METHOD FOR SOLUBILIZING CROSSLINKED EVA, AND METHOD FOR RECOVERING RESOURCE FROM USED SOLAR CELL BY EMPLOYING SOLUBILIZATION METHOD

Abstract

There is provided a method for solubilizing cross-linked EVA which can dissolve cross-linked EVA within a short time such as about 60 minutes. Further, an object of the present invention is to provide a recovering method which uses such a solubilization method to solubilize, within a short time, the cross-linked EVA of a solar battery module containing metal and silicon and recovers valuable resources such as metal and silicon, and the recovering method includes treating the cross-linked EVA with a treatment solution at a temperature within a range from 100 to 300 C. consisting essentially of a solvent selected from an alkyl-based alcohol having 5 to 12 carbon atoms and a phenol and an additive selected from an alkali, an oxoacid, and an oxoacid salt, to recover resources such as metal and silicon.

Claims

1. A method for solubilizing cross-linked EVA comprising treating cross-linked EVA by using a treatment solution at a temperature within a range from 100 C. to 300 C., wherein said treatment solution consists essentially of a solvent selected from the group consisting of an alkyl-based alcohol comprising 5 to 12 carbon atoms and a phenol, and an additive selected from the group consisting of an alkali, an oxoacid, and an oxoacid salt.

2. The method for solubilizing cross-linked EVA according to claim 1, wherein one or two or more alkyl-based alcohols selected from the group consisting of an acyclic alkyl alcohol, an cyclic alkyl alcohol, and an aromatic alcohol are used as said solvent, and one or two or more alkalis selected from the group consisting of potassium hydroxide, sodium hydroxide, and lithium hydroxide are used as said additive, at a temperature of the treatment solution within a range from 100 C. to 300 C.

3. The method for solubilizing cross-linked EVA according to claim 1, wherein an alkylphenol comprising an alkyl group comprising 1 to 5 carbon atoms is used as said solvent, and an oxoacid or an oxoacid salt is used as said additive, at the treatment temperature within a range from 150 C. to 300 C.

4. The method for solubilizing cross-linked EVA according to claim 1, wherein a treatment time is within 60 minutes and a solubilization ratio is 70% or more.

5. The method for solubilizing cross-linked EVA according to claim 1, wherein the solubilization ratio is 100%.

6. A method for recovering a valuable resource in a solar battery module, comprising performing the method for solubilizing cross-linked EVA according to claim 1, wherein cross-linked EVA to be treated is contaminated by silicon and/or metal of a solar battery module, and a solubilized product of cross-linked EVA obtained by the method is separated, to recover the silicon and/or the metal.

7. The method for recovering a valuable resource according to claim 6, wherein a solubilized product is separated from a product to be treated at the treatment temperature or a temperature in the vicinity thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG. 1 is a graph illustrating the influence of a ratio, (weight of additive/weight of EVA), on the solubilization ratio of cross-linked EVA for Example 3 of the present invention.

[0051] FIG. 2 is a graph illustrating the influence of solubilization time and (weight of additive/weight of EVA) on the solubilization ratio of cross-linked EVA for Example 4 of the present invention.

[0052] FIG. 3 is a graph illustrating the influence of treatment temperature on the solubilization ratio of cross-linked EVA for Example 5 of the present invention.

[0053] FIG. 4 is a graph illustrating the influence of solubilization time, treatment temperature, and kind of solvent on the solubilization ratio of cross-linked EVA for Example 7 of the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0054] Hereinafter, embodiments for working the present invention will be described. The method for solubilizing cross-linked EVA includes treating cross-linked EVA with a treatment solution at 100 to 300 C., wherein the treatment solution consists essentially of an additive selected from the group consisting of an alkali, an oxoacid, and an oxoacid salt and, a solvent selected from the group consisting of an alkyl-based alcohol having 5 to 12 carbon atoms and a phenol.

[0055] A product to be treated that is subject to the method for solubilizing cross-linked EVA of the present invention contains cross-linked EVA as the whole or part thereof.

[0056] Examples of the product to be treated containing cross-linked EVA include, but are not limited to, a solar battery module (sometimes referred to as a solar battery panel, a solar panel etc.).

