JPH08190149A - Projection screen - Google Patents

Abstract

PURPOSE: To prevent a white belt and a double image caused by stray light from being formed without damaging effective light and to improve contrast by forming a light absorbing layer at the non-light emitting part of a light emitting surface side. CONSTITUTION: A microlenticular lens 28 is formed in parallel to a ridge line on the side of the light entering surface of a linear Fresnel lens sheet provided with the ridge line in a direction orthogonal to the direction of the ridge line of the lenticular lens sheet 26 out of the horizontal refractive linear Fresnel lens sheet 22 and a perpendicular refractive linear Fresnel lens sheet 24. By the operation of the microlenticular lens 28, the light-emitting part emitting light and the non-light emitting part not emitting the light are formed on the side of the light emitting surface of the linear Fresnel lens sheet, and the light absorbing layer 30 is formed at the non-light emitting part. Only the stray light in the linear Fresnel lens sheet is absorbed by the light absorbing layer 30 at the inside of the linear Fresnel lens sheet, so that the white belt and the double image are prevented from being formed and also a whole image screen is prevented from being whiten and the deterioration of the contrast is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection screen for a rear projection type television, and more particularly to a projection screen having a screen sheet including a horizontal refraction linear Fresnel lens sheet and a vertical refraction linear Fresnel lens sheet.

[0002]

2. Description of the Related Art A projection screen for a rear projection type television is composed of a Fresnel lens part for converging the projection light from a projector (light source) to an observation side and a lenticular lens part for scattering the projection light to form an image. There is a single screen type in which the main part is configured and these are formed on one sheet, but in the case of a consumer projection TV, a double screen type in which these are formed on separate sheets is often used. .

Conventionally, the Fresnel lens sheet on which the Fresnel lens is formed is a "pressing method" in which a transparent resin flat plate is pressed against a heated mold, a "casting method" in which heat polymerization is carried out in a mold cell, and an ultraviolet (UV) curing. It has been manufactured by a method such as "UV method" in which a resin is applied from the top of a mold, a transparent resin flat plate is covered thereover, and ultraviolet rays are irradiated.

However, no matter which manufacturing method is adopted, since the Fresnel lens is a circular Fresnel lens sheet in which the Fresnel lenses are concentrically formed, each sheet has to be produced individually and continuously by the extrusion method. Productivity is worse than the lenticular land sheet that can be produced,
Therefore, it was difficult to reduce the production cost.

Therefore, as disclosed in Japanese Utility Model Publication No. 56-74429, Japanese Utility Model Publication No. 56-74430, etc., instead of the circular Fresnel lens, the ridge lines of a large number of lens portions (prism groups) are formed. It has been proposed to prepare two sheets each having a linear Fresnel lens formed in a shape parallel to each other in one direction, and use the linear Fresnel lenses orthogonally. This linear Fresnel lens sheet can be manufactured by the "extrusion method" or the method of applying UV resin on a rotating roll die, transferring it to a resin film, and curing it, so continuous production is possible, and the manufacturing cost Can be reduced.

In a Fresnel lens sheet such as the above-mentioned circular Fresnel lens sheet or linear Fresnel lens sheet, the light projected from the projector is incident from a smooth surface which is a light incident surface and refracted to form a Fresnel lens. Although it is emitted as image light from the observation side, a part of the light is reflected at the interface between the Fresnel lens and the air, and returns to the lens sheet to become stray light. The stray light is repeatedly reflected within the lens sheet once to several times, and then most of the stray light is emitted to the observation side as unnecessary light. This unnecessary light forms a double image or, in the case of a circular Fresnel lens sheet, is generally observed as a rainbow and causes image interference.

[0007]

However, in the case of an optical system in which two sheets are stacked so that the linear Fresnel lens is orthogonal to the horizontal direction and the vertical direction, the unnecessary light is observed as a white band. That is, since the light diffusion characteristic of the projection screen is usually set to be narrow in the vertical direction and wide in the horizontal direction, the white band extending in the vertical direction due to the linear Fresnel lens refracting in the horizontal direction is not observed. However, since the projection tubes in the projector are arranged in the same direction as the direction in which the linear Fresnel lens for refracting in the vertical direction extends, stray light in the same direction may not be separated, so stray light of three colors is combined, Only the white band extending in the horizontal direction due to the vertically refraction linear Fresnel lens is strongly observed. This white band extending in the horizontal direction has a problem in that it is not preferable for observing an image as compared with the rainbow of the circular Fresnel lens sheet.

