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 pearl layer containing a pearl pigment and an adhesive layer, the stretched resin sheet containing a polyolefin-based resin and having an opacity of less than 30%, wherein the pearl layer has a porosity of 7% or less and contains 1 to 30 mass% of a pearl pigment. A preferable embodiment of the stretched resin sheet has an opacity of 15% or less.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 pearl layer containing a pearl pigment and an adhesive layer, Contains a polyolefin resin and has an opacity of less than 30%; The stretched resin sheet, wherein the pearl layer has a porosity of 7% or less and contains 1 to 30% by mass of a pearl pigment. [2] The stretched resin sheet according to [1], having an opacity of 15% or less. [3] The stretched resin sheet according to [1] or [2], wherein the adhesive layer contains a polyolefin-based elastomer. [4] The stretched resin sheet according to any one of [1] to [3], wherein the orientation angle of the pigment in the pearl layer is 20° or less. [5] Average particle size D of the pearl pigment 50 The stretched resin sheet according to any one of [1] to [4], wherein the thickness is 40 μm or less. [6] The stretched resin sheet according to any one of [1] to [5], wherein the stretched sheet has a total thickness of 40 to 150 μm. [7] The stretched resin sheet according to any one of [1] to [6], wherein the pearl layer has a thickness of 10 μm or less. [8] a lamination step of laminating a resin composition for forming the adhesive layer onto a resin composition for forming the pearl layer to form a laminate; a stretching step of stretching the laminate, In the stretching step, the pearl 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]. [9] A label comprising the 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 a heat-sealable label such as an in-mold label. [Brief explanation of the drawings]

[0010] [Figure 1] Schematic cross-sectional view showing an example of an oriented resin sheet in an embodiment. [Figure 2] Schematic cross-sectional view showing another example of an oriented resin sheet in an embodiment. [Figure 3] Schematic cross-sectional view of a stretched 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 have improved appearance design than a conventional resin sheet (which has a glossy printed layer formed by applying an ink containing a pearl pigment). As will be described in detail below, the stretched resin sheet of this embodiment is more likely to exhibit appearance design when attached to an adherend that is dark in color, such as black.

[0014] Specifically, the stretched resin sheet of this embodiment is 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 is a pigment that has a thin plate-like shape as described in detail below, and exhibits shine due to the interference action of light absorbed and scattered by the pearlescent pigment arranged in layers. In this regard, in a stretched resin sheet containing a polyolefin resin, the pearlescent pigment in the resin sheet is likely to exhibit shine due to the interference action of light (at an angle closer to equilibrium with respect to the surface of the resin sheet).

[0015] 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. Furthermore, polyethylene, which exhibits heat-sealability, belongs to the polyolefin-based resin family, and polyolefin resins are compatible with polyethylene. In contrast, resins such as acrylic and PET have poor heat-sealability and do not mix well with heat-sealable resins. For these reasons, resin sheets containing polyolefin-based resins are particularly suitable for use as heat-sealable labels, such as in-mold labels.

[0016] 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 layer) can be made thin 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 easily losing its pearly luster in appearance. 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 preferably contained in an amount of 60% by mass or more, and more preferably 70 to 95% by mass, based on the resin composition forming the stretched resin sheet.

[0017] <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 pearl layer 100 containing a pearl pigment 110 and an adhesive layer 200. The stretched resin sheet 10 may be a laminate of the pearl layer 100 and the adhesive layer 200, or may be one in which the pearl layer 100 is laminated on the adhesive layer 200. The stretched resin sheet 10 may have one or more layers other than the adhesive layer 200 and the pearl layer 100. For example, the stretched resin sheet 10 may have a base layer 300 between the adhesive layer 200 and the pearl layer 100 (see FIG. 2), or may have a surface layer on the surface of the pearl layer 100 opposite to the adhesive layer 200. In addition, the stretched resin sheet 10 may have a release layer on the surface of the adhesive layer 200 opposite to the pearl layer 100.

[0018] The pearl layer 100 contains a pearl pigment 110 and provides the stretched resin sheet 10 with an aesthetically pleasing appearance. 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 pearl layer 100 is a transparent layer. A surface layer can also be laminated on the outer surface of the pearl layer 100, and in this case, it is preferable that the surface layer is also transparent for the same reasons as above.

[0019] The stretched resin sheet contains a polyolefin-based resin, which is preferably contained in both the adhesive layer and the pearl 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.

