Composition for forming surface layer, surface layer formed from said composition, and surface material for writing on oil-based ink

Abstract

To provide a composition for forming a surface layer capable of repeatedly performing calligraph with a solvent ink on a surface layer having no remained calligraphy, by making it possible to simply erase calligraph written with a solvent ink, with a commercially available plastic eraser, furthermore only by scrubbing with a plastic eraser and a cloth.SOLUTION: A surface layer 12 capable of writing with a solvent ink on a substrate layer 11 and capable of erasing when scrubbing calligraphy with a plastic eraser is formed. The surface layer 12 is a composition containing at least polyol and polyisocyanate belonging to an aliphatic group or an aromatic group, and has a polyurethane structure. In one example of the composition, the polyol is alkyd polyol, and the polyisocyanate is pentamethylene diisocyanate, hexamethylene diisocyanate, xylene diisocyanate or isophorone diisocyanate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a composition for forming a surface layer, etc. More specifically, the present invention relates to a composition for forming a surface layer, etc., which can obtain a surface layer on which writing can be done with oil-based ink, and the handwriting can be erased with a plastic eraser, and further which can be erased with a plastic eraser and a cloth. [Background technology]

[0002] In the past, various proposals have been made regarding inks that can erase handwriting written on paper. The purpose of these is to enable repeated writing on the same paper. However, these technologies are only intended to be written on "paper". There are also technologies that make it possible to erase handwriting written with ink such as a magic marker using a commercially available eraser, but these technologies are mainly based on the composition of the ink components.

[0003] On the other hand, there are surface processing technologies that pursue both writing and erasing functions. For example, the surface of the adhesive tape disclosed in the following Patent Document 1 is a release agent layer that contains an organic resin with a specific glass transition point, such as polyurethane resin, and an addition-reactive silicone. These two components form a seaweed structure, which allows the writing (printing) properties of oil-based marker to be exhibited.

[0004] In addition, the following Patent Document 2 discloses a technology related to a water-based matte paint. The water-based matte paint contains a polyurethane resin, a compound having a polymerizable unsaturated group, a granular filler, and colloidal silica. The surface formed by the water-based matte paint has a stain-resistant effect, as it is possible to erase the handwriting of an oil-based marker with a "cloth." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-228924 [Patent Document 2] JP 2018-178066 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the above Patent Document 1, the use of a surface coating containing a polyurethane resin makes it possible to write with oil-based marker, but no evaluation of the erasability of the handwriting of the oil-based marker is disclosed, and the aim is not to achieve both the writability of the oil-based marker and the erasability of the handwriting. In addition, the above Patent Document 2 is a technology that focuses on "stain resistance", and in order to verify the effect of stain resistance, it is merely verified whether or not the handwriting of the oil-based marker can be erased with "cloth", and it is not a technology that aims to obtain a surface layer that can be repeatedly written on with oil-based ink by erasing the handwriting with a plastic eraser or cloth.

[0007] Therefore, the main object of the present invention is to provide a composition for forming a surface layer, etc., which enables repeated writing with oil-based ink on a surface layer on which no oil-based ink traces remain, by making it possible to easily erase written oil-based ink marks with a commercially available plastic eraser, or even by rubbing with a plastic eraser and a cloth. [Means for solving the problem]

[0008] That is, the present invention is a surface layer forming composition that forms a surface layer that can be written on with an oil-based ink and can erase written marks with a plastic eraser, or even when rubbed with a plastic eraser and cloth. More specifically, a surface layer forming composition that contains at least a polyol and an aliphatic or aromatic polyisocyanate and can form a polyurethane resin surface layer is proposed. An example of a suitable composition for the surface layer forming composition according to the present invention is a surface layer forming composition in which the polyol is an alkyd polyol (also called alkyd polyol) and the polyisocyanate is pentamethylene diisocyanate, hexamethylene diisocyanate, xylene diisocyanate, or isophorone diisocyanate. Among them, when the polyisocyanate is pentamethylene diisocyanate, the equivalent ratio of isocyanate group / hydroxyl group in the surface layer forming composition is preferably 0.5 or more and 2.5 or less. In addition, when the polyisocyanate is hexamethylene diisocyanate, the equivalent ratio of isocyanate group / hydroxyl group of the surface layer forming composition is preferably 0.5 or more and 4.0 or less. In addition, when the polyisocyanate is xylylene diisocyanate, the equivalent ratio of isocyanate group / hydroxyl group of the surface layer forming composition is preferably 0.5 or more and 3.0 or less. In addition, when the polyisocyanate is isophorone diisocyanate, the equivalent ratio of isocyanate group / hydroxyl group of the surface layer forming composition is preferably 0.4 or more and 2.2 or less. Furthermore, from the viewpoint of realizing erasability with both plastic erasers and cloth, a composition having an equivalent ratio of isocyanate group / hydroxyl group of 1.2 or more and 2.0 or less and further containing polyolefin wax is particularly preferable. In addition, one example of a suitable composition of the surface layer forming composition according to the present invention is a composition in which the polyol is a fluorine polyol, the polyisocyanate is pentamethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate or isophorone diisocyanate, and further contains a silicon modified acrylic polymer having a hydroxyl group. In particular, in this composition, it is preferable that the equivalent ratio of isocyanate group / hydroxyl group is 0.65 or more and 2.0 or less. And, it is preferable that the equivalent ratio of the silicon modified acrylic polymer having a hydroxyl group to be added is 0.1 or more and 1.2 or less with respect to 100 parts by mass of the fluorine polyol. The present invention further provides a surface layer formed from the above-mentioned composition for forming a surface layer, and a surface material for writing on oil-based ink, which comprises at least the surface layer. Effect of the Invention

[0009] The composition for forming a surface layer according to the present invention makes it possible to provide a surface layer which can be written on with oil-based ink and which can easily erase the handwriting with a plastic eraser and even with a plastic eraser and cloth, and a surface material for writing on oil-based ink which has such a surface layer. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a diagram for explaining the basic layer structure of a panel having a surface layer according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention provides a composition for forming a surface layer, more specifically, a composition for forming a surface layer that can be written on with an oil-based ink and can easily erase the handwriting with a plastic eraser, or even with a plastic eraser and when rubbed with a cloth.

