JP2011068019A - Transparent fiber reinforced resin sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent fiber reinforced resin sheet securing a high glass transition temperature durable to surface processing while keeping a high transparency, and suppressing birefringence. <P>SOLUTION: The transparent fiber reinforced resin sheet 1 is composed of a laminate formed of a central layer wherein a cured matter 5 of a curable transparent resin is held on a base material 4 of transparent reinforce fiber and an outer layer formed of a cured matter 6 of the curable transparent resin laminated on both outer sides of the central layer. The glass transition temperature of the cured matter 6 of the curable transparent resin of the outer layer in the laminate is higher than that of the cured matter 5 of the curable transparent resin of the central layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a transparent fiber reinforced resin sheet.

  Conventionally, in a flat panel display such as a liquid crystal display, a plasma display, and an EL display, a transparent fiber in which a cured product of a curable transparent resin is held on a substrate of a transparent reinforcing fiber such as a glass fiber as an alternative to a glass plate A reinforced resin sheet has been proposed (see, for example, Patent Document 1).

  When manufacturing such a transparent fiber reinforced resin sheet, for example, a high refractive index resin having a refractive index larger than that of glass fiber and a low refractive index resin having a refractive index smaller than that of glass fiber are mixed to have a refractive index. The resin composition is prepared so as to approximate the refractive index of the glass fiber. A glass fiber base material is impregnated with the resin composition, dried and semi-cured to prepare a prepreg, and the prepreg is heated and pressed to produce a transparent fiber reinforced resin sheet.

  Thus, by combining the refractive indexes of the glass fiber and the transparent resin, the refraction of light in the transparent fiber reinforced resin sheet can be suppressed and used as a transparent film of a display having excellent visibility.

  As a resin composition for producing a transparent fiber reinforced resin sheet, an epoxy resin is generally used, and in order to approximate the refractive index of the glass fiber, the epoxy resin having a refractive index larger than that of the glass fiber and The resin composition is prepared by mixing an epoxy resin having a refractive index smaller than that of the glass fiber so that the refractive index approximates the refractive index of the glass fiber.

  However, in a transparent fiber reinforced resin sheet prepared using a resin composition in which an epoxy resin with a high refractive index and an epoxy resin with a low refractive index are mixed, minute cracks or peeling at the interface between the epoxy resin and the glass fiber substrate If this occurs, haze may increase due to the minute cracks or peeling, and transparency may be reduced. For this reason, it has been studied to suppress minute cracks and peeling occurring at the interface between the epoxy resin and the glass fiber substrate by using an epoxy resin having a low glass transition temperature.

  However, when using an epoxy resin having a low glass transition temperature, there is a problem that the heat resistance of the transparent fiber reinforced resin sheet is lowered and the processing to the surface cannot be endured at the use environment temperature. There has been a demand for a transparent fiber reinforced resin sheet having a high glass transition temperature. Thus, Patent Document 2 discusses the use of a resin system having a high glass transition temperature.

JP 2004-307851 A JP 2009-190378 A

  However, when a resin with a high glass transition temperature is used in subsequent studies, in a transparent fiber reinforced resin sheet after molding and curing, birefringence occurs in the vicinity of the glass fiber, and when used for a liquid crystal display device or the like that requires a polarizing plate. In addition, it has been found that the contrast is lowered due to the occurrence of light leakage. This is because the resin shrinks on the glass fiber surface due to internal shrinkage caused by the thermal shrinkage of the resin and glass fiber in the temperature range below the glass transition temperature during cooling from the curing temperature to room temperature during molding curing. This is considered due to the occurrence of orientation.

  The present invention has been made in view of the circumstances as described above, and while maintaining high transparency, while ensuring a high glass transition temperature that can withstand surface processing, a transparent fiber reinforced resin sheet that suppresses birefringence It is an issue to provide.

  The present invention is characterized by the following.

