WO2013125870A1

WO2013125870A1 - Solar module back sheet, and method for manufacturing same

Info

Publication number: WO2013125870A1
Application number: PCT/KR2013/001370
Authority: WO
Inventors: 김윤조; 최동현; 김시민
Original assignee: 코오롱인더스트리(주)
Priority date: 2012-02-23
Filing date: 2013-02-21
Publication date: 2013-08-29

Abstract

The present invention relates to a polyester white film and to a solar module back sheet using same, and to an improved polyester white film having improved light reflectivity.

Description

PV module backsheet and manufacturing method thereof

The present invention relates to a polyester white film and a solar module backsheet using the same, and to an improved polyester white film having improved light reflectance.

Solar cells for photovoltaic power generation start from silicon or various compounds and become electricity when they form a solar cell. However, one cell does not get enough output, so each cell must be connected in series or in parallel. This connection is called a solar module.

The solar module is formed by laminating glass, EVA (ethylene vinyl acetate, EVA), solar cell, EVA (ethylene vinyl acetate, EVA), and back sheet. The back sheet is laminated at the bottom of the module to protect the solar cell by blocking dust, shock, and moisture. TPT (Tedlar / PET / Tedlar) type is widely used, and ribbon is used as a passage for transmitting current. Therefore, a material coated with silver or tin lead on copper is used.

The solar cell backsheet is the core material that protects the cell by attaching it to the back of the solar cell module. Durability, weather resistance, insulation, moisture permeability, etc. are required. Generally, fluorine film and PET film are laminated.

As the fluorine film, a fluorine film having excellent weatherability and durability is used. Currently, Tedlar film made of PVF resin developed by DuPont in 1961 is mainly used. However, due to the high price and short supply, some companies may replace it with other films such as PET.

EVA co-developed NASA and DuPont in 1970 as materials for solar cells used in satellites. It is currently used as a standard for sealing materials for solar cells. Japanese firms (Mitsui Chemical, Bridgestone) dominate over 70% of the world market. Inside the solar cell serves to seal and fill the cell. It is excellent in strength, transparency and insulation.

Polyester telephthalate (PET) film uses a planar plastic film with a certain thickness and physical properties, and has excellent strength to form a backbone of a back sheet. Due to its excellent physical, chemical, mechanical and optical properties, it is widely used in food packaging materials and office supplies to advanced electric and electronic products such as semiconductors and displays. In recent years, the use of the solar cell back sheet is increasing due to its excellent durability and weather resistance.

Glass uses less iron to prevent light reflection.

Conventionally, a TPT (Tedlar / PET / Tedlar) type backsheet requires a process of laminating through an adhesive in order to stack a Tedlar film and a PET film, and also to adhere the EVA sheet, which is a backsheet and an encapsulant. In order to adhere using a polyurethane adhesive or the like was further required. Tedlar films used in existing backsheets are expensive, accounting for more than 80% of the manufacturing cost of backsheets, which contributes to higher backsheet costs.

Therefore, research on a polyester film to replace the Tedlar film in order to lower the manufacturing cost is being actively conducted.

Korean Patent Publication No. 10-2011-0118953 (2011.11.02) describes that an ethylene vinyl acetate adhesive layer is formed through inline coating on a polyester film to replace the Tedlar film. 2011-0119134 (2011.11.02) describes the formation of a hot melt adhesive layer through the in-line coating on the polyester film to replace the Tedlar film, Korean Patent Publication No. 10-2011-0118271 (2011.10.31) It is described to reduce the process and cost by applying offline fluorine coating composition to replace the conventional Tedlar film layer on the polyester film to form a fluorine coating layer.

As such, previous work has been directed to forming other functional layers to replace Tedlar films.

Current characteristics required for the back sheet in the photovoltaic power generation may include adhesion, long-term durability, light reflectance for improving power generation efficiency.

In the case of solar modules, the power generation efficiency decreases as the temperature rises. Therefore, when a film having a high light reflectance is applied, the power generation efficiency is improved by blocking the temperature rise due to the light reflection and recycling the solar light. Can be.

Therefore, many studies have been conducted on the solar cell back sheet having high light reflectivity and excellent long-term durability.

The present invention is not to form a functional layer to replace the conventional Tedlar film, to improve the physical properties of the polyester film itself to provide excellent hydrolysis resistance without the Tedlar film, high light reflectance, such a polyester An object of the present invention is to provide a solar cell backsheet including a white film.

Specifically, the present invention is to solve the problem that the price increase and supply and demand is not smooth when using the existing fluorine resin, to improve the light reflectivity to improve the power generation efficiency of the photovoltaic module, a solar module bag made of polyester resin To provide a white film for the sheet.

In addition, the present invention is excellent in weatherability for use as a solar module backsheet, and excellent in reflectance to return the light to the solar cell to increase the light efficiency, the object is to provide a white film excellent hydrolysis resistance.

In addition, an object of the present invention is to provide a white film using a combination of specific inorganic particles and fluorescent brighteners in order to satisfy the optical properties of the reflectance is 90% or more in the 550nm visible light region.

The present invention for achieving the above object is as follows.

The present invention provides a color difference of 100 or more, a reflectance of 90% or more at 550 nm, after 30 minutes at 150 ° C., MD direction heat shrinkage of 2.0% or less, and after QUV (1.23 W / m 2 × 340 nm × 60 ° C. × 99 hours) irradiation. (DELTA) E) 2.0 or less, It is related with the polyester white film which is 50% or more of MD direction elongation retention after 50 hours at 121 degreeC and RH100%.

The polyester white film may include a matrix resin made of a polyester resin, a rutile titanium dioxide and a benzoxazole-based fluorescent brightener.

The polyester white film may include 10 to 20% by weight of rutile titanium dioxide based on the total weight of the film, benzoxazol-based optical brightener 100 ~ 900ppm.

An average particle diameter of the rutile titanium dioxide may be 0.1 to 0.5 μm.

The polyester white film may further include an additive selected from an oxazoline-based thickener, oleic acid, and mixtures thereof.

