Laminated sheet and its manufacturing method

Abstract

To provide a laminated sheet with good ink adhesion and laser machinability.SOLUTION: The laminated sheet according to the present disclosure has a main layer containing a methacrylic polymer and a surface layer placed on at least one surface side of the main layer and containing a styrene copolymer, satisfying the following equations and is for inkjet printing and laser cutting: 0.60≤Cst1≤0.95, 1.67×10-2≤z1 / Z≤1.67×10-1, 0≤Cst2≤0.015, 0.02≤Cst3≤0.10. Cst1 is the mass fraction of styrenic monomer units in the surface layer. Cst2 is the mass fraction of styrenic monomer units in the main layer. Cst3 is the mass fraction of styrenic monomer units in the whole laminated sheet. z1 is the thickness of the surface layer. Z is the thickness of the whole laminated sheet.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a laminated sheet and a method for manufacturing the same.

Background Art

[0002] Inkjet (IJ) printing, which can process digital images by computer and record them on a printing medium, has increased the types of printable media and expanded its range of use. For example, it has come to be widely used in various fields such as printing, advertising, sign displays, events, amusement, architecture, and interior. As a printing medium other than paper, a resin sheet can be mentioned (Patent Document 1). Unlike paper, the resin sheet is excellent in water resistance and durability and can also be made transparent.

[0003] The resin sheet for IJ printing can be cut using a laser, an NC router, etc. as necessary after IJ printing and formed into a desired shape. The molded product thus obtained can be preferably used for miscellaneous goods such as key holders and furniture.

Prior Art Documents

Patent Documents

[0006] Generally, in laser cutting, depending on the material of the workpiece, when the workpiece melts and evaporates due to laser light irradiation, abnormal odor or fumes may be generated by the evaporation gas. Further, after the laser cutting is completed, when the melted portion cools and solidifies again, the evaporation gas may adhere to the cutting surface, resulting in poor appearance of the cutting surface. The methacrylic resin is unlikely to cause the above problems due to evaporation gas (abnormal odor or fumes due to evaporation gas, and poor appearance of the cutting surface due to adhesion of evaporation gas), and tends to have good laser cutting properties. On the other hand, a styrene copolymer having an aromatic ring structure in the molecule is likely to cause the above problems due to evaporation gas (abnormal odor or fumes due to evaporation gas, and poor appearance of the cutting surface due to adhesion of evaporation gas), and tends to have poor laser cutting properties.

[0007] The applicant of the present application discloses in Patent Document 2 a laminated sheet having good ink adhesion and laser cutting properties, which has a first resin layer containing a styrene copolymer and constituting the surface layer and a second resin layer containing a methacrylic polymer, and optimizes the relationship between the mass fraction of the styrene monomer unit in the first resin layer, the thickness of the first resin layer, the thickness of the second resin layer, and the thickness of the entire sheet (Claim 1). The inventors of the present invention improved the technology described in Patent Document 2 and invented a laminated sheet with improved ink adhesion while obtaining good laser cutting performance.

[0008] The present disclosure has been made in view of the above problems, and an object thereof is to provide a laminated sheet having good ink adhesion and laser cutting performance.

Means for Solving the Problems

[0009] The present disclosure provides the following laminated sheets [1] to [8] and a method for manufacturing the same. [1] A laminated sheet having a main layer containing a methacrylic polymer and a surface layer containing a styrene copolymer on one surface side of the main layer, satisfying the following formulas (11) to (14), A laminated sheet for inkjet printing and laser cutting. (11) 0.60 ≦ C , , , st3 , , st1 , , st2 , , ―2 , , , , -1 , st2 , , st3 , , ―1 , , st1 ,

[0010] , , , ≦ 0.95 (12) 1.67 × 10 ―2 ≦ z1 / Z ≦ 1.67 × 10 ―1 (13) 0 ≦ C st2 ≦ 0.015 (14) 0.02 ≦ C st3 ≦ 0.10​​​​​​​​​​​​​​​​​​​​​​​A laminated sheet of [1] wherein, under the shear rate conditions, the absolute value of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the surface layer is 0 to 2000 Pa·s.

[0011] [3] A laminated sheet having a main layer containing a methacrylic polymer, a first surface layer containing a styrene copolymer located on one surface side of the main layer, and a second surface layer containing a styrene copolymer located on the other surface side of the main layer, Satisfy equations (21) to (24) below, Laminated sheets for inkjet printing and laser cutting. (21) 0.60 ≤ C st1 ≤0.95 (22) 1.67 × 10 ―2 ≤ z1 / Z ≤ 1.67 × 10 ―1 (23) 0 ≤ C st2 ≤0.015 (24) 0.02 ≤ C st3 ≤0.10 Each abbreviation in the above formula represents the following parameter: C st1 This is the mass fraction of styrene monomer units in the first or second surface layer. C st2 This represents the mass fraction of styrene monomer units in the main layer. C st3 This represents the mass fraction of styrene monomer units in the entire laminated sheet. z1 is the thickness of the first or second surface layer. If the thickness of the first surface layer and the thickness of the second surface layer are not the same, then z1 and C st1 The values ​​of z1 and C are those of the thicker of the two surface layers, the first and second surface layers. st1 The values ​​of are adopted. If the thickness of the first surface layer and the thickness of the second surface layer are the same, and the mass fraction of styrene monomer units in the first surface layer and the mass fraction of styrene monomer units in the second surface layer are different, then z1 and C st1 As values, z1 and C are those of the surface with the larger mass fraction of styrene monomer units among the first and second surface layers. st1The value of will be used. Z is the total thickness of the laminated sheet.

[0012] [4] At a temperature of 245°C and 24.3s -1 A laminated sheet of [3], wherein, under the shear rate conditions, the absolute value of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the first surface layer, and the absolute value of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the second surface layer, are between 0 and 2000 Pa·s.

[0013] [5] A laminated sheet of [1] or [3], which is a co-extruded sheet. [6] Laminated sheets of [1] or [3] for use as keychains.

[0014] [7] The process involves co-extruding a thermoplastic resin laminate having the main layer and the surface layer from a T-die in a molten state, The temperature of the T-die is 190-280°C. A method for manufacturing a laminated sheet of [1], wherein the absolute value of the difference between the melt viscosity of the main layer's constituent resin and the surface layer's constituent resin at the temperature conditions of the T-die is 0 to 2600 Pa·s.

