Fluorine-based resin piezoelectric film and manufacturing method therefor

Abstract

The present invention provides a fluorine-based resin piezoelectric film having a low shrinkage rate when heated and high transparency. This fluorine-based resin piezoelectric film has a maximum shrinkage rate of 2.5% or lower when held at 80°C for 30 minutes, a retardation factor of 50-3000 nm inclusive, internal haze of less than 1.2%, and a piezoelectric constant d33 of 5.0-40.0 pC / N inclusive.

Description

Fluorine-based resin piezoelectric film and its manufacturing method

[0001] The present invention relates to a fluorine-based resin piezoelectric film and a method for producing the same.

[0002] Display and input devices with a touch panel installed on the front of a display device such as a liquid crystal display are widely used, and are used in mobile devices such as mobile phones and operation panels for home appliances. Display and input devices using a touch panel allow users to operate the device by pressing the display on the screen. Therefore, the piezoelectric film used in touch panels must have high piezoelectricity to increase detection sensitivity and high transparency to allow accurate viewing of the display image.

[0003] As described in Patent Document 1 and Patent Document 2, piezoelectricity can be imparted to a fluororesin film by subjecting it to a polarization treatment. Known methods for producing a fluororesin film include a method of producing the film by solution casting a solution obtained by dissolving a fluororesin in an organic solvent (Patent Document 1, etc.), and a method of thermally melting a fluororesin and extruding it (Patent Document 2).

[0004] International Publication No. 2015 / 064324 Japanese Patent Application Laid-Open No. 05-102548 International Publication No. 2022 / 091828

[0005] Piezoelectric films are produced from fluororesin films formed by solution casting by poling without stretching, whereas piezoelectric films are produced from fluororesin films formed by hot melt extrusion by stretching the film and then poling it.

[0006] Fluoropolymer films produced by the solution casting method are characterized by their inherently low shrinkage upon heating, since they are not stretched. However, the solution casting method requires the use of a large amount of polar organic solvent to dissolve the fluoropolymer. This requires the recovery of the evaporated solvent during the drying process, which not only increases production costs but also requires consideration of the impact of the organic solvent on the working environment and the natural environment. Furthermore, if the polar organic solvent used to dissolve the fluoropolymer remains in the film, it can hinder the polarization of the film and impair the smoothness of the film surface as the solvent evaporates.

[0007] In contrast, the method of extrusion molding a fluororesin by thermal melting allows the production of a fluororesin film without using an organic solvent, which is less likely to cause deterioration of the working environment or the natural environment, or to cause insufficient polarization or a decrease in the smoothness of the film surface due to polar organic solvents remaining in the film.

[0008] On the other hand, when imparting piezoelectricity to a fluororesin film formed by the thermal melting method, the film is usually stretched. From the perspective of increasing piezoelectricity, a higher stretching ratio is preferable. However, increasing the stretching ratio increases strain in the film, resulting in greater heat shrinkage. Piezoelectric films are used in sensors and other applications by laminating them with electrode films. The piezoelectric film and electrode film are used by adhering them with adhesives, and drying the adhesive usually involves heat treatment. If the piezoelectric film shrinks due to heat treatment, it can cause a decrease in adhesive strength, curvature of the laminated film, and a decrease in dimensional accuracy. For this reason, piezoelectric films are required to have a low heat shrinkage rate.

[0009] Patent Document 3 discloses a fluororesin piezoelectric film that has been subjected to a stretching process and then a polarization process. However, the piezoelectric film disclosed in Patent Document 3 has high haze and does not disclose the thermal shrinkage rate.

[0010] According to the investigations of the present inventors, a fluororesin piezoelectric film produced at a high stretch ratio has a large thermal shrinkage rate, and further, as crystals grow in the film, the difference in refractive index between the crystalline and non-crystalline parts increases light scattering, which tends to reduce transparency.

[0011] The present invention has been made in view of the above problems, and an object of the present invention is to provide a fluorine-based resin piezoelectric film that has a low thermal shrinkage rate and high transparency, and a method for producing the same.

[0012] One embodiment of the present invention for solving the above problems relates to the following fluorine-based resin piezoelectric film [1] to [5]: [1] A fluorine-based resin piezoelectric film having a maximum shrinkage of 2.5% or less when maintained at 80°C for 30 minutes, a retardation of 50 nm or more and 3000 nm or less, an internal haze of less than 1.2%, and a piezoelectric constant d ３３ [2] A fluorine-based resin piezoelectric film having a shear strength of 5.0 pC / N or more and 40.0 pC / N or less. －１ [3] The fluororesin piezoelectric film according to [1] or [2], which contains a vinylidene fluoride resin as a main component. [4] The number of foreign particles having a size of 100 μm or more, which is the arithmetic mean of the maximum and minimum widths when viewed from above, of the film is 7 / 0.25 m. ２ [5] The fluororesin piezoelectric film according to any one of [1] to [4], wherein the surface roughness in surface height Rz of the surface on the side where the Rz is smaller as measured in accordance with JIS B 0601:2001 is 0.50 μm or less.

[0013] One embodiment of the present invention for solving the above problems relates to a method for producing a piezoelectric film according to the following [6] to [8]. [6] A method for producing a fluorine-based resin piezoelectric film according to any one of [1] to [5], comprising the steps of heating and melting a resin composition containing a fluorine-based resin, extruding the molten resin composition to form a film, stretching the formed film at a stretching temperature of 125°C to 165°C and at a stretching ratio of 4.0 to 8.0 times, and polarizing the formed film at an applied voltage of 7.0 kV to 50.0 kV. [7] A method for producing a fluorine-based resin piezoelectric film according to [6], comprising the step of filtering the resin composition melted in the melting step through a filter having a filtration accuracy of 10 μm to 40 μm. [8] A method for producing a fluorine-based resin piezoelectric film according to [6] or [7], wherein, in the film-forming step, the extruded resin composition is cooled by contacting it with a cooling roll having a surface temperature of 125°C or less.

[0014] According to the present invention, a fluororesin piezoelectric film having a low shrinkage rate when heated and high transparency, and a method for producing the same are provided.

[0015] [Fluorocarbon Resin Piezoelectric Film] One embodiment of the present invention relates to a fluorocarbon resin piezoelectric film.

