Transparent flame-retardant biaxially stretched resin sheet and molded article thereof

Abstract

Provided are: a transparent flame-retardant biaxially stretched resin sheet having excellent rigidity and toughness and also having transparency and excellent flame retardancy; and a molded article thereof. This transparent flame-retardant biaxially stretched resin sheet is characterized by having a structure in which a primer is applied to at least one surface of a biaxially stretched transparent resin sheet (L) having a thickness of 0.1-6 mm and obtained by laminating and thermally fusing a plurality of biaxially stretched polypropylene sheets, and a transparent soft silicone resin layer (α) is further formed. Said sheet is useful as a transparent stand for a perovskite solar cell.

Description

Transparent Flame-Retardant Biaxially Oriented Resin Sheet and Its Molded Product

[0001] The present invention relates to a transparent flame-retardant biaxially oriented resin sheet and its molded product.

[0002] Resin sheets typified by polypropylene sheets are widely used mainly for food trays because of their excellent moldability, heat resistance, and chemical resistance. However, for large molded products such as building materials, vehicles, and automotive parts, they are not used as sheet molded products because they are inferior in mechanical strength. Currently, polypropylene is mainly used to obtain molded products by injection molding. On the other hand, polypropylene sheet molded products have the advantage of being easily recyclable as a single-material, and are materials that meet the recent needs of reducing environmental load, and are expected to be used in industrial products.

[0003] Therefore, as a method for enhancing the rigidity of polypropylene sheet molded products, for example, Patent Document 1 discloses a technique of laminating a plurality of two-layer three-layer stretched polypropylene films in which low-melting-point polypropylene films are located on both surface layers of a high-melting-point polypropylene film and heat-bonding them to obtain a laminated sheet that can be molded.

[0004] However, since the laminated sheet described in Patent Document 1 is sandwiched between rolls and heat-sealed between layers, although it is suitable for small-area members, it is difficult to increase the area for building materials, solar panel substrates, etc. In particular, when the area is increased, it is difficult to obtain high mechanical properties over the entire surface. Furthermore, since the laminated sheet described in Patent Document 1 is composed of polypropylene, it is flammable by itself, and thus it is difficult to apply it to applications that require high flame retardancy such as building materials and substrate sheets for solar cells.

[0005] International Publication No. 2020 / 75755

[0006] Therefore, the problem to be solved by the present invention is to provide a transparent resin sheet and its molded product that are excellent in rigidity and toughness and have both excellent transparency and flame retardancy.

[0007] As a result of diligent research to solve the above problems, the inventors have discovered that a transparent, flame-retardant, biaxially oriented resin sheet possessing rigidity, toughness, transparency, and flame retardancy can be obtained by coating and curing a flexible silicone resin onto a transparent, biaxially oriented resin sheet of a predetermined thickness, thus completing the present invention.

[0008] In other words, the present invention relates to a transparent flame-retardant biaxially oriented resin sheet characterized by having a transparent flexible silicone resin layer (α) on at least one surface of a biaxially oriented transparent resin sheet (L) having a thickness of 0.1 mm to 6 mm.

[0009] The present invention further relates to a molded article formed by shaping the transparent, flame-retardant, biaxially oriented resin sheet described above.

[0010] According to the present invention, it is possible to provide a transparent resin sheet and a molded product thereof that is excellent in rigidity and toughness, and also possesses transparency and excellent flame retardancy.

[0011] Figure 1 is a conceptual diagram showing a state in which a resin film (α), a biaxially oriented polypropylene film (β), and a biaxially oriented laminated polypropylene sheet (P) are laminated. Figure 2 is a conceptual diagram showing the state before and after lamination, in which a laminated sheet precursor (pMS) is heat-fused to form a biaxially oriented laminated polypropylene sheet (P). Figure 3 is a diagram showing a pressurizing device having a continuous pressurizing mechanism. Figure 4 is a diagram showing a planar mold having a plurality of thermally partitioned zones as an example of the continuous pressurizing mechanism of this disclosure. Figure 5 is a conceptual diagram showing a cross-section of a single-wafer vacuum laminating device. Figure 6 is a conceptual diagram showing a cross-section of a solar cell sheet obtained by laminating a perovskite solar cell module by sandwiching it between the transparent flame-retardant biaxially oriented resin sheets of the present invention on both sides. Figure 7 is a diagram showing the sampling positions of test pieces for evaluating the flexural modulus of elasticity in the examples.

[0012] As described above, the transparent flame-retardant biaxially oriented resin sheet of the present invention has a transparent flexible silicone resin layer (α) on at least one surface of a biaxially oriented transparent resin sheet (L) having a thickness of 0.1 mm to 6 mm.

[0013] Here, the biaxially oriented transparent resin sheet (L) with a thickness of 0.1 mm to 6 mm exhibits excellent rigidity, toughness, and transparency, but it is preferable that the resin sheet has a shaping capability through stretching. It can be shaped according to the purpose. Examples of such resin sheets include biaxially oriented sheets of various thermoplastic resin compositions such as polyester, polycarbonate, polypropylene, polyethylene, and polyvinyl chloride. Among these, biaxially oriented polypropylene sheets are particularly preferred due to their excellent rigidity and toughness.

[0014] Here, the biaxially oriented polypropylene sheet may be a single layer sheet, but it is difficult to industrially manufacture a single layer of biaxially oriented polypropylene sheet with a final thickness of 0.1 mm to 6 mm in large area. Furthermore, multilayering broadens the range of raw material film design and makes it easier to adjust the physical properties of the sheet. Therefore, it is preferable to use a biaxially oriented laminated polypropylene sheet (P) manufactured by laminating and fusing multilayer films. Specifically, it is preferable to obtain a multilayer sheet precursor (pMS) by laminating multiple biaxially oriented multilayer polypropylene films (p) having a structure in which a layer made of a single layer sheet of biaxially oriented polypropylene or a biaxially oriented polypropylene film and a b layer made of an olefin resin with a melting point of 110 to 180°C are alternately laminated, and then heat-sealing the layers together.

[0015] The biaxially oriented multilayer polypropylene film (p) used here preferably has a structure in which a layer made of biaxially oriented polypropylene film and a layer made of olefin resin with a melting point of 110 to 180°C are alternately laminated. Furthermore, it is preferable that the stretching ratio in the MD direction of the biaxially oriented multilayer polypropylene film (p) is 2.5 to 9 times and the stretching ratio in the TD direction is 2.5 to 9 times, from the viewpoint of excellent rigidity and toughness of the final sheet.

