JP2023061257A - light guide sheet - Google Patents

Abstract

To provide a manufacturing method of a flexible light guide sheet capable of guiding light to a light-emitting part away from the light source.SOLUTION: The light guide sheet includes: a core layer with a thickness of 30 μm or more and 100 μm or less and a width of 50 μm or more and 10 mm or less; and a clad layer that is arranged to enclose the core layer and has a refractive index lower than that of the core layer and a thickness of 30 μm or more and 200 μm or less. The core layer has a portion that includes multiple core wire lines in the width direction. In the multiple core wire lines in this portion, the ratio of the width of one core wire line to the distance between the core wire line and the adjacent core wire line is 0.5:1 to 20:1, and the core layer has a light extraction part.SELECTED DRAWING: Figure 1

Description

The present invention relates to a light guide sheet.

Light guide plates used in liquid crystal displays, etc. play the role of guiding light from the side to the liquid crystal panel, and are used in a wide range of applications such as televisions, desktop personal computer monitors, notebook personal computers, mobile phones, and car navigation systems. . A backlight using a light guide plate is also used for illumination. Up to now, acrylic resin has generally been used for light guide plates (Patent Document 1, etc.), and prisms, dots, ribs, etc. are formed on acrylic plates and used as light guide plates.

However, since these are configured using a base material such as an acrylic plate, the conventional light guide plate also had the problem of being poor in flexibility and heat resistance. There have been reports of low-loss, high-speed transmission optical waveguides using resins with excellent heat resistance for the core layer and the clad layer (Patent Document 2). It was limited to electrical composite substrates.

Further, in a normal light guide plate, a light source such as an LED and a substrate are integrally molded around the light emitting portion, and it is not assumed that a place distant from the light source is used as the light emitting portion. If the conventional technology is used to provide the light source and the light-emitting part at a distance, there is a problem that the structure becomes complicated. For example, if the LED is incorporated inside the light guide plate, there are restrictions on rib molding and the thickness of the LED itself, which complicates the structure. Furthermore, conventional light guide plates generally emit a uniform light that illuminates the entire surface, but in the future, it will be necessary to guide light in various situations, and there is a need to illuminate only the desired area instead of the entire surface. be. In addition, if there is a bent portion in the optical path between the light source and the light emitting portion, there is a problem that most of the light cannot be bent and is transmitted in the straight direction by simply bending the ordinary core layer, resulting in a large loss. .

JP 2017-141459 A JP 2007-84765 A

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a flexible light guide sheet that can guide light to a light emitting part away from a light source and reduce light loss at a bent part of an optical path.

As a result of extensive studies, the inventors of the present invention have found that the above problems can be solved by a light guide sheet having the following configuration. The present inventors completed the present invention by conducting further studies based on such knowledge.

That is, a light guide sheet according to one aspect of the present invention includes a core layer having a thickness of 30 μm or more and 100 μm or less and a width of 50 μm or more and 10 mm or less; a clad layer having a lower refractive index and a thickness of 30 μm or more and 200 μm or less, the core layer having a portion including a plurality of core wirings in the width direction, and the plurality of core wirings in the portion are , the ratio of the width of one core wiring and the distance between the core wiring and the adjacent core wiring is 0.5:1 to 20:1, and the core layer includes a light extraction part. Characterized by

ADVANTAGE OF THE INVENTION According to this invention, the flexible light guide sheet which can guide|induce light to the light emission part distant from a light source and can reduce the light loss in the bending part of an optical path can be provided.

FIG. 1 is a schematic cross-sectional view showing the configuration of a light guide sheet according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a portion including a plurality of core wirings in the core layer of the light guide sheet of this embodiment. FIG. 3 is a schematic cross-sectional view showing the configuration of a light guide sheet according to another embodiment of the invention. FIG. 4 is a schematic cross-sectional view showing each step in the method for manufacturing a light guide sheet according to one embodiment of the present invention.

Hereinafter, embodiments according to the present invention will be specifically described with reference to the drawings and the like, but the present invention is not limited to these.

[Light guide sheet]
First, the structure of the light guide sheet of this embodiment will be specifically described.

As shown in FIG. 1, the light guide sheet 10 of this embodiment has at least a core layer 1 and a clad layer 2 .

The thickness of the core layer 1, which is the optical path in the light guide sheet, is 30 μm or more and 100 μm or less. Moreover, the pattern width of the core layer 1 is 30 μm or more and 10 mm or less.

The cladding layer 2 is arranged so as to surround the core layer 1 serving as an optical path, and has a lower refractive index than the core layer 1 . The clad layer 2 has a thickness of 30 μm or more and 200 μm or less.

In the light guide sheet 10 of the present embodiment, since the pattern width of the core layer 1 is within the above range, light itself can be transmitted instead of the optical communication that is transmitted by the core layer in the conventional optical waveguide, and the light itself can be transmitted. It can be guided to a light emitting part away from the light source. In this embodiment, the pattern width of the core layer 1 is the pattern width required for one light source. For example, when it is used in an image display device or a lighting device using a plurality of light sources, it is possible to increase the luminance of the light extraction part and expand the area by changing the core layer to a desired pattern.

As described above, the light guide sheet 10 of the present embodiment includes the thin core layer 1 and the thin clad layer 2. Therefore, the light guide sheet 10 is extremely thin and has excellent flexibility. It is also possible to incorporate it into a curved surface.

