KR101227552B1 - MONO-LAYER PVdF ORIENTED FILM AND SOLAR CELL BACK SHEET USING THE SAME - Google Patents

Abstract

50 to 90 parts by weight of polyvinylidene fluoride, 5 to 25 parts by weight of polymethyl methacrylate, and 5 to 25 parts by weight of titanium oxide are melt kneaded, extruded into a single layer and stretched in at least one of the longitudinal and transverse directions. The film manufactured by the present invention has excellent heat resistance, weather resistance, and moisture permeability, but is superior in strength, elongation, and color change rate compared with the prior art, and thus, when used as a solar cell backsheet, the film may exhibit excellent effects.

Description

Monolayer PDF F Stretched Film and Solar Cell Back Sheet Using The Same {MONO-LAYER PVdF ORIENTED FILM AND SOLAR CELL BACK SHEET USING THE SAME}

The present invention relates to a polyvinylidene fluoride (hereinafter referred to as 'PVdF') film that can be used as a back sheet or other coating material of a solar cell.

Solar cells are attracting attention as clean energy because they are less concerned about energy source depletion and environmental pollution. Since the solar cell is mainly used in an external environment, it is common to coat the surface of the solar cell with a polymer material having glass or light transmitting property in order to enhance the environmental resistance. Thin-film crystalline silicon solar cells, amorphous solar cells, and compound semiconductor solar cells have been under active research because of their relatively low cost and large area. Particularly, the amorphous silicon thin film type solar cell in which silicon is bonded onto the conductive metal substrate of the intermediate layer and the transparent conductive layer is formed is promising as a form of future solar cell module because of its light weight, thin film property and flexibility. In such a thin film battery, it is necessary to cover the light incidence side surface with a transparent covering material and protect the solar cell.

The conventional solar cell backsheet mainly used a sheet having a multilayer structure. For example, in Japanese Patent Laid-Open Nos. 1987-273780 and 194-318718, a sheet in which polyvinylidene fluoride (hereinafter referred to as PVdF), ethylene tetrafluoroethylene (ETFE), etc. are laminated on a polyester film Is disclosed. However, in the case of the sheet manufactured by such a method, there is a problem in that the output of the solar cell module is reduced due to heat deformation on the surface of the protective film during the heat treatment process or the actual use during the process.

In addition, in the case of other conventional solar cell backsheet films, even if the basic physical properties such as weather resistance and moisture permeability is excellent, the strength and elongation is weak, so that the tearing or yellowing phenomenon when exposed to the outside for a long time, the output of the module is reduced. have.

Japanese Unexamined Patent Publication No. 1987-273780 Japanese Laid-Open Patent Publication 1994-318718

Accordingly, an object of the present invention is to provide a single layer PVdF film having excellent physical properties and improved strength, elongation, and color change, and a solar cell backsheet using the same.

According to the above object, the present invention is a polyvinylidene fluoride (PVdF) single polymer or copolymer 50 to 90% by weight, polymethyl methacrylate (PMMA) single polymer or copolymer 5-25% by weight, and oxidation It provides a single layer PVdF stretched film made of 5 to 25% by weight of titanium (TiO ₂ ) and stretched in at least one of longitudinal and transverse directions and a method of manufacturing the same.

According to another object, the present invention provides a solar cell backsheet comprising the single layer PVdF stretched film.

The single layer PVdF film according to the present invention has excellent heat resistance, weather resistance, moisture permeability, and the like, but is superior in strength, elongation, and color change rate compared to the prior art, and thus may exhibit excellent effects when used as a solar cell backsheet.

1 and 2 are scanning electron microscope (SEM) images of cross sections of the monolayer PVdF stretched film of Example 1 according to the present invention (10,000 times and 2,000 times, respectively).
3 is an SEM image (4,000 times) of a cross section of the unstretched single layer PVdF film of Comparative Example 1. FIG.

PVdF single layer stretched film of the present invention, comprising a PVdF, PMMA, and TiO _2, characterized in that the stretched in at least one direction of longitudinal and transverse directions.

The stretched film has a stronger strength in the longitudinal / lateral direction than the unstretched film, and less yellowing may occur even in the harsh conditions of the external environment. In addition, the cross-section (FIGS. 1 and 2) of the stretched PVdF film of the present invention, unlike the cross-section (FIG. 3) of the unstretched PVdF film, pores are formed long along the stretching direction by the TiO ₂ particles contained therein. This improves optical properties such as reflectance, moisture permeability, and the like.