[0015] [8] The process includes co-extruding a thermoplastic resin laminate having the first surface layer, the main layer, and the second surface layer from a T-die in a molten state, The temperature of the T-die is 190-280°C. A method for manufacturing a laminated sheet of [3], wherein, under the temperature conditions of the T-die, the absolute value of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the first surface layer, and the absolute value of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the second surface layer, are between 0 and 2600 Pa·s. [Effects of the Invention]

[0016] According to this disclosure, it is possible to provide a laminated sheet with good ink adhesion and laser cutting properties. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic cross-sectional view of a laminated sheet according to the first embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view of a laminated sheet according to a second embodiment of the present invention. [Figure 3] This is a schematic diagram of a manufacturing apparatus for laminated sheets according to one embodiment of the present invention. [Modes for carrying out the invention]

[0018] [Laminated Sheet] The first laminated sheet of this disclosure is a laminated sheet having a main layer containing a methacrylic polymer (B) and a surface layer located on one surface side of the main layer and containing a styrene copolymer (A), satisfying the following formulas (11) to (14), and for use in inkjet printing and laser cutting. (11) 0.60 ≤ C st1 ≤0.95 (12) 1.67 × 10 ―2 ≤ z1 / Z ≤ 1.67 × 10 ―1 (13) 0 ≤ C st2 ≤0.015 (14) 0.02 ≤ C st3 ≤0.10 Each abbreviation in the above formula represents the following parameter: C st1 This represents the mass fraction of styrene monomer units in the surface layer. C st2 This represents the mass fraction of styrene monomer units in the main layer. C st3 This represents the mass fraction of styrene monomer units in the entire laminated sheet. z1 is the thickness of the surface layer. Z is the total thickness of the laminated sheet.

[0019] The first laminated sheet structure of the present disclosure includes a two-layer structure having a surface layer on one side of the main layer of the first embodiment shown in Figure 1. In the figure, reference numeral 16X denotes the laminated sheet, reference numeral 21 denotes the surface layer, and reference numeral 31 denotes the main layer. The thickness of each layer is designed to satisfy equations (11) to (14). The first laminated sheet of this disclosure may include any other layers besides the surface layer and the main layer, as necessary. However, the surface 21S of the surface layer 21 opposite to the main layer is an exposed surface with no other layers on it. This exposed surface may be a printed surface on which printing is applied.

[0020] The second laminated sheet of this disclosure is a laminated sheet having a main layer containing a methacrylic polymer (B), a first surface layer located on one surface side of the main layer and containing a styrene copolymer (A), and a second surface layer located on the other surface side of the main layer and containing a styrene copolymer (A), satisfying the following formulas (21) to (24), and for use in inkjet printing and laser cutting. (21) 0.60 ≤ C st1 ≤0.95 (22) 1.67 × 10 ―2 ≤ z1 / Z ≤ 1.67 × 10 ―1 (23) 0 ≤ C st2 ≤0.015 (24) 0.02 ≤ C st3 ≤0.10 Each abbreviation in the above formula represents the following parameter: C st1 This represents the mass fraction of styrene monomer units in the surface layer. C st2 This represents the mass fraction of styrene monomer units in the main layer. C st3 This represents the mass fraction of styrene monomer units in the entire laminated sheet. z1 is the thickness of the first or second surface layer. The thickness of the first surface layer and the thickness of the second surface layer may be the same or different. The mass fraction of styrene monomer units in the first surface layer and the mass fraction of styrene monomer units in the second surface layer may be the same or different. If the thickness of the first surface layer and the thickness of the second surface layer are not the same, then z1 and C st1 The values ​​of z1 and C are those of the thicker of the two surface layers, the first and second surface layers. st1 The values ​​of are adopted. If the thickness of the first surface layer and the thickness of the second surface layer are the same, and the mass fraction of styrene monomer units in the first surface layer and the mass fraction of styrene monomer units in the second surface layer are different, then z1 and C st1 As values, z1 and C are those of the surface with the larger mass fraction of styrene monomer units among the first and second surface layers. st1 The value of will be used. Z is the total thickness of the laminated sheet.

[0021] In the second laminated sheet of this disclosure, "first surface layer or second surface layer" may be abbreviated as simply "surface layer". In the description of the second laminated sheet of this disclosure, "surface layer C st1 " is the surface C used in equation (21) st1 Therefore, "surface z1" is the surface z1 adopted in equation (22).

[0022] A second laminated sheet structure of the present disclosure is a three-layer structure having surface layers on both sides of the main layer of the second embodiment shown in Figure 2. In the figure, reference numeral 16Y denotes the laminated sheet, reference numeral 22 denotes the first surface layer, reference numeral 23 denotes the second surface layer, and reference numeral 31 denotes the main layer. The thickness of each layer is designed to satisfy equations (21) to (24). The second laminated sheet of this disclosure may include any other layers besides the surface layer and the main layer, as needed. However, the surface 22S of the first surface layer 22 opposite to the main layer, and / or the surface 23S of the second surface layer 23 opposite to the main layer, have no other layers on them and are exposed surfaces. These exposed surfaces may be printed surfaces on which printing is applied.

[0023] In equations (12) and (22) above, the units of z1 and Z are the same and cancel each other out. The units of z1 and Z can be, for example, mm or μm. In this specification, “mass fraction of styrene monomer units” means the mass ratio from a minimum value of 0 to a maximum value of 1.

[0024] The first and second laminated sheets of this disclosure can preferably be used as resin sheets for inkjet (IJ) printing. Examples of IJ printing methods include electrostatic attraction, methods that apply mechanical vibration or displacement to the ink using piezoelectric elements such as piezo elements, methods that heat the ink to cause foaming and utilize the resulting pressure, and methods that use ultraviolet (UV) curable ink. The first and second laminated sheets of this disclosure can be ink-jet printed on the surface layer containing a styrene copolymer (A). The first and second laminated sheets of this disclosure can also be molded into a desired shape by cutting using a laser and NC router, etc., as needed after ink-jet printing. The molded products obtained in this way can be preferably used for miscellaneous goods such as keychains and fixtures. In such applications, UV-curable inks are preferably used as ink-jet printing inks.

