KR20190044434A - Ethylene vinyl acetate copolymer for solar light, the method of preparing the same, and Encapsulant sheet for solar cell employing the same - Google Patents

Abstract

The present invention relates to an ethylene vinyl acetate copolymer (EVA) resin and a method of preparing the same and, more specifically, to a photovoltaic EVA resin characterized by having less than 10% of high molecular weight component (F_HMW) by GPC-LSD deconvolution measured by GPC-LSD and less than 40% of low molecular weight component (F_LMW), and to a method of preparing the same. To this end, the method of preparing an EVA resin includes a step of inserting 65 to 78 wt% of ethylene monomer and 22 to 35 wt% of vinyl acetate monomer to a reactor, and polymerizing the same at a polymerization temperature of 190 to 250°C, a polymerization pressure of 2,600 to 2,700 kg/cm^2, and a polymerization time of 2 to 5 minutes, wherein a peroxide-based polymerization initiator is a mixture of (A) an alkylperoxy neodecanoate-based compound having 4 to 5 carbon atoms in an alkyl group bonded to peroxide, (B) an alkylperoxy pivalate-based compound having 4 to 5 carbon atoms in the alkyl group bonded to peroxide, and (C) an alkylperoxy hexanoate-based compound having 4 to 5 carbon atoms in the alkyl group bonded to peroxide. A mixing weight ratio of the peroxide-based polymerization initiator is (A): (B): (C) = 30 to 50: 20 to 40: 20 to 40 in a first reaction stage, and a mixing ratio of a peroxide injection material is (A): (B): (C) = 1 to 20: 10 to 30: 50 to 80 in the next reaction stage.

Description

TECHNICAL FIELD [0001] The present invention relates to an ethylene vinyl acetate copolymer resin for solar cell, a method for producing the same, and a sheet for a solar cell encapsulant, the encapsulant sheet for solar cell employing the same,

The present invention relates to an ethylene vinyl acetate copolymer (EVA) resin produced by using a reactor, a method for producing the same, and a sheet for a solar cell encapsulant manufactured using the same, And the crosslinking speed is increased compared to a conventional EVA resin, and a process for producing the same.

The solar cell module used for solar power generation normally uses two sheets of EVA on both sides of the cell in order to protect the cell. In addition, the transparent glass substrate on the side where sunlight is incident and the gas shielding and weathering And laminated with a back sheet.

The EVA sheet needs to be crosslinked to a certain level or more in order to ensure weatherability and heat resistance, and the crosslinking proceeds by the decomposition and crosslinking reaction of the crosslinking agent added in the production of the sheet in the lamination step. The dialkyl peroxide, peroxycarbonate and peroxyketal are mainly used as the crosslinking agent used in the crosslinking reaction. In the case of dialkyl peroxide, the half-life temperature is high and the lamination time is long, Lamination time can be shortened due to low temperature, but commercial use is limited because of the abundant side effects due to rapid crosslinking. Currently, peroxycarbonate is most commercially applied in terms of stability in the lamination process and weatherability in long-term use. However, in order to improve module productivity, there is a need to continuously increase the lamination speed in the industry. Japanese Patent JP2012212267A proposes to increase the crosslinking speed by using an organic peroxide having a low decomposition temperature and shorten the time required for crosslinking and adhesion. However, the use of an organic peroxide having a low decomposition temperature is required to lower the sheet forming temperature in order to prevent decomposition at the time of sheet forming, and therefore, the productivity at the time of sheet production is lowered. Also, The problem of increased yellowing due to an increase in cross-linking agent is not fundamentally solved and is not a fundamental solution.

Korean Patent No. 10-928441 discloses a method of increasing the crosslinking speed by partially using an organic peroxide having a low temperature decomposition temperature. However, this does not solve the problem of early crosslinking occurring in sheet production. Essentially, the inherent properties of EVA resin itself require an intrinsic solution to improve the degree of crosslinking and crosslinking.

It is an object of the present invention to solve the above problems, and it is an object of the present invention to provide an EVA resin sheet which is capable of increasing module productivity and crosslinking speed even when a conventional crosslinking agent is used for lamination of a solar module, EVA resin for a solar cell encapsulant sheet and a method for producing the same.

Another object of the present invention is to provide an EVA resin produced by the above method and an EVA sheet produced using the EVA resin.

In order to achieve the above object, the present invention provides an EVA resin for solar cells, characterized in that the high molecular weight component (F _HMW ) by GPC-LSD deconvolution is less than 10%.