[0057] When the product to be treated is a product that contains cross-linked EVA not exposed on the surface thereof, an appropriate pre-treatment is made so that the cross-linked EVA may be at least exposed on the surface before the solubilization treatment of the present invention. Means for such a pre-treatment are not limited, and when the product to be treated is a solar battery module, cross-linked EVA can be exposed on the surface by dismantling the surrounding flame and mechanically removing the glass plate on the surface and the backsheet on the back surface. Cross-linked EVA can be cut or ground into a size suitable for solubilization during such a pre-treatment for exposing cross-linked EVA or a subsequent pre-treatment.

[0058] Cross-linked EVA solubilized in the present invention is cross-linked ethylene/vinyl acetate copolymer, which is poorly solubilized by an organic solvent such as xylene heated to about 110 C. The crosslinking ratio the polymer is usually within the range from 10 to 98% (preferably from 20 to 95%), but is not limited thereto.

[0059] According to the method for solubilizing cross-linked EVA of the present invention, cross-linked EVA, even having a crosslinking ratio as high as 90% or more, can be solubilized within a relatively short time equal to or less than about 60 minutes. Further, the method can achieve a solubilization ratio of 100%, and therefore, when the product to be treated is a product such as a solar battery module which contains valuable resources such as metal and silicon, the valuable resources can be recovered while separated from cross-linked EVA completely.

[0060] To calculate the crosslinking ratio, 1 g of cross-linked EVA is immersed in 100 ml of xylene, heated at 110 C. for 24 hours, and then an insoluble fraction is collected by filtration using a wire mesh of 20 mesh, left at 120 C. at reduced pressure for 10 hours, and then weighted, and the following equation is used for the calculation;

crosslinking ratio(%)=100(W.sub.1/W.sub.0).

[0061] W.sub.1: weight (g) of collected insoluble fraction left at 120 C. at reduced pressure for 10 hours.

[0062] W.sub.0: initial weight of EVA, 1 g.

[0063] In addition, to calculate the solubilization ratio, the insoluble fraction is collected after solubilization, by filtration using a wire mesh of 20 mesh, left at 120 C. at reduced pressure for 10 hours, and then weighed, and the following formula is used for the calculation,

solubilization ratio(%)=100(1W.sub.1/W.sub.0).

[0064] W.sub.1: weight (g) of collected insoluble fraction left at 120 C. at reduced pressure for 10 hours.

[0065] W.sub.0: initial weight of EVA (g).

[0066] In the present invention, the treatment solution used for solubilizing cross-linked EVA is a solution consisting essentially of an additive selected from the group consisting of an alkali, an oxoacid, and an oxoacid salt, and a solvent selected from the group consisting of an alkyl-based alcohol having 5 to 10 carbon atoms and a phenol.

[0067] Examples of the alkyl-based alcohol having 5 to 12 (preferably 5 to 10, more preferably 5 to 8) carbon atoms as a solvent include an acyclic alkyl alcohol and a cyclic alkyl alcohol, and these alkyl-based alcohols may be branched, or may be aromatic alcohols including an alkyl chain containing a hydroxyl group and an aryl group bound to the chain.

[0068] Examples of the acyclic alkyl alcohol include, but are not limited to, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-undecanol, 1-dodecanol, 2-pentanol, 2-hexanol, 2-heptanol, 2-octanol, 2-ethyl-1-hexanol, 2-methyl-1-hexanol, 2-ethyl-1-heptanol, 2-methyl-1-heptanol, and 2-ethyl-1-octanol.

[0069] Examples of the cyclic alkyl alcohol include, but are not limited to, cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol, cyclononanol, cyclodecanol, cycloundecanol, cyclododecanol, 2-ethylcyclohexanol, and 2-methylcyclohexanol.

[0070] Examples of the aromatic alcohol include 1-phenylethanol, 2-phenylethanol, 1-phenyl-1-propanol, 1-phenyl-2-propanol, and 2-phenyl-1-propanol. Preferable examples of the alkyl-based alcohol include 2-ethyl-1-hexanol and 1-hexanol.

