WO2019064739A1 - Piezoelectric film and method of manufacturing film - Google Patents

Abstract

The invention relates to a thin and very smooth piezoelectric film. The piezoelectric film comprises a vinylidene fluoride resin as the main component, the piezoelectric film having a thickness not exceeding 300 μm, and an arithmetic mean roughness Ra not exceeding 0.050 μm on both sides.

Description

Piezoelectric film and method of manufacturing film

The present invention relates to a piezoelectric film and a method of manufacturing the film.

Various organic dielectric films are known as films (piezoelectric films) having piezoelectricity.

Piezoelectric films are often used as sensors or actuators, and various applications can be made, for example, the surfaces of keyboards and display panels of mobile devices.

These piezoelectric films can be obtained by polarization treatment of a film formed of an organic dielectric resin. As a method for producing such a piezoelectric film, for example, in Patent Document 1, when heat treatment is performed on a polarized film subjected to polarization treatment, a protective film is attached to one surface of the polarized film, and the polarized film A method of producing a piezoelectric film is disclosed in which the heat treatment is carried out through a protective film by a heating roller.

Japanese Patent Publication "Japanese Patent Application Laid-Open No. 2015-111640"

However, the piezoelectric film manufacturing method described in Patent Document 1 only uses a protective film when heat-treating the piezoelectric film, and discloses nothing about using the protective film when the piezoelectric film is stretched. Not. Moreover, in order to produce a piezoelectric film, it is necessary to roughen the surface of the stretching roll used in the stretching step before the polarization treatment, regardless of the thickness of the film. Here, there is a problem that the surface of the piezoelectric film is finely scratched by the surface of the stretching roll. On the other hand, since the piezoelectric film is required to have high surface smoothness while having a thinness, there are many cases where it is required that such a flaw does not occur. For example, with the expansion of applications of piezoelectric films, the appearance may be regarded as important, and in such a case, a piezoelectric film without flaws may be required.

The present invention has been made in view of the above problems, and an object thereof is to provide a piezoelectric film having thinness and high smoothness, and a related technology thereof.

In order to solve the above-mentioned subject, a piezoelectric film concerning the present invention is a piezoelectric film which makes vinylidene fluoride resin the main ingredients, and the above-mentioned piezoelectric film is 300 micrometers or less in thickness, and both sides of the above-mentioned piezoelectric film Each is characterized in that the arithmetic mean roughness is 0.050 μm or less.

Further, according to the present invention, a protective film for protecting the surface is laminated on one surface of the resin sheet, and the resin film is stretched together with the protective film from the protective film side by a stretching roll to obtain a stretched film. There is provided a method of producing a film comprising a stretching step, and a removal step of removing the protective film from the stretched film after the stretching step.

According to the present invention, it is an object of the present invention to provide a piezoelectric film having thinness and high smoothness and the related technology.

FIG. 1: is a schematic diagram which shows an example of the manufacturing method of the piezoelectric film which concerns on one aspect. FIG. 2 shows measurement data of three-dimensional surface roughness of the piezoelectric film of Example 1 and the piezoelectric film of Comparative Example 1.

Hereinafter, the piezoelectric film according to an aspect of the present invention will be described in detail.

Piezoelectric film
The piezoelectric film which concerns on one aspect is a film shape | molded from the material containing resin which has piezoelectricity. Here, examples of the resin having piezoelectricity include polyvinylidene fluoride resin and odd chain nylon such as nylon 11, etc. From the viewpoint of high piezoelectricity, weather resistance, heat resistance, etc. Among these, it is most preferable to use a vinylidene fluoride resin.

Moreover, the piezoelectric film which concerns on one aspect may contain another component as materials other than resin which has piezoelectricity.

