Resin sheet

Abstract

To provide a resin sheet exhibiting flame retardancy equal to or higher than a practical passing level, capable of suppressing bleed-out during storage, and having kneadability maintained within a practical range in the manufacturing process.SOLUTION: The present invention relates to a resin sheet comprising a polyolefin-based resin having a melting point of 150°C or lower and a flame retardant, the flame retardant comprising 0.1 mass% or more of a NOR-type HALS compound, 1.0 mass% or more of an aliphatic phosphate ester compound, and 5.0 mass% or more of a nitrogen-phosphorus compound, the resin sheet having a melt tension of 20 mN or more at 250°C. The present invention also relates to a resin sheet having a thickness of 250 μm to 500 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin sheet. [Background technology]

[0002] Resin sheets are generally known to be flammable materials, and may be required to have flame retardancy depending on their applications. For example, particularly high flame retardancy (e.g., DIN 4102, FMVSS-302, etc.) is required for applications such as building materials such as wallpaper, sheet components for home appliances, posters and stickers for stores, and glass stickers for railway vehicles.

[0003] Against this background, Patent Document 1 discloses a resin composition using a flame retardant containing a nitrogen-phosphorus compound as a flame retardant that imparts flame retardancy to a resin sheet. This flame retardant is known to exert its flame retardant effect by forming a foam insulation layer called an intumescent upon combustion. This foam insulation layer prevents the spread of fire and contributes to improving flame retardancy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-113413 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even resin sheets using a flame retardant capable of forming a foamed heat insulating layer as described in Patent Document 1 sometimes fail to exhibit flame retardancy at or above a practically acceptable level, such as V-0, depending on the flame retardancy standards for various applications. Furthermore, after the resin sheet is manufactured, problems with storage may occur, such as the occurrence of bleed-out, mainly in the form of powder. Furthermore, during the manufacture of the resin sheet, there may be manufacturing issues, such as difficulty in kneading.

[0006] Therefore, in order to solve the above problems, the present invention aims to provide a resin sheet that exhibits flame retardancy at or above the practical acceptable level, can suppress the occurrence of bleed-out during storage, and has kneadability during production that is within a practical range. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems and have arrived at the present invention having the following gist.

[0008] That is, the present invention is as follows. [1] A polyolefin resin having a melting point of 150°C or less and a flame retardant, The flame retardant contains 0.1% by mass or more of a NOR type HALS compound, 1.0% by mass or more of an aliphatic phosphate ester compound, and 5.0% by mass or more of a nitrogen-phosphorus compound, A resin sheet having a melt tension of 20 mN or more at 250°C. [2] The resin sheet according to [1], which has a thickness of 250 μm to 500 μm. [3] The resin sheet according to [1] or [2], wherein the polyolefin resin has a melt flow rate (190°C, under a load of 2.16 kg) of 8 g / 10 min or less. [4] The resin sheet according to any one of [1] to [3], wherein the polyolefin resin is a polyethylene resin. [5] The resin sheet according to any one of [1] to [4], which contains 50% by mass or more of the polyolefin resin. [6] The resin sheet according to any one of [1] to [5], which is an unstretched sheet. [7] The resin sheet according to any one of [1] to [6], further comprising titanium oxide. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a resin sheet that exhibits flame retardancy at or above a practically acceptable level, can suppress the occurrence of bleed-out during storage, and has kneadability during production that is within a practical range. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below, but the following description is an example (typical example) of the present invention and is not intended to limit the present invention.

[0011] (resin sheet)

[0012] The resin sheet of this embodiment contains a polyolefin resin having a melting point of 150°C or less and a specific flame retardant, and has a melt tension of 20 mN or more at 250°C. The resin sheet of this embodiment exhibits flame retardancy at or above a practically acceptable level, while suppressing the occurrence of bleed-out and providing good kneading properties during production. This resin sheet also has good printability.