[0012] Here, the type of the "oil-based ink" is not narrowly limited, and for example, oil-based inks generally used in oil-based markers and oil-based ballpoint pens can be widely applied. The "oil-based marker" that is the subject of the present invention is not narrowly limited, but for example, it is a marking pen in which an absorbent body soaked in oil-based ink is placed in a cylindrical container and a fiber or plastic pen tip is attached to the absorbent body.

[0013] The "oil-based ink" of the oil-based marker is not narrowly limited, but is an ink having a composition containing at least an organic solvent, a resin, and a dye. A more detailed representative composition example of the oil-based ink for oil-based marker is an oil-based ink composed of a solvent containing 65 to 91 mass% in total of propylene glycol monomethyl ether, ethyl alcohol, isopropyl alcohol, benzyl alcohol, methyl ethyl ketone, etc., 1 to 10 mass% of resin, and 1 to 20 mass% of dye.

[0014] In addition, the "oil-based ballpoint pen" that can be used in the present invention is not narrowly limited, but can include, for example, a pen that supplies ink from the refill by a rotatable ball attached to the tip of a long, thin, cylindrical refill containing oil-based ink.

[0015] The oil-based ink of the oil-based ballpoint pen is not particularly narrowly limited, but may be a general composition containing at least an organic solvent, a resin, and a dye. A more specific representative example of the ink for the oil-based ballpoint pen is an oil-based ink composed of a solvent containing 40 to 65 mass% in total of phenyl cellosolve and benzyl alcohol, 15 to 25 mass% of resin, and 20 to 30 mass% of dye.

[0016] The "plastic (synthetic resin) eraser" (hereinafter "eraser") applicable to the present invention is a commercially available synthetic resin eraser (so-called rubber eraser) that is generally used to erase drawings made mainly with a pencil or mechanical pencil. One example is a plastic eraser whose main component is polyvinyl chloride.

[0017] The "fabric" applicable to the present invention is a commonly used fibrous fabric. For example, it may be 100% cotton fabric, 100% polyester fabric, or a blend of cotton and polyester. It may also be tissue paper, which is a commonly used fabric, but is not limited to these.

[0018] The surface layer forming composition according to the present invention is used to form a surface layer of various surface materials that require writing with oil-based ink. The surface materials are not limited to flat shapes, and can be used on the surfaces of articles of various shapes, and can be widely used not only for stationery but also for wall materials of structures, cards, furniture such as desks, cases for home appliances, etc.

[0019] The method for forming the surface layer on the substrate is not particularly limited, but for example, the composition for forming the surface layer can be directly applied to the substrate or sprayed. Alternatively, a method of forming a sheet from the composition for forming the surface layer in advance and attaching the sheet to the substrate with an adhesive or the like may be adopted.

[0020] Here, the composition for forming the surface layer contains (A) a polyol and (B) an aliphatic or aromatic polyisocyanate, and constitutes (C) a composition capable of forming a polyurethane structure.

[0021] (A) Regarding polyols. Polyol is a general term for a compound having two or more hydroxyl groups in a molecule, and can be selected from various known polyols. A suitable polyol that can be used in the present invention is, for example, an alkyd polyol. The surface layer formed of a composition having a polyurethane structure formed by an alkyd polyol and a polyisocyanate has a property that the solvent or dye of an oil-based ink is difficult to penetrate appropriately, so that the oil-based ink can be easily fixed to the surface without being repelled when written, and the oil-based ink can be easily erased.

[0022] Examples of polyol components that can be used in the present invention include alkyd polyols, among which polyester polyols derived from vegetable oils (e.g., castor oil, coconut oil fatty acid) are preferred. Examples include alkyd polyols obtained by condensation polymerization of castor oil and polybasic acids and polyhydric alcohols. Here, the polybasic acids may include, for example, adipic acid, phthalic acid, sebacic acid, etc. In addition, other suitable polyol components that can be used in the present invention may also include fluorine polyols.

[0023] Further, as an example of the polyol component that can be used in the present invention, there can be mentioned fluorine polyol. The fluorine polyol contains one or more fluorines in the molecule, and the resin formed from this fluorine polyol has some parts that are partially covered with fluorine. This allows the resin to exhibit properties such as chemical resistance, weather resistance, and heat resistance that are unique to fluorine-containing compounds, and to obtain the same effect on oil-based inks as when alkyd polyols are used. As an example of the fluorine polyol that can be used in the present invention, there can be mentioned one that contains a copolymer of tetrafluoroethylene and a vinyl monomer.

[0024] (B) Regarding polyisocyanates. Polyisocyanate is a general term for compounds having two or more isocyanate groups in the molecule, and in the present invention, it is possible to suitably select from various known aliphatic or aromatic polyisocyanates. Suitable polyisocyanates that can be used in the present invention include, for example, aliphatic polyisocyanates such as pentamethylene diisocyanate and hexamethylene diisocyanate. Examples of aromatic polyisocyanates include xylene diisocyanate. Examples of alicyclic isocyanates include isophorone diisocyanate.

[0025] (C) Polyurethane structure. The surface layer forming composition according to the present invention is configured to form a polyurethane structure by a reaction between an isocyanate group and a hydroxyl group. The surface layer having the polyurethane structure may be either light-transmitting or light-opaque.