[0016] The biaxially oriented multilayer polypropylene film (p) is more specifically a BAB type film containing the biaxially oriented olefin resin film (B) on both surfaces of the biaxially oriented polypropylene film (A), and is preferably a two-type three-layer film with a thickness of 30 to 400 μm. The multilayer sheet precursor (pMS) is preferably made by laminating 2 to 60 sheets of the biaxially oriented multilayer polypropylene film (p), as this provides good interlayer adhesion and excellent sheet rigidity.

[0017] As described above, the multilayer sheet precursor (pMS) can be made by appropriately selecting and combining biaxially oriented multilayer polypropylene films (p) according to the purpose. However, in the present invention, it is preferable to use BA-type films and BAA-type films by stacking multiple BAB-type films as shown below, so that film (A) is located on the surface of the surface layer.

[0018] AB / BAB / BAB / BAB / ... / BAB / BAB / BAB / BA AAB / BAB / BAB / BAB / ... / BAB / BAB / BAB / BAA

[0019] Such biaxially oriented multilayer polypropylene film (p) may be, for example, a BAB type film which is a two-type three-layer film (p-1) with a thickness of 30 μm or more and less than 100 μm, or a two-type three-layer film (p-2) with a thickness of 100 to 400 μm. Furthermore, the thickness ratio of B / A / B in the BAB type film is preferably, for example, B / A / B = 2 to 20 / 96 to 60 / 2 to 20, but from the viewpoint of increasing rigidity, it is desirable to secure as much thickness as possible in the A layer, and in particular, B / A / B = 2 to 15 / 96 to 70 / 2 to 15 is preferred.

[0020] When the biaxially oriented multilayer polypropylene film (p) is a two-type three-layer film (p-1) with a thickness of 30 μm or more and less than 100 μm, it is preferable to laminate 30 to 60 sheets. On the other hand, when the biaxially oriented multilayer polypropylene film (p) is a two-type three-layer film (p-2) with a thickness of 100 to 400 μm, it is preferable to laminate 2 to 20 sheets.

[0021] [Biaxially Oriented Polypropylene Film (A)] The biaxially oriented polypropylene film (A) constituting the biaxially oriented multilayer polypropylene film (p) can be obtained by melt-kneading a polypropylene polymer or a polypropylene composition containing the polypropylene polymer and a nucleating agent or other additives in a known manner, forming a film, and then biaxially stretching it. For example, the polypropylene can be extruded to obtain an unstretched sheet, and the sheet can be biaxially stretched to obtain a biaxially oriented film. However, as described above, in the present invention, it is preferable to form and stretch the film together with other layers by co-extrusion.

[0022] The polypropylene polymers used here specifically include propylene homopolymers, propylene random copolymers obtained by polymerizing a monomer component containing 1% by weight or less of at least one C2-C10-αolefin (excluding C3-αolefin), and mixtures thereof.

[0023] Among these, a propylene random copolymer (hereinafter sometimes simply referred to as "propylene random copolymer") obtained by polymerizing a monomer component containing ethylene at a concentration of 1% by weight or less is particularly preferred because it can impart excellent stretchability to the sheet while maintaining high rigidity and toughness.

[0024] Here, the polypropylene polymer has a relatively broad molecular weight distribution of Mw / Mn from 6 to 20, which is preferable because it allows for good film thickness accuracy, combines high rigidity and high stretchability, and facilitates film formation.

[0025] Furthermore, it is preferable that the amount of xylene-insoluble content in the polypropylene polymer is greater than 96.5% by mass and less than or equal to 99.5% by mass. The xylene-insoluble components of polypropylene correspond to crystalline isotactic components. In contrast, the xylene-soluble components contained in small amounts in polypropylene correspond to non-crystalline atactic components, and have a lower molecular weight compared to the xylene-insoluble components. Moreover, the statement that the amount of xylene-insoluble content in the polypropylene polymer is greater than 96.5% by mass and less than or equal to 99.5% by mass is equivalent to the crystalline component of the polypropylene resin material being greater than 96.5% by mass and less than or equal to 99.5% by mass. Furthermore, from the viewpoint of obtaining good rigidity and heat resistance, particularly rigidity, of the (secondary) molded product obtained by thermoforming the sheet, it is especially preferable that the amount of xylene-insoluble content is in the range of greater than 97.0% by mass and less than or equal to 99.5% by mass.

[0026] Furthermore, the crystalline component of the polypropylene polymer preferably has a stereoregularity (mmmm) of 97.5 to 99.5%. If the mmmm is less than 97.5%, the rigidity and heat resistance, especially the heat resistance, of the (secondary) molded product obtained by thermoforming a sheet made of the polypropylene composition will decrease.

[0027] When using the propylene random copolymer as the polypropylene polymer, the ethylene content in the raw material monomer component is preferably 0.1% by mass or more and less than 1% by mass, preferably 0.1% by mass or more and less than 0.6% by mass, and particularly preferably 0.1% by mass or more and less than 0.3% by mass, in order to enhance the stretchability while maintaining the toughness and rigidity of the sheet.

[0028] Herein, the propylene random copolymer also has the characteristic of improved transparency due to the random copolymerization of propylene with ethylene. Furthermore, since the ethylene content in the raw material monomer components is less than 1% by mass, it exhibits excellent rigidity. The lower limit of the ethylene content is not particularly limited and is greater than 0% by mass, but 0.1% by mass or more is preferred in that a sufficient improvement in transparency can be easily obtained.

[0029] The MFR of the polypropylene polymer is 1 to 15 g / 10 min, and preferably 2 to 6 g / 10 min. When the MFR is within this range, the polypropylene composition exhibits excellent moldability when formed into a sheet.

[0030] In the present invention, it is preferable for the polypropylene polymer used to contain a nucleating agent for transparency. However, in this invention, by using a smaller amount of this nucleating agent than usual, haze can be reduced and transparency can be further improved.

