Stretched resin sheet and method for manufacturing a 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 manufacturing the stretched resin sheet.

Background Art

[0002] There has been proposed and put into practical use a resin sheet (synthetic paper) in which a resin composition containing a resin and a filler is stretched to form a porous layer and made into a sheet shape. These resin sheets are useful as materials for printing paper, labels, and the like.

[0003] There are cases where resin sheets are required to have a decorative property for improving aesthetics according to various applications and the like. As such a resin sheet having a designed appearance, for example, a resin sheet using a pearl pigment, that is, a pigment whose color changes depending on the viewing angle due to the interference action of light, can be mentioned. Patent Document 1 discloses a resin material having a gloss printing layer formed by applying an ink containing a pearl pigment and imparting a decorative property.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Regarding a resin sheet using a pearl pigment, there are cases where it is desired to further enhance the appearance design properties such as the degree of color change and the intensity of gloss depending on the viewing angle, for example, when it is desired to give a more high-class feeling. Also, when recycling a resin sheet in consideration of the environment, it is required that a resin sheet containing a pearl pigment be more easily recyclable.

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

[0007] As a result of diligent research to solve the above-mentioned problems, the inventors have come up with the present invention having the following gist.

[0008] In other words, the present invention is as follows. [1] A stretched resin sheet, It has a pearl layer containing pearl pigment and an adhesive layer, It contains a polyolefin resin and has an opacity of less than 30%. A stretched resin sheet wherein the pearl layer has a porosity of 7% or less and contains 1 to 30% by mass of pearl pigment. [2] The stretched resin sheet described in [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 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] The average particle size D of the pearl pigment 50 A stretched resin sheet as described in any 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 overall thickness of the stretched sheet is 40 to 150 μm. [7] The stretched resin sheet according to any one of [1] to [6], wherein the thickness of the pearl layer is 10 μm or less. [8] A lamination step of laminating the resin composition that forms the pearl layer with the resin composition that forms the adhesive layer to form a laminate, The process includes a stretching step for stretching the laminate, The stretching step involves stretching the pearl layer to a stretching ratio of 3 times or more. A method for manufacturing a stretched resin sheet as described in any of [1] to [7]. A label containing a stretched resin sheet as described in any of [9] [1] to [7]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a resin sheet using pearl pigment that has improved appearance and design compared to conventional resin sheets. Furthermore, the present invention provides a resin sheet that is easy to recycle while using pearl pigment. 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 drawing]

[0010] [Figure 1] A schematic cross-sectional view showing an example of a stretched resin sheet in an embodiment. [Figure 2] Schematic cross-sectional view showing another example of a stretched resin sheet in the embodiment. [Figure 3] Schematic cross-sectional view of a stretched resin sheet showing the orientation angle of pearl pigment in an embodiment. [Modes for carrying out 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 invention of this embodiment relates to a "stretched resin sheet" containing a polyolefin resin, that is, a stretched resin sheet.

[0013] The stretched resin sheet containing polyolefin resin of this embodiment is more likely to improve appearance and design than conventional resin sheets (which form a glossy printed layer by applying an ink containing pearl pigment). As will be described in detail below, the stretched resin sheet of this embodiment exhibits particularly good appearance and design when attached to a dark-colored substrate such as black.

[0014] Specifically, the stretched resin sheet of this embodiment is likely to enhance the appearance design property, that is, the difference in angular gloss reflectance (so-called pearl feeling) in which the color changes depending on the viewing angle, the intensity of shine (glossiness), and the like. Here, the pearl pigment is a pigment that has a shape on a thin plate as described in detail below and exhibits shine due to the interference effect of light absorbed and scattered by the pearl pigments arranged in layers. In this regard, in a stretched resin sheet containing a polyolefin resin, it is easy to arrange the pearl pigments in the resin sheet at an angle that is more likely to exhibit shine due to the interference effect of light (an angle closer to equilibrium with respect to the resin sheet surface).