The oxazoline-based thickener may include 50 to 700 ppm based on the total weight of the film, and the oleic acid may include 40 to 400 ppm based on the total weight of the film.

The polyester resin may be polyethylene terephthalate.

The polyester white film may be used in the solar cell back sheet.

The present invention also relates to a backsheet for a solar module made of the polyester white film or comprising at least one layer of the polyester white film.

In addition, the present invention relates to a method for producing a polyester white film,

a) mixing a polyester resin powder, a rutile titanium dioxide and a benzoxazole-based fluorescent brightener, pulverizing the first polyester resin chip, melt extruding at an extruder temperature of 240 ~ 265 ℃ to produce a first master batch chip ;

b) injecting the first masterbatch chip and the second polyester resin chip into an extruder, followed by melt extrusion at a temperature of 280 to 320 ° C. to produce an unstretched sheet; And

c) uniaxially or biaxially stretching the unstretched sheet to produce a film;

It includes.

In the step b), the content of the first masterbatch chip may be added to include 10 to 20% by weight of rutile titanium dioxide, 100 to 900ppm benzoxazol fluorescent brightener based on the total weight of the film have.

When preparing the first masterbatch chip in step a), it may further comprise an additive selected from oxazoline-based thickener, oleic acid and mixtures thereof.

The oxazoline-based thickener may be added in an amount of 50 to 700 ppm based on the total weight of the film, and the oleic acid may be added in an amount of 40 to 400 ppm based on the total weight of the film.

When manufacturing the first masterbatch chip in step a), using a twin screw extruder including a vacuum vent (Vent) device, so that the residence time of the extruder temperature 240 ~ 265 ℃, the polymer in the extruder 1 minute or less, The tip of the twin screw extruder may be uniformly mixed using a screen changer filter of 300 to 500 mesh.

The polyester white film had a whiteness of 100 or more, a reflectance of 90% or more at 550 nm, after 30 minutes at 150 ° C., MD direction heat shrinkage of 2.0% or less, and after QUV (1.23 W / m 2 × 340 nm × 60 ° C. × 99 hours) irradiation After 50 hours at 121 ° C. and RH100%, the color difference (ΔE) of 2.0 or less may be 50% or more of the MD direction elongation retention.

The polyester white film according to the present invention has a high light reflectance and has excellent effects of weather resistance, durability and mechanical strength.

Therefore, the polyester white film according to the present invention has a high light reflectance to block the temperature rise of the photovoltaic module in an external environment, and is excellent in photovoltaic power generation efficiency due to light recycling due to the light reflection characteristic, and thus the photovoltaic Suitable for use as a module backsheet.

In addition, it is excellent in weatherability and long-term durability, and can be applied to the outermost layer of the backsheet, which can replace the existing fluorine film, which not only reduces manufacturing cost, but also has excellent thermal form stability, making the backsheet manufacturing process excellent. It has excellent UV stability and maintains a beautiful appearance.

Hereinafter, the present invention will be described in more detail.

The present invention relates to a polyester white film, and to replace the film consisting of a polyester film in the structure that was conventionally laminated with a Tedlar film / PET film / Tedlar film, made of a white film of the present invention, or the present invention It relates to a white film for a solar module backsheet comprising at least one white film of.

The present inventors have studied to replace the backsheet used by adhering a fluorine film on both sides of a polyethylene terephthalate (PET) film with a film made of a total polyester resin, and thus blocking light and returning it to a solar cell, thereby improving light efficiency. In order to increase the high reflectivity, weather resistance, and hydrolysis resistance, all of them must be satisfied. In order to satisfy these properties, inorganic particles must be included. Rutile type titanium dioxide is used as the inorganic particles, and the content thereof is controlled. The present invention was completed by discovering that the desired light reflectivity can be achieved by using a mixture of benzoxazol fluorescent brighteners.

The first aspect of the present invention comprises a matrix resin consisting of a polyester resin, rutile titanium dioxide and benzoxazole-based fluorescent brightener, whiteness of 100 or more, reflectance of 90% or more at 550nm, after 30 minutes at 150 ℃, MD direction elongation retention of 2.0% or less, QUV (1.23W / m 2 × 340nm × 60 ° C × 99 hours) irradiation, color difference (ΔE) 2.0 or less, after 121 hours, 50 hours at RH100%, MD direction elongation retention of 50% or more Polyester white film.

The second aspect of the present invention includes a matrix resin made of polyester resin, a rutile titanium dioxide, a benzoxazole-based fluorescent brightener and an oxazoline-based thickener, having a whiteness of 100 or more, 90% or more of reflectance at 550 nm, and 150 ° C. After 30 minutes at MD direction thermal shrinkage of 2.0% or less, after QUV (1.23 W / m 2 × 340 nm × 60 ° C. × 99 hours) irradiation, color difference (ΔE) 2.0 or less, 121 ° C., 50 hours at RH 100%, MD direction It is a polyester white film having elongation retention of 50% or more.

A third aspect of the present invention includes a matrix resin made of a polyester resin, a rutile titanium dioxide, a benzoxazole-based fluorescent brightener, and an oleic acid, having a whiteness of 100 or more, a reflectance of 90% or more at 550 nm, and 30 minutes at 150 ° C. After the MD direction thermal shrinkage of 2.0% or less and QUV (1.23 W / m 2 × 340 nm × 60 ° C. × 99 hours) irradiation, the color difference (ΔE) of 2.0 or less, 121 ° C. and RH 100% after 50 hours, MD direction elongation retention 50 It is polyester white film which is more than%.

A fourth aspect of the present invention includes a matrix resin made of a polyester resin, a rutile titanium dioxide, a benzoxazole-based fluorescent brightener, an oxazoline-based thickener and an oleic acid, a whiteness of 100 or more, a reflectance of 90% or more at 550 nm, After 30 minutes at 150 ° C., MD direction heat shrinkage was 2.0% or less, and after QUV (1.23 W / m 2 × 340 nm × 60 ° C. × 99 hours) irradiation, the color difference (ΔE) was 2.0 or less, 121 ° C., and 50 hours at RH 100%. It is a polyester white film whose MD direction elongation retention is 50% or more.

