KR102287227B1 - Polyester film for back sheet of solar cell and solar cell module comprising the same - Google Patents

Abstract

The embodiment relates to a polyester film for a solar cell back sheet and a solar cell module including the same, and the polyester film has excellent hydrolysis resistance and does not cause delamination, so it is very suitable for use as a solar cell back sheet.

Description

Polyester film for a solar cell back sheet and a solar cell module including the same

The embodiment relates to a polyester film for a solar cell back sheet having excellent hydrolysis resistance and no delamination between layers, and a solar cell module including the same.

Since solar cells are exposed to the outdoors to generate electricity, they are used for a long time in harsh environments with high temperatures and high humidity. In order for a solar cell to be used for a long time, high weather resistance such as heat resistance, UV resistance, and hydrolysis resistance of a back sheet used as a member for a solar cell is required. In order to satisfy such weather resistance conditions, a fluorine-based sheet or film is generally used as a solar cell backsheet (refer to Korean Patent Application Laid-Open No. 2011-0118736). However, since the fluorine-based substrate is very expensive, it is burdening the manufacturing cost of the product. As an alternative to this, a solar cell backsheet having a structure in which weather-resistant PET with excellent weather resistance and general PET are laminated has been proposed.

Republic of Korea Patent Publication No. 2011-0118736

However, as described above, the backsheet in which weather-resistant PET and general PET are laminated has problems in that delamination occurs or does not have the level of weather resistance required by the market.

Accordingly, an object of the embodiment is to provide a polyester film for a solar cell backsheet that has excellent weather resistance such as heat resistance, UV resistance, and hydrolysis resistance, and does not cause delamination, and a solar cell module including the same.

In order to achieve the above object, an embodiment is

A layer comprising a polyester resin and a white pigment; and

A polyester film comprising a; B layer comprising a polyester resin and a white pigment,

The layer A contains the white pigment in an amount of 5 to 11% by weight based on the total weight of the layer A,

The B layer contains the white pigment in an amount of 1 to 6% by weight based on the total weight of the B layer,

It provides a polyester film for a solar cell back sheet, wherein the difference in the content of the white pigment between the layer A and the layer B is less than 6% by weight.

Another embodiment to achieve the above other object,

It provides a solar cell module including the polyester film as described above.

The polyester film according to the embodiment has excellent weather resistance such as heat resistance, UV resistance, and hydrolysis resistance, and is very suitable for application as a solar cell backsheet because delamination does not occur.

1 and 2 schematically show the configuration (exploded view and coupling view, respectively) of a solar cell module according to an embodiment including a solar cell, an encapsulant sheet, and a film for a solar cell back sheet.

The polyester film for the solar cell back sheet of the embodiment is

A layer comprising a polyester resin and a white pigment; and

A polyester film comprising a; B layer comprising a polyester resin and a white pigment,

The layer A contains the white pigment in an amount of 5 to 11% by weight based on the total weight of the layer A,

The B layer contains the white pigment in an amount of 1 to 6% by weight based on the total weight of the B layer,

The difference in the content of the white pigment between the layer A and the layer B is less than 6% by weight.

The polyester film may be in a form in which the A layer and the B layer are co-extruded and laminated in two or three layers.

The polyester film may have a form in which the A layer is laminated on the surface. The polyester film, for example, may be in the form of A layer / B layer or A layer / B layer / A layer. This is because layer A, which contains a relatively large amount of white pigment, is located on the surface to enhance the light reflection effect of the film, and the inner layer, B, contains white pigment with an appropriate content difference from layer A, preventing peeling between layer A and layer B. can do.

Specifically, the polyester film may be in the form of co-extrusion in the form of A layer / B layer or A layer / B layer / A layer.

polyester resin

The polyester resin may have an intrinsic viscosity (IV) of 0.5 dl/g or more. Specifically, the polyester resin may have an intrinsic viscosity (IV) of 0.5 to 0.8 dL/g.

The polyester resin may be polyethylene terephthalate.

monosensory Epoxy compound

The A layer and the B layer may each include a monofunctional epoxy-based compound.

The monofunctional epoxy-based compound not only serves to improve weather resistance such as heat resistance and hydrolysis resistance of the film by sealing the carboxyl terminal group of the polyester resin, but also improves the processability of the film and prevents delamination of the produced film. plays a role

The layer A and layer B may contain a monofunctional epoxy compound in an amount of 0.1 to 1 part by weight based on the total amount of the polyester resin and the white pigment of each layer. Specifically, the A and B layers contain the monofunctional epoxy compound in an amount of 0.1 to 0.8 parts by weight, 0.1 to 0.6 parts by weight, 0.2 to 0.8 parts by weight, or 0.2 to 0.6 based on the total amount of the polyester resin and white pigment of each layer. It may be included in parts by weight. When the content of the monofunctional epoxy-based compound is within the above range, a film having satisfactory weather resistance can be manufactured, and the stability of the extrusion process is excellent, thereby improving processability.

