JP5302935B2 - UV curable ink for light guide plate and light guide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a UV-curing type ink for a light guide plate capable of obtaining suitable UV-curing characteristics, mechanical characteristics, water resistance or the like at the forming of a light diffusion pattern on the light guide plate, and the light guide plate having high luminance and fewer luminance unevenness at the use of the UV-curing type ink. <P>SOLUTION: In the UV-curing type ink for a light guide plate for forming the light diffusion pattern on the light guide plate containing a methacrylic resin base material, the UV-curing type ink is formed by mixing 20-80 pts.wt. of acrylic resin (B), 20-60 pts.wt. of an acrylamide monomer (C), 80-340 pts.wt. of a (meth)acrylate monomer (D), 8-40 pts.wt. of a photo-polymerizing initiator (E), and 30-150 pts.wt. of light-diffusing powder (F) to 100 pts.wt. of a polyester acrylate oligomer (A). <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to an ultraviolet curable ink for a light guide plate and a light guide plate. In particular, it is used in the formation of a light diffusing pattern in a light guide plate, and is excellent in adhesion to the base material of the light guide plate, etc., and a light guide plate having high luminance and less luminance unevenness using the ink. About.

Methacrylic resin is a resin material with excellent transparency, weather resistance, and abrasion resistance, so it is used in many lighting applications, especially as a light guide plate for surface light source devices in liquid crystal display devices. Has been.
The surface light source device is roughly classified into a light source method, a direct light method in which a diffusion plate is sandwiched between a light source and a liquid crystal unit, and an edge light method in which a light source is arranged on the side end surface of the light guide plate. There is.
Up to now, for example, in the light source method such as a large-sized liquid crystal television of 21 inches or more, the direct method has been mainstream, but in order to bring out the characteristics of the light-weight and thin liquid crystal display device more, the edge that can make the light guide plate thinner The use of a light system has been found to be advantageous. Therefore, the edge light system is often used not only for large liquid crystal televisions but also for portable notebook personal computers.

The configuration and mechanism of the edge light system using the light guide plate is as follows. That is, a light diffusion pattern (light diffusion layer) is formed on the back surface of the methacrylic resin base material as the base material of the light guide plate, and a reflection sheet (reflection plate) is laminated.
Further, a light diffusion sheet and a prism sheet are laminated on the surface of the methacrylic resin base material, and a straight tubular light source (cold cathode tube or LED) is disposed on the side end face of the methacrylic resin base material.
The light diffusion pattern is a gradation pattern using dots, and is usually formed such that the area of one dot or the like increases as the distance from the light source increases.
Therefore, the light emitted from the light source is incident from the side surface of the methacrylic resin substrate, proceeds while being totally reflected in the light guide plate, and changes the traveling direction while the light is appropriately scattered by the light diffusion pattern. Thus, light is extracted outside.

Here, when creating a light diffusion pattern in a light guide plate, the use of UV curable ink for the light guide plate has been proposed and used for a surface light source device (backlight unit) that specifies the minimum dot diameter of the light diffusion pattern. A light guide plate is disclosed (see Patent Document 1).
More specifically, light in the light guide plate comprising a polymerizable oligomer, a polymerizable monomer, an acrylic resin soluble in these polymerizable oligomers or monomers, a photopolymerization initiator, and a light diffusion powder. This is an ultraviolet curable ink for a diffusion pattern (hereinafter referred to as an ultraviolet curable ink for a light guide plate).
Then, as shown in FIGS. 6A and 6B, a predetermined UV curable ink for the light guide plate is screen-printed on the base material 1b of the light guide plate 1 and irradiated with ultraviolet rays. Thus, a light diffusion pattern 6 having a minimum dot diameter of 0.15 mm or less is formed.
In addition, a light source 2 is provided at a side end 1 a of the light guide plate 1, a reflection sheet 3 is provided below the light guide plate 1, and a diffusion is provided above the light guide plate 1. The sheet | seat 4 is provided and the surface light source device (backlight unit) 10 is comprised as a whole.

JP 2003-344661 A (Claims)

However, the UV curable ink for a light guide plate disclosed in Patent Document 1 is not only insufficient in UV curable properties due to the blending composition, but also has a light diffusion pattern for a substrate in the light guide plate, particularly a methacrylic resin substrate. There was a problem of poor adhesion and water resistance.
Therefore, when the light diffusion pattern is formed and the light guide plate is configured, the diffusion pattern to be formed is peeled off or the pattern or shape is easily deformed. In addition, there was a problem that the luminance unevenness was increased, and that these characteristics were likely to be further deteriorated with time.

Therefore, the inventor of the present invention, in constructing the ultraviolet curable ink for the light guide plate, (A) polyester acrylate oligomer, (B) acrylic resin, (C) acrylamide monomer, (D) (meth) By blending an acrylate monomer, (E) a photopolymerization initiator, and (F) a light diffusing powder in a predetermined ratio, and limiting the water content to a value within a predetermined range, good UV curing is achieved. As a result, when the light guide plate is configured, the brightness of the diffused light obtained is high, and uneven brightness is obtained. The present invention has been completed by finding a small size.
That is, an object of the present invention is to provide an ultraviolet curable ink for a light guide plate that can provide good ultraviolet curable characteristics, mechanical properties, water resistance, and the like in the formation of a light diffusion pattern in the light guide plate, and a high The object is to provide a light guide plate that is low in luminance and has little luminance unevenness.

  According to the present invention, there is provided an ultraviolet curable ink for a light guide plate constituting a light diffusion pattern of a light guide plate including a methacrylic resin substrate, wherein (A) a polyester acrylate oligomer, (B) an acrylic resin, and (C) It contains an acrylamide monomer, (D) (meth) acrylate monomer, (E) photopolymerization initiator, and (F) light diffusing powder. On the other hand, the blending amount of the acrylic resin of the component (B) is a value within the range of 20 to 80 parts by weight, the blending amount of the acrylamide monomer of the component (C) is a value within the range of 20 to 60 parts by weight, The blending amount of the (D) component (meth) acrylate monomer is set to a value within the range of 80 to 340 parts by weight, and the blending amount of the photopolymerization initiator of the (E) component is within the range of 8 to 40 parts by weight. For the light guide plate, wherein the blending amount of the light diffusing powder of the component (F) is a value within the range of 30 to 150 parts by weight, and the moisture content is 2% by weight or less. An ultraviolet curable ink is provided and can solve the above-mentioned problems.

That is, (A) polyester acrylate oligomer, (B) acrylic resin, (C) acrylamide monomer, (D) (meth) acrylate monomer, (E) photopolymerization initiator, (F) light diffusion powder And by blending at a ratio of a predetermined amount, by limiting the moisture content to a value within a predetermined range, good ultraviolet curability and water resistance, or between the methacrylic resin base material in the light guide plate, Excellent adhesion and the like can be obtained.
In particular, by including an (C) acrylamide monomer as one of the components of the ultraviolet curable ink for the light guide plate, the adhesion to the methacrylic resin substrate is enhanced while maintaining good ultraviolet curability. When the light guide plate is configured, it is possible to satisfy the contradictory characteristics of high luminance and adjustment of luminance unevenness.
Note that (C) the acrylamide monomer is generally easy to absorb moisture, so when it is blended with the UV curable ink for the light guide plate, the UV curable property and the adhesion to the methacrylic resin substrate may be significantly reduced. It was.
However, by limiting the water content in the ultraviolet curable ink for the light guide plate to a value within a predetermined range, such a problem can be prevented beforehand.

In constituting the ultraviolet curable ink for a light guide plate of the present invention, the acrylamide monomer preferably contains dimethylacrylamide.
With this type of acrylamide monomer, it is liquid at room temperature and is easy to handle, and it can further improve the adhesion between the methacrylic resin substrate and UV light for light guide plates. It is easy to control the moisture content of the curable ink.