The above aspect of the present invention is described in one embodiment, but is not limited thereto.

In the present invention, the polyester white film may be used in the solar cell back sheet.

In addition, the backsheet for a photovoltaic module made of the polyester white film or including one or more layers of the polyester white film is also included in the scope of the present invention.

Hereinafter, each configuration of the present invention will be described in more detail.

The polyester resin is a general term for a polymer composed of ester bonds in which monomer residues, which are the main bonds in the main chain, and covalent bonds that bond monomer residues, are usually dicarboxylic acid compounds, dihydroxy compounds, or dicarboxylic acid ester derivatives and dihydrides. It can obtain by condensation polymerization of a hydroxy compound.

Here, as a dicarboxylic acid compound, For example, terephthalic acid, 2, 6- naphthalenedicarboxylic acid, isophthalic acid, diphenyl dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxy ethane dicarboxylic acid, 5- Alicyclic dicarboxylic acids such as aromatic dicarboxylic acid such as sodium sulfoisophthalic acid and phthalic acid, hydroxyl acid, succinic acid, adipic acid, sebacic acid, dimer acid, aliphatic dicarboxylic acid such as maleic acid and fumaric acid, and cyclohexanedicarboxylic acid; And oxycarboxylic acids such as paraoxybenzoic acid.

Moreover, as a dicarboxylic acid ester derivative, the esterified product of the said dicarboxylic acid compound, for example, dimethyl terephthalate, diethyl terephthalate, 2-hydroxyethyl methyl ester, 2, 6- dimethyl dicarboxylic acid, isophthalic acid Dimethyl, dimethyl adipic acid, dimethyl maleate, dimethyl dimer, and the like.

Examples of the hydroxy compound include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6 Aliphatic hydroxy compounds such as hexanediol and neopentyl glycol, alicyclic di such as polyoxyalkylene glycol such as diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and 1,4-cyclohexanedimethanol Aromatic dihydroxy compounds, such as a hydroxy compound, bisphenol A, bisphenol S, etc. are mentioned.

Among these, as the dicarboxylic acid compound, terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid and the like can be preferably used. As the dihydroxy compound, neopentyl glycol, ethylene glycol, 1,3-propanediol, 1, 4-butanediol, polytetramethylene glycol, 1,4-cyclohexanedimethanol and the like can be preferably used.

Especially, it is preferable to use polyethylene terephthalate (PET) which consists of terephthalic acid or terephthalate dimethyl, and ethylene glycol.

In one embodiment of the present invention, rutile titanium dioxide (Rutile) reflects the light passing through the solar cell and returns to the cell to increase the light efficiency, blocking the UV transmitted through the PET film forming the backsheet to prevent the photolysis of PET It acts as a deterrent. In the present invention, it is characterized by using rutile titanium dioxide (Rutile), the use of rutile titanium dioxide (Rutile) in the light absorption area is shifted toward the long wavelength, the photocatalytic activity is lowered to suppress photolysis by UV to improve durability It is preferable because it can improve. The content is preferably used 10 to 20% by weight of the total white film weight. When used at less than 10% by weight, the whiteness and reflectance may be difficult to apply to the backsheet of the solar module as a single layer film, and when used in excess of 20% by weight, the sheet may be brittle due to the high crystallization of the casting sheet. It is very hard to be broken and extended, and film forming stability may fall significantly. In addition, even if the film has sufficient reflectance, it is difficult to use it as a backsheet because the PCT (Pressure Cooker Test; 121 ° C × RH100% × 50 hours) characteristics, which are required for use for the solar module backsheet, are degraded. Do.

The PCT characteristics were measured by cutting a sample 10 times with a knife so as to be 200 mm in the MD direction at intervals of 15 mm in succession in the TD direction with respect to one edge of the sample (MD × TD length; 300 mm × 200 mm). After making the cut film with MD × TD) of 200mm × 15mm hang on one sample, punch it at 270mm from the cutting start point in the TD direction and make a hole, and hang it on the sample rack in the autoclave. The sample is placed in an autoclave so as not to be immersed in it, and the sample is aged for 50 hours under high temperature and high humidity conditions at 121 ° C. × 100% RH × 2 bar. When aging is completed, this means physical properties measured after leaving it at an autoclave for 24 hours at room temperature.

In addition, the inorganic particles preferably use an average particle diameter of 0.1 ~ 0.5㎛, particularly preferably 0.2 ~ 0.40㎛. If the thickness is less than 0.1 μm, the dispersibility is poor due to the re-aggregation of fine particles, and the filter of the film forming process is frequently clogged, which greatly reduces the operability. If the thickness is 0.5 μm or more, the particle size is too large and the inter-particle space is increased during the stretching process. Poor ductility, poor operability such as breakage, and even if the same content is applied, the lower the reflectance, if the particle content is increased in order to achieve the required reflectance, it may be economical due to the increase in manufacturing cost, deterioration of fairness.

In addition, to improve the reflectance and whiteness of the film includes a fluorescent brightener, and preferably contains a Benzoxazol fluorescent brightener 100 to 900ppm of the total content of the film. If it is less than 100ppm, the whiteness falls and the light reflection efficiency is reduced. If it exceeds 900 ppm, the whiteness and reflectance increase, but the UV stability is poor, and yellowing may occur when exposed to the outside for a long time.

Specific examples of the benzoxazol fluorescent brighteners include 2,5-thiophendiylbis (5-tert-butyl-1,3-benzoxazole), 4,4'-bis (2-methoxysty Reel) -1,1'-biphenyl, 2,2 '-(1,2-ethendiyldi-4,1-phenylene) bisbenzooxazole and the like can be used. Commercialized examples of these may be Eastman's OB-1 and the like, but are not limited thereto.