The monofunctional epoxy-based compound may be a glycidyl ester compound. Specifically, the glycidyl ester compound may include a compound represented by the following Chemical Formula 1:

In the above formula,

R ₁ to R ₃ are each independently C _1-7 alkyl. Specifically, R ₁ to R ₃ may each independently be C _1-5 alkyl.

white pigment

The white pigment serves to improve the UV resistance of the film.

The layer A contains 5 to 11% by weight of the white pigment based on the total weight of the layer A. Specifically, the layer A may contain 8 to 10% by weight of the white pigment based on the total weight of the layer A. When the content of the white pigment is within the above range, the UV resistance of the film is improved, and the UV blocking function is excellent compared to the content of the white pigment, so it is economical.

The layer B contains 1 to 6% by weight of the white pigment based on the total weight of the layer B. Specifically, the B layer contains 4 to 5 wt % of the white pigment based on the total weight of the B layer. When the content of the white pigment is within the above range, it is possible to manufacture a film having a high reflectivity in the infrared region.

The white pigment may be at least one selected from the group consisting of titanium dioxide (TiO ₂ ), CaCO ₃ , BaSO _{4 , kaolin, and talc.} Specifically, the white pigment may be titanium dioxide (TiO ₂ ).

The difference in the content of the white pigment between the layer A and the layer B is less than 6% by weight. Specifically, the difference in the content of the white pigment between the layer A and the layer B may be 1 to 5.5 wt%. When the difference in the content of the white pigment of the layer A and the layer B is within the above range, there is an effect of preventing delamination between the layers of the prepared film.

The white pigment may have an average diameter of 0.1 to 2.0 μm. Specifically, the white pigment may have an average diameter of 0.1 to 0.8 μm. When the average diameter of the white pigment is within the above range, a film having a high reflectance with respect to light of 350 to 1,050 nm may be manufactured.

polyester film

When the polyester film is heat-treated at 150° C. for 30 minutes, it may exhibit a longitudinal (MD direction) thermal contraction rate of 1.5% or less and a width direction (TD direction) thermal contraction rate of 1% or less. Specifically, when the polyester film is heat-treated at 150 ° C. for 30 minutes, it may exhibit a heat shrinkage in the MD direction of 0.5 to 1.5% and a heat shrinkage in the TD direction of 0 to 1%.

The polyester film may exhibit a longitudinal elongation retention rate of 7% or more when treated for 76 hours under a pressure test (PCT) condition of 121° C. and 1.2 bar. Specifically, the polyester film may exhibit MD direction elongation retention of 10% or more, 15% or more, or 15 to 50% when treated for 76 hours at 121 ° C. and 1.2 bar pressure test (PCT) conditions. there is.

When the average thickness of the polyester film is 165 μm, light transmittance may be less than 15%. Specifically, when the average thickness of the polyester film is 165 μm, the light transmittance may be 10.5% or less, 1 to 10.5%, or 5 to 10.0%.

The polyester film may have an intrinsic viscosity (IV) of 0.50 to 0.80 dl/g. Specifically, the polyester film may have an intrinsic viscosity (IV) of 0.55 to 0.70 dl/g.

The polyester film may have carboxyl end groups of 40 equivalents/ton (eq/t) or less. Specifically, the polyester film may have a carboxyl end group of 20 to 40 equivalents/ton (eq/t). The term "equivalent/ton, eq/t", which is a unit of the terminal carboxyl group, refers to a molar equivalent of a carboxyl group per ton of the polyester resin.

The polyester film may have an average thickness of 30 to 400 μm. Specifically, the polyester film may have an average thickness of 40 to 300 μm, or 50 to 200 μm.

solar cell module

The solar cell module of the embodiment includes the polyester film for the solar cell back sheet.

1 and 2, the solar cell module 10 includes a solar cell 11 made of amorphous or polycrystalline silicon; one or more encapsulant sheets (12, 12') stacked on at least one surface of the solar cell 11; and a film 13 for a back sheet laminated on one surface of any one of the encapsulant sheets. As a specific example, the solar cell module 10 includes a transparent protective substrate 14 , a first encapsulant sheet 12 , one or more solar cells 11 to which electrodes are connected, a second encapsulant sheet 12 ′, and The back sheet film 13 may be sequentially stacked. The film 13 for the back sheet may be the polyester film for the back sheet of the solar cell described above.

Such a solar cell module 10 is processed (heating and pressurized) after stacking the constituent layers including the solar cell 11, the encapsulant sheets 12 and 12' and the film 13 for the back sheet in order. may be manufactured, and here, as the film 13 for the back sheet, the polyester film for the solar cell back sheet described above may be used.