  1stly, the laminated body formed from the center layer by which the hardened | cured material of curable transparent resin is hold | maintained at the base material of the transparent reinforcing fiber, and the outer layer which consists of hardened | cured material of the curable transparent resin laminated | stacked on the both sides The glass transition temperature of the cured product of the curable transparent resin of the outer layer in the laminate is higher than the glass transition temperature of the cured product of the curable transparent resin of the center layer. Features.

  Second, the first invention is characterized in that a plurality of laminated bodies are formed by being laminated.

  Third, in the first or second invention, the glass transition temperature of the cured product of the curable transparent resin of the outer layer in the laminate is 200 ° C. or higher, and the glass transition of the cured product of the curable transparent resin of the center layer. The temperature is 160 ° C. or lower.

  Fourth, in the first to third inventions, the curable transparent resin of the outer layer in the laminate contains a dicyanate having an aromatic ring and a polyfunctional aliphatic epoxy resin.

  According to the first and second inventions described above, the glass transition temperature of the cured product of the curable transparent resin of the outer layer in the laminate is higher than the glass transition temperature of the cured product of the curable transparent resin of the center layer. While maintaining transparency, the curable transparent resin of the outer layer of the laminate exhibits heat resistance when processing the liquid crystal display device or the like using the transparent fiber reinforced resin sheet according to the present invention. The curable transparent resin in the center layer exhibits an effect of suppressing birefringence by performing a stress relaxation function with the substrate surface of the transparent reinforcing fiber.

  According to the third aspect, the glass transition temperature of the cured product of the curable transparent resin of the outer layer in the laminate is 200 ° C. or higher, and the glass transition temperature of the cured product of the curable transparent resin of the center layer is 160 ° C. or lower. Since the surface rigidity is ensured at a molding temperature of 170 ° C. to 190 ° C. of a general curable transparent resin, the sheet surface after molding can be kept smooth. Further, internal stress generated between the curable transparent resin of the central layer of the laminate and the substrate surface of the transparent reinforcing fiber at the molding temperature can be reduced, and the birefringence of the transparent fiber reinforced resin sheet can be further reduced. .

  According to 4th invention, the curable transparent resin of the outer layer in a laminated body contains the dicyanate which has an aromatic ring, and a polyfunctional aliphatic epoxy resin, The dicyanate which has an aromatic ring, and a polyfunctional aliphatic epoxy Due to the transparency of the resin itself and the ease of preparation for adjusting the refractive index of the resin composition to the refractive index of the transparent reinforcing fiber, it is possible to ensure a high glass transition temperature while maintaining even higher transparency. In addition, since the dicyanate having an aromatic ring is solid at room temperature, in the preparation of a prepreg to be dried by impregnating the transparent reinforcing fiber substrate with the resin composition, the touch drying property is improved and the handling property is improved. Has the advantage of

It is sectional drawing which shows one Embodiment of the transparent fiber reinforced resin sheet concerning this invention. It is sectional drawing which shows another embodiment of the transparent fiber reinforced resin sheet concerning this invention.

Hereinafter, the present invention will be described in detail.

  FIG. 1 is a cross-sectional view showing an embodiment of a transparent fiber reinforced resin sheet according to the present invention. The transparent fiber reinforced resin sheet 1 is composed of a laminate having a three-layer structure formed of a center layer and outer layers on both outer sides thereof. In the center layer of the laminate, a cured product 5 of a curable transparent resin is held on a base 4 of transparent reinforcing fibers such as glass fibers made up of a plurality of warp fiber bundles 2 and a plurality of weft fiber bundles 3. The outer layer of the laminate is a resin layer formed from a cured product 6 of a curable transparent resin, but has a Tg higher than the glass transition temperature (Tg) of the cured product 5 of the curable transparent resin of the center layer. It consists of The transparent fiber reinforced resin sheet 1 concerning this invention is not limited to what is comprised with a single laminated body like FIG. For example, as shown in FIG. 2, the laminate having the three-layer structure shown in FIG. 1 may be formed by stacking two sheets in the thickness direction, or by stacking three or more sheets. It may be what has been done.