In constituting the ultraviolet curable ink for a light guide plate of the present invention, the (meth) acrylate monomer preferably contains 1,6 hexanediol di (meth) acrylate.
By including such a kind of (meth) acrylate monomer, good ultraviolet curability can be obtained while effectively maintaining the adhesion to the methacrylic resin substrate.

Moreover, in constituting the ultraviolet curable ink for a light guide plate of the present invention, the acrylic resin is an acrylic polymer derived from a monomer component containing 50% by weight or more of a (meth) acrylate monomer with respect to the total amount of the monomer component. And it is preferable that it is soluble in a (meth) acrylate monomer.
By using such an acrylic resin, it becomes easy to adjust the water content of the ultraviolet curable ink for the light guide plate, and the adhesion to the methacrylic resin substrate can be further improved.
In addition, by blending such an acrylic resin, the affinity between the mixture of the (meth) acrylate monomer containing a specific acrylamide monomer and the polyester acrylate oligomer can be improved.

Moreover, when comprising the ultraviolet curable ink for light-guide plates of this invention, it is preferable to make the weight average molecular weight of an acrylic resin into the value within the range of 50,000-150,000.
By using such an acrylic resin having a weight average molecular weight, it is possible to obtain good ultraviolet curability while effectively maintaining adhesion with a methacrylic resin substrate, and in addition, a specific acrylamide monomer can be used. The affinity between the mixture of the (meth) acrylate monomer containing and the polyester acrylate oligomer can be further improved.

In constituting the ultraviolet curable ink for a light guide plate of the present invention, the light diffusion powder is preferably at least one of silica powder, titanium oxide powder, acrylic resin powder, and urethane resin powder.
By using such a light diffusing powder, it is possible to effectively maintain the adhesion with the methacrylic resin substrate, and in addition, when a light guide plate is configured, high-intensity diffused light is obtained, The luminance unevenness can also be reduced.

Another aspect of the present invention is a light guide plate comprising a methacrylic resin substrate and a light diffusion pattern made of an ultraviolet cured product of an ultraviolet curable ink for the light guide plate,
An ultraviolet curable ink for a light guide plate includes (A) a polyester acrylate oligomer, (B) an acrylic resin, (C) an acrylamide monomer, (D) a (meth) acrylate monomer, and (E) a photopolymerization initiator. (F) a light diffusing powder, and
(A) For 100 parts by weight of the polyester acrylate oligomer as a component,
(B) The amount of the acrylic resin as the component is set to a value within the range of 20 to 80 parts by weight,
The blending amount of the acrylamide monomer as the component (C) is a value within the range of 20 to 60 parts by weight,
The blending amount of the (meth) acrylate monomer as the component (D) is set to a value within the range of 80 to 340 parts by weight,
(E) The amount of the photopolymerization initiator as a component is set to a value within the range of 8 to 40 parts by weight,
(F) The amount of the light diffusing powder as the component is set to a value within the range of 30 to 150 parts by weight,
And it is a light-guide plate characterized by making a moisture content into the value of 2 weight% or less.
In other words, by using a light guide plate having a light diffusion pattern made of a specific ultraviolet curable ink for a light guide plate in this way, in the obtained diffused light, it is easy to have conflicting characteristics such as high brightness and adjustment of brightness unevenness. Can be satisfied.
In addition, since (C) an ultraviolet curable ink for a light guide plate having a predetermined water content containing an acrylamide monomer or the like is used, the adhesiveness with a methacrylic resin substrate is maintained while maintaining good ultraviolet curability. As a result, the manufacture of the light guide plate is short and stable.

Further, in configuring the light guide plate of the present invention, the 60 ° glossiness in the light diffusion pattern is preferably set to a value of 30% or less.
By limiting the glossiness of the UV cured product to a value within a predetermined range in this way, the obtained diffused light can further satisfy the contradictory characteristics of high brightness and brightness unevenness adjustment. it can.

FIG. 1 is a diagram provided for explaining the influence of the blending amount of an acrylamide monomer on the water content in an ultraviolet curable ink for a light guide plate. FIG. 2 is a diagram provided for explaining the influence of the blending amount of the acrylamide monomer on the ultraviolet curable property in the ultraviolet curable ink for the light guide plate. FIG. 3 is a diagram for explaining the influence of the blending amount of the acrylamide monomer on the 60 ° glossiness in the light diffusion pattern made of the ultraviolet curable ink for the light guide plate. FIG. 4 is a diagram for explaining the influence of the water content of the ultraviolet curable ink for the light guide plate on the central luminance in the light guide plate having the light diffusion pattern made of the ultraviolet curable ink for the light guide plate. FIG. 5 is a diagram for explaining the influence of the water content of the ultraviolet curable ink for the light guide plate on the absolute value of the luminance unevenness in the light guide plate having the light diffusion pattern made of the ultraviolet curable ink for the light guide plate. . 6A is a diagram for explaining a configuration example of a light guide plate including a light diffusion pattern, and FIG. 6B is a configuration example of a surface light source device (backlight unit) including the light guide plate. It is a figure provided in order to demonstrate.

[First Embodiment]
1st Embodiment of this invention is the ultraviolet curable ink for light-guide plates which comprises the light-diffusion pattern of the light-guide plate containing a methacrylic resin base material, Comprising: (A) Polyester acrylate oligomer, (B) Acrylic resin, , (C) an acrylamide monomer, (D) a (meth) acrylate monomer, (E) a photopolymerization initiator, and (F) a light diffusing powder.
And with respect to 100 parts by weight of the polyester acrylate oligomer as the component (A), the amount of the acrylic resin as the component (B) is set to a value within the range of 20 to 80 parts by weight, and the acrylamide system as the component (C) The amount of the monomer is set to a value within the range of 20 to 60 parts by weight, the amount of the (meth) acrylate monomer as the component (D) is set to a value within the range of 80 to 340 parts by weight, and the component (E) The blending amount of the photopolymerization initiator is set to a value within the range of 8 to 40 parts by weight, the blending amount of the light diffusion powder as the component (F) is set to a value within the range of 30 to 150 parts by weight, and the water content is set to It is an ultraviolet curable ink for a light guide plate characterized by having a value of 2% by weight or less.
Hereinafter, each component in the ultraviolet curable ink for light-guide plates of 1st Embodiment is demonstrated concretely.

1. Compounding Component (1) (A) Polyester Acrylate Oligomer When constituting an ultraviolet curable ink for a light guide plate, a polyester acrylate oligomer is blended as a photopolymerizable oligomer.
The reason for this is that polyester acrylate oligomers are excellent in compatibility with acrylamide monomers and (meth) acrylate monomers, and can achieve a predetermined adhesion to a methacrylic resin substrate while maintaining good UV curability. Because it is. Further, when a light diffusion pattern in the light guide plate is configured, predetermined hardness, durability, moisture resistance, and the like are obtained.

Here, the weight average molecular weight of the polyester acrylate oligomer is not particularly limited. For example, it is preferable to set the weight average molecular weight to a value of 1,000 or more.
The reason for this is that when the weight average molecular weight of the polyester acrylate oligomer is less than 1,000, the UV curable property and the adhesion to the methacrylic resin substrate are lowered, or the light diffusion pattern in the light guide plate is configured. This is because it may be difficult to obtain a predetermined hardness or the like.
However, if the weight average molecular weight of the polyester acrylate oligomer becomes excessively large, the compatibility with the acrylamide monomer and the (meth) acrylate monomer is lowered, and the UV curable property or the adhesion to the methacrylic resin substrate is lowered. There is.
Accordingly, the weight average molecular weight of the polyester acrylate oligomer is more preferably set to a value within the range of 3,000 to 15,000.
In addition, the weight average molecular weight of the polyester acrylate oligomer can be measured as a molecular weight in terms of polystyrene by gel permeation chromatography (GPC) (hereinafter, the same applies to the measurement of the weight average molecular weight of other compounding components and the like). is there.)