[0071] Examples of the phenol as a solvent include, but are not limited to, phenol and an alkylphenol containing an alkyl group having 1 to 5 carbon atoms. Examples of the alkylphenol containing an alkyl group having 1 to 5 carbon atoms include, but are not limited to, 3,5-dimethylphenol, cresol, 4-ethylphenol, and 4-tert-butylphenol.

[0072] The alkali as an additive is a hydroxide of alkali metal or of alkali earth metal and is preferably potassium hydroxide, sodium hydroxide, or lithium hydroxide, and more preferably potassium hydroxide or sodium hydroxide. Examples of the oxoacid and the oxoacid salt as an additive include, for example, sulphuric acid, nitric acid, phosphoric acid, and alkali metal salts thereof, and sulphuric acid is preferable.

[0073] The weight fraction of the additive to the solvent is within a range from 0.2 to 4.0%, preferably from 1.0 to 3.0%, and more preferably from 1.5 to 2.5%. The concentration of the additive of alkali or oxoacid in the treatment solution containing the solvents is low, and even when a product to be treated contains valuable resources such as metal and silicon, these valuable resources are unlikely to be invaded by the alkali and oxoacid.

[0074] As will be described in the following embodiments, alkali additives are preferable for solvents of alkyl-based alcohols and additives of oxoacids or oxoacid salts are preferable for solvents of phenols, in that cross-linked EVA can be solubilized at a high solubilizing ratio.

[0075] When the ratio of the weight of the alkali additive to that of cross-linked EVA (weight of only cross-linked EVA exclusive of the weight of contaminating silicon or metal) is lower than 5% by weight, the solubilization ratio is as low as, for example, about 20% or less. The solubilization ratio can be linearly increased with the increase in the ratio of the alkali additive from about 5% by weight, and can reach 100% with 25% by weight or more of the ratio of the alkali additive under a condition of solubilization time of 60 minutes. In addition, the solubilization time for achieving a predetermined solubilization ratio can be shortened with the increase in the ratio of the alkali additive. The upper limit of the amount of the alkali additive is not limited, but for example from the economical viewpoint, it can be set to 70% by weight or lower. Accordingly, a preferable ratio of the alkali additive to the weight of cross-linked EVA is within a range from 5 to 70% by weight, more preferably from 10 to 50% by weight, and still more preferably from 20 to 40% by weight.

[0076] The solution for solubilization treatment of the present invention preferably consists of only the above-described additive and solvent, but other alcohols and organic solvents can be contained in an amount within a range that does not greatly lower the solubilization ratio and the solubilization rate (for example, 10% by weight or less, preferably 5% by weight or less).

[0077] When the treatment temperature at which cross-linked EVA is treated with the solution for solubilization treatment is within the range from 100 to 300 C. (preferably from 120 to 240 C.), a relatively high solubilization ratio can be achieved even for a solubilization time of 60 minutes or shorter. When the treatment temperature is a temperature near the boiling point (boiling point 1 C.) of a solvent to be used, or a temperature lower than the boiling point, for example, by 1 to 30 C. (preferably 1 to 20 C.), the evaporative loss of the solvent can be reduced during the treatment at atmospheric pressure.

[0078] When one or two or more kinds of alkyl-based alcohols selected from the group consisting of an acyclic alkyl alcohol, a cyclic alkyl alcohol, and an aromatic alcohol are used in combination as a solvent, the treatment temperature is within a range from 100 to 300 C., preferably from 130 to 210 C., and more preferably from 140 to 200 C.

[0079] When phenol or an alkylphenol including an alkyl group having 1 to 5 carbon atoms is used as a solvent, the treatment temperature is within a range from 150 to 300 C., preferably from 190 to 240 C., and more preferably from 200 to 240 C. Although the treatment atmosphere is desirably at atmospheric pressure from the economical viewpoint, it may be a pressurized atmosphere (1.5 atm or less, preferably 1.2 atm or less) or an atmosphere of reduced pressure (0.9 to 1 atm), and further, it may be an atmosphere containing an inert gas component such as nitrogen and carbon dioxide in a larger amount than that in air.

[0080] During the solubilization treatment, the treatment solution containing cross-linked EVA is preferably stirred by a well-known appropriate means in terms of the promotion of the solubilization.

