JP2015208869A - Projection black board with dark line excellent in image recognition property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection black board with a dark line excellent in image recognition property.SOLUTION: When a dark line is formed on the surface of a black board having an enamel layer, the dark line is configured such that a brightness L* displayed in an L*a*b* color system is 70 or less, a color difference ΔE*ab with a surface enamel layer is 15 or less, or further, 75° surface glossiness Gs(75°) specified according to JIS Z 8741-1997 is 1 to 35% and a difference ΔGs(75°) between 75° surface glossiness of the dark line and 75° surface glossiness of the surface enamel layer is set within ±10%. The surface enamel layer has such a hue that brightness L* displayed in the L*a*b* color system is 30 to 70, such a surface characteristic that a surface roughness Rz is 5 to 25 μm, such a reflection characteristic that a peak gain is 0.28 or more and it is preferable that a surface glossiness Gs(75°) is 1 to 30%.

Description

  The present invention relates to a blackboard projection blackboard that has a blackboard layer and has both a blackboard function and a projection function, and in particular has a dark line on the blackboard surface as a guide when writing characters, images, etc. with chalk on the blackboard. It relates to improving the video recognition (projection) of a blackboard with a dark line.

  2. Description of the Related Art Conventionally, a blackboard (also called a chalk board) has a function of drawing characters, images, and the like with a chalk on its surface so as to be erasable, and has been used as an aid for various lectures, lectures, explanations and the like. In recent years, however, it has become common to use various projectors such as slides and OHPs to project a prepared material on a screen in advance and give an explanation while pointing with a pointing stick or the like. When using various projectors to provide explanations, in addition to the projection screen, it is necessary to prepare a blackboard that can draw and erase characters with chalk for supplementary explanation.・ It took a lot of work to clean up.

  To deal with such a problem, for example, Patent Document 1 describes a projection blackboard that has both an excellent blackboard function and an excellent projection function. The projection blackboard described in Patent Document 1 is a blackboard having at least one wrinkle layer on a metal substrate. The outermost surface wrinkle layer has a color tone with a brightness V of 3.0 to 7.0, and a surface roughness Ra. Has a surface characteristic of 5 to 25 μm and a reflection characteristic of a peak gain of 0.28 or more, preferably the surface glazing layer is any one of black, gray, green, brown, and amber The projection blackboard has a 75 ° specular gloss Gs (75 °) of 1 to 30%. According to the technique described in Patent Document 1, the blackboard is excellent in chalk character recognizability and chalk character erasability and also in image recognizability.

Japanese Patent No. 4771880

  Conventionally, a thin line (solid line, broken line, etc.) may be drawn on the surface of a blackboard as a guide for drawing characters, images, etc. with chalk (white ink). This thin line is black so that it does not stand out because the blackboard is mainly adjusted to dark green, dark blue, dark brown, black, and gray so that the contrast with chalk (white ink) stands out. It is generally drawn in a system and is also called “dark line”.

  This dark line is useful when using the blackboard function for drawing and erasing characters, images, etc. with chalk (white ink), and even on modern blackboards that have both blackboard and projection functions, There is a strong demand for it.

  However, in recent projection blackboards, the color tone of the blackboard is often adjusted from a dark color to a light color (a weak dark color) in order to improve image recognition. Therefore, if black-colored dark lines are formed (arranged) on the blackboard surface, the light may be reflected at the dark line part during projection, and the dark lines may be too conspicuous, resulting in a disturbance of the image and image recognition (projection) being reduced. There was a problem.

  An object of the present invention is to solve the problems of the prior art and to provide a projection blackboard with a dark line that is excellent in video recognition (projection).

  In order to achieve the above-mentioned object, the present inventor diligently studied the influence of the color, gloss, etc. of the dark line on the image recognition property (projection property) of the projection blackboard. As a result, it was found that the color difference between the surface wrinkle layer and the dark line has a great influence on the image recognizability when the image is projected by the projector.

That is, the color tone of the surface wrinkle layer and the dark line is displayed in the L * a * b * color system, and the color difference between the surface wrinkle layer and the dark line is expressed by the following equation (1) ΔE * ab = ((ΔL *) ² + ( Δa *) ² + (Δb *) ² ) ^1/2 (1)
(Where L *: lightness displayed in the L * a * b * color system, a *, b *: chromaticity displayed in the L * a * b * color system, ΔL *: surface wrinkles and dark lines And difference in brightness, Δa *, Δb *: difference in chromaticity between the surface wrinkle layer and the dark line)
It has been found that adjusting ΔE * ab defined in the above to 15 or less is important for improving the video recognition (projection) of a blackboard with a dark line. Further, it has been found that the difference in 75 degree glossiness Gs (75 °) between the surface wrinkle layer and the dark line needs to be within ± 10% in order to further improve the image recognition property (projection property).

