JP2011137124A - Resin composition for light guide sheet, and the light guide sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition for a light guide sheet excellent in heat resistance, wet heat resistance, light resistance, cuttability and the like, capable of preventing a resin from being deteriorated and getting yellowish, and the light guide sheet. <P>SOLUTION: This resin composition for the light guide sheet contains an urethane acrylate having a polyether in its main chain, a monofunctional acrylate, a polyfunctional acrylate, a photopolymerization initiator, an antioxidant, and an ultraviolet absorbent, and an addition amount of the photopolymerization initiator is made to be lower than that of the ultraviolet absorbent, in the resin composition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a resin composition for a light guide sheet and a light guide sheet.

  Conventionally, as disclosed in, for example, Patent Document 1, a light guide sheet (light guide film) used as a light guide for a backlight for a liquid crystal panel such as a mobile phone and guiding light from a light source to the liquid crystal panel. It has been known.

  Further, as such a light guide sheet, for example, as disclosed in Patent Document 2, from a photocurable resin composition having a urethane acrylate containing a polyether chain, a polyfunctional acrylate, a monofunctional acrylate, and a photopolymerization initiator. What has been proposed.

JP-A-6-186558 JP2007-332169A

By the way, the conventional light guide sheet as described above has the following problems.
(1) When the light guide sheet is exposed to ultraviolet rays, the material of the light guide sheet is deteriorated. Specifically, radicals are generated by ultraviolet rays, and the material of the light guide sheet turns yellow due to oxidation caused by radicals.
(2) Under high temperature and high humidity, the decomposition product bleeds out due to hydrolysis of the main agent (urethane acrylate, monofunctional acrylate or polyfunctional acrylate).
(3) The cutting performance is poor, the end face varies, and in the case of the configuration in which the light source is arranged on the end face of the light guide sheet, the light capturing efficiency differs for each light guide sheet.

  The present invention solves the above-mentioned problems, is excellent in heat resistance, heat and humidity resistance, light resistance, cutting ability, etc., can prevent deterioration and yellowing of the resin, and improve the light capture efficiency. The present invention provides a light guide sheet resin composition and a light guide sheet that are extremely practical.

  The gist of the present invention will be described.

  A resin composition for a light guide sheet comprising a urethane acrylate having a polyether in the main chain, a monofunctional acrylate, a polyfunctional acrylate, a photopolymerization initiator, an antioxidant, and an ultraviolet absorber, The addition amount of the photopolymerization initiator is related to the resin composition for a light guide sheet, which is less than the addition amount of the ultraviolet absorber.

  The resin composition for a light guide sheet according to claim 1, wherein the photopolymerization initiator and the ultraviolet absorber are added in a ratio of 1: 1 to 2. It relates to the composition.

  Moreover, the resin composition for light guide sheets of any one of Claims 1 and 2 WHEREIN: The weight average molecular weights of the said urethane acrylate are 10000-20000, It concerns on the resin composition for light guide sheets characterized by the above-mentioned. Is.

  Moreover, in the resin composition for light guide sheets of any one of Claims 1-3, it is set so that the sum total of the said urethane acrylate, the said monofunctional acrylate, and the said polyfunctional acrylate may be 100 weight part, Of the 100 parts by weight, 55 to 70 parts by weight is the urethane acrylate, and this relates to the resin composition for a light guide sheet.

  Moreover, it is a light guide sheet which guides the light from a light source to a predetermined site | part, Comprising: It is formed with the resin composition for light guide sheets of any one of Claims 1-4, The light guide characterized by the above-mentioned. It relates to the sheet.

  A light guide sheet comprising a resin composition for a light guide sheet comprising urethane acrylate, a monofunctional acrylate, a polyfunctional acrylate, a photopolymerization initiator, an antioxidant, and an ultraviolet absorber, The light guide sheet is characterized in that the thickness is set to 50 to 200 μm, the light transmittance at a wavelength of 250 to 330 nm in the thickness direction is 1% or less, and the light transmittance at a wavelength of 380 nm is 85% or more. It relates to a light guide sheet.

  Since the present invention is configured as described above, it is excellent in heat resistance, moist heat resistance, light resistance, cutting ability, etc., can prevent deterioration and yellowing of the resin, and can also improve the light capture efficiency. The resin composition for a light guide sheet and the light guide sheet are extremely excellent in practicality.

