Resin sheet manufacturing method and resin sheet

Abstract

To provide manufacturing method for resin sheets that can improve whiteness even when thermoplastic resins containing recycled resins are used.SOLUTION: The present invention relates to manufacturing method for resin sheet, comprising a stretching process for forming a resin sheet by stretching a resin composition containing a thermoplastic resin and an inorganic filler and having a whiteness of 80.0% or less, the resin sheet having a whiteness of 85.0% or more. The invention also relates to a method for producing a resin sheet, the thermoplastic resin includes recycled resin, and the recycled resin contains 20 mass% or more of the recycled resin to the resin composition.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a resin sheet and a resin sheet.

Background Art

[0002] Resin sheets (synthetic paper) have been proposed and put into practical use, which are formed by stretching a resin composition containing a thermoplastic resin and an inorganic filler to form a porous layer and then shaping it into a sheet. These resin sheets are useful as materials for printing paper, labels, etc. On the other hand, in recent years, from the perspective of reducing environmental pollution caused by plastic waste, the recycling of waste has been actively carried out (see, for example, Patent Document 1).

[0003] Recycled resins regenerated from plastic waste are reused for various applications again. Among plastic wastes, resins recovered and recycled from plastics used and discarded by consumers are called PCR (Post-consumer recycle) resins. And from the perspective of reducing environmental pollution, technologies to promote the use of recycled sheets using PCR are more strongly demanded.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] PCR may contain dirt, foreign substances, etc. in the recovered plastic waste, and the hue is often not stable and may exhibit various shades. For this reason, resin sheets manufactured by stretching a thermoplastic resin containing a recycled resin such as PCR tend to be difficult to increase the whiteness while stabilizing the hue.

[0006] Under such circumstances, the present invention provides a method for manufacturing a resin sheet capable of improving whiteness even when using a thermoplastic resin containing recycled resin.

Means for Solving the Problems

[0007] As a result of intensive studies to solve the above 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 method for manufacturing a resin sheet, comprising a stretching step of stretching a resin composition containing a thermoplastic resin and an inorganic filler to form a resin sheet, the resin composition having a whiteness of 80.0% or less, wherein the resin sheet has a whiteness of 85.0% or more. [2] The method for manufacturing a resin sheet according to [1], wherein the thermoplastic resin contains a recycled resin, and the resin composition contains 20% by mass or more of the recycled resin with respect to the resin composition. [3] The method for manufacturing a resin sheet according to [1] or [2], wherein the resin sheet has a porosity of 20% or more. [4] The method for manufacturing a resin sheet according to any one of [1] to [3], wherein in the stretching step, the resin composition is stretched at a surface magnification of 8 times or more to form the resin sheet. [5] The method for manufacturing a resin sheet according to any one of [2] to [4], wherein the whiteness of the recycled resin is 75.0% or less. [6] The method for manufacturing a resin sheet according to any one of [2] to [5], wherein the resin composition has a resin content of the thermoplastic resin containing the recycled resin of 50% by mass or more. [7] The method for manufacturing a resin sheet according to any one of [1] to [6], wherein the resin sheet has an overall thickness of 50 to 200 μm. [8] A resin sheet manufactured by the method for manufacturing a resin sheet according to any one of [1] to [7].

Advantages of the Invention

[0009] According to the present invention, even when a thermoplastic resin containing a recycled resin is used, a method for manufacturing a resin sheet capable of improving whiteness can be provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in detail. However, the description given below is an example (representative example) of the present invention and is not limited thereto.

[0012] <Method for Manufacturing Resin Sheet> The method for manufacturing a resin sheet of the present invention includes a stretching step of stretching a resin composition containing a thermoplastic resin and an inorganic filler to form a resin sheet, and the whiteness of the resin composition is 80.0% or less. Further, the resin sheet has a whiteness of 85.0% or more. Hereinafter, the manufacturing method according to the present invention will be described in detail.

