KR20220138702A - Light reflective resin film and method of fabricating the same - Google Patents

Abstract

Provided is a light reflective resin film, which includes a reflective stack including a resin layer, wherein the resin layer has a melting resistance of 2000 MΩ or less. Melting resistance is measured by bringing a copper plate into contact with a resin layer in a melting film state and applying a voltage of 50V to the copper plate. Optical patterns in the light reflective resin film may be reduced or eliminated by improving the conduction performance of the resin layer.

Description

Light reflective resin film and manufacturing method thereof

The present invention relates to a light reflective resin film and a method for manufacturing the same. More particularly, it relates to a light reflective resin film including a plurality of resin layers and a method for manufacturing the same.

Polymer films are widely used in electronics, chemistry, food, medicine, construction, packaging materials, etc. For example, in the case of a decorative polymer film having a specific color, a colorant is used or light of a specific wavelength is reflected or blocked method can be used.

For example, a light reflective film capable of selectively reflecting light having a wavelength in a specific region, such as an infrared reflective film, a visible ray reflective film, and a polarizing reflective film, may be manufactured by repeatedly and alternately laminating resin layers having different refractive indices. have.

However, when a plurality of resin layers are laminated together, poor adhesion of each resin layer may occur. For example, as the resin layers are bonded through a co-extrusion, casting process, etc. Optical defects may result.

Therefore, it is necessary to develop a composition or process for a light reflective resin film to improve optical reliability while maintaining light reflection characteristics of a desired wavelength through a difference in refractive index.

For example, Korean Patent Application Laid-Open No. 2003-0012874 discloses an infrared reflective film having a multilayer structure.

Korean Patent Publication No. 2003-0012874

An object according to exemplary embodiments is to provide a light reflective resin film having improved optical properties and process stability, and a method for manufacturing the same.

A light reflective resin film according to example embodiments includes a reflective stack including a resin layer, and the melt resistance of the resin layer is 2000 MΩ or less. The melt resistance is measured by bringing a copper plate into contact with the resin layer in a molten film state and applying a voltage of 50 V to the copper plate.

In some embodiments, the reflective stack may include a first resin layer and a second resin layer repeatedly stacked alternately, and the refractive index of the first resin layer may be greater than the refractive index of the second resin layer.

In some embodiments, the melt resistance of each of the first resin layer and the second resin layer may be 2000 MΩ or less.

In some embodiments, the melting resistance of each of the first resin layer and the second resin layer may be 50 to 500 MΩ.

In some embodiments, the first resin layer and the second resin layer are defined by Equation 1 below and may satisfy an F-ratio in the range of 0.35 to 0.65.

[Equation 1]

F-ratio = n ₁ d ₁ /(n ₁ d ₁ +n ₂ d ₂ )

(In Equation 1, n ₁ and n ₂ are the refractive indices of the first resin layer and the second resin layer, respectively, and d ₁ and d ₂ are the thicknesses of the first resin layer and the second resin layer, respectively).

In some embodiments, the first resin layer may include polyethylene terephthalate (PET), and the second resin layer may include polymethyl methacrylate (PMMA). The melt resistance of the first resin layer may be measured at 280 ^o C and the melt resistance of the second resin layer may be measured at 240 ^o C.

In some embodiments, each of the first resin layer and the second resin layer may include a resistance modifier including an alkali metal salt or an alkaline earth metal salt.

In some embodiments, the light reflective resin film may further include a first passivation layer and a second passivation layer respectively laminated on an upper surface and a lower surface of the reflective stack.

In the method of manufacturing a light reflective resin film according to exemplary embodiments, a first resin raw material including a first polymer and a first resistance adjusting agent, and a second resin raw material including a second polymer and a second resistance adjusting agent Prepare. The first resin raw material and the second resin raw material are each extruded to form a pre-molten laminate including first molten films and second molten films alternately and repeatedly arranged. A preliminary reflective stack is formed by applying a voltage to the pre-molten laminate in close contact with a casting roll. The preliminary reflective stack is stretched.

In some embodiments, the melt resistance of each of the first molten film and the second molten film is 2,000 MΩ or less, and the melt resistance is adjacent to each of the first molten film and the second molten film with a copper plate and It can be measured by applying a voltage of 50V to the copper plate.

