JP2000143958A - Unsaturated polyester resin for flexible frp sheet and its use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an unsaturated polyester resin for flexible FRP sheet which is excellent in folding property and workability, especially at low temperature and consequently excellent in substrate-following property and is important as a waterproof material and has good water resistance and provide its use. SOLUTION: This unsaturated polyester resin for flexible FRP sheet comprises 40-70 pts.wt. unsaturated polyester having >=3000 number-average molecular weight and obtained by reacting an acid component composed of 10-25 mol% α,β-unsaturated polybasic acid and the balance of a saturated polybasic acid with an alcohol component comprising >=80 mol% polyhydric alcohol having ether bond and 30-60 pts.wt. polymerizable monomer. The flexible FRP sheet is obtained by using the unsaturated polyester resin. A FRP waterproof sheet Comprises the flexible FRP sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an unsaturated polyester resin for a flexible FRP sheet and its use. More specifically, the present invention relates to an unsaturated polyester resin for a flexible FRP sheet containing a specific unsaturated polyester and a specific amount of a polymerizable unsaturated monomer, and its use, that is, a flexible FRP sheet and an FRP waterproof sheet.

[0002]

2. Description of the Related Art Conventionally, asphalt, rubber sheet, PVC sheet, urethane resin, acrylic resin, and the like have been used as a waterproof material for a rooftop or the like, but swelling due to adhesion to a base and low strength of the material itself has been used. Due to the problem of cracks and cracks, methods of lining and coating a resin composition comprising an unsaturated polyester resin and glass fiber are increasing.

However, since this method is a method in which a lining layer is formed directly on an underlayer, defects occur in the lining layer due to variations in the curing time of the resin depending on the skill of the operator and the season. Have a problem. In addition, there is also a problem that a large amount of styrene monomer in the unsaturated polyester resin volatilizes during the formation of the lining layer, thereby damaging the worker's health and the environment around the construction site.

In order to solve these problems, a glass fiber reinforced resin molded plate having flexibility has been proposed (JP-A-1-193329), and a concrete structure having the glass fiber reinforced resin molded plate as a coating layer ( JP-A-9-1137
6) has also been proposed. The glass fiber reinforced resin molded plate having this flexibility is generally called a soft FRP sheet, and is currently used for building materials such as daylighting boards, waterproof materials such as rooftops and outer walls, and outer shell layers of gasoline and other storage tanks. It is used and is formed by combining glass fibers with an unsaturated polyester resin containing an unsaturated polyester and a polymerizable monomer. Then, in order to provide the molded plate with flexibility, the acid component, which is one of the raw materials for producing the unsaturated polyester, is composed of a specific amount of an unsaturated polybasic acid and a saturated polybasic acid, and the alcohol component, which is the other raw material. Is characterized by using a glycol having 4 or more carbon atoms.

[0005]

Although the above-mentioned formed plate overcomes the above-mentioned drawbacks, it is insufficient in flexibility, and has poor bending workability, especially flexibility imparting under low temperatures such as in winter. The problem has not been fully solved. That is,
Because the resin increases in hardness at low temperatures, in the construction in winter, the curl of the molded plate remains, making the construction difficult,
Since the ability to follow the underlying shape is reduced, there remains a problem that it is difficult to perform defect-free construction when the underlying surface has irregularities.
In addition, lack of ground followability, cracking of the material due to impact or the like is also jeopardized.

Accordingly, an object of the present invention is to provide a flexible FRP sheet which has sufficient flexibility even under low temperatures, has excellent base followability, and has good water resistance, and an unsaturated polyester resin suitable for an FRP waterproof sheet. , Its use ie soft FR
An object of the present invention is to provide a P sheet and an FRP waterproof sheet.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that polyhydric alcohol having an ether bond is used as an alcohol component in order to increase flexibility, and an acid component is used as an alcohol component. To reduce the amount of unsaturated polybasic acid, to eliminate the lack of water resistance by reducing the amount of unsaturated polybasic acid can be solved by increasing the molecular weight of the unsaturated polyester, unsaturated polyester by increasing the molecular weight Thus, the present invention has been completed, with the idea that the deterioration of workability due to the increase in viscosity can be eliminated by increasing the amount of the polymerizable monomer. That is, when the unsaturated polyester resin containing the specific unsaturated polyester and the specific amount of the polymerizable monomer is used for the FRP sheet, the bendability, particularly the workability at a low temperature, can be improved. ,
Excellent base-following properties can be exhibited, and F
The inventors have also found that water resistance, which is important as an RP waterproofing material, is good, and completed the present invention.