[0031] The content of the nucleating agent in the polypropylene composition is preferably less than 0.18 parts by mass, and particularly preferably 0.15 parts by mass or less, per 100 parts by mass of the ethylene-containing propylene polymer. Below the above upper limit, excellent thickness-to-thinness accuracy is easily obtained, resulting in a polypropylene composition with excellent film-forming properties while maintaining toughness and rigidity. Here, there is no particular lower limit to the content of the nucleating agent, but it is preferably 0.01 parts by mass or more in terms of the effect of improving transparency.

[0032] The polypropylene composition used in this invention preferably has a crystallization rate parameter (t1 / 2) greater than 1 second, and more preferably 2 seconds or more. Reducing the amount of nucleating agent tends to decrease the crystallization rate and increase (t1 / 2). When (t1 / 2) is greater than the lower limit mentioned above, excellent thickness-to-thinness accuracy is easily obtained. Furthermore, there is no particular upper limit to (t1 / 2), but it is preferably about 5 seconds or less.

[0033] [Crystal Nucleating Agent] The amount of the above-mentioned crystal nucleating agent is greater than 0 parts by weight and less than or equal to 1.0 part by weight, preferably 0.05 to 0.5 parts by weight, per 100 parts by weight of polypropylene. A crystal nucleating agent is an additive (transparent crystal nucleating agent) used to control the size of the crystal components in the resin to reduce its size and improve transparency. The crystal nucleating agent is not particularly limited, and those commonly used in this field may be used, but it is preferable to select from nonitol-based crystal nucleating agents, sorbitol-based crystal nucleating agents, phosphate ester-based crystal nucleating agents, triaminobenzene derivative crystal nucleating agents, carboxylate metal salt crystal nucleating agents, and xylitol-based crystal nucleating agents. An example of a nonitol-based crystal nucleating agent is 1,2,3-trideoxy-4,6:5,7-bis-[(4-propylphenyl)methylene]-nonitol. An example of a sorbitol-based crystal nucleating agent is 1,3:2,4-bis-o-(3,4-dimethylbenzylidene)-D-sorbitol. Examples of phosphate ester-based crystal nucleating agents include lithium phosphate-2,2'-methylenebis(4,6-di-tert-butylphenyl) salt-based crystal nucleating agents.

[0034] [Other Additives] The polypropylene composition used in the present invention may contain other additives other than crystal nucleating agents, as long as they do not impair the effects of the present invention. Examples of other additives include common additives normally used in polyolefins, such as antioxidants, neutralizing agents, chlorine absorbers, heat stabilizers, light stabilizers, ultraviolet absorbers, internal lubricants, external lubricants, antiblocking agents, antistatic agents, antifogging agents, flame retardants, dispersants, copper pollution inhibitors, plasticizers, crosslinking agents, peroxides, oil spreaders, and other organic and inorganic pigments. The amount of each additive may be a known amount.

[0035] [Preparation of Polypropylene Polymers or Polypropylene Compositions] The polypropylene polymers or polypropylene compositions described in detail above can be prepared, for example, by Production Examples 2 to 7 of Japanese Patent No. 6845001.

[0036] <Biaxially Oriented Olefin Resin Film (B)> The biaxially oriented olefin resin film (B), which constitutes the multilayer sheet precursor (pMS) and has a melting point of 110 to 180°C, can be obtained by biaxially stretching an olefin resin or an olefin resin composition containing the olefin resin and additives using a known method. For example, an unstretched sheet can be obtained by extruding the olefin resin, etc., and then a biaxially oriented film can be obtained by biaxially stretching the sheet. However, as described above, in the present invention, it is preferable to form and stretch the film together with other layers by co-extrusion.

[0037] The olefin resin constituting the biaxially oriented olefin resin film (B) has a melting point of 110 to 180°C. Here, the melting point is measured using DSC under the condition of heating from 30°C to 230°C at a heating rate of 10°C / min. Since this melting point range is sufficiently lower than that of the polypropylene constituting layer A, good fusion properties are obtained when heated and pressed. Specifically, it is preferable that such an olefin resin is formed from a propylene homopolymer (HOMO); a propylene random copolymer (RACO) containing 5% by weight or less of at least one comonomer selected from C2 to C10-α-olefins (excluding C3-α-olefins); or a resin composition containing HOMO or RACO. If the comonomer content is too low, the fusion properties with the first layer may not be sufficient, and if it is too high, the rigidity of the multilayer sheet may decrease. From this viewpoint, the comonomer content is preferably more than 0% by weight and 4.5% by weight or less. Ethylene (C2-α-olefin) is preferred as the comonomer. The MFR (at 230°C and under a load of 2.16 kg) of the polymer or resin composition constituting the second layer is not limited, but is preferably 1 to 15 g / 10 min, more preferably 2 to 10 g / 10 min, and even more preferably 3 to 8 g / 10 min.

[0038] The above-mentioned olefin resin may contain a nucleating agent, or it may consist of a resin composition or polymer that does not contain a nucleating agent. If a nucleating agent is included, from an economic standpoint, the amount of the nucleating agent is preferably 1 part by weight or less per 100 parts by weight of the polymer forming the second layer. Therefore, the biaxially oriented olefin resin film (B) is preferably composed of a resin composition containing HOMO and a nucleating agent, or a resin composition containing RACO and a nucleating agent.

[0039] The thickness of the biaxially oriented olefin resin film described above is preferably in the range of 1 to 20 μm per layer, and more preferably in the range of 2 to 10 μm.

[0040] [Method for manufacturing biaxially oriented laminated polypropylene sheet (P)] A method for manufacturing a biaxially oriented laminated polypropylene sheet (P) from the multilayer sheet precursor (pMS) described in detail above includes, for example, a method of heat-sealing the multilayer sheet precursor (pMS) under temperature conditions of, for example, 110 to 170°C and pressure conditions of 1 to 40 MPa.

[0041] Specifically, a manufacturing method that includes a preparation step of stacking a predetermined number of the aforementioned biaxially oriented multilayer polypropylene films (p) to form a multilayer sheet precursor (pMS), and then a pressing step of heating and pressing the multilayer sheet precursor (pMS) across its surface, is preferred because it allows for the production of a large-area, uniform laminated sheet.

[0042] Here, when obtaining a multilayer sheet precursor (pMS) by laminating biaxially oriented multilayer polypropylene films (p), the raw films may be laminated with the MD direction and TD direction aligned, or they may be laminated so that they intersect each other. However, when supplying multiple biaxially oriented multilayer polypropylene films (p) in roll form to a continuous pressure press, it is preferable to laminate them with the MD direction and TD direction aligned.