According to another aspect of the present invention, there is provided a process for preparing an ethylene vinyl acetate copolymer resin, comprising the steps of: feeding a vinyl acetate monomer and ethylene vinyl acetate into a reactor; Adding a polymerization initiator comprising two or more peroxide-based polymerization initiators; And a polymerization temperature of 190 to 250 DEG C, a polymerization pressure of 2,600 to 2,700 kg / cm < ² >, and a polymerization time of 2 to 5 minutes, wherein the peroxide type polymerization initiator is (A) An alkyl peroxyneodecanoate compound having 4 to 5 carbon atoms; And (B) an alkylperoxy pivalate compound having 4 to 5 carbon atoms in an alkyl group bonded with a peroxide, and (C) an alkyl peroxyhexanoate compound having 4 to 5 carbon atoms in an alkyl group bonded with a peroxide (B): (C) = 30 to 50:20 to 40:20 to 40 in the first reaction stage and the mixing ratio of the peroxide polymerization initiator to the reaction stage after the first stage (A): (B): (C) = 1 to 20:10 to 30:50 to 80, and the mixing ratio of the peroxide injected product of the ethylene vinyl acetate copolymer resin by the GPC-LSD decolorization _{Wherein the} high molecular weight component (F _HMW ) is less than 10%.

In order to accomplish still another object of the present invention, there is provided a sheet for a solar cell encapsulant made of a polyvinyl acetate copolymer resin according to the present invention.

INDUSTRIAL APPLICABILITY According to the EVA resin production method of the present invention, the crosslinking characteristics of the resin itself are maximized, and when the encapsulant is manufactured by using the same, the crosslinking speed of the encapsulant is higher than that of the conventional encapsulant, thereby increasing module productivity and mass production . In addition, the EVA sheet produced according to the present invention has a high crosslinking ratio, high weather resistance, excellent heat stability, and does not require a crosslinking agent to be added thereto, thereby causing no incidental problems such as yellowing.

1 is a graph showing the GPC-LSD of Example 2 of the present invention and Comparative Examples 1 and 2. Fig.
2 is a graph showing the GPC-LSD deconvolution of the first embodiment of the present invention.
3 is a graph showing the GPC-LSD deconvolution of the second embodiment of the present invention.
4 is a graph showing the GPC-LSD deconvolution of the third embodiment of the present invention
5 is a graph showing GPC-LSD deconvolution of Comparative Example 1 of the present invention.
6 is a graph showing GPC-LSD deconvolution of Comparative Example 2 of the present invention.
7 is a graph showing ODR measurement results of a solar cell encapsulant made of an EVA resin according to an embodiment of the present invention and a comparative example

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

According to an embodiment of the present invention, there is provided an EVA resin for solar cells, characterized in that the high molecular weight component (F _HMW ) of the GPC-LSD deconvolution is less than 10%.

When the ratio of the high molecular weight component (HMW) is 10% or more, the crosslinking ratio in the self-molecule during crosslinking increases due to the increase of the long-chain branch and the effective crosslinking ratio to form a net work with the whole resin is lowered.

According to one embodiment of the present invention, it is preferable that the ratio of the low molecular weight component (LMW) is less than 40%. When the low molecular weight component (LMW) is 40% or more, the cross-linking between the small molecules is increased, and the cross-linking rate is lowered and the cross-linking rate is lowered.

In the present invention, the light scattering chromatogram of the PVA EVA resin measured by gel permeation chromatography (GPC) may appear in bi-modal form.

Chromatogram deconvolution represents a polymer of two or more components that can be present as a hump, shoulder, or tail relative to the molecular weight distribution (MWD) of a polymer of one component.

According to one embodiment of the present invention, the PVA EVA resin preferably has a weight average molecular weight (Mw) of 60,000 to 100,000 g / mole and a molecular weight distribution (Mw / Mn) of 4.0 to 4.5 as measured by GPC-LSD . If the molecular weight distribution is less than 4, the workability, especially the neck in characteristics, will increase. If the molecular weight distribution is larger than 4.5, the elasticity increases and the shrinkage increases in the lamination process.

According to one embodiment of the present invention, it is preferable that the ethylene vinyl acetate copolymer contains 22 to 35% by weight of vinyl acetate monomer, and the melt viscosity measured at 125 ° C. and 2.16 kg under ASTM D 1238 The index (MI) is preferably 0.4 to 4.0.

When the content of vinyl acetate is less than 22% by weight, it is not preferable because it is not preferable because it is not preferable because it has low light transmittance due to low cell elasticity and flexibility, If the content is more than 10% by weight, not only the electrical insulation is deteriorated but also the moisture permeability is increased and the amount of acetic acid generated is increased to seriously damage the photovoltaic module and the mechanical properties thereof are deteriorated, which is not preferable for the photovoltaic encapsulant.