[0025] Generally, styrene copolymers (A) having an aromatic ring structure within the molecule exhibit good penetration and adhesion of inkjet printing inks such as UV-curable inks. However, styrene copolymers (A) having an aromatic ring structure do not have very good laser machinability, and when the resin melts and evaporates due to laser irradiation, an unpleasant odor or smoke may be produced by the evaporated gas. Furthermore, after laser cutting is completed, when the molten portion cools and solidifies again, the evaporated gas may adhere to the cut surface, resulting in a poor appearance of the cut surface. Generally, methacrylic resins reduce the problems associated with evaporation gases (unpleasant odor or smoke from evaporation gases, and poor surface appearance of the cut surface due to the adhesion of evaporation gases), and have good laser cutting properties. However, they tend to have poor penetration and adhesion of inkjet printing inks, such as UV-curable inks.

[0026] The first and second laminated sheets of this disclosure have a surface layer containing a styrene copolymer (A) having an aromatic ring structure within the molecule, and therefore have good penetration and adhesion of inkjet printing inks such as UV-curable inks. The first and second laminated sheets of this disclosure are C st1 This satisfies the range of 0.60 to 0.95. In this disclosure, the mass fraction of styrene monomer units in the surface layer containing the styrene copolymer (A) is specified to be higher than in Patent Document 2, so the adhesion of the IJ printing ink can be improved compared to Patent Document 2. C st1 If the above upper limit is exceeded, the interlayer adhesion between the surface layer and the main layer will be insufficient, and there is a risk of delamination. st1 It is more preferably 0.70 to 0.85.

[0027] In this disclosure, the mass fraction of styrene monomer units in the surface layer containing the styrene copolymer (A) is specified to be high, as in Patent Document 2, but C st3 The ratio is limited to within the range of 0.02 to 0.10. By limiting the proportion of styrene monomer units in the entire laminated sheet, the above-mentioned problems caused by evaporated gases (unpleasant odor or smoke due to evaporated gases, and poor appearance of the cut surface due to the adhesion of evaporated gases) can be reduced, and good laser cutting performance can be achieved. C st3 If the value is above the lower limit mentioned above, the adhesion of the ink for IJ printing can be effectively improved. st3 However, if the above upper limit is exceeded, the proportion of styrene monomer units in the laminated sheet increases, and there is a risk that the above problems (unusual odor or smoke due to evaporated gas, and poor appearance of the cut surface due to adhesion of evaporated gas) may occur during laser cutting. st3 The ratio is more preferably 0.023 to 0.095, and particularly preferably 0.026 to 0.092.

[0028] The first and second laminated sheets of this disclosure have a ratio (z1 / Z) of the surface layer thickness (z1) to the total thickness (Z) of the laminated sheet of 1.67 × 10⁻⁶ ―2 ~1.67×10―1 If z1 / Z is below the lower limit, the residence time of the surface material containing the styrene copolymer (A) in the extruder will be longer during co-extrusion molding, which may cause foaming in the surface material containing the styrene copolymer (A) and worsen the appearance of the laminated sheet. If z1 / Z exceeds the upper limit, the proportion of styrene monomer units in the laminated sheet will be higher, which may cause the above problems (unpleasant odor or smoke due to evaporated gas, and poor appearance of the cut surface due to adhesion of evaporated gas) during laser cutting. In addition, the proportion of styrene monomer units in the laminated sheet will be higher, which may cause a large difference in melt viscosity between resins and lead to delamination.

[0029] In the first and second laminated sheets of this disclosure, the overall thickness (Z) of the laminated sheet is preferably 1 to 5 mm, as this provides good IJ printability and laser cutting properties. For example, if the overall thickness (Z) of the laminated sheet is 3 mm, the thickness (z1) of the surface layer containing the styrene copolymer (A) is preferably 50 to 200 μm, and the thickness (z2) of the main layer is preferably 2.4 to 2.9 mm.

[0030] In the first and second laminated sheets of this disclosure, the main layer may contain a styrene copolymer (A). However, the mass fraction (C) of styrene monomer units in the main layer may be... st2 The value of ) shall be 0 to 0.015. In other words, the first and second laminated sheets of this disclosure may contain up to 1.5% by mass of styrene monomer units in the main layer. The styrene copolymer (A) in the main layer may be the same as or different from the styrene copolymer (A) in the surface layer. When the main layer contains styrene monomer units, the amount of warping change of the laminated sheet after being left in a high-humidity environment can be effectively reduced. The mass fraction (C) of styrene monomer units in the main layer st2 If the above upper limit is exceeded, the compatibility between the methacrylic resin and the styrene resin in the main layer material will decrease, which may cause the main layer to become cloudy and reduce the transparency of the laminated sheet. st2 The lower limit is more preferably 0.012.

[0031] (surface) The surface layer contains one or more styrene copolymers (A). The styrene copolymer (A) is not particularly limited as long as it is a copolymer of multiple monomers including styrene monomers such as styrene, α-methylstyrene, o-, m-, or p-methylstyrene, and known copolymers can be used. Specifically, examples include methyl methacrylate-styrene copolymer (MS resin), styrene-maleic anhydride copolymer (SMA resin), acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), methyl methacrylate-butadiene-styrene copolymer (MBS resin), and high-impact polystyrene (HIPS resin) obtained by graft copolymerization of butadiene, with MS resin being preferred.

[0032] The styrene-based copolymer (A) may also be a styrene-based block copolymer. Examples of styrene-based block copolymers include XYX-type triblock copolymers and XY-type diblock copolymers, which consist of a styrene polymer block (X) and a butadiene polymer block or isoprene polymer block (Y); and hydrogenated styrene-based block copolymers obtained by hydrogenating the unsaturated bonds in the block copolymer. The surface layer may, if necessary, contain a styrene homopolymer in combination with a styrene copolymer (A). The surface layer may contain other optional components, such as methacrylic polymers (B), as needed. In the three-layer laminated sheet of the embodiment shown in Figure 2, the compositions of the two surface layers may be the same or different.

[0033] The glass transition temperature (Tg) of the surface layer's constituent resin is not particularly limited, but is preferably 80 to 160°C, more preferably 100 to 110°C.

