JP5772155B2 - Decorative sheet for steel plate and decorative steel plate using the same - Google Patents

Description

  The present invention relates to a decorative sheet for steel plate and a decorative steel plate using the same. More specifically, the decorative sheet for a steel sheet in which cracks are not generated in the outermost surface protective layer even when being bent, and the erasing performance as a white board using the decorative sheet for a steel sheet are improved, and the surface design property The present invention relates to a decorative steel sheet having excellent resistance.

  In order to impart a design to a steel plate, a sheet decorated with a polyester resin film such as a vinyl chloride resin film, an olefin resin film, or PET is laminated on the steel plate. In particular, a PET film laminated steel sheet has been proposed as having stain resistance, molding processability and high hardness (see Patent Document 1 and Claims). In addition, a decorative sheet for a steel sheet is proposed in which a pattern layer, a transparent adhesive layer, and a transparent polyester resin layer are sequentially laminated on a base material sheet made of polyolefin resin or polyester resin ( Patent Document 2).

The decorative sheet has high contamination resistance and high hardness, but has a problem that cracks are generated on the surface of the curved surface portion when the steel sheet is bent. When a polyester film such as PET is used, cracks hardly occur and a certain degree of workability is ensured, but there is a problem that resistance to scratches is low. In order to impart scratch resistance to PET or the like, there is a method of hard-coating the surface, but there is also a problem that cracks occur in the hard coat at the curved surface portion. When such a crack occurs, dirt accumulates in the crack portion, and the stain resistance decreases. In addition, when used around water, problems such as the occurrence of mold in the cracks occur, and when used in whiteboards, markers remain on the cracks and the marker erasability is significantly reduced. Problem arises.
In order to solve the above-mentioned problems, the present inventors do not crack in the curved surface part even when laminated and bent on a steel sheet, and have high formability and have stain resistance and scratch resistance. As a decorative sheet for a steel sheet, on a base material made of a biaxially stretched polyester film, a primer layer made of a urethane resin composition and a surface protective layer obtained by crosslinking and curing an ionizing radiation curable resin composition are laminated in this order. A decorative sheet was proposed (see Patent Document 3).

  By the way, as demand for steel sheet whiteboards using steel sheet decorative sheets increases, more stringent marker erasability is required, and at the same time, whiteboards are used in combination as projector reflective screens such as OHP and slides. Projectivity is required as a new performance. However, the decorative sheets for steel sheets described in Patent Documents 1 to 3 may not be able to sufficiently meet these performance requirements, and further improvements are required.

JP 2000-43192 A JP 2005-238498 A JP 2007-290382 A

  The present invention has been made under such circumstances, and as a white board formed using the decorative sheet for steel plate in which cracks are not generated in the outermost surface protective layer even when bent, and the decorative sheet for steel plate It is an object of the present invention to provide a decorative steel sheet that improves the erasing performance of the sheet and is excellent in surface design.

As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge.
An ionizing radiation curable resin (hereinafter sometimes referred to as EB resin) constituting the surface protective layer alone cannot provide sufficient erasing performance as a whiteboard, and an additive is used to reduce the surface energy. It is necessary to add.
Silicone resin, which is a typical additive, can achieve excellent marker erasability with a small amount of addition, but when using some overseas markers (using solvents that are less volatile than those made in Japan) There was a problem that the marker repelled.
In addition, blending with a resin system (clear resin) that does not use a filler in the EB resin makes the silicone resin easy to lift and the surface becomes cocoon-skinned, which is not preferable in appearance, and the environment during production (temperature, humidity) Etc.) and the surface design is not stable.
As a result of further research to solve such problems, whiteboard marker writing erasability and surface design can be achieved by adding a resin having an acrylic skeleton as a leveling agent to the EB resin at a specific ratio. It discovered that the decorative sheet for steel plates excellent in stability was obtained. The present invention has been completed based on such findings.

That is, the present invention
[1] A decorative sheet for steel sheet having at least a primer layer and a surface protective layer in this order on a substrate, wherein the substrate is composed of a biaxially stretched polyester film, the primer layer is composed of a urethane resin composition, and the surface The protective layer is a crosslinked cured product of the ionizing radiation curable resin composition,
(1) The surface protective layer contains a resin having an acrylic skeleton as a leveling agent at a ratio of 0.1 to 4.0 parts by mass with respect to 100 parts by mass of the ionizing radiation curable resin.
(2) At least one selected from (meth) acrylic acid hydroxyalkyl esters and aromatic vinyl compounds, which contains a (meth) acrylic acid alkyl ester having no hydroxy group as a structural unit of the resin having an acrylic skeleton. A decorative sheet for a steel sheet comprising poly (meth) acrylate, and [2] a decorative steel sheet having the decorative sheet for a steel sheet according to [1] above on the steel sheet,
Is to provide.

  ADVANTAGE OF THE INVENTION According to this invention, the decorative sheet for steel plates which a crack does not generate | occur | produce in the outermost surface protective layer, and the makeup | decoration performance which improves the erasing performance as a white board which uses this decorative sheet for steel plates, and is excellent in surface design property A steel plate can be provided.

It is a cross-sectional schematic diagram which shows an example of a structure of the decorative sheet for steel plates of this invention.

First, the decorative sheet for steel plate of the present invention will be described.
[Coating sheet for steel sheet]
The decorative sheet for steel sheet of the present invention is a decorative sheet for steel sheet having at least a primer layer and a surface protective layer in this order on a base material, the base material is made of a biaxially stretched polyester film, and the primer layer is a urethane resin. Comprising a composition, the surface protective layer is a cross-linked cured product of an ionizing radiation curable resin composition,
(1) The surface protective layer contains a resin having an acrylic skeleton as a leveling agent at a ratio of 0.1 to 4.0 parts by mass with respect to 100 parts by mass of the ionizing radiation curable resin.
(2) At least one selected from (meth) acrylic acid hydroxyalkyl esters and aromatic vinyl compounds, which contains a (meth) acrylic acid alkyl ester having no hydroxy group as a structural unit of the resin having an acrylic skeleton. It is poly (meth) acrylate containing.