  In the present invention, the curable transparent resin of the outer layer of the laminate is composed of a curable transparent resin having a Tg higher than the Tg of the cured curable transparent resin of the center layer. In order to realize a transparent transparent resin and a curable transparent resin having a low Tg, it is only necessary to adopt a resin blend in which the cured network density is changed. The higher the polyfunctional content contributing to curing, the higher the Tg, and the lower the Tg. Lower Tg.

  Examples of the epoxy resin constituting the curable transparent resin that contributes to high Tg include, for example, a cresol novolac type epoxy resin, a phenol novolac type epoxy resin, a trifunctional epoxy resin having a bisphenol A skeleton represented by the following formula (1), Examples thereof include polyfunctional aliphatic epoxy resins and hydrogenated bisphenol A type epoxy resins. Further, it may be an acrylic or methacrylic resin as a radical curable resin, and may be a polyfunctional resin having various basic skeletons.

  Specific examples of the polyfunctional aliphatic epoxy resin include an epoxy resin containing 1,2-epoxy-4- (2-oxiranyl) cyclohexane (for example, product number EHPE-3150 manufactured by Daicel Chemical Industries, Ltd.) and trifunctional fat. Group epoxy resin (for example, product number YH300 manufactured by Tohto Kasei Co., Ltd.).

  Examples of the epoxy resin constituting the curable transparent resin that contributes to lowering Tg include, for example, bisphenol A type and F type epoxy resins on the market with various numbers of nuclei, and hydrogenated aliphatics thereof. Epoxy resin, an epoxy resin having an epoxy resin at both ends of a linear skeleton and capable of expressing so-called flexibility (for example, epoxy at both ends of polyalkylene glycol diglycidyl ether type epoxy or cyclic ester ring-opening polymerization) And a reactive diluent which is a monofunctional epoxy resin, etc.). Examples of the radical curable resins include styrenes, bifunctional acrylics, monofunctional acrylics, and methacrylic compounds.

  In the present invention, the curable transparent resin of the central layer of the laminate and the curable transparent resin of the outer layer each have a refractive index that is the refractive index of the transparent reinforcing fiber in order to maintain the transparency of the transparent fiber reinforced resin sheet. It is desirable to adjust to a value approximated to. For example, when the refractive index of the transparent reinforcing fiber is n, the refractive index of each curable transparent resin is desirably adjusted so as to approximate in the range of n−0.02 to n + 0.02. In the present invention, the refractive index of the resin means the refractive index in the state of the cured resin, and is a value tested by ASTM D542.

  Thus, in order to prepare the refractive index of each curable transparent resin close to the refractive index of the transparent reinforcing fiber, it is realized by mixing the high refractive index resin and the low refractive index resin at an appropriate blending ratio. Is done.

  The high refractive index resin is a resin having a refractive index higher than that of the transparent reinforcing fiber. Examples of the curable transparent resin described above include bisphenol A type epoxy resin, bisphenol F type epoxy resin, the above formula ( Examples thereof include a trifunctional epoxy resin having a bisphenol A skeleton represented by 1) and a dicyanate having an aromatic ring.

The low refractive index resin is a resin whose refractive index is lower than that of the transparent reinforcing fiber, and some examples of the above curable transparent resin include 1,2-epoxy-4- (2-oxiranyl) cyclohexane. Examples thereof include an epoxy resin and a hydrogenated bisphenol A type epoxy resin.
The ratio of the high refractive index resin to the low refractive index resin is preferably 40:60 to 55:45 in mass ratio when using E glass that is inexpensive and has stable supply quality as the transparent reinforcing fiber. If the ratio deviates from this ratio, it is difficult to match the refractive index of the resin to the refractive index of E glass in many resins.