[0043] As a method of heat pressing the multilayer sheet precursor (pMS) adjusted in this way on the surface, there are: [Method 1] placing the laminated sheet precursor (pMS) on the lower metal plate in the chamber of a single-sheet vacuum laminating device having planar metal plates above and below, heat pressing while setting the degree of vacuum in the chamber to 170 Pa or less, and after releasing the press, passing through the process of sandwiching with cooling metal plates to produce the biaxially stretched laminated polypropylene sheet (P) used in the present invention, and [Method 2] a continuous heat and pressure pressing method having a process of heat pressing the multilayer sheet precursor (pMS) with a planar mold using a continuous pressure device and then cooling it.

[0044] Here, specifically, for the above-described Method 1, for example, as schematically shown in FIG. 5, the multilayer sheet precursor (pMS) is placed in the chamber (202) of a single-sheet vacuum laminating device (200) between a pair of upper and lower hot plates (204, 205) disposed in the chamber. Then, after closing the chamber (202), while heating the hot plates (204, 205) to a predetermined temperature, the inside is depressurized, then pressurized from the hydraulic cylinder (203), held for a predetermined time, then the internal depressurization is returned to normal pressure, the cylinder pressure is released, the biaxially stretched transparent resin sheet (L) is taken out, and then quickly transferred to a cooling device and sandwiched between a pair of upper and lower cooling metal plates and cooled at room temperature.

[0045] The multilayer sheet laminate (pMS) may be set as it is in the chamber of the single-sheet vacuum laminating device, but as shown in FIG. 5, it is preferable from the viewpoint that the surface state of the biaxially stretched laminated polypropylene sheet (P) obtained by subjecting it to heating and pressurization in a state where its upper and lower surfaces are sandwiched by stainless steel plates (s). Here, the stainless steel plate (s) sandwiching the film laminate preferably has a thickness of 0.3 to 1 mm. Also, a polytetrafluoroethylene sheet (pt) may be interposed between the hot plate and the stainless steel plate (s) for the purpose of protecting the hot plate. The hot plate of such a single-sheet vacuum laminating device preferably has a set temperature of 140 to 155°C, and the pressure of the hydraulic cylinder is preferably 0.1 to 10 MPa.

[0046] [Continuous Heat Pressing Method] Next, the above-described Method 2 is a continuous heat pressing method having a step of continuously heating and pressing a multilayer sheet precursor (pMS) with a planar mold using a continuous pressing device and then cooling it. In the present invention, the continuous heat pressing method of Method 2 is preferable because the obtained laminated sheet has excellent adhesion between layers and surface state, and has good strength throughout the in-plane of the laminated sheet.

[0047] Here, the continuous pressing device has a multi-stage heating zone and a cooling zone. In the heating zone, the multilayer sheet precursor (pMS) is heated and pressed with upper and lower planar molds, and then continuously, in the cooling zone, the multilayer sheet precursor (pMS) is pressed with upper and lower planar molds to continuously produce a multilayer sheet. That is, in the heating zone, the multilayer sheet precursor (pMS) is heated and pressed with upper and lower planar molds, and then continuously, in the cooling zone, the multilayer sheet precursor (pMS) is pressed with upper and lower planar molds to continuously produce a multilayer sheet.

[0048] Here, a method for manufacturing a laminated sheet using a continuous pressing device is, for example, pressing under temperature and pressure conditions of 110 to 170 °C and 1 to 40 MPa in the heating zone, then, after releasing the press, sending the sheet out by a predetermined length in a predetermined traveling direction, heating and pressing again, and repeating this to continuously transfer from the heating zone to the cooling zone, and then, in the cooling zone, pressing under pressure conditions of 25 to 125 °C and 20 to 40 MPa, then, after releasing the press, sending the sheet out in a predetermined traveling direction, and continuously taking out the heat-fused multilayer sheet.

[0049] When such a continuous heat pressing method is adopted, the surface state of the obtained laminated sheet becomes good, so-called surface irregularities appearing on the surface waves and the like become small, and the transparency of the laminated sheet itself is also excellent.

[0050] To elaborate on such a continuous compression pressing method, the multilayer sheet precursor (pMS) is introduced continuously or intermittently into the gap between the upper and lower planar molds constituting the heating zone of a compression device (CCM: continuous compression molding, sometimes referred to as a "continuous compression molding device") having a continuous compression molding mechanism. The sheet is heated to 110 to 170°C and pressed under pressure conditions of 1 to 40 MPa. After the press is released, the sheet is fed forward for a predetermined length in a predetermined direction, and heating and pressing are performed again. This process is repeated to continuously or intermittently transfer the sheet from the heating zone to the cooling zone. In the cooling zone, the sheet is pressed, pressure released, and transferred under pressure conditions of 20 to 40 MPa at a temperature of 60 to 125°C, thereby gradually discharging the heat-fused multilayer sheet from the gap between the upper and lower planar molds.

[0051] Here, the size (pitch) of the multilayer sheets fed out when the press is released is not particularly limited, but it is preferably in the range of 10 to 300 mm. Also, the press release time is preferably 0.5 to 3 seconds from the viewpoint of uniformity of bonding.

[0052] [Continuous Pressure Molding Apparatus] Here, the pressure device (continuous pressure molding apparatus) 100 having a continuous pressure molding mechanism has a pair of upper and lower molds 2 formed in a planar shape, as shown in Figure 3. The upper and lower parts of each of the upper and lower molds 2 have a pair of upper and lower heating / cooling plate modules 4, respectively, which can heat / cool the upper and lower molds 2. In addition, the upper flat mold is configured to be pressurized from above by a hydraulic cylinder 6, a lifting unit 8 and a lifting guide 10.

[0053] Furthermore, the mold unit in the direction of travel has a drawer unit 12 at its front that has the function of drawing out the laminated sheet (LOP) by moving back and forth in the MD direction (machine direction).

[0054] Here, the pair of upper and lower molds 2, formed in a planar shape, are thermally divided into a heating zone and a cooling zone with respect to the sheet travel direction (MD direction). Preferably, they are also thermally divided in a direction perpendicular to the sheet travel direction (TD direction). For example, a planar mold having multiple thermally divided zones can be cited, as shown in Figure 4. Note that "thermally divided" here does not necessarily mean that the set temperatures are different; it is sufficient that the zones are divided so that the heat sources are different.