  The decorative sheet for steel plate of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a decorative sheet for steel sheet (hereinafter sometimes simply referred to as “decorative sheet”) according to the present invention. In addition, a surface protective layer 4 is provided via the intermediate layer 2 and the primer layer 3 that are sequentially provided, and a film 5 constituting a concealing layer is provided on the back side of the substrate 1 via the adhesive layer 6. Have a structure.

(Base material)
The base material 1 in the decorative sheet 20 of the present invention comprises at least a biaxially stretched polyester film. The polyester resin used here is not particularly limited, and those usually used in the field of decorative sheets can be used. Examples thereof include polyethylene terephthalate (hereinafter sometimes referred to as “PET”), polybutylene terephthalate, polyethylene naphthalate, polyarylate, polycarbonate, ethylene terephthalate-isophthalate copolymer, polyarylate, and the like. Among these, polyethylene terephthalate, polybutylene terephthalate, and the like are preferable, and polyethylene terephthalate is particularly preferable.

  As the polyester resin, in addition to various homopolymers, copolymerized polyester resins and polyester thermoplastic elastomers to which various copolymerization components or modifying components are added for the purpose of softening the resin can be used. For example, in the case of PET, in the condensation polymerization reaction of terephthalic acid and ethylene glycol, as the dicarboxylic acid component, for example, long-chain aliphatic dicarboxylic acids such as sebacic acid, eicoic acid, dodecanedioic acid, dimer acid, cyclohexanedicarboxylic acid, and the like / Or an alicyclic dicarboxylic acid can be introduced. In addition, polyether diols having hydroxyl groups at both ends, such as polyethylene glycol and polytetramethylene glycol, can be introduced as the diol component.

In the present invention, the polyester film used as the substrate 1 is prepared by, for example, forming a film by a calendar method, an inflation method, a T-die extrusion method, or the like, and biaxially stretching.
By using a biaxially stretched polyester resin film as the substrate 1, it is possible to suppress the elongation of the surface protective layer 4 described in detail later, and to suppress the occurrence of cracks in the surface protective layer 4.

The thickness of the substrate 1 is not particularly limited and can be set as appropriate according to product characteristics, but a range of 25 to 100 μm is preferable. When the thickness of the substrate 1 is in the range of 25 to 100 μm, the tension applied to the surface protective layer 4 can be sufficiently relaxed.
The biaxially stretched polyester resin film used for the substrate 1 preferably has a tensile strength measured in accordance with JIS C2151 of 150 MPa or more.
When the tensile strength is 150 MPa or more, since it is highly rigid, local elongation generated in the bent portion can be suppressed, and extension of the upper surface protective layer can also be suppressed.

  The polyester resin used for the substrate 1 may be blended with additives as necessary. Examples of the additive include a filler, a flame retardant, an antioxidant, a lubricant, a foaming agent, a colorant, an ultraviolet absorber, and a light stabilizer.

Among the above additives, calcium carbonate and sulfuric acid are particularly used from the viewpoint of improving the elasticity and elongation of the substrate 1, imparting impact resistance, and not causing cracks or cracks in the surface protective layer when subjected to bending. It is preferable to contain inorganic fillers such as barium, clay and talc.
The content of these inorganic fillers is preferably in the range of 5 to 60% by mass with respect to the substrate 1.

Moreover, it does not specifically limit as said coloring agent, Well-known coloring agents, such as a pigment and dye, can be used. The coloring of the substrate 1 includes transparent coloring and opaque coloring (hiding coloring), and these can be arbitrarily selected.
Moreover, about a ultraviolet absorber and a light stabilizer, the thing similar to what can be added to the resin composition which comprises the surface protective layer 4 of this invention explained in full detail later can be used.

  The base material 1 can be subjected to physical or chemical surface treatment such as an oxidation method or a concavo-convex method on one side or both sides as desired in order to improve adhesion with other layers. The surface treatment method is appropriately selected according to the type of the substrate 1, but in general, the corona discharge treatment method is preferably used from the viewpoints of effects and operability.

In the decorative sheet 20 for steel sheet of the present invention, on the back side of the base material 1 made of the above-described biaxially stretched polyester film, in addition to the concealing effect as necessary, further concealment is performed for the purpose of reducing foreign matter defects during the lamination of the steel sheet. The laminated film 10 may be formed by providing the film 5 constituting the layer via the adhesive layer 6.
This concealing layer can be formed in order to stabilize the concealing property even when the substrate 1 is transparent and when the substrate 1 is concealed and colored.
It does not specifically limit as a material of the film 5 which comprises the said concealment layer, A vinyl chloride resin film, an olefin film, a polyester film etc. can be used. Among these, from the viewpoint of suppressing the occurrence of cracks in the surface protective layer 4, it is preferable to use a polyester film such as a biaxially stretched PET film similar to the substrate 1. In consideration of concealability, design properties, cushioning properties, and environment, an olefin film, particularly a polypropylene film is preferable.

The film 5 constituting the concealing layer usually contains a colorant in order to exhibit the function as the concealing layer. The kind of the colorant is not particularly limited, and the same colorant as that which can be used for coloring the substrate 1 can be used.
Although there is no restriction | limiting in particular as thickness of the film 5 which comprises the said concealment layer, The range of 25-100 micrometers is preferable. When the thickness is 25 μm or more, a sufficient hiding effect is obtained, and when the thickness is 100 μm or less, the surface protective layer 4 is not extended more than necessary due to the curvature, and the generation of cracks can be further suppressed.

There is no restriction | limiting in particular as a material used for the adhesive bond layer 6, A well-known adhesive can be used in the field of a decorative sheet. Specific examples thereof include thermoplastic resins such as polyamide resin, acrylic resin and vinyl acetate resin, and curable resins such as thermosetting urethane resin. Further, a two-component curable polyurethane resin or polyester resin using isocyanate as a curing agent can also be applied. Among these, a thermoplastic resin is preferable because it functions as a cushion layer and has an effect of suppressing cracks in the surface protective layer 4 during processing of the decorative steel sheet.
Although there is no restriction | limiting in particular in the thickness of the adhesive bond layer 6, Usually, the thickness after drying is the range of 3-50 micrometers.