  The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.

(1) A blackboard having at least one soot layer on a metal substrate and having dark lines on the outermost surface soot layer of the soot layers, wherein the dark lines are represented by L * a * The lightness L * displayed in the b * color system is 70 or less, and the color difference from the surface wrinkle layer displayed in the L * a * b * color system is expressed by the following equation (1) ΔE * ab = (( ΔL *) ² + (Δa *) ² + (Δb *) ² ) ^1/2 (1)
(Here, ΔL *: difference in lightness L * displayed in the L * a * b * color system, Δa *: difference in chromaticity a * displayed in the L * a * b * color system, Δb *: Difference of chromaticity b * displayed in L * a * b * color system)
A blackboard with a dark line excellent in image recognizability, characterized in that a dark line having a color tone of ΔE * ab of 15 or less defined by ΔE * ab.

  (2) A projection blackboard with a dark line, wherein the dark line is any one of black, gray, amber, brown, and green.

  (3) In (1) or (2), the dark line is 1 to 35% in terms of 75 degree surface glossiness Gs (75 °) specified in JIS Z 8741-1997, and 75 degrees of the dark line. A projection blackboard with dark lines, wherein a difference ΔGs (75 °) between the surface glossiness and the 75 ° surface glossiness of the surface glaze layer is within ± 10%.

  (4) In any one of (1) to (3), the surface wrinkle layer has a color tone having a lightness L * of 30 to 70 displayed in the L * a * b * color system, and JIS B 0601-2001. A projection blackboard with dark lines, characterized by having a surface characteristic Rz of 5 to 25 μm and a reflection characteristic having a peak gain of 0.28 or more.

  (5) In any one of (1) to (4), the surface glaze layer is a glaze layer formed by using a glaze that contains at least titanium oxide-coated particles in a transparent mat glaze. Projection blackboard with dark lines.

  (6) The blackboard with a dark line according to any one of (1) to (5), wherein the surface glazing layer is any one of black, gray, green, brown, and amber.

  (7) In any one of (1) to (6), the surface wrinkle layer is 1 to 30% in terms of 75 degree surface glossiness Gs (75 °) defined in JIS Z 8741-1997. Projection blackboard with dark lines.

  (8) The projection blackboard with a dark line according to any one of (5) to (7), wherein the titanium oxide-coated particles are particles formed by coating titanium oxide on the surfaces of mica particles.

  According to the present invention, even when a dark line, which is a guide for drawing characters, images, etc., with chalk (white ink) is attached to the surface, the video recognition (projection) of the projection blackboard is hindered. In other words, the drawing performance of chalk (white ink) characters, images, etc. is improved, and the projection blackboard is excellent in character recognition and video recognition.

It is a schematic explanatory drawing which shows the measuring method of reflected luminance.

The projection blackboard targeted by the present invention is a blackboard having at least one eaves layer on a metal substrate, and has excellent chalk character recognizability and chalk character erasability as well as video recognizability. The projection blackboard with dark lines according to the present invention is a blackboard in which a desired dark line is attached to the outermost surface layer of the projection blackboards described above.
“Dark line” as used here is a guide function for drawing characters, images, etc. on the blackboard surface as a guide for drawing characters, images, etc. with chalk. Have For this reason, the dark line is clearly visible from the writer (for example, from a distance of 30 cm), and from the person who sees the drawing or video (for example, from a position 2 m away), the dark line is hardly recognizable. In other words, it is necessary that the character recognition is excellent and the image recognition is not affected even when an image is projected. If the dark line is too conspicuous from the drawing or video viewer, the recognizability (character recognition) of the drawn characters, etc., and the recognizability of the projected video (video recognition) deteriorate. In addition, it is needless to say that the dark line formed on the blackboard surface is not particularly limited in shape, thickness, etc., such as a solid line, a broken line, a one-dot chain line, and the like, and can be appropriately determined according to the application.

  The dark line used in the present invention has a lightness L * displayed in the L * a * b * color system defined in JIS Z 8781-4: 2013 of 70 or less, preferably black, gray, amber, It is preferable that the dark color tone of either brown or green is darker than the color tone of the blackboard. If the lightness L * exceeds 70, it becomes too bright and the contrast with the color tone of the blackboard surface layer becomes too large, and it is too conspicuous, so that character recognition such as chalk characters and video projected by the projector is recognized. descend.