[0013] The resin sheet of this embodiment has a melt tension of 20 mN or more. When the melt tension is equal to or greater than this value, the resin sheet is more likely to be torn off and drip during combustion, which would otherwise cause the fire to spread, and the flame retardancy is more likely to be improved. From the viewpoint of further enhancing flame retardancy, the melt tension is preferably 40 mN or more, more preferably 60 mN or more. From the viewpoint of kneading during production, the melt tension is preferably 200 mN or less, more preferably 100 mN or less.

[0014] <Flame retardant> The resin sheet contains three types of flame retardants: a NOR-type HALS compound, an aliphatic phosphate ester compound, and a nitrogen-phosphorus compound. By containing the three types of flame retardants in amounts equal to or greater than a predetermined amount, the resin sheet of this embodiment exhibits flame retardancy equal to or greater than a practical acceptable level, while suppressing the occurrence of bleed-out and allowing the resin sheet to be kneaded within a practical range during production. According to the present inventors, in the prior art, it has tended to be difficult to obtain a resin sheet that achieves a practical level of V-0 in a flame retardancy test such as UL94 V, particularly when the resin sheet is thick, such as 250 μm or more. In contrast, a resin sheet containing three types of flame retardants in a predetermined amount or more as in the present embodiment can provide a resin sheet that achieves a practical level of V-0 in a flame retardancy test such as UL94 V, even when the resin sheet has a thickness of 250 μm or more.

[0015] Specifically, the resin sheet contains, as flame retardants, 0.1% by mass or more of a NOR-type HALS compound (hereinafter also referred to as flame retardant A), 1.0% by mass or more of an aliphatic phosphate ester-based compound (hereinafter also referred to as flame retardant B), and 5.0% by mass or more of a nitrogen-phosphorus-based compound (hereinafter also referred to as flame retardant C). As described above, the resin sheet of this embodiment contains (1) three types of flame retardants, namely, flame retardant A, flame retardant B, and flame retardant C, and (2) flame retardant C together with a polyolefin-based resin having a predetermined melting point or lower. According to the inventors, by satisfying both (1) and (2) above, the resin sheet of this embodiment exhibits flame retardancy at or above a practically acceptable level, while suppressing the occurrence of bleed-out and easily achieving a resin sheet with practically acceptable kneadability during production. Below, in the description of each flame retardant, the above (1) and (2) will also be described in detail. In this specification, the content (mass %) of the flame retardant is expressed as the ratio of the mass of the flame retardant to the mass of the resin sheet (however, when the resin sheet is made up of multiple layers, the mass is the flame retardant layer described below).

[0016] NOR type HALS compound (Flame retardant A) The NOR type HALS compound (flame retardant A) will be described below. The NOR type HALS compound is not particularly limited as long as it is a compound having a piperidine structure with an N-alkoxyl group (>N-OR). Examples include the NOR type HALS compounds described in JP-T-2002-507238, WO-2005 / 082852, WO-2008 / 003605, etc. Specifically, for example, a compound having one or more piperidine structures in the molecule as shown in the following formula (I) can be used as the NOR type HALS compound. In formula (I), an organic group (R 1 ) are bonded to the resin sheet. These NOR-type HALS compounds function as radical scavengers (radical traps) when the resin sheet is burned, and they stop the combustion reaction (self-extinguishing). [ka] (In formula (I), R 1 represents an organic group, and * represents a bond.

[0017] The NOR type HALS compound is preferably one represented by the following formula (IA) or (IB): These compounds tend to function as particularly excellent radical scavengers during combustion, making it easy to obtain a resin sheet that can stop the combustion reaction. [ka] [ka] (In formula (IB), R is a group represented by the following formula (IB-2).) [ka]

[0018] R 1 Examples of the alkyl group include linear hydrocarbon groups having 1 to 20 carbon atoms, branched hydrocarbon groups having 1 to 20 carbon atoms, and cyclic hydrocarbon groups having 5 to 20 carbon atoms. Of these, linear hydrocarbon groups having 2 to 12 carbon atoms are preferred, and linear hydrocarbon groups having 3 to 11 carbon atoms are more preferred. The NOR type HALS compounds may be used alone or in combination of two or more.