In the light guide sheet 10 of this embodiment, the core layer has a portion including a plurality of core wirings in the width direction, as shown in FIG. In this specification, "core wiring" means a linear path (light transmission section) along which light that has entered the core layer from the light entrance section is transmitted to the light extraction section.

In FIG. 2, the core layer includes three core wires as an example, but the number of core wires is not particularly limited, and the pattern can be changed as appropriate depending on the number of light sources to be used. is. In addition, the core layer of the light guide sheet of the present embodiment may be entirely composed of a plurality of core wirings as shown in FIG. , and other portions may be core layers composed of a single core wiring. In the light guide sheet, when the optical path (core layer) has a bent portion, it is preferable that the bent portion is a portion composed of a plurality of core wirings. For example, the core layer may have a single core wiring at the light incident portion and the light emitting portion, and may have a portion composed of a plurality of core wirings only at the bending portion in the middle of the optical path.

In this way, since the core layer is composed of a plurality of core wirings at the bent portion of the optical path, the pattern of the optical path (core layer) can be branched, and the loss of light due to bending can be reduced. Efficiency can be improved.

The plurality of core wirings in the portion containing the plurality of core wirings has a ratio of the width of one core wiring to the distance between the core wiring and the adjacent core wiring is 0.5:1 to 20:1. It has become. Here, the width of the core wiring is the width (w) of one core wiring indicated by w in FIG. 2, and the distance between the core wirings is indicated by d in FIG. It means the distance between adjacent core wirings. The ratio of these, that is, the width (w): the distance (d) is 0.5:1 to 20:1. If the ratio of width (w):distance (d) exceeds 20:1, the loss of light at the bent portion increases, and the light guide efficiency cannot be sufficiently increased. On the other hand, if the ratio of width (w):distance (d) is less than 0.5:1, it is considered difficult to form a core layer having a portion composed of a plurality of core wirings. This is because the width of the pattern on the bottom expands to about 1.1 to 1.3 times the width of the core through the photomask in the process of UV curing the core, so the adjacent core wiring is connected. This is because the striped structure cannot be sufficiently formed by a plurality of core wirings.

Furthermore, in the light guide sheet 10 of the present embodiment, the core layer has a light extraction portion 3 as shown in FIG. The light extraction part 3 is a part for extracting the light incident from the light source and guided by the optical path (core layer).

In addition, as shown in FIG. 3, the light guide sheet 10 of the present embodiment preferably includes a light incident portion 5 and a light emitting portion 6, so that the light emitted from the light source 4 passes through the core layer 1. can be incident from the incident portion 5 of the core layer 1 , reflected at the interface with the clad layer 2 , and transmitted to the exit portion 6 of the core layer 1 .

(core layer)
As described above, the core layer 1 in the light guide sheet 10 of this embodiment has a thickness of 30 μm or more and 100 μm or less. Moreover, the pattern width of the core layer is 50 μm or more and 10 mm or less. Here, the pattern width refers to the length (width) in the direction perpendicular to the traveling direction of light.

A more preferable thickness range is 40 μm or more and 60 μm or less. A more preferable pattern width range is 1 mm or more and 10 mm or less.

The core layer 1 of this embodiment has a light extraction portion 3 as shown in FIG.

The light extraction part 3 preferably has a prism shape. By providing such a prism-shaped light extraction part 3, the efficiency of light extraction is further improved. The prism shape of the light extraction part 3 is not particularly limited as long as the height is within the range of the thickness of the core layer 1, but the height in the thickness direction is preferably 1 μm or more and 30 μm or less. By setting the height of the prism within such a range, there is an advantage that the inside of the light extraction portion can be illuminated uniformly without breaking the light extraction portion. A more preferable range of the height of the prism shape is 1 μm or more and 10 μm or less.

The shape of the prism is not particularly limited, and can be appropriately set according to the type and direction of light to be extracted from the core layer. It may be in a shape such as a triangular prism. Preferably, it has a triangular prism groove shape. Moreover, the light extraction part 3 may have a plurality of prism shapes, and in that case, the shape and height of each prism may be the same or different.

As shown in FIGS. 1 and 3, the light extraction part 3 of the present embodiment preferably has a plurality of prism shapes having a predetermined height. It may have an uneven shape of 0.1 μm or more and 50 μm or less (not shown). The efficiency of light extraction is further improved by having the light extraction part 3 having such an uneven shape. A more preferable range of the arithmetic mean roughness (Ra) is 1 μm or more and 30 μm or less.

At least a portion of the light extraction portion 3 is preferably exposed to the outside. In other words, as shown in FIG. 1, it is preferable that at least part of the light extraction portion 3 is not covered with the clad layer 2 . By exposing the light extraction part 3 to the outside air (air) in this way, light can be extracted more reliably.

Further, as shown in FIG. 3, since a part of the light extraction part 3 is in contact with the outside air, the surface opposite to the side in contact with the outside air becomes the emission part 6, and the light entering from the incidence part 5 is reflected by the light extraction portion 3 and extracted from the emission portion 6 .

In the incident part 5, the core layer has a mirror structure, but the mirror part of the core layer may be covered with the clad layer 2 as shown in FIG. If the unevenness of the exposed surface becomes large due to the processing of the exposed surface, there is a risk that the light will scatter on the rough surface and cause loss. This is because

In addition, although the shape of the core layer 1 is rectangular or square in FIGS. not. Furthermore, as long as the thickness and pattern width are within the ranges described above, the thickness and pattern width of the core layer 1 need not be constant, and the thickness and pattern width may vary depending on the location.

