JP2014152224A - Copolyester resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin which has excellent adhesion to a fluororesin and a polyester resin constituting a back sheet in a photovoltaic power generation module.SOLUTION: The copolyester resin contains a terephthalic acid, an isophthalic acid, and a dimer acid as an acid component. The total content of the terephthalic acid and the isophthalic acid in the acid component is 65-92 mol%. The content of the dimer acid in the acid component is 8-35 mol%. The copolyester resin also contains ethylene glycol and neopentyl glycol as a glycol component. The content of the neopentyl glycol in the glycol component is 30-60 mol%. The amount of terminal hydroxyl groups of the resin is 5-30 mgKOH/g.

Description

  The present invention relates to a polyester resin suitable for use in an adhesive, and more particularly to a copolymerized polyester resin that can be used as an adhesive for laminated sheets such as a photovoltaic module backside sealing sheet. is there.

  In recent years, an increase in average temperature throughout the world has been observed, and interest in global warming is increasing. In a social structure that relies on petroleum resources for much of its energy, the use of new energy is indispensable to reduce carbon dioxide emissions, which are said to be a causative agent of global warming. Among them, photovoltaic power generation has attracted attention as a clean energy that does not pollute the environment and does not emit carbon dioxide, and many researches and practical applications have been advanced. Currently, more than 90% of photovoltaic power generation produced in the world uses crystalline silicon solar cells, including single crystal silicon type, polycrystalline silicon type, microcrystalline silicon type, and amorphous silicon type. These solar power generation modules have a structure in which a silicon cell is disposed under a glass plate, and after sealing with a sealing resin, a back surface sealing sheet (back sheet) is bonded.

  The back sheet is directly exposed outdoors, and since the silicon cell is an electrical device, weather resistance, electrical insulation, etc. are required. In order to satisfy these required characteristics, the back sheet has a structure in which several different types of sheets are laminated with an adhesive, and a conventionally used backside sealing sheet is a white polyvinyl fluoride film made of a polyester film. Examples include a sandwiched laminated sheet and a sheet laminated with a polyester film excellent in weather resistance and gas barrier properties.

  As many photovoltaic power generation modules are put into practical use, the performance required for the back sheet is diversified, and a laminated structure of sheets different from the conventional one is required. Of these, fluororesin and polyethylene terephthalate (hereinafter sometimes abbreviated as “PET”) sheets having weather resistance are the mainstream, and the performance required for the adhesive for laminating the sheets is becoming higher.

  Currently, polyurethane adhesives are the mainstream as adhesives used for backsheets. For example, Patent Document 1 proposes a solar cell back surface sealing sheet laminated with an adhesive in which an isocyanate compound is blended as a curing agent with a polyurethane adhesive. However, polyurethane adhesives have low adhesive strength to the base material, and when used in various outdoor environments, they are inferior in long-term reliability.

  In consideration of long-term reliability, a polyester resin excellent in wet heat durability is desired. Patent document 2 and patent document 3 are disclosed as such polyester resin excellent in wet heat durability, and polytetramethylene glycol is copolymerized as a glycol component. However, these polyester resins were excellent in wet heat durability for about 500 hours, but were inferior in wet heat durability in long-term wet heat treatment for 1000 hours or more.

JP 2008-4691 A Japanese Patent Laid-Open No. 07-070535 JP 2001-200041 A

  The present invention solves the above-mentioned problem, and has excellent adhesion to the fluororesin and polyester resin constituting the back sheet in the photovoltaic power generation module, is excellent in wet heat durability, and is stable for a long period of time. It is a technical problem to provide a copolymerized polyester resin that can be used.

The inventors of the present invention have arrived at the present invention as a result of studies to solve the above problems.
That is, in the polyester resin comprising the acid component and the glycol component, the present invention contains terephthalic acid, isophthalic acid and dimer acid as the acid component, and the total content of terephthalic acid and isophthalic acid in the acid component is 65 to 92. Mol%, the content of dimer acid in the acid component is 8 to 35 mol%, ethylene glycol and neopentyl glycol are contained as the glycol component, and the content of neopentyl glycol in the glycol component is 30 to 60 mol. %, And the amount of hydroxyl terminal groups of the resin is 5 to 30 mg KOH / g.