According to the above-described exemplary embodiments, the resin layer included in the light reflective resin film may have a melt resistance value within a predetermined range, and thus may have appropriate conduction properties. Therefore, for example, in a casting process for forming a resin laminate, uniform adhesion properties are secured, thereby preventing the occurrence of optical defects such as band patterns and mura patterns.

In example embodiments, the resin layer may include a base polymer and a resistance modifier mixed with the base polymer. Melting resistance can be controlled by controlling the content of the resistance modifier, and the above-described optical defects can be prevented while suppressing a color change of the resin layer such as yellowing.

1 is a schematic cross-sectional view showing a light reflective resin film according to exemplary embodiments.
2 and 3 are schematic views illustrating a method of manufacturing a light reflective resin film according to exemplary embodiments.

According to exemplary embodiments, a light reflective resin film having a melt resistance in a predetermined range and having improved optical reliability is provided.

Hereinafter, embodiments of the present invention will be described in detail. However, since the present invention can have various changes and can have various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Unless defined otherwise, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with the context of the related art, and unless explicitly defined in the present application, they are not to be interpreted in an ideal or excessively formal meaning. .

1 is a schematic cross-sectional view showing a light reflective resin film according to exemplary embodiments.

Referring to FIG. 1 , the light reflective resin film 100 may include a reflective stack 110 and protective layers 150a and 150b. In example embodiments, the reflective stack 110 may include a first resin layer 120 and a second resin layer 130 .

The first resin layer 120 and the second resin layer 130 may have different refractive indices. Light reflection or light blocking performance from the reflective stack 110 may be realized by interfacial reflection due to a difference in refractive index between the first resin layer 120 and the second resin layer 130 .

In one embodiment, the difference in refractive index between the first resin layer 120 and the second resin layer 130 may be 0.01 or more, preferably 0.05 or more, and more preferably 0.1 or more.

The first resin layer 120 and the second resin layer 130 may include an appropriate polymer within the range of maintaining the refractive index difference described above.

The first resin layer 120 has a higher refractive index than the second resin layer 130 , and may include, for example, a polyester-based polymer, a polyester-based copolymer, polynaphthalene, and the like. In one embodiment, the first resin layer 120 includes polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and the like. In a preferred embodiment, the first resin layer 120 may include polyethylene terephthalate (PET).

For example, the refractive index of the first resin layer 120 may be in the range of 1.6 to 1.7, and when the first resin layer 120 includes PET, the refractive index may be in the range of 1.64 to 1.66.

The first resin layer 120 may have a birefringence characteristic. As described above, the first resin layer 120 may include PET, and may have a positive birefringence property in which the refractive index increases with stretching.

The melting temperature of the first resin layer 120 may be, for example, 270 ^o C or higher. In one embodiment, the melting temperature of the first resin layer 120 may be in the range of 270 to 290 ^o C.

The second resin layer 130 has a lower refractive index than that of the first resin layer 120 , for example, an acrylic polymer such as polymethyl methacrylate (PMMA), polystyrene (PS), or polyvinyl fluoride (PVF). , polyvinylidene fluoride (PVDF), polylactide (PLA), and the like. In a preferred embodiment, the second resin layer 130 may include PMMA.

In some embodiments, the second resin layer 130 may include a copolymer polyester-based polymer. For example, the second resin layer is a copolymer (co-PET) of polyethylene terephthalate (PET) with neopentine glycol (NPG), cyclohexanedimethanol (CHDM) and/or syndiotactic polystyrene (SPS). may include.

For example, the refractive index of the second resin layer 130 is in the range of 1.4 to 1.5, and when the second resin layer 130 includes PMMA, it may have a refractive index in the range of 1.485 to 1.495.

The second resin layer 130 may include an isotropic polymer. As described above, the second resin layer 130 may include PMMA whose refractive index is not changed by stretching. In this case, the refractive index of the first resin layer 120 may increase by stretching, and a difference in refractive index with the second resin layer 130 may increase.

The melting temperature of the second resin layer 130 may be, for example, 210 ^o C or higher. In one embodiment, the melting temperature of the second resin layer 130 may be in the range of 210 to 240 ^o C.