In the film of the present invention, the preferred stretching ratio is 1.5 to 5 times in the longitudinal direction and 2 to 6 times in the transverse direction.

Although the film of this invention may be extended | stretched in either a direction of a longitudinal direction and a transverse direction, it is more preferable to biaxially stretch about both a longitudinal direction and a transverse direction.

Further, the film of the present invention is more preferably produced through an additional heat treatment step after stretching. The heat treatment step is preferably carried out while giving a relaxation of 85 to 100% at a temperature condition of 90 ~ 180 ℃.

The film of the present invention preferably has a tensile strength of at least 4 kgf / mm 2 and an elongation of at least 90% in at least one of the longitudinal direction (MD) and the transverse direction (TD).

In addition, the film of the present invention is the change value of the yellow index (YI after PCT-YI before PCT) according to the pressure cooker test (PCT) at 2atm, 120 ℃, 100% relative humidity and 75 hours conditions ) Is preferably 3.0 or less.

Moreover, it is preferable that the film of this invention is 85% or more in reflectance in the wavelength of 550 nm.

Moreover, it is preferable that the shrinkage rate of the longitudinal direction (MD) and the transverse direction (TD) with respect to the heat processing on 150 degreeC and 30-minute conditions of the film of this invention is 5% or less, respectively.

Hereinafter, the monolayer PVdF stretched film of the present invention will be described in more detail for each component.

PVdF, the main component of the film of the present invention, may be a homopolymer or copolymer form of vinylidene fluoride (VF 2) monomers.

When PVdF is a copolymer, it is preferable that vinylidene fluoride (VF 2) and the comonomer are polymers copolymerized in a weight ratio of 50:50 to 99: 1,

The comonomer which can be copolymerized is preferably a fluorinated monomer such as vinyl fluoride; Trifluoroethylene (VF3); Chlorofluoroethylene (CTFE); 1,2-difluoroethylene; Tetrafluoroethylene (TFE); Hexafluoropropylene (HFP); Perfluoro (alkyl vinyl) ethers such as perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyl) ether (PPVE); Perfluoro (1,3-dioxol); Perfluoro (2,2-dimethyl-1,3-diosol) (PDD); And mixtures thereof. Among these, chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3), or tetrafluoroethylene (TFE) are preferable.

In order for PVdF to be suitable for extrusion and injection molding, it is preferable that the viscosity measured by the capillary flowmeter on the conditions of shear rate 100s ^-1 and 230 degreeC is 100-2,500 Pa.s, and it is 500-2,000 Pa.s. More preferred.

In addition, the MVI (melt volume index) of PVdF may be 23-25 g / 10 min when measured at a temperature of 230 ° C. under a load of 5 kg.

The content of PVdF or a copolymer thereof is preferably 50 to 90% by weight, particularly 60 to 80% by weight based on the total film weight. If the content is less than 50% by weight, there may be a limit in sufficient weather resistance expression, when it exceeds 90% by weight more than necessary physical properties may be expressed or manufacturing costs may increase.

In the film of the present invention, the other major component, PMMA, can be a homopolymer of methyl methacrylate (MMA) monomer or a copolymer with other comonomers.

When PMMA is a copolymer, it is preferred that the methyl methacrylate and the comonomer are polymers copolymerized in a weight ratio of 50:50 to 99: 1.

Examples of comonomers that can be copolymerized include alkyl (meth) acrylates, acrylonitrile, butadiene, styrene, isoprene, mixtures thereof, and the like. Such alkyl (meth) acrylates are described in Kirk-Othmer Encyclopedia of Chemical Technology, 4 ^th Edition, Vol. 1, p. 292-293 & Vol. 16, p. 475-478.

Preferred copolymers include those in which the methyl acrylate and / or ethyl acrylate comonomer is copolymerized in an amount of 1 to 20% by weight, in particular 5 to 15% by weight.

PMMA may be functionalized, for example, may contain acid, acid chloride, alcohol or anhydride functional groups, which may be introduced by graft or copolymerization of compounds having functional groups. Among these, it is preferable that it is an acid functional group provided with an acrylic acid copolymer. The content of the compound having a functional group may be 15% by weight or less based on the weight of the PMMA containing the functional group.

For example, a compound such as Chemical Formula 1 or 2 in which two adjacent acrylic acid functional groups lose water to form an anhydride may be used. These anhydrides can act to enhance the soft impact structure of PMMA, or to soften the soft structure by alleviating the crystalline behavior of PVdF after blending with PVdF:

In Formula 1, m is an integer of 1 or more.