Several proposals have been made in order to prevent or reduce the above-mentioned white band caused by stray light. However, all of these proposals diffuse stray light to prevent image formation. It does not fundamentally solve the problem, and there is a new problem that the entire screen of the screen becomes whitish due to the scattering of stray light and the contrast is lowered.

In order to prevent such a decrease in contrast, a method of coloring a Fresnel lens sheet or a lenticular lens sheet has been proposed, but this coloring method also absorbs effective light. The problem arises that the output of the projection tube must be increased.

The present invention has been made to solve the above conventional problems, and provides a projection screen including a screen sheet including a horizontal refraction linear Fresnel lens sheet and a vertical refraction linear Fresnel lens sheet.
An object of the present invention is to provide a projection screen that does not impair the effective light, can prevent the occurrence of white bands and double images due to stray light, and has improved contrast.

[0011]

According to the present invention, there is provided a projection screen for a rear projection type television, comprising a screen sheet composed of a plurality of lens sheets, which is used for a rear projection type television.
A horizontal refraction linear Fresnel lens sheet in which a linear Fresnel lens having a ridge line extending vertically is formed to refract projection light mainly in the horizontal direction, and a linear Fresnel lens having a ridge line extending horizontally to refract the projection light mainly in the vertical direction A vertical refraction linear Fresnel lens sheet in which at least three are formed, and a lenticular lens sheet for light diffusion is included. Among the horizontal refraction linear Fresnel lens sheet and the vertical refraction linear funnel lens sheet, the lenticular lens A micro lenticular lens is formed on the light incident surface side of the linear Fresnel lens sheet having a ridge line in a direction orthogonal to the ridge line direction of the sheet, in parallel with the ridge line, and is condensed by the micro lenticular lens on the other light exit face side. Linear Fresnel in the light output part Lens is formed by the light absorbing layer is formed on the non-light exit portion is obtained by achieving the above object.

According to a second aspect of the present invention, in the projection screen, the horizontal refraction linear Fresnel lens sheet, the vertical refraction linear Fresnel lens sheet, and the lenticular lens sheet are arranged in this order from the light source side, and the vertical refraction linear Fresnel lens sheet is arranged. The light absorbing layer may be formed on the light emitting surface side of the Fresnel lens sheet.

Further, according to a third aspect of the present invention, in the projection screen, a flat portion is formed at a peak non-light emitting portion of the linear Fresnel lens in the linear Fresnel lens sheet having the light absorbing layer, The light absorbing layer may be formed on the flat portion, and the non-light emitting flat portion may be formed at an equal distance from the top of the microlenticular lens.

In the projection screen, the distance between the linear Fresnel lens valley portion and the non-light emitting flat portion in the linear Fresnel lens sheet having the light absorption layer may be 50 μm or more.

According to a fifth aspect of the present invention, in the projection screen, the linear Fresnel lens sheet having at least the light absorbing layer among the linear Fresnel lens sheets has a linear Fresnel lens on one surface of a base film. The micro lenticular lenses may be formed on the other surface of either one of the ultraviolet curable resin or the electron beam curable resin.

[0016]

According to the invention of claim 1, by the action of the microlenticular lens, a light emitting portion for emitting light and a non-light emitting portion for not emitting light are formed on the light emitting surface side of the linear Fresnel lens sheet, Since the light absorption layer is formed in this non-light emitting part, only the stray light in the linear Fresnel lens sheet is absorbed by the light absorption layer, and it is possible to prevent the occurrence of white bands and double images, and the entire screen becomes whitish and the contrast is reduced. It can be prevented from lowering.

Further, since the light absorption layer can also absorb the external light incident through the lenticular lens sheet on the observation side, the contrast of the screen can be further improved.