[0013] <Resin Composition> First, the resin composition to be stretched in the stretching step will be described. The resin composition contains a thermoplastic resin and an inorganic filler. The manufacturing method of the present invention can be suitably applied even when the thermoplastic resin in the resin composition contains a recycled resin.

[0014] The manufacturing method of the present invention has a stretching step of stretching a resin composition containing an inorganic filler. Therefore, the manufactured resin sheet has a large number of pores with the inorganic filler as the core, and the whiteness can be increased. According to such a manufacturing method of the present invention, even when a thermoplastic resin containing a recycled resin or the like whose hue is difficult to stabilize is used, the whiteness of the resin sheet is likely to be improved.

[0015] <<Thermoplastic resin>> The thermoplastic resin contained in the resin composition is not particularly limited as long as it can be stretched in the stretching process. The thermoplastic resin may be a resin that is not a recycled product (unrecycled resin or virgin resin), and it is preferably further contained with recycled resin.

[0016] The thermoplastic resin is preferably a polyolefin resin or a polyester resin. From the viewpoint of film formability, a polyolefin resin is more preferable. Among polyolefin resins, a polypropylene resin is even more preferable. Among polyester resins, polyethylene terephthalate is even more preferable.

[0017] Examples of polypropylene resins include isotactic homopolypropylene obtained by homopolymerizing propylene, syndiotactic homopolypropylene, and various stereoregular polypropylene copolymers obtained by copolymerizing propylene as the main component with α-olefins such as ethylene, 1-butene, and 1-pentene. From the viewpoints of high heat resistance and easy void formation, the polypropylene resin is preferably homopolypropylene. The propylene copolymer may be a binary system or a multi-component system of ternary or higher, and may be a random copolymer or a block copolymer.

[0018] <<Recycled resin>> The thermoplastic resin may contain 20% by mass or more of recycled resin based on the resin composition. The content of recycled resin is preferably 30% by mass or more. From the viewpoint of easily making the hue stable, the recycled resin contained in the thermoplastic resin is preferably 80% by mass or less, and more preferably less than 50% by mass.

[0019] "Recycled resin" is a resin made by recycling used plastic products, and is also called recycled plastic or PCR (Post-consumer recycle) resin. The recycled resin is not particularly limited as long as it is a thermoplastic resin. Examples thereof include thermoplastic resins such as polyolefin resins, polyester resins, polyamide resins, polystyrene resins, polyvinyl chloride resins, and polycarbonates. From the viewpoints of water resistance and solvent resistance, polyolefin resins are preferred. Preferred polyolefin resins include polypropylene resins, polyethylene resins, and the like.

[0020] Examples of polypropylene resins include, for example, propylene homopolymers (homopolypropylene), and propylene copolymers obtained by copolymerizing propylene as a main component with α-olefins such as ethylene, butene, hexene, 4-methyl-1-pentene, and the like. The propylene copolymer may be a binary system or a multi-component system of ternary or higher, and may be a random copolymer or a block copolymer.

[0021] Examples of polyethylene resins include, for example, high-density polyethylene having a density of about 0.940 to 0.970 g / cm 3 medium-density polyethylene having a density of about 0.920 to 0.940 g / cm 3 low-density polyethylene having a density of about 0.900 to 0.920 g / cm 3 copolymers obtained by copolymerizing α-olefins such as ethylene, propylene, butene, hexene, 4-methylpentene-1, etc. with ethylene as a main component, maleic acid-modified ethylene-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-cyclic olefin copolymer, maleic acid-modified polyethylene, and the like. The above thermoplastic resins can be used alone or in combination of two or more.

[0022] Among the above polyolefin resins, from the viewpoints of moldability and cost, it is more preferable that the recycled resin contains propylene homopolymer (homopolypropylene) and / or high-density polyethylene.