[0016] Fluorine-based resin piezoelectric films can be produced by stretching and poling a fluororesin film, which is the raw material. The higher the stretching ratio of the fluororesin film, the higher the piezoelectricity of the resulting fluororesin piezoelectric film. However, the strain in the film tends to increase, leading to a higher thermal shrinkage. In contrast, by increasing the temperature of the fluororesin film during stretching, the stress generated in the film during stretching is reduced, making it less likely for strain to occur, and thus preventing an increase in the thermal shrinkage.

[0017] The fluororesin piezoelectric film contains a fluororesin.

[0018] The fluororesin can be a homopolymer or copolymer obtained by polymerizing tetrafluoroethylene (TFE), vinylidene fluoride (VDF), or the like. Examples of fluororesins obtained by polymerizing TFE include copolymers of TFE with ethylene, perfluoroalkyl vinyl ether, hexafluoropropylene (HFP), or the like. Examples of fluororesins obtained by polymerizing VDF include homopolymers of VDF, and copolymers of VDF with 1-chloro-1-fluoroethylene, 1-chloro-2-fluoroethylene, trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), TFE, tetrafluoropropene, HFP, perfluoroalkyl vinyl ether, or the like.

[0019] Among these, from the viewpoint of facilitating polarization of the fluororesin film that is the material of the fluororesin piezoelectric film, VDF resin obtained by polymerizing VDF is preferred, with VDF homopolymer, copolymer of VDF and HFP, copolymer of VDF and TrFE, copolymer of VDF and TFE, and copolymer of VDF, TrFE and TFE being more preferred, and VDF homopolymer being even more preferred. These fluororesins may be used alone or in combination of two or more types.

[0020] When the VDF resin is a copolymer, it is preferably a resin containing VDF as the main component, specifically a resin in which the proportion of VDF-derived structural units is 50% by mass or more. The proportion of the VDF-derived structural units relative to the total mass of the VDF resin is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less.

[0021] The fluororesin piezoelectric film preferably contains a VDF resin, preferably a VDF homopolymer, as a main component. "Containing such a resin as a main component" means that the content of VDF-derived structural units relative to the total mass of the fluororesin piezoelectric film is 50% by mass or more. The content of such a resin relative to the total mass of the fluororesin piezoelectric film is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less.

[0022] The content of the resin having VDF as a constituent unit contained in the fluororesin film and the fluororesin piezoelectric film is １９ It can be measured by quantitative analysis using an internal standard using F-NMR.

[0023] The fluorine-based resin piezoelectric film was measured at a temperature of 260°C and a shear rate of 50 s －１ (Hereinafter, unless otherwise specified, the measurement temperature is 260°C, and the shear rate during measurement is 50 s －１The melt viscosity measured by this method is referred to as "melt viscosity") is preferably 600 Pa·s or more and 4000 Pa·s or less, more preferably 600 Pa·s or more and 3500 Pa·s or less, even more preferably 600 Pa·s or more and 2400 Pa·s or less, particularly preferably 600 Pa·s or more and 2000 Pa·s or less, and very preferably 600 Pa·s or more and 1500 Pa·s or less. The melt viscosity of a fluororesin film hardly changes even when subjected to a stretching treatment or a polarization treatment, so the melt viscosity of a fluororesin piezoelectric film serves as an index indicating the melt viscosity of a resin composition containing a fluororesin as a raw material resin (hereinafter, a resin composition containing a fluororesin is referred to as a "resin composition"). Resin compositions with lower melt viscosities have shorter molecular chains, which reduces the entanglement of molecular chains. This reduces the stretching stress between molecular chains that occurs during stretching. This reduces the likelihood of strain in the film during stretching, making it less likely for the film to break even at high stretch ratios, making it possible to stretch the film at high stretch ratios. Therefore, resin compositions that produce piezoelectric films with a melt viscosity of 4000 Pa·s or less can easily increase the piezoelectricity of the fluororesin piezoelectric film by increasing the stretch ratio, and are less likely to experience an increase in shrinkage during heating due to strain, even at high stretch ratios. In contrast, resin compositions that produce piezoelectric films with a melt viscosity of more than 4000 Pa·s have high molecular weights and long molecular chains. Long molecular chains are more likely to be entangled, making them difficult to stretch at high ratios, and stretching at high ratios can result in the film breaking. Furthermore, the resin composition (fluororesin piezoelectric film) having a melt viscosity of 600 Pa s or more has molecular chains long enough to suppress crystal growth, thereby suppressing light scattering caused by the difference in refractive index between the crystalline portion and the amorphous portion that occurs when the crystallites become large, thereby reducing internal haze.

[0024] Furthermore, the lower the melt viscosity, the easier it is to filter and the lower the melting temperature, which reduces the likelihood of the formation of speckled irregularities on the film surface due to resin denaturation and the generation of low-molecular-weight foreign matter due to thermal decomposition, thereby providing the advantage of preventing the deterioration of visibility due to foreign matter.

[0025] The melt viscosity is measured in accordance with ASTM D 3835:2016 (ISO 11443:2021, JIS K 7199:1999). Specifically, a capillary rheometer (Capillograph 1D, manufactured by Toyo Seiki Seisakusho Co., Ltd.) is used, and the melt viscosity is measured at a measurement temperature of 260°C and a shear rate of 50 s －１ The viscosity measured is taken as the viscosity.

[0026] The fluororesin piezoelectric film has a maximum shrinkage rate of 2.5% or less when kept at 80°C for 30 minutes, preferably 0.0% to 2.3%, more preferably 0.0% to 2.1%, even more preferably 0.0% to 1.9%, particularly preferably 0.0% to 1.7%, very preferably 0.0% to 1.5%, and most preferably 0.0% to 1.3%.