[0081] After the solubilization of cross-linked EVA, the treatment solution containing the solubilized EVA (solubilized product) is subjected to the separation of the solubilized product from the treated product by filtration with a tool such as a wire mesh, and a valuable resource such as metal and silicon is recovered from the remaining insoluble fraction. The temperature during the separation of the solubilized product from the treated product is preferably the treatment temperature or a temperature near the treatment temperature (within the range from the treatment temperature 20 C. to the treatment temperature +5 C., and more preferably from the treatment temperature 10 C. to the treatment temperature).

[0082] In particular, when the solubilization ratio of cross-linked EVA is 100%, the recovery of valuable resources is easy since cross-linked EVA is not contained in the insoluble fraction. The treatment solution after the filtration can be recycled and reused as a solvent for solubilization treatment after the solubilized EVA component is removed by an appropriate means such as distillation.

[0083] Although the mechanism of solubilizing cross-linked EVA by the solubilization method of the present invention has not yet been elucidated clearly, it can be attributed the ester bond contained in the crosslink between EVAs which is cleaved owing to transesterification with the alkyl-based alcohol in the treatment solution or alkali decomposition. In that case, since the main chain of EVA is not decomposed by the solubilization treatment, the solubilized EVA is expected to be recycled for a useful application.

[0084] The solubilization treatment of cross-linked EVA by the treatment solution may be either a batch treatment or a continuous treatment.

[0085] In the case of a batch treatment, the product to be treated may be input into the treatment solution before temperature raise, or it may be input thereinto during or after the temperature raise.

EXAMPLES

[0086] Hereinafter, the present invention will be described in more detail based on Examples, but the invention is not limited to such Examples.

Example 1

Solubilization Test of Cross-Linked EVA Under Various Conditions

[0087] To a vessel containing 5.1 g of EVA (20.0 mm square, crosslinking rate of 83%) which is EVASKY, S-88, from Bridgestone Corporation, cross-linked at 150 C. were added 100.0 g of 1-phenylethanol as a solvent, 1.7 g of potassium hydroxide as an additive, and a magnetic stir bar, and heated from room temperature to a treatment temperature of 204 C. for about 20 minutes, and then the mixture was kept at the same treatment temperature for a solubilization time of 60 minutes while stirred by using a magnetic stirrer. After the solubilization, the sample, not cooled, was filtrated with a wire mesh of 20 mesh, and the recovered solid product was washed several times in tetrahydrofuran with an ultrasonic cleaner, and left as a trial at 50 C. for 10 hours in a vacuum dryer, to remove the solvent. The trial solubilization ratio of EVA was 100.0%, based on the calculation using the following formula,

trial solubilization ratio(%)=100(1W.sub.1/W.sub.0).

[0088] W.sub.1: weight (g) of collected insoluble fraction left at 50 C. at reduced pressure for 10 hours.

[0089] W.sub.0: initial weight (g) of EVA.

[0090] When the drying temperature at reduced pressure is 50 C., the solvent captured in the cross-linked EVA owing to its swelling is difficult to be removed completely, and therefore the trial solubilization ratio is estimated to be lower than the solubilization ratio defined in the paragraph [0026], and is, for example, about 80% for the solubilization ratio of 90%, and about 60% for the solubilization ratio of 80%. (However, when the solubilization ratio is nearly 100%, it is not significantly different from the trial solubilization ratio. In Example 3 or later, the residual solvent was completely removed using vacuum dry at 120 C. in order to calculate the solubilization ratio defined in the paragraph [0026].) The trial solubilization ratio was obtained in the same manner as above except that at least one of the experimental conditions of kind of solvent, treatment temperature, weight of EVA, weight of solvent, kind of additive, and weight of additive was changed, and the result is illustrated in Table 1 together with the experimental conditions.

