Stretched resin sheet and method for producing stretched resin sheet

Abstract

To provide a resin sheet containing a pearl pigment and exhibiting excellent appearance design quality, and to provide a resin sheet which is readily recyclable while containing a pearl pigment.SOLUTION: The present invention relates to a stretched resin sheet comprising a base layer and a pearl luster layer containing a pearl pigment, the stretched resin sheet containing a polyolefin-based resin and having an opacity of 30% or more, wherein the pearl luster layer has a porosity of 7% or less. In a preferable embodiment of the stretched resin sheet, a melting point of a resin forming the pearl luster layer is lower than a melting point of a resin forming the base layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a stretched resin sheet and a method for producing the stretched resin sheet. [Background technology]

[0002] Resin sheets (synthetic papers) have been proposed and put to practical use, and are made by stretching a resin composition containing a resin and a filler to form a porous layer. These resin sheets are useful as materials for printing paper, labels, etc.

[0003] Resin sheets may be required to have decorative properties to improve their appearance depending on various applications. Examples of resin sheets with such decorative appearances include resin sheets that use pearl pigments, that is, pigments whose color changes depending on the viewing angle due to the interference of light. Patent Document 1 discloses a resin material that has been given decorative properties by applying an ink containing a pearl pigment to form a glossy printed layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-10302 Summary of the Invention [Problem to be solved by the invention]

[0005] In resin sheets using pearl pigments, there are cases where it is desired to further improve the appearance design, such as the degree of color change depending on the viewing angle and the intensity of brightness, for example, when it is desired to impart a more luxurious feel to the sheet. Furthermore, when recycling resin sheets with consideration for the environment, resin sheets containing pearl pigments are required to be easier to recycle.

[0006] Therefore, the present invention provides a resin sheet using a pearl pigment that can improve the appearance design compared to conventional resin sheets.The present invention also provides a resin sheet using a pearl pigment that is easy to recycle. [Means for solving the problem]

[0007] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have arrived at the present invention having the following gist.

[0008] That is, the present invention is as follows. [1] A stretched resin sheet, The film has a base layer and a pearlescent layer containing a pearl pigment, Contains polyolefin resin and has an opacity of 30% or more, The pearly luster layer of the stretched resin sheet has a porosity of 7% or less. [2] The stretched resin sheet according to [1], wherein the melting point of the resin forming the pearly luster layer is lower than the melting point of the resin forming the base layer. [3] The stretched resin sheet according to [1] or [2], wherein the orientation angle of the pearl pigment in the pearly luster layer is 20° or less. [4] Average particle size D of the pearl pigment 50 The stretched resin sheet according to any one of [1] to [3], wherein the thickness is 40 μm or less. [5] The stretched resin sheet according to any one of [1] to [4], wherein the content of the pearl pigment is 5 to 20% by mass relative to the pearlescent layer. [6] The stretched resin sheet according to any one of [1] to [5], wherein the pearly luster layer has a thickness of 10 μm or less. [7] The stretched resin sheet according to any one of [1] to [6], which has a total thickness of 40 to 150 μm. [8] The stretched resin sheet according to any one of [1] to [7], wherein the base layer contains 10 to 50% by mass of a filler. [9] a lamination step of laminating a resin composition for forming the pearly luster layer onto a resin composition for forming the base layer to form a laminate; a stretching step of stretching the laminate, In the stretching step, the pearly luster layer is stretched to a stretching ratio of 3 times or more. The method for producing a stretched resin sheet according to any one of [1] to [7]. [Effects of the Invention]

[0009] According to the present invention, a resin sheet using a pearl pigment can be provided that can improve the appearance design compared to conventional ones. Furthermore, the present invention can provide a resin sheet that uses a pearl pigment and is easy to recycle. The resin sheet of the present invention is particularly suitable for use as printing paper. [Brief explanation of the drawings]

[0010] [Figure 1] Schematic cross-sectional view of a resin sheet in an embodiment. [Figure 2] Schematic cross-sectional view of a resin sheet showing the orientation angle of a pearl pigment in an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below with reference to the following embodiments. The following embodiments are examples of the present invention, and the present invention is not limited to these embodiments.

[0012] (Stretched resin sheet) The present invention relates to a "stretched resin sheet" containing a polyolefin resin, that is, a stretched resin sheet.