[0015] A resin sheet containing a polyolefin resin can reduce the amount of pearl pigment used by giving functions to each layer as a laminate. That is, by separately providing a pearl gloss layer responsible for the so-called pearl feeling from other layers, the content of the pearl pigment in the entire laminate can be reduced. For this reason, when recycling the resin sheet, the difficulty of recycling due to the pearl pigment can be reduced, the recyclability can be improved, and the cost of the resin sheet can also be reduced. In addition, a resin sheet containing a polyolefin resin is more likely to have firmness (easier to enhance elasticity) than a resin sheet using other resins such as an acrylic resin or a polyester resin. For this reason, for example, when using the resin sheet as a label, it is easy to adhere following the curved surface even if the adherent surface is a curved surface. Moreover, since polyethylene exhibiting heat sealability belongs to the polyolefin resin, the polyolefin resin has good compatibility with polyethylene. In contrast, resins such as acrylic and PET have little heat sealability and also have poor compatibility with heat sealable resins. From the above, a resin sheet containing a polyolefin resin is particularly suitable for use as a heat sealable label such as an in-mold label.

[0016] Furthermore, using stretched resin sheets containing polyolefin resin makes it easier to reduce the pearl pigment content and the thickness of the pearl pigment layer (pearl layer) while maintaining the aforementioned appearance and design. Therefore, when recycling stretched resin sheets, the amount of pearl pigment, which is considered an impurity in the recovered material, can be reduced, making it easier to improve the purity of the recovered material. In addition, during the mixing process in recycling, the pearl pigment is easily subjected to stress acting on the recovered material and tends to break down into fine fragments (it is less likely to be flat), and the pearl luster of the appearance is also easily lost. Therefore, it tends to have an appearance similar to that of ordinary resin without pearl pigment, and is excellent for recycling. The polyolefin resin is preferably present in an amount of 60% by mass or more, and more preferably in an amount of 70 to 95% by mass, relative to the resin composition that forms the stretched resin sheet.

[0017] <Structure of stretched resin sheet> An example of the structure of a stretched resin sheet will be explained with reference to Figure 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 the pearl layer 100 may be laminated to 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 Figure 2), and may have a surface layer on the side of the pearl layer 100 opposite to the adhesive layer 200. Alternatively, the adhesive layer 200 may have a release layer on the side of the adhesive layer 200 opposite to the pearl layer 100.

[0018] The pearl layer 100 contains pearl pigment 110 and imparts an aesthetic design to the stretched resin sheet 10. Therefore, when the stretched resin sheet 10 is used for various applications, it is preferable to arrange the pearl pigment 110 so that it is visible from the outside (outer surface). For this reason, it is preferable that the pearl layer 100 is a transparent layer. In addition, a surface layer can be laminated on the outer surface of the pearl layer 100, and in that case, for the same reasons as above, it is preferable that the surface layer is also transparent.

[0019] The stretched resin sheet contains a polyolefin resin. Preferably, the polyolefin resin is included in both the adhesive layer and the pearl layer. As for polyolefin resins, polypropylene resins are preferred from the viewpoint of moldability. Examples of polypropylene resins include isotactic homopolypropylene and syndiotactic homopolypropylene obtained by homopolymerizing propylene, as well as polypropylene copolymers with various stereoregularities obtained by copolymerizing propylene with α-olefins such as ethylene, 1-butene, and 1-pentene. The propylene copolymer may be a binary system or a multi-component system of three or more components, and may be a random copolymer or a block copolymer.

[0020] A stretched resin sheet is, as the name suggests, a sheet that has been stretched. This can be confirmed, for example, by examining the sheet's storage modulus. Specifically, the storage modulus of the resin sheet is measured in both the MD (longitudinal) and TD (transverse) directions. For example, in a stretched resin sheet containing polypropylene, if the storage modulus in the MD direction (longitudinal direction, machine direction, the direction in which the resin flows) or the TD direction (transverse direction, the direction perpendicular to the longitudinal direction) exceeds 1500 MPa, it can be confirmed that the sheet is stretched. (A value of 2500 MPa or higher indicates a stretching ratio of 4 times or more, and a value of 5000 MPa or higher indicates a stretching ratio of 9 times or more.) The storage modulus described above can be measured by cutting the film into a test piece measuring 30 mm in length and 15 mm in width, and using a solid viscoelasticity measuring device (T.A. Instruments Japan: RSA-III). The measurement conditions are a chuck distance of 20 mm, a measurement frequency of 10 Hz, a strain of 0.1%, a heating rate of 10 degrees Celsius / minute, and tensile mode, which can be set to 23°C.