The dark line used in the present invention has a color tone consisting of the lightness L * displayed in the L * a * b * color system in the above-mentioned range, and is displayed in the L * a * b * color system. The color difference from the heel layer is the following equation (1): ΔE * ab = ((ΔL *) ² + (Δa *) ² + (Δb *) ² ) ^1/2 (1)
(Here, ΔL *: the difference between the lightness of the dark line and the lightness of the surface wrinkle layer, Δa *, Δb *: the difference between the chromaticity of the dark line and the lightness of the surface wrinkle layer)
The color tone is adjusted so that ΔE * ab defined in (1) satisfies 15 or less.

  If ΔE * ab exceeds 15, the contrast between the dark line and the blackboard becomes too large, and the color reproducibility of the image projected by the projector will be greatly different between the dark line part and the blackboard surface. Make viewers feel uncomfortable and reduce video recognition. For this reason, the color tone of the dark line is adjusted according to the color tone of the surface glaze layer of the projection blackboard so that the color difference ΔE * ab between the surface glaze layer and the dark line is 15 or less.

  Further, the dark line used in the present invention has a surface gloss of 1 to 35% with a 75 ° surface glossiness Gs (75 °) defined in JIS Z 8741-1997. When Gs (75 °) is less than 1%, the character erasability at the dark line portion is lowered. On the other hand, if it exceeds 35%, the image projected by the projector is remarkably reflected in the dark line portion, and the image recognizability is lowered. For this reason, the 75 degree surface glossiness Gs (75 °) of the dark line is limited to a range of 1 to 35%. In addition, Preferably, it is 10 to 30%, More preferably, it is 15 to 30%.

  Further, the dark line used in the present invention has a 75 ° surface glossiness Gs (75 °) in the above-described range, and a difference ΔGs (Gs (75 °) between the dark line portion Gs (75 °) and the surface wrinkle layer Gs (75 °). Adjust so that 75 ° is within ± 10%. The difference ΔGs (75 °) in the 75 ° surface glossiness Gs (75 °) between the surface glazing layer and the dark line, and when ΔGs (75 °) increases beyond ± 10%, the reflection of the image projected by the projector The difference makes the viewer feel uncomfortable and reduces video recognition. For this reason, the difference ΔGs (75 °) in the 75 ° surface glossiness Gs (75 °) between the surface glazing layer and the dark line was limited to ± 10%. Note that ΔGs (75 °) is preferably within ± 5%, more preferably within ± 3%, and the difference in glossiness between the surface wrinkle layer and the dark line is more preferably zero.

  The dark line having the above-described color tone and surface gloss is printed on the surface glazing layer by gravure printing using the ink adjusted to have the above-described color tone and surface gloss, or the above-described color tone, Transfer the desired pattern using transfer paper that can be transferred using ink that has been adjusted in advance to satisfy the surface gloss, or adjust it in advance to satisfy the color tone and surface gloss described above. It is preferable that the ink is formed by drawing with a roller, a syringe or the like using the ink.

  The projection blackboard that forms the dark line having the above-described color tone and glossiness is a blackboard having at least one ridge layer on a metal substrate, similar to that described in Japanese Patent No. 4771880.

  The type of metal substrate used in the projection blackboard is not particularly limited, but is preferably a cold-rolled steel plate. The cold-rolled steel sheet used as the metal substrate is preferably subjected to Ni plating in order to improve the adhesion between the metal substrate and the glaze. Examples of the cold rolled steel sheet include a low carbon steel sheet and a stainless steel sheet. The C content of the low-carbon steel plate is preferably 0.0200% or less in mass%, more preferably 0.0100% or less, and still more preferably 0.0050% or less.

  Moreover, as a metal substrate, it is good also as an aluminum plating steel plate or a Zn-Al alloy plating steel plate. Examples of the Zn-Al alloy-plated steel sheet include a plated steel sheet having a plating layer comprising an Al content of 4 to 70 mass%, the balance Zn and inevitable impurities. Needless to say, the plating layer may contain an additive for improving the properties of the plating film.

  Of the glazing layer formed on the metal substrate, the outermost surface glazing layer has a lightness L * of 30 expressed in the L * a * b * color system defined in JIS Z 8781-4: 2013. Color tone of ~ 70, surface characteristics specified by JIS B 0601-2001 with surface roughness Rz of 5 ~ 25μm, reflection characteristics with peak gain of 0.28 or more, or further specified in JIS Z 8741-1997 It is preferable from the viewpoint of chalk character recognizability, chalk character erasability, and video recognizability that the surface glossiness be 1 to 30% at 75 degree surface glossiness Gs (75 °).