If the melt index is less than 0.4, processing is difficult. If the melt index is more than 4.0, the resin flows out of the module during lamination, which is not preferable.

According to one embodiment of the present invention, there is provided a process for producing an ethylene vinyl acetate copolymer resin, comprising the steps of: feeding a vinyl acetate monomer and ethylene vinyl acetate into a reactor; Adding a polymerization initiator comprising two or more peroxide-based polymerization initiators; And a polymerization temperature of 190 to 250 캜, a polymerization pressure of 2,600 to 2,700 kg / cm ² , and a polymerization time of 2 to 5 minutes; Wherein the peroxide type polymerization initiator is (A) an alkyl peroxyneodecanoate compound having 4 to 5 carbon atoms in an alkyl group bonded to peroxide; And (B) an alkylperoxy pivalate compound having 4 to 5 carbon atoms in an alkyl group bonded with a peroxide, and (C) an alkyl peroxyhexanoate compound having 4 to 5 carbon atoms in an alkyl group bonded with a peroxide (A): (B): (C) = 30 to 50:20 to 40:20 to 40 in the first reaction stage, and the mixing ratio by weight of the peroxide polymerization initiator in the second reaction stage is (A): (B): (C) = 1 to 20:10 to 30:50 to 80, and the ratio of the polymer component (F) by GPC- LSD deconvolution of the ethylene vinyl acetate copolymer resin _HMW ) is less than 10%. The present invention also provides a method for producing an ethylene vinyl acetate copolymer resin.

The ethylene vinyl acetate copolymer (EVA) resin of the present invention is preferably polymerized in a reactor composed of at least two reactors, and is preferably polymerized by injecting ethylene and vinyl acetate only into a single-stage reactor coupled with a monomer inlet in the reactor.

The reactor composed of at least two or more reactors may be referred to as a two-stage reactor or a three-stage reactor in accordance with the number of reactors.

In addition, the reactor may include a monomer injection port connected to one end and an ejector for a copolymer resin bonded to the other end.

A peroxide-based polymerization initiator used as an initiator of the polymerization reaction is injected into the reactor from which the reaction is initiated. The polymerization temperature rapidly increases due to the reaction heat from the position where the peroxide-based polymerization initiator is injected, the ethylene monomer, the vinyl acetate monomer and the produced polymer flow along the reactor, the heat is removed by heat exchange with the cooling water from the wall surface, Is controlled. Once the reactant and the polymer have passed through the reactor, they are transferred to the next stage reactor. In the next stage, the peroxide mixture, which is a polymerization initiator, is injected to further advance the reaction. However, it is preferable that monomers such as ethylene and vinyl acetate are injected at the first stage of the reaction but not at the reaction stage. When the monomer is injected after the first reaction step, the molecular weight distribution increases and the degree of crosslinking is lowered. Thereafter, the polymer and the unreacted monomer are finally discharged to the reactor outlet, separated, and passed through an extruder to obtain a resin in the form of a pellet.

In the method for producing an ethylene vinyl acetate copolymer resin of the present invention, the polymerization initiator comprising two or more peroxide type polymerization initiators is preferably added at a concentration of 1,000 to 3,000 ppm. When the concentration of the peroxide-based polymerization initiator is less than 1,000 ppm, the reaction temperature during polymerization is low and the conversion to ethylene vinyl acetate copolymer resin is low and the molecular weight control is difficult to control. When the concentration is more than 3,000 ppm, The resin may be decomposed due to high temperature, and decomposition of vinyl acetate may cause acetic acid to corrode the reactor.

In the process for producing the EVA copolymer resin of the present invention, specific examples of the alkyl peroxyneodecanoate compound (A) that can be used as the initiator include t-amyl peroxyneodecanoate, tert-butyl peroxyneodecanoate (TBPND), etc. Specific examples of the alkyl peroxypivalate compound (B) include t-amyl peroxypivalate, t-amyl peroxypivalate, Butyl peroxypivalate, and specific examples of the alkylperoxyhexanoate compound (C) include t-amylperoxy-2-ethylhexanoate, t-butyl Tert-butylperoxy-2-ethylhexanoate (TBPO), tert-butylperoxy-3 , 5,5-trimethylhexanoate (TBPIN), and the like.

As the peroxide polymerization initiator, those which can be more preferably used in the present invention include tert-butyl peroxyneodecanoate (TBND), tert-butyl peroxypivalate (TBPV), tert-butyl peroxy (TBPO) and tert-butylperoxy-3,5,5-trimethylhexanoate (TBPIN). Each of the peroxides is diluted in a paraffinic solvent, and each peroxy Mixture is used.