TABLE-US-00001 TABLE 1 treat- ment solubil- weight weight weight solubil- temper- ization of of of additive/ ization ature time EVA solvent additive EVA ratio solvent ( C.) (min) (g) (g) additive (g) (g/g) (%) 1-phenylethanol 204 60 5.1 100.0 KOH 1.7 0.34 100.0 1-octanol 195 60 5.1 100.0 KOH 1.7 0.34 100.0 1-heptanol 176 60 5.1 100.1 KOH 1.7 0.33 100.0 1-hexanol 157 60 5.1 100.1 KOH 1.7 0.34 100.0 1-pentanol 138 60 5.1 100.1 KOH 1.7 0.33 87.7 cyclohexanol 161 60 4.0 80.0 KOH 1.3 0.33 100.0 1-phenylethanol 204 60 5.1 100.1 NaOH 1.1 0.21 100 1-octanol 195 60 5.0 100.4 NaOH 1.1 0.21 99.6 1-hexanol 157 60 5.0 100.0 NaOH 1.1 0.21 99.8 cyclohexanol 161 60 5.1 100.3 NaOH 1.1 0.21 65.7 ethylene gylcol 197 60 5.1 100.7 NaOH 1.1 0.21 0.0 decalin 190 60 5.0 100.0 H.sub.2SO.sub.4 0.52 0.10 0.0 1,2,3,4-tetrahydronapthalene 200 60 5.0 100.0 H.sub.2SO.sub.4 0.52 0.10 0.0 3,5-dimethylphenol 222 60 5.1 100.0 H.sub.2SO.sub.4 0.51 0.10 91 cresol 200 60 5.0 100.4 H.sub.2SO.sub.4 0.54 0.11 100 4-ethylphenol 219 60 5.1 100.1 H.sub.2SO.sub.4 0.52 0.10 100 4-tert-buthyphenol 238 60 5.1 100.2 H.sub.2SO.sub.4 0.54 0.11 100

[0091] As is apparent from Table 1, high solubilization ratios of about 65% or more were exhibited when an acyclic alkyl alcohol such as 1-octanol, a cyclic alcohol such as cyclohexanol, an aromatic alcohol such as 1-phenylethanol, and a phenol such as cresol were used as a solvent, and potassium hydroxide, sodium hydroxide, and sulphuric acid were used as an additive, at about 120 to 240 C. which was a treatment temperature set to be equal to or slightly lower than the boiling points of the respective solvents. The alkyl-based alcohols, whether they were acyclic or cyclic, exhibited high solubilization ratios of or near 100% when an alkali was used as an additive, however the acyclic alkyl-based alcohols exhibited higher solubilization ratios than those of the cyclic alcohols, even when the ratio of weight of the additive to that of EVA was relatively small. In addition, when phenols were used as a solvent and sulphuric acid was used as an additive, high solubilization ratios of 100% were exhibited even when the ratio of weight of the additive to that of EVA was relatively small. On the other hand, solubilization was not able to be achieved when a divalent alcohol such as ethylene glycol or a naphthalene-based solvent such as decalin was used as a solvent.

Example 2

Investigation Test of Influence of Kind of Additive on Solubilization Ratio

[0092] A trial solubilization ratio was calculated to investigate the influence of kind of additive on solubilization ratio in the same manner as that in Example 1, mainly, with the kind of additive changed, the weight of additive set so that the amount of the additive might take an approximately constant molar number (0.025 to 0.03 mol) except for a case with no additive, and other conditions of kind of solvent, treatment temperature, solubilization time, weight of solvent, and sample size kept nearly unchanged (solvent, 1-hexanol: treatment temperature, 157 C.: solubilization time, 30 minutes: weight of EVA, 5.1 g or 5.0 g: weight of solvent, 100.0 to 100.6 g: sample size, 20.0 mm). The result is illustrated in Table 2.

TABLE-US-00002 TABLE 2 treat- ment solubil- weight weight weight solubil- temper- ization of of of additive/ ization ature time EVA solvent additive EVA ratio solvent ( C.) (min) (g) (g) additive (g) (g/g) (%) 1-hexanol 157 30 5.1 100.6 no 0.0 0.00 0.0 additive 1-hexanol 157 30 5.1 100.0 H.sub.2PO.sub.4 2.9 0.57 0.0 1-hexanol 157 30 5.0 100.2 Ca(OH).sub.2 1.9 0.38 4.4 1-hexanol 157 30 5.1 100.1 LiOH 0.6 0.12 19.5 1-hexanol 157 30 5.1 100.0 K.sub.5PO.sub.4 5.6 1.10 30.6 1-hexanol 157 30 5.1 100.2 NaOH 1.1 0.21 91.1 1-hexanol 157 30 5.1 100.1 KOH 1.7 0.33 100.0

[0093] As is apparent from Table 2, no solubilization occurred when the solvent was 1-hexanol, with no additive or with phosphoric acid as an additive. Further, a low solubilization ratio was exhibited when the additive was potassium phosphate, calcium hydroxide, or lithium hydroxide. In contrast, a high solubilization ratio was exhibited when the additive was potassium hydroxide, or sodium hydroxide and the ratio of weight of the additive to that of EVA was 20% by weight or higher.