That is, the unsaturated polyester resin for a flexible FRP sheet according to the present invention comprises a polyolefin having an ether component in an acid component consisting of 10 to 25 mol% of α, β-unsaturated polybasic acid and the balance of saturated polybasic acid. 80 mol% of dihydric alcohol
Unsaturated polyester 4 having a number average molecular weight of 3000 or more obtained by reacting the alcohol component containing
It is characterized by containing 0 to 70 parts by weight and 30 to 60 parts by weight of a polymerizable monomer.

The flexible FRP sheet according to the present invention is formed by combining the unsaturated polyester resin according to the present invention with a reinforcing material to form a sheet. It consists of an FRP sheet.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The unsaturated polyester resin according to the present invention contains a specific unsaturated polyester and a specific amount of a polymerizable monomer. Here, the specific unsaturated polyester is an α, β-unsaturated polybasic acid (including its anhydride) having an acid component of 10 to 25 mol%, preferably an α, β-unsaturated dibasic acid ( Including its anhydride) and the remainder, ie, 75-9
0 mol% of a saturated polybasic acid (including its anhydride), preferably a saturated dibasic acid (including its anhydride), and containing at least 80 mol% of a polyhydric alcohol having an ether bond as an alcohol component. This is one in which a polyhydric alcohol is used.

In the present invention, the α, β-unsaturated polybasic acid or its anhydride is specifically exemplified by, for example,
Maleic acid, maleic anhydride, fumaric acid, itaconic acid,
Examples thereof include itaconic anhydride, citraconic acid, and esters thereof, and maleic acid, maleic anhydride, and fumaric acid are preferably used from the viewpoint of economy and reactivity. In the present invention, as the saturated polysalt acetic acid or anhydride thereof, in addition to isophthalic acid and terephthalic acid, for example, phthalic acid,
Phthalic anhydride, Tetrahydrophthalic acid, Tetrahydrophthalic anhydride, Endomethylenetetraphthalic anhydride, Hexahydrophthalic acid, Hexahydrophthalic anhydride, Cyclohexanedicarboxylic acid, Oxalic acid, Succinic acid, Malonic acid, Glutaric acid, Adipic acid , Azelaic acid, sebacic acid, glutaric acid, l, 12-docanedioic acid, dimer acid,
2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,
Examples thereof include 3-naphthalenedicarboxylic anhydride, 4,4'-biphenyldicarboxylic acid, trimellitic acid, and pyromellitic acid.

In the present invention, specific examples of the polyhydric alcohol having an ether bond include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, polypropylene glycol, and bisphenol. An adduct of A with an alkylene oxide such as propylene oxide or ethylene oxide may, for example, be mentioned.

In the present invention, if it is less than 20% by weight, a polyhydric alcohol other than the above-mentioned polyhydric alcohol having an ether bond can be used in combination. Specific examples of such polyhydric alcohols include, for example, ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. , Neopentyl glycol, 1,4-cyclohexanediol, 1,3-cyclohexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanedimethanol, 2-methylpropane-1,3-diol, hydrogenated bisphenol A, Trimethylolpropane and the like.

In the present invention, the mixing ratio of the alcohol component to the acid component is not particularly limited, but the total hydroxyl group of the alcohol component is based on the total carboxyl groups of the polybasic acid component (anhydrous is converted to water-containing). Is preferably 1.05 times or less. If the proportion of the alcohol component is more than 1.05, it is difficult to make the number average molecular weight 3000 or more.

The reaction conditions for the condensation reaction between the acid component and the alcohol component are not particularly limited. For example, the temperature is 180 to 230 ° C. and the time is 5 to 30.
Time. The reaction temperature and the reaction time are appropriately set so that an unsaturated polyester having a molecular weight described below is obtained and the condensation reaction is completed. When performing this condensation reaction, if necessary, additives such as a catalyst for promoting the condensation reaction and an antifoaming agent can be used. The condensation reaction is preferably performed in an atmosphere of an inert gas such as nitrogen or helium.