[0020] 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.

[0021] 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. Furthermore, the stretched resin sheet of this embodiment is a translucent or nearly transparent sheet as described above, and contains less inorganic filler such as calcium carbonate than white sheets, etc. This is because the resin composition to be stretched contains inorganic filler in order to increase the whiteness of the white sheet. Thus, the stretched resin sheet of this embodiment is advantageous for recycling from the viewpoint of containing fewer impurities (inorganic fillers, etc.).

[0022] <Opacity> The stretched resin sheet has an opacity of less than 30%. The stretched resin sheet exhibits the appearance design (pearl gloss) due to the above-mentioned pearl layer, and has an opacity of a predetermined level or less. The appearance of the stretched resin sheet is observed as a translucent or nearly transparent sheet. The pearl gloss of the stretched resin sheet is difficult to observe when the sheet is translucent or nearly transparent alone, but when the stretched resin sheet is placed (attached) to an adherend, the pearl gloss is particularly easily exhibited. Since the pearl gloss is particularly easily exhibited when attached, it is preferable that the adherend to which the stretched resin sheet is attached has a dark hue (e.g., black).

[0023] The opacity of the stretched resin sheet is preferably 20% or less, more preferably 15% or less, from the viewpoint of easily exhibiting a pearly luster when attached to an adherend. The lower limit of the opacity is not particularly limited and may be more than 0%. 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.

[0024] The stretched resin sheet of this embodiment has an opacity of less than 30%, and the pearlescent layer has a porosity of 7% or less as described below, so that it tends to have high transparency. From the viewpoint of utilizing this transparency, when the stretched resin sheet has any additional layer other than the pearlescent layer and the adhesive layer, it is preferable that the additional layer also has a predetermined opacity or less.

[0025] <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 pearl 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 stretched resin sheet is more preferably 120 μm or less, and even more preferably 100 μm or less.

[0026] (pearl layer) The pearl layer containing the pearl pigment will now be described. The pearl layer has a porosity of 7% or less and contains 1 to 30% by mass of pearl pigment. Thus, the pearl layer in the stretched sheet of this embodiment contains a predetermined amount of pearl pigment and has a porosity of a predetermined level or less. The porosity of the pearl 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 pearl layer with such a low porosity can be observed as a transparent or nearly transparent layer. The lower limit of the porosity of the pearl 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.

[0027] <Pearl pigment> As the pearl pigment, thin plate-like particles such as mica having a coating layer made of a high refractive index material such as titanium oxide can be used. The thin plate-like particles may be aluminum flakes, alumina flakes, silica flakes, or the like, in addition to mica. The metal oxide coating the surface may be titanium oxide, cobalt oxide, cobalt titanate, or the like. Commercially available pearl pigments may be used, and the types that can be used are not particularly limited. For example, pearl pigments whose interference color is adjusted by the thickness of the coating layer are known (white pearl pigments, interference pearl pigments, colored pearl pigments, etc.). While any pearl pigment may be used in this embodiment, mica is preferred, and mica coated with titanium oxide is particularly preferred. Furthermore, artificially produced mica is preferred because it contains fewer impurities and can more effectively achieve a pearlescent effect.

[0028] The pearl pigment content of the pearl layer is 1 to 30% by mass. From the viewpoint of easily improving the appearance design, it is preferably 1 to 12% by mass relative to the pearl layer. The pearl pigment content is more preferably 3% by mass or more, and even more preferably 5% by mass or more. Furthermore, from the viewpoint of easily maintaining the strength of the resin stretched sheet and minimizing the amount of pearl pigment used, the pearl pigment content is more preferably 20% by mass or less, and even more preferably 15% by mass or less. As described above, the stretched resin sheet can be made to easily exhibit pearly luster depending on the hue of the adherend, and therefore the content of the pearl pigment can be reduced depending on the application.

[0029] 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.).

[0030] 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, whereas the thickness is preferably 0.01 μm or more, from the viewpoint of easily improving the strength and production efficiency of the pearl pigment.

[0031] <<Orientation angle of pearl pigment>> The orientation angle of the pearl pigment in the pearl layer is preferably 20° or less. Here, the orientation angle of the pearl pigment refers to the average angle between the surface of the pearl layer and a plane along the major axis direction of the pearl pigment contained in the pearl layer in the pearl 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°.