[0019] From the viewpoint of improving flame retardancy, the NOR type HALS compound preferably has a weight average molecular weight of 1000 or less. Furthermore, from the viewpoint of suppressing stickiness due to bleed-out, the weight average molecular weight is preferably 500 or more. The relatively low molecular weight NOR-type HALS compounds described above are liquid at room temperature (around 25°C) and are easily compatible with polyolefin resins. The ease with which NOR-type HALS compounds are finely dispersed in polyolefin resins makes it easier to capture radicals during combustion, making it easier to prevent the spread of fire.

[0020] The resin sheet of this embodiment contains the above-mentioned NOR type HALS compound in an amount of 0.1 mass % or more relative to the mass of the entire resin sheet, because within this content range, the flame retardant effect is easily improved. The content of the NOR type HALS compound is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, from the viewpoint of easily achieving a flame retardant effect even when the resin sheet is thick. On the other hand, from the viewpoint of suppressing stickiness due to bleed-out, the content of the NOR type HALS compound is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, particularly preferably 1.0% by mass or less.

[0021] Aliphatic phosphate ester compound (flame retardant B) The aliphatic phosphate ester compound (flame retardant B) will be described below. The aliphatic phosphate ester compound is not particularly limited as long as it has an ester structure of an aliphatic alcohol and phosphorous acid. The aliphatic phosphate ester compound preferably contains a pentaerythritol diphosphate ester compound (pentaerythritol diphosphonate compound) having an ester structure of pentaerythritol and two phosphorous acids. Such compounds function as radical scavengers (radical traps) when the resin sheet is burned, and exhibit the ability to stop the combustion reaction (self-extinguishing).

[0022] As the pentaerythritol diphosphate ester-based compound, for example, the organic phosphorus-based compounds described in JP-A Nos. 2011-231338, 2012-092231, and 2016-216382 can be used. Examples of such pentaerythritol diphosphate ester compounds include 3,9-bis(phenylmethyl)-3,9-dioxo-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 3,9-bis(1-phenylethyl)-3,9-dioxo-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 3,9-bis(2-phenylethyl)-3,9-dioxo-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, and 3,9-bis(diphenylmethyl)-3,9-dioxo-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane. Furthermore, commercially available compounds may be used as the pentaerythritol diphosphate ester-based compounds (for example, "Fireguard (registered trademark) FCX-210" manufactured by Teijin Limited). The aliphatic phosphate ester compounds may be used alone or in combination of two or more thereof.

[0023] The resin sheet of this embodiment contains the above-mentioned aliphatic phosphate ester-based compound in an amount of 1.0 mass % or more relative to the mass of the entire resin sheet, because within this content range, the combustion prevention effect is easily improved. The content of the aliphatic phosphate ester-based compound is preferably 2.0% by mass or more, more preferably 3.0% by mass or more, from the viewpoint of easily achieving a flame-retardant effect even when the resin sheet is thick, while the content of the aliphatic phosphate ester-based compound is preferably 10.0% by mass or less, more preferably 6.0% by mass or less, from the viewpoint of suppressing powdery bleed-out during storage.

[0024] Flame retardant A and flame retardant B compounding ratio (Flame retardant A:Flame retardant B)The blending ratio (flame retardant A:flame retardant B) of the NOR type HALS compound (flame retardant A) and the aliphatic phosphate ester compound (flame retardant B) in the resin sheet described above is preferably 1:2 to 1:20, more preferably 1:3 to 1:10, and even more preferably 1:5 to 1:8. Flame retardant A tends to become sticky when bleed-out, and flame retardant B tends to produce powder, so the blending ratio described above makes it easy to obtain a resin sheet that has a practical level of flame retardancy even when thick, while suppressing bleed-out due to stickiness and powdery matter.