[0026] Regarding the equivalent ratio of isocyanate groups to hydroxyl groups. The equivalent ratio of isocyanate group / hydroxyl group is a physical property value that determines the affinity (particularly lipophilicity) of the surface layer formed from the polyurethane resin and the permeability of oil-based ink. In the present invention, depending on the composition of the composition components, for example, in a composition in which the polyol is an alkyd polyol and the polyisocyanate is pentamethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate or isophorone diisocyanate, the suitable range of the equivalent ratio varies depending on the type of the isocyanate. For example, when the polyisocyanate is pentamethylene diisocyanate, the equivalent ratio of isocyanate group / hydroxyl group of the surface layer forming composition is preferably 0.5 or more and 2.5 or less. Also, when the polyisocyanate is hexamethylene diisocyanate, the equivalent ratio of isocyanate group / hydroxyl group of the surface layer forming composition is preferably 0.5 or more and 4.0 or less. When the polyisocyanate is xylylene diisocyanate, the equivalent ratio of isocyanate group / hydroxyl group in the surface layer forming composition is preferably 0.5 to 3.0.When the polyisocyanate is isophorone diisocyanate, the equivalent ratio of isocyanate group / hydroxyl group in the surface layer forming composition is preferably 0.4 to 2.2. Furthermore, for example, in a composition in which the polyol is a fluorine polyol and the polyisocyanate is pentamethylene diisocyanate, hexamethylene diisocyanate, xylene diisocyanate or isophorone diisocyanate, the equivalent ratio is preferably in the range of 0.65 or more and 2.0 or less.

[0027] When the polyol is an alkyd polyol, if the equivalent ratio of isocyanate / hydroxyl group for each isocyanate is less than the lower limit, the hydroxyl group of the unreacted polyol is present in excess, and in some experimental examples, the coating film becomes sticky over time and the erasability with an eraser or cloth is reduced, which is not preferable. In addition, the equivalent ratio is low, so the strength of the polyurethane resin structure is reduced, and the wear resistance and scratch resistance against the friction of the eraser are deteriorated. On the other hand, if the equivalent ratio of isocyanate / hydroxyl group for each isocyanate is more than the upper limit, the isocyanate is present in excess, so the lipophilicity of the coating film increases and the fixability of the oil-based ink is excessively improved, and in some experimental examples, erasing with an eraser or cloth is difficult. That is, although the range varies depending on the type of isocyanate, from the viewpoint of the effect sought by the present invention, as long as the equivalent ratio of isocyanate group / hydroxyl group is at least 0.5 and less than 2.2, the writing property of oil-based ink and erasability with eraser or cloth are compatible regardless of the type of alkyd polyol or isocyanate. Note that when the polyol is a fluorine polyol and the equivalent ratio of isocyanate group / hydroxyl group is less than 0.65, the addition of the hydroxyl group-containing silicon-modified acrylic polymer increases the number of unreacted hydroxyl groups, making the coating surface even more sticky and tending to worsen the writing property of oil-based ink. On the other hand, there are experimental examples in which an equivalent ratio of isocyanate group / hydroxyl group exceeding 2.0 is unsuitable for the same reason as in the case of alkyd polyol.

[0028] About hydroxyl-containing silicone modified acrylic polymer. When a "fluoropolyol" is used as the polyol, the polyisocyanate is preferably pentamethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate or isophorone diisocyanate, and in this case, a composition further containing an appropriate amount of a silicon-modified acrylic polymer having a hydroxyl group is particularly desirable.

[0029] In addition, the silicone-modified acrylic polymer having a hydroxyl group (reactive) is stably fixed to the urethane resin structure by the bond between the reactive hydroxyl group and the isocyanate group, so the silicone is not easily removed, and the erasability of oil-based ink is maintained even over time. In addition, if a non-reactive silicone (no hydroxyl group, does not react with isocyanate) is used, the silicone will fall off over time, reducing the erasability of oil-based ink, so it is not suitable.

[0030] The equivalent ratio of the silicon-modified acrylic polymer having hydroxyl groups to be added is preferably 0.1 or more and 1.2 or less. If the amount added is less than 0.1 equivalent, the erasability with an eraser or cloth is not improved. On the other hand, if the amount added exceeds 1.2, as mentioned above, the hydroxyl groups on the coating surface are excessive, making the coating surface even more sticky and worsening the writing properties of oil-based ink.

[0031] About polyolefin wax. When an alkyd polyol is used as the polyol, and pentamethylene diisocyanate, hexamethylene diisocyanate, xylene diisocyanate or isophorone diisocyanate is used as the polyisocyanate, and the equivalent ratio of isocyanate group / hydroxyl group is 1.2 or more and 2.0 or less, a composition that further contains an appropriate amount of polyolefin wax is particularly desirable. The addition of polyolefin wax improves the slipperiness of the surface, and erasability is achieved not only with plastic erasers but also with cloth.

[0032] Here, the basic layer structure of the panel having a surface layer according to the present invention will be described with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view showing an example of the layer structure.

[0033] First, the facing material denoted by reference numeral 1 at least comprises a base layer 11 and a surface layer 12 laminated on the base layer 11. In a configuration in which the surface layer 12 is formed into a sheet and then laminated on the base layer 11, an adhesive layer (not shown) is interposed between the base layer 11 and the surface layer 12. The surface layer 12 may be formed directly on the base layer 11 by a coating or spraying method. The total number of layers in the layer structure is not particularly limited. In other words, a necessary layer may be interposed between the base layer 11 and the surface layer 12 according to the purpose.

[0034] The present invention will be described below based on experimental examples, but the present invention is not limited to these experimental examples. Each of the experimental examples of the surface layer forming composition having the composition shown in Tables 1 to 5 below was prepared by the following method.

[0035] (Experimental Examples 1 to 3) The polyol component, alkyd polyol (TOKYD-25C, manufactured by Toshin Yushi Co., Ltd., hydroxyl value 105-160) and ethyl acetate (solvent) were stirred and mixed for 3 minutes at 1000 rpm using a propeller stirrer. Ethyl acetate was added in an amount that would result in a solid content of 35 mass% after the addition of isocyanate. Then, 1,5-pentamethylene diisocyanate (STABIO D-370N, Mitsui Chemicals), an aliphatic isocyanate, was added in an amount that would result in an isocyanate group / hydroxyl group equivalent ratio (hereinafter, NCO / OH equivalent ratio) of 0.5-2.5 according to Table 1. These solvents were stirred and mixed for 3 minutes at 1000 rpm using a propeller stirrer to obtain a surface layer forming composition. The alkyd polyol used in Experimental Examples 1 to 3 was a polyester polyol derived from castor oil.

[0036] (Experimental Examples 4 to 9) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 1 to 3, except that a trimer of hexamethylene diisocyanate (hereinafter, hexamethylene diisocyanate) (Coronate HXR, manufactured by Tosoh Corporation), which is an aliphatic isocyanate, was used as the isocyanate component, and the hexamethylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 0.5 to 4.0 according to Table 1.