[0013] The stretched resin sheet containing the polyolefin resin of this embodiment is more likely to improve the appearance design than conventional resin sheets (which have a glossy printed layer formed by applying an ink containing a pearlescent pigment). Specifically, the stretched resin sheet of this embodiment is more likely to improve the appearance design, i.e., the variable angle luminous reflectance difference (so-called pearlescent effect), in which the color changes depending on the viewing angle, and the intensity of the shine (glossiness). Here, the pearlescent pigment has a thin plate-like shape, as described in detail below, and exhibits shine due to the interference of light absorbed and scattered by the pearlescent pigment arranged in layers. In this regard, the stretched resin sheet containing the polyolefin resin makes it easier to arrange the pearlescent pigment in the resin sheet to exhibit shine due to the interference of light (at an angle closer to parallel to the surface of the resin sheet).

[0014] A resin sheet containing a polyolefin resin can reduce the amount of pearl pigment used by providing each layer of the laminate with a specific function. That is, by providing a pearlescent layer that provides the so-called pearly finish separately from the other layers, the content of the pearl pigment in the entire laminate can be reduced. Therefore, when recycling the resin sheet, the difficulty of recycling due to the pearlescent pigment can be reduced, improving recyclability and reducing the cost of the resin sheet. Furthermore, resin sheets containing polyolefin resins are easier to obtain stiffness (i.e., easier to increase elasticity) than resin sheets using other resins such as acrylic resins or polyester resins. For this reason, for example, when using the resin sheet as a label, it is easy to adhere to even curved surfaces.

[0015] Furthermore, with a stretched resin sheet containing a polyolefin resin, the content of the pearl pigment can be reduced and the thickness of the layer containing the pearl pigment (pearl luster layer) can be easily reduced while maintaining the above-mentioned appearance design. Therefore, when recycling the stretched resin sheet, the content of the pearl pigment, which is considered an impurity in the recovered material, can be reduced, making it easy to increase the purity of the recovered material. Furthermore, during the kneading process during recycling, the pearl pigment is subjected to stress on the recovered material, making it easy to break into small fragments (making it less flat), and the pearl luster of the appearance can easily be lost. Therefore, the appearance tends to be similar to that of ordinary resins that do not contain pearl pigment, making it highly suitable for recycling. The polyolefin resin is contained in an amount of preferably 60% by mass or more, and more preferably 70 to 95% by mass, based on the resin composition forming the stretched resin sheet.

[0016] <Stretched resin sheet configuration> An example of the configuration of a stretched resin sheet will be described with reference to Fig. 1. The stretched resin sheet 10 has a base layer 200 and a pearlescent layer 100 containing a pearl pigment 110. The stretched resin sheet 10 may be a laminate of the pearl layer 100 and the base layer 200, or may be one in which the base layer 200 is laminated on the pearl layer 100. The stretched resin sheet 10 may have one or more layers other than the base layer 200 and the pearly luster layer 100. For example, the stretched resin sheet 10 may have an intermediate layer between the base layer 200 and the pearly luster layer 100, or may have a surface layer on the surface of the pearly luster layer 100 opposite to the base layer 200. In addition, the stretched resin sheet 10 may have a back layer or a heat seal layer on the surface of the base layer 200 opposite to the pearly luster layer 100.

[0017] The pearly luster layer 100 contains a pearl pigment 110 and provides the stretched resin sheet 10 with an appearance design. For this reason, when the stretched resin sheet 10 is used for various purposes, it is preferable to arrange the pearl pigment 110 so that it can be seen from the exterior (outer surface). For this reason, it is preferable that the pearly luster layer 100 is a transparent layer. Furthermore, a surface layer can be laminated on the outer surface of the pearly luster layer 100, and in that case, it is preferable that the surface layer is also transparent for the same reasons as above.

[0018] The stretched resin sheet contains a polyolefin-based resin, which is preferably contained in both the base layer and the pearly luster layer. As the polyolefin resin, a polypropylene resin is preferred from the viewpoint of moldability. Examples of polypropylene-based resins include isotactic homopolypropylene and syndiotactic homopolypropylene, which are homopolymerized from propylene, as well as polypropylene-based copolymers having various stereoregularities, which are copolymerized mainly with propylene and α-olefins such as ethylene, 1-butene, and 1-pentene. The propylene-based copolymers may be binary or ternary or higher multi-component systems, and may be random or block copolymers.