The present invention may further include an additive as necessary in the matrix resin, it is preferable that the additive preferably contains one or more inorganic particles and UV stabilizers, antioxidants, heat stabilizers and the like.

In one embodiment of the present invention, the polyester white film may further include an additive selected from an oxazoline-based thickener, oleic acid, and mixtures thereof.

Specifically, the oxazoline-based thickener may be included in an amount of 50 to 700 ppm based on the total weight of the film, and the oleic acid may be included in an amount of 40 to 400 ppm based on the total weight of the film.

Since the oxazoline-based thickener may lower the viscosity due to thermal decomposition of the polymer when the first master batch chip is manufactured, the viscosity of the oxazoline-based thickener is used to improve film manufacturing processability and to prevent degradation of physical properties. It is preferred to include 50 to 700ppm, more preferably 400 to 600ppm based on the total weight. If the content is less than 50ppm, the effect of increasing the molecular weight by the thickener is not sufficient, and thus the film manufacturing processability and the physical property deterioration are not effective, and when it is used over 700ppm, the filter pressure is too high and the filmmaking processability is lowered, making it difficult to use. Can be.

The oleic acid is used to improve the dispersibility of the fluorescent brightener, and preferably 40 to 400 ppm, more preferably 200 to 300 ppm based on the total weight of the film. If the amount is less than 40ppm, the effect is insignificant, and if it is used in excess of 400ppm, contamination may occur on the surface of the film, thereby decreasing whiteness and reflectance.

Next, the method for producing a polyester white film of the present invention

c) uniaxially or biaxially stretching the unstretched sheet to produce a film;

It includes.

Step a) is a process of preparing a first masterbatch so that rutile titanium dioxide and benzoxazol fluorescent brightener are uniformly mixed with a polyester resin chip. In order to increase the compatibility with the material, the polyester resin chip is pulverized at room temperature to prepare a powder form, and then mixed with each material to a certain amount using a quantitative feeder, and then put into an extruder. The extruder used is preferably a twin screw extruder equipped with a vacuum vent device.

It is preferable that the temperature of the twin screw extruder is 240 to 265 ° C, and the melt viscosity (Melt Viscosity; @ Shear-rate 500sec ^-1 , 280 ° C) is 200 by melt extruding with the residence time of the polymer in the extruder being 1 minute or less. It is preferred to prepare a first masterbatch in the range of ˜1200 poise.

In addition, in order to filter out aggregates of polyester resin, inorganic particles and fluorescent brightener at the tip of the twin screw extruder, and to increase shear stress, 300 to 500 mesh (Mesh: 1 inch (24.5) is a unit representing a mesh of stainless steel. mm) refers to the number of meshes between the screens, which is equivalent to 46 ~ 28 micron in terms of filter size) using a screen-changer filter of the inorganic particles and the optical brightener is a uniform master Batch can be prepared.

More specifically, in the step a), the first master batch chip is 40 to 60% by weight of polyester resin powder, 40 to 60% by weight of rutile titanium dioxide, benzoxazol fluorescent brightener 300 to 3000ppm By mixing, the vacuum vent (Vent) and the tip of the twin screw extruder in the twin screw extruder comprising a 300 ~ 500 mesh screen changer filter, it may be prepared by melt extrusion at the extruder temperature 240 ~ 265 ℃. .

In addition, when manufacturing the first masterbatch chip in step a), it may further include an additive selected from oxazoline-based thickener, oleic acid and mixtures thereof.

At this time, the oxazoline-based thickener is added in an amount of 50 to 700ppm based on the total weight of the film, the oleic acid is preferably added in an amount of 40 to 400ppm based on the total weight of the film.

In the step b), the content of the first master batch chip is 10 to 20% by weight of the rutile titanium dioxide (Rutile) of the total film content, the second polyester resin to include 100 ~ 900ppm Benzoxazol fluorescent brightener It is preferably used in combination with the chip. In order to prevent the intermixing between chips due to specific gravity difference in feeding the first master batch chip and the second polyester resin chip to the extruder, a separator is installed inside the hopper at the top of the extruder and the extruder is driven based on the separator. It is preferable to have a quantitative feeding device (side feeder for controlling the amount of addition of the chip by controlling the rotation speed) on the side of the hopper located on the side of the directional viewpoint.

A polyester resin chip is supplied from the upper side of the hopper on the basis of the separator, and the first master batch chip containing rutile titanium dioxide and benzoxazol fluorescent brightener is used at a constant rotation speed. Supply the feeder to the other side of the separator by using side feeder, and by extruder's screw, polyester resin chip and master batch chip are mixed and extruded by screw of extruder. It is preferable to improve the compatibility by.

In addition, in order to improve the miscibility of the polyester resin and the master batch chip, the melt extrusion temperature of step b) is preferably carried out at 280 ~ 320 ℃.

The c) step is to prepare a film by stretching, 2.0 to 4.0 in the machine direction (MD) by IR heater non-contact irradiation between 500 ~ 900 ℃ while passing the unstretched sheet through a preheat roll of 80 ~ 100 ℃ It is preferable to carry out 2 times extending | stretching, to cool to 20-35 degreeC, and to pre-heat at 100-125 degreeC, and to carry out 3.0-4.0 times biaxial stretching in the width direction (TD) at 125-140 degreeC extending | stretching temperature.

The stretched sheet may be heat treated and relaxed in a range of 200 to 240 ° C. in a tenter of 5 to 10 steps. Relax usually gives 1 to 10% of the length in the width direction, thereby giving the film's thermal shrinkage and form stability.

In the present invention, the total film thickness is preferably 50 ~ 300㎛. If it is less than 50 µm, it may not have sufficient reflectance and durability and weather resistance. If it is larger than 300 µm, the stretching stress may be excessively high without a large increase in reflectance, resulting in poor film manufacturing processability and delamination at the surface layer.