[0027] The maximum shrinkage rate when maintained at 80°C for 30 minutes can be determined by the following method. A fluororesin piezoelectric film is cut into a roughly square shape measuring approximately 100 mm x 100 mm from an area including the intersection of the diagonals of the fluororesin piezoelectric film to prepare a shrinkage measurement film (sometimes referred to as a "measurement film"). When the length of one side of the piezoelectric film is 300 mm or more, a rectangle with a side length of 300 mm is arbitrarily assumed, and the measurement film is cut from an area including the intersection of the diagonals of the rectangular film. When both sides of the piezoelectric film are 300 mm or more, a square with a side length of 300 mm is arbitrarily set on the piezoelectric film, and the measurement film is cut out according to the above method. On one side of the measurement film, line segments A and B are marked so that they pass through the intersection of the diagonals of the measurement film (the center of the film) and connect both ends of the measurement film approximately parallel to the two sides of the measurement film, and intersect at right angles at the center of the measurement film. The lengths of the marked line segments A and B are measured using an image dimension measuring instrument (Keyence Corporation, One-Shot 3D Shape Measuring Machine VR-5200). Next, the measurement film is placed in an oven heated to 80°C and held there for 30 minutes, then the measurement film is removed from the oven and allowed to cool to room temperature, and the lengths of line segments A and B of the measurement film are measured using the same image dimension measuring instrument. The length of line segment A after heating is subtracted from the length of line segment A before heating, and this is divided by the length of line segment A before heating to obtain a value expressed as a percentage, which is the shrinkage rate of line segment A. Next, the shrinkage rate of line segment B is calculated in the same manner as for line segment A. The shrinkage rates of line segment A and line segment B are compared, and the larger shrinkage rate is taken as the maximum shrinkage rate of the fluororesin piezoelectric film.

[0028] The fluororesin piezoelectric film has a retardation of 50 nm to 3000 nm, preferably 100 nm to 3000 nm, more preferably 500 nm to 2500 nm, and even more preferably 700 nm to 2000 nm. The larger the retardation, the higher the degree of molecular orientation of the fluororesin film and the more sufficiently the proportion of the β phase, making it easier to obtain a fluororesin piezoelectric film with high piezoelectricity by the polarization step.

[0029] The retardation is measured by the parallel Nicol rotation method using a light source with a wavelength of 587.8 nm, using a film cut into a 20 mm x 20 mm area from the area including the intersection of the diagonals of the fluororesin piezoelectric film, and the measured value is used as the representative value of the retardation of the fluororesin piezoelectric film. If the length of one side of the piezoelectric film is 300 mm or more, an arbitrary rectangle with one side of 300 mm is assumed, and the retardation of the film cut into a 20 mm x 20 mm area from the area including the intersection of the diagonals of the rectangular film is measured. If both sides of the piezoelectric film are 300 mm or more, an arbitrary square with one side of 300 mm is set on the piezoelectric film, and the measurement range is set according to the method described above.

[0030] The fluororesin piezoelectric film has an internal haze of less than 1.2%, preferably 0.1% to 1.1%, more preferably 0.1% to 1.0%, even more preferably 0.1% to 0.8%, particularly preferably 0.1% to 0.6%, and very preferably 0.1% to 0.4%. The lower the internal haze, the more improved the transparency of the fluororesin piezoelectric film.

[0031] The haze of the fluororesin piezoelectric film is preferably 0.0% to 10.0%, more preferably 0.0% to 5.0%, even more preferably 0.0% to 3.0%, and particularly preferably 0.0% to 2.0%. The lower the haze, the more improved the transparency of the fluororesin piezoelectric film.

[0032] The internal haze of a fluororesin piezoelectric film is determined by forming coating layers on both sides of the film, removing external haze due to scratches, etc., and measuring the haze of the film in accordance with ISO 14782:2021. Specifically, a 50 mm x 50 mm rectangular film is cut out of the fluororesin piezoelectric film so as to include the intersection of the diagonals. If the length of one side of the piezoelectric film is 300 mm or more, an arbitrary rectangle with a side of 300 mm is assumed, and the rectangular film is cut out from an area including the intersection of the diagonals of the rectangular film. If both sides of the piezoelectric film are 300 mm or more, an arbitrary square with a side of 300 mm is set on the piezoelectric film, and the measurement range is set according to the above method, and the rectangular film is cut out. Next, a hard coating agent (BS CH271, manufactured by Arakawa Chemical Industries, Ltd.) is applied to one surface (side A) of the rectangular film using a bar coater and dried at 80°C for 30 minutes. Thereafter, an ultraviolet (UV) irradiation device (GS NIPPON DENCHI, CSOT040) was used to irradiate the sample with a target cumulative light dose of 400 mJ / cm. ２ The film is irradiated with UV light so that a coating layer with a thickness of 2 μm is formed. A coating layer similar to that on side A is also formed on the other surface (side B) of the rectangular film with side A coated, and an internal haze measurement film is prepared in which external haze due to scratches on the film surface has been removed. The haze is measured in accordance with ISO 14782:2021 using a haze meter (NDH7700SP II, manufactured by Nippon Denshoku Industries Co., Ltd.) for an area including the intersection of the diagonals of the obtained measurement film, and the value obtained is used as a representative value of the internal haze of the fluororesin piezoelectric film.

[0033] The haze is measured in the same manner as in the internal haze measurement method, except that no surface coating layer is formed on the rectangular film, and the measured value is used as a representative value.

[0034] The fluorine-based resin piezoelectric film has a piezoelectric constant d ３３is 5.0 pC / N or more and 40.0 pC / N or less, preferably 8.0 pC / N or more and 40.0 pC / N or less, more preferably 10.0 pC / N or more and 35.0 pC / N or less, even more preferably 15.0 pC / N or more and 35.0 pC / N or less, and particularly preferably 20.0 pC / N or more and 30.0 pC / N or less.

[0035] Piezoelectric constant d of fluororesin piezoelectric film ３３ is the direct quasi-static method (d ３３ Piezoelectric constant d by Mehta method, Berlincourt method ３３ The piezoelectric constant d of the fluororesin piezoelectric film is measured in accordance with ISO 19622:2018, which is a test method for determining the piezoelectric constant of the fluororesin piezoelectric film. Specifically, a piezoelectric constant measuring device (Piezometer System PM300, manufactured by PIEZOTEST) is used to hold the piezoelectric film as a test piece at a measurement temperature of 25°C with a holding force of 1.0 N, and measure the electric charge generated when an alternating force of 0.15 N and a frequency of 110 Hz is applied. ３３ is the piezoelectric constant d calculated from the electric charge measured by the above method in the range including the intersection of the diagonal lines of the polarization surface of the piezoelectric film. ３３ The absolute value of the piezoelectric constant d ３３ The representative value of the measurement range is set as follows. If the length of one side of the piezoelectric film is 300 mm or more, a rectangle with a side of 300 mm is arbitrarily set, and the area including the intersection of the diagonal lines of the rectangular film is measured. If both sides of the piezoelectric film are 300 mm or more, a square with a side of 300 mm is arbitrarily set on the piezoelectric film, and the measurement range is set according to the above method.

