Insulation sheet

Abstract

To provide an insulation sheet excellent in flame retardancy and tracking resistance.SOLUTION: The insulation sheet of the present invention includes: an intermediate layer containing an aromatic polycarbonate resin and a flame retardant; a first layer laminated on one surface side of the intermediate layer and containing a first resin; and a second layer laminated on the other surface side of the intermediate layer and containing a second resin. The first layer and the second layer have higher tracking resistance than the aromatic polycarbonate resin. The first resin and the second resin preferably have an aromatic ring ratio of 90 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insulating sheet. [Background technology]

[0002] In electronic devices, insulation is required at locations where short circuits are a concern. In particular, insulating sheets that are formed into a sheet shape so that they can be stored in narrow gaps inside electronic devices are preferably used.

[0003] For example, Patent Document 1 discloses a resin composition containing a polycarbonate resin, a phosphate ester compound, and a fibrous material. It also discloses an insulating sheet formed by molding the resin composition. Such an insulating sheet has good flame retardancy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-030209 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the insulating sheet described in Patent Document 1 has a problem of low tracking resistance. Because tracking resistance affects the spatial distance and creepage distance required for electrical insulation, there is a demand for improving this property.

[0006] An object of the present invention is to provide an insulating sheet that is excellent in flame retardancy and tracking resistance. [Means for solving the problem]

[0007] These objects can be achieved by the present invention as set forth in (1) to (10) below. (1) an intermediate layer including an aromatic polycarbonate resin and a flame retardant; a first layer laminated on one surface of the intermediate layer and including a first resin; a second layer laminated on the other surface side of the intermediate layer and including a second resin; and The insulating sheet is characterized in that the first layer and the second layer have higher tracking resistance than the aromatic polycarbonate resin.

[0008] (2) The insulating sheet according to (1), wherein the first resin and the second resin each have an aromatic ring ratio of 90 mass % or less.

[0009] (3) The insulating sheet according to (1) or (2) above, wherein the first resin and the second resin are heat-resistant polycarbonate resins containing bisphenol A carbonate units and bisphenol isophorone carbonate units.

[0010] (4) The insulating sheet according to (1) or (2) above, wherein the first resin and the second resin are aliphatic polycarbonate resins containing a structure formed by two condensed tetrahydrofuran rings.

[0011] (5) The insulating sheet according to (1) or (2) above, wherein the first resin and the second resin are polyamide resins.

[0012] (6) The insulating sheet according to (1) or (2) above, wherein the first resin and the second resin are polyolefin resins.

[0013] (7) The insulating sheet according to (1) or (2), wherein the first resin and the second resin are polymer alloys obtained by alloying an aromatic polycarbonate resin with a compatible resin that is compatible with the aromatic polycarbonate resin.

[0014] (8) The insulating sheet according to any one of (1) to (7) above, wherein the flame retardant is a nitrogen-containing compound.

[0015] (9) An insulating sheet according to any one of (1) to (8) above, which has a comparative tracking index (CTI), which is an index of tracking resistance measured in accordance with ASTM D3638, of 600 V or more.

[0016] (10) An insulating sheet according to any one of (1) to (9) above, in which the flame retardancy rank determined in accordance with the UL94 standard is V-0 or VTM-0 for a test piece having a thickness of 0.4 mm or more. [Effects of the Invention]

[0017] According to the present invention, an insulating sheet having excellent flame retardancy and tracking resistance can be obtained. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a cross-sectional view showing an insulating sheet according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An insulating sheet according to the present invention will now be described in detail with reference to preferred embodiments shown in the accompanying drawings.

[0020] 1.Insulation sheet Fig. 1 is a cross-sectional view showing an insulating sheet 1 according to an embodiment. In the following description, the lower side in Fig. 1 is referred to as "bottom" and the upper side as "top," but the position of the insulating sheet 1 when used is not limited to this.

[0021] The insulating sheet 1 shown in FIG. 1 has a first layer 11, an intermediate layer 13, and a second layer 12 laminated in this order from the bottom. The intermediate layer 13 contains an aromatic polycarbonate resin and a flame retardant. The first layer 11 is laminated on the lower surface (one surface) of the intermediate layer 13 and contains a first resin. The second layer 12 is laminated on the upper surface (the other surface) of the intermediate layer 13 and contains a second resin. The first layer 11 and the second layer 12 have higher tracking resistance than the aromatic polycarbonate resin contained in the intermediate layer 13.

[0022] According to this configuration, the aromatic polycarbonate resin is a polycarbonate resin containing an aromatic ring structure in the main chain, and the high proportion of the aromatic ring structure imparts good heat resistance to the intermediate layer 13. The intermediate layer 13 also contains a flame retardant. These properties contribute to the intermediate layer 13 having good flame retardancy.

[0023] Furthermore, the intermediate layer 13 is sandwiched between the first layer 11 and the second layer 12. Therefore, if creeping discharge occurs on the insulating sheet 1, the intermediate layer 13 is prevented from being directly exposed to arc discharge or the like. The first layer 11 and the second layer 12 each have higher tracking resistance than aromatic polycarbonate resin, and therefore the insulating sheet 1 is endowed with good tracking resistance. Therefore, the insulating sheet 1 has excellent flame retardancy and tracking resistance.

[0024] Furthermore, with this configuration, one of the effects of the multilayer structure is improved pinhole resistance, which can further improve the insulation properties, flame retardancy, and tracking resistance of insulating sheet 1.

[0025] Examples of methods for manufacturing the insulating sheet 1 shown in FIG. 1 include co-extrusion, dry lamination, extrusion lamination, and hot melt.

[0026] The thickness of the insulating sheet 1 is not particularly limited, but is preferably 30 μm or more and 1500 μm or less, more preferably 100 μm or more and 1200 μm or less, and even more preferably 200 μm or more and 1000 μm or less. This results in an insulating sheet 1 with excellent flame retardancy, tracking resistance, and insulating properties. If the thickness of the insulating sheet 1 is below the lower limit, the flame retardancy and insulating properties may be reduced. On the other hand, the thickness of the insulating sheet 1 may be above the upper limit, but in that case, the insulating sheet 1 may be too thick, reducing flexibility and making it difficult to handle, and the heat dissipation properties and shape accuracy during molding may be reduced.

[0027] The insulating sheet 1 is placed in, for example, electrical or electronic equipment in locations where insulation is required. The insulating sheet 1 has good flame retardancy and tracking resistance, and can also increase the breakdown voltage. This allows the insulating sheet 1 to be placed close to electrodes, etc., which has the effect of shortening the insulation spatial distance. As a result, when a circuit board, etc. is housed inside an electrical or electronic equipment, the volume of the space can be reduced, making it easier to miniaturize the equipment.

[0028] Furthermore, when the insulating sheet 1 has formability, it can be thermoformed using a plate material by vacuum forming, pressure forming, vacuum pressure forming, etc. When the insulating sheet 1 has such thermoformability, an insulating sheet formed into any desired uneven shape can be obtained.

[0029] 1.1.Middle Tier The intermediate layer 13 is formed using a resin composition containing an aromatic polycarbonate resin and a flame retardant.