The polyester white film prepared according to the manufacturing method of the present invention has a whiteness of 100 or more, a reflectance of 90% or more at 550 nm, after 30 minutes at 150 ° C., MD direction thermal shrinkage of 2.0% or less, and QUV (1.23 W / m 2 × 340 nm ×). 60 ° C × 99 hours) After irradiation, color difference (ΔE) 2.0 or less, 121 ° C, and RH100% after 50 hours, the physical properties of the MD direction elongation retention of 50% or more can be satisfied. It is suitable to be used as a solar module backsheet in a range satisfying all of the physical properties, if any one of the physical properties does not satisfy the object of the present invention.

The whiteness is 100 or more, preferably 100 to 110, more preferably 104 to 108, less than 100, the effect of increasing the target light reflection efficiency is less, and the light reflection efficiency increases Power generation efficiency by optical conversion in the module can be increased up to 0.2 ~ 0.5%.

In addition, the reflectance at 550 nm is preferably 90% or more, preferably 92 to 99%, more preferably 95 to 99%, and even more preferably 97 to 99%, and when it is less than 90%, the light recycling effect is low. There is no big effect on power generation efficiency increase by optical conversion of module.

In addition, the MD direction heat shrinkage is less than 2.0% (150 ℃ 30 minutes, @Oven), preferably 0.5 to 1.8%, more preferably 1.0 to 1.6%, when exceeding 2.0% heat resistance characteristics It is undesirably deteriorated due to a large change in physical properties due to heat.

Further, after irradiation with QUV (1.23 W / m 2 × 340 nm × 60 ° C. × 99 hours), the color difference (ΔE) is 2.0 or less, preferably the color difference (ΔE) 0 to 1.6, and more preferably the color difference (ΔE) 0 to 0.5 If the color difference (ΔE) 2.0 is exceeded, UV stability is low and long-term durability is low.

In addition, after PCT (121 ° C × RH100% × 50 hours), the MD elongation retention is preferably 50% or more, preferably 50% to 100%, more preferably 70 to 100%, and less than 50% It is difficult to apply due to the rapid decrease in physical properties caused by long-term durability.

Hereinafter, the present invention will be described by way of example for specific description of the present invention, but the present invention is not limited to the following examples.

Hereinafter, the physical properties of the present invention were measured as follows.

1) Whiteness Index

After taking 10 measurement samples within 1m in the longitudinal direction (MD) at the full length of the film roll, and measuring the whiteness index of each film sample using a spectrophotometer (Datacolor 600, Datacolor, Inc.) The average value of eight samples except the value and the minimum value was calculated | required, and it was set as the whiteness index.

2) Reflectance (%)

After taking 10 measurement samples within 1m in the longitudinal direction (MD) at the full length of the film roll, using a spectrophotometer (Varian UV Spectrophotometers Cary 5000) to measure the reflectance at 550nm for each film sample sheet , And the average value of eight samples except the maximum value and the minimum value was calculated | required, and this was made into the reflectance.

Here, the reflectance of the film is a relative reflectance when the barium sulfate standard white plate is 100% in the measuring device, and is measured by visible light at 550 nm. In this case, the measurement angle is 3 ° 20 ", the average time of detecting the signal in the detector is 0.1s, the interval of the analysis data is 1nm, and the scan speed is 600nm / min.

3) Heat Shrinkage (150 ℃ × 30 minutes)

The film was cut in the forward direction of 200 mm × 200 mm with respect to the MD and TD directions, and the lengths of the machine direction (MD) and the width direction (TD) were measured. After heat shrinking for a minute, the lengths of the machine direction (MD) and the width direction (TD) of the heat-shrinked film were measured, and the heat shrinkage ratios of the machine direction (MD) and the width direction (TD) were calculated according to the following formula (1).

[Calculation 1]

4) Color difference (ΔE) after irradiation with QUV (1.23W / m2 × 340nm × 60 ° C × 99 hours)

After taking 20 measurement samples within 2m in the longitudinal direction (MD) at the full width of the film roll, and using the spectrophotometer (Datacolor, Datacolor 600) to measure the L, a, b * value of a single sheet for 10 film samples By measuring the average values of L, a, and b * of 10 samples, L0, a0, and b * 0 were obtained.

The remaining 10 samples were taken using an Accelerated Weathering Tester (Q-Lab model name QUV / SPRAY). The irradiation intensity of UV-Lamp was 1.23 W / m2, UV irradiation wavelength was 340 nm, temperature was 60 ° C, and irradiation time was 99. After irradiating UV under a time condition, the sample was taken out of the UV irradiation apparatus and left at room temperature for 24 hours, and then it was again cut into 10 sheets of the film sample irradiated with UV using a spectrophotometer (Datacolor 600, Datacolor). The L, a, b * values were measured, and the average values of L, a, b * of ten samples were obtained, and L1, a1, and b * 1 were obtained.

Using the average values of L, a, b * values before the UV irradiation and after the UV irradiation, the color difference (ΔE) after the QUV irradiation was obtained according to the following equation (2).

[Calculation 2]

(Where SQRT is the square root)

5) MD elongation retention rate (%) after PCT (Pressure Cooker Test; 121 ℃ × RH100% × 50 hours)

Within the length range of less than 5m in the length direction of the film roll, take two measurements of 300mm × 200mm in the longitudinal direction to the MD direction of the film and the transverse direction to the TD direction. First, make a sample for measuring the physical property by making the length of MD and TD directions 300mm × 15mm for one sample, and measure the width of 15mm, Gauge Length 50mm, and cross head. -up speed) After measuring ten times the cutting elongation in the machine direction (MD) of the film before PCT treatment using a universal tensile test machine (Instron Tensile Test Machine), except the maximum and minimum values The average value was calculated | required.