The MVI (melt volume index) of PMMA can be 4-6 g / 10 min when measured at a temperature of 230 ° C. under a load of 3.8 kg.

The content of PMMA or its copolymer is preferably 5 to 25% by weight, in particular 10 to 25% by weight, based on the total film weight. If the content is less than 5% by weight may cause a decrease in adhesion to the substrate during the lamination, if it exceeds 25% by weight it may be difficult to ensure sufficient weather resistance.

In the film of the present invention, TiO ₂ , another main component, controls the optical characteristics such as light transmittance, reflectance and color, and controls the friction coefficient, the surface roughness and the fine touch. In addition, TiO ₂ serves to form pores long along the stretching direction in the film when the sheet is stretched (see FIG. 1).

TiO ₂ is preferably added in a compounding manner, and the particle diameter is preferably 0.1 to 0.7 µm, and particularly preferably 0.2 to 0.4 µm. When the size of the TiO ₂ particles is within the above range, it is possible to minimize the occurrence of fish eye (fish eye, etc.) on the surface of the film while having better optical and surface properties. .

The content of TiO ₂ is preferably 5 to 25% by weight, particularly 10 to 15% by weight based on the total film weight. If the content of TiO ₂ particles is less than 5 wt%, the effect of addition may be insufficient. If the content of TiO ₂ particles is more than 25 wt%, the particles may aggregate and clog the filter during the film production process. In this case, Life, production efficiency, dispersibility, weatherability, and lightness.

Hereinafter, the manufacturing method of the PVdF film of this invention is demonstrated concretely.

PVdF film of the present invention is a step of melting and kneading PVdF single resin or copolymerized resin 50 to 90 parts by weight, PMMA single resin or copolymerized resin 5 to 25 parts by weight, and TiO ₂ 5 to 25 parts by weight of a single layer sheet ; And stretching the extruded sheet in at least one of longitudinal and transverse directions.

In melt extrusion, a single screw or a twin screw or more multi-screw extruder may be used, and may be formed into a sheet by being seated on a casting roll at 20 to 100 ° C. after extrusion.

In the stretching step, the preferred stretching ratio is 1.5 to 5 times in the longitudinal direction and 2 to 6 times in the transverse direction, more preferably 2 to 4 times in the longitudinal direction and 3.5 to 5 times in the transverse direction.

In addition, the preferred stretching temperature is 60 to 120 ° C in the longitudinal direction, 90 to 180 ° C in the transverse direction, more preferably 80 to 100 ° C in the longitudinal direction and 160 to 170 ° C in the transverse direction.

Although the extending process may be performed only in either of the longitudinal direction and the transverse direction, it is more preferable to perform biaxial stretching in both the longitudinal direction and the transverse direction.

Longitudinal stretching can be achieved with a circumferential speed difference by the rolls, and transverse stretching can be done in the tente.

The film of the present invention may undergo an additional heat treatment step after stretching. The heat treatment step can be performed while giving a relaxation of 85 to 100% at a temperature of 90 to 180 ° C.

It is preferable that the thickness of the produced single layer PVdF stretched film is 10-200 micrometers, More preferably, it is 20-150 micrometers.

The PVdF film of the present invention has little change in physical properties even under excellent dimensional stability and mechanical properties, especially under severe conditions of the external environment. In addition, it exhibits excellent adhesion in the thermal lamination process according to the heterogeneous heterogeneous properties, and there is almost no surface change due to long-term storage.

Accordingly, excellent performance can be achieved when used as a backing material for articles or materials, especially for solar cells.

Hereinafter, the present invention will be described in more detail with reference to Examples, which are presented as a preferred example and do not limit the content of the present invention.

Examples 1-9 and Comparative Example 1

 (1) Raw material preparation

Each of the following ingredients was prepared:

PVdF: single resin, MVI 24g / 10min (ASTM D1238, 230 ° C, 5kg load), Solvay, viscosity 1200 Pa.s (100s ^-1 , 230 ° C, capillary flow meter)

- PMMA: single resin, MVI 5.0 g / 10 min (ASTM D1238, 230 캜, 3.8 kg load), LGMMA

-TiO ₂ : average particle size 230nm, Huntsman Corporation

(2) melt kneading and extrusion

First, a master chip was prepared by compounding 20 parts by weight of PMMA, 20 parts by weight of TiO ₂ , and 60 parts by weight of PVdF.

Using the prepared master chip was melted at a temperature of 200 ~ 240 ℃ in a single or twin multi-screw extruder and extruded into a T-die.

