JPH09290491A - Surface protective sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface protective sheet having no crack at the molding curved part at the time of adhering to the molding surface by making it possible to obtain the low-cost molding having excellent wear resistance and chemical resistance. SOLUTION: This surface protective sheet 5 comprises a protective layer 2 provided at least on one surface of a base sheet 1, and an adhesive layer 4 provided at least on the opposite surface, wherein the layer 2 is formed of a thermal crosslinking reaction product of an active energy beam curable resin composition containing a polymer having (meth)acryl equivalent of 100 to 300g/eq, hydroxyl value of 20 to 500, and weight-average molecular weight of 5,000 to 50,000 and a multifunctional isocyanate as effective components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention provides a molded article excellent in abrasion resistance and chemical resistance at a low cost.
The present invention also relates to a surface protection sheet that does not cause cracks in the curved surface of a molded product.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a surface protective sheet on the surface of a molded article, a surface protective sheet in which at least a protective layer is provided on one surface of a base sheet and at least an adhesive layer is provided on the opposite surface is a molded article. There is a sticking method that sticks to the surface. Further, there is an insert molding method in which the surface protection sheet is sandwiched in a molding die, and the cavity is injection-filled with resin and cooled to obtain a resin molded product, and at the same time, the surface protection sheet is bonded to the surface.

[0003] As a resin constituting the protective layer of the surface protective sheet, a thermosetting resin and an active energy ray-curable resin are generally used.

[0004]

However, when a thermosetting resin is used as the protective layer and the thermosetting resin is cross-linked and cured by heating at the time of producing the surface protective sheet, the chemical resistance of the surface of the molded product is reduced. Abrasion resistance is generally poor.

On the other hand, when an active energy ray-curable resin is used as the protective layer and the active energy ray-curable resin composition is cross-linked and cured by irradiating the active energy ray during preparation of the surface protective sheet, the crosslinking density of the resin is reduced. The chemical resistance and the abrasion resistance can be improved by increasing the thickness, but on the other hand, the protective layer becomes brittle, and cracks occur in the protective layer located on the curved surface of the molded product at the time of bonding.

Therefore, as another method of using the active energy ray-curable resin as the protective layer, the active energy ray-curable resin is partially cross-linked and cured by irradiating the active energy ray with the first step when the surface protective sheet is manufactured. A method has also been proposed in which, after adhering to the surface, the active energy ray-curable resin is completely cured by irradiating the active energy ray again at the second stage. If the active energy ray irradiation is insufficient, the ink containing the active energy ray curable resin remains fluid and tacky in the first step irradiation, so a considerable amount of irradiation is required to make the protective layer tack-free. Becomes On the other hand, if the irradiation amount is excessive, cracks are likely to occur in the protective layer located on the curved surface of the molded product during bonding. In order to prevent the above problems from occurring, the dose of the first-stage irradiation may be adjusted, but in radical polymerization, the reaction rate is generally high, and the dark reaction proceeds even after irradiation with active energy rays. It is not easy to control the irradiation dose. There is also a disadvantage that the irradiation conditions are likely to become unstable due to deterioration of the light source lamp of active energy rays.

Therefore, according to the present invention, the above problems can be eliminated and a molded article having excellent abrasion resistance and chemical resistance can be obtained at low cost, and the molded article can be adhered to the surface of the molded article. It is an object of the present invention to provide a surface protection sheet that does not generate cracks on a curved surface portion.

[0008]

In order to achieve the above object, the surface protective sheet of the present invention is a surface protective sheet in which at least a protective layer is provided on one side of a base sheet and at least an adhesive layer is provided on the opposite side. In, the protective layer has a (meth) acrylic equivalent of 100 to 300 g / eq and a hydroxyl value of 20 to 50.
It was composed of a heat-crosslinking reaction product of an active energy ray-curable resin composition containing, as an active ingredient, a polymer having a weight average molecular weight of 5,000 to 50,000 and a polyfunctional isocyanate.

Further, in the above constitution, the polymer is constituted so as to be a reaction product obtained by subjecting a glycidyl (meth) acrylate polymer to an addition reaction of an α, β-unsaturated monocarboxylic acid.

Further, in the above constitution, the glycidyl (meth) acrylate polymer is a homopolymer of glycidyl (meth) acrylate, or an α, β-unsaturated monomer containing no glycidyl (meth) acrylate and a carboxyl group. Is a copolymer of

Further, in each of the above constitutions, a pattern layer is provided between the base sheet and the adhesive layer.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The surface protective sheet of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing one embodiment of the surface protective sheet according to the present invention,
FIG. 2 is a schematic cross-sectional view showing another embodiment of the surface protective sheet according to the present invention. In the figure, 1 is a base sheet, 2 is a protective layer, 3 is a pattern layer, 4 is an adhesive layer, and 5 is a surface protective sheet.

Regarding the surface protection sheet 5 shown in FIG.
explain in detail.

As the base sheet 1, an acrylic resin,
A resin sheet of polycarbonate resin, vinyl chloride resin, urethane resin, polyester resin or the like can be used.

The protective layer 2 is a layer for protecting the molded product 6 and the pattern layer 3 from chemicals and friction. As its material,
(Meth) acrylic equivalent 100 to 300 g / eq, hydroxyl value 20 to
A thermal crosslinking reaction product of an active energy ray-curable resin composition containing, as an active ingredient, a polymer having a weight average molecular weight of 500 and a weight average molecular weight of 5000 to 50000 and a polyfunctional isocyanate is used.