As shown in FIG. 1 , the reflective stack 110 may include first resin layers 120 and second resin layers 130 that are alternately and repeatedly stacked. For example, the number of stacks of the reflective stack 110 may range from 100 to 200. In a preferred embodiment, the number of stacks of the reflective stack 110 may range from 140 to 160.

In some embodiments, an F-ratio defined by Equation 1 below of the reflective stack 110 may be adjusted in a range of 0.35 to 0.65.

[Equation 1]

F-ratio = n ₁ d ₁ /(n ₁ d ₁ +n ₂ d ₂ )

In Equation 1, n ₁ and n ₂ are the refractive indices of the first resin layer 120 and the second resin layer 130, respectively, and d ₁ and d ₂ are the first resin layer 120 and the second resin layer 130, respectively. ) is the thickness of

The light irradiated to the light reflective resin film 100 may form a primary reflection wavelength at a corresponding wavelength λ, for example, a secondary reflection wavelength at a λ/2 wavelength. If the reflectance at the secondary reflection wavelength is high, light reflection may be excessively increased at a wavelength of an unwanted band.

When the F-ratio is adjusted within the above-described range, while suppressing excessive light reflection at the reflection wavelength, the secondary reflection wavelength may be selectively used together with the primary reflection wavelength.

In one embodiment, the f-ratio may be adjusted in the range of 0.45 to 0.55. In this case, the secondary reflection wavelength is substantially removed and only the primary reflection wavelength can be utilized.

The refractive index and thickness of each of the first resin layer 120 and the second resin layer 130 may be appropriately designed according to a desired wavelength of reflected light while maintaining the above-described F-ratio.

For example, the refractive index and thickness of each of the first resin layer 120 and the second resin layer 130 may be determined according to the desired wavelength λ of the blocking light according to Equation 2 below.

[Equation 2]

λ = 2(n ₁ d ₁ +n ₂ d ₂ )

In Equation 2, n ₁ and n ₂ are the refractive indices of the first resin layer 120 and the second resin layer 130, respectively, and d ₁ and d ₂ are the first resin layer 120 and the second resin layer 130, respectively. ) is the thickness of

According to exemplary embodiments, the melt resistance of the reflective stack 110 may be 500 MΩ or less. According to exemplary embodiments, the melting resistance of each of the first resin layer 120 and the second resin layer 130 may be 2,000 MΩ or less.

When the melt resistance of the first resin layer 120 and the second resin layer 130 exceeds 2,000 MΩ, sufficient conduction characteristics may not be realized in the casting process as will be described later with reference to FIG. 2 . Accordingly, poor adhesion to the casting roll may occur, resulting in a band pattern or a mura pattern in the TD direction or the transverse direction.

In a preferred embodiment, the melt resistance of the first resin layer 120 and the second resin layer 130 may be in the range of 50 to 500 MΩ. In the above range, the reliability of the casting process is improved through uniform energization, and discoloration, for example, yellowing, of the resin layer due to an increase in the content of the resistance modifier to be described later can be prevented.

Melt resistance is measured after applying a voltage of 50V to each of the first resin layer 120 and the second resin layer 130 in the form of a molten film in a state spaced apart from the copper (Cu) plate by a predetermined distance. is the resistance value. For example, the size of the copper plate may be 25 mm wide × 200 mm long × 2 mm thick. The separation distance between the copper plate and the resin layer may be 30 mm.

When the first resin layer 120 includes PET, the melt resistance of the first resin layer 120 may be measured at 280 ^° C. When the second resin layer 130 includes PMMA, the melt resistance of the second resin layer 130 may be measured at 240 ^o C.

According to example embodiments, the first resin layer 120 and the second resin layer 130 may each include a resistance modifier. In some embodiments, the melt resistance in the above-described range may be implemented by adjusting the content of the resistance adjusting agent.

The resistance modifier may include an alkali metal salt or an alkaline earth metal salt. For example, the resistance modifier may include an inorganic salt such as potassium halide, magnesium halide, potassium hydroxide, magnesium hydroxide, or the like, or an organic salt such as potassium acetate or magnesium acetate. These may be used alone or in combination of two or more.