10 is a table showing experimental conditions of Experimental Example 1. 10 is a table showing experimental results of Experimental Example 1. 10 is a table showing experimental conditions of Experimental Example 2. 10 is a table showing experimental results of Experimental Example 2. It is a schematic explanatory drawing explaining the measuring method of tack property. It is a schematic explanatory drawing explaining the measuring method of heat resistance. It is a schematic explanatory drawing explaining the measuring method of wet heat resistance. It is a schematic explanatory drawing explaining the measuring method of light resistance. It is the graph which compared the transmittance | permeability of the Example of thickness 200 micrometers, and a comparative example. It is the graph which compared the transmittance | permeability with the Example and thickness of a comparative example of 100 micrometers. It is the graph which expanded a part of FIG. It is the graph which expanded a part of FIG. It is the graph which expanded a part of FIG.

  The preferred embodiment of the present invention will be briefly described by showing the operation of the present invention.

  In addition to adding antioxidants, the amount of photopolymerization initiator added is less than the amount of UV absorber added, which significantly suppresses deterioration and yellowing of the resin due to UV rays irradiated from the outside after resin curing. Can do. Specifically, it is based on the following mechanism.

  That is, the main role of the photopolymerization initiator is to generate radicals, and these radicals are generated when a certain wavelength (short wavelength = ultraviolet) hits. This radical becomes an active species and reacts with the main monomer or functional group at the end of the polymer to form a resin having a three-dimensional network structure or a desired molecular weight. However, in the cured resin, there is an unreacted photopolymerization initiator, which generates radicals by ultraviolet rays from the outside, attacks molecules in the resin, degrades the resin, and turns yellow. Or it may turn yellow.

  In this respect, the present invention adds an antioxidant for capturing radicals that do not contribute to the reaction, which cause deterioration and yellowing of the above resin, and more UV absorber than the photopolymerization initiator. Therefore, it is possible to efficiently absorb ultraviolet rays irradiated from the outside after the resin is cured, and to significantly suppress deterioration and yellowing of the resin. In addition, sufficient hardening can be achieved by increasing the amount of ultraviolet irradiation during the reaction.

  Further, by adding a polyfunctional acrylate (monomer), the crosslink density is improved and a three-dimensional network structure is formed, thereby exhibiting excellent heat resistance. Further, by adopting urethane acrylate having a polyether skeleton in the main chain, and further adopting monofunctional / polyfunctional acrylate (monomer) having high water resistance, for example, excellent moisture and heat resistance and flexibility are exhibited.

  Accordingly, hydrolysis of the main agent is suppressed under high temperature and high humidity, and bleeding of the decomposed product can be prevented.

  In addition, by reducing the number of photopolymerization initiators that do not contribute to the above-mentioned curing, coupled with the adoption of urethane acrylate with a polyether skeleton, it is less susceptible to the influence of the external environment, and is less susceptible to deterioration and yellowing. It becomes.

  Furthermore, for example, by setting the weight average molecular weight of the urethane acrylate of the polyether skeleton to 10,000 to 20,000, excellent cutting properties are expressed, and the variation of the cut surface is suppressed, and the state of the end face is made uniform, and the transparency This makes it possible to make the light capture efficiency uniform.

  Further, for example, when the total of urethane acrylate, monofunctional acrylate and polyfunctional acrylate is set to 100 parts by weight, and 55 to 70 parts by weight of the 100 parts by weight is urethane acrylate, polyether is used. Monofunctional acrylates and polyfunctional acrylates can be blended into the skeleton urethane acrylate at an optimal ratio to balance heat resistance, surface curability, and flexibility, and processed into a sheet (film) even at low viscosity (Coating process) is easy.

  Specific embodiments of the present invention will be described with reference to the drawings.

  This example is a resin composition for a light guide sheet comprising a urethane acrylate having a polyether in the main chain, a monofunctional acrylate, a polyfunctional acrylate, a photopolymerization initiator, an antioxidant, and an ultraviolet absorber. It is a thing, Comprising: The addition amount of the said photoinitiator is a thing smaller than the addition amount of the said ultraviolet absorber.

  The urethane acrylate (main agent A) is not particularly limited as long as it has an ether group in the main chain from the viewpoint of maintaining water resistance, flexibility and (rebound) elasticity, and various types can be adopted.

