KR20120015551A - Method for producing ethylene vinyl acetate copolymer resin for solar cell encapsulant sheet and its resin - Google Patents

Abstract

The present invention relates to a method for producing an ethylene vinyl acetate copolymer (hereinafter referred to as EVA) resin for a solar cell encapsulant sheet, and more particularly, to 72-68 wt% ethylene monomer and 28 to 28 vinyl acetate monomer in a tubular reactor. 32 to 50% by weight of a peroxide initiator consisting of a mixture of at least one selected from an alkylperoxy ethylhexanoate compound and a dialkyl peroxide compound in an alkylperoxy pivalate compound is 50 to 1,000. After adding at a ppm concentration, the present invention relates to a method for producing an EVA resin comprising the step of polymerizing for 2 to 20 minutes at a pressure of 2500 ~ 3000kg / ㎠ at 200 ~ 260 ℃ and EVA resin produced by the method. The EVA resin of the present invention has a Mz of 250,000 g / mole or less, a molecular weight distribution of 4.0 or less, a vinyl acetate (VA) content of 25 to 32% by weight, and a melt index of 6 at a temperature of 190 ° C. and a load of 2.16 kg. Characterized in that it is ~ 30g / 10 minutes. According to the EVA resin manufacturing method of this invention, the resin for solar cell sealing material sheets excellent in transparency and adhesiveness can be easily provided.

Description

Method for manufacturing ethylene vinyl acetate copolymer resin for solar cell encapsulant sheet and its resin {Method for manufacturing ethylene vinyl acetate copolymer for solar cell encapsulant and the resin obtained by the same}

The present invention relates to a method for producing an ethylene vinyl acetate copolymer (EVA) resin for a solar cell encapsulant sheet using a tubular reactor, and to an EVA resin having excellent transparency and adhesiveness.

Solar cell modules used in solar power generation are usually EVA sheets on both sides to protect the cells, and additionally laminated on transparent glass substrates on the side where solar light is incident and sheets on the other side which have excellent gas barrier and weather resistance. . In the laminating method, the transparent glass substrate, the EVA sheet, the cell, the EVA sheet, and the gas barrier sheet are laminated, and then heated and crosslinked at a specific temperature and pressure to bond.

In general, EVA sheet for solar cell encapsulant requires high transparency, adhesiveness, and weather resistance after crosslinking. Therefore, high purity EVA resin with extremely low density of fish oil or foreign substances in resin is used, and crosslinking agent, crosslinking aid, silane Various additives such as coupling agents, antioxidants, light stabilizers, and ultraviolet absorbers are mixed and melt-kneaded at the melting temperature of the EVA resin and lower than the decomposition temperature of the organic peroxide, which is a crosslinking agent.

The commonly used EVA resin is a resin prepared by using an autoclave reactor, the vinyl acetate content is 25 ~ 33% by weight, the higher the vinyl acetate content, the higher the transparency, but poor electrical insulation, sticky handling Is difficult, and the resin viscosity is low during melting, so that the resin is easily leaked from the glass substrate to the back sheet during lamination, and various additives that compensate for the disadvantages of the sheet manufacturing must be mixed or In order to prevent the blocking, a separate method should be taken. On the other hand, the low vinyl acetate content has a low blocking and water vapor transmission rate of the sheet, and excellent electrical insulation but poor transparency and adhesion. There was a problem that must be prescribed in a relatively excessive amount of various additives.

On the other hand, the EVA resin for solar cell encapsulation material manufactured by using an autoclave reactor has a wide molecular weight distribution and a large Z average molecular weight (Mz), so that the transparency required for solar cell encapsulation material and the density of the presence of fish or foreign substances in the resin It was difficult to secure a high quality resin with low.

SUMMARY OF THE INVENTION An object of the present invention is to prepare an EVA resin for use in a solar cell encapsulant sheet having improved transparency and adhesion compared to a resin using an autoclave reactor having the same vinyl acetate content using a tubular reactor to solve the above problems. To provide a way.

Still another object of the present invention is to provide an EVA resin suitable for use in a solar cell encapsulant sheet having improved transparency and adhesion, and having a low density of fisheye.

In order to achieve the above object of the present invention, the manufacturing method of the EVA resin for solar cell encapsulant sheet according to the present invention, based on the total weight of the monomer in the tubular reactor 72 ~ 68% by weight of ethylene monomer and 28 ~ vinyl acetate monomer 32 wt% is added, and at least one selected from alkylperoxy ethylhexanoate compound and dialkyl peroxide compound in 15-20 wt% of the alkylperoxy pivalate compound based on the total weight of the peroxide initiator. Adding a peroxide initiator consisting of a mixture of 85 to 80% by weight at a concentration of 50 to 1,000 ppm, and then polymerizing at 200 to 260 ° C. under a pressure of 2500 to 3000 kg / cm 2 for 2 to 20 minutes. It is characterized by.