The peroxide mixture used in the first stage in the two or more peroxide polymerization initiators used in the present invention is preferably an alkyl peroxyneodecanoate compound (A) having 4 to 5 carbon atoms in the alkyl group: an alkyl group (A): (B): (A) an alkyl peroxy pivalate compound (B) having 4 to 5 carbon atoms and an alkyl peroxyhexanoate compound (C) having 4 to 5 carbon atoms in an alkyl group (A): (B): (C) = 1 to 20: 10 to 30: 40 to 50:20 to 40:20 to 40: It is preferably 50 to 80. If the mixing ratio of the alkylperoxyhexanoate compound in the first stage is less than 20, the molecular weight distribution will be widened. If the mixing ratio is more than 40, the reaction control problem may occur excessively. When the specific gravity of the alkyl peroxyneodecanoate compound exceeds 20% in the mixing ratio in the two-stage reaction, the production yield is lowered, which is not preferable. Also, when the mixing weight ratio between the peroxide type polymerization initiators is out of the above range, molecular weight control and desired crosslinking properties are not exhibited, which is not preferable.

In the process for producing an EVA copolymer resin of the present invention, it is preferable that the alkyl peroxyneodecanoate compound (A) in the peroxide initiator mixture is tert-butyl peroxyneodecanoate (TBND) Butyl peroxypivalate (TBPV) is most preferably used as the alkyl peroxypivalate compound (B), and tert-butyl peroxy-2- It is most preferable to use one selected from ethylhexanoate (TBPO) or tert-butylperoxy-3,5,5-trimethylhexanoate (TBPIN).

In the method for producing an ethylene vinyl acetate copolymer resin of the present invention, the polymerization temperature is preferably 190 to 250 ° C. If the polymerization temperature is less than 190 캜, the conversion to EVA is low and the desired molecular weight and molecular weight distribution can not be obtained, which is undesirable. If it exceeds 250 캜, it is difficult to obtain a desired molecular weight.

In the method for producing an ethylene vinyl acetate copolymer resin of the present invention, the polymerization pressure is preferably 2,600 to 2,700 kg / cm ² . If the polymerization pressure is less than 2,600 kg / cm ^{2, the} reaction is insufficient and the stability of the operation is low, which is undesirable. When the polymerization pressure is more than 2,700 kg / cm ² , the stability of the high-

In the production method of the ethylene vinyl acetate copolymer resin of the present invention, the polymerization time is preferably 2 to 5 minutes. If the polymerization time is less than 2 minutes, the conversion to EVA resin is low and the molecular weight is low, which is undesirable. If the polymerization time exceeds 5 minutes, the pressure can not be controlled and gel is generated.

The present invention provides an ethylene vinyl acetate copolymer resin produced by a process for producing an ethylene vinyl acetate copolymer resin.

The ethylene vinyl acetate resin produced by the polymerization conditions had a melt index of 0.4 to 4.0 g / 10 min measured at a load of 2.16 kg at 125 DEG C according to ASTM D1238, and a weight average molecular weight (Mw) measured by GPC-LSD of 60,000 To 100,000 g / mole, a molecular weight distribution (Mw / Mn) of 4.0 to 4.5, and an Mz / MW value of 2.0 to 2.5.

If the molecular weight distribution is less than 4.0, the load during extrusion processing becomes high and the neck in phenomenon after die occurs. When the molecular weight distribution exceeds 4.5, elasticity increases and shrinkage increases in the lamination process And the light transmittance is lowered.

In the present invention, the melt index of the ethylene vinyl acetate copolymer resin is preferably 0.4 to 4 g / 10 min at 250 DEG C and 2.16 kg of ASTM D1238.

If the ethylene vinyl acetate copolymer resin has a melt index of less than 0.4 g / 10 min, the extrusion processability is poor, and if it is more than 4 g / 10 min, an edge flow out of the glass during lamination is generated.

In the present invention, the ethylene vinyl acetate copolymer resin preferably has a mass average molecular weight (Mw) of 60,000 to 100,000 g / mole. When the ethylene vinyl acetate copolymer resin is less than 60,000 g / mol, The transparency is poor and a lump gel is generated to lower the light transmittance and to cause microcracking during lamination.

The present invention provides a sheet for a solar cell encapsulant made of an ethylene vinyl acetate copolymer resin. The sheet for the solar cell encapsulation material may be a sheet for the front surface of the solar cell encapsulant or a sheet for the back surface.