[0030] The thickness of the intermediate layer 13 is not particularly limited, but is preferably 10 μm or more and 1500 μm or less, more preferably 50 μm or more and 1200 μm or less, and even more preferably 100 μm or more and 1000 μm or less, thereby improving the flame retardancy and insulating properties of the intermediate layer 13.

[0031] 1.1.1. Aromatic polycarbonate resin Aromatic polycarbonate resins can be obtained by the phosgene method in which various dihydroxydiaryl compounds are reacted with phosgene, the transesterification method in which a dihydroxydiaryl compound is reacted with a carbonate ester such as diphenyl carbonate, the ring-opening polymerization method of a cyclic carbonate compound, the interfacial polycondensation method, etc. Such aromatic polycarbonate resins impart excellent heat resistance and flame retardancy derived from the aromatic ring structure to the resin composition.

[0032] Dihydroxydiaryl compounds include, in addition to bisphenol A, bis(hydroxyaryl)alkanes such as bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)octane, bis(4-hydroxyphenyl)phenylmethane, 2,2-bis(4-hydroxyphenyl-3-methylphenyl)propane, and 1,1-bis(4-hydroxy-3-tert-butylphenyl)propane; and bis(hydroxyaryl)cycloalkanes such as 1,1-bis(4-hydroxyphenyl)cyclopentane and 1,1-bis(4-hydroxyphenyl)cyclohexane. dihydroxydiaryl ethers such as 4,4'-dihydroxydiphenyl ether and 4,4'-dihydroxy-3,3'-dimethyldiphenyl ether, dihydroxydiaryl sulfides such as 4,4'-dihydroxydiphenyl sulfide and 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfide, dihydroxydiaryl sulfoxides such as 4,4'-dihydroxydiphenyl sulfoxide and 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfone, dihydroxydiaryl sulfones such as 4,4'-dihydroxydiphenyl sulfone and 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfone, etc. These may be used alone or in combination of two or more.

[0033] The aromatic polycarbonate resin particularly includes those having a structural unit represented by the following formula (1).

[0034] [ka] (In formula (1), R 1 and R 2 are independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 5 to 7 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom. m and n are independently an integer of 0 to 4. X is a direct bond, O, S, SO, SO2, CR 3 R 4(R 3 and R 4 are independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and may be the same or different from each other.), an alkylene group having 2 to 10 carbon atoms, a polydimethylsiloxane group, or C(CF3)2.

[0035] The aromatic polycarbonate resin having the structural unit represented by the above formula (1) imparts particularly excellent heat resistance and flame retardancy to the resin composition.

[0036] Of all the structural units constituting the aromatic polycarbonate resin, the proportion of the structural units represented by the above formula (1) is preferably 55 mol % or more, more preferably 70 mol % or more, and even more preferably 80 mol % or more.

[0037] In addition, from the viewpoint of ease of acquisition and cost, R 1 and R 2 are each preferably a hydrogen atom, and X is preferably CR 3 R 4 and R 3 and R 4 are preferably each a methyl group or a hydrogen atom.

[0038] The aromatic polycarbonate resin is preferably a polycarbonate resin having structural units derived from bisphenol A (2,2-bis(4-hydroxyphenyl)propane), which can further enhance the flame retardancy and heat resistance of the resin composition.

[0039] The viscosity average molecular weight (M) of the aromatic polycarbonate resin is not particularly limited, but is preferably 5,000 or more and 100,000 or less, more preferably 12,000 or more and 35,000 or less, even more preferably 15,000 or more and 30,000 or less, and particularly preferably 18,000 or more and 28,000 or less.

[0040] The viscosity average molecular weight (M) is calculated from the viscosity (η) of the methylene chloride solution of the resin, η = kM α The viscosity is calculated using the formula below. k and α are constants specific to polymers. Viscosity is measured using an Ubbelohde viscometer at 20°C.

[0041] The aromatic polycarbonate resin may be a blend of a resin with a high viscosity average molecular weight (high viscosity resin) and a resin with a low viscosity average molecular weight (low viscosity resin), which allows for a resin composition with excellent moldability without impairing the heat resistance and flame retardancy inherent to the aromatic polycarbonate resin.

[0042] The difference between the viscosity average molecular weight of the high-viscosity resin and the viscosity average molecular weight of the low-viscosity resin is not particularly limited, but is preferably from 3,000 to 20,000, and more preferably from 5,000 to 10,000. This allows for a resin composition with particularly good moldability to be obtained.

[0043] When the blending amount of the high-viscosity resin is M1 and the blending amount of the low-viscosity resin is M2, the blending ratio M1 / M2 is preferably 0.5 to 8.0 by mass, more preferably 0.8 to 6.0, and even more preferably 0.9 to 5.0, thereby obtaining a resin composition with particularly good moldability.

[0044] The glass transition temperature Tg of the aromatic polycarbonate resin is preferably 130°C or higher and lower than 160°C, and more preferably 140°C or higher and 155°C or lower. If the glass transition temperature Tg of the aromatic polycarbonate resin is within the above range, the heat resistance and flame retardancy of the intermediate layer 13 can be sufficiently improved. The glass transition temperature Tg of the aromatic polycarbonate resin is measured by DSC (differential scanning calorimetry). The heating rate in the DSC method is 10°C / min.

[0045] The content of the aromatic polycarbonate resin in the intermediate layer 13 is not particularly limited, but is preferably 70% by mass or more, and more preferably 80% by mass or more.

[0046] The melt volume rate (MVR) of aromatic polycarbonate resin at 300°C and a load of 1.2 kg is 5 cm 3 / 10min] or more 20[cm 3 / 10min] or less, and 8 [cm 3 / 10min] or more 15[cm 3 / 10 min or less is more preferable. This improves the moldability of the insulating sheet 1 in secondary processing, particularly in vacuum molding, to prevent defects such as distortion. If the melt volume rate is below the lower limit, the flowability may be insufficient, resulting in reduced moldability. On the other hand, if the melt volume rate is above the upper limit, the impact resistance of the molded body may be reduced. The melt volume rate is measured in accordance with the test method specified in JIS K 7210:2014.

[0047] 1.1.2.Flame retardants The flame retardant enhances the flame retardancy of the resin composition. Examples of the flame retardant include inorganic phosphorus-based flame retardants such as halogen-based flame retardants, red phosphorus and polyphosphate-based flame retardants such as ammonium polyphosphate, organic phosphorus-based flame retardants such as triaryl phosphate ester compounds, metal hydroxide-based compounds, antimony oxide-based compounds, nitrogen-containing compounds, etc. Furthermore, the flame retardant may be a combination of two or more of these.

[0048] Among these, phosphorus-based flame retardants or nitrogen-containing compounds are preferably used as the flame retardant, and nitrogen-containing compounds are more preferably used. When the flame retardant contains a nitrogen-containing compound, the flame retardancy of the insulating sheet 1 can be further improved. Furthermore, since the nitrogen-containing compound does not contain halogen atoms, a so-called halogen-free and fluorine-free insulating sheet 1 can be realized.