[0055] For example, as shown in Figure 4, zones H1 to H3 are heating zones, and zones C1 to C2 are cooling zones. Furthermore, the TD direction is thermally divided into five sections.

[0056] In the present invention, the number of stages in the MD direction of the heating zone and cooling zone can be appropriately selected depending on the size of the biaxially oriented laminated polypropylene sheet (P) to be manufactured. However, it is preferable that the heating zone is thermally divided into 2 to 6 stages and the cooling zone into 1 to 5 stages in the MD direction, as this facilitates thermal control, allows for widespread mechanical strength across the surface corresponding to the desired thickness, and enables the manufacture of a laminated sheet with excellent surface smoothness.

[0057] Here, "thermally partitioned" means not only that the mold itself is physically divided into individual parts, but also that, although it appears as a uniformly extended flat metal plate, its temperature is controlled by heaters corresponding to each zone, resulting in a multi-stage thermally controlled state.

[0058] The set temperature for each heating zone can be set as follows: the first heating zone, which is closest to the insertion opening of the multi-layered stretched film, is set to 120 to 160°C; the second heating zone is set to +10 to +40°C above the set temperature of the first heating zone; and thereafter, each zone is set to +0 to +30°C above the set temperature of the preceding zone, preferably up to a maximum of 160°C. On the other hand, the set temperature for the cooling zone is preferably set to -5 to -10°C below the final heating zone, and if there are further cooling zones, to -30 to -60°C above the set temperature of the preceding cooling zone. Furthermore, the temperature of the final cooling zone is preferably 125°C to 25°C. For example, in Figure 4, the first heating zone is H1, the second heating zone is H2, the third heating zone is H3, the cooling zone following the heating zone is C1, and the cooling zone following that is C2.

[0059] Furthermore, as described above, the multilayer sheet precursor (pMS) inserted between the upper and lower molds 2 is pressurized by a plurality of cylinders 6 arranged on the upper part of the upper mold and pressed by the upper and lower molds 2. The press pressure at this time is preferably 1 to 40 MPa, as described above, and when the press is released, a biaxially oriented laminated polypropylene sheet (P) of a predetermined width is fed out.

[0060] Furthermore, in order to improve the surface smoothness of the biaxially oriented laminated polypropylene sheet (P), it is preferable to interpose a sheet-like release material between the biaxially oriented laminated polypropylene sheet (P) and the flat mold 2. Examples of sheet-like release materials used here include paper material, polycarbonate sheet, biaxially oriented homopolypropylene sheet, steel plate, stainless steel plate, and aluminum plate, but among these, stainless steel plate, especially mirror-finished stainless steel plate, is preferred because it can further improve the surface condition of the laminated sheet.

[0061] The biaxially oriented laminated polypropylene sheet (P) obtained in this manner maintains the orientation of the polypropylene constituting each layer appropriately, while the interlayers are sufficiently fused, resulting in a laminated sheet with high overall rigidity. As described above, it exhibits the unique property of exhibiting broad mechanical strength across the entire plane.

[0062] Here, in a biaxially oriented laminated polypropylene sheet (P), having broad and high mechanical strength in the plane means that, specifically, the flexural modulus at three positions including the center position in the MD direction of the biaxially oriented laminated polypropylene sheet (P), and two positions passing through this center position and located 70 mm away from the center position in the TD direction is preferably in the range of: Flexural modulus in the MD direction: 2000 to 6000 MPa Flexural modulus in the TD direction: 2000 to 6000 MPa

[0063] Furthermore, for the three bending moduli in the same direction at the three positions in the MD direction and the three positions in the TD direction, the coefficient of variation is preferably 6.5% or less, more preferably 5.5% or less, and particularly preferably 4.8% or less.

[0064] Here, the coefficient of variation is calculated by dividing the standard deviation by the mean [(standard deviation / mean) × 100 (%)].

[0065] [Biaxially Oriented Laminated Polypropylene Sheet (P)] An example of a biaxially oriented laminated polypropylene sheet (P) obtained by the hot-pressure pressing method described in detail above is shown in Figure 2. A laminated sheet precursor (pMS) containing multiple biaxially oriented multilayer polypropylene films (p) is laminated and fused at the B / B boundary. As a result, the fused layer becomes integrated to form a b layer, resulting in a structure in which a layer and b layer are laminated to each other.

[0066] For example, when the multilayer sheet precursor (pMS) with the following configuration BAB / BAB / BAB / ... / BAB / BAB / BAB is fused together, the B / B interfaces become integrated by thermal fusion, resulting in a biaxially oriented laminated polypropylene sheet (P) with a multilayer structure of bababab...bababab.

[0067] [Transparent Flexible Silicone Resin Layer (α)] As described above, the present invention is characterized in that a transparent flexible silicone resin layer (α) is present on at least one surface of a biaxially oriented transparent resin sheet (L) having a thickness of 0.1 mm to 6 mm. Such a transparent flexible silicone resin layer (α) can be formed by applying a transparent flexible silicone resin coating (α1) to at least one surface of the biaxially oriented transparent resin sheet (L). In the present invention, when applying the transparent flexible silicone resin coating (α1), it is preferable to apply a primer coat agent (β1) constituting a primer layer (β) onto the coated surface of the biaxially oriented transparent resin sheet (L), and then apply the transparent flexible silicone resin coating (α1) on top of that, as this results in good adhesion of the transparent flexible silicone resin layer (α) to the biaxially oriented transparent resin sheet (L), good flame retardancy, and excellent weather resistance.

[0068] The transparent flexible silicone resin coating (α1) used here uses an organopolysiloxane having alkyl groups and alkoxy groups as substituents on the silicon atoms as the resin component, which is a flexible silicone resin. Examples of alkyl groups as substituents on the silicon atoms of the organopolysiloxane include methyl groups, ethyl groups, and propyl groups, and examples of alkoxy groups include methoxy groups and ethoxy groups. Among these, from the viewpoint of curability, methyl groups are preferred as the alkyl group and methoxy groups as the alkoxy group.

[0069] Furthermore, the transparent flexible silicone resin coating (α1) is preferably a so-called moisture-curing flexible silicone coating that hardens due to moisture in the air, and is particularly preferred to have a melt viscosity at 23°C in the range of 0.1 to 50 Pa·s.