Example 3

Investigation Test of Influence of (Weight of Additive/Weight of EVA) on Solubilization Ratio

[0094] A cage made of a wire mesh of 20 mesh in a glass reaction vessel was lifted, without cooling after solubilization, along with a solid product be recovered in the cage, and then the product was washed several times in tetrahydrofuran by using an ultrasonic cleaner, dried at 120 C. using a vacuum dryer for 10 hours, and then weighed, to a calculate solubilization ratio. A solubilization ratio was calculated to investigate the influence of (weight of additive/weight of EVA) on solubilization ratio, mainly, with the weight of EVA and/or that of the additive changed, and other conditions of solvent, treatment temperature, solubilization time, weight of solvent, additives, and sample size kept unchanged or nearly unchanged (solvent, 1-hexanol: treatment temperature, 157 C.: solubilization time, 60 minutes: weight of solvent, 198.1 to 203 g: additives, KOH: sample size, 20.0 mm). The result is illustrated in FIG. 1 and Table 3.

TABLE-US-00003 TABLE 3 treat- ment solubil- weight weight weight solubil- temper- ization of of of additive/ ization ature time EVA solvent additive EVA ratio solvent ( C.) (min) (g) (g) additive (g) (g/g) (%) 1-hexanol 157 60 10.0 198.1 KOH 3.3 0.33 99.80 1-hexanol 157 60 10.0 200.0 KOH 2.6 0.26 99.70 1-hexanol 157 60 10.0 200.0 KOH 2.0 0.20 59.84 1-hexanol 157 60 10.0 200.0 KOH 1.3 0.13 35.44 1-hexanol 157 60 10.0 203.0 KOH 0.7 0.07 19.76 1-hexanol 157 60 10.0 200.0 KOH 0.0 0.00 10.90

[0095] As is apparent from the description of Table 3 and FIG. 1, the solubilization ratio increased almost linearly with the increase in (weight of additive/weight of EVA). Specifically, a solubilization ratio of about 30% was exhibited when the ratio of the weight of the additive to that of EVA was about 10% by weight, and a solubilization ratio of about 60% was exhibited for the ratio of about 20% by weight, and further, a solubilization ratio of or near 100% was exhibited for the ratio of about 25% by weight or higher.

Example 4

Investigation Test of Influence of Solubilization Time and Weight of Additive on Solubilization Ratio

[0096] A solubilization ratio was calculated in the same manner as that in Example 3, to investigate the influence of solubilization time and weight of additive, i.e., (weight of additive/weight of EVA), on solubilization ratio, mainly, with the solubilization time and/or the weight of additive changed, and other conditions of solvent, treatment temperature, weight of EVA, weight of solvent, additive, and sample size kept unchanged or nearly unchanged (solvent, 1-hexanol: treatment temperature, 157 C.: EVA weight, 10.0 g: solvent weight, 200 g or 198.1 g: additive, KOH: sample size, 20.0 mm). The result is illustrated in FIG. 2 and Table 4.

TABLE-US-00004 TABLE 4 treat- ment solubil- weight weight weight solubil- temper- ization of of of additive/ ization ature time EVA solvent additive EVA ratio solvent ( C.) (min) (g) (g) additive (g) (g/g) (%) 1-hexanol 157 30 10.0 200.0 KOH 1.98 0.20 76.4 1-hexanol 157 0 10.0 200.0 KOH 3.30 0.33 41.5 1-hexanol 157 15 10.0 200.0 KOH 3.30 0.33 83.4 1-hexanol 157 30 10.0 200.0 KOH 3.31 0.33 99.7 1-hexanol 157 60 10.0 198.1 KOH 3.27 0.33 99.8 1-hexanol 157 0 10.0 200.0 KOH 6.60 0.66 63.6 1-hexanol 157 15 10.0 200.0 KOH 6.60 0.66 98.7

[0097] As is apparent from the description of Table 4 and FIG. 2, it was revealed that when the weight of the additive with respect to that of EVA was increased from 20% by weight to 66% by weight, the solubilization rate was accelerated and a time taken for solubilization ratio to get close to 100% was able to be shortened to about 15 minutes.