[0023] The recycled resin is often colored because various coloring substances are mixed in during the recycling process and it discolors due to the heat history. In the present invention, from the viewpoint of effectively utilizing a colored resin that is usually difficult to utilize, the whiteness of the recycled resin is preferably 75.0% or less, more preferably 70.0% or less. The lower limit value of the whiteness of the recycled resin is not particularly limited, but from the viewpoint of distribution, the whiteness is usually 30.0% or more.

[0024] The resin composition described above preferably contains a thermoplastic resin as a main component. The "main component" means that the resin content of the thermoplastic resin containing the recycled resin is preferably 50% by mass or more, more preferably 54% by mass or more, based on the total mass (100% by mass) of the entire resin composition. The upper limit of the content of the thermoplastic resin is not particularly limited and may be less than 100% by mass.

[0025] <<Inorganic filler>> Examples of the inorganic filler include heavy calcium carbonate, light calcium carbonate, calcined clay, talc, diatomaceous earth, titanium oxide, zinc oxide, barium sulfate, silicon oxide, magnesium oxide, or inorganic particles obtained by surface-treating these with a fatty acid, a polymer surfactant, an antistatic agent, or the like. Among them, heavy calcium carbonate and light calcium carbonate are preferable because they have good formability of pores and are inexpensive. The inorganic filler may be selected from one of the above and used alone, or two or more of them may be used in combination.

[0026] The average particle diameter (D50) of the inorganic filler is not particularly limited. From the perspective of ease of mixing with the thermoplastic resin, it is preferably large, and from the perspective of making it difficult to cause troubles such as film breakage during stretching, it is preferably small. Specifically, the average particle diameter of the inorganic filler is preferably 0.1 μm or more, more preferably 0.5 μm or more, and still more preferably 1.0 μm or more. Also, the average particle diameter of the inorganic filler is preferably 10.0 μm or less, more preferably 5.0 μm or less, and still more preferably 3.0 μm or less.

[0027] In the particle size distribution of the inorganic filler, D90 / D10 is preferably 15 or less, more preferably 10 or less, and still more preferably 7 or less from the perspective of maintaining strength and preventing cracking. On the other hand, D90 / D10 of the inorganic filler is usually 1.5 or more, and preferably 3 or more from the perspective of easy availability.

[0028] The average particle diameter (D50) of the above inorganic filler refers to the particle diameter corresponding to 50% in cumulative terms in the particle size distribution measured by a particle measuring device, for example, a laser diffraction type particle measuring device "Microtrac" (manufactured by Nikkiso Co., Ltd., trade name) of an inorganic filler dispersed in a suitable solvent. D90 is the particle diameter corresponding to 90% in cumulative terms in the above particle size distribution. Also, D10 is the particle diameter corresponding to 10% in cumulative terms in the above particle size distribution.

[0029] The resin composition can further contain additives such as pigments, heat stabilizers (antioxidants), light stabilizers, dispersants, lubricants, or nucleating agents, as necessary.

[0030] <<White Pigment>> Examples of the pigment include white pigments. As the white pigment, for example, titanium oxide, barium sulfate, calcium sulfate, zinc oxide and the like are preferably used. Among these, titanium oxide is particularly preferred because it has high hiding power and excellent whiteness. As the titanium oxide, any of rutile type (tetragonal high temperature type), anatase type (tetragonal low temperature type), and brookite type (orthorhombic) may be used. Further, as the titanium oxide, surface-modified titanium oxide subjected to alumina surface treatment or silica surface treatment can be used.

[0031] The average particle size of the white pigment may be appropriately set according to desired properties such as pigment dispersibility, hiding power, and printing characteristics, and is not particularly limited. For example, the average particle size of the white pigment is preferably 0.01 μm or more, more preferably 0.1 μm or more. On the other hand, the average particle size is preferably 5.0 μm or less, more preferably 1.0 μm or less. The average particle size of the white pigment refers to the arithmetic mean diameter obtained by observing the white pigment with an electron microscope.