  The range of the molecular weight of urethane acrylate is 10,000 to 20,000, preferably 10,000 to 15,000. When it is 10000 to 15000, the flexibility is high, the elongation at break is improved, the cutting property is good, and the balance of flexibility, cutting property, curability, and durability is excellent. When the molecular weight is significantly greater than 20000, the flexibility and cleavability are improved, but the viscosity is increased and the number of functional groups is decreased, so that the curability is lowered. Thereby, tack (with a solid) is developed and durability is lowered. In addition, molecular weight is a weight average molecular weight, and it calculated | required from GPC in polystyrene conversion.

  Further, the total of urethane acrylate, monofunctional acrylate and polyfunctional acrylate is set to 100 parts by weight, and 55 to 70 parts by weight of 100 parts by weight is the urethane acrylate. By setting the amount to 55 to 70 parts by weight, the characteristics of the main agent can be exhibited, which is preferable from the viewpoint of flexibility, cutability, curability, and durability after curing.

  The compounding quantity of the monofunctional acrylate (main agent B) is set to 10 to 20 parts by weight. In this case, since it disperses | distributes uniformly in a resin composition and is excellent also in compatibility with urethane acrylate, it becomes a preferable thing from the point of dilution property and sclerosis | hardenability.

  Monofunctional monomers have a high dilution ability and are essential for lowering the viscosity of highly viscous urethane acrylates (oligomers). Moreover, since it is monofunctional, a softness | flexibility can be provided. However, when the concentration is increased, the viscosity is lowered, but the curability is lowered, leading to the appearance of tack (with a solid) and the durability (bleed out of unreacted monomer).

  As monofunctional acrylate (main agent B), methyl methacrylate, ethyl methacrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isobornyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, phenoxyethyl (meth) acrylate Dicyclopentenyloxyethyl (meth) acrylate, isostearyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, caprolactone-modified (meth) acrylate, and isomyristyl (meth) acrylate can also be used.

  The compounding quantity of polyfunctional acrylate (main ingredient C) is set to 20-25 weight part. In this case, it reacts with urethane acrylate and monofunctional acrylate, respectively, and forms a three-dimensional network structure at the time of curing, thereby improving heat resistance.

  Moreover, when only a monofunctional monomer is mix | blended with urethane acrylate, although viscosity reduction and a softness | flexibility will improve, it will lead to the expression of tack and the rebound resilience fall by the surface hardenability fall. In order to improve this, an appropriate amount of a polyfunctional monomer is added to increase the crosslinking density, improve the surface curability and durability at high temperatures, and obtain rebound resilience.

  Multifunctional acrylates include dimethylol tricyclodecane (meth) acrylate, tripropylene glycol di (meth) acrylate, 1.6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane tri Ethoxytri (meth) acrylate, modified trimethylolpropane triethoxytri (meth) acrylate, modified glycerin tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) ) Acrylate can be used.

  The compounding quantity of the photoinitiator (auxiliary agent D) is set to 1.0-2.0 weight part. In this case, even if the thickness of the light guide sheet is several hundred μm, it can be sufficiently cured.

  As photopolymerization initiators, 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl-1-phenyl-propane-1- ON, alkylphenones such as 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis (2, Acylphosphine oxides such as 4,6-trimethylbenzoyl) -phenylphosphine oxide can be used. From the viewpoint of clearness (transparency) after UV curing and durability (yellowing), an alkylphenone polymerization initiator is preferred.

  The compounding quantity of antioxidant (auxiliary agent E) is set to 0.5-1 weight part. Thereby, oxidative degradation can be prevented.

  As the antioxidant, hindered phenols, phosphoruss, and sulfurs can be used. A hindered phenolic antioxidant is preferable from the viewpoint of color such as a clear feeling after UV curing.

  An ultraviolet absorber (auxiliary agent F) can be appropriately added according to the coating thickness.

  As the ultraviolet absorber, oxalic acid anilide type and cyanoacrylate type can be used. The ultraviolet absorption wavelength region of these absorbers that absorbs ultraviolet rays is narrower than the ultraviolet absorption wavelength region of the polymerization initiator, and the ultraviolet absorption wavelength region of these absorbers is in the short wavelength region of the absorption wavelength region of the polymerization initiator. . In other words, because there is an ultraviolet absorption wavelength region of the polymerization initiator that does not overlap with the ultraviolet absorption wavelength region of the absorber, it is not easily affected by curing inhibition by the ultraviolet absorber, and the polymerization initiator is kept lower than the conventional addition amount. be able to. Thereby, the initial coloring at the time of ultraviolet curing and the coloring by ultraviolet deterioration can be suppressed. In consideration of the balance between ultraviolet resistance and curability, it is more preferable to use an oxalic anilide ultraviolet absorber.