[0037] (Experimental Examples 10-15) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 1 to 3, except that a trimer of xylene diisocyanate (hereinafter, xylene diisocyanate) (isocyanurate of XDI, Takenate D-131N, manufactured by Mitsui Chemicals, Inc., 78% ethyl acetate solution) which is an aromatic isocyanate, was used as the isocyanate component, and the xylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 0.5 to 3.0 according to Table 1.

[0038] (Experimental Examples 16-18) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 1 to 3, except that an alicyclic isocyanate, isophorone diisocyanate (Desmodur Z 4470 BA, manufactured by Sumika Covestro Urethane Co., Ltd.), was used as the isocyanate component, and the isophorone diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 0.4 to 2.2 according to Table 1.

[0039] (Experimental Example 19) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 1 to 3, except that an alkyd polyol (NT-11NX, manufactured by Toshin Yushi Co., Ltd., hydroxyl value 70 to 80) was used as the polyol component, and the same 1,5-pentamethylene diisocyanate as in Experimental Examples 1 to 3 was used as the isocyanate component, and the 1,5-pentamethylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 1.0. The alkyd polyol used in this Experimental Example 19 was a polyester polyol derived from coconut oil fatty acid.

[0040] (Experimental Example 20) A composition for forming a surface layer was obtained in the same manner as in Experimental Example 19, except that the same hexamethylene diisocyanate as in Experimental Examples 4 to 9 was used as the isocyanate component and that the hexamethylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 1.0.

[0041] (Experimental Example 21) A composition for forming a surface layer was obtained in the same manner as in Experimental Example 19, except that the same xylylene diisocyanate as in Experimental Examples 10 to 15 was used as the isocyanate component and that the xylylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 1.0.

[0042] (Experimental Example 22) A composition for forming a surface layer was obtained in the same manner as in Experimental Example 19, except that the same isophorone diisocyanate as in Experimental Examples 16 to 18 was used as the isocyanate component and that the isophorone diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 1.0.

[0043] (Experimental Examples 23-25) A fluorine polyol (Zeffle GK570, Daikin Industries, Ltd.) as a polyol component, ethyl acetate, and a hydroxyl group-containing silicon modified acrylic polymer (BYK-SILCLEAN3700, BYK-Chemie) as an additive were stirred and mixed with a propeller stirrer at 1000 rpm for 3 minutes. The ethyl acetate as a solvent was added in an amount that would result in a solid content of 35 mass% after the addition of the isocyanate. The hydroxyl group-containing silicon modified acrylic polymer as an additive (auxiliary agent) was added in an amount of 0.7 parts by mass per 100 parts by mass of the fluorine polyol. Then, 1,5-pentamethylene diisocyanate (STABIO D-370N, Mitsui Chemicals, Inc.) as an aliphatic isocyanate was added in an amount that would result in an NCO / OH equivalent ratio of 0.5 to 2.2 according to Table 2. These solvents were stirred and mixed with a propeller stirrer at 1000 rpm for 3 minutes to obtain a surface layer forming composition.

[0044] (Examples 26-30) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 23 to 25, except that a trimer of hexamethylene diisocyanate (hereinafter, hexamethylene diisocyanate) (Coronate HXR, manufactured by Tosoh Corporation), which is an aliphatic isocyanate, was used as the isocyanate component, and the hexamethylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 0.5 to 2.0 according to Table 2.

[0045] (Experimental Examples 31-36) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 23 to 25, except that a trimer of xylene diisocyanate (hereinafter, xylene diisocyanate) (isocyanurate of XDI, Takenate D-131N, manufactured by Mitsui Chemicals, Inc., 78% ethyl acetate solution) was used as the isocyanate component, the xylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 0.65 to 2.5 according to Table 2, and the hydroxyl group-containing silicon-modified acrylic polymer was not added in Experimental Example 31 only.

[0046] (Examples 37-39) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 23 to 25, except that an alicyclic isocyanate, isophorone diisocyanate (Desmodur Z 4470 BA, manufactured by Sumika Covestro Urethane Co., Ltd.), was used as the isocyanate component, and the isophorone diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 0.65 to 2.0 according to Table 2.

[0047] (Experimental Examples 40 and 41) Fluorine polyol (Zeffle GK570, Daikin Industries, Ltd.), ethyl acetate, and hydroxyl group-containing silicon modified acrylic polymer (BYK-SILCLEAN3700, BYK-Chemie, Ltd.), which is a polyol component, were stirred and mixed for 3 minutes at 1000 rpm using a propeller stirrer. The amount of ethyl acetate, which is a solvent, was added so that the solid content would be 35% by mass after the addition of isocyanate. The amount of hydroxyl group-containing silicon modified acrylic polymer, which is an additive (auxiliary agent), was added in amounts of 0.1 and 1.2 parts by mass per 100 parts by mass of fluorine polyol according to Table 2, and 1,5-pentamethylene diisocyanate (Stabio D-370N, Mitsui Chemicals, Inc.) was added in an amount such that the NCO / OH equivalent ratio was 1.6. The solvent was then stirred and mixed for 3 minutes at 1000 rpm using a propeller stirrer to obtain a surface layer forming composition.

[0048] (Experimental Examples 42 and 43) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 40 and 41, except that the same hexamethylene diisocyanate as in Experimental Examples 26 to 30 was used as the isocyanate component.

[0049] (Experimental Examples 44 and 45) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 40 and 41, except that the same xylylene diisocyanate as in Experimental Examples 31 to 36 was used as the isocyanate component.

[0050] (Experimental Example 46) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 40 and 41, except that the same isophorone diisocyanate as in Experimental Examples 37 to 39 was used as the isocyanate component and that the hydroxyl group-containing silicon-modified acrylic polymer was not added.

[0051] (Experimental Examples 47 and 48) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 40 and 41, except that the same isophorone diisocyanate as in Experimental Examples 37 to 39 was used as the isocyanate component.