The number average molecular weight of the unsaturated polyester needs to be 3000 or more, preferably in the range of 3000 to 5000. Number average molecular weight is 30
If it is less than 00, the cured product lacks flexibility and water resistance and becomes brittle, and in consideration of handleability, the amount of the polymerizable monomer decreases and the water resistance of the sheet cannot be sufficiently obtained. The problem arises. The number average molecular weight is 5
When it is larger than 000, the viscosity becomes extremely high, and the handleability of the composition containing the same decreases.

In the present invention, the polymerizable monomer is not particularly limited, but styrene is preferred for improving water resistance. In this case, it is preferable that styrene is mixed in the polymerizable monomer in an amount of 50% by weight or more. In addition to styrene, α-methylstyrene, divinylbenzene, vinyltoluene, paramethylstyrene, t-butylstyrene, diallyl phthalate, methyl (meth) acrylate, ethylene glycol di (meth) acrylate,
Diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, 2-hydroxyethyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, methoxydiethylene glycol (meth) acrylate, trimethylolpropane tri (meth) acrylate May be used in combination.

The weight ratio of the unsaturated polyester to the polymerizable monomer in the unsaturated polyester resin is 7: 3 to 4:
6 is required. If the proportion of the polymerizable monomer is less than the above range, the water resistance of the cured product is reduced, while if the proportion of the polymerizable monomer is more than the above range, the waterproof sheet becomes brittle and the like. This is because physical properties deteriorate.

The unsaturated polyester resin according to the present invention is usually cured by adding a curing agent. Such a curing agent is not particularly limited, but includes, for example, diisopropyl peroxydicarbonate, benzoyl peroxide, methyl ethyl ketone peroxide,
t-butyl peroxy-2-ethylhexanoate,
1,1,3,3-tetramethylbutylperoxy-2-
Ethyl hexanoate, t-amyl peroxy-2-ethyl hexanoate, t-butyl hydroperoxide,
Organic peroxides such as t-butyl peroxy neodikenate, t-butyl peroxy benzoate, cumene hydroperoxide, and azo compounds such as azobisisobutyronitrile and azobisdiethylvaleronitrile. The mixing ratio of the curing agent is 10% for the unsaturated polyester resin.
The amount is preferably in the range of 0.5 to 5 parts by weight with respect to 0 parts by weight.

In the present invention, a curing accelerator may be added to the unsaturated polyester resin. Examples of the curing accelerator include cobalt naphthenate, cobalt octenoate, divalent acetylacetone cobalt, trivalent acetylacetone cobalt, potassium octenoate, zirconium naphthenate, zirconium acetylacetonate, vanadium naphthenate, vanadium octenoate, and vanadium acetonate. And metal salts such as lithium acetylacetonate, and these metal salts may be used in combination with an amine compound, a phosphorus-containing compound, a β-diketone compound, or the like. The amount of the curing accelerator is preferably in the range of 0.005 to 2 parts by weight with respect to 100 parts by weight of the unsaturated polyester resin,
More preferably, it is in the range of 0.01 to 1 part by weight.

The unsaturated polyester resin according to the present invention is preferably blended with a polymerization inhibitor for the purpose of controlling storage stability and curability. As the polymerization inhibitor, known compounds can be used as they are. Typical examples thereof include hydroquinone, methylhydroquinone, p
-T-butylcatechol, t-butylhydroquinone,
Toluhydroquinone, p-benzoquinone, naphthoquinone, methoxyhydroquinone, hydroquinone monomethyl ether, trimethylhydroquinone, 2,5-di-
t-butyl hydroquinone, phenothiazine, copper naphthenate, etc., which are used alone and 2
More than one species may be used in combination.