The EVA sheet is obtained by mixing various additives such as a crosslinking agent, a crosslinking aid, a silane coupling agent, an antioxidant, a light stabilizer, and an ultraviolet absorber to the EVA resin and then melting the EVA resin at a temperature not lower than the melting temperature of the EVA resin and lower than the decomposition temperature of the organic peroxide And kneaded into a sheet form.

In the present invention, the sheet for a solar cell encapsulant comprises 0.3 to 1.0 part by weight of a crosslinking agent, 0.3 to 1.0 part by weight of a crosslinking auxiliary, 0.3 to 1.0 part by weight of a silane coupling agent, 1.0 to 5.0 parts by weight.

The crosslinking agent is preferably tert-butylperoxy-2-ethylhexylcarbonate (TBEC), and the crosslinking aid is preferably triallylisocyanurate (TAICROS). The silane coupling agent is preferably methacryloxypropyltrimethoxysilane.

The lamination process for producing a solar module using the encapsulant is performed by laminating a transparent glass substrate, an upper EVA sheet, a cell, a lower EVA sheet, and a gas barrier back sheet, and heating and crosslinking them under specific temperature and pressure . In order to obtain the target cross-linking ratio in this process, a lamination process at a certain temperature is required for a certain period of time, and the crosslinking time applied to the process requires the productivity of the whole module production.

In the present invention, 0.5 parts by weight of a crosslinking agent, tert-butylperoxy-2-ethylhexyl carbonate (TBEC) and triallyl isocyanurate (TAICROS), is added to the ethylene vinyl acetate copolymer resin, Oscillation Disk Rheometer) to the time sweep (Time sweep) to measure the change in the torque value. The MH-ML value, which is the difference between the maximum value and the minimum value, is 2.0dNm or more (See Table 2 and Fig. 7).

The MH-ML value of the ethylene vinyl acetate copolymer resin is preferably 2.0 dNm at 150 ° C, and when it is less than 2.5, the heat resistance is poor due to insufficient crosslinking, There is a concern.

The degree of crosslinking of the solar cell encapsulant is also measured by the wet process of xylene soluble in addition to the above-mentioned ODR. In this case, the weight ratio of the xylene-insoluble portion in the total sample weight is calculated by the degree of crosslinking, and the crosslinking agent is presumed to have a degree of crosslinking of about 85%, and the lamination conditions are adjusted accordingly. When the degree of crosslinking is as low as 83% or less, the long-term properties of the module deteriorate. When the degree of crosslinking is as high as 90% or more, the hardness of the sheet increases, When the degree of crosslinking is low, there is a problem in that an additional crosslinking agent must be added or the lamination time and temperature must be increased. In this case, yellowing and bubbling of the sheet occur due to increase of the residual crosslinking agent, Is not preferable because the productivity of the module is lowered.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples.

How to measure property

The physical properties of the EVA resin produced in Examples 1 to 2 and Comparative Examples 1 to 3 were measured by the following methods and standards.

1) Melt flow index measurement: measured at 125 DEG C and 2.16 kg according to ASTM D1238.

2) Measurement of VA content: Measured by Fourier Transform Infrared Spectroscopy (FT-IR).

3) GPC-LSD: The gel permeation chromatography (GPC) used herein was a 150 ° C high temperature chromatograph of Polymer Laboratories Model PL-220 equipped with a differential refractometer (RI). As a further detector, the light scattering detector used a dual angle system with a wavelength of 658 nm and capable of measuring two (15 °, 90 °) Rayleigh scattering angles. Three 30 cm long olexis columns and one 7.5 cm length olexis guard column packed with 13 micron bead with mixed pore size or appropriate high temperature GPC columns at the same level were used . The sample carousel section is operated at 120 [deg.], The column section is operated at 150 [deg.], And the residence time in the temperature parallel section before injection is set to 5 minutes. The developing solvent used for chromatography and the sample preparation solvent contained trichlorobenzene (TCB) in an amount of 125 ppm of antioxidant in a solvent, and the solvent used was sparged with nitrogen. The flow rate through the GPC is set at 1 ml / min. The light scattering detector and the concentration detector are arranged in series. The correction of the retention time delay (IDD), the light scattering detector, and the concentration detector according to the arrangement of the two detectors is linear with a molecular weight distribution of approximately 1 or more and a molecular weight Polystyrene homopolymer standards were analyzed. In order to ensure reliability, at least three samples were prepared and injected and analyzed. The polystyrene standards were purchased from Polymer Laboratories and were dissolved at a concentration of 1 mg / ml at 140 < 0 > C for 2 hours with slow stirring and then injected.