  In the present invention, each of the curable transparent resins in the central layer and the outer layer of the laminate is either a type that cures by heat or a photocuring type that initiates a curing reaction with active energy rays (electromagnetic waves of various wavelengths, light, etc.). It may be. In the case of the photo-curing type, the reaction often proceeds further by heating after light irradiation, and it is preferable to perform heat treatment.

  Each curable transparent resin can also contain fine particles of metal oxide such as silica (about 1 nm to 5 μm). Thereby, the thermal expansion coefficient of the transparent fiber reinforced resin sheet can be reduced, and the optical characteristics can be improved.

  In the present invention, in order to more effectively achieve both the heat resistance required for maintaining the surface smoothness of the transparent fiber reinforced resin sheet and the suppression of birefringence, the curing of the curable transparent resin of the outer layer of the laminate is performed. It is desirable to prepare each curable transparent resin such that the Tg of the product is 200 ° C. or higher and the Tg of the cured product of the curable transparent resin of the center layer is 160 ° C. or lower.

  The reason why it is desirable that the Tg of the cured product of the curable transparent resin of the outer layer of the laminate is 200 ° C. or higher is to allow the resin to undergo a curing reaction with heat and to maintain transparency after curing. It is necessary to prevent alteration coloring with heat, and the heat treatment temperature is preferably about 200 ° C. or less. In addition, it is known that the higher the transistor formation temperature of amorphous silicon, the better the characteristics of the transistor. However, development has progressed so that a high-performance transistor can be formed on an organic sheet. Another reason is that formation in the temperature range is becoming possible. When the Tg of the cured curable transparent resin of the outer layer of the laminate is less than 200 ° C., the resin elastic modulus decreases at the use environment temperature of the transparent fiber reinforced resin sheet, cannot resist internal stress, and the surface smoothness deteriorates. May end up. If the Tg of the cured product of the curable transparent resin of the outer layer of the laminate is 200 ° C. or higher, the surface smoothness of the transparent fiber reinforced resin sheet is maintained even at the use environment temperature. Since this effect is more excellent as Tg is higher, more preferable Tg is 230 ° C. or higher. Since the Tg of the cured product of the curable transparent resin can generally be realized only up to about 260 ° C., the upper limit is about 260 ° C.

  The reason why it is desirable that the Tg of the cured curable transparent resin of the central layer of the laminate is 160 ° C. or less is that the birefringence of the transparent fiber reinforced resin sheet can be greatly reduced. Tg is more preferably 120 ° C. or lower. There is no particular limitation on the lower limit, but it is preferable that the glass-like region is at room temperature because the rigidity at room temperature of the transparent fiber reinforced resin sheet can be expressed and handling properties are improved, and generally available resins are considered. Then, it can be said that Tg is about 90 ° C. or more as an industrially valid range. When Tg exceeds 160 ° C., the stress due to shrinkage at the time of curing and the thermal stress due to the difference in thermal expansion between the resin from Tg to room temperature and the transparent reinforcing fiber in the process of cooling from the curing temperature to room temperature. In some cases, the resin in the vicinity of the transparent reinforced fiber is oriented, which causes birefringence in the transparent fiber reinforced resin sheet.

  In the present invention, the glass transition temperature is a value measured according to the JIS C6481 TMA method.

  In this invention, the resin composition containing the dicyanate which has an aromatic ring can be used as curable transparent resin of the outer layer of a laminated body.

  A dicyanate having an aromatic ring is a compound having two or more cyanate groups in one molecule having an aromatic skeleton. For example, 2,2-bis (4-cyanatephenyl) propane, bis (3,5- Aromatic cyanate ester compounds such as dimethyl-4-cyanatephenyl) methane, 2,2-bis (4-cyanatephenyl) ethane, and derivatives thereof. These may be used alone or in combination of two or more. The dicyanate having an aromatic ring has a rigid molecular skeleton and is trimerized in the course of the polymerization reaction to produce a triazine ring. Therefore, the transparency of the cured product is extremely excellent and a high glass transition temperature can be realized. . Moreover, since it is solid at normal temperature, in preparing a prepreg that is impregnated with a resin composition on a transparent reinforcing fiber substrate and dried, there is an advantage that the touch drying property is improved and the handling property is improved.