[0036] When the fluorine-based resin piezoelectric film is viewed in plan, the number of foreign particles having a size of 100 μm or more is 0 / 0.25 m. ２ More than 7 pieces / 0.25m ２ Preferably, 0 pieces / 0.25m or less ２ 5 or more pieces / 0.25m ２ More preferably, 0 pieces / 0.25 m ２ 3 or more pieces / 0.25m ２ More preferably, 0 pieces / 0.25 m ２ 1 piece or more / 0.25m ２ The following are particularly preferred:

[0037] When the fluorine-based resin piezoelectric film is viewed in plan, the number of foreign particles larger than 200 μm is 0 / 0.25 m ２ 3 or more pieces / 0.25m ２ Preferably, 0 pieces / 0.25m or less ２ 2 or more pieces / 0.25m ２ More preferably, 0 pieces / 0.25 m ２ 1 piece or more / 0.25m ２ The following is even more preferred:

[0038] When the fluorine-based resin piezoelectric film is viewed in plan, the number of foreign particles less than 100 μm in size is 0 / 0.25 m ２ More than 50 pieces / 0.25m ２ Preferably, 0 pieces / 0.25m or less ２ More than 25 pieces / 0.25m ２ More preferably, 0 pieces / 0.25 m ２ More than 16 pieces / 0.25m ２ The following is even more preferred:

[0039] The fewer these foreign matters there are, the more transparent the fluororesin piezoelectric film will be, and the more uniform the stretching and polarization will be when the fluororesin piezoelectric film is stretched or polarized.

[0040] The number of these foreign particles is measured by cutting four rectangular films (observation pieces) adjacent to each other from the fluorine-based resin piezoelectric film, and then calculating the sum of the number of foreign particles measured from each observation piece. ２ Four observation pieces each measuring 100 mm x 100 mm were cut out. The sum of the number of foreign particles measured from each observation piece was calculated, and the sum was multiplied by 25 / 4, and the result was rounded to the nearest tenth to obtain a value of 0.25 m. ２ The number of foreign particles per unit area is measured. The foreign particles are observed using transmitted light, marked, and the marked areas are observed under a microscope to determine the size of the foreign particles. The size of the foreign particles is the arithmetic mean value of the maximum and minimum widths of the foreign particles.

[0041] The surface height roughness Rz of the fluororesin piezoelectric film is preferably 0.50 μm or less, more preferably 0.05 μm or more and 0.50 μm or less, even more preferably 0.05 μm or more and 0.40 μm or less, and particularly preferably 0.05 μm or more and 0.30 μm or less. The smoother the surface of the fluororesin piezoelectric film, the less likely it is that haze will occur on the surface of the film and the less likely the film will wrinkle.

[0042] The surface height roughness Rz is measured in accordance with JIS B 0601:2001. Specifically, a surface roughness meter conforming to JIS B 0601:2001 (Keyence Corporation, Shape Analysis Laser Microscope VK-X260) is used. Measurement is then performed over an area including the intersection of the diagonals of the fluororesin piezoelectric film, and the resulting value is used as the representative value of the surface height roughness Rz of the fluororesin piezoelectric film. When the length of one side of the piezoelectric film is 300 mm or more, a rectangle with a side of 300 mm is arbitrarily set, and the area including the intersection of the diagonals of the rectangular film is measured. When both sides of the piezoelectric film are 300 mm or more, a square with a side of 300 mm is arbitrarily set on the piezoelectric film, and the measurement range is set according to the above method. The surface of the fluororesin piezoelectric film that comes into contact with the chill roll tends to have a smaller surface roughness Rz than the surface that does not come into contact with the chill roll. This is because the surface irregularities are reduced by pressing the fluororesin piezoelectric film against the cooling roll. This tendency is maintained even after stretching and polarization. Here, the measurement result for the surface with the smallest surface roughness Rz (the surface in contact with the cooling roll) is taken as the surface height roughness Rz.

[0043] The thickness of the fluororesin piezoelectric film is not particularly limited, but is preferably 10 μm to 200 μm, more preferably 20 μm to 80 μm, and even more preferably 30 μm to 80 μm. A thicker film is more advantageous in terms of electrical properties such as insulation and piezoelectric properties. A thinner film is more advantageous in terms of optical properties such as transparency and cost.

[0044] The thickness of a fluororesin piezoelectric film is generally measured using a micrometer (JIS C 2151:2019), but measurements can also be made using known methods such as a laser displacement meter, a capacitance displacement meter, or an infrared method over an area including the intersection of the diagonals of the fluororesin piezoelectric film, and the resulting value is used as the representative thickness of the fluororesin piezoelectric film. When the length of one side of the piezoelectric film is 300 mm or more, a rectangle with a side of 300 mm is arbitrarily set, and the area including the intersection of the diagonals of the rectangular film is measured. When both sides of the piezoelectric film are 300 mm or more, a square with a side of 300 mm is arbitrarily set on the piezoelectric film, and the measurement area is set according to the above method.

[0045] The fluororesin piezoelectric film may contain resins other than fluororesin or other additives as long as it satisfies the above physical properties.

[0046] [Method of manufacturing fluororesin piezoelectric film]

[0047] The method for producing the above-mentioned fluororesin piezoelectric film is not particularly limited, but preferably includes the steps of: a step of heating and melting a resin composition containing a fluororesin (melting step); a step of extruding the heat-melted resin composition to form a film to produce a fluororesin film (film-forming step); a step of stretching the formed fluororesin film (stretching step); and a step of polarizing the formed fluororesin film (polarization step).

[0048] At this time, a step of filtering the molten resin composition (filtration step) may be carried out as needed.

[0049] (Melting Step) In the melting step, the resin composition containing the fluororesin is heated and melted. This step can be carried out, for example, by melt-kneading the resin composition using an extruder.

[0050] The resin composition melted in the melting step may be any resin composition containing the above-mentioned fluororesin (hereinafter, a resin composition containing a fluororesin will be referred to as a "resin composition"). If the resin composition contains a solvent component, the solvent component remaining without volatilization may interfere with polarization in a subsequent step. Therefore, the content of the solvent component in the resin composition is preferably low, preferably 1% by mass or less, more preferably 0.1% by mass or less, relative to the total mass of the resin composition. In particular, the content of the polar solvent is preferably 100 ppm or less, more preferably 10 ppm or less, and even more preferably 1 ppm or less, relative to the total mass of the resin composition.