According to the invention of claim 2, the horizontal refraction linear Fresnel lens sheet, the vertical refraction linear Fresnel lens sheet and the lenticular lens sheet are arranged in this order from the light source side, and the light emission surface side of the vertical refraction linear Fresnel lens sheet. Since the light absorption layer was formed on the lenticular lens, since the light diffusion angle of the lenticular lens is narrow in the vertical direction, the white band caused by the vertical refraction linear Fresnel lens sheet, which extends horizontally and is strongly observed, is generated. It is possible to prevent stray light from being absorbed and removed by the light absorption layer formed in the above step, and to prevent deterioration of contrast.

Further, the light emitted from the linear Fresnel lens sheet is directed inward toward the outer peripheral portion, and when the vertical refraction linear Fresnel lens sheet is arranged on the projection side, the degree of inward is strong in the vertical direction, and the horizontal refraction linear Fresnel lens sheet. When the is placed on the projection side, the degree becomes stronger in the horizontal direction.However, since the lenticular lens sheet is usually arranged so as to have an overwhelmingly large diffusion angle in the horizontal direction as compared with the vertical direction, the Since there is a larger tolerance in the horizontal direction to the variation of the emission angle of the light in, the lens sheets are arranged in the above order, and the horizontal refraction linear Fresnel lens sheet is arranged on the light projection side. The lenticular lens sheet can alleviate the variation of the outgoing angle in the direction, and the image quality can be improved.

According to the invention of claim 3, the light absorbing layer can be easily formed by a known method such as printing, transferring or painting, and since the thickness of the sheet is constant, the microlenticular lens is formed. When winding the linear Fresnel lens sheet on which the is formed, after winding, it is possible to prevent uneven winding.

According to the fourth aspect of the present invention, since the distance between the linear Fresnel lens valley and the non-light emitting flat portion in the linear Fresnel lens sheet provided with the light absorption layer is set to a certain distance or more, roll coating, gravure printing, offset printing are performed. The light absorbing layer can be formed only on the non-light emitting flat portion by using a known method such as transfer printing, and the light absorbing layer is not printed on the linear Fresnel lens portion.

According to the fifth aspect of the present invention, the linear Fresnel lens sheet having the microlenticular lens formed thereon has the linear Fresnel lens on one surface of the base film and the microlenticular lens sheet on the other surface thereof. When the resin is prepared by curing an electron beam curable resin, it is possible to easily and surely manufacture a linear Fresnel lens sheet having a microlenticular lens attached thereto, and a mold corresponding to each lens portion is formed. When it is formed on the base film by using a die roll, continuous production can be performed.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a perspective view showing a main part of a projection screen according to an embodiment of the present invention with a part thereof cut away.

Projection screen 2 of this embodiment
Reference numeral 0 denotes a horizontal refraction linear Fresnel lens sheet 22 arranged on the projection side facing a projector (not shown) and a vertical refraction linear Fresnel lens 24 on the outer side (observer side).
And a screen sheet including the lenticular lens sheet 26 located on the outer side (observer side).

The horizontal refraction linear Fresnel lens sheet 22 has a function of refracting light projected from the projector in the horizontal direction, and a linear Fresnel lens (lens portion) composed of a large number of continuous prisms on the base film 22A. ) 22B has a structure formed with its ridges parallel to the vertical direction.

The vertical refraction linear Fresnel lens sheet 24 has a function of refracting the projection light in the vertical direction, and a linear Fresnel lens (lens portion) 24B is formed on the base film 24A so that the ridge lines extend in parallel to the horizontal direction. The horizontal refraction linear Fresnel lens sheet 22 and the vertical refraction linear Fresnel lens sheet linear fresnel lenses (lens portions) 22B and 24B are arranged so as to be orthogonal to each other.

The lenticular lens 26 is horizontally aligned with the horizontal refraction linear Fresnel lens sheet 22.
The vertical refraction linear Fresnel lens sheet 24 has a function of diffusing the projection light respectively refracted in the vertical direction as image light, and a light entrance lenticular lens 26A extending in the vertical direction is formed on the light entrance surface side, and on the light exit surface side. Light emitting lenticular lenses 26B extending in the vertical direction and convex light-shielding portions 26C coated with black ink on the surface are alternately formed.

Further, the projection screen 20 mentioned above.
Then, a micro lenticular lens 28 parallel to the linear Fresnel lens 24B formed on the linear Fresnel lens sheet 24 is formed on the light incident surface side of the vertical refraction lenticular lens sheet 24.