  The copolymerized polyester resin of the present invention is obtained by copolymerizing an appropriate amount of a specific component with an acid component and a glycol component. Therefore, the copolymerized polyester resin is excellent in adhesion to the polyester resin and the fluororesin, and also excellent in wet heat durability. For this reason, when it is used as an adhesive for a back sheet in a photovoltaic power generation module, it exhibits excellent adhesive performance, and the back sheet can be used for a long time even when used outdoors (even in a humid heat environment). Become.

Hereinafter, the present invention will be described in detail.
The copolyester resin of the present invention comprises terephthalic acid (hereinafter sometimes abbreviated as TPA), isophthalic acid (hereinafter sometimes abbreviated as IPA) and dimer acid (hereinafter sometimes abbreviated as DA). And a glycol component containing neopentyl glycol (hereinafter sometimes abbreviated as NPG) and ethylene glycol (hereinafter sometimes abbreviated as EG).

First, the total content of terephthalic acid and isophthalic acid in the acid component needs to be 65 to 92 mol%, preferably 70 to 85 mol%. If the total content of terephthalic acid and isophthalic acid in the acid component is less than 65 mol%, the dimer acid content will exceed 35 mol%, so the melting point of the copolyester will be low or amorphous. Therefore, the heat resistance is inferior and the adhesive strength tends to be low.
On the other hand, if the total content of terephthalic acid and isophthalic acid in the acid component exceeds 92 mol%, the content of dimer acid becomes less than 8 mol%, so the effect of containing dimer acid (wet heat durability) It becomes inferior to.

  The mixing ratio (molar ratio) of terephthalic acid and isophthalic acid in the acid component is preferably terephthalic acid / isophthalic acid = 70/30 to 30/70, and more preferably 60/40 to 40/60. . The copolymerized polyester resin of the present invention is preferably used as an adhesive after being dissolved in an organic solvent. If the blending ratio of terephthalic acid and isophthalic acid satisfies the above range, the copolymerized polyester resin of the present invention is used. When a polymerized polyester resin is dissolved in an organic solvent at a solid content of 30 to 60% by mass, it is difficult to cause reprecipitation of insoluble matter and solid content, and the polyester resin has excellent solubility in an organic solvent. Can do.

  Here, the organic solvent means a non-halogen or non-ether solvent, for example, an aromatic solvent such as toluene, xylene, solvent naphtha, or solvesso; methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, or the like. Examples thereof include ketone solvents; ester solvents such as ethyl acetate and normal butyl acetate; acetate solvents such as cellosolve acetate and methoxyacetate. Moreover, these solvents can also be used in mixture of 2 or more types.

And the copolyester resin of this invention contains a dimer acid as an acid component, and it is required that content of the dimer acid in an acid component is 8-35 mol%, and it is 15-30 mol% especially. Preferably there is. By containing dimer acid as a copolymerization component, it becomes possible to maintain good adhesion for a long period of time even in a humid heat environment. That is, the wet heat durability of the obtained copolyester resin can be improved.
When the dimer acid content is less than 8 mol%, the wet heat durability is poor and the adhesive strength is also lowered. On the other hand, when the content of the dimer acid exceeds 35 mol%, the melting point of the copolyester becomes low or becomes amorphous, so that the heat resistance is inferior and the adhesive strength tends to be low.

  The dimer acid in the present invention is obtained by thermally polymerizing unsaturated fatty acids such as purified vegetable fatty acids obtained from drying oils, semi-drying oils, or the like, or obtained by partially or completely hydrogenating them. It refers to saturated fatty acids. These dimer acids are mainly composed of dimers of unsaturated fatty acids or hydrogenated products thereof, but also include trimers and tetramers. These may be known or commercially available products. Examples of commercially available products that can be used include “Pripole”, “Pliplast” (manufactured by Croda), “Empor”, “Sobamol” (manufactured by Cognis), “Unidim” (manufactured by Arizona Chemical), and the like.