[0051] Furthermore, the resin composition melted in the melting step has a melt viscosity of 600 Pa·s or more and 4000 Pa·s or less, preferably 600 Pa·s or more and 3500 Pa·s or less, more preferably 600 Pa·s or more and 2400 Pa·s or less, even more preferably 600 Pa·s or more and 2000 Pa·s or less, and particularly preferably 600 Pa·s or more and 1500 Pa·s or less. In the production of a fluororesin piezoelectric film, the higher the stretching ratio of the fluororesin film, the higher the piezoelectricity tends to be. A resin composition with a lower melt viscosity has shorter molecular chains, which reduces entanglement of the molecular chains. This makes the film less likely to break even at high stretching ratios, making it possible to stretch at high stretching ratios. Therefore, from the perspective of stretching a fluororesin film at a high ratio, the lower the melt viscosity of the resin composition, the more preferable it is. Furthermore, the lower the melt viscosity, the easier it is to filter through a filter, and since the melting temperature can be kept low, it is less likely that speckled irregularities will occur on the film surface due to resin deterioration, and low molecular weight foreign matter will be less likely to be generated due to thermal decomposition. Therefore, there is also the advantage that reduced visibility due to foreign matter can be prevented. The lower the melt viscosity, the easier it is to filter through a filter, and it is less likely that speckled irregularities will occur on the film surface due to resin deterioration, and low molecular weight foreign matter will be less likely to be generated due to thermal decomposition. Furthermore, the lower the melt viscosity, the less likely the film will break even when the stretching ratio is increased.

[0052] The melting temperature of the resin composition is preferably 75°C or more higher than the melting point of the resin composition but not exceeding 105°C, more preferably 75°C or more higher but not exceeding 100°C, even more preferably 80°C or more higher but not exceeding 100°C, and particularly preferably 85°C or more higher but not exceeding 95°C. By setting the melting temperature at 75°C or more higher than the melting point of the resin composition, the viscosity of the resin composition can be reduced to a level that allows filtration in the subsequent process. By setting the melting temperature at 105°C or less higher than the melting point of the fluororesin, decomposition and condensation of the resin composition due to heating can be suppressed, and the resulting generation of decomposition products can be suppressed. By suppressing the generation of the decomposition products, the amount of foreign matter in the fluororesin piezoelectric film can be reduced, and the transparency and smoothness of the fluororesin piezoelectric film can be improved. Furthermore, by suppressing the generation of the decomposition products, the clogging of the filter caused by these products can be suppressed, and the filtration efficiency of the resin composition can be improved. The melting point of the resin composition is a value measured in accordance with JIS K 7121: 1987. Specifically, 5 mg of a measurement sample is sealed in an aluminum pan and placed in a differential scanning calorimeter (DSC-60A, manufactured by Shimadzu Corporation), and the temperature is raised from room temperature to 230°C at a heating rate of 10°C / min in a nitrogen atmosphere to measure a DSC curve, and the maximum melting peak temperature is taken as the melting point of the resin composition.

[0053] (Filtration Step) In the filtration step, the resin composition melted and reduced in viscosity in the melting step is filtered. By setting the melting temperature of the resin composition containing a fluororesin within the above range and filtering the resin composition whose viscosity has been reduced by melting, it becomes possible to filter the resin composition without using a polar solvent. Furthermore, by not using a solvent, polarization due to the polar solvent remaining in the fluororesin film is less likely to be inhibited during polarization treatment. Furthermore, since a polar solvent is not basically used in the film formation step, it is possible to reduce the burden on the working environment and the natural environment and to reduce the production cost for recovering the polar solvent.

[0054] The filtration method is not particularly limited, and the molten resin composition may be passed through a filter, and any known filter type such as a pleated type or leaf disc type filter may be used.

[0055] In the filtration step, the resin composition is preferably filtered through a filter with a filtration accuracy of 10 μm or more and 40 μm or less. Using a filter with a filtration accuracy of 10 μm or more makes it easier to filter the resin composition that has been heated to the above temperature and melted, and also prevents the filtration pressure from becoming too high, allowing the filtration time to be shortened. Using a filter with a filtration accuracy of 40 μm or less allows foreign matter in the resin composition to be sufficiently removed, resulting in a fluororesin film with little foreign matter. The filtration accuracy of the filter is preferably 10 μm or more and 30 μm or less, and more preferably 15 μm or more and 30 μm or less.

[0056] The resin composition is filtered using a multilayer filter consisting of multiple layers with different shapes, mesh sizes, etc. The filtration accuracy of the filter used to filter the resin composition refers to the filtration efficiency of the filter, i.e., the filter's ability to filter out particles of a given size with a given filtration efficiency. For example, in this specification, a filtration accuracy of 10 μm means that the filter can filter out particles of 10 μm or larger with a filtration efficiency of 95% or higher.

[0057] In this step, the resin composition may be passed through multiple filters. For example, a filter with low filtration accuracy (large filtration accuracy value) may be used in the first stage to remove coarse foreign matter, and then a filter with high filtration accuracy (small filtration accuracy value) may be used in the second stage to remove finer foreign matter. In this case, the filtration accuracy is the value of the filter with the highest filtration accuracy.

[0058] The filter may be disposed between the extruder used in the film-forming step and the die. Alternatively, the filter may be disposed in an extruder or melt-kneading apparatus different from the extruder used in the film-forming step, and the resin composition filtered through the filter may be fed into the extruder used in the melting step.

[0059] (Film Forming Step) In the film forming step, the resin composition melted in the melting step and filtered, if necessary, in the filtration step is formed into a film.

[0060] The film-forming method is not particularly limited, and a known method can be used, such as extruding a molten and filtered resin composition through a T-die and cooling it by contacting it with a cooling roll.

[0061] The resin composition crystallizes during film formation. As crystallization progresses, the crystalline particles become larger, and the difference in refractive index between the crystalline and amorphous parts causes light scattering, which can increase the internal haze of the film and reduce the transparency of the film. In particular, resin compositions with low melt viscosity have a low degree of polymerization, which facilitates free movement of molecular chains and facilitates selective alignment of molecular chains, making crystal growth more likely and increasing the internal haze of the fluororesin film. However, by forming the molten resin composition into a film and then rapidly cooling it before crystal growth, the crystal growth of the resin composition can be suppressed, reducing light scattering between the crystalline and amorphous parts, and improving the transparency of the resulting fluororesin film.