[0021] The stretched resin sheet of this embodiment is easier to recycle than conventional resin sheets that form a glossy printed layer by applying an ink containing pearl pigment, because it is formed by stretching. This is because conventional resin sheets use a binder resin to create an ink containing pearl pigment. General binder resins have low heat resistance, and therefore, thermal degradation such as discoloration can occur due to the heat history during recycling. In contrast, since the stretched resin sheet can be formed without using a binder resin, it is easier to suppress deformation due to thermal history than conventional resin sheets formed using ink. Furthermore, as described above, the stretched resin sheet of this embodiment is semi-transparent or nearly transparent, and contains less inorganic filler such as calcium carbonate than white sheets. In the case of white sheets, inorganic fillers are included in the stretched resin composition in order to increase the whiteness. Thus, the stretched resin sheet of this embodiment is advantageous for recycling from the viewpoint of having 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 and design properties (pearlescent luster) due to the pearlescent layer described above, while maintaining an opacity below a predetermined level. The appearance of the stretched resin sheet is observed as a semi-transparent or nearly transparent sheet. The pearlescent luster of the stretched resin sheet is difficult to observe when it is a semi-transparent or nearly transparent sheet alone, but it is particularly easily exhibited when the stretched resin sheet is placed (attached) to an substrate. Because the pearlescent luster is particularly easily exhibited when attached, it is preferable that the substrate to which the stretched resin sheet is attached has a dark hue (such as black).

[0023] The opacity of the stretched resin sheet is preferably 20% or less, and more preferably 15% or less, from the viewpoint of easily exhibiting pearlescent luster when attached to a substrate. The lower limit of opacity is not particularly limited and may be greater than 0%. Opacity can be measured in accordance with the "Paper and cardboard - Opacity test method (paper backing) - Diffuse illumination method" specified in JIS P8149:2000.

[0024] The stretched resin sheet of this embodiment has an opacity of less than 30%, and the pearl layer has a porosity of 7% or less, as described later, making it easy to achieve high transparency. From the viewpoint of utilizing this transparency, if the stretched resin sheet has additional layers other than the pearl gloss layer and the adhesive layer, it is preferable that any additional layers also have an opacity of less than or equal to a predetermined level.

[0025] <Thickness of stretched resin sheet> From the viewpoint of ease of manufacturing, the overall thickness of the stretched resin sheet, including each layer such as the base layer and pearl layer, is preferably 40 to 150 μm. From the viewpoint of maintaining the strength of the stretched resin sheet, the overall 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 ease of handling, the overall thickness of the stretched resin sheet is more preferably 120 μm or less, and even more preferably 100 μm or less.

[0026] (Pearl layer) This section describes the pearl layer containing pearl pigments. 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 while having 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 improving the appearance and design. A pearl layer with such 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 detection limit). The porosity can be determined from the ratio of the area occupied by voids in a certain region of the cross-section of the sample observed with an electron microscope.

[0027] <Pearl pigment> As the pearl pigment, thin, plate-like particles such as mica can be used, which have a coating layer made of a high refractive index material such as titanium dioxide. The thin, plate-like particles may be aluminum flakes, alumina flakes, silica flakes, etc., in addition to mica, and the metal oxide coating the surface may be cobalt oxide, cobalt titanate, etc., in addition to titanium dioxide. Commercially available pearl pigments may be used, and the types that can be used are not particularly limited. For example, pearl pigments are known to have their interference colors adjusted by the thickness of the coating layer, etc. (white pearl pigments, interference pearl pigments, colored pearl pigments, etc.). In this embodiment, any pearl pigment may be used, but mica is preferred, and mica coated with titanium dioxide is particularly preferred. Furthermore, artificially produced mica is preferred from the viewpoint of having fewer impurities and being able to effectively obtain 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 and design, it is preferable that it be 1 to 12% by mass relative to the pearl layer. A pearl pigment content of 3% by mass or more is more preferable, and 5% by mass or more is even more preferable. Furthermore, stretched resin From the viewpoint of maintaining the strength of the 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 mentioned above, stretched resin Since the sheet can easily exhibit pearlescent luster depending on the hue of the substrate, the amount of pearlescent pigment can be reduced depending on the application.