[0070] As described above, the transparent flexible silicone resin coating (α1) hardens with moisture, but a curing agent may be used to accelerate the hardening process. Examples of such curing agents include alkyl titanates, such as tetra-n-butyl titanate, sulfonic acid, phosphoric acid, boric acid, zinc compounds, and acetylacetonate.

[0071] Furthermore, when using organic solvents, examples include aromatic solvents such as ruene and xylene, aliphatic solvents such as cyclohexane, methylcyclohexane, and ethylcyclohexane, ester solvents such as ethyl acetate and butyl acetate, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, and alcohol solvents such as methanol, ethanol, n-propyl alcohol, and i-propyl alcohol. The amount used is preferably in the range of 20 to 80% by mass for the solid content.

[0072] In the transparent flexible silicone resin coating (α1), various additives such as flame retardants, inorganic extender pigments, rheology modifiers, plasticizers, defoamers, adhesion promoters, suspending agents, thixotropes, catalysts, UV light stabilizers, air release agents, dispersion aids, solvents, surfactants, inorganic drying agents, and metal-based dryers can be used, as long as they do not impair transparency or significantly reduce it. Among these, it is particularly preferable to include a phosphate ester-based flame retardant in the coating (α1) at a concentration of 10 to 30% by mass, and nanosilica particles in a solid content of 1 to 20% by mass in the coating (α1), from the viewpoint of improving flame retardancy.

[0073] The application rate of the transparent, flexible silicone resin coating (α1) described above is 200 to 800 g / m². ２ It is preferable that the thickness be within this range, and that the thickness of the transparent, flexible silicone resin layer (α) formed by moisture curing be in the range of 0.2 to 0.8 mm, as this results in good flame retardancy.

[0074] In the present invention, when applying the transparent flexible silicone resin coating (α1) to the biaxially oriented transparent resin sheet (L), it is preferable to apply a primer (β1) as a base to form a primer layer (β), and then apply the transparent flexible silicone resin coating (α1) on top of the primer layer (β) to at least one surface of the biaxially oriented transparent resin sheet (L), and further to form the transparent flexible silicone resin layer (α) on top of the primer layer (β). This structure is preferable because it results in better adhesion of the transparent flexible silicone resin layer (α) to the biaxially oriented transparent resin sheet (L), excellent flame retardancy, and also good weather resistance.

[0075] Examples of primers (β1) that can be used here include those diluted with an organic solvent and a resin component such as an acrylic-urethane resin, a urethane-cellulose resin, an acid-modified polyolefin, a chlorinated polyolefin, or an acid-modified chlorinated polyolefin, or those in which the resin component is dispersed in water. Among these, those containing the resin component and an organic solvent as essential components are preferred because they have excellent wettability to the biaxially oriented transparent resin sheet (L), and those containing an organic solvent as essential components are particularly preferred because they provide good adhesion when a polyolefin sheet is used as the biaxially oriented transparent resin sheet (L).

[0076] Here, acid-modified polyolefins specifically refer to polyolefin resins modified with α,β-unsaturated carboxylic acids or their derivatives. Examples of polyolefin resins include polypropylene, ethylene-propylene copolymer, propylene-butene copolymer, and ethylene-propylene-butene copolymer. These may be used individually or in combination of two or more.

[0077] Here, the polyolefin is preferably in the range of 30,000 to 150,000 in terms of having good adhesive properties. Note that the weight-average molecular weight (Mw) is the value measured by gel permeation chromatography on a polystyrene basis.

[0078] Next, examples of α,β-unsaturated carboxylic acids or their derivatives used to modify the polyolefin include fumaric acid, maleic acid, itaconic acid, their anhydrides, and their alkyl esters. Among these, itaconic anhydride, maleic anhydride, and maleic acid are particularly preferred.

[0079] One method for modifying polyolefins with α,β-unsaturated carboxylic acids or their derivatives is to melt or dissolve the polyolefin in an organic solvent in the presence of a radical reaction initiator and react it with the α,β-unsaturated carboxylic acid or its derivative.

[0080] In the acid-modified polyolefin of the present invention, the amount of α,β-unsaturated carboxylic acid or its derivative modified is preferably 0.10 to 10% by mass of the α,β-unsaturated carboxylic acid or its derivative relative to the total mass of the polyolefin, from the viewpoint of adhesion to the biaxially oriented transparent resin sheet (L).

[0081] Next, chlorinated polyolefins can be obtained by introducing chlorine atoms into the aforementioned polyolefins, for example, by blowing chlorine gas into them.

[0082] Next, acid-modified chlorinated polyolefins can be obtained by introducing chlorine atoms into the aforementioned acid-modified polyolefins, for example, by blowing chlorine gas into them.

[0083] The chlorinated polyolefin or acid-modified chlorinated polyolefin obtained in this manner preferably has a chlorine content in the range of 10 to 40% by mass, as this results in good adhesion when a polypropylene sheet is used as the biaxially oriented transparent resin sheet (L). Here, the chlorine content is a value measured in accordance with JIS-K7229.

[0084] Next, examples of organic solvents used in primer (β1) include aromatic solvents such as toluene and xylene, aliphatic solvents such as cyclohexane, methylcyclohexane, and ethylcyclohexane, ester solvents such as ethyl acetate and butyl acetate, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, and alcohol solvents such as methanol, ethanol, n-propyl alcohol, and i-propyl alcohol, which can be used in combination as appropriate. In this case, the amount of organic solvent used is preferably such that the solid content concentration in primer (β1) is 5 to 50% by mass, and more preferably 10 to 35% by mass.

[0085] The primer (β1) described above can be further enriched with additives such as flame retardants, antioxidants, lubricants, foaming agents, UV absorbers, light stabilizers, and deodorizers, as long as transparency is not compromised.

[0086] [Coating of Primer (β1)] The above-mentioned primer (β1) can be applied using known coating methods such as gravure coating, microgravure coating, fountain bar coating, slide die coating, slot die coating, and screen printing. The drying temperature is preferably around 50 to 100°C.

[0087] The coating thickness of the primer layer (β) after drying is not particularly limited, but is usually preferably in the range of 0.1 μm to 7.0 μm, and more preferably in the range of 0.5 μm to 5.0 μm. If the coating thickness is less than 0.1 μm, there is a problem that adhesion to the substrate film tends to decrease. On the other hand, if the coating thickness exceeds 7.0 μm, it is undesirable because it is costly and whitening tends to occur when the molding film is stretched.