According to some embodiments, in the first resin layer 120 , the content of the resistance modifier relative to the total weight of the first polymer such as PET included in the first resin layer 120 may be 10 ppm or more. In a preferred embodiment, the content of the resistance modifier relative to the total weight of the first polymer may be in the range of 50 to 300 ppm, more preferably 50 to 200 ppm.

According to some embodiments, in the second resin layer 130 , the content of the resistance modifier relative to the total weight of the second polymer such as PMMA included in the second resin layer 130 may be 100 ppm or more. In a preferred embodiment, the content of the resistance modifier relative to the total weight of the second polymer may be in the range of 100 to 300 ppm, more preferably 100 to 200 ppm.

Referring back to FIG. 1 , a first passivation layer 150a and a second passivation layer 150b may be stacked on the top and bottom surfaces of the reflective stack 110 , respectively. For example, the first protective layer 150a and the second protective layer 150b may include a PET film.

In some embodiments, the thickness of the reflective stack 110 may be about 50 to 70%, preferably about 50 to 60% of the total thickness of the light reflective resin film 100 . In the above range, it is possible to effectively implement reflection/blocking of a desired wavelength band without excessively impairing film protection through the protective layers 150a and 150b and the light transmittance of the light-reflecting resin film 100 .

2 and 3 are schematic views illustrating a method of manufacturing a light reflective resin film according to exemplary embodiments.

Referring to FIG. 2 , the resin raw material 50 may be melted and extruded through the extruder 60 . The resin raw material 50 may include a first resin raw material including the above-described first polymer and a resistance adjusting agent, and a second resin raw material including the above-described second polymer and a resistance adjusting agent, respectively.

The first raw material for resin and the second raw material for resin may be manufactured in the form of pellets or chips, respectively, and supplied into the extruder 60 . According to exemplary embodiments, the weight ratio or extrusion amount ratio of the first resin stock to the second resin stock may be 1.7 to 3. Within the above range, it is possible to prevent wavy patterns and film deformation from occurring due to interfacial flow due to a difference in viscosity between the first polymer and the second polymer.

In a preferred embodiment, the weight ratio or extrusion amount ratio may be in the range of 2 to 2.7.

The resin raw material 50 may be melted and extruded through the extruder 60 and moved through the transfer line 70 . Thereafter, the resin raw material 50 may be discharged in the form of a molten film through the extrusion die 80 .

Referring to FIG. 3 , the first raw material for resin and the second raw material for resin may be moved/supplied through a first transfer line 72 and a second transfer line 74 , respectively. Then, the first molten film produced from the first resin raw material from the first extrusion die 82 and the second extrusion die 84 respectively connected to the first transfer line 72 and the second transfer line 74 and The second molten film produced from the second raw material of the resin may be discharged.

The first extrusion die 82 and the second extrusion die 84 may be arranged alternately, repeatedly. Accordingly, the first molten film and the second molten film are alternately and repeatedly discharged to obtain a preliminary molten laminate.

Referring back to FIG. 2 , the pre-molten laminate discharged from the extrusion die 80 may be supplied to the casting roll 90 .

According to exemplary embodiments, the electrostatic applying unit 85 may be disposed adjacent to the casting roll 90 . For example, the electrostatic applying unit 85 may be disposed to face the casting roll 90 with the pre-molten laminate interposed therebetween. The electrostatic applying unit 85 may include a copper wire connected to a power source or a metal wire such as a copper plate or a metal plate.

When a voltage is applied to the electrostatic applying unit 85 through the power source, a negative charge may be induced in the casting roller 90, and the pre-melting by the resistance adjusting agent contained in the first molten film and the second molten film The laminate may be in close contact with the casting roller 90 .

As described above, each of the first molten film and the second molten film may have a melt resistance of 2,000 MΩ or less, preferably in the range of 50 to 500 MΩ. Therefore, when performing the energization or electrostatic application, adhesion through electrical attraction to the casting roller 90 can be promoted, and optical defects due to lack of energization can be prevented.

In some embodiments, the temperature of the casting roller 90 may be maintained at a temperature below room temperature. Accordingly, the preliminary molten laminate may be solidified while in close contact with the casting roller 90 by the above-described energization to form a preliminary reflective stack.