[0029] Average particle size D of pearl pigments 50 The particle size is preferably 40 μm or less. stretched resin From the perspective of maintaining the moldability of the sheet, the average particle size D of the pearl pigment 50 The average particle size D is more preferably 30 μm or less, even more preferably 20 μm or less, and particularly preferably 10 μm or less. From the viewpoint of easily increasing the intensity of the pearl pigment's luster, 50 The particle size is preferably 5 μm or larger, and more preferably 8 μm or larger. The average particle size (D50) is the particle size that accounts for 50% of the cumulative particle size distribution measured by a particle measuring device, such as the laser diffraction particle measuring device "Microtrac" (manufactured by Nikkiso Co., Ltd., product name).

[0030] When the pearl pigment is in the form of thin, plate-like particles, its thickness is preferably 5 μm or less, and more preferably 1 μm or less, from the viewpoint of easily achieving a good orientation angle of the pearl pigment, as described later. On the other hand, from the viewpoint of easily improving the strength and manufacturing efficiency of the pearl pigment, a thickness of 0.01 μm or more is preferable.

[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 value of the angle between the surface of the pearl layer and the plane along the major axis direction of the pearl pigment contained in the pearl layer in the stretched resin sheet. From the viewpoint of enhancing the aesthetic appearance, 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 greater than 0°.

[0032] The orientation angle of the pearl pigment will be explained in detail with reference to Figure 3. Figure 3 is a schematic cross-sectional view of the stretched resin sheet 10 when observed in an arbitrary cross-section. When measuring the orientation angle of the pearl pigment, SEM observation images of an arbitrary cross-section of the stretched resin sheet 10 can be used. In Figure 3, the orientation angle α of the pearl pigment 110 can be measured as the angle α 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 angle α of the pigment measured as described above.

[0033] <Pearl-forming resin> The resin that forms the pearl layer preferably contains the polyolefin resin described above. The resin forming the pearl layer and the resin forming the adhesive layer may be the same, but it is preferable that they be 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 that of the resin forming the adhesive layer. This is because, since the pearl layer contains pearl pigment, stretching tends to easily form pores in the pearl layer with the pearl pigment as the nucleation site. As mentioned above, a lower melting point for the resin forming the pearl layer makes it easier to reduce the formation of pores originating from the pearl pigment. By forming a pearl layer with the low-melting-point resin described above, the stretched resin sheet can be used as a pearl pigment, even if it has a relatively large average particle size within the above range.

[0034] From the viewpoint of minimizing the formation of voids, the melting point of the resin forming the pearl layer is more preferably 10°C or more lower than the melting point of the resin forming the adhesive layer, and even more preferably 20°C or more lower. From the viewpoint of moldability, the difference between the melting point of the resin forming the pearl layer and the melting point of the resin forming the adhesive layer is more preferably 50°C or less, and even more preferably 40°C or less. As the resin forming the pearl layer, random polypropylene is preferred, the pearl layer preferably contains random polypropylene, more preferably contains 50% by mass or more of random polypropylene in the resin components of the pearl layer, and even more preferably contains 70% by mass or more. Furthermore, if the stretched resin sheet has an arbitrary 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 described above. The polyolefin resin is preferably present in an amount of 80% by mass or more, and more preferably in an amount of 88 to 99% by mass, relative to the resin composition that forms the pearl layer.

[0035] <Thickness of the pearl layer> The thickness of the pearl layer is preferably 20 μm or less. This is because within this range, the stretched resin sheet can be made to have both aesthetic appeal and good recyclability. From the viewpoint of moldability, 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 pearl 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 the substrate. The adhesive layer only needs to have adhesive properties, tackiness, heat sealability, etc., and is not particularly limited. Since it is suitably used in the stretching process, it is preferable that the adhesive layer is a layer with heat sealability.

[0037] The resin forming the adhesive layer preferably contains a polyolefin resin. The polyolefin resin of the adhesive layer preferably contains an olefin elastomer, for example, a polypropylene elastomer. Furthermore, as the polyolefin resin of the adhesive layer, preferred examples include low-density 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 polyethylene produced using a metallocene catalyst, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-alkyl acrylate copolymer, ethylene-alkyl methacrylate copolymer with 1 to 8 carbon atoms in the alkyl group, and ethylene resins with a melting point of 60 to 130°C, such as metal salts of Zn, Al, Li, K, Na, etc. of ethylene-methacrylic acid copolymer. In particular, the resin forming the adhesive layer is more preferably composed of 60-90% by mass of polypropylene elastomer and 10-40% of low-density or medium-density polyethylene, from the viewpoint of compatibility with polyolefins.