This was cooled in a casting roll of 20 ~ 30 ℃ to prepare an unstretched single layer sheet.

(3) stretching

The sheet obtained in this step was stretched at the respective draw ratios listed in Table 1 below in the longitudinal and / or transverse directions. Longitudinal stretching was through the rolls and transverse stretching was done in the tenter. At this time, the stretching temperature was 90 ° C. in the longitudinal direction and 170 ° C. in the lateral direction.

 (4) heat treatment

Optionally, a heat treatment process was performed on the stretched film. At this time, the heat treatment process was carried out at 180 ℃ giving a relaxation of 85 ~ 95%.

As a result, a single-layer PVdF film having a thickness of 25 µm was obtained.

SEM images of the cross-sections of the prepared films were obtained and shown in FIGS. 1 and 2 (10,000 times and 2,000 times stretched film of Example 1) and 3 (4 times stretched film of Comparative Example 1, unstretched film). In view of this, unlike the unstretched film, the stretched PVdF film of the present invention is expected to have long pores formed in the stretching direction by TiO ₂ particles, so that optical properties such as reflectance and properties such as moisture permeability are expected to be excellent. can do.

Test Example 1

The physical properties of each film prepared in the Examples were measured as follows and are shown in Table 1 below.

(1) tensile strength and elongation

Strength and elongation in longitudinal (MD) and transverse (TD) were measured according to ASTM D882.

(2) heat shrinkage

After the heat treatment for 30 minutes at 150 ℃ was measured the length change in the longitudinal and transverse direction.

(3) change of yellow index (ΔYI)

The change in yellow index (YI, yellow index) before and after the breakdown pressure test (PCT, Pressure Cooker Test, 2atm, 120 ℃, 100% RH, 75 hours) was measured using a color difference meter (UltraScan ^TM Pro, HunterLab). Calculated by the formula:

ΔYI = YI after PCT-YI before PCT

(4) reflectance

It measured with the light source of wavelength 550nm using the color-difference gauge (UltraScan Pro, HunterLab).

(5) moisture permeability

For the films of Examples 1, 2, 8 and 9, and Comparative Example 1, using a water vapor permeability tester (PERMATRAN-W MODLE 3/33, MOCON Co., Ltd.) at a temperature of 38 ℃ and 100 RH% conditions (g / m ² .day) was measured.

Process conditions Physical property (measured value)
division Stretching cost Heat treatment burglar
(kgf / ㎡) Shindo
(%) Heat shrinkage
(%) ΔYI reflectivity
(%) Moisture permeability
(g / m ² .day) MD TD MD TD MD TD MD TD Example 1 2.0 3.5 X 10.7 14.1 266 128 12.6 41.2 1.3 91.7 49.1 Example 2 2.5 3.5 X 10.8 12.4 166 90 15.5 45.3 1.3 91.5 49.0 Example 3 2.5 3.5 O 10.5 12.5 156 105 1.3 1.7 2.0 91.7 - Example 4 3.0 3.5 X 16.0 14.6 146 123 17.1 47.5 2.2 92.6 - Example 5 3.0 3.5 O 15.8 14.6 155 129 1.8 1.8 1.8 92.5 - Example 6 2.0 4.5 X 10.2 15.8 189 96 11.8 51.2 1.9 92.7 - Example 7 1.5 3.0 X 5.6 18.0 338 108 16.0 12.5 0.9 91.1 - Example 8 4.0 1.0 X 18.2 2.8 60 30 56.2 -14.3 4.8 91.6 44.2 Example 9 1.0 4.0 X 5.2 18.2 70 91 10.5 37.2 4.3 89.7 49.4 Comparative Example 1 1.0 1.0 X 4.1 4.1 320 15 1.0 0.0 2.5 81.8 58.8 MD: longitudinal direction, TD: transverse direction, ΔYI: yellow index change

 As can be seen in Table 1, the films of the examples prepared within the preferred condition range of the present invention exhibited excellent physical properties in strength, yellowness index change (weather resistance), reflectance, moisture permeability, etc., especially in both longitudinal and transverse directions. It showed better physical properties when stretched and showed less heat shrinkage when heat treated.