(Vinylidene fluoride resin)
The vinylidene fluoride resin may be any of homopolymers and copolymers of vinylidene fluoride and mixed resins thereof. When the vinylidene fluoride resin is a vinylidene fluoride copolymer, it is preferable to be composed of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride. Examples of monomers copolymerizable with vinylidene fluoride include hydrocarbon monomers such as ethylene and propylene, or vinyl fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, Copolymers with fluorine-containing monomers other than vinylidene fluoride such as fluoroalkyl vinyl ether are included. When the vinylidene fluoride resin is a copolymer, the content of the vinylidene fluoride monomer in the vinylidene fluoride resin is preferably 90 mol% or more, and more preferably 95 mol% or more.

Further, in the vinylidene fluoride resin, 0.1 to 3 parts by mass of a carboxyl group, an epoxy group, a hydroxyl group, and a carbonyl relative to 100 parts by mass of the monomer constituting the homopolymer or copolymer of vinylidene fluoride described above Using a vinylidene fluoride polymer having at least one adhesive functional group selected from groups and copolymerizable with vinylidene fluoride and a monomer copolymerizable with the introduction of these adhesive functional groups Is also preferred. Examples of the monomer having a carboxyl group include unsaturated monobasic acids such as acrylic acid and crotonic acid, and unsaturated dibasic acids such as maleic acid and citraconic acid or monoalkyl esters thereof. Moreover, as a monomer which has an epoxy group, allyl glycidyl ether, methallyl glycidyl ether, crotonic acid glycidyl ester, allyl acetate glycidyl ester etc. are mentioned. Moreover, as a monomer which has a hydroxyl group, hydroxyethyl acrylate, hydroxypropyl acrylate etc .; Moreover, as a monomer which has a carbonyl group, ethylene carbonate etc. are mentioned. The monomer having the adhesive functional group is a small amount of 0.1 to 3 parts by mass with respect to 100 parts by mass of the vinylidene fluoride polymer-forming monomer not having the adhesive functional group, and therefore, the vinylidene fluoride polymer is formed. It can be formed by suspension polymerization in an aqueous medium with the monomer.

The inherent viscosity of the vinylidene fluoride resin used in the piezoelectric film according to one aspect is preferably 1.1 to 2.0 dl / g. When the inherent viscosity is 1.1 to 2.0 dl / g, high strength can be provided to the piezoelectric film. The inherent viscosity in the present application is the logarithmic viscosity at 30 ° C. of a solution of 4 g of resin in 1 liter of N, N-dimethylformamide (DMF).

(Other ingredients)
The piezoelectric film according to one aspect may contain components other than the resin as needed in order to prepare electrical properties, mechanical properties and the like. Examples of such components include inorganic substances, and inorganic substances include inorganic oxide particles.

When the piezoelectric film contains an inorganic substance, an affinity improver or the like may be contained as another component. The affinity improver enhances the affinity between the inorganic oxide particles and the vinylidene fluoride resin, and the inorganic oxide particles are uniformly dispersed in the vinylidene fluoride resin, and the inorganic oxide particles and the vinylidene fluoride resin are contained in the film. Can be firmly bonded to suppress the generation of voids, and can increase the dielectric constant.

Specific examples of the affinity improver include surfactants and coupling agents. Examples of the surfactants include wetting agents, dispersing agents and antifoaming agents.

In addition, the piezoelectric film may contain, for example, an antioxidant, a lubricant, a plasticizer, a colorant, a UV absorber, an inorganic acid, an organic acid, a pH adjuster, a crosslinking agent, and the like, as necessary.

In addition, what is necessary is just to adjust a compounding quantity suitably in the range which does not lose the effect of this invention in a piezoelectric film.

(Physical properties of piezoelectric film)
In one aspect, the thickness of the piezoelectric film is 300 μm or less, preferably 80 μm or less, and more preferably 30 μm or less. By setting the thickness of the piezoelectric film to 300 μm or less, preferably 80 μm or less, more preferably 30 μm or less, it can be suitably used as a piezoelectric sensor used for a display panel and a keyboard of a mobile device or the like. In addition, although not limited, if the thickness of the piezoelectric film is 10 μm or more, the strength at the time of use can be maintained.