[0052] (Examples 49-51) The polyol component, alkyd polyol (TOKYD-25C, manufactured by Toshin Yushi Co., Ltd., hydroxyl value 105-160), ethyl acetate, and additive polyolefin wax (Disparlon PF-911, manufactured by Kusumoto Chemicals Co., Ltd.) were stirred and mixed for 3 minutes using a propeller stirrer at 1000 rpm. Ethyl acetate was added in an amount that would result in a solid content of 35% by mass after the addition of isocyanate. The additive polyolefin wax was added in an amount of 5 parts by mass per 100 parts by mass of alkyd polyol. Then, the same 1,5-pentamethylene diisocyanate as in Experimental Examples 1 to 3 was added in an amount that would result in an isocyanate group / hydroxyl group equivalent ratio (hereinafter, NCO / OH equivalent ratio) of 1.2 to 2.0 according to Table 3. These solvents were stirred and mixed for 3 minutes using a propeller stirrer at 1000 rpm to obtain a surface layer forming composition.

[0053] (Examples 52-54) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 49 to 51, except that the same hexamethylene diisocyanate as in Experimental Examples 4 to 9 was used as the isocyanate component.

[0054] (Examples 55-57) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 49 to 51, except that the same xylylene diisocyanate as in Experimental Examples 10 to 15 was used as the isocyanate component.

[0055] (Examples 58-60) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 49 to 51, except that the same isophorone diisocyanate as in Experimental Examples 16 to 18 was used as the isocyanate component.

[0056] (Experimental Examples 61 and 62) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 1 to 3, except that the 1,5-pentamethylene diisocyanate was added in an amount according to Table 4 such that the NCO / OH equivalent ratio was 0.4 or 3.0.

[0057] (Experimental Examples 63 and 64) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 4 to 9, except that the hexamethylene diisocyanate was added in an amount according to Table 4 such that the NCO / OH equivalent ratio was 0.4 or 5.0.

[0058] (Experimental Examples 65 and 66) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 10 to 15, except that the xylylene diisocyanate was added in an amount according to Table 4 such that the NCO / OH equivalent ratio was 0.4 or 3.5.

[0059] (Experimental Examples 67 and 68) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 16 to 18, except that the isophorone diisocyanate was added in an amount according to Table 4 such that the NCO / OH equivalent ratio was 0.3 or 2.5.

[0060] (Experimental Examples 69 and 70) A composition for forming a surface layer was obtained in the same manner as in Experimental Examples 26 to 30, except that the hydroxyl-containing silicon-modified acrylic polymer was not added and the hexamethylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 1.1 and 0.65.

[0061] (Example 71) A composition for forming a surface layer was obtained in the same manner as in Experimental Examples 26 to 30, except that the hydroxyl-containing silicon-modified acrylic polymer was not added, fluoropolyol 2 (Lumiflon LF200, manufactured by Asahi Glass Co., Ltd.) was used as the polyol component, and the hexamethylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 1.1.

[0062] (Example 72) A composition for forming a surface layer was obtained in the same manner as in Experimental Examples 26 to 30, except that the hydroxyl-containing silicon-modified acrylic polymer was not added, silicon-modified fluorine polyol 2 (ZX-022-H, manufactured by T&K TOKA) was used as the polyol component, and the hexamethylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 1.0.

[0063] (Example 73) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 26 to 30, except that the hydroxyl-containing silicon-modified acrylic polymer was not added, acrylic polyol 1 (XK-9012, manufactured by Toshin Yushi Co., Ltd.) was used as the polyol component, and the hexamethylene diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 1.0.

[0064] (Example 74) A composition for forming a surface layer was obtained in the same manner as in Experimental Examples 31 to 36, except that the hydroxyl-containing silicon-modified acrylic polymer was not added, acrylic polyol 2 (EXCELOL 821, manufactured by Asia Kogyo Co., Ltd.) was used as the polyol component, and the isophorone diisocyanate was added in an amount such that the NCO / OH equivalent ratio was 1.0.

[0065] (Example 75) The same acrylic polyol as in Experimental Example 74 and 50 parts by mass of ethyl acetate were mixed and stirred with a propeller stirrer at 1000 rpm for 3 minutes to obtain a composition for forming a surface layer. Experimental Example 75 is an experimental example in which no isocyanate component was blended.

[0066] (Experimental Examples 76 and 77) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 23 to 25, except that the 1,5-pentamethylene diisocyanate was added in an amount according to Table 5 such that the NCO / OH equivalent ratio was 0.4 or 2.5.

[0067] (Experimental Examples 78 and 79) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 26 to 30, except that the hexamethylene diisocyanate was added in an amount according to Table 5 such that the NCO / OH equivalent ratio was 0.4 or 2.2.

[0068] (Experimental Examples 80 and 81) Except for adding the xylylene diisocyanate in an amount according to Table 5 such that the NCO / OH equivalent ratio was 0.3 or 3.0, a surface layer-forming composition was obtained in the same manner as in Experimental Examples 31 to 36.

[0069] (Experimental Examples 82 and 83) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 37 to 39, except that the isophorone diisocyanate was added in an amount according to Table 5 such that the NCO / OH equivalent ratio was 0.5 or 2.2.

[0070] (Example 84) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 40 and 41, except that the hydroxyl-containing silicon-modified acrylic polymer was not added.

[0071] (Example 85) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 40 and 41, except that the amount of the hydroxyl-containing silicon-modified acrylic polymer added was 1.5 parts by mass per 100 parts by mass of the fluorine polyol.

[0072] (Example 86) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 42 and 43, except that the hydroxyl-containing silicon-modified acrylic polymer was not added.

[0073] (Example 87) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 42 and 43, except that the amount of the hydroxyl-containing silicon-modified acrylic polymer added was 1.5 parts by mass per 100 parts by mass of the fluorine polyol.

[0074] (Example 88) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 44 and 45, except that the hydroxyl-containing silicon-modified acrylic polymer was not added.

[0075] (Example 89) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 44 and 45, except that the amount of the hydroxyl-containing silicon-modified acrylic polymer added was 2.5 parts by mass per 100 parts by mass of the fluorine polyol.