The core layer 1 has a portion including a plurality of core wirings in the width direction, as described above. The number of core wirings in the portion is not particularly limited, and the pattern can be appropriately changed depending on the number of light sources to be used. Specifically, for example, 3 or more and 40 or less core wirings can be included.

The core layer of the present embodiment only needs to have a portion including a plurality of core wirings in the width direction. The core layer may have a portion composed of a plurality of core wirings, and the other portion may be a core layer composed of a single core wiring.

The plurality of core wirings in the portion containing the plurality of core wirings has a ratio of the width of one core wiring to the distance between the core wiring and the adjacent core wiring is 0.5:1 to 20:1. It has become. Details are as described above.

The plurality of core wirings can be formed with a predetermined pattern by, for example, the exposure/development process of the process (B) of FIG. 4, which will be described later. In that case, the total width of the plurality of core wirings to be formed should be 5 mm or more and 10 mm or less. For example, when forming core wirings with a width of 50 μm, the spacing between the core wirings must also be about 50 μm. A desired core layer 1 can be obtained by forming a wiring pattern so as to be arranged in .

In the present embodiment, the refractive index of the core layer 1 is not particularly limited as long as it is higher than the refractive index of the clad layer 2 described later. For example, the refractive index of the core layer is 0.5% or more with respect to the refractive index of the clad layer. It is preferably in the range of 60% or less. A more preferable refractive index range is 0.5% or more and 20% or less.

The material constituting the core layer 1 of the present embodiment is not particularly limited as long as it is a curable resin capable of obtaining the above-described refractive index. , a cyanate ester curing resin, a combination of these resins, a silicone curing resin, or the like. Since all of them are used as members constituting a light guide path, it is necessary that the cured product has high transparency.

More specifically, resins that are both photocurable and thermally curable are preferred, and for example, epoxy curable resins can be used. This is because it has the advantage of being excellent in heat resistance, chemical resistance, and electrical insulation.

Among these, it is particularly preferable to use a resin obtained by blending two or more resins having slightly different refractive indices and viscosities. This is because there are advantages in that a refractive index distribution is easily generated during heat treatment after exposure and that the refractive index distribution is easily controlled.

Some examples of more specific resin compositions are given below.

A first specific example is an epoxy resin obtained by adding 1,2-epoxy-4-(2-oxiranyl)cyclohexane to 2,2-bis(hydroxymethyl)-1-butanol, and a butyral resin. , and a bisphenol-type epoxy resin are preferably used.

The structure of the epoxy resin obtained by adding 1,2-epoxy-4-(2-oxiranyl)cyclohexane to 2,2-bis(hydroxymethyl)-1-butanol is represented by the following chemical formula (1).

In formula (1), R ₂ is C _m H _2m+1 , n is a natural number, and the value of n may differ among the three repeating units.

For example, EHPE3150 manufactured by Daicel Chemical Industries, Ltd. can be used as the epoxy resin. This epoxy resin is an alicyclic, highly transparent, polyfunctional epoxy resin with a melting point of about 85°C. Heat resistance can also be enhanced.

The epoxy resin is preferably blended at a rate of 30 to 80% by weight based on the total resin. The reason for this is that if the amount of the epoxy resin is less than 30% by weight, the heat resistance after curing is lowered and the tackiness of the film is deteriorated. This is because, although the decrease in the strength of the film can be suppressed, the flexibility (flexibility) of the film is decreased, and cracks may occur during handling.

A butyral resin is represented by the following chemical formula (2).

In formula (2), x, y, and z are natural numbers, and _R1 represents a propyl group.

Butyral resins are sold as industrial reagents and reagents for chemical experiments, and examples of industrial resins include Denka Butyral manufactured by Denki Kagaku Kogyo KK. The butyral resin has a degree of polymerization of about 630 to 2400 (about 70,000 to 300,000 when converted to a weight average molecular weight), and the ratio of x, y, and z is a weight ratio, where x is 2 to 13, y is 12-19, and z is 71-83. Butyral resin has high transparency and can suppress loss during light propagation. In addition, since it contains a hydroxyl group derived from vinyl alcohol, it acts as a chain transfer agent for cationic polymerization, increasing the curability of the resin composition and improving the adhesion to the adherend. The tackiness of the film can be suppressed and the fragility can be reduced. In addition, when a pattern is formed by developing after partial exposure using a mask or the like, it is possible to suppress defects such as cracks and missing patterns during development.

The butyral resin is preferably blended in a proportion of 1 to 30% by weight based on the total resin. The reason for this is that if the amount of the butyral resin is less than 1% by weight, no effect can be obtained. This is because although coating becomes possible, the amount of solvent to be used increases, causing an increase in cost, and the thickness of the wet film significantly decreases after drying.

The molecular weight of the butyral resin is preferably 800 or less in terms of degree of polymerization (about 100,000 or less in terms of weight average molecular weight). The reason for this is that if the degree of polymerization exceeds 800, the viscosity of the varnish becomes significantly high, causing the above-mentioned problems. This is because there is a risk that the In fact, among the butyral resins previously provided by Denki Kagaku Kogyo Co., Ltd., the one with the lowest degree of polymerization is 300 (approximately 30,000 in terms of weight average molecular weight). If so, a sufficient effect can be maintained.