It is preferable that arithmetic mean roughness Ra in each of the surface and back of a piezoelectric film concerning one mode is 0.050 micrometer or less. By reducing the arithmetic mean roughness Ra on each of both surfaces of the piezoelectric film, it is possible to obtain a surface having high smoothness, and thereby a piezoelectric film having high transparency can be obtained. In addition, although not limited, arithmetic mean roughness Ra in each of the surface and back of a piezoelectric film may be 0.001 micrometer or more.

Arithmetic mean roughness Ra of the piezoelectric film can be measured by a method according to JIS B0601-1994, and the surface of the piezoelectric film is measured by a roughness meter, and the unevenness state of a certain section is represented by an average value. .

The surface roughness of the piezoelectric film can also be specified as the maximum height Rz (the difference between the maximum value and the minimum value in the distribution of roughness), and the maximum height Rz is 0.20 μm or less, 0 It is preferable that it is not more than .18 μm. Moreover, arithmetic mean roughness Ra in each of the surface and back surface of a piezoelectric film may be 0.010 micrometer or more.

In the present specification, the surface of the piezoelectric film is the surface on which the protective film was superposed at the time of production of the piezoelectric film, and may be referred to as the first surface. In addition, the back surface of the piezoelectric film is a surface on which the protective film is not overlapped, and may be referred to as a second surface. In the piezoelectric film according to one aspect, the back surface exhibits a smaller value of the arithmetic average roughness Ra than the front surface, and the arithmetic average roughness Ra is 0.05 μm or less in any of the surfaces.

The piezoelectric constant d ₃₁ of the piezoelectric film indicates the amount of displacement with respect to the applied voltage, in other words, indicates the charge density generated for a given stress. Higher piezoelectric constant d ₃₁ is large, the charge density increases raised against stress.

The piezoelectric constant d ₃₁ of the piezoelectric film is preferably in the range of 10 pC / N or more and 40 pC / N or less. It can use suitably for various apparatuses by setting it as the said range. Also, the piezoelectric film has a deviation of ± 20% or less from the local average value of the d ₃₁ piezoelectric constant over almost the entire area. The "piezoelectric film" having a piezoelectric constant d ₃₁ within the range of 10 pC / N or more and 40 pC / N or less by performing polarization treatment as described later is referred to as "polarization film" or "polarization treatment piezoelectric film" Sometimes called.

(Use of piezoelectric film)
The piezoelectric film of the present invention can be used for a piezoelectric panel such as a touch panel. Furthermore, the piezoelectric panel having the piezoelectric film of the present invention can be used for an input device and a touch sensor device. Specific examples of the input device include display devices such as a smartphone, a tablet PC, an ATM, an automatic ticket vending machine, and a television. Specific examples of the touch sensor device include an impact sensor, a robot cleaner, and a keyboard of a PC.

[Method of producing film]
In the method for producing a film according to one aspect, a protective step of laminating a protective film for protecting the surface on one surface (also referred to as surface or first surface) of a resin film, and a protective film from the protective film side by a stretching roll. And a step of stretching the resin film to obtain a piezoelectric film, and a step of removing the protective film from the piezoelectric film after the step of stretching.

In the film manufacturing method, typically, the resin film contains a vinylidene fluoride resin as a main component, and the stretched film manufactured is a piezoelectric film.

Hereinafter, a method of manufacturing a piezoelectric film will be described in detail as a method of manufacturing a film according to one aspect with reference to FIG.

(Protection process)
FIG. 1: is a schematic diagram which shows an example of the manufacturing method of the piezoelectric film which concerns on one aspect. In the method of manufacturing a piezoelectric film according to an aspect, in the protection step, the protective film 12 is superimposed on the surface in contact with the resin film 11 and the stretching roll before stretching the resin film containing a vinylidene fluoride resin as a main component. Here, in the method of manufacturing a piezoelectric film according to one aspect, the resin film 11 is heated in advance by a preheating roll (not shown), and the protective film 12 is not heated in advance by the preheating roll. Overlay the protective film 12.