4) GPC-LSD deconvolution: Ethylene vinyl acetate copolymer with long-term grinding can be distinguished by analyzing the GPC-LSD chromatogram response curve. Measurements are performed using a light scattering (LS) detector reaction on samples that have been processed by GPC, which is typically calibrated over the molecular weight range of the sample. The LS chromatogram of the concentration-normalized sample in the above-described method shows that the polymer of one component can be a two or more component polymer that can exist as a hump, shoulder or tail as compared to the MWD of the polymer of the other component, Can be separated into the most probable peaks for the corresponding molecular weight component (Figures 2, 3, 4). Orin 9.1 software was used for peak separation. The spread of the peak may vary depending on the column conditions, the concentration and molecular weight of the injected sample, the flow rate, and the like. In addition, multiple decomposition algorithms can derive various results depending on the assumptions and methods used. The algorithm used in the present invention is the most probable of the three (high molecular weight component-HMW, medium molecular weight component-MMW, low molecular weight component-LMW) for the LS chromatogram separated in the above described analysis conditions under the following conditions Lt; RTI ID = 0.0 > molecular weight < / RTI > The Gaussian function (gauss) was used as the curve fitting model and the R ² value of the cumulative fit peak created by recombining the three fitting curves applied was based on the condition of 0.999 or more.

The area obtained by performing the integration for each separated peak is divided by the area for the whole peak area, and the area ratio for each peak is calculated.

Equation 1

Sheet manufacturing conditions

To 100 parts by weight of the EVA resin of Examples 1 to 2 and Comparative Examples 1 to 3, 0.3 parts by weight of Chimassorb 81 (2-hydroxy-4-octyloxy-benzophenone) of Shiba and UV absorbing agent Tinuvin , And 0.1 part by weight of bis (2,2,6,6-tetramethyl-4-piperidinyl sebacate) as a crosslinking agent, 0.5 part by weight of Lewerox TBEC (t-butyl-2-ethylhexyl monoperoxycarbonate) , 0.5 part by weight of TAICROS (triallyl isocyanurate) from Ebonic Co., Ltd., and 0.3 part by weight of OFS 6030 (methacryloxypropyltrimethoxysiloxane) of Dow Corning Co. as a silane coupling agent were blended, and the screw diameter was 40 mm And a T-die width of 400 mm, a sheet for an encapsulating material having a thickness of 450 탆 was produced at an extruder temperature of 100 캜 and a screw rotating speed of 50 rpm.

1) MH-ML (Maximum Torque-Minimum Torque) Measurement: Crosslinking speed and degree of crosslinking were measured using an ODR (Oscillation Disk Rheometer) apparatus of Alpha technology. In the case of sheets for additives, the crosslinking speed and degree of crosslinking were measured by applying a time frequency at 150 ° C, which is the same temperature as the lamination process. The measurement conditions were frequency 1.67 Hz and angle 6.98%.

2) Measurement of Wet Crosslinking: The lower use sheet prepared in the above manner was partially sampled and pressured under a vacuum of 6 minutes and a pressure of 1 bar for 11 minutes using a laminator at a temperature of 150 ° C for crosslinking. The crosslinked sheet samples were dried for 4 hours and 12 hours in boiling Xylene, and weight loss was measured. Xylene insoluble was calculated to determine the degree of crosslinking.

Example  One

28% by weight of a vinyl acetate monomer was added to 72% by weight of an ethylene monomer, and tert-butyl peroxyneodecanoate (TBND), tert-butyl peroxypivalate (TBPV) and tert Butyl peroxy-2-ethylhexanoate (TBPO) at a weight ratio of 45:30:25. In the second stage, tert-butyl peroxyneodecanoate (TBND), tert-butyl peroxypivalate (TBPV) and tert-butyl peroxy-2-ethylperoxyhexanoate (TBPO) were mixed at a ratio of 10:20:70 by weight and measured at 2000 ppm relative to ethylene and vinyl acetate monomer. The EVA resin was prepared under polymerization conditions of a polymerization pressure of 2650 kg / cm 2, a polymerization temperature of 230 ° C. and a polymerization time of 4 minutes. The F _HMW and the F _LMW by GPC-LSD deconvolution were 8.2% and 28.6%, respectively.

Example  2

28% by weight of a vinyl acetate monomer was added to 72% by weight of an ethylene monomer, and tert-butyl peroxyneodecanoate (TBND), tert-butyl peroxypivalate (TBPV) and tert (TBPO) and tert-butylperoxy-3,5,5-trimethylhexanoate (TBPIN) in a weight ratio of 40: 30: 25: 5 tert-butyl peroxyneodecanoate (TBND), tert-butyl peroxypivalate (TBPV), tert-butyl peroxy-2-ethylhexanoate (TBPO) (TBPIN) at a weight ratio of 10: 20: 60: 10 and metering at 2000 ppm with respect to ethylene and vinyl acetate monomer. The high pressure pump was continuously injected into the reactor, and polymerization pressure was 2650 kg / The EVA resin was prepared under the conditions of a temperature of 240 ° C. and a polymerization time of 4 minutes. The F _HMW by GPC-LSD deconvolution was 8.0%, and the F _LMW 37.2%.