[0088] [Molded Products] The molded products in this invention are made by molding the transparent flame-retardant biaxially oriented resin sheet of the present invention. Various molded products can be obtained by molding the laminated sheet of this embodiment. Examples of molding methods include press molding, stretch molding, rolling molding, deep drawing molding, pressure welding molding, fusion molding, vacuum forming, and pressure forming. Among these, the present invention has the unprecedented feature of being able to industrially produce large-area laminated sheets, so it is preferable to process the sheets into various molded products by press molding, vacuum pressure forming, or hot plate contact vacuum pressure forming. The temperature conditions when secondary molding the transparent flame-retardant biaxially oriented resin sheet can be appropriately selected depending on the shape and depth of drawing, but for example, it is possible to mold at 100°C or higher and below the melting point of the transparent flame-retardant biaxially oriented resin sheet. In particular, when molding shallow-drawn molded products such as mobility exterior materials and housing building materials, molding can be done at 120 to 150°C.

[0089] [Applications of Transparent Flame-Retardant Biaxially Oriented Resin Sheets] The transparent flame-retardant biaxially oriented resin sheet of the present invention, as detailed above, possesses unprecedented performance, combining transparency, flame retardancy, and mechanical strength. It can be widely applied to applications requiring transparency, flame retardancy, and strength, such as automobile sunroofs, aircraft window materials, ship window materials, silicon solar cell substrates, thin-film silicon solar cell substrates, organic thin-film solar cell substrates, perovskite solar cell mounting sheets, quantum stealth optical materials, balcony parapets, and carport roofing materials. In addition, since it exhibits strength comparable to steel plates, fiber-reinforced resins, and aluminum plates, it can be made transparent in applications where these materials have been used until now. In particular, it is useful as a transparent mounting base when installing perovskite solar cell modules, which are expected to become widely adopted, due to its combination of high transparency and flame retardancy.

[0090] As one embodiment of the transparent mounting frame for the perovskite solar cell module, a film-like or sheet-like flexible solar cell module can be bonded to the front or back surface of the laminated sheet of the present invention, or, as shown in Figure 6, a flexible solar cell module can be sandwiched and bonded from both sides by the laminated sheet of the present invention to form a solar cell sheet. In this case, the transparent soft silicone resin layer (α) must be present at least on the side that receives sunlight (arrow in Figure 6).

[0091] In this case, by pre-shaping the transparent flame-retardant biaxially oriented resin sheet of the present invention to conform to the shape of the building's wall surface, roofing material, or columnar structure, a sense of visual unity with the object to which it is attached is achieved, dramatically improving the aesthetic appearance of the solar panels when installed compared to conventional panel-type silicon solar cells.

[0092] Furthermore, the enhanced sense of integration with the object to which it is attached, such as a building, allows for stable and long-term fixation after installation, enabling longer-term use compared to simply attaching a film-type solar cell module to an existing building. Alternatively, a single-curved solar cell sheet can be obtained by laminating a perovskite solar cell module to the transparent, flame-retardant, biaxially oriented resin sheet of the present invention and then molding it into a single-curved surface with curvature in only one direction. Or, by laminating a perovskite solar cell module to the transparent, flame-retardant, biaxially oriented resin sheet of the present invention and then bending it in one direction to fix it to the object, a solar cell sheet with an arched single-curved surface can be obtained, allowing for a longer period of direct sunlight reception and increasing power generation.

[0093] Furthermore, by laminating a perovskite solar cell module onto the transparent flame-retardant biaxially oriented resin sheet of the present invention, and in particular by three-dimensionally molding a solar cell sheet in which a perovskite solar cell module is sandwiched and laminated from both sides by the transparent flame-retardant biaxially oriented resin sheet of the present invention as shown in Figure 6, a solar cell sheet of a desired shape can be obtained. In addition, since the transparent flame-retardant biaxially oriented resin sheet of the present invention exhibits a low water vapor permeability coefficient, if necessary, a barrier deposition can be applied to the outermost surface, allowing the laminated sheet to function as a barrier substrate and exhibit durability and long-term reliability as a solar cell. Furthermore, by providing a linear groove structure in the transparent flame-retardant biaxially oriented resin sheet of the present invention, the rigidity and strength of the sheet itself can be dramatically increased.

[0094] Furthermore, perovskite solar cells generally have advantages such as being lightweight, highly flexible, and resistant to strain, making them applicable to various structures. They can also generate electricity even in low light conditions and have fewer installation constraints, such as the need to consider sunny locations and orientations. On the other hand, their flexibility makes them difficult to install on building walls and roofs, and there are concerns that they can easily peel off during typhoons, earthquakes, or other disasters if simply attached to walls with adhesive. The challenge lies in how to stably fix these sheet-like solar cells, which are inherently flexible in terms of installation location, to structures over the long term.

[0095] Therefore, by using the transparent flame-retardant biaxially oriented resin sheet of the present invention as a mounting sheet for a perovskite solar cell film, and shaping the laminated sheet to conform to the shape of the structure to be attached or to a desired shape as needed, and fixing the perovskite solar cell film to this laminated sheet or the shaped object in advance, it is possible to stably fix it to a building or the like for a long period of time. Here, methods for fixing the solar cell sheet of the present invention to a building or the like include, for example, shaping the end of the sheet to a predetermined shape and fixing it to the structure by fitting it together, fixing it with bolts, fixing it with a sealing material, and bonding and fixing it to the object with an adhesive.

[0096] Alternatively, the transparent, flame-retardant, biaxially oriented resin sheet itself can be used as a structural material such as an exterior wall material or roofing material.

[0097] Furthermore, the durability of the transparent mounting frame for perovskite solar cells can be further enhanced by adding a barrier layer and an ultraviolet absorbing layer.

[0098] The perovskite solar cell sheets obtained in this way can be used for automotive roofing materials, solar carports, balcony parapets, residential roofing materials, and the like.