[0025] Nitrogen-phosphorus compounds (flame retardant C) The nitrogen-phosphorus compound (flame retardant C) will be described below. The nitrogen-phosphorus compound may be a flame retardant that forms a foaming insulating layer (intemescent) upon combustion. Specific examples include salts of polyphosphoric acid or pyrophosphoric acid with a nitrogen-containing compound. Examples of the nitrogen-phosphorus compound include salts of polyphosphoric acid with ammonia or a triazine derivative. Examples of the nitrogen-phosphorus compound include salts of polyphosphoric acid with diamine, piperazine, or a diamine containing a piperazine ring. Commercially available compounds may be used as the nitrogen-phosphorus compound (for example, "ADK STAB FP2500S," "ADK STAB FP2200S," "ADK STAB FP2100," etc., manufactured by ADEKA CORPORATION).

[0026] The resin sheet of this embodiment contains the nitrogen-phosphorus compound in an amount of 5.0 mass % or more relative to the mass of the entire resin sheet, because within this range of content, the flame retardant effect is easily improved. The content of the nitrogen-phosphorus compound is preferably 10.0% by mass or more, more preferably 20.0% by mass or more, and even more preferably 25.0% by mass or more, from the viewpoint of easily achieving a flame retardant effect even when the resin sheet is thick. From the viewpoint of suppressing powdery bleed-out, the content of the nitrogen-phosphorus compound is preferably 50.0% by mass or less, and even more preferably 35.0% by mass or less.

[0027] Flame retardant compounding ratio (Flame retardant A:Flame retardant B:Flame retardant C)The blending ratio (flame retardant A:flame retardant B:flame retardant C) of the above-described NOR-type HALS compound (flame retardant A), aliphatic phosphate ester compound (flame retardant B), and nitrogen-phosphorus compound (flame retardant C) in the resin sheet is preferably 1:2:20 to 1:20:100, more preferably 1:3:30 to 1:10:80, and even more preferably 1:5:40 to 1:8:60. Flame retardant A tends to become sticky when bleed-out, and flame retardants B and C tend to produce powder. The blending ratios described above make it easy to obtain a resin sheet that has a practical level of flame retardancy even when thick, while suppressing bleed-out due to stickiness and powdery matter.

[0028] Total flame retardant content (Flame retardant A + Flame retardant B + Flame retardant C) From the viewpoint of easily obtaining a resin sheet having a practical level of flame retardancy even when the resin sheet is thick, the total content of flame retardants A, B, and C in the resin sheet (flame retardant A + flame retardant B + flame retardant C) is preferably 10.0 mass% or more, more preferably 20.0 mass% or more. From the viewpoint of easily suppressing bleed-out, the total content of flame retardants A, B, and C in the resin sheet is preferably 50 mass% or less, more preferably 40 mass% or less.

[0029] <Polyolefin resin with a melting point of 150°C or less> The resin sheet of this embodiment contains a polyolefin resin having a melting point of 150° C. or lower. When the melting point of the polyolefin resin is 150°C or less, it is easy to obtain a resin sheet with a practical level of flame retardancy even when the resin is thick. This is because using a resin with a low melting point makes it easier to maintain the flame retardancy-improving effect of the nitrogen-phosphorus compound (flame retardant C) among the flame retardants mentioned above. This is thought to be because using a resin with a low melting point makes it possible to set the temperature rise for melt-kneading and the like lower in the resin sheet manufacturing process, making it easier to suppress deactivation of flame retardant C and the like (making it difficult to form intumescents).

[0030] Polyolefin resins having a melting point of 150°C or less (hereinafter referred to as "low melting point polyolefin resins") are preferably polyethylene resins. Examples of polyethylene resins include those having a density of 0.940 to 0.965 g / cm. 3 High density polyethylene, density 0.920~0.935g / cm 3 of medium density polyethylene, density 0.900 g / cm 3 More than 0.920g / cm 3 Examples of the copolymer include linear low-density polyethylene having a molecular weight of less than 1000, copolymers of ethylene or the like as a main component copolymerized with α-olefins such as propylene and butene, ethylene-acrylic acid copolymers, ethylene-cyclic olefin copolymers, and maleic acid-modified polyethylene. From the viewpoint that the melt tension of the resin sheet can be easily adjusted within the above range, low-density polyethylene is particularly preferred as the polyethylene-based resin.