(Primer layer)
The decorative sheet 20 of the present invention has a primer layer 3 made of a urethane resin composition. The urethane-based resin composition has flexibility, toughness, and elasticity, and bending workability is improved by providing the soft primer layer 3 using such a urethane-based resin composition. That is, the impact, tensile force or shearing force applied to the surface protective layer 4 during bending can be alleviated, and the occurrence of cracks in the surface protective layer 4 can be suppressed. From these viewpoints, the primer layer 3 is preferably a layer adjacent to the surface protective layer 4.
The urethane-based resin composition used here preferably has an elongation of 300% or more in standard temperature state class 2 (23 ± 2 ° C.) defined in JIS K7100, measured according to JIS K6732. When the elongation is 300% or more, the impact, tensile force or shear force applied to the surface protective layer 4 during bending can be sufficiently relaxed. From the above viewpoint, the elongation is more preferably 400% or more, and further preferably 500% or more. Further, the glass transition point (Tg) is −20 ° C. or less from the viewpoint of imparting bending workability at low temperatures in addition to the necessary and sufficient flexibility, toughness and elasticity of the decorative sheet for steel plate. Is preferred.

As urethane-type resin, what satisfies said elongation rate and Tg is preferable, and it can select from conventionally well-known urethane-type resin. For example, a urethane-based resin that does not have a cross-linked structure and that has a structure in which the skeleton structure is linear or branched is preferable. A saturated thermoplastic urethane resin having no isocyanate group is also preferred in that it is not cured by moisture or the like and has good stability over time.
On the other hand, when water resistance is particularly required, a urethane resin having a crosslinked structure to some extent while satisfying the above-described elongation rate and Tg is suitable. When particularly toughness is required, polyester urethane or polycarbonate Urethane is preferred.

As a specific example of such a urethane resin, a urethane resin composed of a linear polymer obtained by reacting a polyol having a hydroxyl group at the terminal and a polyisocyanate can be given.
As the polyol used here, a known polyol can be used, and examples thereof include polyester polyol, polyether polyol, polyalkylene polyol, and polycarbonate polyol.

Polyester polyol is obtained by reaction of polyvalent carboxylic acid and polyol. Examples of polyvalent carboxylic acid include terephthalic acid, isophthalic acid, 1,5-naphthalic acid, 2,6-naphthalic acid, oxalic acid, glutaric acid, Examples include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decamethylene dicarboxylic acid, and dodecamethylene dicarboxylic acid. Examples of the polyol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4- Examples include butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, and cyclohexanediol. The polyvalent carboxylic acid and the polyol may be used alone or in a mixture of two or more.
Polyester such as poly (ethylene adipate), poly (butylene adipate), poly (neopentyl adipate), poly (hexamethylene adipate), poly (butylene azelate), poly (butylene sebacate), polycaprolactone, etc. Diols are mentioned.

  Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Examples of the polyalkylene polyol include polybutadiene polyol, hydrogenated polybutadiene polyol, and hydrogenated polyisoprene polyol.

Moreover, as a polycarbonate polyol, 1 type or 2 or more types of alkylene diol which has a C4-C12 alkylene group, a low molecular carbonate compound (For example, C1-C6 dialkyl carbonate of an alkyl group, C2-C2). Polycarbonate diol produced by condensation from an alkylene carbonate having 6 alkylene groups and a diaryl carbonate having 6 to 9 carbon atoms aryl group). Specifically, polybutylene carbonate polyol, polyhexamethylene carbonate polyol, polycyclohexane dimethylene carbonate polyol and the like can be mentioned.
These polyols described above may be used alone or in combination of two or more in the reaction with the isocyanate compound.

Examples of the diisocyanate component include various aliphatic (or alicyclic) or aromatic diisocyanates conventionally known in the polyurethane field. For example, aliphatic (or alicyclic) systems include aliphatic isocyanates such as 1,6-hexamethylene diisocyanate, alicyclic isocyanates such as isophorone diisocyanate and hydrogenated tolylene diisocyanate, and 2,4-tolylene diisocyanate. 2,6-tolylene diisocyanate, xylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate and other aromatic isocyanates. These can be used alone or in combination of two or more.
As described above, the urethane resin used in the present invention is most preferably an urethane polycarbonate obtained by a reaction between a polycarbonate polyol and a diisocyanate, and a polyester urethane obtained by a reaction between a polyester polyol and a diisocyanate.

Further, the primer layer 3 may contain a colorant such as a pigment which will be described later as long as the effects of the present invention are not impaired. For example, it is preferable that about 1 to 7 parts by mass of pigment fine particles having an average particle diameter of about 1 to 10 μm are included with respect to 100 parts by mass of the resin component. When it contains a pigment, it is preferable from the point of being more excellent in the concealment effect, but when it does not contain a pigment, it is more preferable at the point that generation | occurrence | production of the crack by absorbing the water | moisture content in air is suppressed.
In addition, in order to suppress blocking in the production process of the decorative sheet, the primer layer 3 can also contain silica. Although it does not restrict | limit especially as content of a silica in the range which can prevent blocking property, Usually, it is about 0.5-10 mass%.
Further, the primer layer 3 may contain an ultraviolet absorber as long as the effects of the present invention are not impaired. When an ultraviolet absorber is included, it is desirable from the viewpoint of preventing discoloration of the surface over time.
Preferred examples of the ultraviolet absorber include benzophenone compounds, benzotriazole compounds, benzoate compounds, and triazine compounds.

Although there is no restriction | limiting in particular about the thickness of the primer layer 3, The range of 0.5-10 micrometers is preferable. When the thickness is 0.5 μm or more, the impact, tensile force, or shear force applied to the surface protective layer 4 during bending can be reduced, and the occurrence of cracks in the surface protective layer 4 can be suppressed. Further, when it is 10 μm or less, blocking can be suppressed in the production process of the decorative sheet 20, and when the printing surface comes into contact with the guide roll that leads the printing paper, the printing ink is transferred to the guide roll. There is no such inconvenience. From the above points, the thickness of the primer layer 3 is more preferably in the range of 1 to 5 μm.
The coating weight of the urethane resin composition for forming the primer layer 3 is usually in the range of 0.5 to 10 g / m ^2, more preferably from 1 to 5 g / m ^2.