[0062] The surface temperature of the chill roll is preferably 125°C or lower. By rapidly cooling the resin composition film extruded by the chill roll with a low surface temperature, crystal growth can be suppressed and the internal haze of the resulting fluororesin film can be reduced. The surface temperature of the chill roll is preferably 5°C or higher and 115°C or lower, more preferably 10°C or higher and 100°C or lower, even more preferably 20°C or higher and 90°C or lower, particularly preferably 20°C or higher and 80°C or lower, very preferably 30°C or higher and 70°C or lower, and most preferably 30°C or higher and 60°C or lower.

[0063] The fluorine-based resin film thus obtained may be stored after being wound up, or may be transported to a subsequent process such as a stretching process or a polarization process.

[0064] (Stretching step) In the stretching step, the formed fluororesin film is stretched. In the stretching step, the fluororesin film formed in the film formation step may be stretched as is, or the fluororesin film that has been wound up and stored may be stretched. Furthermore, the film may be stretched under heating, if necessary.

[0065] The stretching can be performed in the conveying direction (MD direction) and, if necessary, in the direction perpendicular to the conveying direction (TD direction) while the fluororesin film is conveyed by multiple rolls. In this embodiment, the stretching ratio (ratio in the MD direction) is set to 4.0 times or more and 8.0 times or less. By increasing the stretching ratio, the molecular chains of the fluororesin in the film can be stretched in the stretching direction, thereby increasing the orientation of the molecular chains and facilitating the alignment of the crystals. This can increase the retardation of the fluororesin piezoelectric film while making the film more rigid. This can also reduce the internal haze of the fluororesin piezoelectric film and make the film more transparent.

[0066] The stretching ratio is preferably 4.3 to 8.0 times, more preferably 4.3 to 7.7 times, even more preferably 4.5 to 7.7 times, particularly preferably 5.0 to 7.7 times, and very preferably 5.5 to 7.5 times. The higher the stretching ratio, the higher the proportion of the β phase, making it easier to obtain a fluororesin piezoelectric film with high piezoelectricity through the polarization step. On the other hand, by setting the stretching ratio to 8.0 times or less, it is possible to suppress the occurrence of distortion during the stretching step and to suppress an increase in the shrinkage rate of the fluororesin piezoelectric film when heated.

[0067] Furthermore, the stretching temperature of the fluororesin film can be controlled by controlling the surface temperature of the stretching roll during the stretching process. Here, the surface temperature of the stretching roll is referred to as the stretching temperature. The surface temperature of the roll during stretching is preferably 125°C or higher and 165°C or lower, more preferably 125°C or higher and 160°C or lower, even more preferably 130°C or higher and 160°C or lower, particularly preferably 130°C or higher and 155°C or lower, and most preferably 130°C or higher and 150°C or lower. Increasing the surface temperature of the roll during stretching can increase the stretching temperature of the fluororesin film. Stretching at a high surface temperature of the stretching roll of 125°C or higher relieves stress generated during the selective alignment of molecular chains, thereby reducing the shrinkage rate of the film during heating. Furthermore, stretching while heating uniformly stretches the film, suppressing localized crystallization and aligning molecular chains uniformly throughout the film, thereby suppressing light scattering due to differences in crystallinity within the film and reducing internal haze. By keeping the surface temperature of the rolls at 165°C or less during stretching, the efficiency of molecular chain alignment due to stretching of the film can be improved, the proportion of the β-phase structure that contributes to the expression of piezoelectricity can be increased, and deformation of the film due to melting of the fluororesin can be suppressed.

[0068] (Polarization Step) In the polarization step, a DC voltage is applied to the fluororesin film to impart piezoelectricity to the fluororesin film. Fluororesin containing a VDF homopolymer or copolymer undergoes a transition from α phase to β phase during the stretching step, increasing the proportion of the β phase. By applying a DC voltage to a fluororesin film with an increased proportion of the polar β phase, a fluororesin piezoelectric film with high piezoelectricity can be obtained.

[0069] The applied DC voltage is preferably 7.0 kV or more and 50.0 kV or less, more preferably 7.5 kV or more and 30 kV or less, even more preferably 8.0 kV or more and 30 kV or less, and particularly preferably 8.5 kV or more and 30 kV or less.

[0070] The stretching step and the polarization step may be carried out simultaneously, or the polarization step may be carried out after the stretching step.

[0071] The fluororesin film after the film-forming step or the fluororesin piezoelectric film after the polarization step can be wound into a roll for storage, transportation, and the like.

[0072] [Uses] The above-described fluorine-based resin piezoelectric film can be used in various applications such as touch sensors and touch panels, piezoelectric films for actuators, protective films, and retardation films.

[0073] [Other Embodiments] It goes without saying that the above-described embodiments are exemplary embodiments of the present invention, and the present invention may include embodiments other than the above-described embodiments within the scope of its core technical concept.

[0074] The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

[0075] The melt viscosity of the fluororesin material was measured in accordance with ASTM D 3835:2016 (ISO 11443:2021, JIS K 7199:1999). Specifically, a capillary rheometer (Capillograph 1D, manufactured by Toyo Seiki Seisaku-sho, Ltd.) was used, and the melt viscosity was measured at a temperature of 260°C and a shear rate of 50 s−1 using a capillary die with an inner diameter of 1 mm and a tube length of 10 mm. －１ The viscosity was measured at 1000 kJ / min.

[0076] The melting point of the resin composition was measured in accordance with JIS K 7121: 1987. Specifically, 5 mg of a measurement sample was sealed in an aluminum pan and placed in a differential scanning calorimeter (DSC-60A, manufactured by Shimadzu Corporation), and the temperature was raised from room temperature to 230°C at a heating rate of 10°C / min in a nitrogen atmosphere to measure a DSC curve. The maximum melting peak temperature in the DSC curve was determined as the melting point of the resin composition.

[0077] The melt temperature was the maximum temperature in the conduit from the extruder to the filtration device.

[0078] 1. Preparation of Fluorine-Based Resin Piezoelectric Films Films 1 to 12, all of which were fluorine-based resin piezoelectric films, were prepared by the following procedure.