[0049] Examples of the nitrogen-containing compound include compounds having a triazine skeleton. Examples of compounds having a triazine skeleton include melamine, melamine derivatives such as butylmelamine, trimethylolmelamine, hexamethylolmelamine, hexamethoxymethylmelamine, and melamine phosphate, cyanuric acid, cyanuric acid derivatives such as methyl cyanurate, diethyl cyanurate, trimethyl cyanurate, and triethyl cyanurate, isocyanuric acid, isocyanuric acid derivatives such as methyl isocyanurate, N,N'-diethyl isocyanurate, trismethyl isocyanurate, trisethyl isocyanurate, bis(2-carboxyethyl) isocyanurate, 1,3,5-tris(2-carboxyethyl) isocyanurate, and tris(2,3-epoxypropyl) isocyanurate, melamine cyanurate, and melamine isocyanurate. These compounds can be used alone or in combination of two or more.

[0050] Among these, the compound having a triazine skeleton is preferably one or more melamine-based compounds selected from the group consisting of melamine, melamine cyanurate, melamine isocyanurate, and derivatives thereof, and more preferably melamine cyanurate, which can particularly enhance the flame retardancy of the resin composition.

[0051] The amount of flame retardant added to the resin composition is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 3 to 10 parts by mass, relative to 100 parts by mass of the aromatic polycarbonate resin. By setting the amount of flame retardant added within this range, the effect of enhancing flame retardancy is fully exerted, and side effects such as a decrease in mechanical properties due to an excess of flame retardant can be suppressed.

[0052] The flame retardant is, for example, in particulate form. In this case, the average particle size of the flame retardant is preferably 0.01 μm or more and 10 μm or less, more preferably 0.05 μm or more and 5 μm or less, and even more preferably 0.2 μm or more and 2 μm or less. When the average particle size of the flame retardant is within the above range, the dispersibility of the flame retardant is particularly good, thereby particularly improving the flame retardancy of the resin composition. The average particle size of the flame retardant is the particle size at which the cumulative amount from the small diameter side in the volume-based particle size distribution measured using a laser diffraction particle size distribution analyzer is 50%.

[0053] Additives The resin composition may contain any additives. Examples of additives include colorants, stabilizers, lubricants, processing aids, antistatic agents, antioxidants, neutralizing agents, UV absorbers, dispersants, thickeners, mold release agents, fillers, flow improvers, plasticizers, and antibacterial agents. The resin composition may contain one type of additive, or two or more types in any combination.

[0054] The total amount of additives added is preferably 0.1 parts by mass or more and 20 parts by mass or less, more preferably 0.3 parts by mass or more and 10 parts by mass or less, and even more preferably 0.5 parts by mass or more and 5 parts by mass or less, per 100 parts by mass of the polymer alloy.

[0055] 1.2. First and second layers The first layer 11 is laminated on the lower surface side (one surface side) of the intermediate layer 13, and the second layer 12 is laminated on the upper surface side (the other surface side) of the intermediate layer 13.

[0056] The thickness of each of the first layer 11 and the second layer 12 is not particularly limited and may be equal to or greater than the thickness of the intermediate layer 13, but is preferably thinner than the thickness of the intermediate layer 13, more preferably 2% to 70%, and even more preferably 4% to 50% of the thickness of the intermediate layer 13. This makes it possible to reduce the overall thickness of the insulating sheet 1 while ensuring sufficient tracking resistance in the first layer 11 and the second layer 12, and to avoid a decrease in flexibility, formability, etc.

[0057] The thickness of each of the first layer 11 and the second layer 12 is preferably 5 μm or more and 700 μm or less, more preferably 10 μm or more and 500 μm or less, and even more preferably 50 μm or more and 400 μm or less.

[0058] The first layer 11 and the second layer 12 are made of a material that has higher tracking resistance than the aromatic polycarbonate resin contained in the intermediate layer 13.

[0059] Tracking resistance refers to the resistance to the phenomenon of forming a conductive path (tracking) due to discharge occurring on the surface of an insulator. Such tracking resistance can be quantified, for example, by the comparative tracking index (CTI), which is an index of tracking resistance measured in accordance with ASTM D3638. Therefore, materials with a comparative tracking index (CTI) higher than aromatic polycarbonate resin are used for the constituent materials of the first layer 11 and the second layer 12. This makes it possible to achieve first layer 11 and second layer 12 with better tracking resistance than intermediate layer 13. As a result, an insulating sheet 1 is obtained that is excellent in both flame retardancy and tracking resistance.

[0060] The comparative tracking index CTI of each of the constituent materials of the first layer 11 and the second layer 12 is preferably 400 V or more, and more preferably 600 V or more, thereby providing the first layer 11 and the second layer 12 with particularly good tracking resistance.

[0061] Furthermore, the comparative tracking index CTI of each of the constituent materials of the first layer 11 and the second layer 12 is preferably at least 50 V higher than the comparative tracking index CTI of the aromatic polycarbonate resin, and more preferably at least 100 V higher. This makes it possible to obtain an insulating sheet 1 that better balances flame retardancy and tracking resistance.

[0062] Methods for improving the tracking resistance of the constituent materials of the first layer 11 and the second layer 12 include using a resin with high tracking resistance and adding an additive that improves tracking resistance.

[0063] Examples of resins that can improve tracking resistance include various resins described below. Examples of additives that enhance tracking resistance include inorganic fillers and heat-absorbing materials.

[0064] Among these, examples of inorganic fillers include fibrous inorganic fillers such as glass fiber, granular inorganic fillers such as silica, quartz powder and glass beads, and plate-like fillers such as mica and glass flakes.

[0065] Examples of heat-absorbing materials include aluminum hydroxide, magnesium hydroxide, calcium borate, and zinc borate.

[0066] 1.2.1. First Resin and Second Resin The first layer 11 contains a first resin, and the second layer 12 contains a second resin. The first resin and the second resin are preferably materials having higher tracking resistance than the aromatic polycarbonate resin contained in the intermediate layer 13.

[0067] The comparative tracking index CTI of each of the first resin and the second resin is preferably at least 400 V, and more preferably at least 600 V. This allows the first resin and the second resin to have particularly good tracking resistance.

[0068] Furthermore, the comparative tracking index CTI of each of the first resin and the second resin is preferably at least 50 V higher than the comparative tracking index CTI of the aromatic polycarbonate resin, and more preferably at least 100 V higher, thereby obtaining an insulating sheet 1 that better balances flame retardancy and tracking resistance.

[0069] The glass transition temperature Tg of each of the first resin and the second resin is preferably 125°C or higher, and more preferably 130°C or higher but lower than 200°C. This provides heat resistance to the first resin and the second resin, making it easier to suppress coloration due to carbonization even if creeping discharge occurs in the first layer 11 and the second layer 12. As a result, it is possible to suppress the occurrence of poor appearance in the first layer 11 and the second layer 12 and the deterioration of insulation due to carbonization. The glass transition temperature Tg of each of the first resin and the second resin is measured by DSC (differential scanning calorimetry). The heating rate in the DSC method is 10°C / min.