(Middle layer)
In the present invention, an intermediate layer 2 may be provided between the substrate 1 and the primer layer 3 as desired. In particular, in order to impart high elongation to the primer layer 3 as a soft primer layer, it is preferable to provide the intermediate layer 2 as a colored layer when it does not contain a colorant such as a pigment.
Although the resin composition used for the intermediate | middle layer 2 is not limited, It is preferable that it is a urethane type resin composition. Moreover, a coloring agent can be contained. The colorant is not particularly limited, and examples thereof include the same ones that can be used for coloring the substrate 1 and carbon black.

In the case where the intermediate layer 2 is provided as a colored layer, particularly as a white layer on the entire surface, an inorganic pigment such as titanium white (titanium oxide) is preferable among the above colorants. These inorganic pigments have a high effect of concealing the base, and also have an effect of cutting off ultraviolet rays. Furthermore, there is an effect of preventing blocking in the production process of the decorative sheet 20.
In the present invention, the intermediate layer 2 is preferably an entire white layer made of a urethane resin composition containing an inorganic pigment such as titanium white. In this case, the content of the inorganic pigment is preferably in the range of 5 to 300 parts by mass with respect to 100 parts by mass of the urethane resin. The effect as an inorganic pigment can fully be exhibited as it is 5 mass parts or more. On the other hand, when the content of the inorganic pigment is too large, the elongation rate of the urethane-based resin composition is decreased. However, if it is 300 parts by mass or less, sufficient toughness is maintained even if the elongation rate is decreased.
The particle size of the inorganic pigment is preferably 5 μm or less. If it is 5 μm or less, there is no problem that cracks are generated starting from the inorganic particles. From the above points, the particle size is preferably 2 μm or less.

Although there is no restriction | limiting in particular about the thickness of the intermediate | middle layer 2, The range of 0.5-10 micrometers is preferable and the range of 1-5 micrometers is more preferable.
The coating amount of the resin composition forming the intermediate layer 2 is usually in the range of 0.5 to 10 g / m ^2, more preferably from 1 to 5 g / m ^2.

(Pattern pattern layer)
In the decorative sheet 20 of the present invention, a pattern layer is provided between the substrate 1 and the intermediate layer 2, or between the intermediate layer 2 and the primer layer 3, or between the substrate 1 and the film 5 constituting the concealing layer. It may be provided (not shown). The design pattern layer imparts design properties with a desired design to the decorative sheet 20 and the decorative steel plate, and the type of the design is not particularly limited.
The method of forming the pattern layer is not particularly limited. For example, a colored ink obtained by dissolving (or dispersing) a known colorant (dye or pigment) in a solvent (or dispersion medium) together with a known binder resin. It may be formed by a printing method using a coating agent or the like.
Examples of the printing method used for forming the pattern layer include known various printing methods and various coating methods.
The thickness of the pattern layer is not particularly limited, and can be set as appropriate according to product characteristics, but the layer thickness after drying is about 0.1 to 10 μm.

(Surface protective layer)
In the decorative sheet 20 for steel sheet of the present invention, the surface protective layer 4 provided on the primer layer 3 described above is a cross-linked cured product of an ionizing radiation curable resin composition, and a resin having an acrylic skeleton as a leveling agent, It is contained at a ratio of 0.1 to 4.0 parts by mass with respect to 100 parts by mass of the ionizing radiation curable resin.
Here, the leveling agent refers to an additive added to the ionizing radiation curable resin composition in order to lower the surface energy of the surface protective layer, and the ionizing radiation refers to polymerizing molecules or electromagnetic waves or charged particle beams. It means that it has energy quanta that can be cross-linked, and usually ultraviolet (UV) or electron beam (EB) is used, but other electromagnetic waves such as X-rays and γ-rays, and charged particle beams such as α-rays and ion rays are also used. It can be used. The ionizing radiation curable resin composition refers to a resin composition that is crosslinked and cured by irradiation with the ionizing radiation. Specifically, it can be appropriately selected from polymerizable monomers, polymerizable oligomers, or prepolymers conventionally used as ionizing radiation curable resins.

  In the decorative sheet 20 for a steel sheet of the present invention, the average number of functional groups of the ionizing radiation curable resin in the ionizing radiation curable resin composition is preferably 3.1 to 4.5. If the average number of functional groups is 3.1 or more, sufficient crosslinking and curing will proceed, and the surface properties of the decorative sheet for metal plates, specifically, the stain resistance will be good. On the other hand, when the average number of functional groups is 4.5 or less, excellent processability can be obtained while maintaining the above surface physical properties.

<Ionizing radiation curable resin>
The ionizing radiation curable resin refers to a resin having an energy quantum capable of crosslinking and polymerizing molecules in an electromagnetic wave or a charged particle beam, that is, a resin that is crosslinked and cured by irradiation with ultraviolet rays or electron beams. Specifically, it can be appropriately selected from polymerizable monomers, polymerizable oligomers, or prepolymers conventionally used as ionizing radiation curable resins.
Typically, a (meth) acrylate monomer having a radical polymerizable unsaturated group in the molecule is suitable as the polymerizable monomer, and among them, a polyfunctional (meth) acrylate is preferable. Here, “(meth) acrylate” means “acrylate or methacrylate”, and other similar ones have the same meaning. The polyfunctional (meth) acrylate is not particularly limited as long as it is a (meth) acrylate having two or more ethylenically unsaturated bonds in the molecule. These polyfunctional (meth) acrylates may be used singly or in combination of two or more.