  Characters and images drawn with chalk are easy to see, that is, in order to ensure the recognition of chalk characters, in the projection blackboard used in the present invention, the surface wrinkle layer is an L * a * b * color system. The displayed lightness L * is 30 to 70, preferably any one of black, gray, green, brown, and amber, and more preferably any one of black, green, brown It is preferable to use a soot layer of a system color tone. If the lightness L * deviates from the above range, it becomes too dark and the image recognition performance is reduced when the image is projected. On the other hand, if the lightness L * deviates from the above range, it becomes too bright and choke. Character recognition is reduced. In addition, the color tone and brightness of the soot layer can be adjusted by the type and amount of the additive pigment. In order to adjust the lightness L * displayed in the L * a * b * color system to 30 to 70, it is possible to add Co, Cr, Ti metals or their oxides alone or in combination as pigments. preferable. The lightness L * is preferably 40-60.

  In addition, in the projection blackboard used in the present invention, the surface characteristics of the surface glazing layer are set in accordance with JIS B 0601 in order to ensure the writing and erasing of chalk characters, which makes it easy to write and erase characters, images, etc. with chalk. -Adjust so that the surface roughness Rz specified in 2001 is 5 to 25 µm. In addition, Preferably it is 10-22 micrometers, More preferably, it is 14-20 micrometers.

  When the surface roughness Rz of the surface ridge layer is out of the above range and approaches flat, the chalk slips, the chalk drawing performance deteriorates, and the image recognition performance also deteriorates. On the other hand, if the above-mentioned range is exceeded and the unevenness is too large, the chalk character erasability is lowered and the image recognizability is lowered. The surface properties of the surface glaze layer described above can be achieved by setting the combination of the composition of the glaze applied to the metal substrate and the firing conditions after the glaze application within an appropriate range.

  In the projection blackboard used in the present invention, the surface glazing layer has the above-mentioned color tone and surface characteristics, maintains an excellent blackboard function, and further has a peak gain of 0.28 or more, preferably a half gain of 13 or more. A blackboard with reflective properties is preferred.

  For example, as shown in FIG. 1, the reflection characteristic of the plate to be measured is as follows. The magnitude of the reflected light 2 (reflection luminance) at a point shifted by 5 ° in the range is obtained from a reflection characteristic curve (see FIG. 1) obtained by measuring with the luminance meter 11. The “peak gain” in the present invention is the ratio of the reflected luminance of the blackboard to be measured measured under the same conditions to the reflected luminance when light is applied to a standard white plate (complete diffuser plate: pure white plate baked with magnesium sulfate). In this case, however, the reflected luminance at a viewing angle of 5 ° is usually used. Further, the “half gain” in the present invention refers to a viewing angle width (degrees) when the reflection luminance in the reflection characteristic curve becomes 1/2 of the peak.

  If the peak gain is less than 0.28, the projected image is dark and inferior in image recognizability and cannot satisfy the requirements for a projection blackboard. Therefore, 0.28 is set as the lower limit of the peak gain. The peak gain is preferably 0.35 to 1.0, more preferably 0.35 to 0.60. In order to obtain a wide viewing angle, the half gain is preferably set to 13 or more. For this reason, it is preferable that the projection blackboard used in the present invention has a reflective surface layer having a peak gain of 0.28 or more, and preferably a half gain of 13 or more.

  The reflection characteristics of the surface glaze layer described above are obtained by adding an appropriate amount of titanium oxide-coated particles having an appropriate particle size distribution, preferably mica particles coated with titanium oxide, to the glaze applied to the metal substrate, and setting the firing temperature in an appropriate range. This can be achieved by adjusting to

  It is preferable that the surface wrinkle layer having the above-described properties has a surface gloss of 75% specular gloss Gs (75 °) defined by JIS Z 8741-1997 and 1 to 30%. If Gs (75 °) is less than 1%, the choke character erasability deteriorates, the reflection luminance decreases, and the image becomes unclear. On the other hand, if Gs (75 °) exceeds 30%, the drawing performance of chalk characters deteriorates and halation is likely to occur and the viewing angle becomes narrow. More preferably, Gs (75 °) is 15 to 25%, more preferably more than 20% and 25% or less.

  The surface soot layer contains titanium oxide-coated particles. By including titanium oxide-coated particles in the surface glazing layer, sharpness is improved, irregularities are formed on the surface, diffuse reflectance is improved, halation is suppressed, and reflection characteristics are improved. The surface soot layer preferably contains 2 to 40%, more preferably 3 to 20% by mass of titanium oxide-coated particles in terms of mass% based on the total amount of the surface soot layer. When the titanium oxide-coated particles are less than 2% by mass, the effect of improving the reflection characteristics is small. If the titanium oxide-coated particles are contained in an amount exceeding 40% by mass, the surface roughness Rz becomes excessively large, the choke character erasability deteriorates, the lightness becomes excessive, and the choke character is recognized. Sex is reduced.