[0070] The melt volume rate (MVR) of the first and second resins at 300°C and a load of 1.2 kg is 5 cm 3 / 10min] or more 30[cm 3 / 10min] or less, and 8 [cm 3 / 10min] or more 20[cm 3 / 10 min or less is more preferable. This improves the moldability of the insulating sheet 1 in secondary processing, particularly in vacuum molding, to prevent defects such as distortion. If the melt volume rate is below the lower limit, the flowability may be insufficient, resulting in reduced moldability. On the other hand, if the melt volume rate is above the upper limit, the impact resistance of the molded body may be reduced. The melt volume rate is measured in accordance with the test method specified in JIS K 7210:2014.

[0071] Furthermore, the first resin and the second resin preferably have a ratio of aromatic rings of 90% by mass or less, more preferably 70% by mass or less, even more preferably 50% by mass or less, and particularly preferably 30% by mass or less. Such first resins and second resins have a relatively high ratio of aliphatic structures. This makes it possible to impart good tracking resistance to the first resin and the second resin. This results in first resins and second resins that are better in both flame retardancy and tracking resistance. Furthermore, even if creeping discharge occurs in the insulating sheet 1, for example, coloration due to carbonization can be easily suppressed. As a result, the occurrence of poor appearance in the insulating sheet 1 and deterioration of insulating properties due to carbonization can be suppressed.

[0072] Furthermore, the ratio of aromatic rings in the first layer 11 and the ratio of aromatic rings in the second layer 12 are each preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. The first layer 11 and the second layer 12 each have a relatively high ratio of aliphatic structures. This allows the first layer 11 and the second layer 12 to be endowed with good tracking resistance. This provides an insulating sheet 1 that is excellent in both flame retardancy and tracking resistance. Furthermore, even if creeping discharge occurs in the insulating sheet 1, for example, coloration due to carbonization can be easily suppressed. As a result, the occurrence of poor appearance in the insulating sheet 1 and the deterioration of insulating properties due to carbonization can be suppressed.

[0073] Furthermore, the ratio of aromatic rings in the first layer 11 and the ratio of aromatic rings in the second layer 12 are each preferably lower than the ratio of aromatic rings in the aromatic polycarbonate resin contained in the intermediate layer 13, more preferably lower by 5 mass % or more, and even more preferably lower by 10 mass % or more. This makes it possible to obtain an insulating sheet 1 that is excellent in both flame retardancy and tracking resistance.

[0074] The ratio of aromatic rings can be determined as follows: Here, as an example, the ratio of aromatic rings in carbonate units represented by the following formula is calculated.

[0075] [ka]

[0076] The carbonate unit has 16 carbon atoms, 3 oxygen atoms, and 14 hydrogen atoms. Therefore, the molecular weight of the carbonate unit is 254.

[0077] In addition, one aromatic ring has 6 carbon atoms and 4 hydrogen atoms. Therefore, the molecular weight of one aromatic ring is 12 × 6 + 1 × 4 = 76.

[0078] The number of aromatic rings in the carbonate unit is 2. Therefore, the ratio [mass %] of aromatic rings in the carbonate unit is 76×2 / 254×100=59.8.

[0079] The content of the first resin in the first layer 11 and the content of the second resin in the second layer 12 are preferably 70% by mass or more, and more preferably 80% by mass or more.

[0080] Examples of the first and second resins include polyolefin resins, polyamide resins, polyester resins, aliphatic polycarbonate resins, heat-resistant polycarbonate resins, polyarylate resins, polyethylene terephthalate resins, polybutylene terephthalate resins, polylactic acid, styrene copolymers, polyacetal resins, polyphenylene ether resins, polyphenylene sulfide resins, polymethyl methacrylate resins, and cellulose ester resins. The first and second resins may be composed of one or more of these resins in combination. Among these, polyolefin resins, polyamide resins, aliphatic polycarbonate resins, and heat-resistant polycarbonate resins are preferred.

[0081] 1.2.1.1. Polyolefin resin Examples of polyolefin resins include high-density polyethylene resins, polypropylene resins, polybutene resins, ethylene-(meth)acrylic acid copolymers, ethylene-methyl (meth)acrylate copolymers, ethylene-ethyl (meth)acrylate copolymers, ethylene-vinyl acetate copolymers, maleic anhydride-modified polyethylene, carboxylic acid-modified polyethylene, ethylene-propylene copolymers, and ethylene-propylene-diene copolymers.

[0082] Polyolefin resins have superior chemical resistance to various chemicals compared to aromatic polycarbonate resins. Furthermore, polyolefin resins have good tracking resistance due to their hydrocarbon chain structure. Therefore, polyolefin resins contribute to improving the chemical resistance and tracking resistance of the insulating sheet 1. Of these, polypropylene resin is preferably used, which particularly improves the chemical resistance and tracking resistance of the insulating sheet 1.

[0083] Polyamide resin Examples of polyamide resins include polycaproamide (polyamide 6), polytetramethylene adipamide (polyamide 46), polyhexamethylene adipamide (polyamide 66), polyhexamethylene sebacamide (polyamide 610), polyhexamethylene dodecamide (polyamide 612), polyundecamethylene adipamide (polyamide 116), polyundecane amide (polyamide 11), polydodecanamide (polyamide 12), polytrimethylhexamethylene terephthalamide (polyamide TMHT), polyhexamethylene terephthalamide (polyamide 6T), polyhexamethylene isophthalamide (polyamide 6I), and polyhexamethylene. Examples of the polyisopropyl terephthalamide include polyethylene terephthalate / isophthalamide (polyamide 6T / 6I), polybis(4-aminocyclohexyl)methanedodecamide (polyamide PACM12), polybis(3-methyl-4-aminocyclohexyl)methanedodecamide (polyamide dimethyl PACM12), polymetaxylylene adipamide (polyamide MXD6), polynonamethylene terephthalamide (polyamide 9T), polydecamethylene terephthalamide (polyamide 10T), polyundecamethylene terephthalamide (polyamide 11T), and polyundecamethylene hexahydroterephthalamide (polyamide 11T(H)). These may also be copolymers or mixtures thereof.

[0084] The polyamide resin can be obtained by polymerizing or copolymerizing nylon salts made from diamines and dicarboxylic acids using known methods such as melt polymerization, solution polymerization, solid-state polymerization, etc. By using polyamide resins as the first resin and the second resin, the tracking resistance of the insulating sheet 1 can be further improved.

[0085] The diamine may be an aliphatic diamine, but an alicyclic diamine or aromatic diamine is preferably used, with an alicyclic diamine being more preferred. By using these, a polyamide resin having a cyclic structure such as an aromatic ring structure or an alicyclic structure can be prepared. Such a polyamide resin contributes to improving the heat resistance of the first layer 11 and the second layer 12. Furthermore, the alicyclic diamine in particular contributes to improving the tracking resistance of the first layer 11 and the second layer 12.