For another sample taken (MD × TD length; 300mm × 200mm), cut the sample with a knife so that it becomes 200mm in the MD direction at intervals of 15mm continuously in the TD direction with respect to one edge. Cut out the cut film having a sample size (MD × TD) of 200mm × 15mm to hang on one sample, punch it at 270mm from the cutting start point in the TD direction, and make a hole in the sample in the autoclave. The sample is placed in an autoclave so as not to be immersed in a hanger and immersed in water, and the sample is aged for 50 hours under high temperature and high humidity conditions at 121 ° C. × 100% RH × 2 bar. After aging is completed, take it out of the autoclave and leave it at room temperature for 24 hours, and then take a small sample of 200mm × 15mm size cut out with a knife before aging from the sample and measure the width of the sample to 15mm as above. Elongation at the machine direction (MD) of the film after PCT treatment using a universal tension test machine (Instron's Tensile Test Machine) at 50mm / gauge length and 500mm / min cross head-up speed After measuring 10 times, the average value was calculated except the maximum value and the minimum value.

Using the elongation values in the MD direction before and after the PCT treatment, the elongation retention ratio after the PCT was calculated according to the following Equation 3.

[Calculation 3]

6) Intrinsic viscosity (I.V .; dl / g)

After dissolving with OCP (Ortho Chloro Phenol) at 160 ± 2 ℃, and measuring the sample viscosity in a viscosity tube using an automatic viscosity meter (Skyvis-4000) at 25 ℃, the intrinsic viscosity of the sample was calculated using Equation 4 below. viscosity, IV) was obtained.

[Calculation 4]

Intrinsic Viscosity (IV) = {(0.0242 × Rel) +0.2634} × F

7) Melt viscosity (M.V .; poise)

After drying the master batch chip for 10 hours in a vacuum dryer at 160 ° C., the melt viscosity of the master batch chip was measured at a shear rate of 500 sec ⁻¹ at 280 ° C. using a melt viscosity measuring apparatus (Gottfert Rheo-Tester). Obtained.

Example 1

Preparation of the First Masterbatch Chip

The first polyethylene terephthalate chip having an intrinsic viscosity of 0.85 dl / g was processed into a powder at room temperature using a grind. Using a quantitative feeder, 200Kg (50% by weight) of powder of polyethylene terephthalate chip and 199.52Kg (49.88% by weight) of rutile titanium dioxide and Benzoxazol fluorescent brightener (Eastman) having an average particle diameter of 0.22 µm OB-1) 0.48Kg (1200ppm, 0.12% by weight) and blended into a twin screw extruder equipped with a vacuum vent (Vent), the residence time in the extruder at 245 ℃ to 25 seconds, at the tip of the extruder The first master batch chip (A) was manufactured by melt extrusion through a 400 mesh screen changer filter.

As a result of measuring physical properties of the prepared first master batch chip (A), the melt viscosity was 315 poise (@ 280 ° C., Shear-rate 500 sec ⁻¹ ).

Manufacture of film

The first master batch chip (A) prepared above and a second polyethylene terephthalate chip having an intrinsic viscosity of 0.85 dl / g were supplied to an extruder. At this time, in order to prevent the compatibility between chips due to specific gravity difference, a separator is installed inside the hopper and the master is disposed on the side of the hopper located at the starting point side (one end of the separator) of the extruder based on the separator. A side feeder was provided for feeding batch chips. The polyethylene terephthalate chip is supplied from the upper side of the hopper on the basis of the separator, and the master batch chip is provided on the other side of the separator using a side feeder device capable of supplying the chip at a constant rotation speed. By feeding the extruder by rotating the extruder polyethylene terephthalate chip and the master batch chip by mixing the screw to eliminate the problem of compatibility due to chip size and specific gravity difference.

The content of the first master batch chip (A) and the second polyethylene terephthalate chip is 40% by weight of the first master batch chip (19.95% by weight of rutile titanium dioxide based on the total film, 480 ppm of a fluorescent brightener), 2 polyethylene terephthalate chip was used at 60% by weight, which was fed to an extruder, melted at 285 ° C., and then extruded through a T-die to prepare an unstretched sheet on a casting roll (cold roll) at 21 ° C. At this time, the residence time in the casting roll was 22.5 seconds, the casting speed is 12.5m / min, the temperature of the air chamber was 20 ℃. This was stretched 3.0 times in the machine (MD) direction at an IR heater temperature of 860 ° C. via a 92 ° C. preheating roll, cooled through a 22 ° C. cooling roll, and subsequently in a width direction at 130 ° C. through a preheating section of 120 ° C. TD) was stretched 3.85 times, heat-treated at 225 ° C., and then, at 200 ° C., a 5.0% relaxation process was performed to prepare a film having a total thickness of 188 μm.

The physical properties of the prepared white film are measured and shown in Table 1 below.

Example 2

Preparation of the First Masterbatch Chip

The first masterbatch chip (B) was prepared by the method of Example 1, the composition of the masterbatch chip is a rutile type (Rutile) of 180kg (45% by weight) powder of polyethylene terephthalate chip, 0.4㎛ average particle diameter Titanium 218.2Kg (54.55% by weight), Benzoxazol fluorescent whitening agent (Eastman OB-1) 1.0Kg (2500ppm, 0.25% by weight), oxazoline type thickener (Chain-Extender) 0.8Kg (2000ppm, 0.20 Weight%), a first master batch chip B was prepared using an extruder temperature of 260 ° C, a residence time of 55 seconds in the extruder, and a 350-mesh screen changer filter at the tip of the extruder.

As a result of measuring physical properties of the prepared first master batch chip (B), the melt viscosity was 850 poise (@ 280 ° C., Shear-rate 500 sec ⁻¹ ).

Manufacture of film

A film was prepared in the same manner as in Example 1. 30 wt% of the first master batch chip (B) in the extruder (16.37 wt% of rutile titanium dioxide based on the entire film, 750 ppm of fluorescent brightener, 600 ppm of oxazoline-based thickener) and 0.85 dl / g of intrinsic viscosity 70 wt% of polyethylene terephthalate chip was supplied, and the unstretched sheet was manufactured at an extruder temperature of 295 ° C., a residence time of 18.8 seconds in a casting roll, a casting speed of 15.0 m / min, a draw ratio of 3.2 times in the machine (MD) direction, A film having a total thickness of 188 μm was produced in the same manner except that 3.1 times the width direction (TD) draw ratio was applied.