  Moreover, it is preferable to add more ultraviolet absorbers than a photoinitiator for the purpose of improving light resistance more. The ratio is preferably such that the ultraviolet absorber is in a ratio of 1 to 2 with respect to the photopolymerization initiator. Here, the ratio means a value obtained by dividing the number of added parts of the ultraviolet absorber by the number of added parts of the photopolymerization initiator. If it is this ratio, yellowing at the time of ultraviolet irradiation will be improved. In the case of less than 1, since the ultraviolet rays irradiated from the outside after resin formation cannot be absorbed efficiently, the light resistance is deteriorated. When it is larger than 2, the reaction of the resin composition is inhibited, and tackiness occurs during curing. Further, in order to obtain a desired cured state, an additional ultraviolet curing process is required in the subsequent process, which is not preferable because production efficiency is lowered.

  In this example, the relationship between the ultraviolet absorber and the wavelength region of the photopolymerization initiator that absorbs ultraviolet rays is the absorption wavelength region of the ultraviolet absorber (˜350 nm: the value when the concentration in the cyclohexane solution is 0.001%. (Value obtained from the spectral transmittance)) is more than the absorption wavelength region of the polymerization initiator (200 to 380 nm: the value when the concentration in the acetonitrile solution is 0.01% (value obtained from the spectral transmittance))) It is assumed that the absorption wavelength region of the ultraviolet absorber is in a short wavelength region shorter than the absorption wavelength region of the polymerization initiator. That is, the absorption wavelength region of the polymerization initiator that does not overlap with the absorption wavelength region of the ultraviolet absorber exists on the long wavelength side. With this relationship, curing inhibition does not occur, and the ultraviolet absorber absorbs high-energy ultraviolet light on the short wavelength side that causes material deterioration (decomposition, yellowing, etc.), and has the effect of improving light resistance.

  Further, in order to improve ultraviolet resistance (light resistance), a hindered amine-based weather resistance (light) stabilizer may be added in addition to the ultraviolet absorber.

  Moreover, the viscosity of the resin composition of a present Example is set to 10000 mPa * s or less near room temperature 25 degreeC.

Further, the elongation at break of the resin composition after curing of this example is set to 50% or more and the tensile stress is set to 5 to 50 MPa or less. Here, the breaking elongation and the tensile stress are measured as follows. First, five dumbbell-shaped No. 3 test pieces based on JIS K6251 are prepared. Next, using a tensile test apparatus (manufactured by Shimadzu Corporation), the tensile speed is set to 200 mm / min, and measurement is performed until the test piece breaks. The breaking elongation is a value obtained from the difference between the length of the test piece before measurement and the length after the measurement, and the tensile stress is a value obtained by dividing the maximum tensile force (N) by the cross-sectional area (mm ² ) of the test piece. is there.

  A light guide sheet is prepared using the resin composition having the above-described configuration.

  Specifically, it is produced by applying the resin composition onto a separate film using a coating apparatus (for example, a slit die coater). In addition, you may apply | coat not only with a slit die coater but with other coating apparatuses, such as a blade (knife) coater, a comma coater, and a roll coater.

By the way, if there is variation in the coating amount, it will be reflected in the thickness of the resin sheet as it is. In particular, when a highly viscous material is applied, it is necessary to apply the resin after heating the resin to lower the viscosity. At this time, since it is simultaneously coated on the separate film and cooled, the viscosity increases, the thickness adjustment is difficult, and bubbles are embraced. In this respect, in this example, since the viscosity of the resin composition is 10000 mPa · s or less at room temperature and the applicability at room temperature is adjusted, a resin sheet having a highly accurate thickness is obtained by curing after application. be able to. In addition, although the integrated light quantity at the time of hardening changes with thickness of the resin sheet, the integrated light quantity when the thickness of the resin sheet is 200 μm is 600 mJ / cm ² .

  In addition, by setting the elongation at break of the resin composition to 50% or more and the tensile stress to 5 to 50 MPa or less, it can be used for breakage and breakage in applications that receive repeated loads, such as button operations on mobile phones. Resistance is improved.