[0034] (main layer) The main layer contains one or more methacrylic polymers (B). The methacrylic polymer (B) may be a methacrylic polymer that does not have an aromatic ring structure within the molecule, or a methacrylic polymer that has an aromatic ring structure within the molecule. Preferably, one or more methacrylic polymers (B) include methacrylic polymers that do not have an aromatic ring structure within the molecule.

[0035] Examples of methacrylic polymers (B) include homopolymers of methyl methacrylate (MMA) and copolymers of MMA with one or more other monomers. Examples of monomers other than MMA include acrylic acid esters such as methyl acrylate and ethyl acrylate; methacrylic acid esters other than MMA; unsaturated carboxylic acids; olefins; and conjugated dienes. As methacrylic polymer (B), a methyl methacrylate (co)polymer obtained by (co)polymerizing 100 to 90% by mass of MMA and optionally 0 to 10% by mass of an alkyl acrylate having 4 to 5 carbon atoms is preferred. The stereoregularity of methacrylic polymer (B) is usually atactic, but other stereoregularities such as syndiotactic are also acceptable.

[0036] The main layer may contain other optional components as needed. The main layer may include, for example, a styrene copolymer (A). The styrene copolymer (A) in the main layer may be the same as or different from the styrene copolymer (A) in the surface layer. As described above, the first and second laminated sheets of this disclosure may contain up to 1.5% by mass of styrene monomer units in the main layer.

[0037] As described above, when the main layer contains styrene monomer units, the amount of warping change of the laminated sheet after being left in a high-humidity environment can be effectively reduced. Furthermore, in the general manufacturing of laminated sheets by co-extrusion molding, there are defective products that are deemed not to meet product specifications after inspection for defects and foreign matter, as well as scraps generated by cutting off both ends of the sheet. In recent years, efforts toward a sustainable society have been progressing, and it is preferable to reuse (material recycling or chemical recycling) the above-mentioned defective products and scraps rather than discarding them. The main layer may contain recycled styrene copolymer obtained from the defective products and / or scraps mentioned above. Even in this case, by limiting the content of styrene monomer units in the main layer to 1.5% by mass or less, the compatibility between the methacrylic resin and the styrene resin is improved, and the laminated sheet can maintain sufficient transparency. It is preferable from the viewpoint of reusing defective products and scraps (material recycling or chemical recycling) that the main layer can contain styrene copolymer (A) while maintaining the transparency of the laminated sheet.

[0038] The glass transition temperature (Tg) of the main layer's constituent resin is not particularly limited, but is preferably 100 to 140°C, more preferably 105 to 135°C, and most preferably 105 to 125°C.

[0039] [Method for manufacturing laminated sheets] The first and second laminated sheets of this disclosure can be manufactured by known sheet molding methods, and from the viewpoint of production efficiency and interlayer adhesion, extrusion molding is preferred. In the case of extrusion molding, the surface material containing a styrene copolymer (A) and the main layer material containing a methacrylic polymer (B), which have been melt-kneaded using different extruders, may be extruded into sheets from different extrusion dies (such as T-dies) and then laminated, or the surface material containing a styrene copolymer (A) and the main layer material containing a methacrylic polymer (B), which have been melt-kneaded using different extruders, may be co-extruded from a common extrusion die. Examples of co-extrusion die systems include multi-manifold die systems and field block systems.

[0040] The first and second laminated sheets of this disclosure are preferably co-extruded sheets. Examples of co-extrusion die types include multi-manifold die type and field block type. In the feed block method, a molten surface layer material containing a styrene copolymer (A) and a molten main layer material containing a methacrylic polymer (B) are laminated within the feed block, then guided to a T-die or the like to form a sheet and co-extruded. In the multi-manifold die method, a molten surface layer material containing a styrene copolymer (A) and a molten main layer material containing a methacrylic polymer (B) are guided to a T-die or the like to form a sheet, then laminated and co-extruded. In either method, the molten thermoplastic resin laminate extruded from the T-die or the like is cooled by passing through the gap between at least one pair of cooling pressure rolls, and then taken up by a pair of take-up rolls. The above processes of co-extrusion, cooling, and take-up are carried out continuously. In this specification, materials in a heated and molten state are mainly referred to as "thermoplastic resin laminates," and solidified materials are referred to as "laminated sheets," but there is no clear boundary between the two.

[0041] Figure 3 shows a schematic diagram of a manufacturing apparatus, as one embodiment, including a T-die 11, first to third cooling rolls 12 to 14, and a pair of take-up rolls 15. The thermoplastic resin laminate co-extruded from the T-die 11 is cooled using the first to third cooling rolls 12 to 14, and the resulting laminated sheet 16 is taken up by the pair of take-up rolls 15. The configuration of the manufacturing apparatus can be modified as appropriate.

[0042] In the first and second laminated sheets of this disclosure, the ratio of the surface layer thickness (z1) to the total thickness (Z) of the laminated sheet (z1 / Z) is 1.67 × 10⁻⁶. ―1 The following configuration is used, where the surface layer is designed to be considerably thinner than the main layer. In this case, a multi-manifold die system is preferred. In the co-extrusion molding of the first and second laminated sheets of this disclosure (preferably by a multi-manifold die), the T-die temperature (Td) is preferably 190 to 280°C. If Td is less than 190°C, the melt viscosity of the styrene copolymer (A) and the methacrylic polymer (B) may become too high, making it difficult to extrude these resins properly. If Td is greater than 280°C, the styrene copolymer (A) may decompose due to the high temperature. Td is more preferably 210 to 270°C, and particularly preferably 230 to 260°C or lower. The lip thickness of the T-die is designed according to the desired overall thickness (Z) of the laminated sheet (preferably 1 to 5 mm).

[0043] In the first laminated sheet of this disclosure, at a temperature of 245°C and 24.3s -1 It is preferable that the absolute value (Δη) of the difference between the melt viscosity of the main layer's constituent resin and the melt viscosity of the surface layer's constituent resin, under the given shear rate conditions, is between 0 and 2000 Pa·s. The first method for manufacturing a laminated sheet according to this disclosure may include a step of co-extruding a thermoplastic resin laminate having a main layer and a surface layer from a T-die in a molten state. In this step, it is preferable that the temperature of the T-die is 190 to 280°C, and the absolute value (Δη) of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the surface layer is 0 to 2600 Pa·s under conditions of T-die temperature and shear rate corresponding to the thickness of each layer.