A bisphenol type epoxy resin is a bisphenol A type epoxy resin or a bisphenol F type epoxy resin, and has a liquid to solid state at room temperature depending on the molecular weight. Since the bisphenol-type epoxy resin has a benzene ring, it can increase the refractive index of the cured product, and is suitable for forming a core having a higher refractive index than the clad. In order to increase the refractive index, a resin with a high content of benzene rings is suitable. In this regard, naphthalene-type epoxy resins and biphenyl-type epoxy resins are also suitable. Since it absorbs ultraviolet rays in the region used for patterning, it is not preferable because the curability deteriorates.

The bisphenol type epoxy resin is preferably blended in the range of 5 to 60% by weight based on the total resin. The reason for this is that if the blending amount is less than 5% by weight, the refractive index of the cured product of the composition is not improved, and it becomes difficult to exhibit the function as a core. Conversely, if the blending amount exceeds 60% by weight, the refractive index increases, but the heat resistance of the cured product decreases, and the heat resistance temperature (Tg ), and the reliability in the usage environment may decrease.

In general, curing a curable resin requires a curing agent and/or a curing initiator (curing catalyst), but any of them can be used without limitation as long as it can achieve high transparency in the cured product. For example, a cationic polymerization initiator is preferably exemplified.

When forming the light guide sheet of the present embodiment, it is preferable to form the above-described resin into a film form and use it as a resin film for forming the core layer, from the viewpoint of easier production.

As the cationic polymerization initiator, any one can be used as long as it generates a Lewis acid or Bronsted acid by light, heat, electron beams, or the like and does not impair the transparency. Cationic polymerization initiators are suitable for use in optical waveguides (core layers) because they can promote the self-polymerization of epoxy resins and are less colored than addition-type curing compounds such as compounds with phenolic hydroxyl groups and amines. there is In addition, photo-curing initiators that generate cations by light, once the curing reaction is initiated by light irradiation for a short time, the curing reaction is accelerated by heating without light irradiation, so the manufacturing process can also be simplified to improve manufacturing efficiency.

Furthermore, the resin composition may contain epoxy resins and polymers other than those described above, as long as the effects of the present invention are not impaired. Moreover, other additives such as a coupling agent may be blended.

A second specific example of the core layer resin composition is obtained by adding 1,2-epoxy-4-(2-oxiranyl)cyclohexane to 2,2-bis(hydroxymethyl)-1-butanol. A resin composition containing an epoxy resin, a butyral resin represented by the chemical formula (2), an epoxidized polybutadiene having a hydroxyl group, and a cationic polymerization initiator may be used.

Epoxidized polybutadiene having a hydroxyl group is represented by CAS number 68441-49-6, and has a hydroxyl group in the molecular chain and a hydroxyl group at the end of the molecular chain. For example, Epolead (registered trademark) manufactured by Daicel Chemical Industries, Ltd. includes product number PB3600 having a hydroxyl group in the molecule and at the molecular end, and product number PB4700 having a hydroxyl group in the molecule.

Epoxidized polybutadiene having a hydroxyl group is liquid, has a mobile molecular chain, and has a hydroxyl group. Therefore, it has a chain transfer effect in a cationic curing system, and can increase the polymerization rate (curing rate). In addition, it has good compatibility with epoxy resins and can maintain transparency. Furthermore, unlike the polyfunctional alcohol that is the chain transfer agent described above, since it is an aliphatic non-glycidyl ether epoxy resin with a large molecular weight, the reactivity of the epoxy group is about the same as that of alicyclic epoxy, and the curing system Since it is taken in, it becomes difficult to deteriorate the hygroscopicity and heat resistance of the cured product. As a result, when the cured product is used for the clad of the optical waveguide, the adhesion to metal can be enhanced.

The epoxidized polybutadiene having a hydroxyl group is preferably blended in a proportion of 1 to 30% by weight based on the total resin. The reason for this is that if the blending amount is less than 1% by weight, the effect of increasing the polymerization rate cannot be obtained. This is because the tackiness of the coating deteriorates. Furthermore, the blending amount of epoxidized polybutadiene having hydroxyl groups is preferably in the range of 2 to 15% by weight.

Further, in the resin composition, an epoxy resin different from the epoxy resin or various polymers may be used in combination as long as the object of the present invention is not impaired.

As the cationic polymerization initiator, the same cationic polymerization initiator as described above can be used, and as for other additives, the same additives as those described above can be used.

A third specific example is a resin composition containing a phenoxy resin, a bisphenol epoxy resin that is solid at room temperature, a bisphenol epoxy resin that is liquid at room temperature, and a cationic polymerization initiator.

Phenoxy resin is a bisphenol-type epoxy resin with a molecular weight of tens of thousands or more. Bisphenol-type epoxy resin that is solid at room temperature is an oligomer, and bisphenol-type epoxy resin that is liquid at room temperature is a mixture of a monomer and a dimer or trimer. is. The phenoxy resin is preferably blended in a proportion of 1 to 10% by weight based on the total resin. The reason for this is that if the blending amount is less than 1% by weight, the effects of the phenoxy resin (good varnish coatability, suppression of tackiness, suppression of core defects during development, etc.) are not exhibited. If the amount exceeds 10% by weight, the viscosity of the varnish increases significantly, and although the solvent content of the varnish can be increased, coating becomes possible, but the amount of solvent used increases, the cost rises, and the wet film becomes wet. This is because the thickness may be significantly reduced after drying.