Example 3

Preparation of the First Masterbatch Chip

In preparing the master batch chip (C), the composition of the master batch chip is 200Kg (50 wt%) of the powder of polyethylene terephthalate chip, Rutile titanium dioxide (98.2Kg (49.55 wt%)) having an average particle diameter of 0.22㎛, Benzoxazol fluorescent brightener (Eastman OB-1) 0.6Kg (1500ppm, 0.15% by weight), oxazoline-based thickener (Chain-Extender) 0.8Kg (2000ppm, 0.20% by weight), oleic acid 0.4Kg (1000ppm , 0.10 wt%), the master batch chip (C) was prepared in the same manner except that the extruder temperature was 240 ° C., the residence time in the extruder was 10 seconds, and a 400-mesh screen changer filter was used at the tip of the extruder.

As a result of measuring the physical properties of the prepared master batch chip (C), the melt viscosity was 1100poise (@ 280 ℃, Shear-rate 500sec ^-1 ).

Manufacture of film

A film was prepared in the same manner as in Example 1. 21 wt% of master batch chip (C) in the extruder (10.41 wt% of rutile titanium dioxide based on the entire film, 315 ppm of fluorescent brightener, 420 ppm of oxazoline-based thickener, 210 ppm of oleic acid) and 0.85 dl / g of intrinsic viscosity 79 wt% of the second polyethylene terephthalate chip was supplied, and the unstretched sheet was manufactured at an extruder temperature of 295 ° C., a residence time of 25.5 seconds in a casting roll, a casting speed of 11.3 m / min, and a draw ratio of 3.1 times in the machine (MD) direction. A film having a total thickness of 250 µm was prepared in the same manner, except that the width was applied at a draw ratio of 3.1 times.

Comparative Example 1

In preparing the master batch chip (D) by the method of Example 1 except that the inorganic particles using a barium sulfate (BaSO ₄ ) having an average particle diameter of 0.85㎛ the film having a total thickness of 188㎛ in the same composition and method Prepared.

Comparative Example 2

In preparing the first masterbatch chip E, no fluorescent brightener was used.

180kg (45% by weight) powder of polyethylene terephthalate chip, 219.2Kg (54.8% by weight) rutile titanium dioxide with an average particle diameter of 0.8 kg (2000ppm, 0.20% by weight of oxazoline-based thickener) %), The first master batch chip (E) was manufactured using an extruder temperature of 260 DEG C, a residence time of 55 seconds in the extruder, and a 350-mesh screen changer filter at the tip of the extruder.

As a result of measuring the physical properties of the prepared first master batch chip (E), the melt viscosity was 850 poise (@ 280 ℃, Shear-rate 500 sec ^-1 ).

Manufacture of film

A film was prepared in the same manner as in Example 1. 30 wt% of the first master batch chip (E) in the extruder (16.44 wt% of rutile titanium dioxide based on the entire film, 600ppm of oxazoline-based thickener) and a second polyethylene terephthalate chip having an intrinsic viscosity of 0.85 dl / g70 An unstretched sheet was prepared by supplying a weight% and an extruder temperature of 295 ° C., a residence time of 18.8 seconds in a casting roll, a casting speed of 15.0 m / min, a draw ratio of 3.2 in the machine (MD) direction, and a draw ratio in the width direction (TD). A film having a total thickness of 188 μm was prepared in the same manner except that 3.1 times was applied.

Comparative Example 3

15 wt% of the first masterbatch chip (A) of Example 1 (7.48 wt% of rutile titanium dioxide based on the total film, 180 ppm of a fluorescent brightener), and 85 wt% of the second polyethylene terephthalate chip in manufacturing the film A film was prepared in the same manner as in Example 1 except for using.

[Comparative Example 4]

60 wt% of the first masterbatch chip (A) of Example 1 (29.93 wt% of rutile titanium dioxide based on the total film, 720 ppm of fluorescent brightener) and 40 wt% of the second polyethylene terephthalate chip during film preparation A film was prepared in the same manner as in Example 1 except for using.

[Comparative Example 5]

Preparation of the First Masterbatch Chip

In preparing the master batch chip (F), the composition of the master batch chip is 200Kg (50.25 wt%) of the powder of polyethylene terephthalate chip, Rutile titanium dioxide 197.9Kg (49.72 wt%) having an average particle diameter of 0.22㎛, Benzoxazol fluorescent brightener (Eastman OB-1) 0.1kg (251ppm, 0.025% by weight), extruder temperature 240 ℃, residence time in the extruder 10 seconds, 400 mesh screen changer filter at the tip of the extruder Master batch chip (F) was prepared in the same manner except for the use.

Manufacture of film

A film was prepared in the same manner as in Example 1. 30 wt% of master batch chip (F) in extruder (14.92 wt% of rutile titanium dioxide based on total film, 75ppm of Benzoxazol fluorescent brightener) and second polyethylene tere with intrinsic viscosity of 0.85 dl / g An unstretched sheet was prepared by supplying 70% by weight of a phthalate chip and an extruder temperature of 295 ° C., a retention time of 18.8 seconds in a casting roll, a casting speed of 15.0 m / min, a draw ratio of 3.2 times in the machine (MD) direction, and a width direction ( TD) A film having a total thickness of 188 μm was prepared in the same manner except that the draw ratio was applied at a draw ratio of 3.1 times.

Comparative Example 6

Preparation of the First Masterbatch Chip

In preparing the masterbatch chip (G), the composition of the masterbatch chip was 200Kg (50% by weight) of powder of polyethylene terephthalate chip, 199Kg (49.75% by weight) of rutile titanium dioxide having an average particle diameter of 0.22 µm, and Ben Benzoxazol fluorescent brightener (Eastman OB-1) 1.0Kg (2500ppm, 0.25% by weight), extruder temperature 240 ℃, residence time in the extruder 10 seconds, 400 mesh screen changer filter at the tip of the extruder Except that the master batch chip (G) was prepared in the same manner.