Moreover, it is preferable to make the addition amount of a polyester acrylate oligomer into the value within the range of 20-40 weight% with respect to the whole quantity (100 weight%) of the ultraviolet curable ink for light-guide plates.
The reason for this is that the adhesiveness to the methacrylic resin substrate can be further improved while maintaining good ultraviolet curability more effectively by using such a blending amount.
That is, when the compounding amount of the polyester acrylate oligomer is less than 20% by weight, the ultraviolet curability is excessively lowered, and thereby the hardness in the light diffusion pattern as the cured film obtained and the adhesion to the methacrylic resin substrate are increased. This is because it may decrease.
On the other hand, when the blending amount of the polyester acrylate oligomer exceeds 40% by weight, the ultraviolet curability is excessively increased and handling becomes difficult. This is because there is a case where it becomes easy to cause poor adhesion.
Therefore, the addition amount of the polyester acrylate oligomer is more preferably set to a value within the range of 25 to 35% by weight with respect to the total amount of the ultraviolet curable ink for the light guide plate.

(2) (B) Acrylic Resin Further, in constituting the ultraviolet curable ink for the light guide plate, a predetermined amount of (B) acrylic resin is blended.
This is because, by blending such an acrylic resin, the compatibility with the acrylamide monomer and the (meth) acrylate monomer is improved, and the water content of the UV curable ink for the light guide plate can be easily adjusted. It is to do.
Also, by blending the acrylic resin, it is possible to improve the UV curability and adhesion to the methacrylic resin base material, or to obtain a predetermined hardness and strength when a light diffusion pattern in the light guide plate is configured. .

Here, it is preferable that the weight average molecular weight of the acrylic resin is a value within the range of 50,000 to 150,000.
The reason for this is that when the weight average molecular weight of the acrylic resin is less than 50,000, the ultraviolet curability is excessively increased and the adhesion to the methacrylic resin substrate may be lowered.
On the other hand, when the weight average molecular weight of the acrylic resin exceeds 150,000, the ultraviolet curability is excessively decreased, and the strength of the resulting cured film may be decreased.
Therefore, the weight average molecular weight of the acrylic resin is more preferably set to a value within the range of 65,000 to 100,000, and further preferably set to a value within the range of 75,000 to 90,000.

Moreover, it is preferable to use an acrylic resin in a powder state at room temperature as such an acrylic resin.
This is because not only the adhesion to the methacrylic resin base material is improved, but also the water content of the UV curable ink for the light guide plate can be easily adjusted, and the (meth) acrylate monomer containing a specific acrylamide monomer is used. This is because the affinity between the mixture and the polyester acrylate oligomer can be further improved.

Therefore, the acrylic resin is methyl methacrylate, ethyl methacrylate, propyl methacrylate, isooctyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, methacrylamide, hydroxymethacrylamide hydroxymethacrylamide, acrylic acid, methyl acrylate, ethyl acrylate, An acrylic polymer derived from at least one monomer component such as propyl acrylate, isooctyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, acrylamide, and hydroxyacrylamide is preferred.
Furthermore, the acrylic resin is mainly composed of methacrylate monomers such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, isooctyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, methacrylamide and hydroxymethacrylamide (methacrylamide) ( For example, the acrylic polymer is preferably 80% by weight or more of the total amount of monomers).

The acrylic resin is an acrylic polymer derived from a monomer component containing 50% by weight or more of a (meth) acrylate monomer with respect to the total amount of the monomer component, and is soluble in the (meth) acrylate monomer. It is preferable.
This is because the use of an acrylic resin obtained by polymerizing such a (meth) acrylate monomer as a main component makes it easy to adjust the water content of the UV curable ink for the light guide plate, This is because the compatibility is improved and the adhesion can be further improved.
Further, with such an acrylic resin, the affinity between the mixture of the (meth) acrylate monomer containing a specific acrylamide monomer and the polyester acrylate oligomer can be further improved.
In addition, by using an acrylic resin having a high glass transition point, for example, a glass transition point of 75 to 120 ° C., the adhesion with the methacrylic resin substrate can be further improved.

Moreover, when an acrylic resin is a powder state, it is preferable to make the average particle diameter into the value within the range of 0.01-4 mm.
This is because when the average particle size of the acrylic resin in the powder state is less than 0.01 mm, it may be difficult to handle or the moisture content may be difficult to control.
On the other hand, if the average particle size of the acrylic resin in the powder state exceeds 4 mm, the dissolution time for the (meth) acrylate monomer may be remarkably delayed.
Therefore, the average particle diameter of the acrylic resin in the powder state is more preferably in the range of 0.03 to 3 mm, and further preferably in the range of 0.05 to 2 mm.
The average particle size of the acrylic resin can be measured and calculated by a microscope method or an image processing method according to JIS Z 8901.

Furthermore, it is preferable that the water content of the acrylic resin in such a powder state is set to a value of 0.01 to 5% by weight or less with respect to the total amount of the nuclear acrylic resin.
The reason for this is that when the moisture content is less than 0.01% by weight, it becomes difficult to stably produce an acrylic resin, or conversely, the moisture content becomes extremely hygroscopic and the moisture content of the UV curable ink for the light guide plate is controlled. This may be difficult.
On the other hand, when the moisture content exceeds 5% by weight, the affinity with the polyester acrylate oligomer may be lowered, or the moisture content of the UV curable ink for the light guide plate may be difficult to control.
Therefore, it is more preferable that the moisture content of the acrylic resin in the powder state is set to a value within the range of 0.05 to 3% by weight.

Moreover, it is preferable to make the compounding quantity of an acrylic resin into the value within the range of 20-80 weight part with respect to 100 weight part of polyester acrylate oligomers.
The reason for this is that when the amount of the acrylic resin is less than 20 parts by weight, the ultraviolet curability is excessively increased and the adhesion to the substrate may be lowered. On the other hand, when the blending amount of the acrylic resin exceeds 80 parts by weight, the ultraviolet curability is excessively lowered, the strength of the cured film is lowered, and the light-diffused pattern printed film is uniformly formed. This is because luminance unevenness may occur due to the inability to perform the above.
Therefore, the blending amount of the acrylic resin is more preferably 25 to 60 parts by weight and further preferably 30 to 50 parts by weight with respect to 100 parts by weight of the polyester acrylate oligomer.

(3) (C) Acrylamide monomer Further, when constituting an ultraviolet curable ink for a light guide plate, a predetermined amount of (C) acrylamide monomer is blended as one of the curing components.
The reason for this is that by blending such an acrylamide-based monomer, it is possible to improve the adhesion between the methacrylic resin base material while maintaining good ultraviolet curability. This is because it is possible to satisfy the mutually conflicting characteristics of the expression of luminance and the adjustment of luminance unevenness.

Here, the types of acrylamide monomers include diacetone acrylamide, N-methylol acrylamide, isobutoxymethyl acrylamide, N, N-dimethyl acrylamide, N-methoxymethyl acrylamide, t-octyl acrylamide, N, N-diethyl acrylamide, Examples thereof include N-hydroxymethyl acrylamide, N, N-butoxymethyl acrylamide, N, N-dimethylaminopropyl acrylamide and the like alone or in combination of two or more.
In particular, N, N-dimethylacrylamide is a preferred acrylamide monomer because of its good adhesion to the substrate and appropriate ultraviolet curability.

Moreover, it is preferable to make the compounding quantity of an acrylamide-type monomer into the value within the range of 20-60 weight part with respect to 100 weight part of polyester acrylate oligomers.
The reason for this is that when the amount of the acrylamide monomer is less than 20 parts by weight, the effect of addition may not appear.
On the other hand, when the blending amount of the acrylamide monomer exceeds 60 parts by weight, it is difficult to control the water content, the ultraviolet curing property is lowered, or the hardness of the obtained diffusion pattern is lowered. Because there is.
Therefore, the blending amount of the acrylamide monomer is more preferably 25 to 55 parts by weight and further preferably 30 to 50 parts by weight with respect to 100 parts by weight of the polyester acrylate oligomer.