Next, as the polymerizable oligomer, an oligomer having a radical polymerizable unsaturated group in the molecule, for example, epoxy (meth) acrylate, urethane (meth) acrylate, polyester (meth) acrylate, polyether (meth) acrylate The system etc. are mentioned.
Furthermore, other polymerizable oligomers include polybutadiene (meth) acrylate oligomers with high hydrophobicity that have (meth) acrylate groups in the side chain of polybutadiene oligomers, and silicone (meth) acrylate oligomers that have polysiloxane bonds in the main chain. In a molecule such as an aminoplast resin (meth) acrylate oligomer modified with an aminoplast resin having many reactive groups in a small molecule, or a novolak epoxy resin, bisphenol epoxy resin, aliphatic vinyl ether, aromatic vinyl ether, etc. There are oligomers having a cationic polymerizable functional group.

  In the present invention, a monofunctional (meth) acrylate can be appropriately used in combination with the polyfunctional (meth) acrylate and the like within a range that does not impair the object of the present invention, for the purpose of reducing the viscosity. . These monofunctional (meth) acrylates may be used alone or in combination of two or more.

  Moreover, it is preferable that the number average molecular weights (number average molecular weight of standard polystyrene conversion measured by GPC method) of ionizing radiation curable resin are 1000-10000, and 2000-10000 are more preferable. When the number average molecular weight is within the above range, the processability is excellent, and the coating agent composition has an appropriate thixotropy, so that the surface protective layer can be easily formed.

<Initiator for photopolymerization>
When an ultraviolet curable resin composition is used as the ionizing radiation curable resin composition, it is desirable to add about 0.1 to 5 parts by mass of the photopolymerization initiator with respect to 100 parts by mass of the resin composition. The initiator for photopolymerization can be appropriately selected from those conventionally used and is not particularly limited.

In the present invention, it is preferable to use an electron beam curable resin composition as the ionizing radiation curable resin composition. This is because the electron beam curable resin composition can be made solvent-free, is more preferable from the viewpoint of environment and health, and does not require a photopolymerization initiator and can provide stable curing characteristics.
Moreover, in the decorative sheet for steel plates of this invention, it is preferable to contain an isocyanate type hardening | curing agent in an ionizing radiation curable resin composition. By containing an isocyanate curing agent, the adhesion with the primer layer 3 is improved, and further the adhesion between the ionizing radiation curable resin compositions is improved. Further, it is possible to suppress deterioration in performance such as excellent stain resistance and scratch resistance.
As the isocyanate curing agent used here, hexamethylene diisocyanate HMDI curing agent is preferable. Further, similarly to the primer layer 3 described above, a terminal isocyanate prepolymer is also preferable, and a urethane polycarbonate is more preferable. By using these, adhesiveness with the primer layer 3 becomes higher.

<Leveling agent>
In the decorative sheet 20 for steel sheet of the present invention, the leveling agent contained in the surface protective layer 4 has excellent writing erasability, in particular, repeat erasability, when the decorative sheet 20 for steel sheet is used as a whiteboard decorative sheet for steel sheet. Used to impart surface design stability.
In the present invention, the leveling agent is a resin having an acrylic skeleton, and includes, as a structural unit, a (meth) acrylic acid alkyl ester having no hydroxy group, and a (meth) acrylic acid hydroxyalkyl ester and fragrance. A poly (meth) acrylate containing at least one selected from the group vinyl compounds is used.

The alkyl group of the (meth) acrylic acid alkyl ester having no hydroxy group may be linear, branched or cyclic, and the alkyl group preferably has 1 to 10 carbon atoms. Specific examples of the (meth) acrylic acid alkyl ester having no hydroxy group include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, and tert-butyl acrylate. Acrylates such as cyclohexyl acrylate, 2-ethylhexyl acrylate, and octyl acrylate, and the corresponding methacrylates.
In the present invention, the structural unit of the resin having an acrylic skeleton is selected from (meth) acrylic acid hydroxyalkyl esters and aromatic vinyl compounds in addition to the hydroxy group-free (meth) acrylic acid alkyl esters. Including at least one.

In the present invention, as the (meth) acrylic acid hydroxyalkyl ester which is a structural unit of a resin having an acrylic skeleton, those having a hydroxyalkyl group having 1 to 10 carbon atoms are preferable, and a hydroxyalkyl group having 1 to 5 carbon atoms. It is more preferable to have Specific examples of the hydroxyalkyl ester of (meth) acrylic acid having a C1-C10 hydroxyalkyl group include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 3 Examples thereof include acrylates such as -hydroxybutyl acrylate and 4-hydroxybutyl acrylate, and methacrylates corresponding thereto.
Examples of the aromatic vinyl compound that is a structural unit of a resin having an acrylic skeleton include styrene and α-methylstyrene.

  In this invention, it is preferable not to have an unsaturated fatty acid, a polyether component, and a polyhydric alcohol component as a structural unit of resin which has an acrylic skeleton. This is because if these unsaturated fatty acids, polyether components and / or polyhydric alcohol components are contained, the erasability is lowered due to the affinity with the whiteboard marker.

In the present invention, the number average molecular weight of the resin (poly (meth) acrylate) having an acrylic skeleton used as a leveling agent is 1,000 to 20,000 from the viewpoint of improving marker writing property, marker erasability and repeated erasability. It is preferable that it exists in the range, and it is more preferable that it exists in the range of 1,500-13,000.
In addition, the said number average molecular weight is a value of standard polystyrene conversion measured by a gel permeation chromatography (GPC) method.
The content of the leveling agent in the surface protective layer 4 is ionizing radiation curable from the viewpoint of marker erasability and repeated erasability when the steel sheet decorative sheet 20 of the present invention is used as a steel sheet whiteboard decorative sheet. It is required to be 0.1 to 4.0 parts by mass with respect to 100 parts by mass of the resin, and preferably 0.2 to 2.0 parts by mass.

Various additives can be blended in the ionizing radiation curable resin composition in the present invention according to the desired physical properties of the surface protective layer 4 to be formed. Examples of the additive include a weather resistance improver, an abrasion resistance improver, a polymerization inhibitor, a crosslinking agent, an infrared absorber, an antistatic agent, an adhesion improver, a thixotropic agent, a coupling agent, and a plasticizer. , Antifoaming agents, fillers, solvents, colorants and the like.
Here, as the weather resistance improving agent, an ultraviolet absorber or a light stabilizer can be used. Examples of ultraviolet absorbers include benzotriazole ultraviolet absorbers and triazine ultraviolet absorbers. On the other hand, examples of the light stabilizer include hindered amines.