[0079] 1-1. Film 1 A VDF homopolymer (PVDF) with a melt viscosity of 800 Pa s and a melting point of 173°C was melted at a melting temperature of 260°C in a single-screw extruder with a diameter of φ50 mm, and then filtered through a sintered metal filter element (Fuji Metal Fiber, manufactured by Fuji Filter Industrial Co., Ltd.) with a filtration accuracy of 20 μm. The filtered resin was extruded into a film from a T-die and cooled by contacting it with the surface of a cooling roll whose surface was heated to 70°C, yielding an unstretched film with a thickness of 160 μm.

[0080] The unstretched film was introduced into a uniaxial stretching device equipped with multiple metal rolls and pinch rolls, and the surface temperature and rotation speed ratio of each roll was adjusted to stretch the film 5.9 times in the machine direction (MD direction) at 130° C. A voltage of 9.6 kV was applied from the surface of the film in the thickness direction to obtain Film 1.

[0081] 1-2. Film 2 Film 2 was obtained in the same manner as in Film 1, except that an unstretched film having a thickness of 190 μm, which had been produced by setting the surface temperature of the cooling roll at 50° C., was stretched to a stretching ratio of 7.5 at a stretching temperature of 140° C. and an applied voltage of 12.8 kV.

[0082] 1-3. Film 3 Film 3 was obtained in the same manner as in film 2, except that the stretching temperature was 150, the stretching ratio was 7.1 times, and the applied voltage was 12.0 kV.

[0083] 1-4. Film 4 Film 4 was obtained in the same manner as Film 1, except that PVDF having a melt viscosity of 2500 Pa·s and a melting point of 173°C was used, the stretching ratio was 4.5 times, and the applied voltage was 7.2 kV.

[0084] 1-5. Film 5 Film 5 was obtained in the same manner as in the production of Film 4, except that the stretching temperature was 150° C., the stretching ratio was 4.9 times, and the applied voltage was 7.6 kV.

[0085] 1-6. Film 6 Film 6 was obtained in the same manner as in the production of Film 4, except that the surface temperature of the cooling roll was 110° C., the draw ratio was 4.4 times, and the applied voltage was 7.1 kV.

[0086] 1-7. Film 7 Film 7 was obtained in the same manner as in the production of Film 1, except that the stretching temperature was 110° C., the stretching ratio was 5.0 times, and the applied voltage was 8.2 kV.

[0087] 1-8. Film 8 Film 8 was obtained in the same manner as Film 7, except that PVDF having a melt viscosity of 2500 Pa·s and a melting point of 173°C was used, the stretching ratio was 3.5 times, and the applied voltage was 7.2 kV.

[0088] 1-9. Film 9 Film 9 was obtained in the same manner as in Film 6, except that a 190 μm thick unstretched film was stretched at a temperature of 120° C., a stretch ratio of 4.8 times, and an applied voltage of 7.4 kV.

[0089] 1-10. Film 10 Film 10 was obtained in the same manner as in the production of Film 4, except that no polymer filter was used, the cooling roll temperature was 130°C, the stretching temperature was 110°C, the stretching ratio was 4.2 times, and the applied voltage was 7.5 kV.

[0090] 1-11. Film 11 Film 11 was obtained in the same manner as film 10, except that PVDF having a melt viscosity of 4500 Pa s and a melting point of 173°C was used, the melting temperature was 280°C, no polymer filter was used, the stretching temperature was 130°C, the stretching ratio was 3.6 times, and the applied voltage was 8.8 kV.

[0091] 1-12. Film 12 100 g of PVDF with a melt viscosity of 2500 Pa s and a melting point of 173°C was weighed and added to 900 ml of n-methylpyrrolidone (NMP). The temperature was raised to 60°C while stirring with a stirrer, and stirring was continued for 6 hours to prepare a resin solution. This resin solution was filtered through a filter with a filtration accuracy of 40 μm. The filtered resin solution was added to an automatic coater to prepare a coating film with a liquid thickness of 600 μm. The film was dried at 120°C for 1 hour, and a voltage of 10.0 kV was applied from the surface to the thickness direction to obtain film 12.

[0092] 2. Evaluation of Fluoroplastic Resin Piezoelectric Films Unless otherwise specified, Films 1 to 12 were cut into squares measuring 300 mm on a side, and the area including the intersection of the diagonals of the square film was measured for maximum shrinkage, retardation, internal haze, and piezoelectric constant d using the following methods. ３３ The surface height roughness Rz, the number of foreign particles, and the thickness were measured, and the values ​​were taken as representative values.

[0093] 2-1. Maximum Shrinkage Ratio The maximum shrinkage ratio when maintained at 80°C for 30 minutes was determined using the following method. A fluororesin piezoelectric film was cut into a roughly square shape measuring approximately 100 mm x 100 mm from within an area including the intersection of the diagonals of the square film to prepare a measurement film. On one side of the measurement film, line segments A and B were marked, passing through the intersection of the diagonals of the measurement film (the center of the film) and extending roughly parallel to the two sides of the measurement film, so that they intersected at right angles at the center of the measurement film. The lengths of the marked line segments A and B were measured using an image dimension measuring instrument (Keyence Corporation, One-Shot 3D Shape Measuring Instrument VR-5200). The measurement film was then placed in an oven heated to 80°C and maintained there for 30 minutes, then removed from the oven and allowed to cool to room temperature. The lengths of line segments A and B were then measured using the same image dimension measuring instrument. The length of line segment A after heating was subtracted from the length of line segment A before heating, and the resulting value, expressed as a percentage, was taken as the shrinkage rate of line segment A. Next, the shrinkage rate of line segment B was calculated in the same manner as for line segment A. The shrinkage rates of line segment A and line segment B were compared, and the larger shrinkage rate was taken as the maximum shrinkage rate.

[0094] 2-2. Retardation Using a KOBRA-HB manufactured by Oji Scientific Instruments, the retardation of a film cut into a 20 mm x 20 mm area from the area including the intersection of the diagonal lines of the square film was measured by the parallel Nicol rotation method. The value at a measurement wavelength of 587.8 nm was taken as the retardation of the film.