.

Example  3

28 wt% of a vinyl acetate monomer was added to 72 wt% of an ethylene monomer and divided into 70 wt% and 70 wt% of a reactor, and as a radical generating initiator, tert-butyl tin peroxide neodecanoate (TBND) tert-butyl peroxypivalate (TBPV) and tert-butyl peroxy-2-ethylhexanoate (TBPO) were fed at a ratio of 45:30:25 in a weight ratio, tert-butyl peroxyneodecano Butyl peroxypivalate (TBPV), tert-butyl peroxy-2-ethylhexanoate (TBPO) in a weight ratio of 15: 25: The EVA resin was prepared under polymerization conditions of polymerization pressure of 2650 kg / cm2, polymerization temperature of 230 ℃ and polymerization time of 4 minutes. The F _HMW by GPC-LSD deconvolution was 5.6% and F _LMW is 34.2%.

Comparative Example  One

Polymerization was carried out in the same manner as in Example 1 except that tertiary butyl peroxyneodecanoate (TBND), tert-butyl peroxypivalate (TBPV) and tert-butyl peroxy-2- Butyl peroxy neodecanoate (TBND), tert-butyl peroxypivalate (TBPV), tert-butyl peroxide (TBPO) Peroxy-2-ethylhexanoate (TBPO) at a weight ratio of 30:10:60. The F _HMW by GPC-LSD deconvolution was 12.9% and the F _LMW by 23.2%.

Comparative Example  2

The resin used in Comparative Example 2 is an EVA product for solar light by TPC (EVA commercial product, product name VF024). The VA content was 28.6% and the melt index (MI) measured at 125 ° C. and 2.16 kg under the load of ASTM D 1238 was 3.3, which was comparable to that of Example 2 using the EVA resin for solar PV having the same VA content and melt index Respectively. F _HMW by GPC-LSD deconvolution is 15%, and F _LMW is 59.4%.

Example 1 Example 2 Example 3 Comparative Example 1 Polymerization conditions Monomer injection form single single dual single The ethylene monomer (T / hr) 72 72 72 72 Vinyl acetate monomer (T / hr) 28 28 28 28 Polymerization temperature (캜) 230 240 230 240 Pressure (kg / cm2) 2650 2650 2650 2650 Polymerization time (min) 4 4 4 4 Peroxide (ppm) 2,000 2,000 2,000 2,000 1 stage peroxide weight ratio
(weight%) TBND 45 40 45 40 TBPV 30 30 30 30 TBPO 25 25 25 10 TBPIN 5 5 2 step peroxide weight ratio
(weight%) TBND 10 10 10 30 TBPV 20 20 20 10 TBPO 70 60 70 60 TBPIN 10

The physical properties of the EVA resin prepared under the conditions of the examples and the comparative examples were measured by the above physical property measuring method, and the solar cell encapsulation material sheet was formed using the EVA resin thus prepared to evaluate the physical properties related to the sunlight. Table 2 shows the results.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Melt Index M.I (g / 10 min) 2.5 3.4 2.1 3.1 3.3 VA VA content (% by weight) 28.1 28.3 28.2 28.7 28.6 GPC Mn (g / mole) 20600 20,300 19,300 18800 9,700 Mw (g / mole) 82500 76,500 84,000 79900 123,900 MWD (Mw / Mn) 4.0 3.8
4.4 4.2 12.8 GPC-LSD
deconvolution (%) chromatogram type Bimodal Bimodal Bimodal Bimodal Monomodal F _HMW 8.2 8.0 5.6 12.9 15.0 F _MMW 63.2 54.8 60.2 63.9 25.6 F _LMW 28.6 37.2 34.2 23.2 59.4 ODR
(150 DEG C) Torque
(dNm) Min S '(ML) 0.048 0.036 0.048 0.053 0.046 Max S '(MH) 2.23 2.41 2.10 2.01 1.87 MH-ML (degree of crosslinking) 2.19 2.38 2.05 1.96 1.82 Cross-linking time (min)
@ 90% cure 10.40 10.74 10.67 11.20 11.27 Crosslinking rate Xylene insolubility (wt%) 87.5 85.7 86.1 82.0 80.7

As shown in Table 2, in the case of the EVA resin of the examples prepared by the method of the present invention, the light scattering chromatogram measured by GPC appears as a bimodal shape, and a high molecular weight component (HMW) and a low molecular weight component (LMW) ratio was less than 10% and less than 40%, respectively, and the results of the ODR (Oscillation Disk Rheometer) measurement of the sheet prepared by adding the crosslinking agent and additives used for the solar cell sheet showed that the value of MH-ML was 2.0 dNm or more , The crosslinking time was less than 11 minutes, and the value of Xylene insoluble was more than 85%, showing relatively fast crosslinking time and high degree of crosslinking as compared with the resins of Comparative Examples 1 and 2.