In the present invention, the crosslinked cured product of the ionizing radiation curable resin composition constituting the surface protective layer has a breaking elongation measured by a tensile test under the following conditions of 25 to 45%, which improves the steel sheet bending workability. It is preferable from a viewpoint to make it, More preferably, it is 30 to 35%.
Here, the tensile test method is to apply and cure the ionizing radiation curable resin composition to a thickness of 3.5 μm on a polypropylene film having a thickness of 90 μm, and then tensile at a temperature of 25 ° C. and a pulling speed of 50 mm / min. This is a method of measuring the elongation at the time of breaking by performing a test. As curing conditions, conditions for complete curing may be selected according to the ionizing radiation resin used. Complete curing means a state in which all ionizing radiation reactive groups in the ionizing radiation curable resin have reacted and the ionizing radiation curable resin has been completely cured. As an apparatus used for the tensile test, for example, “RTC-1250A” manufactured by ORIENTEC can be used.

<Formation of surface protective layer>
The above-mentioned polymerizable monomer or polymerizable oligomer that is an electron beam curable resin, a resin (poly (meth) acrylate) having an acrylic skeleton that is a leveling agent, and various additives are uniformly mixed at a predetermined ratio, respectively. A coating solution comprising a linear curable resin composition is prepared. The viscosity of the coating solution is not particularly limited as long as it is a viscosity capable of forming an uncured resin layer on the surface of the substrate by a coating method described later.
In the present invention, the coating solution prepared in this way is applied to the surface of the primer layer 3 provided on the substrate so that the thickness after curing is about 1 to 20 μm. , Roll coating, reverse roll coating, comma coating and the like, preferably gravure coating, to form an uncured resin layer.
The preferable film thickness after curing is appropriately determined in the range of 1 to 20 μm according to the type of resin used. When the resin composition is composed of a hard system, the relatively thin film thickness is less likely to cause cracks in the surface protective layer. Conversely, when the resin composition is a soft system, the film thickness is relatively thick. Cracks in the surface protective layer are unlikely to occur.

The uncured resin layer formed as described above is irradiated with an electron beam to cure the uncured resin layer. The acceleration voltage can be appropriately selected according to the resin to be used and the thickness of the layer, but it is preferable to cure the uncured resin layer at an acceleration voltage of about 70 to 300 kV.
In electron beam irradiation, the transmission capability increases as the acceleration voltage increases. Therefore, when using a base material that deteriorates due to the electron beam as the base material, the transmission depth of the electron beam and the thickness of the resin layer are substantially equal. By selecting the accelerating voltage so as to be equal to each other, it is possible to suppress the irradiation of the electron beam to the base material, and to minimize the deterioration of the base material due to the excessive electron beam.
The irradiation dose is preferably an amount that saturates the crosslink density of the resin layer, and is usually selected in the range of 5 to 300 kGy.

  The electron beam source is not particularly limited, and for example, various electron beam accelerators such as a Cockloft Walton type, a bandegraft type, a resonant transformer type, an insulated core transformer type, a linear type, a dynamitron type, and a high frequency type are used. be able to.

The surface protective layer thus formed has various functions by adding various additives, for example, a so-called hard coat function, anti-fogging coat function, and anti-fouling coat having high hardness and scratch resistance. A function, an antiglare coating function, an antireflection coating function, an ultraviolet shielding coating function, an infrared shielding coating function, and the like can also be imparted.
The decorative sheet 20 for steel sheet of the present invention is excellent in that cracks are not generated in the outermost surface protective layer even when the sheet is bent, and the surface protective layer contains a leveling agent made of a resin having an acrylic skeleton. It becomes suitable as a whiteboard decorative sheet for steel sheet to which writing erasability, particularly repetitive erasability and surface design stability are imparted.

Next, the decorative steel sheet of the present invention will be described.
[Decorative steel plate]
The decorative steel sheet of the present invention has the decorative sheet 20 of the present invention described above on the steel sheet. Examples of the steel plate to be adhered include metal materials such as iron, aluminum, and copper, and these may be subjected to surface treatment such as hot dip galvanizing or electrogalvanizing. Moreover, the shape of a to-be-adhered body is not specifically limited, For example, shapes, such as a flat plate, a curved surface board, a polygonal column, can be employ | adopted arbitrarily.
Moreover, there is no restriction | limiting in particular about the thickness of a steel plate, Usually, it is about 0.2-1 mm. In addition, in order to give the steel plate which is a to-be-adhered body concealment property, you may provide a coating layer by coloring directly to a steel plate.

The adhesive or pressure-sensitive adhesive used for laminating the decorative sheet 20 on the steel plate as the adherend is not particularly limited, and any adhesive or pressure-sensitive adhesive known in the field of decorative sheets can be used. As an adhesive agent, the thing similar to what is used with the adhesive bond layer 6 for adhere | attaching the film 5 which comprises a concealment layer can be used. Further, as the pressure-sensitive adhesive, an acrylic, urethane-based, silicone-based, rubber-based or the like can be appropriately selected and used. Among these, from the viewpoint of weather resistance and the like, an acrylic pressure-sensitive adhesive mainly composed of a polymer or copolymer of an acrylic monomer such as acrylic acid ester or methacrylic acid ester is preferable, and in particular, n-butyl acrylate, 2- Ethylhexyl acrylate and the like are suitable.
Moreover, a crosslinking agent can also be added and specifically, an isocyanate type, a metal chelate, an epoxy type, and a melamine type are mentioned.
Although there is no restriction | limiting in particular about the thickness of this adhesive agent or an adhesive, Usually, it is the range of 1-100 micrometers.