[0019] A stretched resin sheet is a stretched sheet, and it can be confirmed that it is a stretched sheet, for example, from the storage modulus of the sheet. Specifically, the storage modulus of the resin sheet in the MD (machine direction) and TD (transverse direction) directions is measured. For example, in the case of a stretched resin sheet containing a polypropylene-based resin, if the storage modulus in the MD direction (machine direction, the direction in which the resin flows) or TD direction (transverse direction, the direction perpendicular to the machine direction) exceeds 1500 MPa, it can be confirmed that the sheet is stretched. (A stretch ratio of 2500 MPa or more can be confirmed as 4 times or more, and a stretch ratio of 5000 MPa or more can be confirmed as 9 times or more.) The storage modulus was measured by cutting the film into a 30 mm x 15 mm test piece and using a solid viscoelasticity measuring device (RSA-III, manufactured by TA Instruments Japan, Inc.) under the following measurement conditions: chuck distance 20 mm, measurement frequency 10 Hz, strain 0.1%, heating rate 10°C / min, tensile mode, and temperature 23°C.

[0020] The stretched resin sheet of the present embodiment is formed by stretching, and therefore is easier to recycle than conventional resin sheets in which a glossy printed layer is formed by applying an ink containing a pearl pigment. This is because conventional resin sheets use a binder resin to create an ink containing a pearl pigment. Typical binder resins have low heat resistance, and therefore thermal deterioration such as discoloration can occur due to the thermal history during recycling. In contrast, the stretched resin sheet can be formed without using a binder resin, and therefore, denaturation due to thermal history is more easily suppressed than resin sheets formed using conventional inks.

[0021] <Opacity> The stretched resin sheet has an opacity of 30% or more. The stretched resin sheet exhibits the appearance design (pearl luster) provided by the pearl luster layer described above, while also having a predetermined level of opacity. Therefore, for example, when used for printing purposes, it can improve the readability of characters (readability improvement) and prevent printing on one side of the stretched resin sheet from showing through when viewed from the other side (prevention of show-through). The opacity of the stretched resin sheet is preferably 50% or more, more preferably 80% or more, from the viewpoint of being more likely to exhibit pearly luster. The upper limit of the opacity is not particularly limited, and may be less than 100%. The opacity can be measured in accordance with "Paper and paperboard - Opacity test method (paper backing) - Diffuse illumination method" as specified in JIS P8149:2000.

[0022] The stretched resin sheet of this embodiment has an opacity of 30% or more, and the pearly luster layer has a porosity of 7% or less, as described below, and is therefore likely to have high transparency. Therefore, it is preferable that the stretched resin sheet has a predetermined opacity imparted to the stretched resin sheet by any layer other than the pearly luster layer. For example, the opacity of the stretched resin sheet may be due to the opacity of the base layer or the opacity of the intermediate layer.

[0023] The hue of the stretched resin sheet is not particularly limited. When the stretched resin sheet is used for applications in which a pop impression is desired or when visibility as printing paper is desired, the hue of the stretched resin sheet is preferably a light color (bright color), for example, white, pastel colors (light blue, pink), etc.

[0024] <Thickness of stretched resin sheet> From the viewpoint of ease of production, the stretched resin sheet preferably has a total thickness of 40 to 150 μm, including each layer such as the base layer and the pearlescent layer. From the viewpoint of ease of maintaining the strength of the stretched resin sheet, the total thickness of the stretched resin sheet is more preferably 60 μm or more, and even more preferably 70 μm or more. Furthermore, from the viewpoint of handleability, the total thickness of the resin sheet is more preferably 120 μm or less, and even more preferably 100 μm or less.

[0025] (Pearl gloss layer) The pearlescent layer containing a pearl pigment will now be described. The pearlescent layer may be laminated on a base layer. The pearly luster layer has a porosity of 7% or less. As described above, the pearly luster layer in the stretched sheet of this embodiment contains a pearl pigment and has a porosity of a predetermined level or less. The porosity of the pearly luster layer is preferably 5% or less, more preferably 3% or less, and particularly preferably 1% or less, from the viewpoint of easily improving the appearance design. A pearly luster layer with such a low porosity can be observed as a transparent or nearly transparent layer. The lower limit of the porosity of the pearly luster layer is not particularly limited, and may be 0% (below the measurement limit). The porosity can be determined from the ratio of the area occupied by pores to a certain region of the cross section of a sample observed under an electron microscope.

[0026] <Pearl pigment> The pearl pigment may be a thin plate-like particle such as mica, coated with a high refractive index material such as titanium oxide. The thin plate-like particle may be aluminum flakes, alumina flakes, silica flakes, or the like, in addition to mica, and the metal oxide coating the surface may be cobalt oxide, cobalt titanate, or the like, in addition to titanium oxide. Commercially available pearl pigments may be used, and there is no particular limitation on the types that can be used. For example, pearl pigments whose interference color is adjusted by the thickness of the coating layer or the like are known (white pearl pigments, interference pearl pigments, colored pearl pigments, etc.). Any pearl pigment may be used in this embodiment, but mica is preferred, and mica coated with titanium oxide is particularly preferred. Furthermore, artificially produced mica is preferred from the viewpoint of having fewer impurities and easily achieving a pearly finish.