Thereby, in the extending process mentioned later, the damage | wound of the resin film 11 surface which generate | occur | produces due to the surface of the extending | stretching roll 21 being rough can be reduced significantly. In addition, since the resin film 11 can be stretched together in a state supported by the protective film 12 by the protective film, the resin film 11 is prevented from being damaged while the thickness of the resin film 11 becomes thinner. It can be stretched.

In the present specification, the resin film 11 is a film which has not been subjected to a stretching step, and may be referred to as a "non-stretched film". In addition, after the stretching step, the stretched resin film may be referred to as "piezoelectric film" or "stretched film". From the viewpoint of processability in the stretching step and ease of overlapping with the protective film 12, the thickness of the unstretched film is preferably 50 μm or more and 500 μm or less.

The protective film 12 is used to protect the resin film 11 from scratches caused by contact between the rough surface of the stretching roll 21 and the resin film 11 when the resin film 11 is stretched in the stretching step. The protective film 12 is stretched together with the resin film 11 when the resin film 11 is stretched.

The protective film 12 is not particularly limited as long as it does not fuse with the resin film 11, but a polyolefin resin film or a polyester resin film is preferable. More specifically, polypropylene film (PP), polyethylene terephthalate film (PET), polyethylene naphthalate film (PEN), polyethylene film (PE) and the like can be mentioned. In the stretching step to be described later, a polypropylene film (PP) is most preferable in terms of excellent stretchability. Moreover, the protective film 12 may combine two or more films mentioned above.

The thickness of the protective film 12 before stretching with the resin film 11 is not particularly limited, but is preferably in the range of 10 μm to 200 μm, and is in the range of 20 μm to 100 μm. Is more preferred. Further, the thickness of the protective film 12 is more preferably thicker than the thickness of the resin film 11 which is stretched together, from the viewpoint of supporting the resin film 11 while stretching together with the resin film 11.

The surface roughness Ra of the surface of the protective film 12 facing the resin film is not particularly limited, but may be 30 μm or less, more preferably 0.1 μm or less, and more preferably 0.05 μm or less It is most preferable that By this, it can prevent that arithmetic mean roughness Ra in the surface of a piezoelectric film becomes large. In addition, although the lower limit value of protective film surface roughness Ra is not limited, it may be 0.01 micrometer or more.

The method of stacking the protective film 12 is not particularly limited as long as the protective film 12 and the resin film 11 are not fused to each other and can not be peeled off, but for example, an apparatus for supplying the resin film 11 There is a method in which the protective film 12 is supplied from different devices and the resin film 11 and the protective film 12 are stacked immediately before being introduced into the stretching roll 21. The stretching rolls 21 are each heated, and heat the introduced resin film 11 and protective film 12. In addition, the temperature of the preheating roll (not shown) which heats the resin film 11 beforehand, and the temperature of the drawing roll 21 which heats the resin film 11 and the protective film 12 are resin for shape | molding the resin film 11 and the protective film 12 It may be appropriately adjusted according to the melting temperature of the material and the like.

(Stretching process)
In the stretching step of one embodiment, the piezoelectric film 11a and the stretched protective film 12a, which is a stretched protective film, are stretched by stretching the resin film 11 using the rough stretching roll 21 on the surface together with the protective film 12 stacked in the protecting step. Can be obtained.

Moreover, the pinch roll 26 which clamps the laminated body of the piezoelectric film 11a and the extending | stretching protective film 12a may be provided in the extending | stretching roll 21. As shown in FIG. By providing the pinch roll 26, the laminate of the resin film 11 and the protective film 12 introduced into the drawing roll 21 can be sandwiched and fixed, so the drawing process can be performed under certain conditions. In the manufacturing method according to one aspect, the drawing process may be performed by necking drawing. By this, it is possible to make the α crystal of vinylidene fluoride resin transition to the polar β crystal. Thus, the stretched film can be provided with piezoelectricity. Also, in the stretching step, the protective film 12 and the resin film 11 are laminated, and the protective film 12 is stretched by stretching the protective film 12 so that the roll surface is in contact with the roughened stretching roll 21. It is possible to prevent the resin film 11 from being damaged by the roughened roll surface while performing necking stretching stably with the film 11.