[0076] (Example 90) A surface layer-forming composition was obtained in the same manner as in Experimental Examples 47 and 48, except that the amount of the hydroxyl-containing silicon-modified acrylic polymer added was 1.5 parts by mass per 100 parts by mass of the fluorine polyol.

[0077] Regarding evaluation. In the surface layer forming composition produced by the above method, (1) the NCO / OH equivalent ratio of each blended composition was calculated by the following method, and (2) PET (polyethylene terephthalate) adhesion, (3) oil-based marker writing ability, (4) oil-based marker writing erasability, (5) oil-based marker writing cloth erasability, (6) oil-based ballpoint pen writing ability, (7) oil-based ballpoint pen writing erasability, and (8) oil-based ballpoint pen writing cloth erasability were evaluated by the following methods. The results of each experiment are shown in Tables 1 and 2 below together with the respective compositions.

[0078] (1) Calculation method for equivalent ratio of isocyanate group to hydroxyl group The equivalent ratio of isocyanate group / hydroxyl group was calculated by respectively calculating the molecular weight per one isocyanate group and the molecular weight per one hydroxyl group, and expressed as the ratio between them. The isocyanate group equivalent, which indicates the molecular weight per one isocyanate group, was calculated according to the following formula 1.

[0079]

number

[0080] In addition, since the hydroxyl value range of the polyols used in the present invention is known, the median value was used in the calculation as the hydroxyl value to determine the hydroxyl equivalent, which indicates the molecular weight per hydroxyl group, using the following formula 2. The hydroxyl values ​​of the polyols used in the calculation were 128 (TOKYD-25C) and 75 (NT-11NX), respectively.

[0081]

number

[0082] Here, the hydroxyl value of a polyol is a value expressed by the amount of potassium hydroxide (converted into mg) equivalent to the hydroxyl group contained in 1 g of polyol when the polyol is acetylated with acetic anhydride and the free acetic acid is quantified with potassium hydroxide. Note that the molecular weight of KOH is 56.1.

[0083] (2) PET (polyethylene terephthalate) adhesion This evaluation item evaluates the adhesion of the surface layer to the substrate. The composition of each experimental example was applied to a PET film (Torell Mirror S10, thickness 100 μm) using a No. 10 bar coder, and then heated in an oven at 150°C for 10 minutes. The obtained laminate was subjected to an adhesion test (cross-cut method; JIS K 5600-5-6:1999 General test method for paints - Part 5: Mechanical properties of coatings - Section 6). More specifically, a grid pattern (6 cuts, grid width 1 mm, 100 squares) was applied to the surface layer using a cutter knife. Cellophane adhesive tape (width 25 mm) was completely pressed onto this grid pattern, and the end of the tape was grasped at an angle of 60° and instantly pulled away in 0.5 to 1.0 seconds so as to be sure to pull it away. The state of the grid pattern was then visually confirmed.

[0084] The adhesion to PET was evaluated on a three-level scale according to the following criteria: ◎ (Good): The edges of the cut are completely smooth and there is no peeling on any of the grid cells. Good (pass): There is minor peeling of the coating at the intersections of the cuts. The cross-cut area affected does not appreciably exceed 5%. × (fail): The coating has peeled off along the edges of the cuts and / or at the intersections. More than 5% of the cross-cut area is clearly affected.

[0085] (3) Ability to write with oil-based marker The composition of each experimental example was applied to a PET film (Toray Mirror S10, 100 μm thick) using a No. 10 bar coder, and then heated in an oven at 150° C. for 10 minutes. After 24 hours, the film was written on with a permanent marker and the handwriting was visually evaluated. The permanent marker used in this experiment was Zebra's Mackie (registered trademark).

[0086] The writability was evaluated on a three-level scale according to the following criteria: ◎ (Good); I was able to write with oil-based ink without it repelling. ○ (passed): Less than 5% of the oil-based ink was repelled. × (Failed): More than 5% of the oil-based ink was repelled, or writing was not possible.

[0087] (4) Ability to erase oil-based marker marks The composition obtained in each experimental example was applied to a PET film (Toray Mirror S10, 100 μm thick) using a No. 10 bar coder, and then heated in an oven at 150°C for 10 minutes. After 24 hours, the film was written on with an oil-based marker, and after another 24 hours, the film was rubbed with a plastic eraser under specified conditions, and the handwriting was visually evaluated. The rub conditions were distance: 10 cm, speed: 10 round trips / 6 seconds, and load: 800 g.

[0088] The erasability was evaluated on a three-level scale according to the following criteria: ◎ (Good): Erased with less pressure and fewer reciprocations than the test conditions. 〇(Pass); Erased successfully. × (failed); could not be erased.

[0089] (5) Ability to erase ink marks from oil-based markers with cloth The composition obtained in each experimental example was applied to a PET film (Toray Mirror S10, 100 μm thick) using a No. 10 bar coder, and then heated in an oven at 150°C for 10 minutes. After 24 hours, the film was written on with a permanent marker, and after another 24 hours, the film was rubbed with a cloth under specified conditions, and the handwriting was visually evaluated. The conditions were: distance: 10 cm, speed: 10 round trips / 6 seconds, and load: 800 g. The erasability was evaluated in the same manner as the evaluation of erasability using the eraser. The cloth used in this experiment was 100% cotton cloth and tissue paper (Lorena, Nippon Paper Crecia Co., Ltd.).

[0090] (6) Writability with an oil-based ballpoint pen, (7) Erasability of marks left by the oil-based ballpoint pen, and (8) Erasability of marks left by the oil-based ballpoint pen on fabric were evaluated in the same manner as in the evaluation of the oil-based marker pen.

[0091] Tables 1 to 5 show the composition ratios and evaluation results of the experimental examples of the present invention. Table 1 shows experimental examples of alkyd polyol and various isocyanates. Table 2 shows experimental examples of fluorine polyol and various isocyanates, and hydroxyl-containing silicon-modified acrylic polymer is added to all except experimental example 31. Table 3 shows experimental examples of alkyd polyol and various isocyanates, and polyolefin wax is added to all except experimental example 31. The experimental examples shown in Tables 1 to 3 can be examples from the viewpoint of achieving both the writability of oil-based ink and the erasability by erasing or cloth. Table 4 shows experimental examples mainly of various polyols and various isocyanates. Only experimental example 75 has a composition that does not contain isocyanate. Table 5 shows experimental examples mainly of fluorine polyol and various isocyanates, and hydroxyl-containing silicon-modified acrylic polymer is added to all except experimental examples 84, 86, and 88.