The micro lenticular lens 28 has a linear Fresnel lens 2 whose pitch is formed on the light emitting side.
4B is formed so as to be optically synchronized with 4B. That is, a lens group composed of a single microlenticular lens or a plurality of pitch microlenticular lenses and a linear Fresnel lens are formed in a 1: 1 relationship so that light incident on the former passes through the latter and exits. There is a need. Further, the cross-sectional shape of the microlenticular lens 28 can be formed as a convex lens which is a part of a circle or an ellipse. As for the diffusion angle of the micro lenticular lens 28, the diffusion half-value angle in the vertical direction of the screen used for a rear projection television for consumer use is usually 5 to 10 °.
Therefore, it is within this range.

Due to the action of the microlenticular lens 28, a light emitting portion 28A and a non-light emitting portion 28B are formed on the light emitting surface side thereof as shown in FIG.

In this embodiment, the lens valley portion 24C
Linear fresnel lens 24B of the vertical refraction linear fresnel lens sheet 24 formed to have a constant depth
A flat portion is formed (the distance between the lens valley portion 24C and the flat portion is 85 μm) in the portion which becomes the non-light emitting portion 28B in the peak portion of the light absorption layer 30 is formed by applying black ink or the like on the flat portion. The linear Fresnel lenses 24B and the light absorption layers 30 are alternately formed at a pitch of 0.112 mm. The shape of the flat part is such that the flat part of the lens part is projected at the center of the seat, and the both ends of the seat have a trapezoidal cross section with the tip of the lens part cut off. It is formed so as to be constant in any part of the. The shape of the flat portion is not limited to the present embodiment, and the flat portions may be formed at both end portions of the sheet similarly to the central portion of the sheet.

In the linear Fresnel lens, the lens angle is small at the center of the sheet, and the lens surface is formed substantially horizontal to the flat surface of the sheet. Therefore, when the printing roll 52, which will be described later, prints the light absorbing layer on the non-light emitting flat portion, the light absorbing layer may be printed on the linear Fresnel lens surface. In order to prevent this, it is preferable to provide a distance between the valley portion 24C of the linear Fresnel lens and the non-light emitting flat portion by 50 μm or more, and to provide a difference in height between the lens portion and the non-light emitting flat portion.

The width of the flat portion (light absorbing layer) is determined by the diffusion angle of the microlenticular lens formed on the light entrance surface side and the thickness of the sheet, and this width is the same as that of the microlenticular lens. It changes slightly at both ends of the sheet due to the difference in the incident angle of the projected light.

Horizontal refraction linear Fresnel lens sheet 2
2. In the case where the vertical refraction linear Fresnel lens sheet 24 is a flexible film lens sheet, since it does not have a self-supporting mechanical strength, a combination with a relatively rigid lenticular lens sheet 26, Alternatively, a transparent resin plate is added to the observer side of the lenticular lens 26, and these are fixed together in a frame (both not shown) to reinforce the lens sheet, thereby improving the structural strength such as self-supporting property and surface. It is possible to impart strength to friction and the like.

In this embodiment, the linear Fresnel lens 2 is formed by the light absorption layer 30 formed on the non-light emitting portion 28B of the linear Fresnel lens sheet 24, as shown in FIG.
The stray light S that is reflected by the interface between 4B and the air and returns to the inside of the linear Fresnel lens sheet 24 to cause white bands, rainbow, and the like can be absorbed. Particularly in this embodiment, since the non-light emitting portion 28B is provided on the light emitting surface side of the linear Fresnel lens sheet 24 other than the portion where the incident light is emitted by the microlenticular lens 28, and the light absorbing layer 30 is formed on the top thereof. Since only the stray light S is absorbed by the light absorption layer 30 and the projection light L is emitted, the screen does not become dark.

Further, as described above, in the projection screen 20 of this embodiment, the light is diffused in the vertical (V) direction to the incident surface side of the second vertical refraction linear Fresnel lens sheet 24 counted from the light projection side. Since the micro lenticular lens 28 is provided, it is possible to effectively diffuse the internal stray light. Therefore, in the projection screen 20 using the linear Fresnel lens sheet as shown in FIG. Can be removed.

Of course, since the light absorbing layer 30 in this embodiment also absorbs the diffused internal stray light, it is possible to prevent the entire screen from becoming whitish and reducing the contrast.