The preliminary reflection stack may be moved by being tensioned through a tensioner 95 .

Thereafter, the reflective stack 110 may be obtained after a stretching process using a stretching roller is performed on the preliminary reflective stack. As shown in FIG. 1 , the light reflective resin film 100 may be manufactured by laminating a first passivation layer 150a and a second passivation layer 150b on the upper and lower surfaces of the reflective stack 110 , respectively.

Hereinafter, embodiments of the present invention will be further described with reference to specific experimental examples. Examples and comparative examples included in the experimental examples are merely illustrative of the present invention and do not limit the appended claims, and that various changes and modifications to the examples are possible within the scope and spirit of the present invention. It will be apparent to those skilled in the art, and it should be understood that such variations and modifications fall within the scope of the appended claims.

Examples and Comparative Examples

Melting and extruding the first resin raw material (including the first polymer and the first resistance adjusting agent) and the second resin raw material (including the second polymer and the second resistance adjusting agent) in pellet form with the composition and content shown in Table 1 through an extruder, respectively and alternately and repeatedly supplying the first molten film and the second molten film through a feed block die including extrusion dies to form a preliminary molten laminate of a total of 143 layers.

The melting and extrusion temperature of the first resin raw material was maintained at 280 ^o C, and the melting and extrusion temperature of the second resin raw material was maintained at 240 ^o C. The weight ratio of the first raw resin material and the second raw resin material was maintained at 2:1.

Thereafter, as described with reference to FIG. 2 , the pre-molten laminate was supplied between a casting roller adjusted to 20 ^° C and a copper wire, and a voltage was applied to the copper wire to perform a casting process.

Thereafter, the pre-melted laminate, which was adhered and solidified by a casting roller, was tensioned using a tension roller to form a reflective stack including first and second resin layers repeatedly laminated alternately. The thickness of the first resin layer was 140 nm, and the thickness of the second resin layer was 155 nm.

A protective layer was formed by coating a PET resin on the upper and lower surfaces of the reflective stack, and the light reflective resin film was prepared by stretching 3.5 times in the longitudinal direction and 4.5 times in the transverse direction.

division Example 1 Example 2 Example 3 Example 4 first polymer PET PET PET PET second polymer PMMA co-PET
(comonomer NPG) co-PET
(comonomer CHDM) first resistor
modifier
(content relative to the weight of the first polymer)
(ppm) Mg
acetate 100 100 100 100 K
acetate 5 5 5 5 second resistor
modifier
(content relative to the weight of the second polymer)
(ppm) Mg
acetate 150 150 150 - K
acetate 10 5 5 -

division Example 5 Example 6 Example 7 Example 8 first polymer PET PET PET PET second polymer PMMA PMMA PMMA PMMA first resistor
modifier
(content relative to the weight of the first polymer)
(ppm) Mg
acetate 100 60 100 100 K
acetate 5 5 5 5 second resistor
modifier
(content relative to the weight of the second polymer)
(ppm) Mg
acetate 200 130 150 100 K
acetate 10 5 5 5

division Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 first polymer PET PET PET PET second polymer PMMA co-PET
(comonomer NPG) co-PET
(comonomer CHDM) first resistor
modifier
(content relative to the weight of the first polymer)
(ppm) Mg
acetate 100 100 100 100 K
acetate 5 5 5 10 second resistor
modifier
(content relative to the weight of the second polymer)
(ppm) Mg
acetate - - - - K
acetate - - - -

Experimental example

(1) Melt resistance measurement

The first molten film and the second molten film formed from each of the first resin raw material and the second resin raw material were placed on a copper plate, and a voltage of 50V was applied to the copper plate. Then, resistance values in the first molten film and the second molten film were measured. As described above, the resistance measurement temperature of the first molten film was 280 ^o C, and the resistance measurement temperature of the second molten film was 240 ^o C.

(2) TD direction fringing evaluation

The light reflective resin films prepared according to Examples and Comparative Examples were observed with the naked eye and a polarizing device (model name: LSM-401, manufactured by LUCEO) to evaluate whether or not a mura pattern was generated in the TD direction.