  According to the above production method, a light guide comprising a resin composition for a light guide sheet comprising urethane acrylate, monofunctional acrylate, polyfunctional acrylate, a photopolymerization initiator, an antioxidant, and an ultraviolet absorber. A sheet having a thickness of 50 to 200 μm, a light transmittance at a wavelength of 250 to 330 nm in the thickness direction of 1% or less, and a light transmittance at a wavelength of 380 nm of 85% or more is produced. It becomes possible.

Specifically, for example, the transmittance of Example 4 to be described later is about 90% at a wavelength of 380 nm as shown in FIGS. 9 and 11 (thickness 200 μm) and FIGS. 10 and 12 (thickness 100 μm). The transmittance at 380 to 780 nm) is also 90% or more, and it is less transparent and more transparent. On the other hand, the transmittance of Comparative Example 9, which will be described later, shown in FIG. In this case, there is much absorption in the same wavelength region, and yellowness increases (the same applies to FIG. 12). Moreover, the transmittance | permeability of Example 4 in wavelength 250-330 nm becomes 1% or less as shown in FIG. Thereby, it is possible to prevent deterioration of the material due to ultraviolet rays on the short wavelength side having particularly high energy. In addition, this effect can be expressed regardless of the thickness of the light guide sheet (in Comparative Example 9, there is a portion where the transmittance of ultraviolet light on the short wavelength side exceeds 1%, and the material of the material due to ultraviolet light on the short wavelength side is present. Degradation occurs.) In addition, in FIG. 13, in order to clarify the difference of the transmittance | permeability of Example 4 and the comparative example 9 in wavelength 250-330nm in the said description, the thickness of each light guide sheet was set to 100 micrometers, and the transmittance | permeability was measured. . Further, transmittance, using Hitachi Ltd. spectrophotometer, a value obtained by dividing the previous incident light amount (T ₀₎ through the light guide sheet in the transmitted light amount (T ₁₎ to enter the light guide sheet (T ₁ / T ₀ ) as a percentage (%).

  Moreover, it is preferable to set the Shore A hardness of a light guide sheet to the range of 85-98. In this case, hand handling becomes easy and the operability of buttons such as a cellular phone is improved.

  In addition, although the present Example demonstrates the resin composition for light guide sheets, the said resin composition is apply | coated to base materials, such as a film, and this is pressed on the stamper by which the shape which controls directivity was patterned By curing, a highly transparent (low haze) and highly durable directivity control member (lens) can be obtained. This is because the light guide sheet material can be directly used for the lens material. Moreover, an isotropic and highly transparent film is obtained by apply | coating the said resin composition to a base material. This is because the resin composition uses a highly compatible material, so that the curing rate proceeds uniformly and a uniform cured state can be maintained, resulting in the development of isotropic properties.

  Since this example is configured as described above, an ultraviolet ray irradiated from the outside after resin curing is obtained by adding an antioxidant and making the addition amount of the photopolymerization initiator smaller than the addition amount of the ultraviolet absorber. It is possible to remarkably suppress the deterioration and yellowing of the resin.

  Further, by adding a polyfunctional acrylate (monomer), the crosslink density is improved and a three-dimensional network structure is formed, thereby exhibiting excellent heat resistance. Further, by adopting urethane acrylate having a polyether skeleton in the main chain, and further employing, for example, a monofunctional / polyfunctional acrylate (monomer) having high water resistance, excellent moisture and heat resistance is exhibited.

  Accordingly, hydrolysis of the main agent is suppressed under high temperature and high humidity, and bleeding of the decomposed product can be prevented.

  In addition, by reducing the number of photopolymerization initiators that do not contribute to the above-mentioned curing, coupled with the adoption of urethane acrylate with a polyether skeleton, it is less susceptible to the influence of the external environment, and is less susceptible to deterioration and yellowing. It becomes.

  Further, in this example, the compatibility of the blended materials is good, the composition is cured uniformly, and there are few photopolymerization initiators that do not contribute to the curing, and the UV absorber is not excessively contained, so that unreacted substances and reactions Additives that do not contribute to the decrease are reduced, and bleeding out of the unreacted substances and the like is suppressed.