The bisphenol type epoxy resin, which is liquid at room temperature, is preferably blended at a ratio of 10 to 40% by weight. The reason for this is that if the blending amount is less than 10% by weight, it becomes difficult to develop appropriate tackiness of the film, the meltability is deteriorated, and lamination may become difficult. This is because if the weight percentage is exceeded, the tackiness of the film becomes too strong.

Except for the phenoxy resin and the bisphenol type epoxy resin which is liquid at room temperature, only the bisphenol type epoxy resin which is solid at room temperature may be used for the remainder. In addition, the above-described epoxy resin, oxetane resin, or various polymers, which are different resins from the epoxy resin, may be used in combination as long as the object of the present invention is not impaired.

As the cationic polymerization initiator, the same cationic polymerization initiator as described above can be used, and as for other additives, the same additives as those described above can be used.

When forming the light guide sheet of the present embodiment, it is preferable to form the above-described resin into a film and use it as the film for the core layer, from the viewpoint of simplifying the production.

Therefore, the resin composition as described above is dissolved in a solvent such as an organic solvent to prepare a varnish in order to finally form a film. A general method can be used to form the film. Specifically, it is obtained by coating the resin varnish on a support and drying it. At this time, various surfactants may be blended in order to improve coatability in the processing step. Furthermore, a leveling agent for improving the wettability to the support, an antifoaming agent for preventing the generation of air bubbles, and the like may be used.

As the support, commonly used supports (such as carrier films) can be used without limitation.

(cladding layer)
As shown in FIG. 2, the clad layer 2 is arranged so as to surround the core layer 1 described above. The thickness of the cladding layer 2 is 30 μm or more and 200 μm or less, and the thickness here refers to the thickness of the dry film before lamination. This corresponds to the thickness of the dry film (the first clad layer film 2' or the second clad layer film 2'') in FIG. 4C, which will be described later.

By laminating the dry film (first clad layer film 2' or second clad layer film 2'') and laminating (heat + pressure), the clad layer is also filled between the core wirings. .

By setting the thickness of the clad layer 2 within the above range, there is an advantage that both flexibility and protection of the core layer can be achieved. More preferably, the clad layer 2 has a thickness of 35 μm or more and 150 μm or less.

In the present embodiment, the refractive index of the clad layer 2 is not particularly limited as long as it is lower than the refractive index of the core layer 1. % or less. A more preferable refractive index range is a refractive index in the range of 0.5% to 20%.

In the present embodiment, the material constituting the clad layer 2 is not particularly limited, and a material having a lower refractive index at the transmission wavelength of the guided light than the material constituting the core layer 1 described above may be appropriately selected and used. can be done. Specific examples include epoxy resins, acrylic resins, polycarbonate resins, polyimide resins, and the like.

More specifically, resins that are both photocurable and thermally curable are preferred, and for example, epoxy curable resins can be used. This is because it has the advantage of being excellent in heat resistance, chemical resistance, and electrical insulation.

A more specific example of the resin composition is an epoxy resin obtained by adding 1,2-epoxy-4-(2-oxiranyl)cyclohexane to 2,2-bis(hydroxymethyl)-1-butanol. , a butyral resin, and a resin composition containing a photopolymerization initiator.

Details of the epoxy resin, butyral resin, photopolymerization initiator, and their blending amounts are the same as those described for the core layer.

Furthermore, the resin composition may contain epoxy resins and polymers other than those described above, as long as the effects of the present invention are not impaired. For example, if necessary, it preferably contains at least one selected from epoxidized polybutadiene having a hydroxyl group, a bisphenol type epoxy resin, and a hydrogenated bisphenol type epoxy resin.

The epoxidized polybutadiene having a hydroxyl group and the bisphenol type epoxy resin are the same as those described for the core layer.

In particular, the cured product of the composition containing the hydrogenated bisphenol type epoxy resin is not used for compositing with a substrate having heat resistance and moisture resistance such as FR4, but for a clad with a low refractive index that requires flexibility. suitable for the application.

Hydrogenated bisphenol-type epoxy resin is obtained by adding hydrogen to the benzene ring of bisphenol A-type or bisphenol F-type epoxy resin to modify it into a cyclohexane ring, and has excellent transparency and a flexible molecular skeleton. It is a functional epoxy. Furthermore, since it is a so-called external epoxy that protrudes as a side chain in the form of glycidyl ether from the molecular skeleton, the reactivity in the cationic curing system is inferior to that of the internal epoxy, and the glass transition temperature (Tg) of the cured product of the composition is lower than that of the internal epoxy. is reduced, and a light guide sheet having excellent flexibility can be obtained.

Furthermore, since the resin composition is in the form of a film, it is necessary to suppress the tackiness of the film. From this point of view, it is preferable to use a resin that is solid at room temperature, obtained by adding hydrogen to an oligomer-type bisphenol epoxy resin.

The hydrogenated bisphenol type epoxy resin is preferably blended at a rate of 20 to 60% by weight based on the total resin. The reason for this is that when the blending amount is less than 20% by weight, it becomes difficult to develop flexibility, and conversely, when the blending amount exceeds 60% by weight, the crosslink density of the cured product is too low, resulting in poor handleability. Because it does.

In addition, additives such as a coupling agent may be added to the clad layer resin composition.

When forming the light guide sheet of the present embodiment, it is preferable to form the above-described resin into a film and use it as a resin film for forming the clad layer, from the viewpoint of simplifying the production. As for the formation of the film, the same means as those for the above core layer film can be used.