[0031] From the viewpoint of moldability, the content of the low-melting-point polyolefin resin in the resin composition forming the resin sheet is preferably 50% by mass or more, more preferably 60% by mass or more, and from the viewpoint of easily improving flame retardancy, the content of the polyolefin resin is preferably 90% by mass or less, more preferably 70% by mass or less. The resin composition forming the resin sheet may contain a thermoplastic resin other than the low-melting-point polyolefin-based resin, provided that the effects of the present invention are not impaired. Such a thermoplastic resin is preferably a polyolefin-based resin having a melting point of more than 150°C (hereinafter referred to as "high-melting-point polyolefin-based resin"). Examples of high-melting-point polyolefin-based resins include polypropylene-based resins, polyethylene-based resins, and polymethyl-1-pentene.

[0032] <Melt flow rate> The low-melting-point polyolefin resin preferably has a melt flow rate of 8 g / 10 min or less at 190°C under a load of 2.16 kg. When the melt flow rate is within the above range, it is easy to obtain a resin sheet having a practical level of flame retardancy even when the thickness is large. From the viewpoint of easily improving flame retardancy, the melt flow rate is more preferably 6 g / 10 min or less, and particularly preferably 5 g / 10 min or less. The lower limit of the melt flow rate is not particularly limited, but from the viewpoint of availability, it is preferably 0.1 g / 10 min or more. The melt flow rate is a value measured using an appropriate method depending on the type of low-melting polyolefin resin. For example, for polyethylene, the value measured at 190°C under a load of 2.16 kg in accordance with JIS K6922-2 was used.

[0033] <Other ingredients> The resin sheet of this embodiment may contain components other than those described above, as long as it can exhibit flame retardancy. For example, it may contain one or more inorganic fillers selected from talc, calcium carbonate, aluminum oxide, silicon oxide, titanium oxide, barium oxide, and zeolite. The inorganic filler may be selected from the above and used alone, or two or more may be used in combination. From the viewpoint of easily improving flame retardancy, the content of the inorganic filler is preferably 10% by mass or less, more preferably 5% by mass or less. From the viewpoint of imparting functionality, the content of the inorganic filler is preferably 0.1% by mass or more, more preferably 1% by mass or more.

[0034] <Thickness> The thickness of the resin sheet of this embodiment is not particularly limited. As described above, from the viewpoint that even a thick resin sheet can easily have a practical level of flame retardancy, the thickness of the resin sheet can be set to 250 μm to 500 μm. From the viewpoint of handleability, the total thickness of the resin sheet is more preferably 500 μm or less, and even more preferably 400 μm or less. From the viewpoint of easily maintaining the strength of the resin sheet, the total thickness of the resin sheet is more preferably 280 μm or more, and even more preferably 300 μm or more.

[0035] <Stretching (non-stretching)> The resin sheet of the present embodiment may be either a stretched sheet or a non-stretched sheet, and if it is a non-stretched sheet, it is easier to make the thickness within the above range. Whether a resin sheet is stretched or unstretched can be confirmed, for example, from the storage modulus of the resin sheet. Specifically, the storage modulus of the resin sheet is measured in the MD (machine direction) and TD (transverse direction). For example, 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, the sheet can be confirmed as stretched. (A stretch ratio of 2500 MPa or higher can be confirmed as 4 times or more, and a stretch ratio of 5000 MPa or higher can be confirmed as 9 times or more.)

[0036] The storage modulus was measured by cutting the sheet 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, tension mode, and temperature 23°C.

[0037] <Porosity> When the resin sheet of this embodiment is a stretched sheet, it may be a porous sheet having pores in the layer. In this case, the porosity of the stretched sheet is not particularly limited. From the viewpoint of easily improving flame retardancy, the porosity is preferably 10% or less, more preferably 5% or less. The lower limit of the porosity is not particularly limited, and the sheet may be less than 1%, i.e., the sheet may have no pores or almost no pores. 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.

[0038] The resin sheet of this embodiment may be a single-layer resin sheet having only the layer containing the low-melting-point polyolefin resin, the flame retardant, and any inorganic filler, etc., as described above (hereinafter referred to as the "flame-retardant layer"). The resin sheet may also be a laminated resin sheet having a layer (hereinafter referred to as the "other layer") different from the flame-retardant layer. When the resin sheet is a laminated resin sheet, it is preferable that the other layer has appropriate flame retardancy to achieve the desired flame retardancy.