The titanium oxide-coated particles preferably have an average particle size of 100 μm or less. More preferably, it is 5-80 micrometers. When the average particle size of the titanium oxide-coated particles is less than 5 μm, the diffuse reflectivity decreases, whereas when the average particle size of the titanium oxide-coated particles exceeds 100 μm, the surface roughness of the surface layer becomes excessively large and chalk characters Eraseability is reduced. In addition, the average particle diameter of a particle | grain here shall mean the 50% cumulative particle diameter measured using the laser diffraction type particle size distribution measuring apparatus. The titanium oxide-coated particles are preferably particles in which the surface of mica particles is coated with titanium oxide (TiO ₂ ), and the mica particles are more preferably lamellar mica particles.

  The surface glaze layer having the above-mentioned characteristics is a glaze layer formed using a glaze glaze containing at least titanium oxide-coated particles, or further a titanium oxide glaze, or even a transparent gloss glaze in a transparent mat glaze. It is preferable to do. The thickness of the surface ridge layer is preferably 200 μm or less from the viewpoint of peelability. More preferably, it is 150 μm or less.

The surface glaze layer formed by using the above glaze glaze is in mass%, and the total amount of titanium oxide containing titanium oxide in the titanium oxide-coated particles is TiO ₂ , TiO ₂ : 0.5-15%, more preferably less than 0.5% to 10%, further preferably comprises 2-5%, _{further, SiO 2: 15~45%, Al} 2 O 3: 5~30%, Na 2 O, K 2 O, selected from Li ₂ O In addition, it is preferable to use one layer or two or more types as a soot layer containing a total of 2 to 20% and B ₂ O ₃ : 2 to 20%. In the present invention, a blackboard surface gray layer is selected from black pigments, gray pigments, green pigments, brown pigments, yellow pigments, and amber pigments in order to obtain a desired color. Needless to say, the total amount of pigments contained is 40% by mass or less.

  The projection blackboard used in the present invention is coated with a glaze glaze on the surface of a metal substrate and baked to form a base glaze layer, or without forming a ground glaze layer, and then at least oxidized into a transparent mat glaze. It is preferable to produce the surface coating layer by applying a coated glaze containing titanium-coated particles, further titanium oxide glaze, or further transparent gloss glaze, and baking at 400 to 850 ° C. The metal substrate is preferably a cold-rolled steel plate, an aluminum-plated steel plate, or a Zn-Al alloy-plated steel plate.

  When a cold-rolled steel sheet is used as the metal substrate, it is preferable to apply Ni plating to the surface of the cold-rolled steel sheet (metal substrate) after applying Ni plating to the cold-rolled steel sheet, and baked to form an undercoat layer . The agate glaze is not particularly limited, and any of the agate glazes used in conventional smoked blackboards is suitable. Any known coating method such as spray or roll coater can be applied to apply the laxative glaze.

As the laxative glaze, for example, SiO ₂ : 20 to 80% is contained in mass% with respect to the total solid content, and the remainder is TiO ₂ : 0 to 15%, ZrO ₂ : 0 to 20%, B _{2 O 3: 0~25%, Al 2} O 3: 0~25%, Na 2 O: 0~20%, Li 2 O: 0~20%, K 2 O: 0~20%, PbO: 0~40 %, ZnO: 0~50%, BaO : 0~15%, CaO: 0~15%, CaF 2: 0~10%, CoO: 0~20%, NiO: 0~20%, MnO: 0~20 It is preferable to use a SiO ₂ -based glaze containing%.

  A surface glaze is applied to the surface of the obtained base glaze layer, and then fired at 600 to 850 ° C. to form a surface glaze layer. For the application of the glaze glaze, any known application method such as spray or roll coater can be applied.

  Glaze glaze is 100 to 20 parts by weight of titanium oxide glaze (frit), or 20 parts by weight of transparent gloss glaze (frit), or 100 parts by weight of transparent mat glaze (frit). It is preferable to use a glaze in which an appropriate amount of titanium oxide-coated particles is added to the glaze to which no more than a part is added. Moreover, it is preferable that the addition amount of a titanium oxide coating particle shall be 1-25 weight part with respect to transparent mat | matte glaze or mixed glaze (slip): 100 weight part (weight conversion after baking).

  Glaze glaze is obtained by grinding a transparent mat glaze frit, or a transparent mat glaze, titanium oxide glaze, or even a transparent gloss glaze frit and, if necessary, a mixture of various additives and pigments and water. An appropriate amount of titanium oxide-coated particle powder is added to and mixed with the resulting mud (slip). As the pigment, it is necessary to add any one of black pigment, gray pigment, green pigment, brown pigment, yellow pigment, and amber pigment according to the desired color tone of the blackboard. . The added amount of the pigment is preferably 20 parts by weight or less in total with respect to 100 parts by weight of slip (in terms of weight after firing). If the amount added exceeds 20 parts by weight, the fluidity of the slip will decrease.