Manufacture of film

A film was prepared in the same manner as in Example 1. 40% by weight of the master batch chip (G) in the extruder (19.9% by weight of rutile titanium dioxide based on the entire film, 1000 ppm of benzoxazol fluorescent brightener) and a second polyethylene tere with an intrinsic viscosity of 0.85 dl / g An unstretched sheet was prepared by supplying 60 wt% of phthalate chips and an extruder temperature of 295 ° C., a retention time of 18.8 seconds in a casting roll, a casting speed of 15.0 m / min, a draw ratio of 3.2 times in the machine (MD) direction, and a width direction ( TD) A film having a total thickness of 188 μm was prepared in the same manner except that the draw ratio was applied at a draw ratio of 3.1 times.

TABLE 1

As shown in Table 1, the embodiment according to the present invention has a whiteness of 100 or more, a reflectance of 90% or more at 550 nm, after 30 minutes at 150 ° C., MD direction thermal shrinkage of 2.0% or less, and QUV (1.23 W / m 2 × 340 nm). × 60 ° C × 99 hours) After irradiation, color difference (ΔE) 2.0 or less, 121 ° C, RH100%, and 50 hours later, all properties of MD direction elongation retention of 50% or more are satisfied. Could know.

In Comparative Example 1, barium sulfate was used instead of rutile titanium dioxide, and although the same content as in Example 1 was used, it was found that the reflectance was lower, and the whiteness was high, and the heat shrinkage, color difference, and elongation of MD direction were poor. Could know.

In addition, Comparative Example 2 was a case where the benzoxazole-based fluorescent brightener was not used, it was found that the whiteness and reflectance is lower than in Example 2 experimented under the same conditions, it was found that the light reflection efficiency is lowered.

In addition, as shown in Comparative Examples 3 and 4, when the content of rutile titanium dioxide is less than the range of the present invention, it is difficult to apply to the backsheet as a single layer film due to low whiteness and reflectance. In the case of use, the sheet was brittle and broken well due to the high crystallization progress of the casting sheet, and it was found that the film forming stability greatly decreased.

In addition, as shown in Comparative Examples 5 and 6, when the content of the Benzoxazol fluorescent brightener is used less than the range of the present invention, it can be seen that the light reflectance is lowered, the whiteness is lowered, and used in excess of In this case, the whiteness and the reflectance increase, but the UV stability is lowered, and the yellowing phenomenon occurs when exposed to the outside for a long time.

Claims

Color difference (ΔE) 2.0 after irradiation of QUV (1.23 W / m 2 × 340 nm × 60 ° C. × 99 hours) at 100 degrees or more, reflectance at 550 nm of at least 90%, at 30 ° C. after 30 minutes at 150 ° C. Or less, after 121 hours, RH100% 50 hours, MD direction elongation retention of more than 50% polyester white film.
The method of claim 1,

The polyester white film is a polyester white film comprising a matrix resin consisting of a polyester resin, rutile titanium dioxide and benzoxazole-based fluorescent brightener.
The method of claim 2,

The polyester white film is a polyester white film comprising 10 to 20% by weight of rutile titanium dioxide, 100 to 900ppm Benzoxazol fluorescent brightener based on the total weight of the film.
The method of claim 3,

The average particle diameter of the rutile titanium dioxide is 0.1 ~ 0.5㎛ polyester white film.
The method of claim 3,

The polyester white film further comprises an additive selected from an oxazoline-based thickener, oleic acid and mixtures thereof.
The method of claim 5,

The oxazoline-based thickener includes 50 to 700ppm based on the total weight of the film, the oleic acid is 40 to 400ppm based on the total weight of the film polyester white film.
The method of claim 2,

The polyester resin is a polyethylene white terephthalate polyester white film.
The method according to any one of claims 1 to 7, wherein

The polyester white film is used in the solar cell back sheet polyester white film.
The solar cell module back sheet made of a polyester white film according to any one of claims 1 to 7, or comprising at least one layer of the polyester white film.
a) mixing a polyester resin powder, a rutile titanium dioxide and a benzoxazole-based fluorescent brightener, pulverizing the first polyester resin chip, melt extruding at an extruder temperature of 240 ~ 265 ℃ to produce a first master batch chip ;

b) injecting the first masterbatch chip and the second polyester resin chip into an extruder, followed by melt extrusion at a temperature of 280 to 320 ° C. to produce an unstretched sheet; And

c) uniaxially or biaxially stretching the unstretched sheet to produce a film;

Method for producing a polyester white film comprising a.
The method of claim 10,

In step b), the content of the first masterbatch chip is added to include 10 to 20% by weight of rutile titanium dioxide, 100 to 900ppm Benzoxazol fluorescent brightener based on the total weight of the film Method for producing a polyester white film.
The method of claim 10,

The method of manufacturing a polyester white film further comprises an additive selected from oxazoline-based thickeners, oleic acid, and mixtures thereof when the first master batch chip is manufactured in step a).
The method of claim 12,

The oxazoline-based thickener is added in an amount of 50 to 700ppm based on the total weight of the film, and the oleic acid is added in an amount of 40 to 400ppm based on the total weight of the film Way.
The method of claim 10,

When manufacturing the first masterbatch chip in step a), using a twin screw extruder including a vacuum vent (Vent) device, so that the residence time of the extruder temperature 240 ~ 265 ℃, the polymer in the extruder 1 minute or less, Method for producing a polyester white film that is uniformly mixed using a 300 ~ 500 mesh screen changer filter on the tip of the twin screw extruder.
The method of claim 10,

The polyester white film had a whiteness of 100 or more, a reflectance of 90% or more at 550 nm, after 30 minutes at 150 ° C., MD direction heat shrinkage of 2.0% or less, and after QUV (1.23 W / m 2 × 340 nm × 60 ° C. × 99 hours) irradiation , Color difference (ΔE) 2.0 or less, 121 ℃, RH 100% After 50 hours, MD direction elongation retention of 50% or more of the manufacturing method of the polyester white film.