[0092] [Table 1]

[0093] [Table 2]

[0094] [Table 3]

[0095] [Table 4]

[0096] [Table 5]

[0097] (Discussion of the experimental example) As shown in Tables 1 to 3 above, the compositions for forming a surface layer of Experimental Examples 1 to 60 passed the judgment results (◯ or ◎ symbol) for all evaluation items except for the evaluation item of the erasability of handwriting by oil-based marker and oil-based ballpoint pen on fabric. That is, all of the compositions for forming a surface layer of Experimental Examples 1 to 60 were excellent in both the writability with an oil-based ballpoint pen and oil-based marker and the erasability with an eraser, and further, were excellent in the adhesion of the surface layer to the substrate.

[0098] On the other hand, as shown in Tables 4 and 5, the compositions for forming a surface layer of Experimental Examples 61 to 90 failed (marked with x) in at least one of the seven evaluation items (2) to (8). More specifically, Experimental Examples 61 to 75, Experimental Examples 77, Experimental Examples 79 to 81, Experimental Examples 83, Experimental Examples 84, Experimental Examples 86, and Experimental Examples 88 failed at least the evaluation of (4) erasability of handwritten oil-based markers by erasing. In addition, among the Experimental Examples listed in Tables 4 and 5 that failed the evaluation of (4), the erasability of oil-based markers with a cloth was also failed. On the other hand, Experimental Examples 76, Experimental Example 78, Experimental Example 82, Experimental Example 85, Experimental Example 87, Experimental Example 89, and Experimental Example 90 that at least passed the evaluation of (4) erasability of handwritten oil-based markers by erasing, all of them failed at least the evaluation of (3) writability of oil-based markers. That is, all of the compositions for forming a surface layer in Experimental Examples 1 to 60 were superior to Experimental Examples 61 to 90 in the effect sought by the present invention, ie, in achieving both the writability of oil-based ink and erasability with an eraser or cloth.

[0099] Comparison of Experimental Examples 1 to 22 (all using alkyd polyol) with Experimental Example 72 (using silicon-modified fluorine polyol), Experimental Example 73 (using acrylic polyol 1), and Experimental Example 74 (using acrylic polyol 2) showed that the effects of the writability and erasability of the present invention are influenced by the type of polyol selected. According to these Experimental Examples, it was found that alkyd polyol is superior to silicon-modified fluorine polyol and acrylic polyol in terms of writability and erasability with an eraser, regardless of whether the isocyanate is pentamethylene diisocyanate, hexamethylene diisocyanate, xylene diisocyanate, or isophorone diisocyanate.

[0100] Furthermore, the results of Experimental Examples 1 to 18 (all of which used alkyd polyol 1) and Experimental Examples 19 to 22 (all of which used alkyd polyol 2) showed that any selected polyol was suitable.

[0101] Regarding the effect of NCO / OH equivalent ratio. As can be seen from the results of Experimental Examples 1 to 18 and Experimental Examples 61 to 68, when an alkyd polyol is used as the polyol, there is a suitable range for the NCO / OH equivalent ratio depending on the type of isocyanate selected.

[0102] From the results of Experimental Examples 1 to 3, 61 and 62, it is found that when 1,5-pentamethylene diisocyanate is selected as the isocyanate, the NCO / OH equivalent ratio is preferably 0.5 or more and 2.5 or less.

[0103] Similarly, the results of Experimental Examples 4 to 9, 63 and 64 show that when hexamethylene diisocyanate is selected as the isocyanate, the NCO / OH equivalent ratio is preferably 0.5 or more and 4.0 or less.

[0104] Similarly, the results of Experimental Examples 10 to 15, 65 and 66 show that when xylylene diisocyanate is selected as the isocyanate, the NCO / OH equivalent ratio is preferably 0.5 or more and 3.0 or less.

[0105] Furthermore, the results of Experimental Examples 16 to 18, 67 and 68 show that when isophorone diisocyanate is selected as the isocyanate, the NCO / OH equivalent ratio is preferably 0.4 or more and 2.2 or less.

[0106] Next, in Experimental Examples 23 to 48, in which a fluorine polyol was used as the polyol, any of pentamethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, or isophorone diisocyanate could be used as the isocyanate, and in any case of the isocyanate, in the composition in which a hydroxyl-containing silicon-modified acrylic polymer was added, both the writability of the oil-based ink and the erasability by the eraser were evaluated as pass or better. On the other hand, in Experimental Examples 69, 70, 71, 84, 86, and 88, in which a fluorine polyol was used but a hydroxyl-containing silicon-modified acrylic polymer was not added, the writability of the oil-based ink and the erasability by the eraser could not be achieved at the same time. In other words, when a fluorine polyol is used and the isocyanate is pentamethylene diisocyanate, hexamethylene diisocyanate or xylene diisocyanate, it was found that the addition of a hydroxyl group-containing silicon-modified acrylic polymer is essential to achieve both good writability and good erasability with an eraser.

[0107] Regarding the effect of NCO / OH equivalent ratio. Even when a fluorine polyol is used as the polyol, there is a suitable range for the NCO / OH equivalent ratio depending on the type of isocyanate selected, as can be seen from the results of Experimental Examples 23 to 39 and Experimental Examples 76 to 83. For example, the results of Experimental Examples 23 to 25 and Experimental Examples 76 and 77 show that when 1,5-pentamethylene diisocyanate is selected as the isocyanate, the NCO / OH equivalent ratio is preferably 0.5 or more and 2.2 or less.

[0108] Similarly, the results of Experimental Examples 26 to 30 and Experimental Examples 78 and 79 show that when hexamethylene diisocyanate is selected as the isocyanate, the NCO / OH equivalent ratio is preferably 0.5 or more and 2.0 or less.