The diameters of the stretching roll 21 and the stretching roll 22 are not particularly limited, and may be appropriately designed in accordance with the sizes of the resin film 11 and the protective film 12.

As the drawing roll 21, for example, a roll having a mirror-finished metal roll surface sanded or blasted is used, or a roll made of a nonmetallic conductive material which has been roughened in advance is used. Can. Arithmetic mean roughness Ra (JIS B0601-1994) of the drawing roll 21 according to one aspect is 0.1 μm to 30 μm, preferably 0.2 μm to 2 μm in the width direction (TD direction) of the drawing roll. By setting Ra of the surface of the stretching roll 21 to the above range, the friction coefficient of the surface of the stretching roll 21 can be suitably adjusted, and cutting of the piezoelectric film 11 a and the stretching protection film 12 a can be prevented. Further, the stretching roll is preferably a thermal spray roll made of tungsten carbide, a ceramic roll or the like from the viewpoint of high abrasion resistance. In addition, lubricants such as perfluoropolyethylene fine particles such as Teflon (registered trademark), higher fatty acid salts or esters, and fluorinated lubricants may be applied to the surfaces of the stretching rolls 21 and 22 if necessary. It is also good.

The laminate of the piezoelectric film 11 a and the stretched protective film (hereinafter, also referred to as a stretched protective film) 12 a has rotational speeds of the stretching roll 21 and the stretching roll 22 in which the surface of the laminate of the resin film 11 and the protective film 12 is roughened. The draw ratio can be adjusted by the difference of Here, the rotational speed R ₁ of the drawing roll 21 is not particularly limited as long as it is slower than the rotational speed R ₂ of the drawing roll 22, but the rotational speed ratio R ₂ / R ₁ is 2.5 or more Is preferable, and 6 or less is more preferable.

The stretching ratio in the stretching step is preferably 2.5 times or more and 6 times or less. By setting it as the said draw ratio, a fracture | rupture of a film can be prevented. In addition, the extending | stretching process of this invention is not limited to the method of using two extending | stretching rolls 21 and 22 as mentioned above, You may extend | stretch using several extending | stretching rolls. Moreover, also in the stretching roll 22, a pinch roll (not shown) may be provided similarly to the stretching roll 21.

(Removal process)
After the laminate of the piezoelectric film 11a and the stretched protective film 12a obtained in the stretching step passes through the stretching roll 21, the stretched protective film 12a is removed (removal step). The method for removing the protective film is not particularly limited as long as the protective film does not remain on the piezoelectric film, but for example, a method of sliding and removing the laminate of the piezoelectric film 11a and the stretched protective film 12a is mentioned Be In addition, when the pinch roll is provided in the extending | stretching roll 22, after passing the said pinched roll, the extending | stretching protective film 12a is removed from a laminated body.

In the production method according to one aspect, in the case of providing a polarization step described later after the stretching step, the removal step is preferably performed before the polarization step. By performing the polarization process after the removal process, it is possible to prevent the dielectric breakdown of the piezoelectric film (hereinafter referred to as a polarization process piezoelectric film) 11b obtained after the polarization process.

(Polarization process)
In the manufacturing method according to one aspect, the direct current between the noncontact tip electrode 24 connected to the direct current high voltage power supply 25 and the polarized roll 23 (counter electrode) grounded is further connected to the piezoelectric film 11a obtained in the stretching step. Polarization is performed by the action of a high electric field.