[0038] From the viewpoint of facilitating control of adhesive strength, the adhesive layer may contain a tackifier or a plasticizer. Examples of tackifiers include hydrogenated petroleum resins, aromatic hydrocarbon resins, or aliphatic hydrocarbon resins. Examples of hydrogenated petroleum resins include partially hydrogenated petroleum resins. Examples of aromatic hydrocarbon resins include terpene resins, rosin resins, or styrene resins. The tackifier or plasticizer may be used alone or in combination of two or more, but from the viewpoint of suppressing peeling of the adhesive layer during normal use, it is preferable that it has high compatibility with the thermoplastic resin used in the adhesive layer.

[0039] From the viewpoint of improving adhesion, 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 suppressing cohesive failure within the adhesive layer, the thickness is preferably 10 μm or less, and more preferably 6 μm or less.

[0040] (base material layer) The stretched resin sheet preferably has a base layer. Having a 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 polyolefin resin described above. 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, the base layer preferably contains homopolypropylene, more preferably contains 50% by mass or more homopolypropylene in the resin components of the base layer, and even more preferably contains 80% by mass or more.

[0041] The thickness of the base layer is preferably 30 to 130 μm. Within this range, it is easy to keep it within the preferred thickness range of the stretched resin sheet described above. From the viewpoint of ease of handling, the thickness of the base layer is more preferably 100 μm or less, and even more preferably 80 μm or less. From the viewpoint of moldability, the thickness of the base 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 this embodiment can be used for various printing papers, adhesive labels, etc., and is particularly suitable for use as a label. As a label, it can be applied to various types of labels such as in-mold labels and adhesive labels, and is particularly suitable for use as an in-mold label. When the stretched resin sheet of this embodiment is adhered to an adherend, a pearlescent luster is exhibited according to the hue of the adherend. Specifically, as described above, when adhered to an adherend with a dark hue, such as black, the pearlescent luster is particularly easily exhibited. Since the degree of pearlescent luster differs depending on the hue of the adherend, it is also preferable to select a suitable hue of the adherend according to the desired pearlescent luster. For example, if the hue of the adherend is a lighter gray than black, a more subtle pearlescent luster is likely to be exhibited.

[0043] (Method for manufacturing stretched resin sheets) The stretched resin sheet of this embodiment is A lamination step of laminating the resin composition that forms the pearl layer with the resin composition that forms the adhesive layer to form a laminate, The process includes a stretching step for stretching the laminate, The stretching process can be carried out by a method of stretching the pearl layer to a stretching ratio of 3 times or more. The method for manufacturing the stretched resin sheet of this embodiment will be described in detail below.

[0044] <Lamination process> The manufacturing method of this embodiment includes a lamination step in which a resin composition that forms an adhesive layer is laminated 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, if necessary, further contain additives such as pigments, heat stabilizers (antioxidants), light stabilizers, dispersants, lubricants, or nucleating agents in addition to fillers.

[0046] <Stretching process> The stretching process is a process of stretching the laminate. In the stretching process, the pearl layer is stretched to a stretching ratio of 3 times or more. The stretching ratio may differ for each layer of the stretched resin sheet, but as described above, it is preferable to stretch it so that the stretching ratio is 3 times or more when the pearl layer is used as the reference. This is because when the stretching ratio of the pearl layer is 3 times or more, the orientation angle of the pearl pigment tends to be low, and it tends to exhibit pearl luster. From the viewpoint of making it easier to set the orientation angle of the pearl pigment to 20° or less, the stretching ratio of the pearl layer is more preferably 4 times or more, and even more preferably 8 times or more. From the viewpoint of maintaining strength, the stretching ratio of the pearl layer is preferably 40 times or less, and even more preferably 20 times or less.

[0047] In the stretching process, the stretching ratio of the laminate may be appropriately determined so that the stretching ratio of the pearl layer falls within the above preferred range. For example, when stretching the laminate in one direction, the stretching ratio is usually about 1.2 times or more, preferably 2 times or more, while it is usually 12 times or less, preferably 10 times or less. In the case of biaxial stretching, the stretching ratio is usually 1.5 times or more in terms of surface stretching ratio (area stretching ratio), preferably 8 times or more, and more preferably 15 times or more. On the other hand, from the viewpoint of strength and manufacturing difficulty, the surface stretching ratio is usually 40 times or less, preferably 20 times or less.