  And as an acid component of the copolyester resin of this invention, if it is a range which does not impair a characteristic, you may contain things other than an above-described component. For example, saturated aliphatic dicarboxylic acids exemplified by succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, 1,3-cyclobutanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, etc. Or these ester-forming derivatives, unsaturated aliphatic dicarboxylic acids exemplified by fumaric acid, maleic acid, itaconic acid or the like, or ester-forming derivatives thereof, phthalic acid, 5- (alkali metal) sulfoisophthalic acid, 2, Examples thereof include aromatic dicarboxylic acids exemplified by 6-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, and the like, and ester-forming derivatives thereof. Examples of polyvalent carboxylic acids other than dicarboxylic acids include butanetetracarboxylic acid, pyromellitic acid, trimellitic acid, trimesic acid, 3,4,3 ′, 4′-biphenyltetracarboxylic acid, and ester-forming derivatives thereof. Can be mentioned.

  As a glycol component which comprises the copolymerization polyester resin of this invention, ethylene glycol and neopentyl glycol are included as a copolymerization component. The content of neopentyl glycol needs to be 30 to 60 mol%, preferably 35 to 55 mol%. By containing neopentyl glycol, excellent adhesiveness can be imparted to the resin. When the content of neopentyl glycol is less than 30 mol%, such an effect cannot be imparted, and insoluble matter when dissolved in an organic solvent at a solid content of 30 to 60% by mass, Prone to reprecipitation of solids. On the other hand, when the content of neopentyl glycol exceeds 60 mol%, a cyclic oligomer composed of terephthalic acid and neopentyl glycol is likely to be formed, and in this case, it is dissolved in an organic solvent at a solid content of 30 to 60% by mass. In this case, re-precipitation of insoluble matter and solid content is likely to occur.

  Moreover, it is preferable to contain 20-70 mol% of ethylene glycol as a glycol component, and it is preferable to contain 25-60 mol% especially. Ethylene glycol is preferably used because it is inexpensive and has excellent heat resistance. When the content of ethylene glycol is less than 20 mol%, the heat resistance is poor. On the other hand, when the content of ethylene glycol exceeds 70 mol%, the content of neopentyl glycol decreases and the effect of improving adhesiveness is poor. Also, when dissolved in an organic solvent, insoluble matter and solid reprecipitation Is likely to occur.

  As a glycol component of the copolyester resin of the present invention, a component other than the components described above may be contained as long as the characteristics are not impaired. For example, 1,4-butanediol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6 -Aliphatic glycol exemplified by hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, polyethylene glycol, polytrimethylene glycol, polytetramethylene glycol and the like, hydroquinone, 4,4'-dihydroxybisphenol, Use of aromatic glycols exemplified by 1,4-bis (β-hydroxyethoxy) benzene, bisphenol A, 2,5-naphthalenediol, glycols obtained by adding ethylene oxide to these glycols, and the like Kill. Examples of the polyhydric alcohol other than glycol include trimethylolmethane, trimethylolethane, trimethylolpropane, pentaerythritol, glycerol, hexanetriol and the like.

And the copolymer polyester resin of this invention needs that the amount of hydroxyl terminal groups is 5-30 mgKOH / g, and it is preferable that it is 10-20 mgKOH / g especially. The reason why it is necessary to make the hydroxyl group end group amount within the above range will be described below.
The copolymerized polyester resin of the present invention is preferably used as an adhesive, and particularly preferably used after being dissolved in the organic solvent as described above. And after dissolving copolyester resin in the organic solvent, it is preferable to add and use a hardening agent just before using it as an adhesive agent.

  Here, it is preferable to use an isocyanate compound as the curing agent. Examples of the isocyanate compound include 2,4- or 2,6-tolylene diisocyanate, xylylene diisocyanate, 4,4′-diphenylmethane diisocyanate, methylene diisocyanate, isopropylene diisocyanate, lysine diisocyanate, 2,2,4- or 2, Of an isocyanate compound selected from 4,4-trimethylhexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, isopropylidene dicyclohexyl-4,4′-diisocyanate, etc. Adducts comprising the above isocyanate compounds selected from a single substance or at least one kind, DOO body, can be used isocyanurate.