Here, with reference to FIG. 1, the influence of the blending amount of the acrylamide monomer on the water content in the ultraviolet curable ink for the light guide plate will be described.
That is, the horizontal axis of FIG. 1 shows the blending amount (part by weight) of the acrylamide monomer in the UV curable ink for light guide plate blended according to the blending composition of Example 1, and the vertical axis of FIG. Further, the moisture content value (% by weight) in the UV curable ink for the light guide plate is shown.
The characteristic curve A corresponds to dimethylacrylamide, and the characteristic curve B corresponds to N-methoxymethylacrylamide.
As can be easily understood from these characteristic curves A and B, the water content in the UV curable ink for the light guide plate varies greatly depending on the blending amount of the acrylamide monomer, and also depends on the type of the acrylamide monomer. It is understood that the moisture content in the ultraviolet curable ink for optical plates varies.
Therefore, it is understood that it is effective to change the amount and type of the acrylamide monomer when controlling the water content in the ultraviolet curable ink for the light guide plate to a value within a predetermined range.

Next, with reference to FIG. 2, the influence of the blending amount of the acrylamide monomer on the ultraviolet curing characteristics in the ultraviolet curable ink for the light guide plate will be described.
That is, the horizontal axis of FIG. 2 shows the blending amount (part by weight) of the acrylamide monomer in the UV curable ink for light guide plate blended according to the blending composition of Example 1, and the vertical axis of FIG. In addition, the evaluation point of the curing characteristics in the ultraviolet curable ink for light guide plate evaluated according to Example 1 (the evaluation point of ◎ is 3, the evaluation point of ◯ is 2, the evaluation point of △ is 1, the evaluation point of x is 0).
The characteristic curve A corresponds to dimethylacrylamide that is relatively difficult to absorb moisture, and the characteristic curve B corresponds to N-methoxymethylacrylamide that is relatively easy to absorb moisture.
As can be easily understood from these characteristic curves A and B, the ultraviolet curability in the ultraviolet curable ink for the light guide plate varies greatly depending on the blending amount of the acrylamide monomer, and also depending on the type of the acrylamide monomer, It is understood that the UV curable properties change.
Therefore, it is understood that it is effective to change the blending amount and type of the acrylamide monomer in obtaining good ultraviolet curability in the ultraviolet curable ink for the light guide plate.

Moreover, with reference to FIG. 3, the influence of the compounding quantity of the acrylamide type monomer with respect to the 60 degree glossiness of the diffusion pattern which consists of the ultraviolet curable ink for light-guide plates is demonstrated.
That is, the horizontal axis of FIG. 3 shows the blending amount (part by weight) of the acrylamide monomer in the UV curable ink for light guide plate blended according to the blending composition of Example 1, and the vertical axis of FIG. The 60 ° gloss value measured according to Example 1 is shown.
As can be easily understood from the characteristic curve, it is understood that the value of the 60 ° glossiness of the diffusion pattern made of the ultraviolet curable ink for the light guide plate greatly varies depending on the blending amount of the acrylamide monomer.
Therefore, it is understood that it is effective to change the blending amount of the acrylamide monomer when limiting the 60 ° glossiness of the diffusion pattern to a value within a predetermined range.

(4) (D) (Meth) acrylate monomer In addition, when constituting an ultraviolet curable ink for a light guide plate, a predetermined amount of (D) (meth) acrylate monomer is blended as one of the ultraviolet curing components. And
The reason for this is to adjust the ultraviolet curing characteristics and viscosity of the ultraviolet curable ink for the light guide plate, to control the adhesion to the methacrylic substrate, or to adjust the characteristics of the resulting cured film.

  Here, regarding the type of (meth) acrylate monomer, for example, a (meth) acrylate monomer, a carboxyl group or an acid anhydride obtained by an amidation or esterification reaction between a compound containing an amino group or a hydroxyl group and acrylic acid (Meth) acrylate monomers obtained by esterification reaction of a compound having a group and an acrylate having a hydroxyl group are included.

  More specifically, as the (meth) acrylate monomer, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, isobutyl acrylate, benzyl acrylate, ethyl carbitol acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methoxyethyl acrylate, methoxypolyethylene glycol acrylate , Butoxyethyl acrylate, butoxypolyethylene glycol acrylate, phenoxyethyl acrylate, nonylphenoxyethyl acrylate, phenoxypolyethylene glycol acrylate, 3-chloro-2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-hydroxybutyl acrylate, Diethylene glycol monoa Relate, dipropylene glycol monoacrylate, polyethylene glycol monoacrylate, polypropylene glycol monoacrylate, trifluoroethyl acrylate, dicyclopentadiene acrylate, isobornyl acrylate, dicyclopentenyloxyalkyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate , Tricyclodecanyl acrylate, tricyclodecanyloxyethyl acrylate and the like.

  Moreover, as a bifunctional (meth) acrylate monomer, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, Pentyl glycol diacrylate, neopentyl glycol diacrylate, 1,6 hexanediol diacrylate, 1,2-hexyldiol diacrylate, 1,5-hexyldiol diacrylate, bisphenol A tetraethylene oxide adduct diacrylate, bisphenol F Examples include tetraethylene oxide adduct diacrylate.

  Trifunctional (meth) acrylate monomers include glycerin triacrylate, trimethylolpropane triacrylate, trimethylolpropane tricaprolactonate triacrylate, trimethylolethane triacrylate, trimethylolhexane triacrylate, trimethylolethane triacrylate, Examples include trimethylol hexane triacrylate, trimethylol octane triacrylate, pentaerythritol triacrylate and the like.

Moreover, it is preferable to make the compounding quantity of a (meth) acrylate monomer into the value within the range of 80-340 weight part with respect to 100 weight part of polyester acrylate oligomers.
The reason for this is that by adjusting to a value within such a range, it is possible not only to improve the adhesion to the base material while effectively maintaining the UV curability, but also to form a printed film uniformly. This is because it can be done.
Therefore, the blending amount of the (meth) acrylate monomer is more preferably 100 to 300 parts by weight and further preferably 150 to 250 parts by weight with respect to 100 parts by weight of the polyester acrylate oligomer. .
In addition, (D) (meth) acrylate monomer is easily mixed with the above-mentioned (C) acrylamide monomer in advance at a predetermined ratio because a light diffusion pattern as a cured coating film having uniform characteristics is easily obtained. It is preferable to use in a state.

(5) (E) Photopolymerization initiator The photopolymerization initiator used in the present invention generates radicals by irradiation with ultraviolet rays, and the radicals contain a polyester acrylate oligomer or an acrylamide monomer (meth) acrylate monomer. Any mixture may be used so long as it undergoes a polymerization reaction.
Specific examples of such a photopolymerization initiator include benzyl dimethyl ketal compounds such as 2,2-dimethoxy-1,2-diphenylethane-1-one; oligo [2-hydroxy-2-methyl-1- [ Α-hydroxy ketone compounds such as 4- (1-methylvinyl) phenyl] propanone] and 1-hydroxycyclohexyl phenyl ketone; 2-methyl-1 [4- (methylthio) phenyl] -2-morpholinopropane-1 -One, α-aminoketone compounds such as 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1; diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, etc. Acylphosphine oxide compounds of 1- [4- (4-benzoylphenylsulfanyl) phenyl] -2-methyl Ketosulfone compounds such as -2- (4-methylphenylsulfonyl) propan-1-one; bis (η5-2,4-cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H) Metallocene compounds such as -pyrrol-1-yl) -phenyl) titanium; 2,4-diethylthioxanthone, isopropylthioxanthone, 1-chloro-4-propoxythioxanthone, 2- (3-dimethylamino-2-hydroxypropoxy) 3 , 4-dimethyl-9H-thioxanthone-9-one-mesochloride and the like thioxanthone compounds such as single or a combination of two or more.