[0086] Examples of alicyclic diamines include 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 1,3-cyclohexanedimethylamine, 1,4-cyclohexanedimethylamine, bis(4-aminocyclohexyl)methane, bis(4-aminocyclohexyl)propane, bis(3-methyl-4-aminocyclohexyl)methane, bis(3-methyl-4-aminocyclohexyl)propane, 5-amino-2,2,4-trimethyl-1-cyclopentanemethylamine, 5-amino-1,3,3-trimethylcyclohexanemethylamine (isophoronediamine), bis(aminopropyl)piperazine, bis(aminoethyl)piperazine, norbornanedimethylamine, and tricyclodecanedimethylamine, and one or more of these may be used. Examples of aromatic diamines include m-xylylenediamine and p-xylylenediamine.

[0087] The dicarboxylic acid may be an alicyclic dicarboxylic acid or an aromatic dicarboxylic acid, but an aliphatic dicarboxylic acid is preferably used. This allows the preparation of a polyamide resin having a hydrocarbon chain structure. Such a polyamide resin contributes to improving the tracking resistance of the first layer 11 and the second layer 12.

[0088] Examples of dicarboxylic acids include aliphatic dicarboxylic acids such as adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, octadecanedioic acid, and eicosanedioic acid; alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, dicyclohexanemethane-4,4'-dicarboxylic acid, and norbornanedicarboxylic acid; and aromatic dicarboxylic acids such as isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. One or more of these may be used.

[0089] The polyamide resin preferably used is polyamide 6T, polyamide PACM12, polyamide dimethyl PACM12, polyamide MXD6, polyamide 9T, polyamide 10T, polyamide 11T, or polyamide 11T(H), and more preferably polyamide PACM12 or polyamide dimethyl PACM12. These have both a cyclic structure such as an aromatic ring structure or an alicyclic structure, and an aliphatic structure, and therefore contribute to improving both the heat resistance and tracking resistance of the first layer 11 and the second layer 12. Polyamide PACM12 contains a structural unit represented by the following formula (2).

[0090] [ka]

[0091] The polyamide PACM12 is synthesized from bis(4-aminocyclohexyl)methane (PACM) and dodecanedioic acid. Polyamide dimethyl PACM12 contains a structural unit represented by the following formula (3).

[0092] [ka]

[0093] The polyamide dimethyl PACM12 is synthesized using bis(3-methyl-4-aminocyclohexyl)methane (MACM) and dodecanedioic acid as raw materials.

[0094] Aliphatic polycarbonate resin Examples of aliphatic polycarbonate resins include those containing an aliphatic carbonate unit having a carbon number of 2 to 12. Specific examples include polyethylene carbonate, polypropylene carbonate, polytrimethylene carbonate, polytetramethylene carbonate, polypentamethylene carbonate, polyhexamethylene carbonate, polyheptamethylene carbonate, polyoctamethylene carbonate, polynonamemethylene carbonate, polydecamethylene carbonate, polyoxydiethylene carbonate, poly-3,6-dioxyoctane carbonate, poly-3,6,9-trioxyundecane carbonate, polyoxydipropylene carbonate, polycyclopentene carbonate, and polycyclohexene carbonate.

[0095] The aliphatic polycarbonate resin may also be a resin containing an aliphatic carbonate unit containing a diol residue represented by the following formula (4).

[0096] [ka] (In formula (4), R 5 ~R 8 are each independently a hydrogen atom, an alkyl group, a cycloalkyl group, or an aryl group.

[0097] The aliphatic polycarbonate resin preferably contains 30 mol % to 100 mol %, and more preferably 50 mol % to 90 mol %, of all structural units of the aliphatic carbonate unit containing the diol residue represented by the above formula (4).

[0098] The diol residue represented by the formula (4) has a structure in which two tetrahydrofuran rings are fused together. By including such a structure in the structural unit, the glass transition temperature Tg of the first resin and the second resin can be increased. As a result, the first layer 11 and the second layer 12 have excellent heat resistance and tracking resistance.

[0099] Examples of diols constituting the diol residue represented by the above formula (4) include isosorbide, isomannide, isoidide, etc. These carbohydrate-derived diols are useful in that they are substances that can also be obtained from biomass in nature.

[0100] 1.2.1.4.Heat-resistant polycarbonate resin The first resin and the second resin may be polycarbonate resins other than aliphatic polycarbonate resins.

[0101] Other polycarbonate resins include, for example, resins containing carbonate units (bisphenolisophorone carbonate units) represented by the following formula (5). Such polycarbonate resins have higher heat resistance than aromatic polycarbonate resins. Hereinafter, polycarbonate resins containing bisphenolisophorone carbonate units may be referred to as "heat-resistant polycarbonate resins."

[0102] [ka] (In formula (5), R a and R b are each independently an alkyl group having 1 to 12 carbon atoms, and R g is an alkyl group having 1 to 12 carbon atoms, p and q each independently represent an integer of 0 to 4, and t represents an integer of 0 to 10.

[0103] In addition, each R a and R b Preferably, at least one of is positioned meta to the cyclohexylidene bridging group.

[0104] Also, R a and R b are each independently an alkyl group having 1 to 4 carbon atoms, and R g is an alkyl group having 1 to 4 carbon atoms, p and q are each 0 or 1, and t may be 0 to 5.

[0105] Furthermore, R a , R b , and R g are each a methyl group, p and q are each 0 or 1, and t is 0 or 3, preferably 0.

[0106] A specific example of such a heat-resistant polycarbonate resin is a resin containing carbonate units (bisphenol A carbonate units) derived from bisphenol A (2,2-bis(4-hydroxyphenyl)propane) and carbonate units (bisphenol isophorone carbonate units) represented by formula (5). In this case, p and q in the bisphenol isophorone carbonate units are each 0, and each R g is preferably a methyl group, and t is preferably 3. In this case, the bisphenol isophorone carbonate unit is particularly a carbonate unit containing a structure derived from bisphenol TMC (1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane).

[0107] Such bisphenol isophorone carbonate units contain both an aromatic ring structure and an alicyclic structure, and therefore contribute particularly to improving both the heat resistance (flame retardancy) and tracking resistance of the first resin and the second resin.

[0108] Of all the structural units constituting the heat-resistant polycarbonate resin, the proportion of bisphenol isophorone carbonate units is preferably 30 mol% or more, more preferably 50 mol% or more, and even more preferably 55 mol% or more, which contributes to improving both the heat resistance (flame retardancy) and tracking resistance of the first resin and the second resin.

[0109] The glass transition temperature Tg of the heat-resistant polycarbonate resin is preferably higher (preferably by at least 5°C) than the glass transition temperature Tg of the aromatic polycarbonate resin, more preferably 160°C or higher but 200°C or lower, and even more preferably 165°C or higher but lower than 200°C. If the glass transition temperature Tg of the heat-resistant polycarbonate resin is within the above range, the heat resistance of the first resin and the second resin can be particularly improved. As a result, even if creeping discharge occurs in the first layer 11 and the second layer 12, coloration due to carbonization can be particularly suppressed, and therefore, the occurrence of poor appearance and the deterioration of insulation due to carbonization can be particularly suppressed.