The copolyester resin of the present invention dissolved in an organic solvent has a high cohesive force as the hydroxyl terminal in the resin reacts with the isocyanate group in the curing agent to increase the molecular weight. Alternatively, the adhesiveness of the copolyester resin is improved by curing due to the occurrence of a crosslinking reaction. Due to such actions and effects, an adhesive having excellent adhesiveness can be obtained.
When the hydroxyl group end group content in the copolymerized polyester resin is less than the above range, the resin has a high molecular weight, so the solubility in a solvent is lowered, and the number of sites that react with isocyanate groups in the curing agent is reduced. Therefore, the adhesive has a low crosslinking density and a poor effect of improving adhesiveness. On the other hand, when the amount of hydroxyl terminal groups is larger than the above range, the resin has a low molecular weight and a low cohesive force, resulting in an adhesive having poor adhesion.

  The solution viscosity when the copolymerized polyester resin of the present invention is dissolved in a solvent so as to have a solid content of 40% by mass is preferably 50 to 2000 mPa · s, and more preferably 200 to 1500 mPa · s. . By setting the solution viscosity within this range, a solution having excellent coatability can be obtained. If it is less than 50 mPa · s, the solution tends to flow and it becomes difficult to obtain a uniform coating film. If it exceeds 2000 mPa · s, it is difficult for the solution to flow and the leveling property is lowered, so that coating becomes difficult.

  In addition, in order to make the hydroxyl group terminal group amount and solution viscosity of the copolyester resin of the present invention within the above ranges, by adjusting the reaction conditions for the polycondensation reaction and the depolymerization reaction in the production method as described later. It becomes possible.

  Moreover, although the copolyester resin of this invention can make a glass transition point into -10 degrees C or less by having the above compositions, it is preferable that it is -30 degreeC--15 degreeC especially. When the glass transition point is higher than −10 ° C., the adhesive strength of the resin is inferior, so that the adhesive strength with the substrate is low.

  And, the copolyester resin of the present invention is excellent in adhesion to polyester resins and fluorine resins, among others, as the polyester resin, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene succinate, Examples of the fluororesin include polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride (hereinafter sometimes abbreviated as PVF), and polychlorotrifluoroethylene.

  Furthermore, the copolymer polyester resin of the present invention can have a molecular weight of 3000 or more by having the composition as described above, and among these, it is preferably 5000 to 30000. When the molecular weight is 3000 or more, the adhesiveness with the above-described polyester resin or fluorine-based resin is excellent.

The copolyester resin of the present invention can further improve wet heat durability by using a resin composition to which a carbodiimide compound is added.
It is preferable to add 0.1-20 mass parts of carbodiimide compounds with respect to 100 mass parts of copolyester resin.
The carbodiimide compound is preferably a polycarbodiimide having two or more carbodiimide groups in one molecule in order to suppress an apparent decrease in molecular weight due to a cross-linking reaction between an acid terminal and a carbodiimide group generated by hydrolysis of the polyester resin.

Next, the manufacturing method of the copolyester resin of this invention is demonstrated. After the esterification reaction of the acid component and glycol component at 150 to 250 ° C., polycondensation is performed at 230 to 300 ° C. under reduced pressure to obtain a copolyester resin. Alternatively, a copolyester resin is obtained by polycondensation at 230 ° C. to 300 ° C. under reduced pressure after a transesterification reaction at 150 ° C. to 250 ° C. using a derivative such as dimethyl ester of the acid component and a glycol component. At this time, in order to obtain the desired amount of the hydroxyl terminal group of the obtained copolymer polyester resin, the temperature and time are appropriately adjusted.
And, in order to adjust the amount of hydroxyl terminal groups, 0 to 10 parts by weight of an acid component and a glycol component are added to the copolymer polyester resin obtained by the polycondensation reaction as described above, and 220 to The depolymerization reaction is performed at a temperature of 280 ° C. At this time, in order to obtain the desired amount of the hydroxyl terminal group of the obtained copolymer polyester resin, the temperature and time are appropriately adjusted.