[0027] From the viewpoint of easily improving the appearance design, the content of the pearl pigment in the pearly luster layer is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more. Also, from the viewpoint of easily maintaining the strength of the resin stretched sheet and minimizing the amount of pearl pigment used, the content of the pearl pigment is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less.

[0028] Average particle size of pearl pigment D 50 From the viewpoint of easily maintaining the formability of the stretched resin sheet, the average particle diameter D of the pearl pigment is preferably 40 μm or less. 50 From the viewpoint of easily increasing the brightness of the pearl pigment, the average particle size D is more preferably 30 μm or less, further preferably 20 μm or less, and particularly preferably 10 μm or less. 50 is preferably 5 μm or more, and more preferably 8 μm or more. The average particle diameter (D50) is the particle diameter corresponding to 50% cumulatively (50% cumulative particle diameter) in a particle size distribution measured using a particle measuring device, for example, a laser diffraction particle measuring device "Microtrac" (trade name, manufactured by Nikkiso Co., Ltd.).

[0029] When the pearl pigment is a thin plate-like particle, the thickness is preferably 5 μm or less, more preferably 1 μm or less, from the viewpoint of easily achieving a good orientation angle of the pearl pigment, which will be described later. On the other hand, the thickness of the pearl pigment is preferably 0.01 μm or more, from the viewpoint of easily improving the strength and production efficiency of the pearl pigment.

[0030] <<Orientation angle of pearl pigment>> The orientation angle of the pearl pigment in the pearlescent layer is preferably 20° or less. Here, the orientation angle of the pearlescent pigment refers to the average angle between the surface of the pearlescent layer and a plane along the major axis direction of the pearlescent pigment contained in the pearlescent layer, in the pearlescent pigment in the stretched resin sheet. From the viewpoint of easily improving the appearance design, the orientation angle of the pearl pigment is more preferably less than 15°, even more preferably less than 8°, and particularly preferably less than 5°. The lower limit of the orientation angle of the pearl pigment is not particularly limited, and may be more than 0°.

[0031] The orientation angle of the pearl pigment will be specifically described with reference to Fig. 2. Fig. 2 is a schematic cross-sectional view of an arbitrary cross section of the stretched resin sheet 10. When measuring the orientation angle of the pearl pigment, an SEM observation photograph of an arbitrary cross section of the stretched resin sheet 10 can be used. 2, the orientation angle α of the pearl pigment 110 can be measured as the angle α formed between the surface 100A of the pearly luster layer 100 and a plane along the major axis direction of the thin plate-like pearl pigment 110B. The orientation angle of the pearl pigment 110 in the stretched resin sheet 10 can be calculated from the average value of the orientation angles α of the pigment measured as described above.

[0032] <Resin that forms the pearly gloss layer> The resin forming the pearly luster layer preferably contains the above-mentioned polyolefin resin. The resin forming the pearly luster layer and the resin forming the base layer may be the same, but are preferably different. From the viewpoint of easily reducing the porosity of the pearly luster layer, it is preferable that the melting point of the resin forming the pearly luster layer is lower than the melting point of the resin forming the base layer. This is because, since the pearly luster layer contains a pearl pigment, voids centered on the pearl pigment tend to be easily formed in the pearly luster layer by stretching, and the low melting point of the resin forming the pearly luster layer as described above makes it easier to reduce the formation of voids originating from the pearl pigment. By forming the pearlescent layer of the stretched resin sheet using the above-mentioned low-melting-point resin, it becomes possible to use pearl pigments having a relatively large average particle size within the above-mentioned range.

[0033] From the viewpoint of making it more difficult to form voids, the melting point of the resin forming the pearly luster layer is preferably at least 10° C. lower than the melting point of the resin forming the base layer, and more preferably at least 20° C. lower. From the viewpoint of formability, the difference between the melting points of the resin forming the pearly luster layer and the resin forming the base layer is preferably not more than 50° C., and even more preferably not more than 40° C. The resin forming the pearly luster layer is preferably random polypropylene, and the pearly luster layer preferably contains random polypropylene. It is more preferable that the resin component in the pearly luster layer contains random polypropylene in an amount of 50% by mass or more, and even more preferable that the resin component contains random polypropylene in an amount of 70% by mass or more. The polyolefin resin is preferably contained in an amount of 70% by mass or more, and more preferably 80 to 95% by mass, based on the resin composition forming the pearly luster layer.