This rapid crosslinking speed and relatively high crosslinking ratio can reduce the amount of crosslinking agent used and reduce the lamination time, thereby improving the module productivity and improving the long-term properties of the module.

In the comparative example, the MWD is in the range of 4.0 to 4.5 in the range of 4.2, but the degree of crosslinking is low because the high molecular weight component (F _{HMW )} is 10% or more.

Claims (12)

And the high molecular weight component (F _HMW ) by GPC-LSD deconvolution is less than 10%. The method according to claim 1,
And the low-molecular-weight component (F _LMW ) of the EVA resin for solar PV by GPC-LSD decolorization is less than 40%. The method according to claim 1,
Wherein the PVA EVA resin has a molecular weight distribution (Mw / Mn) of 4.0 to 4.5. A process for producing an ethylene vinyl acetate copolymer resin,
Introducing vinyl acetate monomer and ethylene vinyl acetate into the reactor;
Adding a polymerization initiator comprising two or more peroxide-based polymerization initiators; And
A polymerization temperature of 190 to 250 캜, a polymerization pressure of 2,600 to 2,700 kg / cm ² , and a polymerization time of 2 to 5 minutes; Lt; / RTI >
The peroxide type polymerization initiator may be (A) an alkyl peroxyneodecanoate compound having 4 to 5 carbon atoms in an alkyl group bonded to peroxide; And (B) an alkylperoxy pivalate compound having 4 to 5 carbon atoms in an alkyl group bonded with a peroxide, and (C) an alkyl peroxyhexanoate compound having 4 to 5 carbon atoms in an alkyl group bonded with a peroxide Lt; / RTI >
The mixing ratio by weight of the peroxide type polymerization initiator is (A): (B): (C) = 30 to 50:20 to 40:20 to 40 in the first reaction stage
(B): (C) = 1 to 20:10 to 30:50 to 80 in the mixing ratio of peroxide in the second reaction stage,
Wherein the ethylene vinyl acetate copolymer resin has a high molecular weight component (F _HMW ) by GPC-LSD deconvolution of less than 10%. 5. The method of claim 4,
Wherein the ethylene vinyl acetate copolymer resin has a low molecular weight component (F _LMW ) of less than 40% by GPC-LSD deconvolution. 5. The method of claim 4,
Wherein the PVA EVA resin has a molecular weight distribution (Mw / Mn) of 4.0 to 4.5. 5. The method of claim 4,
Wherein the alkyl peroxyneodecanoate compound (A) in the peroxide initiator mixture is tert-butyl peroxyneodecanoate (TBND) and the alkyl peroxy pivalate compound (B) is tert-butyl peroxy (TBPV), and the alkylperoxyhexanoate compound (C) is a compound selected from the group consisting of tert-butylperoxy-2-ethylhexanoate (TBPO) or tert- butylperoxy-3,5,5-trimethylhexano (TBPIN). ≪ RTI ID = 0.0 > 11. < / RTI > 5. The method of claim 4,
Wherein the polymerization initiator is added at a concentration of 1,000 to 3,000 ppm. ≪ RTI ID = 0.0 > 11. < / RTI > A sheet for a solar cell encapsulant, which is produced by the EVA resin for solar light according to any one of claims 1 to 3. 10. The method of claim 9,
Wherein the sheet for a solar cell encapsulant comprises 0.3 to 1.0 parts by weight of a crosslinking agent relative to 100 parts by weight of the ethylene vinyl acetate copolymer resin; 0.3 to 1.0 part by weight of a crosslinking auxiliary; 0.3 to 1.0 part by weight of a silane coupling agent; And a sheet for a solar cell encapsulation material. 10. The method of claim 9,
Wherein the sheet for a solar cell encapsulation material has a torque change value (MH-ML) measured at 150 캜 by an ODR (Oscillation Disk Rheometer) of 2.0 dNm or more. 10. The method of claim 9,
Wherein the crosslinking degree is at least 85% by xylene solubility after crosslinking at 130 to 160 ° C.

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