Claims (13)

50% to 90% by weight of polyvinylidene fluoride (PVdF) single polymer or copolymer thereof, 5 to 25% by weight of polymethyl methacrylate (PMMA) single polymer or copolymer thereof, and 5 to 25 of titanium oxide (TiO ₂ ) Weight percent,
A single-layer PVdF stretched film, which is stretched in at least one of the longitudinal direction and the transverse direction, has a stretch ratio of 1.5 to 5 times in the longitudinal direction, and a stretch ratio of 2 to 6 times in the transverse direction.
50% to 90% by weight of polyvinylidene fluoride (PVdF) single polymer or copolymer thereof, 5 to 25% by weight of polymethyl methacrylate (PMMA) single polymer or copolymer thereof, and 5 to 25 of titanium oxide (TiO ₂ ) Weight percent,
A film stretched in at least one of the longitudinal and transverse directions,
A single-layer PVdF stretched film, characterized in that the tensile strength is at least 4.5 kgf / mm 2 and at least 90% of the elongation in at least one of the longitudinal and transverse directions.
50% to 90% by weight of polyvinylidene fluoride (PVdF) single polymer or copolymer thereof, 5 to 25% by weight of polymethyl methacrylate (PMMA) single polymer or copolymer thereof, and 5 to 25 of titanium oxide (TiO ₂ ) Weight percent,
A film stretched in at least one of the longitudinal and transverse directions,
The film is a single layer PVdF stretched film, characterized in that the change value of the yellow index according to the pressure resistance test (PCT) at 2 atm, 120 ° C, 100% relative humidity and 75 hours.
The method of claim 1,
The single layer PVdF stretched film is biaxially stretched in the longitudinal direction and the transverse direction, The single layer PVdF stretched film.
delete The method of claim 1,
The copolymer of PVdF is a polymer in which vinylidene fluoride (VF 2) and a comonomer are copolymerized in a weight ratio of 50:50 to 99: 1, and the comonomer is vinyl fluoride, trifluoroethylene (VF 3), chlorofluoro Low ethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro (alkylvinyl) ether, perfluoro (1,3-dioxol ), Perfluoro (2,2-dimethyl-1,3-diosol) (PDD), and mixtures thereof.
The method of claim 1,
The copolymer of PMMA is a polymer in which methyl methacrylate (MMA) and comonomer are copolymerized in a weight ratio of 50:50 to 99: 1, and the comonomer is alkyl (meth) acrylate, acrylonitrile, butadiene, Single layer PVdF stretched film, characterized in that it is selected from the group consisting of styrene, isoprene, and mixtures thereof.
50 to 90 parts by weight of polyvinylidene fluoride (PVdF) single resin or copolymerized resin thereof, 5 to 25 parts by weight of polymethyl methacrylate (PMMA) single resin or copolymerized resin thereof, and 5 to 25 titanium oxide (TiO ₂ ) Melt-kneading the parts by weight and then extruding the monolayer sheet; And
Stretching the extruded sheet in at least one of longitudinal and transverse directions, wherein the stretching ratio in the longitudinal direction is 1.5 to 5 times and the stretching ratio in the transverse direction is 2 to 6 times. The manufacturing method of the single | mono layer PVdF stretched film which do.
9. The method of claim 8,
The stretching step is characterized in that the biaxial stretching in the longitudinal and transverse direction, the manufacturing method of a single layer PVdF stretched film.
delete 50 to 90 parts by weight of polyvinylidene fluoride (PVdF) single resin or copolymerized resin thereof, 5 to 25 parts by weight of polymethyl methacrylate (PMMA) single resin or copolymerized resin thereof, and 5 to 25 titanium oxide (TiO ₂ ) Melt-kneading the parts by weight and then extruding the monolayer sheet; And
Stretching the extruded sheet in at least one of longitudinal and transverse directions, wherein the stretching temperature in the longitudinal direction is 60 to 120 ° C. and the stretching temperature in the transverse direction is 90 to 180 ° C. The manufacturing method of the single | mono layer PVdF stretched film characterized by the above-mentioned.
50 to 90 parts by weight of polyvinylidene fluoride (PVdF) single resin or copolymerized resin thereof, 5 to 25 parts by weight of polymethyl methacrylate (PMMA) single resin or copolymerized resin thereof, and 5 to 25 titanium oxide (TiO ₂ ) Melt-kneading the parts by weight and then extruding the monolayer sheet; And
Stretching the extruded sheet in at least one of longitudinal and transverse directions,
After the stretching step, the step of performing a heat treatment at a temperature condition of 90 ~ 180 ℃ while giving a relaxation of 85 to 100%, characterized in that, further comprising the manufacturing method of a single layer PVdF stretched film.
A solar cell back sheet comprising the single layer PVdF stretched film according to any one of claims 1 to 4, 6 and 7.

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