[0044] In the second laminated sheet of this disclosure, at a temperature of 245°C and 24.3s -1 It is preferable that, under the given shear rate conditions, both the absolute value (Δη) of the difference between the melt viscosity of the main layer's constituent resin and the melt viscosity of the first surface layer's constituent resin, and the absolute value (Δη) of the difference between the melt viscosity of the main layer's constituent resin and the melt viscosity of the second surface layer's constituent resin, are between 0 and 2000 Pa·s. The second method for manufacturing a laminated sheet according to the present disclosure may include a step of co-extruding a thermoplastic resin laminate having a first surface layer, a main layer, and a second surface layer from a T-die in a molten state. In this step, the temperature of the T-die is preferably 190 to 280°C, and under conditions of shear rate corresponding to the temperature of the T-die and the thickness of each layer, the absolute value (Δη) of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the first surface layer, and the absolute value (Δη) of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the second surface layer are both preferably 0 to 2600 Pa·s.

[0045] In addition, in the first and second laminated sheets of this disclosure, if the main layer contains two or more types of resins, the "melt viscosity of the constituent resins of the main layer" is the melt viscosity of the mixture of the two or more resins constituting the main layer. The same applies to the surface layer.

[0046] In the co-extrusion molding process, if the difference (Δη) between the melt viscosity of the surface layer's constituent resin and the main layer's constituent resin at the time of extrusion from the T-die is large, the interlayer adhesion between the main layer and the surface layer becomes insufficient, potentially leading to the formation of streaks (also called delamination streaks) between the layers or delamination. If the T-die temperature is 190-280°C and Δη is 2600 Pa·s or less under conditions of T-die temperature and shear rate corresponding to the thickness of each layer, the interlayer adhesion between the main layer and the surface layer becomes good, effectively suppressing the formation of streaks and delamination between layers.

[0047] The take-up speed (V) of the laminated sheet by the pair of take-up rolls is not particularly limited, but is preferably 0.5 to 2.0 m / min.

[0048] [Printed materials, molded products] The first and second laminated sheets of this disclosure can preferably be used as resin sheets for inkjet printing. Printed materials can be provided by applying inkjet printing to the surface layer containing the styrene copolymer (A) contained in the first and second laminated sheets of this disclosure. The first and second laminated sheets of this disclosure can also be molded into a desired shape by cutting using a laser and NC router or the like, as needed, after inkjet printing. The first and second laminated sheets of this disclosure have good laser machinability, enabling fine cutting. For example, molded products having curved cut sections with a radius of 0.5 to 2 mm can be manufactured with high shape accuracy. Since the first and second laminated sheets of this disclosure have good laser machinability, they can be cut at high speed and with good productivity using a high-power laser processing machine. For example, molded products can be manufactured by cutting the first and second laminated sheets of this disclosure at a speed of 350 cm / min or more using a laser processing machine with an output of 100 W or more.

[0049] [Application] The first and second laminated sheets and molded articles of this disclosure can be used in a variety of fields, including printing, advertising, signage and displays, events, amusement, architecture, and interiors. The first and second laminated sheets and molded articles of this disclosure can preferably be used for miscellaneous goods such as keychains and fixtures.

[0050] As described above, this disclosure makes it possible to provide a laminated sheet with good ink adhesion and laser cutting properties. [Examples]

[0051] Examples and comparative examples of the present invention will be described below. [Evaluation items and evaluation methods] (exterior) Appearance evaluation was performed on laminated or single-layer resin sheets that were extruded. Rectangular test specimens with a long side of 297 mm and a short side of 130 mm were cut from the resin sheets. The long side was parallel to the extrusion direction, and the short side was perpendicular to the extrusion direction (width direction). The presence or absence of streaks and foam was checked by visual inspection. The evaluation criteria are as follows. <Presence or absence of tendons> ◎ (Excellent): No visible veins or streaks. ○ (Good): The occurrence of streaks was minimal and within acceptable limits. × (Defective): Clear lines were visible. <Presence or absence of effervescence> ◎ (Excellent): No foaming was observed at all. ○ (Good): Some foaming was observed in certain areas, but it was within acceptable limits. × (Defective): Foaming was observed in more than half of the area.

[0052] (Ink adhesion) Ink adhesion was evaluated on laminated or single-layer resin sheets with IJ printing. A 10mm square evaluation area was cross-cut into 100 squares (10x10 grids) at 1mm intervals in both the vertical and horizontal directions within the cured white and black UV-curable ink layers. Cellophane tape was applied to the entire evaluation area, and then rubbed with an eraser to ensure sufficient adhesion to the printed surface. The cellophane tape was then peeled off at a 90° angle. The number of squares from which the ink had peeled off the resin sheet was determined visually. This test was performed three times. The evaluation criteria are as follows: ◎(Excellent): No ink peeling was observed in any of the squares in any of the tests. ○ (Good): In one or more tests, ink peeling was observed in 1 to less than 10 squares. △ (Acceptable): In one or more tests, ink peeling was observed in 10 to less than 50 squares. × (Defective): In one or more tests, ink peeling was observed in 50 or more squares.

[0053] (Laser cuttable) Laser cutting performance was evaluated for laminated or single-layer resin sheets that had been inkjet printed. <Appearance of the machined surface> Ten molded product samples obtained after laser cutting were evaluated for defects on the cut surface of a 30cm straight cut section using optical microscopy and tactile inspection. The main defects are as follows: Roughness: The cut surface was not uniform overall and felt rough to the touch. Corner roughness: The corners of the machined surface were partially rough and felt rough to the touch. Resin accumulation: Molten resin accumulation was observed on a portion of the cut surface. Foreign matter: A colored foreign substance was observed on the cut surface. The evaluation criteria are as follows: ◎ (Excellent): Defects were found in 0-1 molded product samples. ○ (Good): Defects were found in 2 to 4 molded product samples. △ (Acceptable): Defects were found in 5-7 molded product samples. × (Defective): Defects were found in 8-10 molded product samples.

[0054] <Presence or absence of smoke or odor> The presence or absence of smoke or odor during laser cutting was evaluated using sensory perception. The evaluation criteria were as follows: ◎(Excellent): No smoke or odor was present. ○ (Good): There was some smoke or odor. △ (OK): Somewhere between ○ and ×. × (Defective): There was noticeable smoke or odor.