  Furthermore, by setting the weight average molecular weight of the urethane acrylate of the polyether skeleton to 10,000 to 20,000, excellent cutting properties are expressed, and the variation in the cut surface is suppressed, the end face state is made uniform, and the transparency is also improved. It will be excellent and it will be possible to make the light capture efficiency uniform.

  In addition, the total of urethane acrylate, monofunctional acrylate and polyfunctional acrylate is set to 100 parts by weight, and 55 to 70 parts by weight of the 100 parts by weight is urethane acrylate. Monofunctional acrylates and polyfunctional acrylates can be blended with acrylates in an optimal ratio to balance heat resistance, surface curability, and flexibility, and processed (coated) into a sheet (film) Is easy.

  Therefore, this example is excellent in heat resistance, moist heat resistance, light resistance, cutting ability, etc., can prevent deterioration and yellowing of the resin, and can also improve the light capture efficiency. It will be excellent.

  An experimental example supporting the effect of the present embodiment will be described.

  A method for measuring each characteristic in the experimental example will be described below.

  Cutting performance is achieved by mounting a Thomson punching blade (tip blade angle 20 degrees-double-edged 0.7 mm thickness, punching size 10 x 53 mm) to a punching device (manufactured by Amada), punching out a UV cured resin sheet, and then cutting surface Was evaluated by observing with a microscope.

  The cutting conditions were 23 ° C. and 60% humidity, and the cut surface was magnified 500 times with a microscope (manufactured by KEYENCE). There are few, and it can be said that cutting property is good.)

The evaluation results are shown as follows.
(Double-circle): It was a surface where there was little unevenness | corrugation and roughness on a cut surface and there were few unevenness | corrugations.
◯: Although the cut surface had some cracks, it was a surface with little unevenness.
X: The cut surface had a lot of scratches and was a rough uneven surface (if the uneven surface, a sufficient light guiding function is not exhibited).

  As shown in FIG. 5, the tackiness is prepared by preparing a PET film (manufactured by Toray Industries Inc.) having a thickness of 50 μm and a satin surface, and gently placing a light guide sheet on the pear surface, Place a jig in R shape (R at the tip is 7 mm, cylindrical rubber weight (Shore A hardness 80 °)) on the light guide sheet, hold it for 200 seconds with a load of 200 g, and remove the weight. After that, whether or not the light guide sheet (the surface opposite to the surface irradiated with UV) was peeled off from the PET film and the time until peeling were evaluated.

  The test was conducted under the conditions of 23 ° C. and 60% humidity. After the separation film was peeled from the light guide sheet to remove the peeling charge, the above-described tack evaluation was performed after 10 minutes.

The evaluation results are shown as follows.
(Double-circle): It peeled within 5 seconds, without sticking to a PET film.
○: The light guide sheet adhered to the PET film, but the light guide sheet and the PET film were separated within 20 seconds.
X: The light guide sheet was in close contact with the PET film and was not peeled off even after 1 minute or more.

  As shown in FIG. 6, the heat resistance is as follows. The light guide sheet alone is placed on a satin-finished PET film and placed in a hot air dryer (Espec Corp.) set to an atmosphere of 125 ° C. The appearance after the lapse of time was visually observed, and the change in color was evaluated by the degree of yellowing (ΔYI) using a spectrophotometer (manufactured by Hitachi, Ltd.).

  Here, ΔYI is a difference between the yellowness index YI (Yellowness Index) before the test and the yellowness index YI after the test, and is calculated by the following formula ΔYI = post-test YI−pre-test YI. The yellowness YI is determined from the following formula YI = 100 (1.28X-1.06Z) from tristimulus values (sensitivity of each color (stimulus amount) felt by human eyes) X, Y, Z measured with a spectrophotometer. / Y.

The evaluation results are shown as follows.
(Double-circle): There was no shrinkage | contraction, curl, and stickiness, and (DELTA) YI was +1.0 or less. In addition, there is no adhesion to the satin PET film.
◯: There was no shrinkage, curling and stickiness, and ΔYI was +2.0 or less. In addition, there is no adhesion to the satin PET film.
X: Stickiness (bleed-out product) was generated on the surface and adhered to the satin PET film.

  As shown in FIG. 7, the moisture and heat resistance is a constant temperature and humidity tester (ESPEC) in which a light guide sheet is placed on a satin-finished PET film and set in a constant temperature and humidity atmosphere of 85 ° C. to 85% RH. The appearance after 1000 hours was visually observed, and the color change was evaluated by the yellowing degree (ΔYI) using a spectrophotometer (manufactured by Hitachi, Ltd.).