As the transparent mat glaze (frit), by mass% with respect to total _{solids, SiO 2: 30~45%, Al} 2 O 3: 20~35%, B 2 O 3: 5~15%, K 2 O _{: 5~15%, Na 2 O:} 10~25%, hints, the balance, BaO: 0~15%, CaO: 0~15%, F 2: 0~10%, TiO 2: 0~10% It is preferable to use a glaze containing the above.

The titanium oxide glaze (frit) is 10% by mass with respect to the total solid content and contains 10 to 30% TiO ₂ , and the balance is SiO ₂ : 0 to 80%, Al ₂ O ₃ : 0 to 20%, B _{2 O 3: 0~25%, Na 2} O: 0~20%, K 2 O: 0~20%, Li 2 O: 0~20%, P 2 O 5: 0~10%, ZrO 2: 0~ 20%, BaO: 0~15%, CaO: 0~15%, MgO: 0~5%, PbO: 0~40%, ZnO: 0~50%, CaF 2: the glaze, including 0 to 10% It is preferable to do. In addition, it may replace with the titanium oxide which is a pigment of a titanium oxide glaze, and it is good also as 1 type, or 2 or more types of pigments among a zirconium oxide, an antimony oxide, and a zinc oxide.

As the transparent gloss glaze (frit), by mass% with respect to total solids, SiO _2: comprises 40 to 65%, the _{balance, B 2 O 3: 5~20%} , Na 2 O, K 2 O, Li 2 5-40% in total of one or more one of _{O, F 2: 0~10%,} Al 2 O 3: 0~10%, CaO: 0~10%, TiO 2: 0~10%, ZnO: It is preferable to use a glaze containing 0 to 10%, MgO: 0 to 5%, and the like. In addition, it may replace with the titanium oxide which is a pigment of a titanium oxide glaze, and it is good also as 1 type, or 2 or more types of pigments among a zirconium oxide, an antimony oxide, and a zinc oxide.

  When the firing temperature is less than 600 ° C., the surface roughness becomes too rough and the reflection characteristics deteriorate. On the other hand, when the temperature exceeds 850 ° C., the surface becomes too smooth, and the chalk character recognizability and the chalk character drawing / erasing property deteriorate.

  Moreover, when using an aluminum plating steel plate or a Zn-Al alloy plating steel plate as a metal substrate, it is preferable to apply a glaze on the surface of the metal substrate and to fire at 400 to 600 ° C. to form a surface glaze layer.

  In this case, it is necessary to use a low melting point glaze from the viewpoint of preventing melting of the plating layer. For this reason, it is preferable to use a glaze obtained by blending a glaze in which phosphoric acid is blended in place of the above-described transparent matte glaze with titanium oxide-coated particles or further with a titanium oxide glaze. The content of phosphoric acid in the glaze containing phosphoric acid is 40% by mass or more, preferably 80% by mass or less, and more preferably 70% by mass or less.

The glaze (frit) containing phosphoric acid contains P ₂ O ₅ : 40 to 80% by mass% with respect to the total solid content, and the balance is SiO ₂ : 0 to 40%, Al ₂ O ₃ : 0 _{~50%, B 2 O 3:} 0~25%, Na 2 O: 0~20%, K 2 O: 0~20%, Li 2 O: 0~20%, TiO 2: 0~30%, Sb _{2 O 3: 0~25%, ZnO} : 0~20%, BaO: 0~15%, CaO: 0~15%, MgO: 0~5%, PbO: 0~10%, SrO: 0~20% It is preferable to use a glaze containing the above.

  In addition, when using an aluminum-plated steel sheet or a Zn-Al alloy-plated steel sheet as a metal substrate, from the viewpoint of preventing melting of the plating layer, a low melting point glaze is used, so that adhesion is improved, and Application is not always necessary.

  Moreover, when using an aluminum plating steel plate or a Zn-Al alloy plating steel plate as a metal substrate, if the firing temperature is less than 400 ° C., the adhesion of the soot layer decreases. On the other hand, when it exceeds 600 degreeC, the problem that a plating layer will fuse | melt will arise.

A cold-rolled steel plate (C: 0.0050 mass% ultra-low carbon steel plate) was used as the metal substrate. A nickel plating layer was formed on the surface of the cold rolled steel sheet in a nickel sulfate bath. A glaze glaze was applied to both sides of the nickel-plated cold-rolled steel sheet by a roll coater method, and then fired at 800 ° C. to form a 30 μm-thick base layer. In addition, the armpit glaze is SiO ₂ type glaze (frit): 100 parts by mass, clay: 6 parts by mass, magnesium carbonate: 0.15 parts by mass, borax: 0.4 parts by mass, silica: 1 part by mass, water: 70 parts by mass The blended raw material to which was added was put into a ball mill and crushed into a slip.