  The copolymerized polyester resin of the present invention can be suitably used as an adhesive. However, when the adhesive is used as an adhesive, the copolymerized polyester resin of the present invention is solidified in an organic solvent as described above. It is preferable to dissolve at a concentration of 30 to 60% by mass.

  In addition, when the adhesive is used, after the copolymer polyester resin of the present invention is dissolved in an organic solvent as described above, an isocyanate compound as described above is added and used as a curing agent immediately before use. It is preferable. At this time, the addition amount of the curing agent (isocyanate compound) should be such that the molar ratio of the isocyanate group of the curing agent to the terminal hydroxyl group of the polyester resin is in the range of NCO / OH = 0.5 to 2.0. Is preferred.

  Next, the present invention will be specifically described using examples. The measurement and evaluation methods for various characteristic values in the examples are as follows.

(A) Intrinsic viscosity [η]
Measurement was performed under the conditions of a sample concentration of 0.5 mass% and a temperature of 20 ° C. using a mixture of equal mass of phenol and ethane tetrachloride as a solvent.
(B) Solution viscosity The obtained copolymer polyester resin was melt | dissolved in ethyl acetate so that it might become 40 mass% of non volatile matters, and it measured on 25 degreeC conditions with the VT-04 bisco tester by Rion Co., Ltd.

(C) Glass transition point Using a Perkin Elmer diamond DSC, the temperature was increased and decreased at 10 ° C./min. The glass transition temperature (extrapolated glass transition start temperature) in the temperature rise curve of 2nd scan was defined as Tg.

(D) Polymer composition The obtained copolyester resin was dissolved in a mixed solvent having a volume ratio of 1/20 of deuterated hexafluoroisopropanol and deuterated chloroform, and the LA-400 NMR apparatus manufactured by JEOL Ltd. was used. 1H-NMR was measured and determined from the integrated intensity of the proton peak of each copolymer component in the obtained chart.

(E) Amount of hydroxyl terminal groups The obtained copolymer polyester resin was acetylated with excess acetic anhydride, and then measured by neutralization titration according to a conventional method.

(F) Solubility Solubility when the obtained copolymer polyester resin was dissolved in ethyl acetate so as to have a nonvolatile content of 40% by mass was visually evaluated in the following three stages.
○: Uniformly dissolved Δ: Turbidity is observed, but there is no practical problem ×: Insoluble matter is generated, and there is a practical problem

(G) Peel strength (adhesiveness)
For the solution obtained by dissolving the obtained copolymer polyester resin in ethyl acetate so as to have a nonvolatile content of 40% by mass, the molar ratio of the isocyanate group to the terminal hydroxyl group of the copolymer polyester resin is NCO / OH = hexamethylene diisocyanate as a curing agent. It added so that it might become 1.2, and it was set as the adhesive agent.
Two base films were prepared, and the obtained adhesive was applied to one base film using a bar coater, heat treated at 100 ° C. for 1 minute, and a laminate sheet having an adhesive layer having a dry thickness of 10 μm Was made. The laminating sheet was overlaid with the corona surface of the other substrate film, pressed at a temperature of 80 ° C. and a pressure of 100 kPa for 30 seconds, and laminated. The obtained laminate sheet was aged at 50 ° C. for 96 hours, and then cut into a width of 15 mm to obtain a sample. Using this sample, a T-type peel test was performed at 23 ° C., and peel strength was measured according to JIS K-6854-3 using an AGS-100A autograph manufactured by Shimadzu Corporation. The base material composition was the following [Composition], and the peel strength was 5.0 N / 15 mm or more.
[Configuration]: <Base film> / Adhesive / <Base film>
Base film =: Toray Industries, trade name Lumirror X10S, thickness 125 μm

(H) Wet heat durability (adhesiveness)
Prepare a sample similar to (g), and use a thermo-hygrostat (Yamato Scientific Co., Ltd., model IG420) to hold the sample for 1000 hours under the conditions of a temperature of 85 ° C. and a humidity of 85%. went. The peel strength after the wet heat treatment was measured by the same method as in the above (g), and the retention with respect to the peel strength before the wet heat treatment (untreated) was calculated by the following formula. A retention rate of 90% or more was accepted.
Retention rate (%) = [(peel strength after wet heat treatment) / (untreated peel strength)] × 100