[0048] The stretching method in the stretching process is not particularly limited. Examples include longitudinal stretching using the peripheral speed difference of a roll group, transverse stretching using a tenter oven, sequential biaxial stretching combining these methods, rolling, simultaneous biaxial stretching using a combination of a tenter oven and a pantograph, and simultaneous biaxial stretching using a combination of a tenter oven and a linear motor. In addition, simultaneous biaxial stretching (inflation molding), in which molten resin is extruded into a tube shape using a circular die connected to a screw-type extruder and then air is blown into it, can also be used.

[0049] The stretching temperature when stretching can be set as appropriate. If the melting point of the resin forming the pearl layer is lower than the melting point of the resin forming the adhesive layer (and any substrate layer), it is preferable to set the stretching temperature to match the melting point of the resin forming the adhesive layer (and any substrate layer). This is to stretch the adhesive layer (and any substrate layer) to an appropriate stretching ratio. It is preferable that the stretching temperature be within the range of the melting point of the resin forming the adhesive layer. Specifically, it is preferable that the stretching temperature be 2 to 60°C lower than the melting point of the resin forming the adhesive layer. From the viewpoint of easily increasing the porosity of the adhesive layer while easily preventing breakage, etc., it is more preferable that the stretching temperature be 5 to 50°C lower than the melting point of the resin forming the adhesive layer, and even more preferable that it be 10 to 30°C lower. The stretching speed is not particularly limited, but from the viewpoint of stable stretch molding, it is preferably in the range of 20 to 350 m / min. [Examples]

[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 unless it exceeds the gist of the invention. In the examples, unless otherwise specified, "parts," "%," etc., refer to mass.

[0051] (Preparation of resin composition) The stretched resin sheets of Examples 1-4 and Comparative Examples 1-3 were manufactured according to the following procedure. Details of the materials used in each example and comparative example are summarized in Table 1. Furthermore, Table 2 summarizes the types of materials used, their mixing ratios (mass%), stretching conditions, and evaluations for the production of the resin sheets in each example and comparative example. The material symbols shown in Table 2 correspond to the material symbols shown in Table 1.

[0052] [Table 1]

[0053] [Example 1] As the resin composition for forming the base layer, 100% by mass of h-PP, a polypropylene resin, was melt-kneaded in an extruder set to 270°C to prepare the resin composition. 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 heated again to 150°C, and then stretched four times in the sheet flow direction (longitudinal direction) using the speed difference between multiple rolls to obtain the base layer (longitudinal uniaxially stretched layer).

[0054] Next, as the resin composition for forming the pearl layer, 90% by mass of polypropylene resin r-PP and 10% by mass of pearl pigment Pearl 1 were melt-kneaded in an extruder set to 270°C to prepare a resin composition. 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 to one side of the above-mentioned substrate layer.

[0055] Furthermore, as a resin composition for forming the adhesive layer (heat seal layer), 70% by mass of PP-based elastomer (a polypropylene resin) and 30% by mass of LD-PE (a polyethylene resin) were melt-kneaded in an extruder set to 270°C to prepare a resin composition. 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 to one side of the substrate layer opposite to the pearl layer.

[0056] The resulting laminate was heated to 150°C in an oven, then stretched nine times laterally using a tenter stretcher, and subsequently heat-treated at 170°C to obtain a stretched resin sheet consisting of a pearl layer (uniaxially oriented layer), a base layer (biaxially oriented layer), and an adhesive layer (uniaxially oriented layer).

[0057] The resulting stretched resin film had a thickness of 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 using the same method 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 using the same method 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 using the same method 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 a pearl layer / base layer (uniaxially oriented layer) / adhesive layer, a (unstretched) resin sheet was obtained in the same manner as in Example 1, except that quadruple stretching using a tenter stretcher was not performed.

[0062] [Comparative Example 2] A stretched resin sheet was obtained using the same method as in Example 1, except that 90% by mass of h-PP was used as the polypropylene resin for the pearl layer instead of r-PP, and 10% by mass of pearl 3 was used as the pearl pigment for the pearl layer instead of pearl 1.

[0063] [Comparative Example 3] A stretched resin sheet was obtained using the same method as in Example 1, except that 70% by mass of h-PP was used as the polypropylene resin for the pearl layer instead of r-PP, and the content of pearl 1, which is the pearl pigment in the pearl layer, was set to 30% by mass.