[0032] From the viewpoint of enhancing whiteness, the content of the white pigment in the hiding surface layer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and still more preferably 0.5% by mass or more. On the other hand, from the viewpoint of enhancing interlayer strength, the content is preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 5% by mass or less.

[0033] <<Other Additives>> As the heat stabilizer, for example, a sterically hindered phenol-based antioxidant, a phosphorus-based antioxidant, or an amine-based antioxidant can be used usually in the range of 0.001 to 1.0% by mass. As the light stabilizer, for example, a sterically hindered amine-based light stabilizer, a benzotriazole-based light stabilizer, or a benzophenone-based light stabilizer can be used usually in the range of 0.001 to 1.0% by mass. Examples of the dispersant or lubricant include silane coupling agents, higher fatty acids such as oleic acid and stearic acid, metal soaps, polyacrylic acid, polymethacrylic acid, or their salts. These can be used usually in the range of 0.01 to 4.0% by mass, for example, for the purpose of dispersing fillers.

[0034] <Whiteness of the resin composition> In the production method of the present invention, as the resin composition described above, one with a whiteness of 80.0% or less is used. Here, when the thermoplastic resin contains recycled resin, as described above, the hue may not be stable and it tends to be one with a whiteness of 80.0% or less. According to the production method of the present invention, even when such a resin composition with a whiteness of 80.0% or less is used, it is easy to improve the whiteness.

[0035] The whiteness of the resin composition used in the production method of the present invention is 80.0% or less. From the viewpoint of easily expanding the range of raw materials that can be used and efficiently obtaining the whitening effect, the whiteness of the resin composition is preferably 76.0% or less. When not containing a white pigment such as titanium oxide, the whiteness of the resin composition is preferably 70.0% or less. From the viewpoint of obtaining a resin sheet with a whiteness suitable for practical use, the whiteness of the resin composition is preferably 30.0% or more, more preferably 50.0% or more, and even more preferably 60.0% or more.

[0036] "Whiteness" means a value calculated from the L, a, b values measured using a Hunter type color difference meter in accordance with JIS L1015:1999. As the Hunter type color difference meter, for example, the SM Color Meter SM-T manufactured by Suga Test Instruments Co., Ltd. can be used.

[0037] <Stretching step> In the stretching process, the resin composition described above is stretched to form a resin sheet. The stretching method (stretching method) in the stretching process is not particularly limited. For example, a longitudinal stretching method using the peripheral speed difference of a roll group, a transverse stretching method using a tenter oven, a sequential biaxial stretching method combining these, a rolling method, a simultaneous biaxial stretching method by combining a tenter oven and a pantograph, and a simultaneous biaxial stretching method by combining a tenter oven and a linear motor can be mentioned. Further, after extruding the molten resin into a tube shape using a circular die connected to a screw type extruder, a simultaneous biaxial stretching (inflation molding) method of blowing air into it can also be used.

[0038] When performing stretching, the stretching temperature is preferably in the range of not less than the glass transition point of the thermoplastic resin in the case of an amorphous resin. Further, when the thermoplastic resin is a crystalline resin, the stretching temperature is preferably in the range of not less than the glass transition point of the amorphous part of the thermoplastic resin and not more than the melting point of the crystalline part of the thermoplastic resin. Specifically, a temperature 2 to 60 °C lower than the melting point of the thermoplastic resin is preferable. From the viewpoint of easily increasing the porosity and on the other hand, easily preventing breakage, etc., the stretching temperature is more preferably 5 to 50 °C lower than the melting point of the thermoplastic resin, and further preferably 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.