[0039] Specifically, the resin sheet may be a laminate having another layer on one or both sides of the main surface of the flame-retardant layer. The other layer may be one layer or two or more layers. The resin sheet may also have a surface layer as another layer on one main surface side of the flame-retardant layer. The resin sheet may also have a back layer or a heat seal layer as another layer on the main surface side opposite the surface layer of the flame-retardant layer. The resin sheet may also have other layers asymmetrically arranged with respect to the central layer.

[0040] (Applications of resin sheets) The resin sheet of this embodiment is suitable for a wide range of applications requiring flame retardancy, such as building materials such as wallpaper, sheet members for home appliances, posters and stickers for stores, and glass stickers for railway cars.

[0041] (Method of manufacturing resin sheet) The resin sheet of this embodiment can be produced by a method including a preparation step of preparing a resin composition for forming the resin sheet, etc. Hereinafter, the method for producing the resin sheet of this embodiment will be described in detail.

[0042] In the preparation step, a resin composition for forming the resin sheet is prepared. Specifically, the resin composition contains a low-melting-point polyolefin resin, a flame retardant, and an optional inorganic filler. The resin composition may further contain additives such as pigments, heat stabilizers (antioxidants), light stabilizers, dispersants, lubricants, or nucleating agents, as needed. When preparing the resin composition, the temperature rise when melt-kneading the resin composition in a kneader or the like is preferably 250°C or less, more preferably 230°C or less. Kneading under such low-temperature conditions makes it easier to suppress deactivation of the above-mentioned flame retardant. For the same reason, when the temperature condition is raised in the method for producing a resin sheet, it is preferably the above-mentioned temperature or less. The resin composition obtained in the preparation step is molded into a sheet by an extrusion step. For example, by extruding the melt-kneaded resin composition through a T-die, an unstretched sheet containing a low-melting-point polyolefin resin, a flame retardant, and an optional inorganic filler is formed. This unstretched sheet can be used as the resin sheet itself if the resin sheet is a single layer, or as a flame-retardant layer included in the resin sheet if the resin sheet is a laminate.

[0043] When the resin sheet is a laminate having layers other than the flame-retardant layer, a lamination step may be further carried out after the extrusion step. In the lamination step, the layers constituting the resin sheet are laminated in any order. Each layer may be uniaxially stretched before lamination, or a non-stretched sheet-like layer may be laminated.

[0044] <Stretching process> After the extrusion step, a stretching step may be optionally performed. The stretching step is a step of stretching the resin composition. In the stretching step, the resin sheet may be stretched biaxially. The stretching step can be appropriately adjusted so as to achieve a desired stretch ratio.

[0045] 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.

[0046] The stretching temperature when stretching may be set appropriately. The stretching temperature is preferably set within a range equal to or lower than the melting point of the resin forming the flame-retardant layer. Specifically, the stretching temperature is preferably 2 to 60°C lower than the melting point of the resin forming the flame-retardant 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]

[0047] 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.

[0048] (Preparation of Resin Composition) According to the following procedures, resin sheets of Examples 1 to 5 and Comparative Examples 1 to 5 were produced. 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.

[0049] [Table 1]

[0050] [Example 1] 61.2% by mass of polyethylene resin LD-PE1, 0.6% by mass of flame retardants HALS1, 5% by mass of PFR1, 30% by mass of INT, and 3% by mass of additives TiO2 and 0.2% by mass of AntiOX were mixed in a mixer (super mixer). The mixed resin composition was melt-kneaded in a twin-screw kneader set at 220°C to obtain resin pellets. The obtained resin pellets were melt-kneaded again using an extruder set at 220°C, and the kneaded product was extruded into a sheet from a T-die. The extruded kneaded product was cooled to 60°C in a cooling device to obtain a single-layer, unstretched resin sheet.