The solar cell 11, the encapsulant sheets 12 and 12', and the transparent protective substrate 14 constituting the solar cell module 10 may be appropriately selected and used in general.

However, the solar cell backsheet of the embodiment is not limited to the above-described structure, and can be variously modified as necessary.

[Example]

Hereinafter, the present invention will be described in more detail by way of Examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example 1. Solar cell for back seat Polyester film production

The surface layer (layer A) is 94 wt% of PET (polyethylene terephthalate, intrinsic viscosity (IV): 0.72 dl/g, weight average molecular weight: 35,000 g/mol) and _{6 wt% of TiO 2} (average particle size: 0.2 μm) with an extruder put in Thereafter, 0.2 parts by weight of a monofunctional epoxy-based compound (momentive, Cardura E10P) was supplied onto the extruder through a feeder and melt-extruded at 280°C.

In addition, the base layer (layer B) is an extruder with 95.5 wt% of PET (polyethylene terephthalate, intrinsic viscosity (IV): 0.71 dl/g, weight average molecular weight: 40,000) and _{4.5 wt% of TiO 2} (average particle size: 0.2 μm) put in Thereafter, 0.2 parts by weight of a monofunctional epoxy-based compound (momentive, Cardura E10P) was supplied on the extruder through a feeder and melt-extruded at 280°C.

The resin composition melted by each extruder was joined using a three-layer feed block device, and the layer A/layer B/layer A was molded into a laminated film so as to have a thickness ratio of 1:8:1. Further, the laminated film was solidified by cooling with a cooling drum having a surface temperature of 25°C, and then stretched 3.1 times in the longitudinal direction (longitudinal direction) at 90°C. While supporting both ends of the film stretched in the longitudinal direction with clips, it was induced by a tenter and stretched 3.7 times in the direction perpendicular to the length (transverse direction) in an atmosphere heated to 130°C. Thereafter, heat setting was performed in an atmosphere heated to 220° C. in a tenter, and 4% relaxation was performed in the transverse direction to prepare a film for a back sheet having an average thickness of 165 μm.

Example 2 to 6 and comparative example One.

A film for a back sheet was prepared in the same manner as in Example 1, except that the content of the components shown in Table 1 was used.

A floor B floor TiO ₂ content Additives (parts by weight) TiO ₂ content Additives (parts by weight) Example 1 6% by weight 0.2 4.5 wt% 0.2 Example 2 9% by weight 0.0 4.5 wt% 0.0 Example 3 9% by weight 0.2 4.5 wt% 0.2 Example 4 9% by weight 0.5 4.5 wt% 0.5 Example 5 9% by weight 1.0 4.5 wt% 1.0 Example 6 9% by weight 1.5 4.5 wt% 1.5 Example 7 8% by weight 0.2 4% by weight 0.2 Example 8 10% by weight 0.2 4.5 wt% 0.2 Example 9 8% by weight 0.2 5% by weight 0.2 Comparative Example 1 12% by weight 0.2 4.5 wt% 0.2 Comparative Example 2 9% by weight 0.2 2% by weight 0.2 Comparative Example 3 9% by weight 0.2 2.5% by weight 0.2 Comparative Example 4 10% by weight 0.2 4% by weight 0.2

Experimental example 1. Measurement of film properties

Physical properties were measured for the polyester films prepared in Examples 1 to 9 and Comparative Examples 1 to 4 or as described below.

(1) Intrinsic Viscosity (IV)

After dissolving the polyester chip at a concentration of 1.2 g/dL in orthochlorophenol at 150 °C, the intrinsic viscosity (dl/g) was measured using a relative viscosity Ubbelohde viscometer in a constant temperature bath at 35 °C.

(2) carboxyl group content of terminal groups

A mixed solution was prepared by dissolving 0.1 g of a polyester film in 5 ml of benzyl alcohol and then adding 5 ml of chloroform. Using the phenol red indicator in the mixed solution

After changing the carboxyl group in the polyester film to -COONa with a 0.1N-NaOH benzyl alcohol solution, the concentration of the carboxyl group in the terminal group was calculated as equivalent/ton by using the 0.1N-NaOH benzyl alcohol solution.

(3) Pressure cooker test (PCT)

After the polyester film was treated for 76 hours at 121° C. and 1.2 bar under pressure test (PCT) conditions, elongation in the MD direction was measured by the method of ASTM D 882.

(4) light transmittance

After the polyester film was cut into 100 mm × 100 mm (width × length), the light transmittance of the film was measured using a Haze-Gardner measuring instrument from Gardner BYK by the method of ASTM D 1003.