[0064] [Various measurements and evaluations] The stretched resin sheets obtained from Examples 1-4 and Comparative Examples 1-3 were evaluated using 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 Co., Ltd., product name: PG-01J).

[0066] <Opacity (%)> In accordance with the method described in JIS-P-8149:2000, the opacity was calculated as a percentage by dividing the luminous reflectance measured with a standard black board backing by the intrinsic luminous reflectance measured with a standard white board backing.

[0067] <Orientation angle of pearl pigment> An arbitrary cross-section of a stretched resin sheet was photographed using a 10 μm × 10 μm SEM, and the orientation angle (°) was measured based on the observed images. The orientation angle of the pearl pigment was defined as the angle between the surface of the pearl layer and a plane along the long axis direction of the thin, plate-like pearl pigment. The orientation angle was checked for each pearl pigment in the observed images, and the average value was taken as the orientation angle. In Table 2, the evaluation is indicated as follows: "◎" if the average orientation angle is less than 5°, "〇" if it is less than 8°, "△" if it is less than 10°, and "×" if it is 10° or more.

[0068] <Porosity of the pearl layer (%)> The porosity was determined by creating a cross-sectional area (observation surface) in the thickness direction by cutting while cooling to avoid crushing the voids in the pearlescent layer, attaching it to an observation sample stage, and depositing gold or the like onto the observation surface. The voids were then observed using a scanning electron microscope (instrument name: SM-200, manufactured by TOPCON Corporation). The voids were observed at any magnification (500 to 3000x) that was easy to observe. The areas where voids were observed were captured as image data, and these images were processed using an image analysis device (instrument name: Luzex AP, manufactured by Nireco Corporation) to determine the porosity (void ratio) as the area ratio of the voids.

[0069] <Appearance evaluation 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 visual gloss of each example and comparative example stretched resin sheet placed on white paper was evaluated according to the following criteria. Similarly, the visual gloss of each example and comparative example stretched resin sheet placed on black paper was also evaluated according to the following criteria. 1: A slight pearlescent finish can be seen. 2: A slight pearlescent finish can be seen. 3: The pearlescent finish is visible. 4: A slightly strong pearlescent finish is noticeable. 5: A strong pearlescent finish can be observed. 6: A very strong pearlescent finish can be observed.

[0070] (Appearance evaluation Δ) Based on the results of the appearance evaluations under the white and black backgrounds described above, an appearance evaluation Δ (delta) was calculated, and the calculated value was comprehensively evaluated according to the following criteria. A larger appearance evaluation Δ indicates that the difference in pearl gloss before and after placing (attaching) the stretched resin sheet to the substrate is more clearly exhibited. ◎: Appearance evaluation Δ is 4 or higher ○: Appearance evaluation Δ is 3 or higher. ×: Appearance evaluation Δ is 2 or less.

[0071] The evaluation results for the resin sheets of Examples 1-4 and Comparative Examples 1-3 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 7% or less in the pearl layer. In the evaluation of the pearl layer of these stretched resin sheets, the degree of improvement in appearance evaluation against a black background compared to the appearance evaluation against a white background (appearance evaluation Δ) was 3 or higher.

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

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

Claims

1. A stretched resin sheet, It has a stretched pearl layer containing pearl pigment and a stretched adhesive layer, The stretched resin sheet contains a polyolefin resin and has an opacity of less than 30%. A stretched resin sheet wherein the pearl layer has a porosity of 7% or less, contains 80% by mass or more of polyolefin resin, contains 50% by mass or more of random polypropylene, contains 1 to 20% by mass of pearl pigment, and the average particle size D50 of the pearl pigment is 40 μm or less.

2. The stretched resin sheet according to claim 1, wherein the opacity is 15% or less.

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

4. The stretched resin sheet according to claim 1 or 2, wherein the orientation angle of the pearl pigment between the surface of the pearl layer and a plane along the major axis direction of the pearl pigment in the pearl layer is 20° or less.

5. The stretched resin sheet according to claim 1 or 2, wherein the overall thickness of the stretched sheet is 40 to 150 μm.

6. The stretched resin sheet according to claim 1 or 2, wherein the thickness of the pearl layer is 3 μm or more and 10 μm or less.

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

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