[0032] The orientation angle of the pearl pigment will be specifically described with reference to Fig. 3. Fig. 3 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. 3, the orientation angle α of the pearl pigment 110 can be measured as the angle α formed between the surface 100A of the pearl 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.

[0033] <Resin that forms the pearl layer> The resin forming the pearl layer preferably contains the above-mentioned polyolefin resin. The resin forming the pearl layer and the resin forming the adhesive layer may be the same, but are preferably different. From the viewpoint of easily reducing the porosity of the pearl layer, it is preferable that the melting point of the resin forming the pearl layer is lower than the melting point of the resin forming the adhesive layer. This is because, since the pearl layer contains a pearl pigment, voids centered on the pearl pigment tend to be formed in the pearl layer by stretching, and the low melting point of the resin forming the pearl layer as described above makes it easier to reduce the formation of voids originating from the pearl pigment. By forming the pearl 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.

[0034] From the viewpoint of making it less likely that voids will form, the melting point of the resin that forms the pearl layer is preferably at least 10° C. lower than the melting point of the resin that forms the adhesive layer, and even more preferably at least 20° C. From the viewpoint of formability, the difference between the melting points of the resin that forms the pearl layer and the resin that forms the adhesive layer is preferably no more than 50° C., and even more preferably no more than 40° C. The resin forming the pearl layer is preferably random polypropylene, and the pearl layer preferably contains random polypropylene. The resin component in the pearl layer preferably contains random polypropylene in an amount of 50% by mass or more, and even more preferably 70% by mass or more. When the stretched resin sheet has an optional base layer, it is preferable that the melting point of the resin forming the pearl layer is lower than the melting point of the resin forming the base layer, similar to the adhesive layer. The polyolefin resin is preferably contained in an amount of 80% by mass or more, and more preferably 88 to 99% by mass, based on the resin composition forming the pearl layer.

[0035] <Thickness of the pearl layer> The thickness of the pearl layer is preferably 20 μm or less, 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 pearl 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 pearl layer is preferably 3 μm or more, and more preferably 5 μm or more.

[0036] (adhesive layer) The adhesive layer functions to adhere the stretched resin sheet to an adherend. The adhesive layer is not particularly limited as long as it has adhesiveness, pressure-sensitive adhesiveness, heat-sealability, etc. Since the adhesive layer is suitably used in the stretching step, it is preferable that the adhesive layer has heat-sealability.

[0037] The resin forming the adhesive layer preferably contains a polyolefin-based resin. The polyolefin-based resin for the adhesive layer preferably contains an olefin-based elastomer, such as a polypropylene-based elastomer. Preferred examples of the polyolefin-based resin for the adhesive layer include low- or medium-density polyethylene with a density of 0.900 to 0.935 g / cm3, linear low-density polyethylene with a density of 0.880 to 0.940 g / cm3, metallocene-based polyethylene produced using a metallocene catalyst, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid alkyl ester copolymer, ethylene-methacrylic acid alkyl ester copolymer with an alkyl group having 1 to 8 carbon atoms, and ethylene-methacrylic acid copolymers with a melting point of 60 to 130°C, such as metal salts of ethylene-methacrylic acid copolymers, such as Zn, Al, Li, K, and Na. In particular, from the viewpoint of compatibility with polyolefins, it is more preferable that the resin forming the adhesive layer contains 60 to 90 mass % of polypropylene elastomer and 10 to 40 mass % of low-density or medium-density polyethylene.

[0038] To facilitate control of adhesive strength, the adhesive layer may contain a tackifier or plasticizer. Examples of tackifiers include hydrogenated petroleum resins, aromatic hydrocarbon resins, and aliphatic hydrocarbon resins. Examples of hydrogenated petroleum resins include partially hydrogenated petroleum resins. Examples of aromatic hydrocarbon resins include terpene resins, rosin resins, and styrene resins. One type of tackifier or plasticizer may be used alone, or two or more types may be used in combination. However, from the viewpoint of preventing peeling of the adhesive layer during normal use, it is preferable that the tackifier or plasticizer is highly compatible with the thermoplastic resin used in the adhesive layer.

[0039] The thickness of the adhesive layer is preferably 0.5 μm or more, more preferably 0.7 μm or more, and even more preferably 1 μm or more from the viewpoint of enhancing adhesiveness, and is preferably 10 μm or less, more preferably 6 μm or less from the viewpoint of suppressing cohesive failure within the adhesive layer.