The unsaturated polyester resin according to the present invention may have a thixotropic property. For this purpose, for example, colloidal silica, fimed silica, silica airgel, organically modified clay, clay, silica powder, acetic acid Cellulose and Aerosil (Nippon Aerosil),
A thixotropic agent such as thixogel (Yokohama Kasei Co., Ltd.), Dispalon (Kusumoto Kasei Co., Ltd.), or Leolo Seal (Tokuyama Soda Co., Ltd.) is added. The compounding amount of the thixotropy-imparting agent is 0.5 to 5 with respect to 100 parts by weight of the unsaturated polyester resin.
It is preferably within the range of 1 part by weight, more preferably within the range of 1 to 3 parts by weight.

The unsaturated polyester resin according to the present invention is blended with an auxiliary material (additive) as required.
Such auxiliary materials include colorants such as dyes, extenders, ultraviolet absorbers, antioxidants, antibacterial agents, antifungal agents, plasticizers, leveling agents, defoamers, silane coupling agents,
Examples include an antistatic agent, a flame retardant, a lubricant, a viscosity reducing agent, a low shrinkage agent, an inorganic filler, an organic filler, a desiccant, a dispersant, and the like.

Although the unsaturated polyester resin according to the present invention is used for various uses, it is preferably used for producing a flexible FRP sheet, particularly preferably for producing an FRP waterproof sheet. When forming a soft FRP sheet, the above-mentioned various compounding materials are added to the unsaturated polyester resin according to the present invention as needed, and then a reinforcing material is combined. As such a reinforcing material, for example, glass fibers such as glass cloth, roving cloth, chopped strand, chopped strand mat, and organic fibers such as aramid fiber, amide, vinylon, polyester, and phenol are used alone or in combination. Is done. An integrated fiber of glass fiber and organic fiber may be used. The form of the fiber includes plain weave, satin weave, non-woven fabric, and mat, and is selected in consideration of workability, sheet strength, sheet flexibility, and economy.

The content of the above fibers in the soft FRP sheet is suitably not more than 60% by weight. However, from the viewpoint of exhibiting bending workability and flexibility while maintaining mechanical strength, in the case of glass cloth and roving cloth, 30 to 60% by weight, 10 to 30% by weight for chopped strand or chopped strand mat, 5 to 15 for organic fiber
% By weight is preferred.

The flexible FRP sheet according to the present invention is a sheet in which a cured resin is reinforced with reinforcing fibers. The width of this sheet is preferably 500 to 2000 mm, and more preferably 500 to 1200 mm in consideration of portability. The thickness of this sheet is preferably from 0.3 to 2.5 mm, more preferably from 0.6 to 1.2 mm. The flexible FRP sheet according to the present invention is manufactured by a batch method from a resin syrup obtained by mixing a polymerizable monomer and various additives with a curable resin, or by a continuous molding method as exemplified below.
The continuous molding method is preferable because of good productivity and good quality stability.

The flexible FRP sheet is generally manufactured by a continuous forming method called a film forming method (sheet forming method). This method includes, for example, steps shown in FIG. That is, the lower surface release film 1 is continuously fed, and a resin syrup 3 containing a curable resin is flown from the resin tank 2 thereon, thereby sequentially forming the resin layer 4. Since the roller cutter 5 is disposed at the subsequent stage of the resin tank 2 and the glass roving 6 is continuously supplied, the chopped strands 7 are sequentially obtained by the roller cutter 5, and the chopped strands 7 are sequentially formed on the resin layer 4 which is sequentially formed. And the reinforcing fiber layer 8 is sequentially formed. The reinforcing fiber layer 8 once formed in this way is sequentially impregnated with the resin of the resin layer 4 therebelow, so that the curable resin 3 and the reinforcing fibers (chopped A mixed layer 9 of strands 7 is made. Therefore,
An upper release film 10 is continuously stacked on the mixed layer 9 and sequentially fed into a thickness adjusting roller 11 to adjust the thickness of the mixed layer 9, and then, the mixed layer 9 is sent to a curing furnace 12 to cure the curable resin. By continuously curing, the flexible FRP sheet 13 is continuously obtained. The obtained soft FRP sheet 13
The product is wound into a roll through a process of peeling off the lower surface release film 1 and the upper surface release film 10 and a width cutting process for uniforming the width dimension, thereby obtaining a product.