  The decorative steel sheet to which the decorative sheet 20 of the present invention is attached is suitably used for, for example, a whiteboard or a wall surface of a unit bath that is easily soiled, which requires excellent marker erasure and repeated erasability. From the viewpoint of effectively utilizing the features, it is particularly preferable to be used for a whiteboard. In addition, for building interior materials such as walls and ceilings, surface materials for fittings such as doors, door frames and window frames, surface materials for construction parts such as skirts and skirting boards, surface materials for furniture such as fences and cabinets, etc. Can also be used. Further, the decorative sheet itself can be used as a laminate material, a wrapping material, or the like for a building material member without using a steel plate as an adherend. For example, the decorative sheet 20 of the present invention may be attached to the surface of a steel plate substrate used in a bathroom or the like for decoration.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by this example.
<Evaluation method of decorative sheet>
(1) Surface design property The surface design of the decorative sheet was determined according to the following criteria.
○: The surface state is smooth and the surface design is excellent.
Δ: The surface is slightly crumpled, but the surface design is not impaired.
X: The surface becomes crusty and greatly impairs the surface design. (2) Marker writing ability (repellency)
Using “Expo Low Order Bold Black” manufactured by Sanford as a whiteboard marker and drawing on the surface of the decorative sheet, the degree of marker repelling is determined according to the following criteria.
○: Marker does not flip on the decorative sheet ×: Marker flips on the decorative sheet (3) Marker erasability As a whiteboard marker, “Whiteboard Marker Knockle Bold Round Core Black” manufactured by Pentel Co., Ltd. is used. After drawing on the sheet surface, it is dried in a room temperature environment for 24 hours. Next, “magnet eraser” manufactured by Magex Co., Ltd. is used as an eraser, and the remaining state of the marker after erasing twice with a load of 20 g / cm ^{2 is} determined according to the following criteria.
◎: Marker remaining rate on decorative sheet less than 5% ○: Marker remaining rate on decorative sheet is from 5% to less than 10% △: Marker remaining rate on decorative sheet is from 10% to less than 50% ×: Those with a marker remaining rate of 50% or more on the decorative sheet (4) Repeatable erasability As a whiteboard marker, “Whiteboard Marker Knockle Bold Round Core Black” made by Pentel Co., Ltd. is used for drawing on the decorative sheet surface. After drying for 1 minute in a room temperature environment. The eraser is erased with a load of 50 g / cm ² using a “magnet eraser” manufactured by MAGEX as an eraser.
The degree of contamination of the surface after repeating this operation 200 times is evaluated by color difference measurement using a decorative sheet before the start of the test as a blank.
○: ΔE is less than 1.0 ×: ΔE is 1.0 or more (5) Steel plate bending workability 90 ° at a test temperature of 25 ± 5 ° C. and an outer radius of 1.50 mm according to JIS K 6744 Observe the processed part after the bending test.
○: No crack is generated ×: Crack is generated

<Measurement of number average molecular weight (Mn) and weight average molecular weight (Mw) of leveling agent>
A high-speed GPC apparatus manufactured by Tosoh Corporation was used. The column used was a trade name “TSKgel αM” manufactured by Tosoh Corporation. The solvent was chloroform, and the column temperature was 40 ° C. and the flow rate was 0.5 cm ³ / min. In addition, the molecular weight and molecular weight distribution in this invention performed standard polystyrene conversion.

Example 1
A biaxially stretched transparent PET film (“Cosmo Shine A4300” manufactured by Toyobo Co., Ltd.) having a thickness of 50 μm was used as the base material 1, and a polyester urethane resin (adhesive made by Dainichi Seika Kogyo Co., Ltd.) as an adhesive on the back side. Laminate to which a polypropylene film (“PB-013” (trade name) manufactured by Mitsubishi Chemical MKV Co., Ltd.) 5 constituting a 60 μm thick concealing layer is attached via “E-295L)” (trade name)) 6 A film 10 was prepared.
An ink (“ILPA White” manufactured by DIC Graphics Co., Ltd.) containing 50% by mass of titanium white (titanium oxide, particle size 0.2 to 0.3 μm) using urethane resin as a binder on the surface side of the laminated film. It was applied (trade name)) at a coverage of 2.1 g / m ^2, to form an intermediate layer 2.
Next, a polyester polyol obtained by reacting a polyvalent carboxylic acid composed of terephthalic acid, isophthalic acid and sebacic acid with a polyol composed of neopentyl glycol and ethylene glycol ("E-256-" manufactured by Dainichi Seikagaku Corporation). 40 ”) 100 parts by mass, 3 parts by mass of isocyanate curing agent“ C-55 ”, and 2 parts by mass of untreated silica having a particle size of 5 μm were applied at a coating amount of 1.5 g / m ² to obtain primer layer 3 A soft primer layer was formed. The elongation in the standard temperature state class 2 (23 ± 2 ° C.) of the urethane resin composition constituting the primer layer 3 was 710%. The thickness of the intermediate layer 2 was 1.2 μm, and the thickness of the primer layer 3 was 1.0 μm.
Next, on the primer layer (soft primer layer) 3, 60 parts by mass of ethylene oxide-modified trimethylolpropane ethylene oxide triacrylate as a trifunctional acrylate monomer and 40 parts by mass of dipentaerythritol hexaacrylate as a hexafunctional acrylate monomer An ionizing radiation curable resin [EB resin] consisting of (+33 parts by mass of diluted solvent ethyl acetate) (“WBW-C” manufactured by DIC Graphics; resin content = 75 mass%, average number of functional groups = 3.6) 0.2 parts by weight of leveling agent acrylic resin (W-1) having 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, butyl acrylate, butyl methacrylate, 2-hydroxyethyl acrylate, styrene and α-methylstyrene as a unit , Hexame And 2.0 g / m ² (layer thickness 2.0 .mu.m) applied by the diisocyanate HMDI-based curing agent 3 parts by weight added to a gravure direct coating method an electron beam curable resin composition comprising. After coating, the surface protective layer 4 was obtained by irradiating an electron beam with an acceleration voltage of 165 kV and an irradiation dose of 50 kGy (5 Mrad) to cure the electron beam curable resin composition. Next, curing was performed at 70 ° C. for 24 hours to obtain a decorative sheet of the present invention.
The decorative sheet was attached to a galvanized steel sheet having a thickness of 0.4 mm using a urethane-based adhesive to obtain the decorative steel sheet of the present invention.
Table 1 shows the Mn, Mw and Mw / Mn ratio as well as the structural units of the resin as the properties of the acrylic resin (W-1) as the leveling agent, and Table 2 shows the evaluation results of the decorative sheet.