  Furthermore, in this invention, it is preferable to use the resin composition which also contains the above-mentioned polyfunctional aliphatic epoxy resin with said dicyanate which has an aromatic ring as curable transparent resin of the outer layer of a laminated body. While maintaining even higher transparency by the transparency of the dicyanate having an aromatic ring and the transparency of the polyfunctional aliphatic epoxy resin itself and the ease of preparation to match the refractive index of the resin composition with the refractive index of the transparent reinforcing fiber, This is because a high glass transition temperature can be secured.

  In the present invention, each of the curable transparent resins of the central layer and the outer layer of the laminate can be a resin composition containing a curing initiator (curing agent). An organic metal salt can be used as the curing initiator. Specific examples thereof include salts of organic acids such as octanoic acid, stearic acid, acetylacetonate, naphthenic acid and salicylic acid with metals such as Zn, Cu and Fe. These may be used alone or in combination of two or more. Of these, zinc octoate is preferable. By using zinc octoate as the curing initiator, the Tg of the curable transparent resin can be increased. The content of an organic metal salt such as zinc octoate in the resin composition is preferably in the range of 0.01 to 0.1 PHR.

  A cationic curing agent can also be used as the curing initiator. By using a cationic curing agent, the transparency of the cured product of the resin composition can be enhanced. Specific examples of the cationic curing agent include aromatic sulfonium salts, aromatic iodonium salts, ammonium salts, aluminum chelates, and boron trifluoride amine complexes. The content of the cationic curing agent in the resin composition is preferably in the range of 0.2 to 3.0 PHR.

  Further, a curing catalyst such as a tertiary amine such as triethylamine or triethanolamine, 2-ethyl-4-imidazole, 4-methylimidazole, 2-ethyl-4-methylimidazole or the like can also be used as a curing initiator. The content of the curing catalyst in the resin composition is preferably in the range of 0.5 to 5.0 PHR.

  The present invention can prepare a resin composition having a high Tg and a resin composition having a low Tg by blending the above-described plurality of resins and, if necessary, a curing initiator. . These resin compositions can be prepared as a resin varnish by dissolving or dispersing in a solvent as necessary. Examples of the solvent include benzene, toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, acetone, methanol, ethanol, isopropyl alcohol, 2-butanol, ethyl acetate, butyl acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, Acetone alcohol, N, N'-dimethylacetamide, etc. are mentioned.

  The transparent reinforcing fibers constituting the base material in the central layer of the laminate need only be ones that are not colored and have a thermal expansion coefficient that is an order of magnitude lower than that of the curable transparent resin. For example, glass fibers are suitable, but transparent liquid crystalline polymer fibers may also be used. As the glass fiber, fiber of E glass or NE glass is preferably used from the viewpoint of enhancing the impact resistance of the transparent fiber reinforced resin sheet. E glass is also referred to as non-alkali glass, and is a glass fiber that is widely used as a glass fiber for resin reinforcement. NE glass is NewE glass.

  The glass fiber is preferably surface-treated with a silane coupling agent usually used as a glass fiber treating agent for the purpose of improving impact resistance. The refractive index of the glass fiber is preferably 1.55 to 1.57, more preferably 1.555 to 1.565. If the refractive index of glass fiber is this range, the transparent fiber reinforced resin sheet excellent in visibility can be obtained. In the present invention, a woven or non-woven fabric of glass fiber can be used as a substrate.

  And a prepreg can be produced by coating or impregnating a glass fiber substrate with a resin composition, heating and drying. The drying conditions are not particularly limited, but a drying temperature of 100 to 160 ° C. and a drying time of 1 to 10 minutes are preferable.