[0109] Similarly, the results of Experimental Examples 31 to 36 and Experimental Examples 80 and 81 show that when xylylene diisocyanate is selected as the isocyanate, the NCO / OH equivalent ratio is preferably 0.65 or more and 2.5 or less.

[0110] Furthermore, the results of Experimental Examples 37 to 39, 82, and 83 show that when isophorone diisocyanate is selected as the isocyanate, the NCO / OH equivalent ratio is preferably 0.65 or more and 2.0 or less.

[0111] To summarize the above results, when a fluoropolyol is used as the polyol, it is shown that the NCO / OH equivalent ratio is preferably in the range of 0.65 or more and 2.0 or less.

[0112] Regarding the amount of hydroxyl-containing silicone modified acrylic polymer to be added. In addition, this experimental example shows that there is a suitable range for the amount of the hydroxyl-containing silicon-modified acrylic polymer added. For example, the results of experimental examples 40 and 41, and experimental examples 84 and 85 show that when 1,5-pentamethylene diisocyanate is selected as the isocyanate, the amount of the hydroxyl-containing silicon-modified acrylic polymer added is preferably in the range of 0.1 to 1.2 parts by mass per 100 parts by mass of the fluoropolyol.

[0113] Similarly, from the results of Experimental Examples 42 and 43 and Experimental Examples 86 and 87, it can be seen that when hexamethylene diisocyanate is selected as the isocyanate, the amount of hydroxyl-containing silicon-modified acrylic polymer added is preferably in the range of 0.1 parts by mass or more and 1.2 parts by mass or less per 100 parts by mass of the fluoropolyol.

[0114] Similarly, the results of Experimental Examples 44, 45, 88, and 89 show that when xylylene diisocyanate is selected as the isocyanate, the amount of hydroxyl-containing silicon-modified acrylic polymer added is preferably in the range of 0.1 parts by mass or more and 1.2 parts by mass or less per 100 parts by mass of the fluoropolyol.

[0115] Furthermore, the results of Experimental Examples 46 to 48 and Experimental Example 90 show that when isophorone diisocyanate is selected as the isocyanate, the amount of hydroxyl-containing silicon-modified acrylic polymer added is preferably in the range of 1.2 parts by mass or less per 100 parts by mass of fluorine polyol.

[0116] From the above results, it was found that the suitable range for the amount of hydroxyl-containing silicon-modified acrylic polymer to be added is from 0.1 to 1.2 per 100 equivalents of fluoropolyol.

[0117] Experimental Example 75 is an experimental example of a composition containing acrylic polyol and not containing isocyanate, and no polyurethane structure is formed in such a composition. In such an experimental example, the erasability of the handwriting of oil-based marker or oil-based ballpoint pen with an eraser or cloth was unacceptable. According to Experimental Example 75, it is considered that the polyurethane structure is essential for the composition according to the present invention. In the surface layer of Experimental Example 75, the surface layer itself is scraped off by the friction of an eraser or cloth, and the evaluation of PET adhesion is unacceptable, and as a result, the evaluation of erasability is also unacceptable. Therefore, it was concluded that a surface layer formed only by polyol is not suitable as a composition example of the present invention.

[0118] From the above, experimental examples that can achieve both the writability of oil-based markers and oil-based ballpoint pens and the erasability by erasing with an eraser have been described, but even in these experimental examples, it is difficult to achieve erasability with a cloth. For example, among the experimental examples in which alkyd polyol is used as the polyol, experimental examples 1, 3 to 5, 8 to 13, and 16 fail the erasability of the handwriting of oil-based markers or oil-based ballpoint pens with a cloth. In contrast, by adding polyolefin wax as an additive, it becomes possible to achieve both the writability of oil-based markers and oil-based ballpoint pens and the erasability by erasing with an eraser and a cloth.

[0119] From the results of Experimental Examples 49 to 60, all the evaluations were passed or better. In other words, when an alkyd polyol is used as the polyol and any of pentamethylene diisocyanate, hexamethylene diisocyanate, xylene diisocyanate, and isophorone diisocyanate is used as the isocyanate, by adding a polyolefin wax in a range of NCO / OH ratio of 1.2 to 2.0, it becomes possible to achieve both the writability of oil-based markers and oil-based ballpoint pens and the erasability and erasability by cloth. [Explanation of symbols]

[0120] 1. Surface material 11 Base material layer 12 Surface layer

Claims

1. A surface layer forming composition that contains at least an alkyd polyol and pentamethylene diisocyanate and forms a polyurethane structure, an equivalent ratio of isocyanate group / hydroxyl group is 0.5 or more and 2.5 or less; The composition for forming a surface layer forms a surface layer on which writing can be performed with an oil-based ink and on which written marks can be erased when rubbed with a plastic eraser.

2. A composition for forming a surface layer, comprising at least a polyol, an aliphatic or aromatic polyisocyanate, and a polyolefin wax, and forming a polyurethane structure, the polyol is an alkyd polyol, The polyisocyanate is selected from pentamethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and isophorone diisocyanate; an equivalent ratio of isocyanate group / hydroxyl group is 1.2 or more and 2.0 or less; The composition for forming a surface layer forms a surface layer on which writing can be done with oil-based ink, the written handwriting can be erased when rubbed with a plastic eraser, and the written handwriting can be erased with a cloth.

3. A composition for forming a surface layer, comprising at least a polyol, an aliphatic or aromatic polyisocyanate, and a silicon-modified acrylic polymer having a hydroxyl group, and forming a polyurethane structure, The polyol is a fluorine polyol, The polyisocyanate is selected from pentamethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and isophorone diisocyanate; an isocyanate group / hydroxyl group equivalent ratio of 0.65 or more and 2.0 or less; the amount of the silicon-modified acrylic polymer having a hydroxyl group added is 0.1 or more and 1.2 or less relative to 100 parts by mass of the fluorine polyol; The composition for forming a surface layer forms a surface layer on which writing can be performed with an oil-based ink and on which written marks can be erased when rubbed with a plastic eraser.

4. A surface layer formed from the composition for forming a surface layer according to claim 1 .

5. A surface material for writing on oil-based ink, comprising at least the surface layer according to claim 4.

Images