Example 2
The decorative sheet of the present invention and the present invention were obtained by performing the same operation using the same material as in Example 1 except that the acrylic resin (W-2) having the properties shown in Table 1 was used as the leveling agent. A decorative steel sheet was obtained.
Table 2 shows the evaluation results of the decorative sheet.

Example 3
The decorative sheet of the present invention and the present invention are obtained by performing the same operation using the same material as in Example 1 except that the leveling agent is an acrylic resin (W-3) having the properties shown in Table 1. A decorative steel sheet was obtained.
Table 2 shows the evaluation results of the decorative sheet.

Example 4
As the leveling agent, except that the acrylic resin (W-1) having the properties shown in Table 1 is used and the addition amount is 2.0 parts by mass with respect to 100 parts by mass of the resin content of the EB resin, The same operation was performed using the same material as in Example 1 to obtain the decorative sheet of the present invention and the decorative steel sheet of the present invention.
Table 2 shows the evaluation results of the decorative sheet.

Comparative Example 1
Except having used the polyester acrylate (W-4) which has the property shown in Table 1 as a leveling agent, the same operation was performed using the material similar to Example 1, and the decorative sheet and the decorative steel plate were obtained.
Table 2 shows the evaluation results of the decorative sheet.

Comparative Example 2
Except using the acrylic resin (W-5) having the properties shown in Table 1 as the leveling agent, the same operation was performed using the same material as in Example 1 to obtain a decorative sheet and a decorative steel sheet. .
Table 2 shows the evaluation results of the decorative sheet.

Comparative Example 3
Except having used silicone-vinyl acetate copolymer resin (W-6) as a leveling agent, the same operation was performed using the same material as Example 1, and the decorative sheet and the decorative steel plate were obtained.
Table 2 shows the evaluation results of the decorative sheet.

Comparative Example 4
Except for changing the addition amount of the leveling agent to 5.0 parts by mass with respect to 100 parts by mass of the resin content of the EB resin, the same operation was performed using the same material as in Example 1, and the decorative sheet and the cosmetics were used. A steel plate was obtained.
Table 2 shows the evaluation results of the decorative sheet.

Comparative Example 5
Except not using a leveling agent, the same operation was performed using the same material as Example 1, and the decorative sheet and the decorative steel plate were obtained.
Table 2 shows the evaluation results of the decorative sheet.

From the evaluation results in Table 2, the following can be understood.
As the leveling agent, an acrylic resin that satisfies the requirements of the present invention is used, and the amount added is in the range of 0.1 to 4.0 parts by mass with respect to 100 parts by mass of the EB resin. Each of the evaluation results is “◯” or “◎” and is passed. On the other hand, as the leveling agent, Comparative Examples 1 to 3 using a resin that does not satisfy the requirements of the present invention, an acrylic resin that satisfies the requirements of the present invention is used, but the addition amount exceeds 4.0 parts by mass. In Example 4 and Comparative Example 5 without the addition of a leveling agent, two of the evaluation results of the decorative sheet were “x”, “x”, and “Δ”, respectively.

The decorative sheet for steel sheet of the present invention is excellent in writing erasability, particularly repetitive erasability, and surface design stability, as cracks are not generated in the outermost surface protective layer even when it is bent. The attached decorative steel sheet is preferably used for, for example, whiteboards that require excellent marker erasure and repeated erasability, and wall surfaces of unit baths that are prone to get dirty, and from the viewpoint of effectively utilizing the features of the decorative sheet of the present invention. It is particularly preferred to be used for a whiteboard. In addition, for building interior materials such as walls and ceilings, surface materials for fittings such as doors, door frames and window frames, surface materials for construction parts such as skirts and skirting boards, surface materials for furniture such as fences and cabinets, etc. Can also be used.
[Explanation of symbols]

20 decorative sheet 10 laminated film 1 substrate 2 intermediate layer 3 primer layer 4 surface protective layer 5 film constituting concealing layer 6 adhesive layer

Claims (5)

A decorative sheet for steel sheet having at least a primer layer and a surface protective layer in this order on a substrate, wherein the substrate is composed of a biaxially stretched polyester film, the primer layer is composed of a urethane resin composition, and the surface protective layer is It is a crosslinked cured product of an ionizing radiation curable resin composition,
(1) The surface protective layer contains a resin having an acrylic skeleton as a leveling agent at a ratio of 0.1 to 4.0 parts by mass with respect to 100 parts by mass of the ionizing radiation curable resin.
(2) At least one selected from (meth) acrylic acid hydroxyalkyl esters and aromatic vinyl compounds, which contains a (meth) acrylic acid alkyl ester having no hydroxy group as a structural unit of the resin having an acrylic skeleton. A decorative sheet for steel sheet, which is a poly (meth) acrylate containing The primer layer is a polyester polyol obtained by reacting a polyvalent carboxylic acid composed of terephthalic acid, isophthalic acid, and sebacic acid with a polyol composed of neopentyl glycol and ethylene glycol, an isocyanate-based curing agent, and an uncoated particle having a particle size of 5 μm. The decorative sheet for steel sheet according to claim 1, comprising a urethane-based resin composition containing treated silica. The makeup for steel sheet according to claim 1 or 2 , wherein the crosslinked cured product of the ionizing radiation curable resin composition constituting the surface protective layer has a breaking elongation of 25 to 45% measured by a tensile test under the following conditions. Sheet.
Tensile test method: An ionizing radiation curable resin composition was applied to a 90 μm-thick polypropylene film and cured to a thickness of 3.5 μm, and then subjected to a tensile test at a temperature of 25 ° C. and a tensile speed of 50 mm / min to break. Measure the elongation when The decorative sheet for steel sheets according to any one of claims 1 to 3, wherein the ionizing radiation curable resin has an average functional group number of 3.1 to 4.5. The decorative steel plate which has the decorative sheet for steel plates in any one of Claims 1-4 on a steel plate.

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