In the EVA resin production method of the present invention, when the amount of the ethylene monomer introduced into the reactor exceeds 72% by weight or the amount of the vinyl acetate monomer is less than 28% by weight, the transparency is lowered or the processability is lowered, and the obtained film is hard. Degassing property is lowered, and there is a risk of damaging the cell during fabrication of the module, which is not preferable. The amount of ethylene monomer introduced into the reactor is less than 68% by weight or the amount of vinyl acetate monomer exceeds 32% by weight. In this case, the viscosity of the resin decreases and may flow between the glass substrate and the back sheet during lamination, and may be easily deteriorated by light or heat, which is not preferable.

Specific examples of the alkyl peroxy pivalate compound that can be used as an initiator in the present invention include t-amyl peroxy pivalate, t-butyl peroxy pivalate and the like, and alkyl peroxy ethylhexanoate based Specific examples of the compound include t-amylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate and the like, and specific examples of the dialkyl peroxide compound include -t-butyl peroxide, di-t-amyl peroxide, etc. are mentioned.

In the peroxide initiator mixture used in the present invention, the mixing weight ratio of the alkyl peroxy pivalate compound: the alkyl peroxy ethylhexanoate compound and / or the dialkyl peroxide compound is 15-20: 85-80. Although it is preferable that it is in the range, when the mixing weight ratio between the peroxide initiators is out of the above range, it is not preferable because the molecular weight adjustment is not easy.

In the EVA resin manufacturing method of the present invention, when the concentration of the peroxide initiator is less than 50 ppm, the polymerization temperature is low because the reaction temperature during polymerization is low, and the molecular weight is not easy to control. When the reaction temperature is high, the resin may be decomposed, and the vinyl acetate is decomposed to generate an acetic acid which corrodes the reactor.

In the EVA resin manufacturing method of this invention, it is preferable that superposition | polymerization temperature is 200-260 degreeC, but when superposition | polymerization temperature is less than 200 degreeC, conversion to EVA is low, it is not preferable because a desired molecular weight and molecular weight distribution are not obtained, and it is 260 degreeC. If exceeded, the decomposition reaction occurs and the reactor is corroded. In addition, the polymerization pressure is preferably 2500 ~ 3000kg / ㎠, the polymerization pressure is 2500kg / ㎠ If less than, gas and liquid phase separation occurs, the reaction is insufficient, and the working stability is not preferable, and if it exceeds 3000 kg / cm 2, the performance limit of the high pressure pump is not preferable because of stability problems. And, the polymerization time is preferably 2 to 20 minutes, but if the polymerization time is less than 2 minutes, the conversion to EVA is low, and the molecular weight is low, which is not preferable. not.

In the EVA resin production method of the present invention, in addition to the above components, conventional additives used in the production of EVA resin, for example, additives such as chain transfer agents may be used in an appropriate amount.

In order to achieve another object of the present invention, in the present invention, the Z average molecular weight (Mz) of the EVA resin is 250,000 g / mole or less, the molecular weight distribution (Mw / Mn) is 4.0 or less, and the VA content is 25 to 32 weight. %, And a melt index of 6 to 30 g / 10 min, measured at 190 ° C. and a load of 2.16 kg, provides an EVA resin for a solar cell encapsulant sheet.

When Mz of EVA resin exceeds 250,000 g / mole, transparency is bad and a gel is not preferable, and when molecular weight distribution exceeds 4, transparency is bad, a gel is generated and it is not preferable, VA content When the content is less than 25% by weight, the transparency and the adhesion are deteriorated, which is not preferable. When the content of VA exceeds 32% by weight, the electrical insulation is poor, the adhesive is difficult to handle, and the resin viscosity at the time of melting is low. It is not preferable because there is a problem that the resin is likely to leak during laminating. If the melt index of the EVA resin is less than 6 g / 10 minutes, the workability is poor, and if the melt index is more than 30 g / 10 minutes, the molten resin may flow out between the glass substrate and the backsheet during lamination. not.

According to the EVA resin manufacturing method of the present invention, the resin for solar cell encapsulant which is excellent in transparency and adhesiveness and low in the density of fisheye can be easily provided.

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 the examples.

Example # 1

According to the method of the present invention, based on the total weight of the monomers, monomers of 72% by weight of ethylene monomer and 28% by weight of vinyl acetate monomer, t-butylperoxy pivalate, t-butylperoxy-2-ethylhexa as initiator 80 ppm of a mixture of noate and di-t-butyl peroxide (weight ratio: 15/80/5) and propionaldehyde as a chain transfer agent, which is a molecular weight regulator, were added to 70 ppm and then pumped into a tubular reactor by using a high pressure pump. In addition, an EVA resin was prepared under polymerization conditions of a reaction pressure of 2500 kg / cm 2, a reaction temperature of 240 ° C., and a polymerization time of 10 minutes.