[0051] The resulting resin sheet had a thickness of 300 μm and a porosity of 0%. The method for measuring the thickness and porosity of the resin sheet will be described later.

[0052] [Example 2] A resin sheet was obtained in the same manner as in Example 1, except that 0.6% by mass of HALS2 was used as the flame retardant instead of HALS1.

[0053] [Example 3] A resin sheet was obtained in the same manner as in Example 1, except that the amount of LD-PE1, which is a polyethylene resin, added was 63.2 mass %, and the amount of PFR1, which is a flame retardant, added was 3 mass %.

[0054] [Example 4] A resin sheet was obtained in the same manner as in Example 1, except that the amount of LD-PE1, which is a polyethylene resin, added was 51.2 mass %, and the amount of INT, which is a flame retardant, added was 40 mass %.

[0055] [Example 5] A resin sheet was obtained in the same manner as in Example 1, except that 5% by mass of PFR2 was used instead of PFR1 as a flame retardant.

[0056] [Comparative Example 1] A resin sheet was obtained in the same manner as in Example 1, except that the amount of HALS1 added as a flame retardant was 0.7 mass %, the amount of INT added was 34.9 mass %, and no PFR2 was added.

[0057] Comparative Example 2 A resin sheet was obtained in the same manner as in Example 1, except that the added amount of PFR1, which is a flame retardant, was 5.1 mass %, the added amount of INT was 30.5 mass %, and no HALS1 was added.

[0058] Comparative Example 3 A resin sheet was obtained in the same manner as in Example 1, except that LD-PE2 was used at 61.2 mass % instead of LD-PE1, which is a polyethylene resin.

[0059] Comparative Example 4 A resin sheet was obtained in the same manner as in Example 1, except that the polyethylene resin LD-PE1 was replaced with 61.2 mass % HD-PE.

[0060] Comparative Example 5 A resin sheet was obtained in the same manner as in Example 1, except that 15.2 mass % of h-PP and 46 mass % of HMS-PP, which are polypropylene, were used instead of polyethylene as the resin.

[0061] [Various measurements and evaluations] The resin sheets of Examples 1 to 5 and Comparative Examples 1 to 5 obtained above were evaluated in various ways by the following methods.

[0062] <Thickness (μm)> The thickness (μm) of the 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).

[0063] <Porosity (%)> The porosity was measured by cutting the resin sheet to prepare a cross section (observation surface) in the thickness direction, attaching it to an observation sample stage, and vapor-depositing gold or the like onto the observation surface, followed by observing the pores using a scanning electron microscope (device name: SM-200, manufactured by TOPCON Corporation). The pores were observed at an arbitrary magnification (500-3000x) 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).

[0064] <Melt tension> The melt tension of the resin sheet was measured using a capillary rheometer Capilograph 1D (Capilograph (registered trademark), manufactured by Toyo Seiki Seisakusho, Ltd.) at a test temperature of 250°C and a take-up speed of 5 mm / min using a capillary having a length of 20 mm and a diameter of 2 mm.

[0065] <Bleed-out prevention> The bleed-out suppression property was confirmed by printing on the resin sheet obtained above and visually inspecting the finished product. First, a resin sheet was subjected to a surface corona treatment at a density of 30 watts using a desktop corona discharge treatment device (Kasuga Electric Co., Ltd., CORONA GENERATOR, model: AGF-B10). After the corona treatment, the resin sheet was subjected to a black solid print using an RI tester (Ishikawajima Industrial Machinery Co., Ltd.) in accordance with JIS K5701-1:2000 "Lithographic Inks - Part 1: Test Methods." For the black solid print, UV offset ink (product name: BC161, T&K TOKA Corporation) was used. The hardness of the rubber roll used to transfer the ink to the resin sheet was set to 90, the printing pressure was adjusted to 10 mm, and the ink buildup was 1.5 g / m. 2 Printed in.