[0055] (transparency) Transparency was evaluated for extruded laminated or single-layer resin sheets. Three 30mm x 30mm test pieces were cut from the resin sheet, and the total light transmittance of each test piece was measured using the "HM-150" manufactured by Murakami Color Technology Laboratory. The evaluation criteria were as follows: ○ (Good): The total light transmittance of all three test specimens was 90% or higher. × (Defective): The total light transmittance of one or more test specimens was less than 90%.

[0056] (Change in warping after exposure to a high-humidity environment) A rectangular test piece with a long side of 200 mm and a short side of 130 mm was cut out from the extruded laminated or single-layer resin sheet. The long side direction was parallel to the extrusion direction, and the short side direction was perpendicular to the extrusion direction (width direction). The obtained test piece was placed on a glass surface plate such that the upper surface in the extrusion molding became the uppermost surface, and left for 24 hours in an environment of temperature 23°C / relative humidity 50%. Then, the maximum value of the gap between the test piece and the surface plate was measured using a gap gauge, and this value was taken as the initial warp amount. Next, in an environmental test chamber, the test piece was placed on a glass surface plate such that the upper surface in the extrusion molding became the uppermost surface, left for 72 hours in an environment of temperature 23°C / relative humidity 85%, and then left for 24 hours in an environment of temperature 23°C / relative humidity 50%. Thereafter, the warp amount was measured in the same manner as in the initial stage, and the warp change amount from the initial stage was determined. Evaluation was carried out according to the following criteria. ◎ (Excellent): The warp change amount from the initial stage was 0.75 mm or less. 〇 (Good): The warp change amount from the initial stage exceeded 0.75 mm and was 1.0 mm or less. × (Poor): The warp change amount from the initial stage exceeded 1.0 mm. <​​​​​​​​​​​​​​​​​​​​​​

[0059] <Methacrylic resin composition> The following methacrylic resin compositions were prepared by mixing methacrylic resin (B1) or (B2) with MS resin (A2) in the following mass ratio. (MR1-1)(B1) / (A2)=97 / 3, (MR1-2)(B2) / (A2)=97 / 3, (MR2-1)(B1) / (A2)=94 / 6, (MR2-2)(B2) / (A2)=94 / 6, (MR3-1)(B1) / (A2)=82 / 18, (MR3-2)(B2) / (A2)=82 / 18.

[0060] [Example 1] (Manufacturing of laminated sheets) <Example 1-1 (First example of Example 1)> MS resin (A1) was melted using a 65mmφ single-screw extruder manufactured by Toshiba Machine Co., Ltd. as the material for the first and second surface layers. Methacrylic resin (B1) was melted using a 150mmφ single-screw extruder manufactured by Toshiba Machine Co., Ltd. as the material for the main layer. Molten MS resin (A1), molten methacrylic resin (B1), and molten MS resin (A1) were laminated in this order using a multi-manifold die, extruded from a T-die set to 245°C, cooled using four adjacent cooling rolls, and taken up at a speed of 1.6 m / min with a pair of take-up rolls. Through the above co-extrusion molding, a laminated sheet with two types and three layers was manufactured: MS resin (A1) (first surface layer, 0.075 mm thick) / methacrylic resin (B1) (main layer, 2.85 mm thick) / MS resin (A1) (second surface layer, 0.075 mm thick). The first and second surface layers were manufactured under identical conditions for composition and thickness. Table 1 shows the main manufacturing conditions and various parameter values. In Tables 1 and 2, conditions not listed in the tables were considered common conditions. The melt viscosity of the constituent resins of each layer was measured using a capillary rheometer (Capillograph 1D, manufactured by Toyo Seiki Seisakusho Co., Ltd.) in the following manner. From a capillary tube with a diameter of 1 mm and a length of 40 mm, at 245°C and a piston speed of 2 mm / min (shear rate of 24.3 s) -1 The resin was extruded under the specified conditions, and the melt viscosity was determined from the shear stress generated during the process.

[0061] <Example 1-2 (Second example of Example 1)> A laminated sheet consisting of two types of resins and three layers was manufactured in the same manner as in Example 1-1, except that methacrylic resin (B2) was used instead of methacrylic resin (B1). The layers were MS resin (A1) (first surface layer, 0.075 mm thick), methacrylic resin (B2) (main layer, 2.85 mm thick), and MS resin (A1) (second surface layer, 0.075 mm thick). The main manufacturing conditions and various parameter values ​​are shown in Table 1.

[0062] (IJ printing) In each of Examples 1-1 and 1-2, inkjet printing was performed on one of the surface layers of the laminated sheets obtained under the following conditions, and the ink adhesion was evaluated as described above. The printed pattern was a solid ellipse with a short diameter of 1.8 cm and a long diameter of 2.8 cm. Equipment: Roland DG Corporation "LEF-300", Temperature: room temperature (20~25℃), UV-curable ink (white): Roland DG Corporation "EUV-BK", UV-curable ink (black): Roland DG Corporation's "EUV-WH".

[0063] (Laser cutting) Laser cutting was performed on the laminated sheet after the above IJ printing under the following conditions to obtain a molded product in the shape of a TV anime character, with dimensions of 20 mm in short diameter x 30 mm in long diameter and a curved cut section with a radius of 1 mm. Equipment: SEI Corporation's "MERCURY609" Temperature: room temperature (20~30℃), Laser type: CO2 laser, Laser output: 200W, Cutting speed: 350~400cm / min.

[0064] [Examples 2-3, Comparative Examples 1-5] A laminated sheet consisting of two types of materials (MS resin (first surface layer), methacrylic resin (main layer), and MS resin (second surface layer)) was manufactured in the same manner as in Example 1, except that the thickness of each layer was changed to the conditions shown in Tables 1 and 2. Inkjet printing and laser cutting were performed on the obtained laminated sheet in the same manner as in Example 1. In each example, as in Example 1, a first example using methacrylic resin (B1) and a second example using methacrylic resin (B2) were carried out. In Example 2, the first example using methacrylic resin (B1) was designated as Example 2-1, and the second example using methacrylic resin (B2) was designated as Example 2-2. The same applies to other examples and comparative examples. In all examples, the first and second surface layers were subjected to the same conditions for composition and thickness. The main manufacturing conditions and various parameter values ​​are shown in Tables 1 and 2.