[0034] <Thickness of pearlescent layer> The thickness of the pearly luster layer is preferably 2 to 20 μm, because within this range the stretched resin sheet has a good appearance design and is easily recyclable. From the viewpoint of formability, the thickness of the pearly luster layer is more preferably 15 μm or less, and even more preferably 10 μm or less.From the viewpoint of easily exhibiting pearly luster, the thickness of the pearly luster layer is more preferably 3 μm or more, and even more preferably 5 μm or more.

[0035] (base material layer) The base layer is not particularly limited as long as it can laminate a pearlescent layer. From the viewpoint of making it easier to set the opacity of the stretched resin sheet within the above range, the base layer preferably has a porosity of 10% or more. In this case, the base layer may be an opaque base layer having a suitable opacity. From the viewpoint of easily improving the whiteness of the stretched resin sheet, the porosity of the base layer is preferably 20% or more, and more preferably 25% or more. From the viewpoint of preventing sheet tearing, etc., the porosity of the base layer is preferably 50% or less, more preferably 40% or less, and even more preferably 35% or less.

[0036] The resin forming the base layer preferably contains the above-mentioned polyolefin resin. In relation to the melting point of the resin forming the pearly luster layer described above, homopolypropylene is preferred as the resin forming the base layer, and the base layer preferably contains homopolypropylene. It is more preferred that the resin components in the base layer contain 50% by mass or more of homopolypropylene, and even more preferred that the resin components contain 80% by mass or more of homopolypropylene. From the viewpoint of providing moldability and stiffness (hardness required for handling and printing), the polyolefin resin is preferably contained in the resin composition forming the base layer in an amount of 50 to 95% by mass, and more preferably 60 to 90% by mass.

[0037] The thickness of the base layer is preferably 30 to 130 μm. Within this range, it is easy to achieve the thickness within the above-mentioned preferred range of the stretched resin sheet. From the viewpoint of ease of handling, the thickness of the substrate layer is more preferably 100 μm or less, and even more preferably 80 μm or less. From the viewpoint of formability, the thickness of the substrate layer is more preferably 40 μm or more, and even more preferably 50 μm or more.

[0038] (Applications of stretched resin sheets) The stretched resin sheet of the present embodiment is suitable for use in various printing papers, adhesive labels, etc. The stretched resin sheet of the present invention is particularly suitable as printing paper in that it can be given a pop impression by selecting a hue as described above, and visibility as printing paper can be easily ensured.

[0039] (Method of manufacturing stretched resin sheet) The stretched resin sheet of this embodiment is a lamination step of laminating a resin composition for forming a pearly luster layer onto a resin composition for forming a base layer to form a laminate; a stretching step of stretching the laminate, The stretching step can be carried out by stretching the pearly luster layer to a stretching ratio of 4 times or more. The method for producing a stretched resin sheet according to this embodiment will be described in detail below.

[0040] <Lamination process> The manufacturing method of this embodiment includes a lamination step of laminating a resin composition that forms a pearly luster layer onto a resin composition that forms a base layer to form a laminate. The base layer may be uniaxially stretched before laminating the pearly luster layer, or the pearly luster layer may be laminated on an unstretched sheet-like base layer.

[0041] Furthermore, the manufacturing method of this embodiment preferably further includes a step of forming the base layer by stretching a resin composition containing 10 to 50% by mass of filler relative to the base layer. This is because using a resin composition containing a predetermined amount of filler makes it easier to form a base layer with the above-mentioned suitable porosity range. Specifically, by containing a predetermined amount of filler, an appropriate number of pores are more likely to be formed in the base layer with the filler as nuclei during the stretching step. The filler content of the base layer is more preferably 12% by mass or more, and even more preferably 15% by mass or more, from the viewpoint of easily adjusting the opacity of the sheet within the above range, and more preferably 35% by mass or less, and even more preferably 30% by mass or less, from the viewpoint of easily maintaining the strength of the base layer.

[0042] <<Filler>> The filler contained in the resin composition forming the base layer may be an inorganic filler or an organic filler. The organic filler is not particularly limited, but is preferably organic particles that are incompatible with the thermoplastic resin, have a melting point or glass transition temperature higher than that of the thermoplastic resin, and are finely dispersed under the melt-kneading conditions of the thermoplastic resin. The melting point (°C) and glass transition temperature (°C) of the resin can be measured by differential scanning calorimetry (DSC).