The evaluation results are shown as follows.
(Double-circle): There was no shrinkage | contraction, curl, and stickiness, and (DELTA) YI was +1.0 or less. In addition, there is no adhesion to the satin PET film.
◯: There was no shrinkage, curling and stickiness, and ΔYI was +2.0 or less. In addition, there is no adhesion to the satin PET film.
X: Stickiness (bleed-out product) was generated on the surface and adhered to the satin PET film.

Evaluation of light resistance (UV (ultraviolet) resistance) was performed using a UV (ultraviolet) irradiation apparatus illustrated in FIG. First, the yellowness before the test of the light guide sheet before irradiation with ultraviolet rays was measured using a spectrophotometer (manufactured by Hitachi, Ltd.). Next, place the light guide sheet alone on clean paper, the peak illuminance of the high-pressure mercury lamp and 120 mW / cm ^2, integrated light quantity adjusting the conveyor speed so that the 1000 mJ / cm ^2, was irradiated with ultraviolet rays. Next, the irradiated light guide sheet alone was left at room temperature for 120 hours in a dark room where outside light such as sunlight did not enter. Thereafter, the post-test yellowness of the light guide sheet was measured using a spectrophotometer, and the yellowing degree (ΔYI) was determined and evaluated.

The evaluation results are shown as follows.
A: ΔYI was +0.1 or less after 120 hours of UV irradiation, and there was no curl.
A: ΔYI after +120 hours of UV irradiation exceeded +0.1 and was +0.2 or less.
X: ΔYI exceeded +0.2 after 120 hours of UV irradiation.

  In addition, the solubility was visually confirmed to be completely dissolved, and when dissolved, it was evaluated as ◯, and when not dissolved, it was evaluated as ×.

・ Experimental example 1
FIG. 1 shows the names and compounding ratios (experimental conditions) of main agents A to C and auxiliary agents D to F in Comparative Examples 1 to 3 and Examples 1 to 3. Moreover, FIG. 2 shows the experimental result of the characteristic of each comparative example and an Example.

  1 and 2, if too much polyfunctional acrylate is present, the cutting property is inferior (Comparative Example 1), and if too much monofunctional acrylate is present, the tackiness, heat resistance and moist heat resistance are inferior (Comparative Example 2). When the type of urethane acrylate was employed, it was confirmed that the cutting ability was inferior to the polymer type (Comparative Example 3).

  In Examples 1 to 3, the characteristics of each of the main agents A to C were changed and the characteristics were confirmed. The main agent A was 55 to 70 parts by weight, the main agent B was 11.3 to 16.9 parts by weight, and the main agent. When C was 18.7 to 28.1 parts by weight, good results were obtained in all cases. In particular, it was confirmed that Example 1 was excellent in light resistance, Example 2 was excellent in tackiness, and Example 3 was excellent in cutting property.

・ Experimental example 2
In Experimental Example 2, each characteristic was confirmed by changing the mixing ratio and materials of the auxiliary D and auxiliary F based on the mixing ratio of Example 1 of the above Experimental Example 1.

  FIG. 3 shows the names and blending ratios and coating thicknesses (experimental conditions) of the main agents A to C and auxiliary agents D to F in Comparative Examples 4 to 10 and Examples 4 to 8. FIG. 4 shows the experimental results of the characteristics of the comparative examples and examples. In Comparative Examples and Examples, the relationship between the ultraviolet absorber and the wavelength region of the photopolymerization initiator that absorbs ultraviolet rays is the absorption wavelength region of the ultraviolet absorber (˜350 nm: the concentration in the cyclohexane solution is 0.001%. Value (value obtained from spectral transmittance)) is the absorption wavelength region of the polymerization initiator (200 to 380 nm: value when the concentration in the acetonitrile solution is 0.01% (value obtained from the spectral transmittance)) And a material such that the absorption wavelength region of the ultraviolet absorbent is in the short wavelength region of the absorption wavelength region of the polymerization initiator.