[0065] [Example 4, Comparative Example 6] A two-layer laminated sheet was manufactured in the same manner as in Example 1, except that the structure was changed to a two-layer configuration of MS resin (surface layer) / methacrylic resin (main layer) and the thickness of the surface layer was changed. Inkjet printing and laser cutting were performed on the obtained laminated sheet in the same manner as in Example 1. In each example, similar to Example 1, a first example using methacrylic resin (B1) and a second example using methacrylic resin (B2) were carried out. The main manufacturing conditions and various parameter values ​​are shown in Tables 1 and 2.

[0066] [Example 5, Comparative Examples 7 and 8] Laminated sheets consisting of two types and three layers were manufactured in the same manner as in Example 1, except that a methacrylic resin composition consisting of a methacrylic resin and an MS resin was used as the main layer material: MS resin (first surface layer) / methacrylic resin composition (methacrylic resin + MS resin) (main layer) / MS resin (second surface layer). Inkjet printing and laser cutting were performed on the obtained laminated sheets in the same manner as in Example 1. In each example, a first example using methacrylic resin (B1) and a second example using methacrylic resin (B2) were carried out, as in Example 1. The main manufacturing conditions and various parameter values ​​are shown in Tables 1 and 2.

[0067] [Comparative Examples 11, 12] A single-layer resin sheet was manufactured in the same manner as in Example 1, except that MS resin (A1) or (A2) was single-layer extruded. Inkjet printing and laser cutting were then performed in the same manner as in Example 1. The main manufacturing conditions and various parameter values ​​are shown in Table 2.

[0068] [Comparative Examples 11, 13] A methacrylic resin sheet (B3) was prepared, and IJ printing and laser cutting were performed in the same manner as in Example 1. The main manufacturing conditions and various parameter values ​​are shown in Table 2.

[0069] [Table 1]

[0070] [Table 2]

[0071] [Evaluation Results] The evaluation results are shown in Tables 3 and 4. [Table 3]

[0072] [Table 4]

[0073] In Examples 1-4, laminated sheets with a two-layer or three-layer structure were manufactured, having a main layer made of a methacrylic polymer that does not have an aromatic ring structure in its molecule, and a surface layer made of a styrene copolymer on at least one surface of that main layer. The composition and thickness of each layer of the laminated sheet were designed to satisfy equations (11)-(14) in the two-layer structure and equations (21)-(24) in the three-layer structure. In Examples 1-4, the T-die temperature was set to 245°C. In these examples, the composition of each layer was designed so that the absolute value (Δη) of the difference between the melt viscosity of the main layer's constituent resin and the melt viscosity of the surface layer's constituent resin was 2600 Pa·s or less under the conditions of a temperature of 245°C and shear rate at the thickness of each layer.

[0074] The laminated sheets obtained in Examples 1 to 4 all had a surface layer made of MS resin with a relatively high proportion of styrene monomer units having an aromatic ring structure in the molecule, resulting in good ink penetration and good ink adhesion. In all of the laminated sheets obtained in Examples 1 to 4, the proportion of styrene monomer units in the entire laminated sheet was limited, resulting in good laser machinability. The laminated sheets obtained in Examples 1-4 all exhibited good interlayer adhesion and showed no delamination streaks. Furthermore, no foaming occurred during co-extrusion molding. The laminated sheets obtained in Examples 1 to 4 all exhibited good transparency and showed minimal warping after exposure to a high-humidity environment.

[0075] In Example 5, a three-layer laminated sheet was manufactured, having a surface layer made of a styrene copolymer on both surfaces of a main layer made of a methacrylic polymer and a styrene copolymer. The composition and thickness of each layer of the laminated sheet were designed to satisfy equations (21) to (24). The temperature of the T-die was set to 245°C. The composition of each layer was designed such that the absolute value (Δη) of the difference between the melt viscosity of the main layer's constituent resin and the melt viscosity of the surface layer's constituent resin was 2600 Pa·s or less under the conditions of a temperature of 245°C and shear rate at the thickness of each layer.

[0076] The laminated sheet obtained in Example 5 had a surface layer made of MS resin with a relatively high proportion of styrene monomer units having an aromatic ring structure in the molecule, resulting in good ink permeability and good ink adhesion. The laminated sheet obtained in Example 5 exhibited good laser machinability because the proportion of styrene monomer units in the entire laminated sheet was limited. The laminated sheet obtained in Example 5 exhibited good interlayer adhesion and showed no peeling streaks. Furthermore, no foaming occurred during co-extrusion molding. The laminated sheet obtained in Example 5 had a small amount of styrene copolymer added to the main layer, resulting in a smaller change in warping after exposure to a high-humidity environment compared to Example 1. In Example 5, a styrene copolymer was added to the main layer, but the amount added was limited, resulting in good compatibility between the methacrylic polymer and the styrene copolymer in the main layer material. Therefore, the resulting laminated sheet had good transparency.

[0077] In Comparative Examples 1 to 6, laminated sheets with a two-layer or three-layer structure were produced, in which a main layer made of a methacrylic polymer that does not have an aromatic ring structure in its molecule had a surface layer made of a styrene copolymer on at least one of its surfaces.

[0078] The laminated sheets obtained in Comparative Examples 1-3 and 6 did not satisfy formula (11) or (21), and had poor ink adhesion because the proportion of styrene monomer units in the surface layer was low.

[0079] The laminated sheet obtained in Comparative Example 4 did not satisfy formula (24), and the proportion of styrene monomer units in the entire laminated sheet was greater than the preferred range, resulting in the generation of a styrene odor during laser cutting. The laminated sheet obtained in Comparative Example 4 also failed to satisfy equation (22), and the ratio of the surface layer thickness was greater than the preferred range. In this example, the shear rate applied to the surface layer increased when it was extruded from the T-die. In addition, the absolute value (Δη) of the difference between the melt viscosity of the main layer's constituent resin and the surface layer's constituent resin was greater than the preferred range. As a result, interlayer adhesion was poor, and delamination streaks occurred between the layers.