The point electrode 24 is for polarizing the piezoelectric film 11a by holding the charge generated by the corona discharge generated at the point on the surface of the piezoelectric film 11a and performing direct current electrolysis with the polarization roll 23. It is. The tip electrode 24 includes a noncontact electrode and a contact electrode. Examples of non-contact electrodes include electrodes having needle-like tips (needle-like electrodes). The contact type electrode performs polarization processing using the electrode directly in contact with the piezoelectric film 11a, but in order to prevent the dielectric breakdown of the piezoelectric film 11a and the shutdown of the power source accompanying it, the noncontact type electrode may be used preferable.

The DC voltage applied to the piezoelectric film in the polarization step may be greater than 0 kV, more preferably 5 kV or more, and most preferably 7 to 50 kV. However, the required conductivity is not necessarily high, and the specific electrical resistance may be about 10 ⁴ to 10 ⁵ Ω · cm or less realized with titanium oxide / alumina ceramic.

The diameter of the polarization roll 23 is not particularly limited, and may be appropriately designed according to the size of the piezoelectric film 11a.

In the production method according to this aspect, the polarization step is performed after the stretching step, but in the production method according to one aspect, the film may be subjected to polarization treatment while being stretched. That is, in the manufacturing method according to one aspect, the drawing process and the polarization process may be performed simultaneously, and in this case, the polarization treatment may be performed while necking drawing is performed.

(Other process)
The polarization-treated piezoelectric film 11b obtained as described above may be subjected to a post-treatment such as a heat treatment step for dimensional stabilization. The heat treatment method is not particularly limited.

The temperature in the heating step varies depending on the composition of the piezoelectric film to be heat-treated, but is preferably in the range of 60 ° C. or more and 150 ° C. or less. The heating time is not limited, but is preferably in the range of 10 seconds to 60 seconds.

The piezoelectric film subjected to the above-mentioned post-treatment is taken up on a take-up roll, and stored or supplied to the market as a product piezoelectric film, or a film-like piezoelectric provided with double-sided or single-sided electrodes by vapor deposition or via an adhesive. Used as an element product.

[Method of Manufacturing Piezoelectric Film According to Another Embodiment]
The method for producing a piezoelectric film according to one aspect is not limited to the above aspect. For example, the method for producing a piezoelectric film according to one aspect further includes a resin film forming step of obtaining a resin film by extruding a resin material containing a vinylidene fluoride resin before the protection step. .

In the present embodiment, the method for obtaining the resin film 11 is not particularly limited, but can be obtained, for example, by melting and extruding a resin material containing a vinylidene fluoride resin. In addition, since the thickness of the resin film shape | molded by extrusion molding conforms to the thickness of the above-mentioned unstretched film, description is abbreviate | omitted. Moreover, in the manufacturing method which concerns on this aspect, the resin film 11 and the protective film 12 which were extrusion-molded may be piled up, and an extending process may be performed. That is, after the extrusion process, the protection process and the stretching process may be performed continuously.

Further, in the manufacturing method according to still another aspect, the resin material containing the vinylidene fluoride resin and the resin material for forming the protective film are separately melted and co-extruded with, for example, a T die or the like. It includes a co-extrusion step of simultaneously forming the resin film 11 and the protective film 12 superimposed on each other. That is, in the manufacturing method according to this aspect, the resin film forming step and the protection step are simultaneously performed.

[Summary]
A piezoelectric film according to an embodiment of the present invention is a piezoelectric film containing vinylidene fluoride resin as a main component, and the piezoelectric film has a thickness of 300 μm or less, and both sides of the piezoelectric film are arithmetic. It is characterized in that the average roughness is 0.050 μm or less.

Moreover, as for the piezoelectric film which concerns on one Embodiment of this invention, it is more preferable that the thickness of the said piezoelectric film is 80 micrometers or less.

In the piezoelectric film according to an embodiment of the present invention, the vinylidene fluoride resin is more preferably a homopolymer of vinylidene fluoride.

In the piezoelectric film according to an embodiment of the present invention, the piezoelectric constant d ₃₁ is preferably in the range of 10 pC / N or more and 40 pC / N or less.