Example 1
A slurry of terephthalic acid and ethylene glycol (EG) (molar ratio 1 / 1.6) is continuously supplied to the esterification reactor, and reacted under the conditions of a temperature of 250 ° C. and a pressure of 0.2 MPa, and the residence time is 8 As a time, a reaction product having an esterification reaction rate of 95% was obtained.
The obtained esterified product 40.2 parts by weight, isophthalic acid 24.9 parts by weight, dimer acid 87.2 parts by weight, neopentyl glycol 23.4 parts by weight, bisphenol A ethylene oxide adduct 39.5 parts by weight, ethylene glycol 4.7 parts by weight were put into a reaction vessel, and an esterification reaction was performed at 240 ° C. for 3 hours. Next, 0.1 part by weight of tetra-n-butyl titanate is added to the reaction vessel, and the pressure is gradually reduced to 1.3 hPa over 60 minutes, and then 250 ° C. until the desired intrinsic viscosity is reached. The polycondensation reaction was carried out. Thereafter, 0.7 parts by weight of trimethylolpropane was put into a reaction vessel, and a depolymerization reaction was performed while stirring at 250 ° C. for 1 hour to obtain a copolymer polyester resin having the composition and characteristic values shown in Table 1.

Examples 2-5, Comparative Examples 1-6
Using the acid components and glycol components shown in Table 1, in the same manner as in Example 1, the raw materials were added so as to have the resin composition shown in Table 1, and esterification reaction and polycondensation reaction were carried out to obtain a copolyester resin. Got. At this time, the copolymerization resin was obtained while appropriately adjusting the time and temperature of the depolymerization reaction so that the obtained copolymer polyester resin had the hydroxyl group end group amount shown in Table 1.

  Table 1 shows the compositions and characteristic values of the copolyester resins obtained in Examples 1 to 5 and Comparative Examples 1 to 6.

As is clear from Table 1, the copolymer polyester resins obtained in Examples 1 to 5 were excellent in solubility in organic solvents, good adhesion to the substrate, and excellent in wet heat durability. .
On the other hand, the copolyester resin obtained in Comparative Example 1 contained more than 35 mol% of dimer acid, and thus the resin cohesive force was low and the adhesive strength was poor. Since the copolymerized polyester resin obtained in Comparative Example 2 had a dimer acid content of less than 8 mol%, the adhesive strength was low and the wet heat durability was also poor. Since the copolymerized polyester resin obtained in Comparative Example 3 had a neopentyl glycol content of less than 30 mol%, it was poor in solubility in organic solvents and inferior in adhesive strength. Since the copolymerized polyester resin obtained in Comparative Example 4 had a neopentyl glycol content of more than 60 mol%, it was poor in solubility in organic solvents. Since the copolymerized polyester resin of Comparative Example 5 had a hydroxyl terminal group amount of less than 5 mgKOH / g, it was inferior in solubility in an organic solvent and had low adhesive strength. The copolymerized polyester resin of Comparative Example 6 had a hydroxyl terminal group amount exceeding 30 mgKOH / g, and therefore had poor adhesion and low adhesive strength.

Claims (2)

In the polyester resin consisting of an acid component and a glycol component, the acid component contains terephthalic acid, isophthalic acid and dimer acid, the total content of terephthalic acid and isophthalic acid in the acid component is 65 to 92 mol%, in the acid component The dimer acid content is 8 to 35 mol%, the glycol component contains ethylene glycol and neopentyl glycol, the neopentyl glycol content in the glycol component is 30 to 60 mol%, and A copolymer polyester resin, wherein the resin has a hydroxyl group end group content of 5 to 30 mg KOH / g. The copolymerization polyester resin of Claim 1 whose compounding ratio (molar ratio) of the terephthalic acid and isophthalic acid in an acid component is terephthalic acid / isophthalic acid = 60 / 40-40 / 60.