[0039] Also, the stretching ratio can be appropriately determined in consideration of the characteristics of the thermoplastic resin used, etc. For example, when stretching the resin composition in one direction, the stretching ratio is usually about 1.2 times or more, preferably 2 times or more, while usually 12 times or less, preferably 10 times or less. Further, when performing biaxial stretching, the stretching ratio in terms of area ratio (area stretching ratio) is usually 1.5 times or more, preferably 8 times or more, more preferably 15 times or more. On the other hand, from the viewpoints of strength and manufacturing difficulty, the area ratio is usually 60 times or less, preferably 40 times or less. EmptyFrom the viewpoint of easily increasing the porosity, it is particularly preferable to biaxially stretch the resin composition. The above surface magnification also applies to the case of uniaxial stretching. The surface magnification in the case of uniaxial stretching is calculated as 1×(stretching magnification of uniaxial stretching). When within the above range of the stretching magnification, the target porosity can be obtained and it is easy to improve the whiteness. Also, film breakage is less likely to occur, and there is a tendency that stable stretch molding can be achieved.

[0040] <Resin sheet> The resin sheet produced by the production method of the present invention will be described in detail below.

[0041] <<Whiteness of resin sheet>> The resin sheet produced by the production method of the present invention has a whiteness of 85.0% or more. The whiteness of the resin sheet is preferably 87.0% or more, more preferably 90.0% or more. The resin sheet produced by the production method of the present invention can improve the whiteness with respect to the whiteness before stretching the resin composition. The upper limit of the whiteness of the resin sheet is not limited, but since it is likely to be overly costly to make it completely white, it is preferably 95.0% or less.

[0042] <<Other physical properties of resin sheet>> The resin sheet preferably has a porosity of 20% or more. The porosity is more preferably 30% or more, still more preferably 40% or more. From the viewpoint of preventing sheet breakage and the like, the porosity of the resin sheet is preferably 50% or less, more preferably 45% or less. When within the above range of the porosity, it is easy to improve the whiteness of the resin sheet and it is likely to become a resin sheet having appropriate strength in practical use.

[0043] The resin sheet preferably has an overall thickness of 50.0 to 200.0 μm. From the viewpoint of easily obtaining a high whiteness, the overall thickness of the resin sheet is more preferably 80.0 μm or more, still more preferably 100.0 μm or more. Also, from the viewpoint of handleability, the overall thickness of the resin sheet is more preferably 150.0 μm or less, still more preferably 120.0 μm or less.

[0044] <<Configuration Example of Resin Sheet>> The resin sheet only needs to have a sheet-like layer obtained by stretching a resin composition (hereinafter, sometimes referred to as the "base material layer"). It may also have layers other than the base material layer. For example, it may have a surface layer in addition to the base material layer, and may further have one or more intermediate layers between the base material layer and the surface layer. The surface layer and the intermediate layer may be provided on only one side of the base material, or may be provided on both sides. Also, a heat seal layer may be provided on the surface of the surface layer (the surface opposite to the base material layer).

[0045] Examples of the laminated structure of the resin sheet include, for example, the examples shown in FIGS. 1 to 3. The laminate 1 illustrated in FIG. 1 has a base material layer 11 and a first surface layer 12. For example, when this laminate is used as printing paper and printing is performed on the laminate, the A side in FIG. 1 may be used as the printing surface. FIG. 2 shows the configuration of the laminate 1 as another embodiment of the present invention. The laminate 1 illustrated in FIG. 2 has a base material layer 11, a first surface layer 12, and a second surface layer 13. The second surface layer is provided on the surface of the base material layer 11 opposite to the surface on which the first surface layer 12 is provided. For example, when this laminate is used as printing paper, both the A side and the B side in FIG. 2 may be used as the printing surfaces. FIG. 3 shows the configuration of the laminate 1 as another embodiment of the present invention. The laminate 1 illustrated in FIG. 3 has a base material layer 11, a first surface layer 12, and a third surface layer 14. The third surface layer is provided on the surface of the base material layer 11 opposite to the surface on which the first surface layer 12 is provided. Also, the third surface layer 14 includes a heat seal layer 15. The heat seal layer 15 is preferably located on the outermost surface of the third surface layer 14. For example, when this laminate is used as a printing label, the A side in FIG. 3 may be used as the printing surface. Note that the C side (heat seal side) in FIG. 3 is, for example, an adhesive surface that serves as an attachment portion when attaching the printing label to a plastic container body as an in-mold molding label.