Further, in this embodiment, as shown in FIG. 4, external light incident through the lenticular lens sheet 26 on the viewing side can be absorbed, so that the contrast of the screen can be further improved. Figure 4
In FIG. 1, in the lower half thereof, a vertically refraction linear Fresnel lens sheet in which a light absorption layer is not formed is shown for comparison.

Further, in FIG. 4, for the sake of explanation, a linear Fresnel lens 24B is provided for the lenticular lens.
Are displayed so that their ridge lines are parallel to each other, but in reality, they are arranged orthogonally as shown in FIG. Therefore, refraction by the lenticular lens is not taken into consideration in FIG.

The light absorbing layer as described above can be formed on a conventional circular Fresnel lens, but it is not preferable because strong Moire fringes are generated between the light absorbing layer and the lenticular lens. Similarly, in the case of a horizontal refraction linear Fresnel lens sheet whose ridge line direction is parallel to the lenticular lens, it is not preferable to form the light absorption layer as described above because strong Moire fringes occur, but in this embodiment, Since the light absorbing layer 30 is formed on the vertical refraction linear Fresnel lens sheet 24 whose ridge line direction is orthogonal to the lenticular lens, the strong moire fringes as described above do not occur.

The refractive index of the microlenticular lens 28 in the projection screen 20 is preferably lower than that of the base film 24A. The reason is that the lower the refractive index of the microlenticular lens 28, the higher the utilization efficiency of the projected light and the easier the stray light escapes to the projection side.

Further, there is a case where moire fringes are generated between the microlenticular lens 28 and the linear Fresnel lens 24B. In the case of a circular Fresnel lens sheet, the moire fringes can be made invisible by selecting the pitch ratio, but in principle cannot be completely removed. On the other hand, as in the present embodiment, the moire fringes generated between the linear Fresnel lens 24B for refracting in the vertical direction and the microlenticular lens 28 are due to the microlenticular lens 28 on the incident surface side and the linear Fresnel on the exit surface side. It can be prevented from occurring by perfectly synchronizing the registration of the lens 24B.

Next, an example of a method of manufacturing the linear Fresnel lens sheet applied to this embodiment will be described with reference to FIG.

The manufacturing apparatus shown in FIG. 4 is capable of continuously producing the vertical refraction linear Fresnel lens sheet 24. The linear Fresnel lens 24B and the non-light-emitting portion are formed around the mold (concavo-convex) of the opposite shape. Type 1 roll 40,
The micro lenticular lens 28 is provided with a second mold roll 42 around which a mold having an inverse shape is formed.

Here, when the base film 24A pulled out from the original roll 44 is guided between the nip roll 46 and the first die roll 40, it is between the surface of the base film 24A and the die of the first die roll. UV curable resin (UV
After the resin 47 is supplied and filled, the base film 24 in this state is irradiated with UV from below the first type roll 40 by a UV lamp 48 to cure and form the linear Fresnel lens portion.

Next, the base film 24A is sent to the second mold roll 42, and the UV resin 51 pulled up by the finisher roll 50 is supplied between the back surface of the base film 24A and the mold of the second mold roll 42. The micro lenticular lens 28 is formed by being irradiated with the UV lamp 49 from above, and the base film 24A is further sent to the light absorbing layer (BS) printing roll 52, and the linear Fresnel side of the surface thereof. The black ink is applied to the flat portion of the non-light emitting portion, and then the black ink is dried in the drying oven 54 to form the light absorbing layer 30. In this way, the lens sheet on which the lenses are formed on both the front and back sides and the light absorption layer 30 is formed is continuously manufactured and wound by the winding roll 56.

The horizontal refraction linear Fresnel lens sheet 22 for forming only the linear Fresnel lens (without forming the microlenticular lens) is formed by the second type roll, the printing process by the BS printing roll 52, and the drying oven. It can be manufactured by omitting the drying step by 54.

As described above, both the horizontal refraction linear Fresnel lens sheet 22 and the vertical refraction linear Fresnel lens sheet 24 of this embodiment can be continuously manufactured, and the cost can be reduced.