Example 5

Investigation Test of Influence of Treatment Temperature on Solubilization Ratio

[0098] A solubilization rate was calculated in the same manner as that in Example 3, to investigate the influence of treatment temperature on solubilization ratio, mainly, with the treatment temperature changed, and other conditions of solvent, solubilization time, weight of EVA, weight of solvent, additive, weight of additive, and sample size kept unchanged or nearly unchanged (solvent, 1-hexanol: solubilization time, 60 minutes: weight of EVA, 10.0 g: weight of solvent, 200 g or 198 g: additive, KOH: weight of additive, 3.3 g: sample size, 20.0 mm). The result is illustrated in Table 5. Further, FIG. 3 illustrates a relation between the treatment temperature and the solubilization ratio.

TABLE-US-00005 TABLE 5 treat- ment solubil- weight weight weight solubil- temper- ization of of of additive/ ization ature time EVA solvent additive EVA ratio solvent ( C.) (min) (g) (g) additive (g) (g/g) (%) 1-hexanol 120 60 10.0 200 KOH 3.3 0.33 57 1-hexanol 140 60 10.0 200 KOH 3.3 0.33 98 1-hexanol 157 60 10.0 198 KOH 3.3 0.33 100

[0099] As is apparent from the description in Table 5 and FIG. 3, the solubilization ratio was increased almost linearly from 60% to up to about 100% with the increase in the treatment temperature from about 120 C. to about 150 C., when 1-hexanol was used as a solvent.

Example 6

Investigation Test of Influence of Sample Size on Solubilization Ratio

[0100] A solubilization rate was calculated in the same manner as that in Example 3 to investigate the influence of sample size on solubilization ratio, with sample size changed, and other conditions of solvent, treatment temperature, solubilization time, weight of EVA, weight of solvent, additives, and weight of additive kept unchanged (solvent, 1-hexanol: treatment temperature, 157 C.: solubilization time, 0 minutes: weight of EVA, 10.0 g: weight of solvent, 200 g: additive, KOH: weight of additive, 6.6 g). The result is illustrated in Table 6.

TABLE-US-00006 TABLE 6 treat- ment solubil- weight weight weight solubil- temper- ization of of of additive/ sample ization ature time EVA solvent additive EVA size ratio solvent ( C.) (min) (g) (g) additive (g) (g/g) (mm) (%) 1-hexanol 157 0 10.0 200.0 KOH 6.6 0.66 20.0 63.6 1-hexanol 157 0 10.0 200.0 KOH 6.6 0.66 5.0 88.7

[0101] As is apparent from the description of Table 6, a solubilization ratio of 63.6% was exhibited when the sample size was 20.0 mm, and a solubilization ratio close to 90% was exhibited when the sample size was as small as 5.0 mm despite a solubilization time as short as 0 minutes.

Example 7

Investigation Test of Influence of Kind of Alkyl-Based Alcohol on Solubilization Ratio

[0102] To a cage made of a wire mesh of 20 mesh were added 10.0 g of EVA cross-linked at 160 C. (5.0 mm square, crosslinking ratio of 92%) which was cross-linked EVASKY, S-88, from Bridgestone Corporation, and a magnetic stir bar. To a vessel were added 200.0 g of 2-ethyl-1-hexanol as a solvent and 3.3 g of potassium hydroxide as an additive, and heated to 184 C., and upon the reaching of the temperature, the cage was dropped into the solvent to start solubilization for 4 minutes, with the solution kept stirred by using a magnetic stirrer, after which solubilization the cage was lifted from the solution along with a solid product to be recovered in the cage, and then the product was washed several times in tetrahydrofuran by using an ultrasonic cleaner, dried at 120 C. using a vacuum dryer for 10 hours, and then weighed, to calculate solubilization ratio.