[0066] Next, a UV irradiation device (Eye Inverter Grandage, model ECS-401GX, manufactured by Eye Graphics Co., Ltd.) was used to set the irradiation intensity to 100 mJ / cm 2 UV irradiation was carried out so that the bleed-out suppression test sample was obtained. The above confirmation samples were evaluated according to the following criteria. ◎: No ink peeling was observed, even after leaving the sheet for a long period (1 week) under high temperature and humidity conditions (temperature 40°C, humidity 90%) ○: No ink peeling, but ink peeling was observed after leaving the product for a long time (1 week) under high temperature and humidity conditions (temperature 40°C, humidity 90%) ×: Peeling of ink was observed

[0067] <Compounding> The compounding properties were evaluated according to the following criteria during the production of each resin sheet. 〇: When the resin composition was added to the twin-screw kneader, it was able to be added and kneaded without any problems. △: When the resin composition was added to the twin-screw mixer, there was a slight tendency for clogging to occur, but the mixer was able to mix successfully. ×: When the resin composition was introduced into the twin-screw kneader, clogging occurred, making kneading difficult.

[0068] <Flame retardancy> Flame retardancy was measured in accordance with the UL94 V test. First, the resulting resin sheet was cut into a rectangular piece measuring 13 mm x 125 mm to obtain a resin sheet piece. The resin sheet piece was left standing for at least 48 hours under conditions of 23°C and 50% relative humidity. The upper end of the resin sheet piece was clamped and hung, and 0.05 g or less of 100% cotton was placed 300 mm below the lower end. Using a 10 mm diameter burner, a blue flame of 105 mL / min and 20 mm in diameter was applied to the test piece, with the lower end positioned 10 mm above the tip of the flame. After 10 seconds of flame application, the test piece was checked for melting to the marked line, the time it took for the flame on the test piece to extinguish, and whether the 100% cotton placed below the test piece burned. If the test piece did not melt to the marked line during the first flame application, the same test piece was subjected to a second flame application in the same manner as the first, and the same confirmation was carried out. The above-described series of operations, starting with cutting the resin sheet into rectangular shapes, was performed five times on the same resin sheet, with these five operations constituting one set.

[0069] The above confirmations were evaluated according to the following criteria. V-0: Afterflame time for the first time is 10 seconds or less, total afterflame time for all five sheets is 50 seconds or less, afterflame time for the second time is 30 seconds or less, the clamp does not burn, and the cotton underneath does not burn due to dripping. V-1: First flame duration is 30 seconds or less, total flame duration for all five panels is 250 seconds or less, second flame duration is 60 seconds or less, the clamp does not burn, and the cotton underneath does not burn due to dripping. V-2: The first flame lasted less than 30 seconds, the total flame lasted less than 250 seconds for all five panels, the second flame lasted less than 60 seconds, and the clamp did not burn, but the cotton underneath caught fire due to dripping.

[0070] The evaluation results for the resin sheets of Examples 1 to 5 and Comparative Examples 1 to 5 are shown in Table 2. [Table 2]

[0071] The resin sheets of Examples 1 to 5 all had a flame retardancy rating of V-0, and the bleed-out suppression and compoundability were also within practical ranges. In contrast, the resin sheets of Comparative Examples 1 to 5 all had a flame retardancy rating of V-2.

Claims

1. The present invention includes a polyolefin resin having a melting point of 150°C or less and a flame retardant, The flame retardant contains 0.1% by mass or more of a NOR-type HALS compound, 1.0% by mass or more of an aliphatic phosphate ester compound, and 5.0% by mass or more of a nitrogen-phosphorus compound, A resin sheet having a melt tension of 20 mN or more at 250°C.

2. 2. The resin sheet according to claim 1, having a thickness of 250 μm to 500 μm.

3. 3. The resin sheet according to claim 1, wherein the polyolefin resin has a melt flow rate (at 190°C under a load of 2.16 kg) of 8 g / 10 min or less.

4. The resin sheet according to claim 1 or 2, wherein the polyolefin resin is a polyethylene resin.

5. The resin sheet according to claim 1 or 2, comprising 50% by mass or more of the polyolefin resin.

6. The resin sheet according to claim 1 or 2, which is an unstretched sheet.

7. The resin sheet according to claim 1 or 2, further comprising titanium oxide.

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