[0040] (base material layer) The stretched resin sheet preferably has a base layer. The base layer can improve stiffness and moldability. The resin forming the base layer is not particularly limited as long as it can laminate the pearl layer. For example, the resin forming the base layer preferably contains the above-mentioned polyolefin resin. As described above, the base layer, like the adhesive layer, is preferably formed from a resin with a lower melting point than the resin forming the pearl layer. For this reason, the resin forming the base layer is preferably homopolypropylene, and the base layer preferably contains homopolypropylene, more preferably 50% by mass or more, and even more preferably 80% by mass or more of the resin components in the base layer being homopolypropylene.

[0041] 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.

[0042] (Applications of stretched resin sheets) The stretched resin sheet of the present embodiment can be used for various printing papers, adhesive labels, etc., and is particularly suitable for use as a label. As the label, it can be applied to various labels such as an in-mold label and an adhesive label, and is particularly suitable as an in-mold label. When the stretched resin sheet of this embodiment is adhered to an adherend, it exhibits a pearly luster that corresponds to the hue of the adherend. Specifically, as described above, when the sheet is adhered to an adherend with a dark hue, such as black, it is particularly likely to exhibit a pearly luster. Since the degree of pearly luster varies depending on the hue of the adherend, it is also preferable to select a suitable hue of the adherend depending on the desired pearly luster. For example, when the hue of the adherend is a lighter gray than black, it is likely to exhibit a modest pearly luster.

[0043] (Method of manufacturing stretched resin sheet) The stretched resin sheet of this embodiment is a lamination step of laminating a resin composition for forming the adhesive layer onto a resin composition for forming the pearl layer to form a laminate; a stretching step of stretching the laminate, The stretching step can be carried out by a method in which the pearl layer is stretched to a stretching ratio of 3 times or more. The method for producing a stretched resin sheet according to this embodiment will be described in detail below.

[0044] <Lamination process> The manufacturing method of this embodiment includes a lamination step of laminating a resin composition that forms an adhesive layer onto a resin composition that forms a pearl layer to form a laminate.

[0045] 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.

[0046] <Stretching process> The stretching step is a step of stretching the laminate. In the stretching step, the pearl 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 pearl layer to a stretching ratio of 3 or more based on the pearl layer. This is because if the stretching ratio of the pearl layer is 3 or more, the orientation angle of the pearl pigment tends to be low, and pearl luster tends to be exhibited. The stretching ratio of the pearl layer is preferably 4 times or more, and more preferably 8 times or more, from the viewpoint of easily setting the orientation angle of the pearl pigment to 20° or less.From the viewpoint of maintaining strength, the stretching ratio of the pearl layer is preferably 40 times or less, and more preferably 20 times or less.

[0047] In the stretching step, the stretching ratio of the laminate may be appropriately determined so that the stretching ratio of the pearl 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, and 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.

[0048] 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.

[0049] The stretching temperature when stretching may be set as appropriate. When the melting point of the resin forming the pearl layer is set lower than the melting point of the resin forming the adhesive layer (and any base layer), the stretching temperature is preferably set in accordance with the melting point of the resin forming the adhesive layer (and any base layer). This is to stretch the adhesive layer (and any base 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 adhesive layer. Specifically, the stretching temperature is preferably 2 to 60°C lower than the melting point of the resin forming the adhesive layer. From the viewpoints of easily increasing the porosity of the adhesive 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 adhesive 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]

[0050] 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.

[0051] (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.

[0052] [Table 1]

[0053] [Example 1] The resin composition forming the base layer was prepared by melt-kneading 100% by mass of h-PP, a polypropylene resin, 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 reheated to 150°C and then 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).

[0054] Next, a resin composition for forming the pearl 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.

[0055] Furthermore, a resin composition for forming the adhesive layer (heat seal layer) was prepared by melt-kneading 70% by mass of a PP-based elastomer, which is a polypropylene resin, and 30% by mass of LD-PE, a polyethylene resin, 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, opposite the pearl layer.

[0056] The obtained laminate was heated to 150°C in 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 pearl layer (uniaxially stretched layer), a base layer (biaxially stretched layer), and an adhesive layer (uniaxially stretched layer).

[0057] The thickness of the obtained stretched resin film was 80 μm, of which the pearl layer was 5 μm thick and the adhesive layer was 5 μm thick. The method for measuring the thickness of the stretched resin sheet will be described later.