[0110] 1.2.1.5. Polymer alloys The first resin and the second resin may be a polymer alloy formed by alloying an aromatic polycarbonate resin with a compatible resin. A polymer alloy refers to a single-phase or stable multi-phase material formed by mixing multiple types of polymers, preferably a single-phase material. In this specification, "alloying" refers to the preparation of such a single-phase or multi-phase material by kneading raw materials containing multiple types of polymers. Aromatic polycarbonate resins are polycarbonate resins containing aromatic ring structures in their main chains, and their high proportion of aromatic ring structures provides excellent heat resistance. Therefore, alloying such aromatic polycarbonate resins with compatible resins provides first and second resins that combine the heat resistance inherent in the aromatic polycarbonate resin with additional properties inherent in the compatible resin. This results in an insulating sheet 1 with even higher heat resistance and various added value.

[0111] The compatible resin is preferably a resin having higher tracking resistance than the aromatic polycarbonate resin, for example, a resin having a higher comparative tracking index (CTI) than the aromatic polycarbonate resin, thereby obtaining a first resin and a second resin having both heat resistance and tracking resistance. As the compatible resin, the various resins exemplified as the first resin and the second resin can be used.

[0112] The proportion of the compatible resin in the polymer alloy is not particularly limited, but is preferably 5% by mass to 80% by mass, more preferably 10% by mass to 75% by mass, even more preferably 20% by mass to 70% by mass, and particularly preferably 40% by mass to 65% by mass. This configuration makes it possible to realize a polymer alloy that has a good balance between the properties of the aromatic polycarbonate resin, such as heat resistance and flame retardancy, and the properties of the compatible resin.

[0113] The polymer alloy may contain a resin other than the aromatic polycarbonate resin and the compatible resin. That is, the polymer alloy may be an alloy of three or more resins. Examples of resins that can be contained include the resins listed as the first resin and the second resin.

[0114] Examples of compatible resins include aromatic polycarbonate resins, heat-resistant polycarbonate resins, polyamide resins, and polyolefin resins.

[0115] Here, an example of a method for preparing a polymer alloy will be described. First, the raw materials are premixed and melted and kneaded using a batch kneader, twin-screw extruder, or the like. This mechanically stirs the raw materials, resulting in a kneaded product containing a polymer alloy. The kneading and melting conditions are appropriately set depending on the type and blending ratio of the raw materials, and examples include a temperature of 200 to 250°C, a screw rotation speed of 300 to 1000 rpm, and a kneading time of about 3 to 20 minutes. Next, the kneaded product is pelletized as necessary.

[0116] Furthermore, a compatibilizer may be added to the raw materials as needed, which can further enhance the compatibility between the aromatic polycarbonate resin and the compatible resin.

[0117] The amount of the compatibilizer added is preferably 2 parts by mass or more and 30 parts by mass or less, and more preferably 5 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the resin.

[0118] The distance between the HSP values ​​of the aromatic polycarbonate resin and the compatible resin in the polymer alloy is preferably 0 to 15, more preferably 0 to 10, and even more preferably 0 to 7. By selecting the aromatic polycarbonate resin and the compatible resin so as to satisfy this distance between the HSP values, it is possible to obtain a first resin and a second resin that are excellent in homogeneity and have further improved flame retardancy and heat resistance.

[0119] The HSP value is calculated by multiplying the solubility parameter SP of each substance by the dispersion force term (δ D ), polarity term (δ P ), hydrogen bond term (δ H ) and the value of each term is regarded as a coordinate in three-dimensional space. It is also called the Hansen solubility parameter. D ) is a value that represents the square root of the cohesive energy density of a substance, and takes into account the dispersion forces between molecules. P ) is a value that indicates the polarity of a substance and takes into account the polar interactions between molecules. H ) is a value that represents the hydrogen bonding ability of a substance and takes into account hydrogen bonds between molecules.

[0120] The distance between the HSP values ​​of the aromatic polycarbonate resin and the compatible resin can be calculated by the following formula.

[0121] Distance between HSP values={4×(δ D1 -δ D2 ) 2 +(δ P1 -δ P2 ) 2 +(δH1 -δ H2 ) 2} 0.5

[0122] In addition, δ in the above formula D1 , δ D2 , δ P1 , δ P2 , δ H1 , δ H2 is as follows:

[0123] δ D1 is the dispersion term of aromatic polycarbonate resin δ D2 is the dispersion force term of the compatible resin δ P1 is the polar term of aromatic polycarbonate resin δ P2 is the polar term of the compatible resin δ H1 is the hydrogen bond term of aromatic polycarbonate resin δ H2 is the hydrogen bond term of the compatible resin

[0124] Additives The first layer 11 and the second layer 12 may contain any additives. Examples of additives include colorants, stabilizers, lubricants, processing aids, antistatic agents, antioxidants, neutralizing agents, UV absorbers, dispersants, thickeners, mold release agents, fillers, flow improvers, plasticizers, and antibacterial agents. The first layer 11 and the second layer 12 may contain one type of additive, or two or more types in any combination.

[0125] The total amount of additives added is preferably 0.1 parts by mass or more and 10 parts by mass or less, more preferably 0.3 parts by mass or more and 5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 3 parts by mass or less, per 100 parts by mass of the first resin or the second resin.

[0126] Furthermore, it is preferable that the first layer 11 and the second layer 12 do not contain a flame retardant. Specifically, the content of the flame retardant in the first layer 11 and the second layer 12 is preferably less than 0.1 mass %, and more preferably 0.05 mass % or less. This can prevent the flame retardant from falling off the insulating sheet 1 and becoming foreign matter.

[0127] 1.3.Characteristics of the insulation sheet Next, the characteristics of the insulating sheet 1 according to the embodiment will be described.

[0128] 1.3.1. Tracking resistance The tracking resistance of the insulating sheet 1 according to the embodiment can be quantified by the comparative tracking index CTI, which is an index of tracking resistance measured in accordance with ASTM D3638.

[0129] The comparative tracking index CTI (CTI value) of the insulating sheet 1 according to the embodiment is preferably 600 V or more. If the CTI value is within this range, the rank PLC, which indicates tracking resistance, will be the highest rank of 0. Therefore, it can be said that an insulating sheet 1 having a CTI value within this range has particularly good tracking resistance.

[0130] The measurement method specified in ASTM D3638 measures the CTI value using a 0.1% by mass aqueous solution of ammonium chloride and a platinum electrode. More specifically, the ammonium chloride aqueous solution is dropped a specified number of times (50 drops) and the voltage at which none of the test pieces (n=5) breaks down is determined, and this is taken as the CTI value.

[0131] The test piece used is an insulating sheet 1 having a thickness of 3 mm or more. The test piece may be one in which a plurality of insulating sheets 1 are stacked.

[0132] The comparative tracking indexes CTI of the first and second resins and the aromatic polycarbonate resin are measured in the same manner as above. In this case, test pieces are made of sheets of these resins extruded to a thickness of 3 mm or more.

[0133] 1.3.2.Flame retardancy The flame retardancy of the insulating sheet 1 according to the embodiment can be quantified by the flame retardancy rank determined in accordance with the UL94 standard (rank determined by the UL94V test or UL94VTM test).