  Next, a glaze was applied to one surface of the obtained lower glaze layer by a spray method, followed by baking at 780 ° C. to form a 70 μm surface glaze layer, which was used as a sample blackboard.

In addition, transparent matte glaze (frit) having the composition shown in Table 1: 90 parts by mass, transparent gloss glaze shown in Table 2: 10 parts by mass, clay: 5.5 parts by mass, sodium nitrite: 0.15 parts by mass, silica: 0.5 parts by mass Part, water: 70 parts by mass, and, as a pigment, TiO ₂ , Sb ₂ O ₅ , NiO are total: 1 part by mass, Cr ₂ O ₃ : 8.2 parts by mass, Co, Cr are total: 7.5 parts by mass , Fe ₂ O ₃ , CuO, CoO, MnO, etc .: 0.1 part by mass is added, and a slip A obtained by mixing and pulverizing with a ball mill is prepared, and the titanium oxide glazes shown in Table 3 (frit) : 100 parts by mass, clay: 7.5 parts by mass, potassium chloride: 0.2 parts by mass, sodium aluminate: 0.3 parts by mass, water: 54 parts by mass, and as a pigment, Co and Cr total: 1.2 parts by mass After adding and obtaining slip B obtained by mixing and pulverizing with a ball mill, slip B: 100 parts by mass (calculated in terms of mass after firing) Titanium oxide-coated particle powder: 20 parts by mass with water: 45 parts by mass are added and mixed to produce slip C. These slip A and slip C are blended at a ratio of 3: 1, mixed, and mixed. It was made into an upper glaze. The titanium oxide-coated particles used were particles in which the surface of the thin plate-like mica particles was coated with titanium oxide (TiO ₂ ), the average particle size was 20 μm, and the titanium oxide coating rate was 30%. The average particle size is indicated by a 50% cumulative particle size measured using a laser diffraction particle size distribution measuring device.

  The surface chalk layer of the sample blackboard obtained was examined for its composition, and the surface roughness, color tone, glossiness, and reflection characteristics were further investigated. The obtained results are shown in Tables 4 and 5.

  In addition, the surface roughness calculated | required arithmetic mean roughness Ra and maximum height Rz based on prescription | regulation of JIS B 0601-2001. The color tone was measured in accordance with JIS Z 8722-2000, and the color tone displayed in the L * a * b * color system was displayed in accordance with JIS Z 8781-4: 2013. The glossiness was determined as 75 ° specular glossiness Gs (75 °) according to JIS Z 8741-1991. The reflection characteristic is a point where incident light 1 is irradiated from the light source 10 perpendicularly to the center of the plate (blackboard) S to be measured, and the same arc shape is moved from the center point by 5 ° within a range of 75 ° to the left and right. The magnitude of the reflected light 2 (reflection brightness) was measured with a luminance meter 11, and peak gain and half gain were obtained. The peak gain refers to the ratio of the reflection luminance of the sample blackboard measured under the same conditions to the reflection luminance when light is applied to standard white. Note that the reflection luminance at a viewing angle of 5 ° was used.

  A desired pattern (lattice fine line) was formed on the surface of the above-mentioned projection blackboard (sample blackboard) using transfer paper. The transfer paper used uses ink that has been pre-adjusted to satisfy the various color tones and 75-degree specular gloss Gs (75 °) shown in Table 6, and has a desired pattern (thickness of grid-like fine lines: 1 mm). What was screen-printed on the transfer paper was used.

  The dark line color tone and 75-degree specular gloss Gs (75 °) used were measured in the same manner as in the case of the above-mentioned surface glazing layer, and are shown in Table 6. The color tone and glossiness of the dark line were measured in an area of 40 × 60 mm drawn with the same kind of ink.