Unlike the above, the reinforcing fiber, for example, glass chopped strand mat, is first placed on the lower release film 1.
In some cases, the mixed layer 9 is formed by continuously laying the resin syrup 3 thereon and flowing the resin syrup 3 from above. The reinforcing fiber may be a non-woven fabric or a woven fabric. In the above method, the release films 1 and 10 are not particularly limited,
Examples include a polyester film such as a T film, a polyvinyl alcohol film, and a nylon film.

[0029]

The present invention will now be described by way of examples, which should not be construed as limiting the invention. In the text, "part" means
Indicates parts by weight. (Synthesis Example 1) In a four-necked flask equipped with a thermometer, a stirrer, an inert gas injection pipe and a reflux condenser, 8.0 mol of triethylene glycol, 2.3 mol of propylene glycol, 4.5 mol of isophthalic acid, Adipic acid (3 mol) was charged, and a condensation reaction was performed at 210 ° C. to an acid value of 10 while blowing nitrogen gas. Cool to 150 ° C., charge 2.5 mol of maleic anhydride, raise the temperature to 210 ° C., 15 hours
The condensation reaction was carried out to obtain an unsaturated polyester having a number average molecular weight of 3,200. By adding 35 parts of styrene and 0.01 part of hydroquinone to 65 parts of the obtained unsaturated polyester, an unsaturated polyester resin A having an acid value of 7 and a viscosity of 8 poise was obtained. (Synthesis Example 2) In the same reactor as in Synthesis Example l, 10.3 moles of diethylene glycol, 3 moles of terephthalic acid, and 5.5 moles of phthalic anhydride were charged.
The condensation reaction was carried out at 20 ° C. to an acid value of 5. Cool to 150 ° C. and add fumaric acid l. 5 mol was charged and the temperature was raised to 210 ° C.
The condensation reaction was performed for 15 hours to obtain an unsaturated polyester having a number average molecular weight of 3,500. Obtained unsaturated polyester 6
By adding 40 parts of styrene and 0.01 part of hydroquinone to 0 parts, an unsaturated polyester resin B having an acid value of 10 and a viscosity of 4.5 poise was obtained. (Comparative Synthesis Example 1) In the same reactor as in Synthesis Example 1, 9.0 moles of diethylene glycol and propylene glycol l. 5
Mol, 3.0 mol of terephthalic acid, 2.5 mol of phthalic anhydride, and 1.5 mol of adipic acid, and a condensation reaction was performed at 220 ° C. to an acid value of 10 while blowing nitrogen gas. 150
C. and cooled to 3.0 moles of maleic anhydride.
The temperature was raised to 5 ° C., and a condensation reaction was performed for 15 hours to obtain an unsaturated polyester having a number average molecular weight of 2500. By adding 35 parts of styrene and 0.01 part of hydroquinone to 65 parts of the obtained unsaturated polyester, an unsaturated polyester resin C having an acid value of 26 and a viscosity of 6 poise was obtained. (Comparative Synthesis Example 2) In the same reactor as in Synthesis Example 1, 5.0 mol of dipropylene glycol and 5.5 of ethylene glycol were used.
Mol, 9.2 mol of phthalic anhydride and 0.8 mol of fumaric acid, and a condensation reaction was performed at 210 ° C. for 15 hours while blowing nitrogen gas to obtain an unsaturated polyester having a number average molecular weight of 2,000. By adding 30 parts of styrene and 0.01 part of hydroquinone to 70 parts of the obtained unsaturated polyester, an unsaturated polyester resin D having an acid value of 27 and a viscosity of 4.0 poise was obtained. (Examples 1 to 4, Comparative Examples 1 to 4) Cobalt octenoate (metal content 8%) and Permec N (manufactured by NOF Corporation) were 0.3% and 1%, respectively, for the resins of the above synthesis examples and comparative synthesis examples. Was stirred and mixed, impregnated with a reinforcing material, covered on both sides with a Tetron film, and cured at room temperature. Furthermore, it cured at 80 degreeC for 2 hours, produced the soft FRP sheet, and evaluated flexibility and water resistance. The results are shown in Table 1.