[0134] The flame retardancy of the insulating sheet 1 according to the embodiment is preferably such that the UL94V test rank is V-0 for a test piece thickness of 0.4 mm or more, or the UL94VTM test rank is VTM-0 for a test piece thickness of 0.4 mm or more.

[0135] An insulating sheet 1 that satisfies such a judgment rank satisfies the highest rank in each test, and therefore can be said to have particularly good flame retardancy.

[0136] In the UL94V test, a vertical combustion test is performed using test pieces measuring 125±5mm x 13.0±0.5mm.

[0137] The UL94VTM test is performed when the test specimen is too thin to perform the UL94V test. The UL94VTM test is a vertical flame test using a test specimen measuring 200mm x 50mm.

[0138] 1.3.3.Breakdown voltage The breakdown voltage of the insulating sheet 1 according to the embodiment is a breakdown voltage measured in accordance with the standard test method for breakdown voltage specified in ASTM D149.

[0139] The breakdown voltage of the insulating sheet 1 according to the embodiment is preferably 15 kV / mm or higher, more preferably 18 kV / mm to 300 kV / mm, and even more preferably 20 kV / mm to 200 kV / mm. An insulating sheet 1 satisfying such a breakdown voltage contributes to ensuring sufficient insulation even with a short insulation clearance. This contributes to reducing dead space in spaces where components to which high voltages are applied are housed, thereby enabling the miniaturization of electronic devices. While the breakdown voltage may exceed the upper limit, it is preferable that the breakdown voltage be equal to or lower than the upper limit in order to minimize individual variations.

[0140] 2. Effects of the above embodiment The insulating sheet 1 according to the embodiment includes an intermediate layer 13, a first layer 11, and a second layer 12. The intermediate layer 13 contains an aromatic polycarbonate resin and a flame retardant. The first layer 11 is laminated on one surface of the intermediate layer 13 and contains a first resin. The second layer 12 is laminated on the other surface of the intermediate layer 13 and contains a second resin. The first layer 11 and the second layer 12 have higher tracking resistance than aromatic polycarbonate resin.

[0141] With this configuration, an insulating sheet 1 is obtained that has both good flame retardancy derived from the aromatic polycarbonate resin and the flame retardant, and good tracking resistance derived from the first layer 11 and the second layer 12.

[0142] Furthermore, the first resin and the second resin preferably have an aromatic ring ratio of 90 mass % or less.

[0143] With this configuration, the ratio of aliphatic structures in the first resin and the second resin is relatively high. This allows the first resin and the second resin to have good tracking resistance. This results in a first resin and a second resin that are better in both flame retardancy and tracking resistance. Furthermore, even if creeping discharge occurs in the insulating sheet 1, coloring due to carbonization can be easily suppressed. As a result, the occurrence of poor appearance in the insulating sheet 1 and the deterioration of insulating properties due to carbonization can be suppressed.

[0144] The first resin and the second resin may also be a heat-resistant polycarbonate resin containing bisphenol A carbonate units and bisphenol isophorone carbonate units.

[0145] According to this configuration, since the bisphenol isophorone carbonate unit contains both an aromatic ring structure and an alicyclic structure, it is possible to particularly improve both the heat resistance (flame retardancy) and tracking resistance of the first layer 11 and the second layer 12.

[0146] The first resin and the second resin may also be an aliphatic polycarbonate resin containing a structure formed by two condensed tetrahydrofuran rings.

[0147] With this configuration, the glass transition temperatures Tg of the first resin and the second resin can be increased, and therefore the first layer 11 and the second layer 12 can be obtained that are excellent in heat resistance and tracking resistance.

[0148] The first resin and the second resin may be polyamide resins. With this configuration, an insulating sheet 1 with particularly high tracking resistance is obtained.

[0149] The first resin and the second resin may be polyolefin resins. With this configuration, an insulating sheet 1 having particularly high chemical resistance and tracking resistance is obtained.

[0150] The first resin and the second resin may be a polymer alloy obtained by alloying an aromatic polycarbonate resin with a compatible resin that is compatible with the aromatic polycarbonate resin.

[0151] This configuration provides the first and second resins that combine the heat resistance inherent in the aromatic polycarbonate resin with other properties inherent in the compatible resin, thereby providing an insulating sheet 1 with even higher heat resistance and various added values.

[0152] The flame retardant is preferably a nitrogen-containing compound. This configuration can further improve the flame retardancy of the insulating sheet 1. Furthermore, since the nitrogen-containing compound does not contain halogen atoms, a so-called halogen-free and fluorine-free insulating sheet 1 can be realized.

[0153] Furthermore, the insulating sheet 1 according to the embodiment has a comparative tracking index CTI, which is an index of tracking resistance measured in accordance with ASTM D3638, of 600 V or more. With this configuration, an insulating sheet 1 with particularly good tracking resistance is obtained.

[0154] Furthermore, the insulating sheet 1 according to the embodiment has a flame retardancy rating of V-0 or VTM-0 when judged in accordance with the UL94 standard using a test piece with a thickness of 0.4 mm or more. With this configuration, an insulating sheet 1 with particularly good flame retardancy is obtained.

[0155] Although the insulating sheet of the present invention has been described above, the present invention is not limited to the above-described embodiment.

[0156] For example, the insulating sheet of the present invention may contain additives other than the additives described in the above embodiment.

[0157] Furthermore, the insulating sheet of the present invention may have a layer having an optional function added to the layer configuration described in the above embodiment, such as an adhesive layer, a pressure-sensitive adhesive layer, a protective layer, a release layer, etc. The layer having an optional function may be laminated on the lower surface of the first layer, on the upper surface of the second layer, or may be interposed between the first layer and the intermediate layer or between the second layer and the intermediate layer. [Example]

[0158] Next, specific examples of the present invention will be described, but the present invention is not limited to the descriptions of these examples.

[0159] 3. Preparation of Insulation Sheet The first resin, second resin, PC resin, and flame retardant shown in Table 1 were each melted and kneaded in a twin-screw extruder to prepare pelletized resin compositions. The three resin compositions produced were extruded into a three-layer sheet using a multi-layer co-extruder to obtain an insulating sheet consisting of a first layer, an intermediate layer, and a second layer. The thicknesses of the insulating sheets are as shown in Tables 3 and 4. The thicknesses of the first and second layers were each set to 30% of the thickness of the intermediate layer.

[0160] Table 1 shows the attributes of the first resin, second resin, PC resin, and flame retardant, such as compound name, viscosity average molecular weight, tracking resistance (CTI value), glass transition temperature, ratio of aromatic rings, and average particle size.

[0161] The second resin a1 shown in Table 1 is a heat-resistant polycarbonate resin derived from bisphenol A and bisphenol TMC. The content of structural units derived from bisphenol TMC in the second resin a1 is 60 mol %.

[0162] Furthermore, the second resin a2 shown in Table 1 is an aliphatic polycarbonate resin containing 60 mol % of aliphatic carbonate units containing a diol residue represented by the formula (4) above.

[0163] Table 2 also shows the compounds that make up the second resin a0 and the first resin d0, their mixing ratios, the proportions of aromatic rings, and so on.