[0043] Examples of inorganic fillers include heavy calcium carbonate, light calcium carbonate, calcined clay, talc, diatomaceous earth, titanium oxide, zinc oxide, barium sulfate, silicon oxide, magnesium oxide, and inorganic particles of these that have been surface-treated with a fatty acid, a polymer surfactant, an antistatic agent, etc. Among these, heavy calcium carbonate and light calcium carbonate are preferred because they have good pore formability and are inexpensive. The inorganic filler may be selected from the above and used alone, or two or more types may be used in combination.

[0044] The average particle size (D50) of the inorganic filler is not particularly limited. The average particle size of the inorganic filler is preferably large from the viewpoint of ease of mixing with the thermoplastic resin, and is preferably small from the viewpoint of reducing the occurrence of problems such as film breakage during stretching. Specifically, the average particle size of the inorganic filler is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1.0 μm or more. In addition, the average particle size of the inorganic filler is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. The average particle diameter (D50) of the inorganic filler refers to the particle diameter corresponding to a cumulative 50% (cumulative 50% particle diameter) in the particle size distribution measured by a particle measuring device, for example, a laser diffraction particle measuring device "Microtrac" (trade name, manufactured by Nikkiso Co., Ltd.), of an inorganic filler dispersed in a suitable solvent.

[0045] The filler may be applied to any layer other than the base layer, provided that the layer is a layer other than the transparent pearl layer. When a filler is used in any layer other than the base layer, the type and content of the filler may be selected appropriately.

[0046] The resin composition forming each layer of the stretched resin sheet may further contain additives such as pigments, heat stabilizers (antioxidants), light stabilizers, dispersants, lubricants, or nucleating agents in addition to fillers, as needed.

[0047] <Stretching process> The stretching step is a step of stretching the laminate. In the stretching step, the pearly luster layer is stretched to a stretching ratio of 3 or more. The stretching ratio may be different for each layer of the stretched resin sheet, and as described above, it is preferable to stretch the layer to a stretching ratio of 3 or more with the pearly luster layer as the reference. This is because when the stretching ratio of the pearly luster layer is 3 or more, the orientation angle of the pearl pigment tends to be low, and pearly luster is easily exhibited. The stretching ratio of the pearly luster layer is preferably 4 times or more, and more preferably 8 times or more, from the viewpoint of easily adjusting the orientation angle of the pearl pigment to 20° or less.From the viewpoint of maintaining strength, the stretching ratio of the pearly luster layer is preferably 40 times or less, and more preferably 20 times or less.

[0048] In the stretching step, the stretching ratio of the laminate may be appropriately determined so that the stretching ratio of the pearly luster layer falls within the above-mentioned preferred range. For example, when the laminate is stretched in one direction, the stretching ratio is usually about 1.2 times or more, preferably 2 times or more, and usually 12 times or less, preferably 10 times or less. When the laminate is stretched biaxially, the stretching ratio is usually 1.5 times or more, preferably 8 times or more, more preferably 15 times or more, in terms of areal stretching ratio. On the other hand, from the viewpoints of strength and manufacturing difficulty, the areal stretching ratio is usually 40 times or less, preferably 20 times or less.

[0049] The stretching method in the stretching step (stretching method) is not particularly limited. Examples include longitudinal stretching using the difference in peripheral speed between rolls, transverse stretching using a tenter oven, sequential biaxial stretching combining these, rolling, simultaneous biaxial stretching using a tenter oven and a pantograph, and simultaneous biaxial stretching using a tenter oven and a linear motor. Also usable is simultaneous biaxial stretching (inflation molding) in which a molten resin is extruded into a tube using a circular die connected to a screw extruder, and then air is blown into the extruded tube.

[0050] The stretching temperature when stretching may be set appropriately. When the melting point of the resin forming the pearly luster layer is set lower than the melting point of the resin forming the substrate layer, the stretching temperature is preferably set in accordance with the melting point of the resin forming the substrate layer. This is to stretch the substrate layer to an appropriate stretch ratio. The stretching temperature is preferably set within a range equal to or lower than the melting point of the resin forming the substrate layer. Specifically, the stretching temperature is preferably 2 to 60°C lower than the melting point of the resin forming the substrate layer. From the viewpoints of easily increasing the porosity of the substrate layer and easily preventing breakage, etc., the stretching temperature is more preferably 5 to 50°C lower, and even more preferably 10 to 30°C lower, than the melting point of the resin forming the substrate layer. The stretching speed is not particularly limited, but is preferably within the range of 20 to 350 m / min from the viewpoint of stable stretching. [Example]

[0051] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts", "%", and the like are based on mass unless otherwise specified.