Abbreviations of various alcohol components and abbreviations of various acid components in Table 1 are as follows. EG: ethylene glycol PG: propylene glycol DEG: diethylene glycol DPG: dipropylene glycol TEG: triethylene glycol FA: fumaric acid MA: maleic anhydride PA: phthalic anhydride IPA: isophthalic acid TPA: terephthalic acid AA: adipic acid As material, glass mat MC-300A
(Manufactured by Nitto Bo) or a polyester nonwoven fabric (manufactured by Toyobo, Spunbond-Volans, model number 4172P) was used.

The flexibility was evaluated as follows. ×: Cracks occur in the sheet when wound around a 10 mmφ iron pipe. Δ: No crack was formed in the sheet even when wound around a 10 mmφ iron pipe. ：: No crack was formed in the sheet even when wound around an iron pipe of 5 mmφ. Water resistance was evaluated by immersing each sheet in hot water at 80 ° C. as follows. ×: Cracks and blisters occur along the fiber within 100 hours. ：: No change in appearance even after immersion for 100 hours or more.

[0032]

[Table 1]

[0033]

The unsaturated polyester resin for a flexible FRP sheet according to the present invention is rich in flexibility at low temperatures, has good water resistance, and has good workability. Since the flexible FRP sheet according to the present invention uses the unsaturated polyester resin according to the present invention, it has excellent bendability, particularly excellent workability at a low temperature, excellent base followability, and good water resistance. Has become.

Since the FRP waterproof sheet according to the present invention is composed of the flexible FRP sheet according to the present invention, it has good water resistance, which is important as a waterproof sheet, and exhibits more excellent waterproof performance.

[Brief description of the drawings]

Fig. 1 Flexible FR by film forming method (sheet forming method)
Explanatory drawing which shows the process of manufacturing a P sheet

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lower surface release film 2 Resin tank 3 Resin syrup 4 Resin layer 5 Roller cutter 6 Glass roving 7 Chopped strand 8 Reinforcement fiber layer 9 Mixing layer 10 Top release film 11 Thickness adjustment roller 12 Curing furnace 13 Soft FRP sheet

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiki Nagai 8-1 Techno Park, Mita-shi, Hyogo Japan Polyester Co., Ltd. (72) Inventor Yoshinori Uno 5-8 Nishi-Otabicho, Suita-shi, Osaka Japan Within the catalyst (72) Inventor Masahiko Kajino 5-8, Nishiomitabi-cho, Suita-shi, Osaka F-term (reference) 4F071 AA22 AA49 AA81 AC02 AF01 AF17 AF26 AF53 BC01 4J002 CF221 EA046 EH076 FD146 4J027 AB06 AB07 AB08 AB23 AB24 AB25 AC03 AC04 AJ01 BA05 CA14 CA15 CA17 CA32 CA36 CA38 CB03 CB09 CC02 CD02 4J029 AA07 AB04 AB07 AC02 AD01 AE03 AE18 BA02 BA03 BA05 BA07 BA08 BA09 BA10 BD03A BD04A BD07A BD10 BF09 BF10 CA05 BF18 CA05 BF18 CA02 CB10A CC03A CC05A CC06A CD03 CD04 FC05 FC12 FC14 GA12 GA13 GA14 GA15 GA17 GA23 HA01 HB01 JE182 KD01 KD09 KE 05 KH01

Claims (5)

[Claims] 1. An α, β-unsaturated polybasic acid in an amount of 10 to 25 mol%.
And an alcohol component containing at least 80 mol% of a polyhydric alcohol having an ether bond with an acid component consisting of a saturated polybasic acid as a balance, to obtain a number average molecular weight of 3
An unsaturated polyester resin for a flexible FRP sheet, comprising 40 to 70 parts by weight of an unsaturated polyester of 000 or more and 30 to 60 parts by weight of a polymerizable monomer. 2. The method according to claim 1, wherein said saturated polybasic acid is isophthalic acid and / or
The unsaturated polyester resin for a flexible FRP sheet according to claim 1, which is a saturated polybasic acid containing terephthalic acid in an amount of 30 mol% or more. 3. The unsaturated polyester resin for a flexible FRP sheet according to claim 1, wherein the polymerizable monomer is styrene. 4. A flexible FRP sheet formed by combining the unsaturated polyester resin according to claim 1 with a reinforcing material to form a sheet. 5. An FRP waterproof sheet comprising the flexible FRP sheet according to claim 4.