[0046] In the manufacturing method of the present invention, when the resin sheet is formed of a plurality of layers, at least the base material layer may have the stretching step described above. That is, the presence or absence of the stretching step can be arbitrarily selected for the layers other than the base material layer. Further, the stretching step may be performed after laminating the base material layer and other layers.

[0047] The resin sheet preferably has a plurality of layers. In this case, the resin forming at least the base material layer preferably contains recycled resin in the above content. Further, the resin forming the layers other than the base material layer may contain recycled resin. It is preferable that the outermost layer among the plurality of layers does not contain recycled resin. This is because recycled resin may contain foreign substances (coarse particles) with a large size, and voids may be formed during stretching starting from the coarse particles, or appearance defects may occur.

Examples

[0048] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. In addition, descriptions such as "parts" and "%" in the examples mean descriptions based on mass unless otherwise specified.

[0049] (Adjustment of resin composition) According to the following procedure, resin sheets of Examples 1 to 5 and Comparative Examples 1 and 2 were manufactured. The details of the materials used in each example and comparative example are summarized in Table 1. In addition, the types and blending ratios (mass%) of the materials used in the production of the resin sheets of each example and comparative example, the stretching conditions, and the evaluations are summarized in Table 2. The symbols of the materials shown in Table 2 correspond to the symbols of the materials shown in Table 1.

[0050]

Table 1

[0051] [Example 1] As raw materials for the resin composition, 24.9% by mass of h-PP, which is a non-recycled polypropylene resin, 29.8% by mass of PCR, which is a recycled resin, 44.8% by mass of heavy calcium carbonate particles (CaCO3), which are inorganic fillers, and 0.5% by mass of titanium dioxide TiO2 were melt-kneaded using an extruder set at 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 non-stretched film. This non-stretched film was reheated to 150°C and then stretched 4 times in the sheet flow direction (longitudinal direction) using the speed difference between a number of rolls to obtain a longitudinally uniaxially stretched film.

[0052] Thereafter, after heating to 150°C using an oven, it was stretched 4 times in the transverse direction using a tenter stretching machine to obtain a biaxially stretched resin sheet. The total thickness of the obtained resin sheet was 115 μm. The method for measuring the total thickness of the resin sheet will be described later.

[0053] [Example 2] A uniaxially stretched resin sheet was obtained in the same manner as in Example 1, except that longitudinal uniaxial stretching using the speed difference between rolls was not performed. The total thickness of the obtained resin sheet was 100 μm.

[0054] [Example 3] A uniaxially stretched resin sheet was obtained in the same manner as in Example 2, except that the heating temperature of the oven before stretching using the tenter stretching machine was set to 160°C. The total thickness of the obtained resin sheet was 80 μm.

[0055] [Example 4] A biaxially stretched resin sheet was obtained in the same manner as in Example 1, except that titanium dioxide TiO2 was not used and the raw material composition was as described in Table 2. The total thickness of the obtained resin sheet was 115 μm.

[0056] [Example 5] A resin sheet that was biaxially stretched was obtained in the same manner as in Example 2, except that titanium dioxide TiO2 was not used and the raw material composition was as described in Table 2. The total thickness of the obtained resin sheet was 100 μm.

[0057] [Conventional Example 1] As raw materials for the resin composition, 54.7% by mass of h-PP, which is a polypropylene resin, 44.8% by mass of heavy calcium carbonate particles (CaCO3), which is an inorganic filler, and 0.5% by mass of titanium dioxide TiO2 were melt-kneaded using an extruder set at 270°C to prepare a resin composition. Thereafter, the resin composition was stretched in the same manner as in Example 2 to obtain a uniaxially stretched resin sheet. The total thickness of the obtained resin sheet was 100 μm.