[0095] 2-3. Internal haze A rectangular film was cut into a size of 50 mm x 50 mm so as to include the intersection of the diagonals of the square film. One surface (side A) of the rectangular film was coated with a hard coating agent (BS CH271, manufactured by Arakawa Chemical Industries, Ltd.) using a bar coater, and dried at 80°C for 30 minutes. Thereafter, an ultraviolet (UV) irradiation device (CSOT040, manufactured by GS NIPPON DENCHI Co., Ltd.) was used to apply a hard coating agent to the surface of the rectangular film (side A) until the target integrated light dose reached 400 mJ / cm. ２ The film was irradiated with UV light so that the thickness of the coating layer was 2 μm. A coating layer similar to that on the A side was also formed on the other surface (side B) of the rectangular film with the A side coated. Coating layers were formed on both sides of the film by the above method, and external haze due to scratches on the film surface, etc., was removed. The internal haze of the fluororesin piezoelectric film was measured in accordance with ISO 14782:2021 using a haze meter (NDH7700SP II, manufactured by Nippon Denshoku Industries Co., Ltd.) for a range including the intersection of the diagonals of the film for internal haze measurement, and the result was used as a representative value.

[0096] 2-4. Haze Measurement was performed using a haze meter (NDH7700SP II, manufactured by Nippon Denshoku Industries Co., Ltd.) In accordance with ISO 14782:2021, the haze was measured in an area including the intersection of the diagonal lines of the rectangular film before the coating layer was formed, and the measured value was used as the representative haze value of the fluororesin piezoelectric film.

[0097] 2-5. Piezoelectric constant d ３３ Piezoelectric constant d ３３ is the direct quasi-static method (d ３３ The piezoelectric constant d of the piezoelectric ceramic measured by the Meter method and the Berlincoat method ３３ The measurement was carried out in accordance with the test method ISO 19622:2018. Specifically, a piezoelectric constant measuring device (Piezometer System PM300, manufactured by PIEZOTEST) was used to hold the test film as a test piece at a measurement temperature of 25°C with a holding force of 1.0 N, and an alternating force of 0.15 N and a frequency of 110 Hz was applied, and the generated charge was measured. The absolute value of the piezoelectric constant calculated from the value was used as the piezoelectric constant d ３３ was used as a representative value.

[0098] 2-6. Surface Height Roughness Rz The surface height roughness Rz of the measurement film was measured using a surface roughness meter (Keyence Corporation, shape analysis laser microscope VK-X260) conforming to JIS B 0601:2001. The surface height roughness Rz was measured in an area including the intersection of the diagonal lines of the fluororesin piezoelectric film, and this value was used as the representative value of the surface height roughness Rz of the film. The Rz measurement was performed on the surface of the fluororesin piezoelectric film that had been in contact with the cooling roll.

[0099] 2-7. Number of foreign objects: 0.010 m so that each film is cut out from adjacent positions in succession. ２ Four rectangular films (observation pieces) each measuring 100 mm x 100 mm were cut out from the fluorine-based resin piezoelectric film. The sum of the number of foreign particles measured by observing each observation piece was multiplied by 25 / 4, and the resulting value was rounded to the first decimal place to obtain a value of 0.25 m. ２ The number of foreign particles per unit area was calculated. At this time, foreign particles were observed using transmitted light, marked, and the marked areas were observed under a microscope to determine the size of the foreign particles. The size of the foreign particles was calculated as the arithmetic mean value of the maximum and minimum widths of the foreign particles. In this way, the number of foreign particles larger than 200 μm, foreign particles with a size of 100 μm to 200 μm, and foreign particles with a size of less than 100 μm was calculated.

[0100] 2-8. Thickness: A digital linear gauge (DG525H, manufactured by Ono Sokki Co., Ltd.) and a gauge stand (SH-022, manufactured by Ono Sokki Co., Ltd.) were used. The thickness was measured in the area including the intersection of the diagonal lines of the square film, and the average value of these measurements was taken as the thickness of the film.

[0101] 3. Results The production conditions and evaluation results for each film are shown in Tables 1 and 2. Film 12 had a high haze and was very opaque, making it impossible to measure the number of foreign particles.

[0102]

[0103]

[0104] This application claims priority to Japanese Patent Application No. 2024-124972 filed on July 31, 2024, and Japanese Patent Application No. 2024-124978 filed on July 31, 2024. The entire contents of the specification, claims, and drawings of those applications as originally filed are incorporated herein by reference.

[0105] The fluororesin piezoelectric film according to the present invention is useful as a piezoelectric film having high transparency and a small maximum shrinkage rate during heat treatment.

Claims

1. The maximum shrinkage rate when kept at 80°C for 30 minutes is 2.5% or less, the retardation is 50nm or more and 3000nm or less, the internal haze is less than 1.2%, and the piezoelectric constant d ３３ A fluorine-based resin piezoelectric film having a piezoelectric constant of 5.0 pC / N or more and 40.0 pC / N or less.

2. Measurement temperature: 260°C, shear rate: 50 s －１ The fluorine-containing resin piezoelectric film according to claim 1 , wherein the melt viscosity η measured by the method is 600 Pa·s or more and 4000 Pa·s or less.

3. The fluororesin piezoelectric film according to claim 1, which is primarily composed of vinylidene fluoride resin.

4. The number of foreign particles whose size, which is the arithmetic mean value of the maximum and minimum widths when the film is viewed in a plane, is 100 μm or more is 7 / 0.25 m ２ The fluorine-based resin piezoelectric film according to claim 1 , wherein:

5. The fluorine-based resin piezoelectric film according to claim 1, wherein the surface roughness in surface height Rz measured in accordance with JIS B 0601:2001 on the surface having a smaller Rz is 0.50 μm or less.

6. A method for producing a fluorine-based resin piezoelectric film according to any one of claims 1 to 5, comprising the steps of: heating and melting a resin composition containing a fluorine-based resin; extruding the molten resin composition to form a film; stretching the formed film at a stretching temperature of 125°C to 165°C and at a stretching ratio of 4.0 to 8.0 times; and polarizing the formed film by applying a voltage of 7.0 kV to 50.0 kV.

7. The method for producing a fluorine-based resin piezoelectric film according to claim 6, further comprising a step of filtering the resin composition melted in the melting step through a filter having a filtration accuracy of 10 μm or more and 40 μm or less.

8. The method for producing a fluorine-based resin piezoelectric film according to claim 6, wherein in the film-forming step, the extruded resin composition is cooled by contacting it with a cooling roll having a surface temperature of 125°C or less.

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