[0052] (Preparation of Resin Composition) According to the following procedures, stretched resin sheets were produced in Examples 1 to 4 and Comparative Examples 1 to 3. Details of the materials used in each of the Examples and Comparative Examples are summarized in Table 1. The types and blending ratios (mass%) of materials used in the production of the resin sheets of each Example and Comparative Example, as well as the stretching conditions and evaluations, are summarized in Table 2. The material symbols shown in Table 2 correspond to the material symbols shown in Table 1.

[0053] [Table 1]

[0054] [Example 1] The resin composition forming the base layer was prepared by melt-kneading 84% by mass of h-PP, a polypropylene resin, and 16% by mass of heavy calcium carbonate particles (CaCO3), an inorganic filler, in an extruder set at 270°C. This resin composition was extruded into a sheet through a die and cooled to 70°C using a cooling roll to obtain a single-layer unstretched film. This unstretched film was then reheated to 150°C and stretched four times in the sheet flow direction (longitudinal direction) using the speed difference between multiple rolls to obtain a base layer (longitudinal uniaxially stretched layer).

[0055] Next, a resin composition for forming the pearly luster layer was prepared by melt-kneading 90% by mass of r-PP, a polypropylene resin, and 10% by mass of Pearl 1, a pearl pigment, in an extruder set at 270°C. This resin composition was extruded into a sheet through a die and cooled to 70°C with a cooling roll to obtain a single-layer unstretched film. This unstretched film was laminated on one side of the above-mentioned base layer.

[0056] The resin composition for forming the back surface layer was prepared by melt-kneading 55% by mass of h-PP, a polypropylene resin, and 45% by mass of heavy calcium carbonate particles (CaCO3), an inorganic filler, in an extruder set at 270°C. This resin composition was extruded into a sheet through a die and cooled to 70°C using a cooling roll to obtain a single-layer unstretched film. This unstretched film was laminated on the surface of the substrate layer opposite the transparent pearl layer (referred to as the back surface side).

[0057] The obtained laminate was heated to 150°C using an oven, stretched 9 times in the transverse direction using a tenter stretching machine, and then heat-treated at 170°C to obtain a stretched resin sheet consisting of a pearlescent layer (uniaxially stretched layer), a base layer (biaxially stretched layer), and a back surface layer (uniaxially stretched layer).

[0058] The obtained stretched resin film had a thickness of 80 μm, of which the thickness of the base layer was 70 μm and the porosity was 36%, and the thickness of the pearly luster layer was 5 μm. The method for measuring the thickness of the stretched resin sheet will be described later.

[0059] [Example 2] A stretched resin sheet was obtained in the same manner as in Example 1, except that 10% by mass of Pearl 2 was used instead of Pearl 1 as the pearl pigment.

[0060] [Example 3] A stretched resin sheet was obtained in the same manner as in Example 1, except that 10% by mass of Pearl 3 was used instead of Pearl 1 as the pearl pigment for the pearly luster layer.

[0061] [Example 4] A stretched resin sheet was obtained in the same manner as in Example 1, except that 90% by mass of h-PP was used instead of r-PP as the polypropylene resin for the pearly luster layer.

[0062] [Comparative Example 1] After obtaining a laminate of the pearly luster layer / substrate layer (uniaxially stretched layer) / back surface layer, an (unstretched) resin sheet was obtained in the same manner as in Example 1, except that the 9-fold stretching using a tenter stretching machine was not performed.

[0063] Comparative Example 2 A stretched resin sheet was obtained in the same manner as in Example 1, except that 90% by mass of h-PP was used instead of r-PP as the polypropylene resin for the pearly luster layer, and 10% by mass of Pearl 3 was used instead of Pearl 1 as the pearl pigment for the pearly luster layer.

[0064] Comparative Example 3 A stretched resin sheet was obtained in the same manner as in Example 1, except that 70% by mass of h-PP was used instead of r-PP as the polypropylene resin for the pearly luster layer, and the content of Pearl 1, the pearl pigment for the pearly luster layer, was 30% by mass.

[0065] [Various measurements and evaluations] The stretched resin sheets of Examples 1 to 4 and Comparative Examples 1 to 3 obtained above were evaluated in various ways by the following methods.

[0066] <Layer thickness (μm)> The total thickness (μm) of the stretched resin sheet was measured in accordance with JIS K7130:1999 using a constant pressure thickness measuring instrument (manufactured by Teclock Corporation, trade name: PG-01J).