[0103] The solubilization ratio of EVA was 33.4%. The solubilization ratio was calculated in substantially the same manner as above except that at least one of the experimental conditions of kind of solvent, treatment temperature, and solubilization time was changed, and the result is illustrated in Table 7 together with the experimental conditions, and the relation between solubilization time and solubilization ratio is also illustrated for each kind of solvent and each treatment temperature in FIG. 4.

TABLE-US-00007 TABLE 7 treat- ment solubil- weight weight weight solubil- temper- ization of of of additive/ sample ization ature time EVA solvent additive EVA size ratio solvent ( C.) (min) (g) (g) additive (g) (g/g) (mm) (%) 2-ethyl-1-hexanol 184 4 10.0 200 KOH 3.3 0.33 5 33.4 2-ethyl-1-hexanol 184 7 10.0 200 KOH 3.3 0.33 5 68.0 2-ethyl-1-hexanol 184 15 10.0 200 KOH 3.3 0.33 8 93.7 2-ethyl-1-hexanol 184 30 10.0 200 KOH 3.3 0.33 8 98.9 1-hexanol 157 15 10.0 200 KOH 3.4 0.34 8 44.4 1-hexanol 157 30 10.0 200 KOH 3.3 0.33 8 67.4 1-hexanol 157 30 10.0 200 KOH 3.3 0.33 5 70.1 1-hexanol 157 80 10.0 200 KOH 3.3 0.33 5 100.0 2-ethyl-1-hexanol 157 15 10.0 200 KOH 3.3 0.33 5 71.2 2-ethyl-1-hexanol 157 30 10.0 200 KOH 3.3 0.33 5 90.0

[0104] As is apparent from the description of Table 7 and FIG. 4, a higher solubilization rate was exhibited at a relatively low temperature of 157 C. when 2-ethyl-1-hexanol was used as a solvent than when 1-hexanol was used. Further, it was revealed that an even higher solubilization rate was able to be exhibited at a treatment temperature increased to 184 C., when 2-ethyl-1-hexanol was used as a solvent.

Comparative Example 1

[0105] A model sample of solar battery module was fabricated which included a glass plate of 6 inch square and EVA (EVASKY, S-88, from Bridgestone Corporation, crosslinking ratio of 92%) thereon. The model sample was separated into the glass plate and EVA by using a hot knife, and to 5 g of the EVA (about 4 cm square) were added 20 g of methanol, 25 g of butanol, 53 g of N-methyl-pyrrolidone, and 2 g of potassium hydroxide, and the sample was then left in the solvent at 90 C. for 3 hours (heated within 30 minutes, kept 3 hours at the temperature, and then allowed to cool). After the treatment, the EVA was washed with methanol and immersed in THF (50 C.). A very small fraction of the cross-linked EVA was dissolved or swelled owing to these treatments, but neither metal nor silicon plate was able to be recovered.

Comparative Example 2

[0106] To 10 g of EVA, which was EVASKY, S-88, from Bridgestone Corporation, cross-linked at 160 C. (5 mm square, crosslinking rate of 92%) were added 40 g of methanol, 50 g of butanol, 106 g of N-methyl-pyrrolidone, and 4.7 g of potassium hydroxide, and heated while stirred by using a magnetic stirrer at 90 C. for 1 hour. After the reaction, the sample was filtrated by using a wire mesh of 20 mesh, and the recovered solid product was left at 120 C. for 10 hours in a vacuum dryer, to remove the solvent. The solubilization ratio of EVA was 13.6%.

INDUSTRIAL APPLICABILITY

[0107] According to the method for solubilizing cross-linked EVA of the present invention, cross-linked EVA can be solubilized for a short time of about 60 minutes at a solubilization ratio of or near 100%, and therefore the method can be effectively used for recovering valuable resources such as metal and silicon from a product to be treated, such as a solar battery module, that contains cross-linked EVA. Further, the method for solubilizing cross-linked EVA of the present invention can fluidize cross-linked EVA, with no cleavage of the main chain of EVA, and therefore the method can be used as a useful recycling method of cross-linked EVA.