  3 and 4, it was confirmed that when the amount of the ultraviolet absorber was too large, the tackiness, heat resistance, and moist heat resistance (in addition to solubility in Comparative Example 4 were poor) (Comparative Examples 4 and 5). This is presumably because the amount of the polymerization initiator added is small and an ultraviolet absorber is also added, so that the curing reaction does not proceed sufficiently even when irradiated with ultraviolet rays, thereby resulting in an uncured state. Moreover, if the curing is insufficient, bleeding out of unreacted monomer alone and three-dimensional crosslinking (crosslinking density) are insufficient, resulting in poor heat resistance and moist heat resistance. Specifically, in Comparative Example 4, since there are many ultraviolet absorbers, a strong tack occurs and a problem arises in the solubility of the ultraviolet absorber. In Comparative Example 5, since the addition amount of the photoinitiator is small, the curing reaction does not proceed and tack occurs.

  Moreover, when there were too few ultraviolet absorbers, it has confirmed that it was inferior to light resistance (Comparative Examples 6 and 7). This is because ultraviolet rays cannot be sufficiently absorbed after curing. In addition, Comparative Example 8 is inferior in tackiness, heat resistance and moist heat resistance. this is. Since a large amount of polymerization initiator is added, the reaction in the planar direction proceeds when irradiated with ultraviolet rays, but the reaction in the thickness direction does not proceed, resulting in This is considered to be because the curing becomes uneven, the curing of the surface opposite to the ultraviolet irradiation surface becomes insufficient, and tack (stickiness) occurs.

  Moreover, even if it changed the material of the ultraviolet absorber, when there were too few ultraviolet absorbers, it has confirmed that it was inferior to light resistance (Comparative Examples 9 and 10). In Comparative Example 9, although the absorption wavelength region of the polymerization initiator that does not overlap with the absorption wavelength region of the ultraviolet absorber exists on the long wavelength side, since the non-overlapping region extends to the visible region, it is easily affected by visible light, It is thought that it is inferior to light resistance. Comparative Example 10 is considered to be inferior in light resistance because there are many portions where the ultraviolet absorption wavelength region of the ultraviolet absorber overlaps with the ultraviolet absorption wavelength region of the polymerization initiator, and a large amount of the ultraviolet absorber cannot be added.

  Moreover, in Examples 4-6, when each application | coating thickness was changed and each characteristic was confirmed, as for Example 4 and 5, the favorable result was obtained. In Example 6, since the sheet was thick, the amount of UV irradiation was insufficient in the thickness direction, an uncured portion was formed, and tackiness was considered to be slightly inferior.

  Moreover, both Example 7 which increased the ratio of the ultraviolet absorber compared with Example 4 and Example 8 which reduced the quantity of the ultraviolet absorber compared with Example 4 showed the favorable result. Therefore, it has confirmed that it was preferable to mix | blend an ultraviolet absorber so that it might become a ratio used as the ratio of 1-2 with respect to a photoinitiator.

Claims (6)

  A resin composition for a light guide sheet comprising a urethane acrylate having a polyether in the main chain, a monofunctional acrylate, a polyfunctional acrylate, a photopolymerization initiator, an antioxidant, and an ultraviolet absorber, The resin composition for a light guide sheet, wherein the addition amount of the photopolymerization initiator is less than the addition amount of the ultraviolet absorber.   The resin composition for a light guide sheet according to claim 1, wherein the photopolymerization initiator and the ultraviolet absorber are added in a ratio of 1: 1 to 2. .   The resin composition for a light guide sheet according to any one of claims 1 and 2, wherein the urethane acrylate has a weight average molecular weight of 10,000 to 20,000.   In the resin composition for light guide sheets of any one of Claims 1-3, it sets so that the sum total of the said urethane acrylate, the said monofunctional acrylate, and the said polyfunctional acrylate may be 100 weight part, The said 100 weight 55-70 weight part is a urethane acrylate among the parts, The resin composition for light guide sheets characterized by the above-mentioned.   It is a light guide sheet which guides the light from a light source to a predetermined part, Comprising: It forms with the resin composition for light guide sheets of any one of Claims 1-4, The light guide sheet characterized by the above-mentioned.   A light guide sheet comprising a resin composition for a light guide sheet comprising urethane acrylate, a monofunctional acrylate, a polyfunctional acrylate, a photopolymerization initiator, an antioxidant, and an ultraviolet absorber. The sheet is characterized in that the thickness is set to 50 to 200 μm, the light transmittance at a wavelength of 250 to 330 nm in the thickness direction is 1% or less, and the light transmittance at a wavelength of 380 nm is 85% or more. Light sheet.