Moreover, according to one embodiment of the present invention, the protective film for protecting the surface is stacked on one surface of the resin sheet, and the resin film is stretched together with the protective film from the protective film side by the stretching roll. There is provided a method for producing a film, comprising a stretching step of obtaining a stretched film, and a removal step of removing the protective film from the stretched film after the stretching step.

In the film manufacturing method, the resin film may be a resin film containing a vinylidene fluoride resin as a main component, and the stretched film may be a piezoelectric film.

In addition, according to the method for producing a film according to one embodiment of the present invention, a resin film forming step of obtaining a resin film by extruding a resin material containing a vinylidene fluoride resin before the protection step is further included. Is preferred.

Moreover, according to the method of manufacturing a piezoelectric film according to an embodiment of the present invention, it is preferable that the method includes a polarization step of obtaining a polarized film by polarizing the piezoelectric film after the stretching step.

Further, according to the method of manufacturing a piezoelectric film according to an embodiment of the present invention, the protective film is preferably a polyolefin resin film or a polyester resin film.

Moreover, according to the manufacturing method of the piezoelectric film which concerns on one Embodiment of this invention, it is preferable that a protective film is 10 micrometers or more and 200 micrometers or less in thickness.

Moreover, according to the manufacturing method of the piezoelectric film which concerns on one Embodiment of this invention, it is preferable that arithmetic mean roughness Ra in the surface of a draw roll is 0.1 micrometer or more and 30 micrometers or less.

Examples will be shown below, and the embodiment of the present invention will be described in more detail. Of course, the present invention is not limited to the following examples, and it is needless to say that various aspects are possible as to details. Furthermore, the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining the disclosed technical means are also included. It is included in the technical scope of the invention. Also, all of the documents described in the present specification are incorporated by reference.

The piezoelectric films of Examples and Comparative Examples were prepared, and the thickness of the obtained piezoelectric film, the piezoelectric constant d ₃₁ , the arithmetic surface roughness Ra, and the maximum height Rz were evaluated for each.

(1) Piezoelectric constant d ₃₁
A 100-500 Å thick Al deposited electrode was formed on both sides of the piezoelectric film, and a 7 mm × 30 mm sample was cut out from a predetermined location (near the center of the flat surface of the film) of the Al deposited piezoelectric film. Next, the test piece is clamped in the sample chamber of a piezoelectric constant measuring device (“Leorograph solid” manufactured by Toyo Seiki Seisakusho Co., Ltd.), and tension: 1 newton (N), frequency: 10 Hz along the long side direction Vibration was applied under the conditions of and the piezoelectric constant d ₃₁ was measured.

(2) Surface roughness Ra
Arithmetic mean roughness (surface roughness) Ra was measured with a surface roughness tester ("Surfcorder SE1700" manufactured by Kosaka Laboratory Ltd.) according to JIS B0601-1994. In addition, arithmetic mean roughness (surface roughness) Ra was measured in the width direction (TD direction) of a piezoelectric film.

(3) Maximum height Rz
Similar to the surface roughness Ra, the maximum height Rz was also evaluated using a surface roughness meter ("Surfcorder SE1700" manufactured by Kosaka Laboratory Ltd.). The maximum height Rz was also measured in the width direction (TD direction) of the piezoelectric film in the same manner as the arithmetic average roughness (surface roughness) Ra.

Example 1
Protective film of PP (polypropylene: made by Kureha Co., Ltd.) on the back of a resin film (thickness: 110 μm) molded from PVDF (polyvinylidene fluoride: made by Kureha Co., Ltd.) with an inherent viscosity of 1.3 dl / g , 40 μm). The PVDF resin film and the protective film are passed through a hard chrome plated mirror finish preheated roll (diameter 300 mm, surface roughness Ra = 0.012 μm) heated to a surface temperature of 110 ° C., and subsequently, a surface temperature of 120 ° C. Through a ceramic drawing roll (diameter 150 mm, surface roughness Ra = 0.44 μm) heated to a draw speed of 3.6 m under the conditions of a feed speed of 0.8 m / min. (Stretching process).