[0058] [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.

[0059] [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 pearl layer.

[0060] [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 pearl layer.

[0061] [Comparative Example 1] After obtaining a laminate of pearl layer / substrate layer (uniaxially stretched layer) / adhesive layer, an (unstretched) resin sheet was obtained in the same manner as in Example 1, except that the laminate was not stretched four times using a tenter stretching machine.

[0062] 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 pearl layer, and 10% by mass of Pearl 3 was used instead of Pearl 1 as the pearl pigment for the pearl layer.

[0063] 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 pearl layer, and the content of Pearl 1, the pearl pigment for the pearl layer, was 30% by mass.

[0064] [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.

[0065] <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).

[0066] <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.

[0067] <Orientation angle of pearl pigment> An arbitrary cross section of the stretched resin sheet was photographed using an SEM with a field of view of 10 μm x 10 μm, 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 pearl layer and the plane along the major axis direction of the thin plate-like pearl pigment. The orientation angle was confirmed for the pearl pigment in the observation photograph, and the average value was defined as the orientation angle. In Table 2, the evaluation is shown with the following markings: an average orientation angle of less than 5° is "◎", an average of less than 8° is "◯", an average of less than 10° is "△", and an average of 10° or more is "X".

[0068] <Porosity of pearl 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).

[0069] <Evaluation of the appearance of the pearl layer> Table 2 shows the results of the appearance evaluation of the pearl layer according to the following criteria. (white background, black background) The stretched resin sheets of each Example and Comparative Example were placed on white paper and the visual glossiness was evaluated according to the following criteria: The stretched resin sheets of each Example and Comparative Example were placed on black paper and the visual glossiness was also evaluated according to the following criteria. 1: A slight pearly effect can be seen 2: A slight pearly finish can be seen 3: Pearly finish can be seen 4: A slightly strong pearly effect can be seen 5: A strong pearly finish can be seen 6: A very strong pearly finish can be seen

[0070] (Appearance rating Δ) From the results of the appearance evaluation on the white background and the black background, an appearance evaluation Δ (delta) was calculated, and the calculated value was comprehensively evaluated based on the following criteria: The larger the appearance evaluation Δ, the more clearly the difference in pearly gloss before and after placing (affixing) the stretched resin sheet to the adherend is likely to be exhibited. ◎: Appearance evaluation Δ is 4 or more ○: Appearance rating Δ is 3 or more ×: Appearance evaluation Δ is 2 or less

[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 less than 30% and a porosity of the pearl layer of 7% or less. In the evaluation of the pearl layer of these stretched resin sheets, the improvement in appearance evaluation against a black background relative to the appearance evaluation against a white background (appearance evaluation Δ) was 3 or more.

[0073] In contrast, the resin sheet of Comparative Example 1, which was not stretched, had an appearance rating Δ of 3 for the pearl layer, and the pearly texture was noticeable against a black background. The stretched resin sheet of Comparative Example 2 had an appearance rating Δ of 2, and the pearly texture was noticeable against a black background. The stretched resin sheet of Comparative Example 3 had an appearance rating Δ of 1, and the pearly texture was slightly noticeable against a black background. [Explanation of symbols]

[0074] 10 Resin sheet 100 pearl layers 100A Pearl layer surface 110, 110B pearl pigment 200 Adhesive layer 300 Base material layer α orientation angle

Claims

1. A stretched resin sheet, The film has a pearl layer containing a pearl pigment and an adhesive layer, The film contains a polyolefin resin and has an opacity of less than 30%; the pearl layer has a porosity of 7% or less and contains 1 to 30% by mass of a pearl pigment; Stretched resin sheet.

2. 2. The stretched resin sheet according to claim 1, which has an opacity of 15% or less.

3. The stretched resin sheet according to claim 1 or 2, wherein the adhesive layer contains a polyolefin-based elastomer.

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

5. 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.

6. 3. The stretched resin sheet according to claim 1, wherein the stretched sheet has a total thickness of 40 to 150 μm.

7. 3. The stretched resin sheet according to claim 1, wherein the pearl layer has a thickness of 10 μm or less.

8. a lamination step of laminating a resin composition for forming the adhesive layer onto a resin composition for forming the pearl layer to form a laminate; a stretching step of stretching the laminate, In the stretching step, the pearl 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.

9. A label comprising the stretched resin sheet according to claim 1 or 2.

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