[0099] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

[0100] (Raw materials) ・BAB co-extruded film 1: A co-extruded film formed using a Bruckner simultaneous biaxial stretching machine "BAL", with a layer structure of B / A / B, thickness of 100 μm, B / A / B thickness ratio of 5 / 90 / 5, and stretching ratio of 5.5 × 5.5 times. A: Polypropylene (ethylene content 0.2 mass%, Mw / Mn = 9, xylene insoluble content 98.2 mass%, mmmm = 98.3, nucleating agent content 0.05 mass%, t1 / 2: 2.3 seconds) B: Ethylene-propylene random copolymer (melting point 151℃)

[0101] - Flexible silicone resin coating material 1: A silicone resin with a hardness of 20-23 (shore D), elongation of 50-70%, and solids content of 70%, a phosphate ester-based flame retardant, an organosilica sol with a particle size of 10-20 nm and solids content of 30%, and a titanium-based catalyst were mixed in a weight ratio of 100:25:100:3 to create flexible silicone resin coating material 1.

[0102] - Flexible silicone resin coating material 2: A silicone resin with a hardness of 20-23 (shoreD), elongation of 50-70%, and solids content of 70% was used as the flexible silicone resin coating material 2.

[0103] Primer 1: Primer 1 was prepared by mixing FECTO's "FOC Multi-Primer" and BASF's "Flamestab NORTM116 FF" in a mass ratio of 100:5.

[0104] Primer 2: Primer 2 was prepared by mixing Ohashi Chemical Industries' "Oflex Primer SL" and BASF's "Flamestab NORTM116 FF" in a mass ratio of 100:5.

[0105] Examples 1-3 and Comparative Example 1: As a preparation step, ten 200 mm square BAB co-extruded films were stacked to obtain a precursor (pMS1). Next, it was pressed in a flat press molding machine at 155°C for 75 seconds at 25 MPa. After that, it was sandwiched between 40 mm thick aluminum plates at 25°C, a 5 kg weight was placed on top, and a cooling press was performed for 60 seconds to obtain a transparent flame-retardant biaxially oriented resin sheet LOP1. Multiple sheets of this laminated sheet LOP1 were prepared.

[0106] Furthermore, a primer was applied to the obtained transparent flame-retardant biaxially oriented resin sheet LOP1 in the following manner, and after drying, a soft silicone resin was applied and cured under the conditions of 40°C for 8 hours and 23°C for 48 hours.

[0107]

[0108] <Flexural Modulus> From the transparent flame-retardant biaxially oriented resin sheet LOP1, a central point (1) in the TD direction, (2) located 70 mm from the center of (1), and (3) located 70 mm opposite to the center of (2), were obtained as strip-shaped test pieces TT1, TT2, and TT3, each measuring 40 mm x 10 mm with the TD direction as the longer side, centered at positions (1) to (3) and with the TD direction as the longer side (see Figure 7). Similarly, from the transparent flame-retardant biaxially oriented resin sheet LOP1, a central point (1) in the MD direction, (2) located 70 mm from the center of (1), and (3) located 70 mm opposite to the center of (2), were obtained as strip-shaped test pieces MT1, MT2, and MT3, each measuring 40 mm x 10 mm with the MD direction as the longer side, centered at positions (1) to (3) and with the MD direction as the longer side (see Figure 7). The bending modulus of elasticity in the TD and MD directions was measured using these test specimens in accordance with JIS K7171. • Equipment used: AUTOGRAPH AG-X plus (Shimadzu Corporation) • Distance between lower supports: 20 mm • Test speed: 1 mm / min • Stroke: 1 mm • Test temperature: 23°C • Indenter and support base: 5R / 2R Here, the coefficient of variation is calculated by dividing the standard deviation by the mean [(standard deviation / mean) × 100 (%)].

[0109]

[0110] As is clear from the results in Table 2, the bending modulus was high at each of the positions (1), (2), and (3), and high strength was exhibited throughout the entire plane.

[0111] α: Soft silicone resin layer β: Primer layer L: Biaxially oriented transparent resin sheet A: Polypropylene B: Ethylene-propylene random copolymer 100: Continuous pressure molding apparatus 2: Mold 4: Hot plate / cooling plate module 6: Hydraulic cylinder 8: Lifting unit 10: Lifting guide 12: Pulling unit 20: Product direction of travel 60: Laminated sheet precursor (pMS) 200: Single-wafer vacuum laminating apparatus 201: Apparatus body 202: Chamber 203: Hydraulic cylinder 204: Hot plate 205: Hot plate 300: Cooling device 301: Cooling metal plate 302: Cooling metal plate d: Diaphragm s: ​​Stainless steel plate sl: Silicone sheet pt: Polytetrafluoroethylene sheet

Claims

1. A transparent, flame-retardant biaxially oriented resin sheet characterized by having a transparent, flexible silicone resin layer (α) on at least one surface of a biaxially oriented transparent resin sheet (L) having a thickness of 0.1 mm to 6 mm.

2. The transparent flame-retardant biaxially oriented resin sheet according to claim 5, wherein a primer layer (β) is provided between the biaxially oriented transparent resin sheet (L) and the transparent flexible silicone resin layer (α).

3. The transparent flame-retardant biaxially oriented resin sheet according to claim 2, wherein the biaxially oriented transparent resin sheet (L) is a biaxially oriented laminated polypropylene sheet (P).

4. The transparent flame-retardant biaxially oriented resin sheet according to claim 3, wherein the biaxially oriented laminated polypropylene sheet (P) has a multilayer structure in which a layer made of a biaxially oriented polypropylene film and a layer made of an olefin resin having a melting point of 110 to 180°C are alternately laminated.

5. The transparent flame-retardant biaxially oriented resin sheet according to claim 4, wherein the biaxially oriented laminated polypropylene sheet (P) is formed by stacking and heat-sealing multiple multilayer films in which a biaxially oriented polypropylene film (A) constituting the a layer and a biaxially oriented olefin resin film (B) constituting the b layer are laminated on at least one surface thereof, and the stretching ratio in the MD direction of the multilayer film is 2.5 to 9 times, and the stretching ratio in the TD direction is 2.5 to 9 times.

6. The transparent, flame-retardant, biaxially oriented resin sheet according to claim 5, wherein the transparent, flexible silicone resin layer (α) has a thickness of 0.2 to 0.8 mm.

7. The transparent flame-retardant biaxially oriented resin sheet according to claim 6, wherein the transparent flexible silicone resin layer (α) is a cured product of a moisture-curing transparent flexible silicone resin.

8. A molded article formed by shaping a transparent flame-retardant biaxially oriented resin sheet according to any one of claims 1 to 7.

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