Among the photopolymerization initiators mentioned above, acylphosphine oxide compounds having a phenyl group, ketosulfone compounds, α-aminoketone compounds, and α-hydroxyketone compounds are preferred.
This is because radicals are generated by ultraviolet rays, and the radicals react efficiently with the photopolymerization oligomer and the photopolymerization monomer mixture to accelerate the curing reaction.
And, in constituting the curing component of the light diffusion pattern, ultraviolet curability and weather resistance are appropriate, and the durability of the light diffusion pattern as a cured coating film can be adjusted effectively and easily. It is more preferable to use a hydroxyketone compound.

In addition, a photopolymerization initiator of a type that generates radicals by hydrogen abstraction such as a thioxanthone compound is a more preferable embodiment because the curing reaction is accelerated by combining with a hydrogen donor.
Examples of such hydrogen donors include mercapto compounds and amine compounds, and among them, amine compounds are preferable.
As suitable amine compounds, triethylamine, methyldiethanolamine, triethanolamine, diethylaminoethyl acrylate, p-dimethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, N, N-dimethylbenzylamine 4,4′-bis (diethylamino) benzophenone, p-dimethylaminobenzoic acid ethyl ester, pentyl 4-dimethylaminobenzoate, and the like.

Moreover, it is preferable to make the compounding quantity of such a photoinitiator into the value within the range of 8-40 weight part with respect to 100 weight part of polyester acrylate oligomers.
This is because when the amount of the photopolymerization initiator added is less than 8 parts by weight, curing may be poor and a light diffusion pattern may not be formed uniformly.
On the other hand, when the added amount of the photopolymerization initiator exceeds 40 parts by weight, the amount of unreacted photopolymerization initiator increases after UV curing, the cross-linking reaction with time progresses easily, and the formed light diffusion pattern This is because deterioration with time may occur.
Therefore, it is more preferable to set the addition amount of the photopolymerization initiator to a value within the range of 10 to 30 parts by weight with respect to 100 parts by weight of the polyester acrylate oligomer, and to a value within the range of 15 to 25 parts by weight. More preferably.

(6) (F) Light diffusing powder Further, when the ultraviolet curable ink for a light guide plate is constituted, a predetermined amount of (F) light diffusing powder is blended.
This is because the light diffusibility can be remarkably improved by blending such a light diffusing powder.

Here, as such light diffusion powder, inorganic powder such as glass beads, silica powder, calcium carbonate powder, barium sulfate powder, titanium oxide powder, aluminum oxide, silicone powder, acrylic resin powder, styrene resin powder, urethane resin Examples thereof include inorganic powders such as powder and nylon resin powder.
Among them, in particular, since the light diffusivity can be improved while effectively maintaining the adhesion to the substrate, at least one of silica powder, titanium oxide powder, acrylic resin powder, and urethane resin powder. It is more preferable that

Further, the shape of the light diffusing powder may be a spherical shape, a spherical shape, a scale shape, an indefinite shape or the like, and is not particularly limited, but the average particle size of the nuclear light diffusing powder is 0.5 μm to A value within the range of 40 μm is preferable.
The reason for this is that when the average particle size of the light diffusing powder becomes a value of less than 0.5 μm, the scattering effect is excessively lowered and a predetermined luminance may not be obtained. On the other hand, when the average particle size of the light diffusing powder becomes a value exceeding 40 μm, the scattering effect is excessively increased, and not only glare due to the diffused light occurs but also the adhesion to the substrate may be lowered. Because.
Therefore, the average particle diameter of the light diffusing powder is more preferably a value within the range of 1 μm to 20 μm, and even more preferably a value within the range of 3 μm to 15 μm.

Moreover, it is preferable to make the addition amount of such a light-diffusion powder into the value within the range of 30-150 weight part with respect to 100 weight part of polyester acrylate oligomers.
The reason for this is that when the amount of light diffusion powder added is less than 30 parts by weight, the light diffusivity is excessively reduced and uneven brightness occurs, as well as the 60 ° glossiness of the cured film of the light diffusion pattern. This is because there may be a case where the value of 30% or less cannot be stably achieved.
On the other hand, if the added amount of the light diffusing powder exceeds 150 parts by weight, the light diffusivity is excessively increased, and not only a predetermined luminance cannot be obtained, but also the adhesion to the substrate may be lowered. It is.
Therefore, it is more preferable to set the addition amount of the light diffusing powder to a value within the range of 45 to 120 parts by weight, and to a value within the range of 50 to 100 parts by weight with respect to 100 parts by weight of the polyester acrylate oligomer. Further preferred.

(7) (G) Additive In addition, for the purpose of adjusting ink and printing suitability in the UV curable ink for light guide plate, (G) Additives include surfactants, antifoaming agents, leveling agents, pigments It is preferable to further blend a wetting agent, a dispersing agent, a flow regulator, a thermal polymerization inhibitor, an oxidation polymerization inhibitor, and the like.
Although the compounding quantity of this additive can be changed with the kind etc. of an additive, it is set as the value within the range of 0.1-20 weight part with respect to 100 weight part of (A) polyester acrylate oligomers, for example. More preferably, the value is more preferably in the range of 0.5 to 10 parts by weight, and even more preferably in the range of 1 to 5 parts by weight.

2. Water content The water content of the UV curable ink for the light guide plate is set to a value of 2% by weight or less. That is, the ultraviolet curable ink for a light guide plate having a predetermined blending component is configured, and the water content is controlled to a value of 2% by weight or less.
The reason for this is that when the water content of the UV curable ink for the light guide plate exceeds 2% by weight, the light emitted from the light source enters from the side surface and proceeds while being totally reflected in the light guide plate. When the refractive index becomes excessively large due to light scattering and the direction is changed, the prescribed brightness cannot be obtained, or when the pattern or shape of the diffusion pattern changes, the brightness unevenness increases, and it is placed on the light guide plate. This is because sufficient light transmission cannot be ensured for the diffusion sheet to be formed.
On the other hand, if the water content of the ultraviolet curable ink for the light guide plate is excessively reduced, the types of compounding components that can be used may be excessively limited, or the yield may be excessively reduced.
Therefore, the water content of the UV curable ink for the light guide plate is preferably set to a value within the range of 0.001 to 1% by weight, and more preferably set to a value within the range of 0.01 to 0.6% by weight. preferable.
In addition, the measuring method of the moisture content of the ultraviolet curable ink for light-guide plates is explained in full detail in Example 1 mentioned later.

Moreover, with reference to FIG. 4, the influence of the moisture content of the ultraviolet curable ink for light guide plates on the brightness | luminance of the light guide plate which uses the predetermined ultraviolet curable ink for light guide plates is demonstrated.
That is, the horizontal axis of FIG. 4 shows the moisture content (% by weight) in the UV curable ink for light guide plate formulated according to the composition of Example 1, and the vertical axis of FIG. The brightness value of the light guide plate measured according to 1 is shown.
As can be easily understood from the characteristic curve, it is understood that the luminance value of the light guide plate varies greatly depending on the water content in the ultraviolet curable ink for the light guide plate.
More specifically, by setting the water content in the UV curable ink for the light guide plate to 2% by weight or less, a high luminance of 3800 cd / m ² or more can be obtained, and similarly, the water content is set to 1% by weight or less. Thus, a high luminance of 4600 cd / m ² or more is obtained.
On the other hand, when the water content in the UV curable ink for the light guide plate exceeds 2% by weight and becomes 3% by weight, the luminance decreases to about 3400 cd / m ^2, and when the water content becomes 4% by weight, the water content becomes 3200 cd / m ² . The value is low.
Therefore, it is understood that it is effective to control the water content in the ultraviolet curable ink for the light guide plate to a value within a predetermined range when the luminance of the light guide plate is increased to a predetermined value or more.