(Application)
The light guide sheet of the present embodiment, which includes the core layer and the clad layer as described above, is flexible, has excellent light transmission efficiency and reliability, and can guide light away from the light source. Therefore, it can be suitably used for various electronic devices. In addition, the light guide sheet of the present embodiment, which includes the core layer and the clad layer as described above, has a higher degree of transparency, and thus has the advantage of not being limited in its usage. For example, it can be used for display panels of automobiles, indicator lights of instrument panels manufactured by insert molding of automobiles, ambient lights, etc., and is very useful industrially.

[Method for producing light guide sheet]
Although the method for manufacturing the light guide sheet as described above is not particularly limited, some embodiments will be specifically described below.

(First embodiment)
In the case where the light guide sheet of the present embodiment includes a prism-shaped light extraction part, the manufacturing method includes at least the following steps:
Step (1): A step of forming a light-outcoupling part in the core layer film using a prism-forming mold having a light-outcoupling prism-forming part;
Step (2): removing a portion of the core layer film;
Step (3): A step of laminating the film for the first clad layer on the upper surface of the film for the core layer and filling the portion removed in the step (2);
Step (4): a step of subjecting the core layer film and the first clad layer film to a curing treatment to form a first clad-core laminate comprising a core layer and a first clad layer;
Step (5): A step of peeling the first clad-core laminate from the prism-forming mold and laminating the first clad layer side of the first clad-core laminate on a temporary fixing material;
Step (6): A second clad layer film is laminated on the first clad-core laminate, and the second clad layer film is subjected to a curing treatment to form a first clad layer, a core layer and a second clad layer. forming a laminated sheet having
Step (7): removing a portion of the second clad layer of the laminated sheet that overlaps at least a portion of the light extraction portion of the core layer;
Step (8): a step of peeling the laminated sheet from the temporary fixing material; and
Step (9): A step of exposing a portion of the core layer at the edge of the laminated sheet and providing a light incident portion.
A manufacturing method comprising:

These steps are preferably performed in the above order.

Each step of the manufacturing method will be specifically described below with reference to the drawings.

(Step (1))
Step (1), as shown in FIG. 4A, is a step of forming prism-shaped light extraction portions 3 in the core layer film 1′.

Specifically, the core layer film 1′ formed using the core layer resin composition is brought into contact with the prism-forming mold 30 having the light-outcoupling prism-forming portion 31, and optionally under reduced pressure. They are laminated by heating and pressurizing them. Thereby, the light extraction part 3 can be formed by transferring the shape of the prism forming part to the core layer film.

The core layer film 1 ′ is an uncured resin film, and the resin composition described above can be used as the core layer resin composition used for the film. After lamination, the support 7 of the core layer film 1' is peeled off.

The prism-forming mold 30 is not particularly limited as long as it has the prism-forming portion 31 . Both the material and shape (dimensions) can be appropriately selected according to the application. By way of example, a mold such as a chromium alloy stainless tool steel plate machined into the desired prism shape can be used.

The shape of the light extraction part can be appropriately set according to the type and direction of light to be extracted from the core layer. Preferably, in this step, a plurality of prism-shaped light extraction portions having a height of 1 μm or more and 30 μm or less in the thickness direction are formed.

(Step (2))
Step (2) is a step of removing part of the core layer film to form a core layer. That is, in order to arrange the clad layer 2 so as to surround the core layer 1, the core layer film is removed from the portions (for example, both ends of the core layer) where the clad layer is to be filled.

Specifically, as shown in FIG. 4B, a mask 8 is used to irradiate the core layer film 1′ with active energy rays such as ultraviolet rays (indicated by arrows in FIG. 4B). Then, the resin in the irradiated portion is cured by heat treatment, and then the unnecessary uncured portion is removed by development to obtain the desired pattern of the core layer.

(Step (3))
Next, as shown in FIG. 4C, a first clad layer film 2' is laminated on the upper surface of the core layer film 1'. Specifically, the first cladding layer film 2' is brought into contact with the core layer film 1' laminated on the prism forming mold 30, and bonded together by heating and pressurizing under reduced pressure. The surface of the core layer film 1' may be surface-treated by plasma treatment or the like before being laminated.

Here, the first clad layer refers to the clad layer on the upper surface of the core layer. The first clad layer film 2' is an uncured resin film formed using a clad layer resin composition, and the resin composition described above can be used as the clad layer resin composition. can. Since the first clad layer film 2' is uncured, the portion removed in the step (2) is also filled by laminating it on the upper surface of the core layer film 1'. After lamination, the support 7 of the first clad layer film 2' is peeled off.

(Step (4))
In step (4), as shown in FIG. 4(D), the core layer film 1 ′ and the first clad layer film 2 ′ are subjected to a curing treatment, and from the core layer 1 and the first clad layer 2 This is a step of forming a first clad-core laminate.

As the curing treatment, the core layer film 1 ′ and the first clad layer film 2 ′ can be cured by irradiating active energy rays such as ultraviolet rays and heat-treating.

In the irradiation with the active energy ray, the exposure conditions are appropriately selected according to the type of the resin composition used ^. The exposure conditions and the like are selected so that .