  In the present invention, the prepreg is produced by the following procedure. First, a resin varnish of a resin composition having a cured product having a low Tg is applied to both surfaces of a transparent reinforcing fiber substrate, and then the cured product having a high Tg is applied to both outer sides of the coated surface. The resin varnish is coated and dried. Alternatively, a resin varnish of a resin composition having a cured product having a low Tg is applied to both sides of the substrate of the transparent reinforcing fiber and dried, and then the cured product has a high Tg on both outer sides of the coated surface. A resin varnish of the resulting resin composition may be applied and dried. In order to apply the resin varnish, a general coating apparatus can be used. For example, any material that can be applied to both sides of a sheet-like object such as a dip coater, a lip coater, a comma coater, a die coater, and a gravure coater may be used.

  Next, one or a plurality of the prepregs are stacked and heated and pressed to cure the resin composition, thereby obtaining a transparent fiber reinforced resin sheet. The one produced by heat-pressing one prepreg is the transparent fiber reinforced resin sheet shown in FIG. 1, and the one produced by heat-pressing two prepregs laminated is the transparent fiber shown in FIG. It is a reinforced resin sheet.

  The conditions for the heat and pressure molding are not particularly limited, but a temperature of 150 to 200 ° C., a pressure of 1 to 4 MPa, and a time of 10 to 120 minutes are preferable. The apparatus for performing heat and pressure molding may be a flat plate press capable of being heated, or may be a press apparatus of a type that passes between two sets of looped metal plate belts in a heat and pressure state.

  In the transparent fiber reinforced resin sheet obtained as described above, the content of the transparent reinforcing fiber substrate is preferably in the range of 25 to 65% by mass, more preferably in the range of 35 to 60% by mass. If it is this range, while being able to acquire high impact resistance with the reinforcement effect by a transparent reinforcing fiber, sufficient transparency can be acquired. When there are too many transparent reinforcing fibers, the unevenness | corrugation of the surface will become large and transparency will also fall. On the other hand, when there are too few transparent reinforcement fibers, the problem that a linear expansion coefficient becomes large will arise.

  In addition, as a base material of a transparent reinforcement fiber, in order to obtain transparency, what laminated | stacked multiple thin things can be used. Specifically, a substrate having a thickness of 50 μm or less can be used as the substrate of the transparent reinforcing fiber, and two or more substrates of the transparent reinforcing fiber having a thickness of 50 μm or less can be used. Although the minimum of the thickness of the base material of a transparent reinforcing fiber is not specifically limited, About 10 micrometers is a practical minimum. Further, the number of transparent reinforcing fiber substrates is not particularly limited, but about 20 is the practical upper limit.

EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to these Examples at all. In addition, the compounding quantity of Table 1 shows a mass part.
<Raw materials used>
1. High refractive index resin / BADCy, manufactured by Lonza, 2,2-bis (4-cyanatephenyl) propane (dicyanate having an aromatic ring), refractive index 1.59
VG3101, manufactured by Printec Co., Ltd., a solid trifunctional epoxy resin having a bisphenol A skeleton represented by the above formula (1), refractive index 1.59
・ Epicoat 1006, manufactured by Japan Epoxy Resin Co., Ltd., solid bisphenol A type epoxy resin, refractive index 1.60
EPICLON N695, manufactured by DIC Corporation, solid cresol novolac epoxy resin, refractive index 1.59
2. Low refractive index resin / EHPE3150, manufactured by Daicel Chemical Industries, Ltd., an epoxy resin containing solid 1,2-epoxy-4- (2-oxiranyl) cyclohexane, refractive index 1.51
・ YL7170, manufactured by Japan Epoxy Resin Co., Ltd., solid hydrogenated bisphenol A type epoxy resin (polyfunctional epoxy resin having 3 or more epoxy groups on average in one molecule)
3. Curing initiator, industrial reagents zinc octoate, SI-150L, available from Sanshin Chemical Industry Co., Ltd., cationic curing agent (SbF ₆ ^- sulfonium salt)
4). Transparent reinforcing fiber base material, glass fiber cloth with a thickness of 25 μm, manufactured by Asahi Kasei Electronics Co., Ltd., product number “1037”, E glass, refractive index 1.562
<Method for preparing resin varnish>
The above-mentioned high refractive index resin, low refractive index resin, and curing initiator are blended in the amounts shown in Table 1 (blending amount is parts by mass), to which 50 parts by mass of toluene and 50 parts by mass of methyl ethyl ketone are added, and the temperature is 70 A resin varnish of the resin composition was prepared by stirring and dissolving at ° C.
<Prepreg production method>
Preparation method of prepreg of Example 1-7 After applying a resin varnish of a resin composition having a cured product having a low Tg on both surfaces of a transparent reinforcing fiber substrate, the solvent is dried at 130 ° C. for 3 minutes. Remove. Next, a resin varnish of a resin composition having a cured product having a high Tg is applied to both outer sides of the coated surface, and dried at 150 ° C. for 5 minutes, thereby removing the solvent and semi-curing the resin. A prepreg was prepared. Adjust the first coating amount to 60 to 80% and the second coating amount to 20 to 40% with respect to the total amount of resin after being applied and dried twice on the transparent reinforcing fiber substrate. did.
Preparation Method of Prepreg of Comparative Example 1-2 A resin varnish is applied to both surfaces of a transparent reinforcing fiber substrate, and dried at 150 ° C. for 5 minutes, thereby removing the solvent and semi-curing the resin to produce a prepreg. did. The amount of the resin applied to the substrate of the transparent reinforcing fiber and the amount after drying were adjusted so as to be the same amount as in the example.
<Method for producing transparent fiber reinforced resin sheet>
Two sheets of prepreg are stacked and set in a press machine, and heated and pressed under conditions of 170 ° C., 2 MPa, 30 minutes to obtain a transparent fiber reinforced resin sheet having a resin content of 63 mass% and a thickness of about 80 μm. Obtained.
<Characteristic evaluation method>
・ Glass transition temperature (Tg)
The resin component was scraped off from the prepared prepreg, and a resin plate obtained by direct pressure molding under the same conditions as the molding conditions of the transparent fiber reinforced resin sheet was used as a test sample and measured according to JIS C6481 TMA method.
-Refractive index The resin board obtained by the method similar to the test sample preparation method of Tg was grind | polished, and it measured with the refractive index measuring apparatus by an Atago company.
-Haze The transparent fiber reinforced resin sheet was measured based on JIS K7136 using Nippon Denshoku Industries Co., Ltd. haze meter NDH2000.
-Birefringence With a polarizing microscope (manufactured by Nikon Corporation, model number MM-40), the optical axes of the two polarizing plates are set at a right angle, a dark field is observed with a microscope, and in that state, between the two polarizing plates, The transparent fiber reinforced resin sheet is put, and the transparent fiber reinforced resin sheet is rotated in a horizontal plane so that the visual field around the fiber is brightest while observing with a microscope. The difference from the dark field is evaluated in the state where the visual field around the fiber is brightest. The case where there was no difference from the dark field was evaluated as “◯”, the case where the periphery of the fiber was slightly brighter than the dark field was evaluated as “Δ”, and the case where it was clearly bright was evaluated as “×”.
・ Surface roughness (flatness)
Surface unevenness (Ra value) was measured. For the measurement, a surface roughness tester SURFCOM 130A made by Tokyo Seimitsu Co., Ltd. was used, and the surface irregularities (Ra value) of the transparent fiber reinforced resin sheet were measured at three points in the vertical, horizontal, and 45 ° bias directions, The average value of the measured values of 9 points in total was taken as the Ra value of the transparent fiber reinforced resin sheet.
-Surface roughness after heat treatment The transparent fiber reinforced resin sheet was heated at 180 ° C for 30 minutes, and the surface roughness was measured in the same manner as described above. The case where the surface roughness was 90 nm or less was evaluated as “◎”, the case where the surface roughness was more than 90 nm and 100 nm or less was evaluated as “◯”, the case where the surface roughness was more than 100 nm and 200 nm or less was evaluated as “Δ”, and the case where the surface roughness was exceeded 200 nm . This evaluation is an index for determining whether the surface smoothness is maintained by the temperature history received in the process of processing the transparent fiber reinforced resin sheet into various devices. This is because, depending on the heat treatment, the internal stress inherent in the resin layer whose deformation is prevented by the transparent reinforcing fibers is relieved, and the surface roughness may be deteriorated as compared with that before the heat treatment.
Color change after heat treatment The transparent fiber reinforced resin sheet was heated at 180 ° C. for 30 minutes, and the color difference before and after that was measured with a spectrocolorimeter CM-3600d manufactured by Konica Minolta Holdings Co., Ltd. The discoloration after heat treatment was evaluated by the difference in values (Δb *).
<Example 1-7>
In the configuration shown in Table 2, a prepreg obtained by coating and drying a resin varnish serving as a center layer resin of a prepreg on a transparent reinforcing fiber substrate and then coating and drying a resin varnish serving as an outer layer resin of the prepreg. Were laminated and molded to produce a transparent fiber reinforced resin sheet. The transparent fiber reinforced resin sheet was evaluated for haze, birefringence, surface roughness, surface roughness after heat treatment, and discoloration due to the color value Δb *. The results are also shown in Table 2.
<Comparative Example 1-2>
With the structure shown in Table 2, the same resin varnish was used for the center layer resin and the outer layer resin, and a transparent fiber reinforced resin sheet was produced and evaluated in the same manner as in the examples.