Next, with reference to FIG. 5, the influence of the moisture content of the UV curable ink for the light guide plate on the luminance unevenness of the light guide plate using the predetermined UV curable ink for the light guide plate will be described.
That is, the horizontal axis of FIG. 5 shows the water content (% by weight) in the UV curable ink for light guide plate formulated according to the composition of Example 1, and the vertical axis of FIG. The brightness unevenness value of the light guide plate measured according to 1 is shown.
As can be easily understood from the characteristic curve, it is understood that the luminance unevenness value of the light guide plate varies greatly depending on the water content in the ultraviolet curable ink for the light guide plate.
More specifically, by setting the water content in the UV curable ink for light guide plate to 2% by weight or less, the absolute value of luminance unevenness becomes 30% or less, and similarly, the water content is set to 1% by weight or less. As a result, a low value with an absolute value of luminance unevenness of 20% or less is obtained.
On the other hand, when the water content in the UV curable ink for the light guide plate exceeds 2% by weight and becomes 3% by weight, the absolute value of the luminance unevenness increases to about 50, and when the water content becomes 4% by weight, it reaches about 70%. Is rising.
Therefore, it is understood that it is effective to control the water content in the ultraviolet curable ink for the light guide plate to a value within a predetermined range when reducing the luminance unevenness of the light guide plate.

[Second Embodiment]
The second embodiment is a light guide plate including a methacrylic resin substrate and a light diffusion pattern made of an ultraviolet cured product of an ultraviolet curable ink for a light guide plate, wherein the ultraviolet curable ink for the light guide plate is (A A) a polyester acrylate oligomer, (B) an acrylic resin, (C) an acrylamide monomer, (D) a (meth) acrylate monomer, (E) a photopolymerization initiator, and (F) a light diffusing powder. In addition, with respect to 100 parts by weight of the polyester acrylate oligomer as the component (A), the blending amount of the acrylic resin as the component (B) is set to a value within the range of 20 to 80 parts by weight, and acrylamide as the component (C). The amount of the system monomer is set to a value in the range of 20 to 60 parts by weight, and the amount of the (meth) acrylate monomer as the component (D) is 80 to 340 parts by weight. The value within the range, the amount of the photopolymerization initiator as the component (E) is within the range of 8 to 40 parts by weight, and the amount of the light diffusion powder as the component (F) is 30 to 150 parts by weight. The light guide plate is characterized by having a value within the range of 2 and a moisture content of 2% by weight or less.

1. Basic Configuration In the configuration of the light guide plate in the present invention, a light diffusion pattern (light diffusion layer) is formed by printing on the back surface of a methacrylic resin substrate, and a reflection sheet (reflection plate) is laminated. Further, a light diffusion sheet and a prism sheet are provided on the surface of the methacrylic resin substrate, and a straight tubular light source is disposed on the side end face of the light guide plate.
More specifically, as shown in FIG. 6B, as shown in FIG. 6B, a light diffusion pattern 6 made of a methacrylic resin substrate 1b and a predetermined ultraviolet curable ink for a light guide plate provided on the back surface thereof. And the light guide plate 1 is comprised.
A light source 2 such as an LED is provided at the side end 1a of the light guide plate 1, and a reflection sheet 3 that reflects light in a predetermined direction is provided below the light guide plate 1. A diffusion sheet 4 for diffusing light in a predetermined direction is provided above the light guide plate 1, and a surface light source device (backlight unit) 10 is configured as a whole.

2. Methacrylic resin base material Further, as the type of base material used in the present invention, it is excellent in economy and has excellent transparency, weather resistance, abrasion resistance and the like. The main component is preferred.
Further, the thickness of the methacrylic resin base material can be determined in consideration of the use and configuration of the surface light source device, but is preferably set to a value within the range of 1 mm to 30 mm, preferably 2 mm to 10 mm. It is more preferable to set the value within the range.

3. Light Diffusion Pattern Further, the diffusion pattern layer is a cured coating film made of the ultraviolet light curable ink for the light guide plate described in the first embodiment, and exhibits a predetermined light diffusion function by having a predetermined pattern. It is a resin layer.
The mode of the light diffusion pattern can be appropriately changed. For example, the planar shape is changed to a circle, an ellipse, a quadrangle, an irregular shape, and the size (equivalent circle diameter) is usually 0. It is preferable to set the value within the range of 1 mm to 2.0 mm.
Also, the arrangement of the dots constituting the light diffusion pattern is not particularly limited. For example, the uniform arrangement pattern in which dots having the same size or the same planar shape are uniformly provided, or in a direction away from the light source. For example, a gradation pattern in which the dot area is sequentially increased, or a gradation pattern in which the dot pitch is decreased as the distance from the light source is increased.

And it is preferable to make 60 degree glossiness of this light-diffusion pattern into the value of 30% or less.
This is because the light diffusivity may be excessively lowered when the 60 ° glossiness of the light diffusion pattern becomes a value of 30% or more.
Therefore, the function of the reflective sheet disposed under the light guide plate cannot be sufficiently generated, or the difference between the luminance of the diffusion pattern layer closest to the light source and the luminance of the diffusion pattern layer farthest from the light source becomes large. Even if the emission angle from the optical plate is changed, high luminance may not be obtained.
However, if the 60 ° glossiness of the light diffusion pattern becomes excessively small, the light is scattered and the refractive index difference when the traveling direction is changed becomes excessively large, and a predetermined light luminance may not be obtained.
Accordingly, the 60 ° glossiness of the light diffusion pattern is more preferably set to a value within the range of 3 to 25%, and further preferably set to a value within the range of 5 to 20%.
A method for measuring the 60 ° glossiness of the light diffusion pattern will be described in detail in Example 1 described later.

4). Manufacturing method Moreover, the light-diffusion pattern of a light-guide plate can be manufactured by the printing method on the back surface of a methacrylic resin base material using the ultraviolet curable ink for light-guide plates.
Examples of suitable printing methods include screen printing, pad printing, offset printing, flexographic printing, and the like.
However, screen printing is a particularly preferable printing method because a sufficient printing film thickness can be secured for the dots for diffusing light and the dots can be printed at accurate positions.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, it is not limited to these Examples for no particular reason.

[Example 1]
1. Preparation of UV curable ink for light guide plate In the container, add the following ingredients so that the following blending ratio (weight part standard) is obtained, and mix until uniform using a stirrer. A curable ink was prepared.
(A1) Polyester acrylate oligomer: 100 parts by weight (B1) Acrylic resin: 36 parts by weight (C1) Dimethylacrylamide: 40 parts by weight (D1) 1,6 hexanediol diacrylate: 148 parts by weight (E1) Photopolymerization initiator: 16 parts by weight (F1) Light diffusing powder (silica powder): 86 parts by weight (G1) Silicone-based additive: 4 parts by weight (G2) Dispersant (carboxylic acid-based dispersant): 10 parts by weight

More specifically, as the (A1) polyester acrylate oligomer, a commercially available polyester acrylate oligomer having a weight average molecular weight of 5,000 was used.
Further, as the (B1) acrylic resin, a commercially available powdered acrylic resin resin (weight average molecular weight 85,000) was used.
Further, (E1) a commercially available IRGACURE 184 (chemical name: 1-hydroxycyclohexyl phenyl ketone / α-hydroxy ketone compound, manufactured by CIBA Corporation) was used as a photopolymerization initiator.
Further, as the (F1) light diffusing powder, a commercially available silica powder (average particle size: 6 μm) was used.
Further, as the (G1) silicone-based additive, a commercially available modified silicone antifoaming agent was used.
Furthermore, a leveling agent made of a commercially available dicarboxylic acid ester compound was used as the dispersant (G2).

2. Evaluation of UV curable ink composition for light guide plate The obtained UV curable ink for light guide plate was measured for water content and evaluated for UV curable property and the like. The obtained results are shown in Table 1.