(5) delamination

Polyurethane adhesive (manufacturer: Toyo Morton, product name: LIS 7210) is applied on one side of the polyester (PET) film, and PE (polyethylene, melt flow index at 190 ° C: 10 g/10 min) film (average thickness: 50 μm) was attached. After that, the other side of the PE film was attached to the SUS plate (thickness: 1.5 mm) and a 180˚ peeling test was performed. When peeling normally between the PE film and the PET film, delamination was evaluated as ○, and when internal delamination of the PET film occurred, delamination was evaluated as X.

(6) Fairness

The stability of the extrusion process was evaluated by the temperature change and pressure change of the extruder during the process, and the evaluation criteria are as follows:

- Extrusion fairness O : Temperature fluctuation less than 3℃, pressure fluctuation less than 5 kgf/㎠

- Extrusion Fairness △ : Temperature fluctuation 3 to 5° C., pressure fluctuation 5 to 10 kgf/cm2

- Extrusion Fairness X : Temperature fluctuation exceeding 5℃, pressure fluctuation exceeding 10 kgf/cm2

The results of the measurement of the physical properties are shown in Table 2 below.

After PCT treatment
Elongation in MD direction (%) Intrinsic Viscosity (IV)
(㎗/g) carboxyl end group
Amount (equivalent/ton) light transmittance delamination fairness Example 1 33% 0.612 35.4 14.0% ○ ○ Example 2 7% 0.562 50.7 10.0% ○ ○ Example 3 31% 0.626 36.2 9.8% ○ ○ Example 4 38% 0.632 33.7 9.9% ○ ○ Example 5 41% 0.638 31.2 10.2% ○ △ Example 6 44% 0.641 30.5 10.1% ○ X Example 7 35% 0.626 32.4 11.6% ○ ○ Example 8 25% 0.615 34.5 8.2% △ ○ Example 9 28% 0.628 33.3 10.5% ○ ○ Comparative Example 1 32% 0.609 35.3 8.3% X ○ Comparative Example 2 35% 0.630 34.7 13.1% X ○ Comparative Example 3 37% 0.625 35.2 12.3% X ○ Comparative Example 4 32% 0.618 35.9 8.8% X ○

As shown in Table 2, the films of Examples 1 to 9 do not cause delamination, have high elongation in the MD direction after PCT treatment, and have low light transmittance of less than 15%, which is very suitable for application as a solar cell backsheet And it was found.

On the other hand, Comparative Examples 1 to 4 in which the content difference of the white pigment between the A layer and the B layer was 6% or more was not suitable for application as a solar cell backsheet because delamination occurred. In addition, the film of Example 2 not including the additive did not have excellent light transmittance of 10%, and the film of Example 6 including an excess of the additive had poor fairness.

10: solar cell module 11: solar cell
12: first encapsulant sheet 12': second encapsulant sheet
13: film for back sheet 14: transparent protective substrate

Claims (9)

A layer comprising a polyester resin and a white pigment; and
A polyester film comprising a; B layer comprising a polyester resin and a white pigment,
The polyester resin has an intrinsic viscosity (IV) of 0.5 to 0.8 dl / g,
The layer A contains the white pigment in an amount of 6 to 10% by weight based on the total weight of the layer A,
The B layer contains the white pigment in an amount of 4 to 5% by weight based on the total weight of the B layer,
The difference in the content of the white pigment between the layer A and the layer B is less than 6% by weight, a polyester film for a solar cell backsheet.
According to claim 1,
The polyester film is a form in which the A layer and the B layer are co-extruded and laminated in two or three layers, a polyester film for a solar cell back sheet.
According to claim 1,
A polyester film for a solar cell back sheet, wherein the A layer and the B layer each contain a monofunctional epoxy-based compound.
4. The method of claim 3,
A polyester film for a solar cell back sheet, wherein the A and B layers contain a monofunctional epoxy compound in an amount of 0.1 to 1 part by weight based on the total amount of the polyester resin and white pigment of each layer.
4. The method of claim 3,
The monofunctional epoxy-based compound is a glycidyl ester compound, a polyester film for a solar cell backsheet.
6. The method of claim 5,
A polyester film for a solar cell back sheet, wherein the glycidyl ester compound includes a compound represented by the following Chemical Formula 1:
[Formula 1]

In the above formula,
R ₁ to R ₃ are each independently C _1-7 alkyl.
According to claim 1,
A polyester film for a solar cell backsheet, wherein the A layer contains 8 to 10% by weight of a white pigment based on the total weight of the A layer.
According to claim 1,
When the polyester film is treated for 76 hours at 121 ° C. and a pressure test (PCT) condition of 1.2 bar, the polyester film for a solar cell back sheet exhibits a retention rate of 7% or more of elongation in the longitudinal direction.
A solar cell module comprising the polyester film of any one of claims 1 to 8.

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