressed at 260°C, resulting in poor peel strength and inferior adhesion evaluation results. It should be noted that preliminary experiments have confirmed that wrinkles and bubbles occur when the polyester film of Comparative Example 5 is heat-pressed to the metal plate at 280°C to ensure firm adhesion. Although the residual internal stress index in Comparative Example 8 was similar to that of Example 1, thermal shrinkage was significant (i.e., the thermal shrinkage rate was high), resulting in wrinkles and bubbles during 260°C heat bonding. Furthermore, Comparative Example 8 exhibited poor peel strength, leading to a lower evaluation of its adhesive properties.

Claims

1. A laminated film comprising a B layer and an A layer for bonding to a metal plate, The aforementioned layer A contains 60% by mass or more of the first crystalline polyester in 100% by mass of the layer A, The aforementioned B layer contains 60% by mass or more of the second crystalline polyester in 100% by mass of the B layer. The surface orientation coefficient of the aforementioned B layer is 0.165 or more and 0.180 or less. The melting point of layer B is higher than the melting point of layer A, and the difference between the melting point of layer B and the melting point of layer A is 25°C or more and 35°C or less. When the laminated film was subjected to a tensile test, the residual internal stress index was 25% or less in both the flow direction and the width direction of the laminated film. The aforementioned remaining index rate is expressed by |1 - (Ub / Ua)| × 100, The tensile test described above was performed by gripping a 15 mm wide test specimen with a pair of chucks at a distance of 50 mm between the chucks, widening the distance between the chucks at a tensile speed of 1000 mm / min at 100°C until a 20% strain occurred, and then returning the distance between the chucks to 50 mm at a speed of 2000 mm / min at 100°C. The aforementioned Ua is a value obtained by integrating the stress-strain curve obtained from the tensile test from 0% strain to yield strain. The aforementioned Ub is a value obtained by integrating the stress-strain curve from 20% strain to the strain at which the stress is 0 MPa. Paint substitute film.

2. The coating substitute film according to claim 1, wherein the laminated film has a 20% strain tensile stress of 60 MPa or more and 110 MPa or less in both the flow direction and the width direction of the tensile test.

3. The paint substitute film according to claim 1, wherein the surface orientation coefficient of layer B is greater than the surface orientation coefficient of layer A, and the difference between the surface orientation coefficient of layer B and the surface orientation coefficient of layer A is 0.03 or more.

4. The coating substitute film according to claim 1, wherein when the laminated film is heat-treated at 150°C for 15 minutes, the sum of the thermal shrinkage rate in the flow direction and the thermal shrinkage rate in the width direction is 1.0% or more and 5.0% or less.

5. The coating substitute film according to claim 1, wherein the coating substitute film is laminated to the metal substrate at 230°C such that the A layer is in contact with the metal substrate, and the peel strength when the coating substitute film is peeled from the metal substrate at a tensile speed of 50 mm / min and 180° is 10 N / 20 mm or more.

6. An easy-adhesion layer provided on the surface of the B layer of the laminated film, The functional layer, and further including, The A layer, the B layer, the easy-adhesion layer, and the functional layer are arranged in this order. The functional layer includes at least one of a coloring layer and a surface protection layer. The paint substitute film according to claim 1.

7. The easy-adhesion layer comprises a resin having at least one functional group selected from the group consisting of epoxy groups, oxazoline groups, silanol groups, and isocyanate groups. The paint substitute film according to claim 6.

8. The functional layer includes the coloring layer and the surface protective layer, The A layer, the B layer, the easy-adhesion layer, the coloring layer, and the surface protection layer are arranged in this order. The paint substitute film according to claim 6.

9. The functional layer includes the colored layer, The colored layer contains 0.5% by mass or more and less than 40% by mass of a coloring agent based on 100% by mass of the resin composition constituting the colored layer. The paint substitute film according to claim 6.

10. The functional layer includes the surface protective layer, The surface protective layer comprises at least one of a thermosetting resin and a photocurable resin. The paint substitute film according to claim 6.

11. The coating substitute film according to claim 6, wherein the thickness of the easy-adhesion layer is 10 nm to 200 nm.

12. A metal plate and The metal plate is laminated with a coating substitute film according to any one of claims 1 to 11, Laminated structure.

13. A metal member formed by press-molding the laminate according to claim 12.

14. A vehicle exterior part comprising the laminate described in claim 12.

15. A step of heating a metal plate to a temperature above the melting point of layer A and below the melting point of layer B in the coating substitute film according to any one of claims 1 to 11, The process includes pressing the metal plate, heated to the temperature, against the coating substitute film so that the metal plate and the A layer are in contact, A method for producing laminates.

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