(1) Moisture content The moisture content (% by weight) in the UV curable ink for the light guide plate was measured three times with a Karl Fischer device KF-100 (manufactured by Mitsubishi Chemical Corporation), and the average value was adopted. As a result, it was confirmed that the water content was 0.6% by weight.

(2) Ultraviolet curing property An ultraviolet curable ink for a light guide plate was printed on a transparent methacryl plate having a thickness of 8 mm (manufactured by Mitsubishi Rayon, LX-N865) under the following printing conditions.
Subsequently, using a UV irradiation machine CS-60 (manufactured by GS Yuasa Lighting Co., Ltd.), ultraviolet irradiation was performed under the following curing conditions to form a cured coating film.
Next, the obtained cured coating film was measured for pencil hardness three times in accordance with JIS K-5600 5.4 to calculate an average value, and UV curing of the UV curable ink for the light guide plate from the following criteria. Sex was evaluated. The obtained results are shown in Table 1.

(Printing conditions)
Printing plate: Polyester screen 300 mesh Emulsion film thickness: 8 μm
Average cured film: about 14 μm

(Curing conditions)
Metal halide lamp: 120W / cm (one lamp type)
Lamp height: 100mm
Conveyor speed: 5m / min
Integrated lamp light quantity: 600 mJ / cm ²

(Evaluation criteria)
A: Pencil hardness is 3H or more.
○: Pencil hardness is 2H.
Δ: The pencil hardness is H.
X: Pencil hardness is less than H.

(3) Adhesion The cured coating film obtained under the same conditions as the UV curable evaluation was subjected to a cross-cut peel test according to JIS K-5600 5.6, and the UV curable ink for the light guide plate to the methacrylic resin substrate. Adhesion was evaluated.
That is, on the formed cured coating film, after creating a 100th grid using a cutter guide with a gap interval of 1 mm, the tape method is used to measure the adhesion three times, and the average value is calculated. Evaluation was performed according to the criteria. In addition, the evaluation result showed the number of grids which were not peeled off expressed in%. The obtained results are shown in Table 1.
(Evaluation criteria)
A: The number of grids not peeled off is 99% or more.
○: The number of grids not peeled off is less than 95 to 99%.
Δ: The number of grids not peeled off is less than 75 to 95%.
X: The number of grids not peeled off is less than 75%.

(4) Water resistance The cured coating film obtained under the same conditions as in the UV curability evaluation was immersed in warm water at 40 ° C. for 1 week. Next, the measurement was performed three times, the average value was calculated, and the water resistance of the UV curable ink for the light guide plate was evaluated from the appearance change (white phenomenon or peeling phenomenon) in light of the following evaluation criteria. The obtained results are shown in Table 1.
(Evaluation criteria)
A: No change in appearance is observed.
○: Almost no change in appearance is observed.
Δ: A slight change in appearance is observed.
X: A remarkable change in appearance is observed.

(5) 60 ° Glossiness About a cured coating film obtained under the same conditions as the UV curable evaluation, 60 ° glossiness is converted to UGV-5D (manufactured by Suga Test Instruments Co., Ltd.), a digital variable angle glossiness meter. And measured three times, and the average value was calculated. As a result, it was confirmed that the 60 ° glossiness was 10% and 30% or less.

(6) Luminance A transparent methacrylic plate (LX-N865, manufactured by Mitsubishi Rayon Co., Ltd.) having a length of 270 mm, a width of 160 mm, and a thickness of 8 mm is prepared, and an ultraviolet curable ink for a light guide plate is prepared using a screen printing device. Screen printed.
Next, ultraviolet light was irradiated under the same conditions as in the ultraviolet curable evaluation, a light diffusion pattern having a predetermined pattern was formed, and a light guide plate was obtained.
In addition, the light diffusion pattern is composed of dots with a circular planar shape, the dot long diameter on the light source side is 0.6 mm, the dot long diameter at the center of the light guide plate is 0.8 mm, and the width direction and the length direction Each pitch is a gradation pattern of 1.25 mm.

Next, using a luminance meter EyeScale2W (manufactured by Eye System Co., Ltd.), the central luminance (cd / m ² ) in the light diffusion pattern is measured three times, an average value is calculated, and in light of the following criteria, The brightness was evaluated. The obtained results are shown in Table 1.
(Evaluation criteria)
A: The central luminance is a value of 4200 cd / m ² or more.
A: The central luminance is a value less than 3800-4200 cd / m ² .
(Triangle | delta): A center brightness | luminance is a value below 3400-3800cd / m < ² >.
X: The center luminance is a value less than 3400 cd / m ² .

(7) Luminance unevenness For the luminance of the light guide plate having the light diffusion pattern obtained under the same conditions as the luminance measurement evaluation, the absolute value of the luminance unevenness based on the difference from the central luminance is measured three times, and the average value is calculated. In view of the following criteria, luminance unevenness was evaluated. The obtained results are shown in Table 1.
(Evaluation criteria)
A: Absolute value of luminance unevenness is less than 25%.
○: Absolute value of luminance unevenness is a value of 25% or more and less than 35%.
Δ: The absolute value of luminance unevenness is a value of 35% or more and less than 45%.
X: The absolute value of luminance unevenness is 45% or more.

[Examples 2 to 4]
In Examples 2-4, the influence of the moisture content in the ultraviolet curable ink for light-guide plates was examined.
That is, for the light guide plate having water content of 1.0%, 1.5%, and 1.8% by forcibly adding water to the UV curable ink for the light guide plate of Example 1. An ultraviolet curable ink was prepared and evaluated in the same manner as in Example 1. The obtained results are shown in Table 1.

[Comparative Example 1]
In Comparative Example 1, water was forcibly added to the ultraviolet curable ink for light guide plate of Example 1 to produce an ultraviolet curable ink for light guide plate having a water content of 4%. Evaluation was performed in the same manner as in 1. The obtained results are shown in Table 1.

[Examples 5 to 8]
In Examples 5 to 8, the types of (B) acrylic resin, (C) type of acrylamide monomer, (D) type of acrylate monomer, and (E) type of photopolymerization initiator in the UV curable ink for light guide plate. The effect of moisture content was examined with each change.
That is, in Examples 5 to 8, the following commercially available polyester acrylate oligomer and acrylic resin were used as (A) polyester acrylate oligomer and (B) acrylic resin.
(A2) Polyester acrylate oligomer (weight average molecular weight 10,000)
(A3) Polyester acrylate oligomer (weight average molecular weight 3,000)
(B2) Powdery thermoplastic acrylic resin (weight average molecular weight 65,000)
(B3) Powdery thermoplastic acrylic resin (weight average molecular weight 120,000)
In Examples 5 to 8, the following compounds were used as (C) acrylamide monomers.
(C2) Acrylamide monomer (N-methoxymethylacrylamide)
(C3) Acrylamide monomer (N-hydroxymethylacrylamide)
Moreover, in Examples 5-8, the combination of the following compounds was used as (D) acrylate monomer.
(D2) Acrylate monomer (tripropylene glycol diacrylate)
(D3) Acrylate monomer (phenoxyethyl acrylate)
Furthermore, in Examples 5 to 8, (E) A combination of the following compounds was used as a photopolymerization initiator.
(E2) Photopolymerization initiator (manufactured by CIBA, DAROCUR1173)
(E3) Photopolymerization initiator (CIGACURE907, IRGACURE907)

[Examples 9 to 12]
In Examples 9 to 12, (B) type of acrylic resin, (C) type of acrylamide monomer, (D) type of acrylate monomer, (E) photopolymerization initiator, (F) ) The effect of the type and blending ratio of the light diffusion powder was examined.
That is, the following compounds were used as (F) light diffusion powder.
(F2) Titanium oxide (average particle size 0.15 μm)
(F3) Acrylic resin powder (average particle size 6 μm)
(F4) Urethane resin powder (average particle size 8 μm)

Moreover, as shown in Table 3, the ultraviolet curable ink for light-guide plates was produced by changing the kind and mixture ratio of a composition, and it evaluated similarly to Example 1. FIG.
The obtained results are shown in Table 3.