[0058] [Conventional Example 2] A resin sheet that was biaxially stretched was obtained in the same manner as in Conventional Example 1, except that titanium dioxide TiO2 was not used and the raw material composition was as described in Table 2. The total thickness of the obtained resin sheet was 100 μm.

[0059] [Various Measurements and Evaluations] For the resin sheets of Examples 1 to 5 and Conventional Examples 1 and 2 obtained above, various evaluations were performed by the following methods.

[0060] <Thickness of Layer (μm)> The total thickness (μm) of the resin sheet was measured in accordance with JIS K7130:1999 using a constant-pressure thickness measuring instrument (manufactured by Techlock Co., Ltd., product name: PG-01J).

[0061] <Porosity (%)> The void ratio was measured by cutting while cooling so as not to crush the voids in the resin sheet to create a cross-sectional (observation surface) in the thickness direction, attaching it to an observation sample stage, depositing gold or the like on the observation surface, and observing the voids using a scanning electron microscope (device name: SM-200, manufactured by TOPCON CORPORATION). The voids were observed at an arbitrary magnification (500 to 3000 times) that was easy to observe. The region where the voids were observed was captured as image data, and the image was processed with an image analyzer (device name: LUZEX AP, manufactured by NIRECO CORPORATION), and the area ratio of the voids was defined as the void ratio (void fraction).

[0062] <Whiteness (%)> Using a Hunter color difference meter (product name "SM Color Meter SM-T", manufactured by Suga Test Instruments Co., Ltd.), the hue, that is, the lightness index L and chromaticness indices a and b of the Hunter color system, were measured for the resin sheets before and after stretching in each example and the conventional examples. The whiteness was calculated according to the method described in JIS L1015:1999.

[0063] The above evaluation results for the resin sheets of Examples 1 to 6 and Conventional Examples 1 and 2 are shown in Table 2.

Table 2

[0064] In Examples 1 to 5, the resin composition contained PCR, and the whiteness before stretching was all 80.0% or less. On the other hand, in the resin sheets obtained by stretching the resin compositions of Examples 1 to 5, the whiteness was all 85.0% or more. From the above, it was shown that the whiteness can be improved even when using a resin composition containing PCR by the production method of the present invention. In addition, each resin sheet of Examples 1 to 5 obtained by the production method of the present invention had the same whiteness as the resin sheets of Conventional Examples 1 and 2 using only non-recycled resin without using PCR.

Explanation of Reference Numerals

[0065] 1 Laminated body 11 Base material layer 12 First surface layer 13 Second surface layer 14 Third surface layer 15 Heat-sealing layer A Printing surface B Printing surface C Adhesive surface

Claims

1. A method for manufacturing a resin sheet, comprising: a stretching step of stretching a resin composition containing a thermoplastic resin and an inorganic filler and having a whiteness of 80.0% or less to form a resin sheet, wherein the resin sheet has a whiteness of 85.0% or more.

2. The thermoplastic resin contains a recycled resin, The method for manufacturing a resin sheet according to Claim 1, wherein the resin composition contains 20% by mass or more of the recycled resin.

3. The method for manufacturing a resin sheet according to Claim 1, wherein the resin sheet has a porosity of 20% or more.

4. In the stretching step, the resin composition is stretched by a surface magnification of 8 times or more to form the resin sheet. The method for manufacturing a resin sheet according to Claim 1.

5. The method for manufacturing a resin sheet according to Claim 2, wherein the whiteness of the recycled resin is 75.0% or less.

6. The method for manufacturing a resin sheet according to Claim 1, wherein the resin composition has a resin content of the thermoplastic resin containing the recycled resin of 50% by mass or more.

7. The method for manufacturing a resin sheet according to Claim 1, wherein the resin sheet has an overall thickness of 50 to 200 μm.

8. A resin sheet manufactured by the method for manufacturing a resin sheet according to any one of Claims 1 to 7.

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