Here, as an optical system using both the horizontal refraction and vertical refraction linear Fresnel lens sheets, the refractive index of the linear Fresnel lens refracting in the vertical direction is higher than that of the linear Fresnel lens refracting in the horizontal direction. Since it is preferable to use a low refractive index, for example, a polyester such as PET (refractive index ratio of 1.6 or more) is used as the base film, and the linear Fresnel lens portion for refracting in the horizontal direction is provided with a refractive index of 1.55 to A linear Fresnel lens made of a high-refractive-index urethane acrylate UV resin of 0.57 (or higher) and refracting in the vertical direction, and a micro-lenticular lens on its incident surface are made of urethane acrylate of a normal refractive index of about 1.49. It can be formed of UV resin.

In this case, a resin having a lower refractive index may be molded on the incident surface side of the horizontal refraction linear Fresnel lens sheet 22 with a flat mold, or may be applied by coating or the like.

In the linear Fresnel lens sheet forming the microlenticular lens, for example, a light diffusing material may be mixed in the base film.

[Brief description of drawings]

FIG. 1 is a perspective view showing a partially cutaway main part of a projection screen according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state in which a light emitting portion and a non-light emitting portion are formed by the microlenticular lens of the projection screen.

FIG. 3 is a cross-sectional view showing a state in which stray light is erased in the vertical refraction linear Fresnel lens sheet of the projection screen according to the above example.

FIG. 4 is a cross-sectional view showing a state in which light incident from an observation side is erased by the vertical refraction linear Fresnel lens sheet.

FIG. 5 is a schematic side view showing a manufacturing process of the projection screen.

[Explanation of symbols]

 20 ... Projection screen 22 ... Horizontal refraction linear Fresnel lens sheet 22A, 24A ... Base film 22B, 24B ... Linear Fresnel lens 24 ... Vertical refraction linear Fresnel lens sheet 24C ... Lens trough 26 ... Lenticular lens sheet 26A ... Incident light lenticular lens 26B Light output lenticular lens 26C Light blocking portion 28 Micro lenticular lens 28A Light output portion 28B Non-light output portion 30 Light absorbing layer 47, 51 UV resin 48, 49 UV lamp

Claims (5)

[Claims] 1. A projection screen for a rear projection television, comprising a screen sheet composed of a plurality of lens sheets, wherein the screen sheet linearly bends projection light mainly in the horizontal direction and has a ridge line extending in the vertical direction. A horizontal refraction linear Fresnel lens sheet having a Fresnel lens formed thereon, a vertical refraction linear Fresnel lens sheet having a linear Fresnel lens having a ridge extending horizontally for refracting projection light mainly in the vertical direction, and a lenticular for light diffusion A linear Fresnel lens sheet including at least three lens sheets and having a ridgeline in a direction orthogonal to the ridgeline direction of the lenticular lens sheet, of the horizontal refraction linear Fresnel lens sheet and the vertical refraction linear Fresnel lens sheet. On the light entrance side of , A microlenticular lens is formed in parallel with the ridgeline,
A projection screen characterized in that a linear Fresnel lens is formed on a light emitting portion of the light condensed by the micro lenticular lens on the other light emitting surface side, and a light absorbing layer is formed on a non-light emitting portion. 2. The horizontal refraction linear Fresnel lens sheet, the vertical refraction linear Fresnel lens sheet and the lenticular lens sheet are arranged in this order from the light source side, and the light exit surface side of the vertical refraction linear Fresnel lens sheet according to claim 1. A projection screen characterized in that the light absorption layer is formed on. 3. A flat portion is formed at a peak non-light emitting portion of the linear Fresnel lens in the linear Fresnel lens sheet provided with the light absorbing layer, and the flat portion is provided with the flat portion. A projection screen, wherein a light absorption layer is formed, and the non-light emitting flat portion is formed at an equal distance from the top of the microlenticular lens. 4. The projection screen according to claim 3, wherein the distance between the linear Fresnel lens valley portion and the non-light emitting flat portion in the linear Fresnel lens sheet having the light absorbing layer is 50 μm or more. 5. The linear Fresnel lens sheet having at least the light absorbing layer among the linear Fresnel lens sheets according to claim 1, wherein the linear Fresnel lens is provided on one surface of the base film A projection screen characterized in that a micro-lenticular lens is formed on either side of one of an ultraviolet curable resin and an electron beam curable resin.