  In addition, compared with Example 1, Example 9 is ((B1) acrylic resin 30 weight part, (D1) acrylate monomer 100 weight part, (E1) 10 weight part of photoinitiators, and (F1) light. This is an example of the same blending ratio as in Example 1 except that it is changed to 50 parts by weight of the diffusion powder.

  In addition, Example 10 was compared with Example 1 ((B2) acrylic resin 40 parts by weight, (C1) acrylamide monomer 20 parts by weight, (D1) acrylate monomer 160 parts by weight, and (E1) photopolymerization initiation. 20 parts by weight of the agent, (F1) 60 parts by weight of the light diffusing powder, and (F2) the same blending ratio as in Example 1 except for changing to 2 parts by weight of the light diffusing powder).

  Moreover, Example 11 is different from Example 1 in that (polyester acrylate oligomer is changed to (A2), (B3) acrylic resin 50 parts by weight, (C2) acrylamide monomer 50 parts by weight, and (D2) acrylate. This is an example of 250 parts by weight of the monomer, (E2) 30 parts by weight of the photopolymerization initiator, and (F3) the same blending ratio as in Example 1 except that the light diffusion powder is changed to 100 parts by weight).

  Further, in Example 12, compared with Example 1, (polyester acrylate oligomer is changed to (A3), (B3) acrylic resin 36 parts by weight, (C2) acrylamide monomer 44 parts by weight, (D2) acrylate) This is an example of 300 parts by weight of the monomer, (E3) 35 parts by weight of the photopolymerization initiator, and (F4) the same mixing ratio as in Example 1 except that the light diffusion powder is changed to 130 parts by weight).

[Comparative Example 2]
In Comparative Example 2, although the water content is 2% by weight or less, the blending ratio of the ultraviolet curable ink for the light guide plate is considerably small in the blending ratio of (B) acrylic resin and (C) acrylamide monomer, (F) In this example, light diffusing powder was not blended, and an ultraviolet curable ink for a light guide plate was prepared and evaluated in the same manner as in Example 1. Table 4 shows the obtained results.

[Comparative Example 3]
Although the comparative example 3 has a water content of 2% by weight or less, in the blending composition of the UV curable ink for the light guide plate, the blending ratio of (B) acrylic resin, (C) acrylamide monomer and (F) light diffusion powder Although there are few examples, the ultraviolet curable ink for light-guide plates was created and evaluated similarly to Example 1. FIG. Table 4 shows the obtained results.

[Comparative Example 4]
Comparative Example 4 is an example in which the blending composition of the UV curable ink for the light guide plate has a high blending ratio of (C) acrylamide monomer and a high water content, but as in Example 1, the UV curable type for the light guide plate. Inks were made and evaluated. Table 4 shows the obtained results.

[Comparative Example 5]
In Comparative Example 5, the composition of the ultraviolet curable ink for the light guide plate is such that (A) the polyurethane acrylate oligomer is used as the (A) acrylate oligomer, and (C) the proportion of the acrylamide monomer is higher, and the moisture content In this example, an ultraviolet curable ink for a light guide plate was prepared and evaluated in the same manner as in Example 1. Table 4 shows the obtained results.

[Comparative Example 6]
In Comparative Example 6, in the blending composition of the UV curable ink for the light guide plate, (A) the acrylate oligomer is used as the (A) acrylate oligomer, and (C) the blending ratio of the acrylamide monomer is further increased, and the moisture content In this example, an ultraviolet curable ink for a light guide plate was prepared and evaluated in the same manner as in Example 1. Table 4 shows the obtained results.

According to the present invention, in a light guide plate provided with a light diffusion pattern on at least the back surface of the methacrylic resin substrate, a predetermined blending amount of (A) polyester acrylate oligomer is used as the ultraviolet curable ink for the light guide plate constituting the light diffusion pattern. And (B) an acrylic resin, (C) an acrylamide monomer, (D) a (meth) acrylate monomer, (E) a photopolymerization initiator, and (F) a light diffusing powder. By limiting the moisture content to a predetermined range, it has become possible to satisfy the conflicting characteristics of high luminance and adjustment of luminance unevenness.
Therefore, if it is a light guide plate provided with such a light diffusion pattern made of UV curable ink for light guide plates, it can be used as a light guide plate for a surface light source device (backlight unit) used in portable notebook computers, large liquid crystal televisions and the like. Therefore, it can be expected to be applied suitably.

1: Light guide plate 1a: Side end 1b: Base material (methacrylic resin base material)
2: Light source 3: Reflection sheet 4: Diffusion sheet 6: Light diffusion pattern 10: Surface light source device (backlight unit)

Claims (8)

An ultraviolet curable ink for a light guide plate constituting a light diffusion pattern in a light guide plate containing a methacrylic resin base material,
(A) polyester acrylate oligomer, (B) acrylic resin, (C) acrylamide monomer, (D) (meth) acrylate monomer, (E) photopolymerization initiator, (F) light diffusion powder, And containing
With respect to 100 parts by weight of the (A) polyester acrylate oligomer,
The blending amount of the (B) acrylic resin is a value within the range of 20 to 80 parts by weight,
The blending amount of the (C) acrylamide monomer is set to a value within the range of 20 to 60 parts by weight,
The blending amount of the (D) (meth) acrylate monomer is a value within the range of 80 to 340 parts by weight,
The blending amount of the (E) photopolymerization initiator is set to a value within the range of 8 to 40 parts by weight,
(F) The amount of the light diffusing powder is a value within the range of 30 to 150 parts by weight,
An ultraviolet curable ink for a light guide plate, characterized in that the moisture content is 2% by weight or less.   The ultraviolet curable ink for a light guide plate according to claim 1, wherein the (C) acrylamide monomer contains dimethylacrylamide.   The ultraviolet curable ink for a light guide plate according to claim 1, wherein the (D) (meth) acrylate monomer contains 1,6 hexanediol di (meth) acrylate.   The (B) acrylic resin is an acrylic polymer derived from a monomer component containing 50% by weight or more of a (meth) acrylate monomer with respect to the total amount of the monomer component, and can be used as the (meth) acrylate monomer. The ultraviolet curable ink for a light guide plate according to any one of claims 1 to 3, wherein the ink is a melt.   The weight average molecular weight of said (B) acrylic resin shall be the value within the range of 50,000-150,000, The ultraviolet curable ink for light-guide plates as described in any one of Claims 1-4 characterized by the above-mentioned. .   6. The ultraviolet curable type for a light guide plate according to claim 1, wherein the light diffusion powder is at least one of silica powder, titanium oxide powder, acrylic resin powder, and urethane resin powder. ink. A light guide plate comprising a methacrylic resin base material and a light diffusion pattern made of an ultraviolet cured product of an ultraviolet curable ink for the light guide plate,
The ultraviolet curable ink for a light guide plate comprises (A) a polyester acrylate oligomer, (B) an acrylic resin, (C) an acrylamide monomer, (D) a (meth) acrylate monomer, and (E) a photopolymerization initiator. And (F) a light diffusing powder,
(A) For 100 parts by weight of the polyester acrylate oligomer as a component,
The blending amount of the acrylic resin as the component (B) is a value within the range of 20 to 80 parts by weight,
(C) The amount of the acrylamide monomer as a component is a value within the range of 20 to 60 parts by weight,
The blending amount of the (meth) acrylate monomer as the component (D) is set to a value within the range of 80 to 340 parts by weight,
(E) The amount of the photopolymerization initiator as a component is set to a value within the range of 8 to 40 parts by weight,
(F) The amount of the light diffusing powder as a component is a value within the range of 30 to 150 parts by weight,
A light guide plate characterized by having a moisture content of 2% by weight or less.   The light guide plate according to claim 7, wherein the 60 ° glossiness in the light diffusion pattern is set to a value of 30% or less.

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