  From the result of Example 1-7, when the Tg of the outer layer resin of the prepreg is higher than the Tg of the center layer resin, the birefringence is higher than that of Comparative Example 1-2 in which the Tg of the outer layer resin and the center layer resin is the same. It was confirmed that there was little deterioration in surface roughness after heat treatment, and there was little discoloration after heat treatment.

  Further, in Example 4-7, the Tg of the outer layer resin of the prepreg is 200 ° C. or higher, and the Tg of the center layer resin is 160 ° C. or lower, so that after birefringence or heat treatment, as compared with Example 1-3. It was confirmed that the deterioration of the surface roughness was further suppressed.

  Further, from the results of Example 6-7, the outer layer resin of the prepreg contained a dicyanate having an aromatic ring and a polyfunctional aliphatic epoxy resin, so that the surface roughness after the heat treatment was compared with Example 1-5. It was confirmed that the degree of deterioration was extremely small. It was also confirmed that there was very little discoloration after heat treatment.

DESCRIPTION OF SYMBOLS 1 Transparent fiber reinforced resin sheet 4 Base material of transparent reinforcement fiber 5 Hardened | cured material of curable transparent resin of center layer 6 Hardened | cured material of curable transparent resin of outer layer

Claims (4)

  Consists of a laminate formed of a central layer in which a cured product of a curable transparent resin is held on a transparent reinforcing fiber substrate and an outer layer made of a cured product of a curable transparent resin laminated on both outer sides thereof. A transparent fiber reinforced resin sheet, wherein the glass transition temperature of the cured product of the curable transparent resin of the outer layer in the laminate is higher than the glass transition temperature of the cured product of the curable transparent resin of the center layer Fiber reinforced resin sheet.   The transparent fiber reinforced resin sheet according to claim 1, wherein a plurality of laminates are laminated.   The glass transition temperature of the cured product of the curable transparent resin of the outer layer in the laminate is 200 ° C or higher, and the glass transition temperature of the cured product of the curable transparent resin of the center layer is 160 ° C or lower. The transparent fiber reinforced resin sheet according to 1 or 2.   The transparent fiber-reinforced resin sheet according to any one of claims 1 to 3, wherein the curable transparent resin of the outer layer in the laminate contains a dicyanate having an aromatic ring and a polyfunctional aliphatic epoxy resin. .

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