[0080] In Comparative Example 5, equation (22) was not satisfied, and the ratio of the surface layer thickness was smaller than the preferred range. In this example, the decrease in the amount of surface layer material extruded resulted in a longer residence time of the surface layer material in the extruder, and foaming was observed in the surface layer.

[0081] In Comparative Examples 7 and 8, a three-layer laminated sheet was produced, having a surface layer made of a styrene copolymer on both surfaces of a main layer consisting of a methacrylic polymer without an aromatic ring structure in the molecule and a styrene copolymer. The laminated sheets obtained in these comparative examples did not satisfy formula (23), and the mass fraction of styrene monomer units in the main layer was greater than the preferred range. The laminated sheet obtained in Comparative Example 8 had poor laser machinability. In Comparative Examples 7 and 8, the amount of warping change after exposure to a high-humidity environment was smaller than in Example 1. However, because the compatibility between the methacrylic polymer and the styrene copolymer in the main layer material was poor, the resulting laminated sheets had poor transparency.

[0082] The single-layer sheets made of styrene copolymers in Comparative Examples 11 and 12 had good ink adhesion, but poor laser cutting performance. The single-layer sheet made of a methacrylic polymer without an aromatic ring structure in its molecule, Comparative Example 13, exhibited good laser machinability but poor ink adhesion. It is believed that methacrylic polymers without an aromatic ring structure have lower ink penetration and inferior ink adhesion compared to styrene copolymers that do have an aromatic ring structure.

[0083] The present invention is not limited to the embodiments and examples described above, and design modifications can be made as appropriate without departing from the spirit of the invention. [Explanation of symbols]

[0084] 11 T-die 16X, 16Y laminated sheet 21, 22, 23 Surface layer 31 Main layer

Claims

1. A laminated sheet having a main layer containing a methacrylic polymer and a surface layer located on one surface side of the main layer and containing a styrene copolymer, The styrene copolymer comprises at least one selected from the group consisting of methyl methacrylate-styrene copolymer and acrylonitrile-styrene copolymer. The following equations (11) to (14) are satisfied, Laminated sheets for inkjet printing and laser cutting. (11)0.60≦C ｓｔ１ ≦0.95 (12)1.67×10 ―２ ≦z １ / Z≦1.67×10 ―１ (13)0.012≦C ｓｔ２ ≦0.015 (14)0.02≦C ｓｔ３ ≦0.10 Each abbreviation in the above formula represents the following parameter: C ｓｔ１ This represents the mass fraction of styrene monomer units in the surface layer. C ｓｔ２ This represents the mass fraction of styrene monomer units in the main layer. C ｓｔ３ is the mass fraction of styrene monomer units in the entire laminated sheet. z １ This is the thickness of the surface layer. Z is the total thickness of the laminated sheet.

2. 0.04 ≤ C ｓｔ３ The laminated sheet according to claim 1, satisfying ≤ 0.

10.

3. 245°C temperature and 24.3 seconds －１ The laminated sheet according to claim 1, wherein the absolute value of the difference between the melt viscosity of the main layer's constituent resin and the melt viscosity of the surface layer's constituent resin, under the given shear rate conditions, is 0 to 2000 Pa·s.

4. A laminated sheet having a main layer containing a methacrylic polymer, a first surface layer containing a styrene copolymer located on one surface side of the main layer, and a second surface layer containing a styrene copolymer located on the other surface side of the main layer, The styrene copolymer contained in the first surface layer and the second surface layer each independently contains at least one selected from the group consisting of methyl methacrylate-styrene copolymer and acrylonitrile-styrene copolymer. The following equations (21) to (24) are satisfied, Laminated sheets for inkjet printing and laser cutting. (21)0.60≦C ｓｔ１ ≦0.95 (22)1.67×10 ―２ ≦z １ / Z≦1.67×10 ―１ (23)0.012≦C ｓｔ２ ≦0.015 (24)0.02≦C ｓｔ３ ≦0.10 Each abbreviation in the above formula represents the following parameter: C ｓｔ１ This is the mass fraction of styrene monomer units in the first or second surface layer. C ｓｔ２ This represents the mass fraction of styrene monomer units in the main layer. C ｓｔ３ This represents the mass fraction of styrene monomer units in the entire laminated sheet. z １ This is the thickness of the first or second surface layer. If the thickness of the first surface layer and the thickness of the second surface layer are not the same, z １ and C ｓｔ１ The z value is the thickness of the first and second surface layers, whichever has the greater thickness. １ and C ｓｔ１ The value of is adopted. If the thickness of the first surface layer and the thickness of the second surface layer are the same, and the mass fraction of styrene monomer units in the first surface layer and the mass fraction of styrene monomer units in the second surface layer are different, then z １ and C ｓｔ１ As the value of z, the z of the surface with the larger mass fraction of styrene monomer units among the first and second surface layers. １ and C ｓｔ１ The value of will be used. Z is the total thickness of the laminated sheet.

5. 0.04 ≤ C ｓｔ３ The laminated sheet according to claim 4, satisfying ≤ 0.

10.

6. 245°C temperature and 24.3 seconds －１ The laminated sheet according to claim 4, wherein, under the shear rate conditions, the absolute value of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the first surface layer, and the absolute value of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the second surface layer, are between 0 and 2000 Pa·s.

7. The laminated sheet according to claim 1 or 4, which is a co-extruded sheet.

8. A laminated sheet according to claim 1 or 4, for use as a keychain.

9. The process includes co-extruding a thermoplastic resin laminate having the main layer and the surface layer from a T-die in a molten state, The temperature of the T-die is 190 to 280°C. The method for manufacturing a laminated sheet according to claim 1, wherein the absolute value of the difference between the melt viscosity of the main layer's constituent resin and the melt viscosity of the surface layer's constituent resin at the temperature conditions of the T-die is 0 to 2600 Pa·s.

10. The process includes a step of co-extruding a thermoplastic resin laminate having the first surface layer, the main layer, and the second surface layer from a T-die in a molten state. The temperature of the T-die is 190 to 280°C. The method for manufacturing a laminated sheet according to claim 4, wherein, under the temperature conditions of the T-die, the absolute value of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the first surface layer, and the absolute value of the difference between the melt viscosity of the constituent resin of the main layer and the melt viscosity of the constituent resin of the second surface layer, are between 0 and 2600 Pa·s.

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