Example # 2

An EVA resin was prepared under the same polymerization conditions as in Example 1 except that no chain transfer agent was added.

Example # 3

An EVA resin was prepared under the same polymerization conditions as in Example 1 except that the amount of the chain transfer agent was 200 ppm.

Example # 4

An EVA resin was prepared under the same polymerization conditions as in Example 1 except that the reaction pressure was 2750 kg / cm 2 and the reaction temperature was 230 ° C.

Comparative Example 1

An EVA resin was prepared under the same polymerization conditions as in Example 1 except that the reaction pressure was 2400 kg / cm 2.

Comparative Examples 2-4

Using an autoclave reactor, an EVA resin was prepared under polymerization conditions of a reaction pressure of 2000 kg / cm 2, a reaction temperature of 240 ° C. (comparative example 2), 190 ° C. (comparative example 3), and 260 ° C. (comparative example 4).

The physical properties of the EVA resins prepared in Examples and Comparative Examples were measured by the following physical property measurement methods, and the results are shown in Table 1 (Example) and Table 2 (Comparative Example). Using the prepared EVA resin, the film was molded according to the following film production conditions to evaluate physical properties, and the results are shown together in Tables 1 and 2 below.

Property measurement method

The physical properties of the EVA resins prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were measured by the following methods and criteria.

1) Melt flow index measurement: measured at 190 ℃, 2.16kg according to ASTM D1238.

2) VA content measurement: Differential scanning calorimetry (DSC) and infrared spectrophotometer (Fourier Transform Infrared Spectroscopy: FTIR) was measured.

3) Measurement of average molecular weight (Mw, Mn, and Mz): Measurement was performed by gel permeation chromatography.

4) Transparency: Haze was measured and compared. The smaller the haze value, the more transparent it is.

5) Fish eye: Means the optical non-uniformity observed from the transmitted light of the film, a laser counter is attached to the film winder to quantitatively analyze the number of fish eyes per unit area of the film by size. If there are many fish eye, it is good to have as few as possible because it causes poor film smoothness and poor appearance.

Film manufacturing conditions

The EVA resins of Examples 1 to 4 and Comparative Examples 1 to 4 were formed in a single screw extruder having a screw diameter of 40 mm and a T-die width of 400 mm with an extruder temperature of 120 ° C. and a screw rotational speed of 50 rpm. A sheet-like film having a thickness of 200 μm was prepared.

As shown in Table 1, in the case of the EVA resin of the examples prepared by the method of the present invention, the molecular weight distribution is 4 or less, Mz value is 250,000g / mole or less, compared with the comparative examples of Table 2 The film made of the EVA resin of the examples had a smaller haze value and a significantly lower density of fisheye compared to the film made of the EVA resin of the comparative examples.

Adhesion experiment

The EVA resin of Example 1 and Comparative Example 2, using a T-die single screw extruder to produce a film having a thickness of 40㎛, after the corona treatment with 50dyne, to a laminating machine (Photonex 325 LSI: GMP company) After laminating a PET film substrate having a thickness of 15 μm, the corona treated EVA film, and printing paper in sequence, the laminating speed was 5 m / min, and the sealing temperature was set at 80 to 130 ° C., followed by lamination. Adhesion between the laminated EVA film and paper was 25 mm, width 100 mm, tensile shear rate 200 mm / t, 50% relative humidity, 23 ° C. according to T peel test presented in ASTM D1876. Measured as min, the results are shown in Table 3.

As shown in Table 3, in the case of the EVA resin of Example 1 prepared by the method of the present invention, the adhesive strength was excellent in the entire sealing temperature area compared to EVA resin of Comparative Example 2.

Claims (2)

In the tubular reactor, 72 to 68% by weight of the ethylene monomer and 28 to 32% by weight of vinyl acetate monomer are added to the tubular reactor, and 15 to 20% by weight of the alkylperoxy pivalate compound based on the total weight of the peroxide initiator. 200-200 parts of a peroxide initiator consisting of a mixture of 85 to 80% by weight of at least one selected from alkylperoxy ethylhexanoate compounds and dialkyl peroxide compounds was added to the mixture. Method for producing a ethylene vinyl acetate copolymer resin for a solar cell encapsulant sheet comprising the step of polymerization for 2 to 20 minutes at a pressure of 2500 ~ 3000kg / ㎠ at 260 ℃. Prepared by the method according to claim 1, Mz is 250,000g / mole or less, molecular weight distribution (Mw / Mn) is 4.0 or less, vinyl acetate content is 25-32% by weight, 190 ℃, with a load of 2.16kg Ethylene vinyl acetate copolymer resin for solar cell sealing material sheets characterized by measured melt index of 6-30g / 10min.