About the obtained sample blackboard with a dark line, the appearance of a dark line, character recognition property, and image recognition property were evaluated first.
(1) Evaluation method for the appearance of dark lines after drawing characters, etc. When the dark line is seen from a position 30 cm away from the blackboard, the dark line is clearly visible, and characters can be drawn along the dark line. If the character is difficult to draw along the dark line because it is thin and difficult to see, “△” indicates that the character is difficult to draw along the dark line, and “X” indicates that the character cannot be drawn along the dark line because it is difficult to see the dark line. The degree of function was evaluated.
(2) Evaluation method of character recognition after drawing characters, etc. After drawing the characters with chalk along the dark line, look at the dark line from a position 2m or 3m away from the sample blackboard with dark line. The dark line can be seen faintly from the position 2m away, the dark line is almost invisible from the position 3m away, and the case where it does not obstruct the recognition of drawn characters etc. The dark line is clearly visible, the dark line appears faint from a position 3m away, and the case where the written characters etc. are slightly obstructed is marked as "△", the dark line is clearly visible from a position 2m away, and the position 3m away The case where the dark line was clearly visible and the recognition of the drawn characters was obstructed was evaluated as “x”, and the influence of the dark line on the character recognition was evaluated.
(3) Evaluation method of video recognizability when an image (video) is projected from a projector Project an image (video) from a projector onto a sample blackboard with dark lines, and view the image (video) projected from a position 2 m away. “○” indicates that the dark line is hardly visible and does not affect the image recognition, “△” indicates that the dark line is slightly visible and slightly affects the image recognition, “Δ” indicates that the dark line is clearly visible and affects the image recognition. The effect of dark lines on video recognition was evaluated as “×”.
(4) Evaluation method of dark line appearance when projecting an image (video) from a projector Project an image (video) from a projector onto a sample blackboard with a dark line, and view the projected image (video) from a position 2 m away. The degree of reflection of dark lines will be investigated mainly. There is no difference in reflection and gloss between the blackboard surface and the dark line, and it does not affect the reproducibility of the video, “○”, there is a slight difference in reflection and gloss between the blackboard surface and the dark line, and the video reproducibility Evaluate the effect of dark lines on video reproducibility with “△” if there is a slight impact, and “X” if there is a difference in reflection and gloss between the blackboard surface and the dark line, affecting the reproducibility of the video. did.

  The results obtained are shown in Table 6.

  In all of the examples of the present invention, the dark line effectively functions as a guide when drawing characters, images, etc. with chalk (white ink), and has the ability to recognize characters drawn with chalk (white ink). Furthermore, the blackboard is a projection blackboard with dark lines that retains excellent video recognition (projection) without affecting the reproducibility of the video (image) projected by the dark lines. On the other hand, in the comparative example that is out of the scope of the present invention, the character recognizability and / or the image recognizability (projection property) is lowered.

1 Incident light 2 Reflected light 3s Blackboard to be measured (sample)
10 Light source
11 Luminance meter

Claims (8)

A blackboard having at least one glazing layer on a metal substrate, and having a dark line on the outermost surface glazing layer of the glazing layer, wherein the dark line is represented by an L * a * b * table The lightness L * displayed in the color system is 70 or less, and the color difference from the surface wrinkle layer displayed in the L * a * b * color system is ΔE * ab defined by the following equation (1): 15 A projection blackboard with a dark line excellent in image recognizability, characterized in that the dark line has the following color tone.
ΔE * ab = ((ΔL *) ² + (Δa *) ² + (Δb *) ² ) ^1/2 (1)
Here, ΔL *: difference in lightness L * displayed in the L * a * b * color system, Δa *: difference in chromaticity a * displayed in the L * a * b * color system, Δb *: L Difference of chromaticity b * displayed in * a * b * color system   2. The projection blackboard with dark lines according to claim 1, wherein the dark lines are any one of black, gray, amber, brown, and green.   The dark line is 1 to 35% of 75 degree surface glossiness Gs (75 °) defined in JIS Z 8741-1997, and the 75 degree surface glossiness of the dark line and the surface glaze layer is 75 degree surface glossiness. 3. The projection blackboard with dark lines according to claim 1, wherein a difference ΔGs (75 °) from the degree is within ± 10%.   The surface wrinkle layer has a color tone with a lightness L * of 30 to 70 displayed in the L * a * b * color system, and a surface with a surface roughness Rz specified in JIS B 0601-2001 of 5 to 25 μm. 4. The projection blackboard with dark lines according to claim 1, wherein the blackboard has a characteristic and a reflection characteristic having a peak gain of 0.28 or more.   5. The dark lined projection according to claim 1, wherein the surface glaze layer is a glaze layer formed using a glaze with at least titanium oxide-coated particles blended with a transparent mat glaze. blackboard.   6. The projection blackboard with dark lines according to claim 1, wherein the surface glazing layer is any one of black, gray, green, brown, and amber.   7. The dark line according to claim 1, wherein the surface wrinkle layer is 1 to 30% in terms of 75 ° surface glossiness Gs (75 °) defined in JIS Z 8741-1997. Projection blackboard.   The projection blackboard with dark lines according to any one of claims 5 to 7, wherein the titanium oxide-coated particles are particles formed by coating titanium oxide on the surfaces of mica particles.

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