In addition, post-curing with heat after photo-curing is also effective from the point of ensuring curing. Heat treatment conditions for the post-curing are preferably about 80 to 160° C. for about 20 to 120 minutes. However, it is needless to say that the range is not particularly limited to this range, and it is important to optimize it according to the resin composition and the like to be used.

(Step (5))
Step (5) is a step of separating the first clad-core laminate from the prism forming mold 30 and laminating the first clad layer side of the first clad-core laminate on the temporary fixing material 9. be.

Specifically, as shown in FIG. 4(E), the first clad-core laminate is brought into contact with the temporary fixing material 9 so that the first clad layer 2 side is in contact with the temporary fixing material 9, and if necessary, The substrates are heated and pressurized under reduced pressure to bond them together. In this step, in the first clad-core laminate, the side of the core layer having the light extraction part 3 becomes the upper surface.

The temporary fixing material 9 used here is not particularly limited, but for example, a substrate coated with a low-adhesive resin layer, such as a temporary fixing substrate for process transportation, can be used.

Thus, by using the prism forming mold 30 and the temporary fixing member 9, there is an advantage that a light guide sheet can be manufactured instead of a conventional light guide plate having a substrate.

(Step (6))
In step (6), as shown in FIG. 4(F), first, the second clad layer film 2'' laminated on the support 7 and the core layer in the first clad-core laminate are exposed. The surfaces are brought into contact with each other, and if necessary, they are heated and pressurized under reduced pressure to bond and laminate. Before bonding, the surface of the core layer 1 may be surface-treated by plasma treatment or the like. After laminating the second clad layer film 2'', the support 7 of the second clad layer film 2'' is peeled off.

Here, the second clad layer refers to the clad layer on the lower surface of the core layer in the finally obtained light guide sheet. The second clad layer film 2'' is an uncured resin film formed by using the clad layer resin composition, and as the clad layer resin composition, the above resin composition may be used. can be done.

After that, the second clad layer film 2 ″ is subjected to the same curing treatment as the first clad layer film 2 ′ and the like to cure the second clad layer film 2 ″, and the first clad is cured. A laminated sheet is formed having a layer, a core layer and a second clad layer.

(Step (7))
The step (7) is a step of removing a portion of the second clad layer of the laminated sheet that overlaps at least a portion of the light extraction portion of the core layer.

Specifically, as shown in FIG. 4(G), a mask 8 is used to irradiate the second cladding layer 2 with active energy rays such as ultraviolet rays (indicated by arrows in FIG. 4(G)). , the resin in the irradiated portion is cured by heat treatment (so-called after-cure). After that, by development, unnecessary uncured portions can be removed, and the second clad layer other than desired portions can be removed.

At least a part of the light extraction part 3 of the obtained light guide sheet is exposed to the outside by this step. By exposing the light extraction 3 to the outside air (air) in this way, light can be extracted more reliably.

(Step (8))
Next, the laminated sheet is peeled off from the temporary fixing material 9 .

In the laminated sheet obtained, as shown in FIG. 4H, the second cladding layer 2 is formed with an opening a by the step (7), and the light extraction part 3 of the core layer 1 is exposed.

The laminated sheet peeled off from the temporary fixing material 9 is turned over as shown in FIG. to

(Step (9))
In step (9), as shown in FIG. 4(J), the clad layer is removed at the edge of the laminated sheet to expose part of the core layer to obtain the light guide sheet 10 of the present embodiment. The exposed portion of the core layer becomes the incident portion of the light guide sheet 10 .

Although the shape of the exposed portion is not particularly limited, it may be an inclined surface (mirror portion) as shown in FIG. 4(J).

The means for forming the inclined surface is not particularly limited, and for example, the incident light from below the light guide sheet is polarized to 90° by forming an inclined surface of 45° at the end of the light entrance portion. For example, it can be formed by using a 45 degree blade on a dicing machine.

According to the manufacturing method as described above, a thin and flexible light guide sheet can be obtained without using a substrate that is conventionally required for a light guide plate.

(Second embodiment)
In addition to the manufacturing method described above, the method for manufacturing the light guide sheet of the present embodiment includes at least the following steps:
Step (1): Laminating the core layer film on the first temporary fixing material,
Step (2): removing a portion of the core layer film to form a core layer;
Step (3): A step of laminating the film for the first clad layer on the upper surface of the film for the core layer and filling the portion removed in the step (2);
Step (4): a step of subjecting the core layer film and the first clad layer film to a curing treatment to form a first clad-core laminate comprising a core layer and a first clad layer;
Step (5): The first clad-core laminate is peeled off from the first temporary fixing material, turned over, and the first clad layer side of the first clad-core laminate is laminated on the second temporary fixing material. process,
Step (6): A step of forming a light extraction portion having an uneven shape on the exposed core layer;
Step (7): A second clad layer film is laminated on the first clad-core laminate, and the second clad layer film is subjected to a curing treatment to form a first clad layer, a core layer and a second clad layer. forming a laminated sheet having
Step (8): removing a portion of the second clad layer of the laminated sheet that overlaps at least a portion of the light extraction portion of the core layer;
Step (9): a step of peeling the laminated sheet from the second temporary fixing material; and
Step (10): A manufacturing method including a step of exposing a portion of the core layer at the edge of the laminated sheet and providing a light incident portion.

These steps are preferably performed in the above order.