[0067] <Opacity (%)> In accordance with the method described in JIS-P-8149:2000, the luminous reflectance measured with a standard black board as the backing was divided by the intrinsic luminous reflectance measured with a standard white board as the backing, and the resulting value was used as the opacity, which was calculated as a percentage.

[0068] <Orientation angle of pearl pigment> A cross section of an arbitrary stretched resin sheet is viewed in a field of view of 5 μm × 10 μm (= 50 μm 2) and the orientation angle (°) was measured based on the observation photograph. The orientation angle of the pearl pigment was defined as the angle between the surface of the pearlescent layer and the plane along the major axis direction of the thin plate-like pearl pigment. The orientation angles of the pearl pigment in the observation photograph were confirmed, and the average value was defined as the orientation angle. In Table 2, the evaluation is shown as follows: an average orientation angle of less than 5° is marked "◎", an average of less than 8° is marked "◯", an average of 20° or less is marked "△", and an average of more than 20° is marked "X".

[0069] <Porosity of pearlescent layer (%)> To measure the porosity, the pearlescent layer was cut while being cooled so as not to crush the pores, to prepare a cross section (observation surface) in the thickness direction, which was then attached to an observation sample stage. Gold or the like was vapor-deposited on the observation surface, and the pores were observed using a scanning electron microscope (device name: SM-200, manufactured by TOPCON Corporation). The pores were observed at an arbitrary magnification (500 to 3000 times) that was easy to observe. The area where the pores were observed was captured as image data, and the image was processed using an image analyzer (device name: Luzex AP, manufactured by Nireco Corporation), and the area ratio of the pores was taken as the porosity (void ratio).

[0070] <Appearance evaluation of pearly luster layer> Table 2 shows the results of the appearance evaluation of the pearly luster layer according to the following criteria. 〇: Both vividness (strength of light reflection) and the degree of color change depending on the observation angle (color change depending on angle) were observed. △: Only one of the intensity of light reflection and color change depending on the angle was observed ×: Neither the intensity of light reflection nor the color change depending on the angle could be observed.

[0071] The evaluation results for the resin sheets of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 2. [Table 2]

[0072] The stretched resin sheets of Examples 1 to 4 all had an opacity of 30% or more and a porosity of the pearly luster layer of 7% or less. In the evaluation of the pearly luster layer, these stretched resin sheets all had good results in appearance evaluation.

[0073] In contrast, in the resin sheet of Comparative Example 1, which was not stretched, no so-called pearly feeling was observed in the appearance evaluation of the pearly luster layer. The stretched resin sheet of Comparative Example 2 had a high porosity of 17%, and in the appearance evaluation of the pearly luster layer, the pearly luster layer turned white and became opaque, and no pearly feeling was observed. The stretched resin sheet of Comparative Example 3 also had a high porosity of 24%, and in the appearance evaluation of the pearly luster layer, the pearly luster layer turned white and became opaque, and no pearly feeling was observed. [Explanation of symbols]

[0074] 10 Resin sheet 100 pearlescent layer 100A Pearlescent layer surface 110, 110B pearl pigment 200 Base material layer α orientation angle

Claims

1. A stretched resin sheet, The film has a base layer and a pearlescent layer containing a pearl pigment, Contains a polyolefin resin and has an opacity of 30% or more; The pearly luster layer is a stretched resin sheet having a porosity of 7% or less.

2. The stretched resin sheet according to claim 1 , wherein the melting point of the resin forming the pearly luster layer is lower than the melting point of the resin forming the base layer.

3. 3. The stretched resin sheet according to claim 1, wherein the orientation angle of the pearl pigment in the pearly luster layer is 20° or less.

4. Average particle diameter D of the pearl pigment ５０ 3. The stretched resin sheet according to claim 1, wherein the thickness is 40 μm or less.

5. 3. The stretched resin sheet according to claim 1, wherein the content of the pearl pigment is 5 to 20% by mass with respect to the pearlescent layer.

6. 3. The stretched resin sheet according to claim 1, wherein the pearly luster layer has a thickness of 10 [mu]m or less.

7. 3. The stretched resin sheet according to claim 1, wherein the total thickness is 40 to 150 μm.

8. The stretched resin sheet according to claim 1 or 2, wherein the base layer contains 10 to 50% by mass of a filler.

9. a lamination step of laminating a resin composition for forming the pearly luster layer onto a resin composition for forming the base layer to form a laminate; a stretching step of stretching the laminate, In the stretching step, the pearly luster layer is stretched to a stretching ratio of 3 times or more. A method for producing the stretched resin sheet according to claim 1 or 2.

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