[0164] Furthermore, Tables 3 and 4 show the compounding ratios of the resin and the flame retardant in the first layer, the intermediate layer, and the second layer.

[0165] Meanwhile, the first and second layers shown in Tables 5 and 6 are each composed of a polymer alloy. The polymer alloys shown in Tables 5 and 6 are resins formed by alloying two types of resins. One of the two resins was a blend of PC resins b1 and b2 shown in Table 2. The three resin compositions thus prepared were then extruded into a three-layer sheet using a multi-layer co-extruder to obtain an insulating sheet consisting of a first layer, an intermediate layer, and a second layer. The thicknesses of the insulating sheet are as shown in Tables 5 and 6. The thicknesses of the first and second layers were set to 30% of the thickness of the intermediate layer.

[0166] Tables 5 and 6 also show the compounding ratios of the resin and the flame retardant in the first layer (polymer alloy), the intermediate layer, and the second layer (polymer alloy).

[0167] [Table 1]

[0168] [Table 2]

[0169] 4. Evaluation of insulation sheets Next, the prepared insulating sheets were evaluated for the following items.

[0170] 4.1.Flame retardancy The insulating sheets of each example and each comparative example were tested in accordance with the UL94 standard and ranked for flame retardancy. The thickness of the test specimens was the same as that shown in Tables 3 to 6. The results were evaluated in accordance with the following evaluation criteria. The evaluation results are shown in Tables 3 to 6.

[0171] A: Flame retardancy rating is V-0 or VTM-0 B: Flame retardancy rating is V-1 or V-2, or VTM-1 or VTM-2 C: Flame retardancy rating is less than V-2 or VTM-2

[0172] 4.2. Tracking resistance The CTI values ​​of the insulating sheets of each example and each comparative example were measured by the above-mentioned tracking resistance evaluation test. The thickness of the test pieces was the same as that shown in Tables 3 to 6. The measured CTI values ​​were evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 3 to 6.

[0173] A: The CTI value is 600V or more (rank is PLC0) B: The CTI value is 400V or more and less than 600V (rank is PLC1) C: The CTI value is less than 400V (rank is PLC2 or higher)

[0174] 4.3.Carbonization due to tracking For the insulating sheets of each example and each comparative example, the above-mentioned tracking resistance evaluation test was carried out, and then the test site was visually observed. The observation results were then evaluated in accordance with the following evaluation criteria. The evaluation results are shown in Tables 3 to 6.

[0175] A: Little discoloration due to carbonization (good appearance) B: There is a little bit of coloring due to carbonization (appearance is a little poor) C: A lot of discoloration due to carbonization (poor appearance)

[0176] 4.4. Processability The insulating sheets of each of the examples and comparative examples were subjected to bending processing as described below, and the appearance of the processed result was evaluated to evaluate the processability of the insulating sheets.

[0177] [1] Cut the insulating sheet into roughly square test pieces measuring 15 mm ± 1 mm in the MD direction and 15 mm ± 1 mm in the TD direction. [2] The test piece is bent in the center, a 3 kg weight is placed on it, and after leaving it for 1 minute, the weight is removed. [3] Open the test piece and visually observe the condition of the bent part and record it. [4] With the test piece open, place a 3 kg weight on it, leave it for 1 minute, and then remove the weight. [5] Visually inspect the condition of the bent part and record it. [6] Repeat steps [2] to [5] above and count the number of repetitions until cracks or holes appear in the folded part. [7] The number of repetitions was evaluated against the following evaluation criteria to evaluate the processability of the insulating sheet. The evaluation results are shown in Tables 3 to 6.

[0178] A: No cracks or holes were observed even after 10 or more repeated tests. B: Either cracks or holes occurred after 5 to 9 cycles C: Either cracks or holes occurred after 4 or fewer cycles

[0179] 4.5.Pinhole resistance The insulating sheets of each example and each comparative example were inspected for pinholes. A pinhole detector manufactured by Kasuga Electric Co., Ltd. was used for the pinhole inspection. The area of ​​the inspection range was 1 m 2 The test results were evaluated in accordance with the following evaluation criteria. The evaluation results are shown in Tables 3 to 6.

[0180] A: No pinholes B: One pinhole C: Two or more pinholes

[0181] In Tables 3 to 6, examples corresponding to the present invention are designated as "Examples," and examples not corresponding to the present invention are designated as "Comparative Examples."

[0182] [Table 3]

[0183] [Table 4]

[0184] [Table 5]

[0185] [Table 6]

[0186] From the results shown in Tables 3 to 6, the following was observed. The insulating sheets of each example with a three-layer structure were excellent in both flame retardancy and tracking resistance. In contrast, the insulating sheets of each comparative example had difficulty achieving both flame retardancy and tracking resistance.

[0187] The insulating sheets of the examples had better pinhole resistance than the insulating sheets of the comparative examples, which had a layer structure of two or less layers.

[0188] - It was found that when resins with a low aromatic content are used as the first and second resins, carbonization due to tracking can be suppressed.

[0189] Although not shown in Tables 3 to 6, for example, flame-retardant polypropylene resin and flame-retardant polyethylene terephthalate resin had poorer processability than the insulating sheets of the respective examples. [Explanation of symbols]

[0190] 1 Insulation sheet 11 1st layer 12 2nd layer 13 Middle class

Claims

1. an intermediate layer comprising an aromatic polycarbonate resin and a flame retardant; a first layer laminated on one surface of the intermediate layer and including a first resin; a second layer laminated on the other surface side of the intermediate layer and including a second resin; and The insulating sheet is characterized in that the first layer and the second layer have higher tracking resistance than the aromatic polycarbonate resin.

2. The insulating sheet according to claim 1 , wherein the first resin and the second resin each have an aromatic ring ratio of 90 mass % or less.

3. 3. The insulating sheet according to claim 1, wherein the first resin and the second resin are heat-resistant polycarbonate resins containing bisphenol A carbonate units and bisphenol isophorone carbonate units.

4. 3. The insulating sheet according to claim 1, wherein the first resin and the second resin are aliphatic polycarbonate resins containing a structure in which two tetrahydrofuran rings are condensed.

5. The insulating sheet according to claim 1 or 2, wherein the first resin and the second resin are polyamide resins.

6. The insulating sheet according to claim 1 or 2, wherein the first resin and the second resin are polyolefin resins.

7. The insulating sheet according to claim 1 or 2, wherein the first resin and the second resin are polymer alloys obtained by alloying an aromatic polycarbonate resin with a compatible resin that is compatible with the aromatic polycarbonate resin.

8. The insulating sheet according to claim 1 , wherein the flame retardant is a nitrogen-containing compound.

9. 2. The insulating sheet according to claim 1, wherein a comparative tracking index (CTI), which is an index of tracking resistance, measured in accordance with ASTM D3638 is 600 V or more.

10. 2. The insulating sheet according to claim 1, wherein the flame retardancy rank determined in accordance with the UL94 standard is V-0 or VTM-0 for a test piece having a thickness of 0.4 mm or more.

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