The evaluation criteria are as follows.

(circle): all patterns were not recognized by the naked eye and a polarizing device

△: The pattern is not recognized by the naked eye, but the pattern is recognized by the polarizing device

×: both patterns are visually recognized by the naked eye and a polarizing device

The evaluation results are as described in Tables 4 and 5 below.

division Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 melt
resistance
(MΩ) first resin layer
(1st molten film) 111 111 111 111 111 550 2nd resin layer
(2nd molten film) 119 308 414 48 530 TD Mura pattern ○ ○ ○ ○ ○ △

division Example 7 Example 8 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 melt
resistance
(MΩ) first resin layer
(1st molten film) 111 111 111 111 111 2141 2nd resin layer
(2nd molten film) 742 1453 3418 4306 2013 TD Mura pattern △ △ × × × ×

Referring to Tables 4 and 5, in the case of Comparative Examples in which the melt resistance of the first resin layer or the second resin layer exceeds 2000 MΩ, the TD direction pattern was observed with the naked eye.

On the other hand, in the case of Examples 1 to 5 in which both the first resin layer and the second resin layer had a melt resistance of 500 MΩ or less, TD direction fringes were not observed with both the naked eye and the polarizing device.

However, in Example 5, in which the melt resistance of the second resin layer was excessively decreased, discoloration of the second resin layer was observed as the content of the resistance modifier was excessively increased.

50: resin raw material 60: extruder
70: transfer line 80: extrusion die
85: electrostatic applying unit 90: casting roll
100: light reflective resin film 110: reflective stack
120: first resin layer 130: second resin layer
150a: first passivation layer 150b: second passivation layer

Claims (10)

A reflective stack including a resin layer, wherein the resin layer has a melting resistance of 2,000 MΩ or less,
The melt resistance is measured by contacting a copper plate to the resin layer in a molten film state and applying a voltage of 50V to the copper plate. The light reflective resin film of claim 1 , wherein the reflective stack includes a first resin layer and a second resin layer that are alternately stacked repeatedly, the refractive index of the first resin layer being greater than the refractive index of the second resin layer. The method according to claim 2, The melt resistance of each of the first resin layer and the second resin layer is 2,000 MΩ or less, the light reflective resin film. The method according to claim 3, The melt resistance of each of the first resin layer and the second resin layer is 50 to 500 MΩ, light reflective resin film. The method according to claim 2, wherein the first resin layer and the second resin layer is defined by Equation 1 and satisfies an F-ratio in the range of 0.35 to 0.65, the light reflective resin film:
[Equation 1]
F-ratio = n ₁ d ₁ /(n ₁ d ₁ +n ₂ d ₂ )
(In Equation 1, n ₁ and n ₂ are the refractive indices of the first resin layer and the second resin layer, respectively, and d ₁ and d ₂ are the thicknesses of the first resin layer and the second resin layer, respectively). The method according to claim 2, wherein the first resin layer comprises polyethylene terephthalate (PET), the second resin layer comprises polymethyl methacrylate (PMMA),
The melt resistance of the first resin layer is measured at 280 ^o C and the melt resistance of the second resin layer is measured at 240 ^o C, the light reflective resin film. The light reflection resin film of claim 2, wherein each of the first resin layer and the second resin layer includes a resistance modifier including an alkali metal salt or an alkaline earth metal salt. The light reflective resin film of claim 1 , further comprising a first protective layer and a second protective layer laminated on an upper surface and a lower surface of the reflective stack, respectively. preparing a first raw resin material including a first polymer and a first resistance adjusting agent, and a second raw resin material including a second polymer and a second resistance adjusting agent;
extruding each of the first raw material resin and the second raw material resin to form a pre-molten laminate including first molten films and second molten films alternately and repeatedly disposed;
forming a preliminary reflective stack by attaching the preliminary molten laminate to a casting roll through voltage application; and
A method of manufacturing a light reflective resin film comprising the step of stretching the preliminary reflective stack. The method according to claim 9, wherein the melt resistance of each of the first molten film and the second molten film is 2,000 MΩ or less,
The melt resistance is measured by adjoining a copper plate to each of the first molten film and the second molten film and applying a voltage of 50V to the copper plate.

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