The main difference between the second embodiment and the first embodiment is the timing and means of forming the light extraction part in the core layer. In the second embodiment, the light extraction part is formed after forming the core layer and the like, and the light extraction part having an uneven shape is formed without using a prism forming mold as in the first embodiment. Specifically, in the step (6), the light extracting portion 3 capable of diffusing light is formed by making unevenness by sandblasting, laser processing, or the like. The uneven shape is preferably an uneven shape with an arithmetic mean roughness (Ra) of 0.1 μm or more and 50 μm or less.

In addition, since the prism forming mold is not used, instead, the first temporary fixing material is used in steps (1) to (4), and the second temporary fixing material is used to invert the laminated sheet in step (5). to use. As the first temporary fixing material and the second temporary fixing material, the same temporary fixing material as in the first embodiment can be used.

Processes other than those described above can be performed in the same manner as in the first embodiment.

(Third embodiment)
Furthermore, the method for producing the light guide sheet of this embodiment includes at least the following steps:
Step (1): A step of laminating a core layer film formed using a core layer resin composition on the first temporary fixing material,
Step (2): removing a portion of the core layer film to form a core layer;
Step (3): A step of laminating the film for the first clad layer on the upper surface of the film for the core layer and filling the portion removed in the step (2);
Step (4): a step of subjecting the core layer film and the first clad layer film to a curing treatment to form a first clad-core laminate comprising a core layer and a first clad layer;
Step (5): The first clad-core laminate is peeled off from the first temporary fixing material, turned over, and the first clad layer side of the first clad-core laminate is laminated on the second temporary fixing material. process,
Step (6): A second clad layer film is laminated on the first clad-core laminate, and the second clad layer film is subjected to a curing treatment to form a first clad layer, a core layer and a second clad layer. forming a laminated sheet having
Step (7): removing a portion of the second clad layer in the laminated sheet to form an opening exposing the core layer;
Step (8): A step of forming a light extraction portion having an uneven shape on the exposed core layer;
Step (9): a step of peeling the laminated sheet from the second temporary fixing material; and
Step (10): A manufacturing method including a step of exposing a portion of the core layer at the edge of the laminated sheet and providing a light incident portion can also be used.

The main difference between the third embodiment and the second embodiment is the timing of forming the light extraction part in the core layer. In the second embodiment, the light extraction portion is formed in the core layer, then the second clad layer is formed, and then the portion of the second clad layer that overlaps the light extraction portion is removed, but in the third embodiment. First, after forming a laminated sheet having a first clad layer, a core layer and a second clad layer, an opening is provided in the second clad layer and a light extraction part is formed in the exposed core layer.

For the formation of the light extraction portion in this case, means such as sandblasting can be used as in the second embodiment.

Processes other than those described above can be performed in the same manner as in the second embodiment.

(Fourth embodiment)
In the above-described embodiments, the core layer is formed first, but the first clad layer can also be formed first. Specifically, at least the following steps:
Step (1): A step of laminating a film for the first clad layer using a prism-forming mold having a light-outcoupling prism-forming portion;
Step (2): a step of removing a portion corresponding to the light extraction portion in the film for the first clad layer;
Step (3): A step of laminating a core layer film on the upper surface of the first clad layer film and filling the portion removed in step (2) to form a light extraction portion having a prism shape;
Step (4): a step of subjecting the core layer film and the first clad layer film to a curing treatment to form a first clad-core laminate comprising a core layer and a first clad layer;
Step (5): A second clad layer film is laminated on the first clad-core laminate, and the second clad layer film is subjected to a curing treatment to form a first clad layer, a core layer and a second clad layer. forming a laminated sheet having
Step (6): A step of exposing a portion of the core layer at the edge of the laminated sheet and providing a light incident portion;
A manufacturing method comprising: can also be used.

The light guide sheet of the present embodiment has a portion including a plurality of core wirings in at least a part of the core layer. It is formed by exposure and development of the core layer. More specifically, the core wiring is formed by curing the wiring portion using a negative mask of a desired wiring pattern, and then removing unnecessary portions by development.

INDUSTRIAL APPLICABILITY The present invention has broad industrial applicability in technical fields related to light guide materials, light guide sheets, and manufacturing methods thereof.

1 core layer 1' core layer film 2 clad layer 2' first clad layer film 2'' second clad layer film 3 light extraction portion 4 light source 5 incident portion 6 exit portion 7 support 8 mask 9 temporary fixing material 10 Light guide sheet 30 Prism forming mold 31 Prism forming part a Opening

Claims (5)

a core layer having a thickness of 30 μm or more and 100 μm or less and a width of 50 μm or more and 10 mm or less;
A cladding layer disposed so as to surround the core layer, having a lower refractive index than the core layer, and having a thickness of 30 μm or more and 200 μm or less,
The core layer has a portion including a plurality of core wirings in the width direction, and the plurality of core wirings in the portion has a width of one core wiring and a width between the core wiring and an adjacent core wiring. the ratio to the distance is 0.5:1 to 20:1;
The light guide sheet, wherein the core layer has a light extraction part. The light guide sheet according to claim 1, wherein the light extraction part has a plurality of prism shapes with a height of 1 µm or more and 30 µm or less in the thickness direction. The light guide sheet according to claim 1, wherein the light extraction part has an uneven shape with an arithmetic mean roughness (Ra) of 0.1 µm or more and 50 µm or less. 4. The light guide sheet according to any one of claims 1 to 3, wherein at least part of said light extraction part is exposed to the outside. The light guide sheet according to any one of claims 1 to 4, wherein the portion including the plurality of core wirings is at least partially bent.

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