After stretching, the PP film overlapping the PVDF film is peeled off, and a DC voltage is applied between the needle electrodes disposed at a distance of about 10 mm from the surface of the polarization roll to increase the DC voltage from 0 kV to 20 kV. And polarization treatment (polarization step). Physical properties of the obtained piezoelectric film are shown in Table 1.

(Example 2)
A piezoelectric film was obtained in the same manner as in Example 1 except that polyethylene naphthalate (hereinafter abbreviated as PEN) was used as a protective film. Physical properties of the obtained film are shown in Table 1.

(Example 3)
A piezoelectric film was obtained in the same manner as in Example 1 except that polyethylene terephthalate (hereinafter abbreviated as PET) was used as a protective film. Physical properties of the obtained film are shown in Table 1.

(Comparative example 1)
A piezoelectric film was obtained in the same manner as in Example 1 except that the protective film was not used. Physical properties of the obtained film are shown in Table 1.

As shown in Table 1, the surface roughness Ra in each example was 0.050 μm or less, and the thickness was 30 μm or less. From this, the piezoelectric film of the example has a smooth surface although being thin. I understand that there is. About this, (a) of FIG. 2 is measurement data of three-dimensional surface roughness in the piezoelectric film of Example 1, and (b) of FIG. 2 shows three-dimensional surface roughness in the piezoelectric film of Comparative Example 1. It is measurement data. The unit of the scale (X-axis direction, Z-axis direction) in each measurement data is μm, and the magnification of the Z-axis (height) is 20000 times. Comparing (a) and (b) of FIG. 2, the piezoelectric film of Example 1 is smooth without scratch scratches along the flow direction (MD direction), while the piezoelectric film of Comparative Example 1 is smooth. It can be clearly confirmed that the scratch damage along the MD direction is deep.

The present invention can be suitably used as a piezoelectric film for a piezoelectric panel used in an input device such as a smartphone, a touch panel such as a tablet PC, and the like.

Claims (11)

A piezoelectric film mainly composed of vinylidene fluoride resin,
The piezoelectric film has a thickness of 300 μm or less,
A piezoelectric film characterized in that each of both surfaces of the piezoelectric film has an arithmetic average roughness Ra of 0.050 μm or less. The thickness of the said piezoelectric film is 80 micrometers or less, The piezoelectric film of Claim 1 characterized by the above-mentioned. The piezoelectric film according to claim 1 or 2, wherein the vinylidene fluoride resin is a homopolymer of vinylidene fluoride. The piezoelectric constant _{d 31} is, 10pC / N or more, the piezoelectric film according to any one of claims 1 to 3, characterized in that within the scope of the following 40 pC / N. A protective step of laminating a protective film for protecting the surface on one side of the resin film;
A stretching step of stretching the resin film together with the protective film from the protective film side by a stretching roll to obtain a stretched film;
And removing the protective film from the stretched film after the stretching step. The method for producing a film according to claim 5, wherein the resin film is a resin film containing a vinylidene fluoride resin as a main component, and the stretched film is a piezoelectric film. The method for producing a film according to claim 5 or 6, further comprising a resin film molding step of obtaining the resin film by extruding a resin material before the protection step. 7. The method according to claim 6, further comprising a polarization step of obtaining a polarized film by polarizing the piezoelectric film after the stretching step. The method for producing a film according to any one of claims 5 to 8, wherein the protective film is a polyolefin resin film or a polyester resin film. The method for producing a film according to any one of claims 5 to 9, wherein the protective film has a thickness of 10 μm to 200 μm. The method for producing a film according to any one of claims 5 to 10, wherein the arithmetic mean roughness Ra on the surface of the stretching roll is 0.1 μm or more and 30 μm or less.

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