The polymer of the protective layer 2 is selected in consideration of the physicochemical required performance of the protective layer 2 before and after irradiation with active energy rays.
It is set to a specific amount. That is, from the viewpoint of curability during irradiation with active energy rays, (meth) acrylic equivalent 100 to 300
g / eq. (Meth) acrylic equivalent is 300g / e
When it is larger than q, the abrasion resistance after irradiation with active energy rays is insufficient, and it is difficult to obtain a material having less than 100 g / eq. From the viewpoint of reactivity with the polyfunctional isocyanate used in combination, the hydroxyl value of the polymer is 20 to 500,
It is preferably 100 to 300. If the hydroxyl value is less than 20, the reaction with the polyfunctional isocyanate is insufficient,
The degree of crosslinking of the protective layer 2 before irradiation with active energy rays is low. Therefore, the adhesiveness remains or the solvent resistance is insufficient, which makes it difficult to wind up the surface protection sheet 5, and there is a disadvantage that a clear pattern cannot be obtained. Further, it is difficult to obtain one having a hydroxyl value of more than 500. If the weight-average molecular weight of the polymer is less than 5000, the protective layer 2 before irradiation with active energy rays may remain sticky, or the solvent resistance may be insufficient, so that it is difficult to wind the surface protective sheet 5 again. There is. Also, 50,000
If it exceeds, the viscosity of the resin becomes too high, and the workability of ink coating is deteriorated.

The method for producing the polymer is not particularly limited, and conventionally known methods can be adopted. For example, [1] a method of introducing a (meth) acryloyl group into a part of a side chain of a polymer containing a hydroxyl group, [2] α, β-unsaturation containing a hydroxyl group in a copolymer containing a carboxyl group A method of subjecting a monomer to a condensation reaction, [3] a method of adding an α, β-unsaturated monomer containing an epoxy group to a copolymer containing a carboxyl group, and [4] a method of adding an epoxy group-containing polymer. There is a method of reacting an α, β-unsaturated carboxylic acid.

The method for producing a polymer will be described more specifically by taking the method [4] as an example. The polymer can be easily obtained by a method of reacting a homopolymer or a copolymer of glycidyl (meth) acrylate with an α, β-unsaturated carboxylic acid such as acrylic acid. Examples of the glycidyl (meth) acrylate copolymer include a copolymer of glycidyl (meth) acrylate and an α, β-unsaturated monomer that does not contain a carboxyl group, and does not contain this carboxyl group. Examples of the α, β-unsaturated monomer include various (meth) acrylic acid esters, styrene, vinyl acetate, and acrylonitrile. In the case of an α, β-unsaturated monomer containing a carboxyl group, crosslinking occurs during the copolymerization reaction with glycidyl (meth) acrylate, resulting in high viscosity and gelation, which is not preferable.

In any case, when each of the above methods [1] to [4] is adopted, the types of monomers and polymers used, the amounts used, etc., should be set so as to satisfy the above-mentioned numerical limit range relating to the polymer. It is necessary to appropriately set the conditions of.

The polyfunctional isocyanate used together with the polymer in the present invention is not particularly limited, and various known ones can be used. For example, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, 1,6-hexane diisocyanate, the above trimer, a prepolymer obtained by reacting a polyhydric alcohol with the above diisocyanate, etc. Can be used. The reason why the polyfunctional isocyanate is used in combination with the polymer in the present invention is to keep the tackiness of the protective layer 2 before irradiation with active energy rays low. That is, the hydroxyl group contained in the polymer is reacted with the isocyanate group of the polyfunctional isocyanate to form a mildly thermally crosslinked product to impart the above performance.

The ratio of the polymer to the polyfunctional isocyanate used is determined in consideration of the hydroxyl value of the polymer and the number of functional groups of the polyfunctional isocyanate, but usually 1 to 30 parts by weight of the polyfunctional isocyanate per 100 parts by weight of the polymer. It is about a part.

In addition to the polymer and polyfunctional isocyanate, the protective layer 2 may contain the following components, if necessary. That is, it is a reactive diluent monomer, a solvent, a colorant, and the like. Further, when an electron beam is used for irradiation with active energy rays, curing can be sufficiently performed without using a photopolymerization initiator, but when ultraviolet rays are used, various known photopolymerization initiators are added. There is a need. The protective layer 2 may be colored or uncolored.

As the method of forming the protective layer 2, there are a coating method such as a gravure coating method, a roll coating method and a comma coating method, and a printing method such as a gravure coating method and a screen printing method.

The active energy ray-curable resin composition constituting the protective layer 2 becomes a thermal crosslinking reaction product by heat treatment, and the protective layer 2 becomes tack-free. In this case, it is easier to control the degree of curing than irradiation with active energy rays. The heat treatment conditions are determined according to the active energy ray-curable resin composition.

The pattern layer 3 is usually formed as a printing layer on the surface of the base sheet 1 opposite to the surface on which the protective layer 2 is provided.
As the material of the printing layer, polyvinyl resin, polyamide resin, polyester resin, polyacrylic resin, polyurethane resin, polyvinyl acetal resin, polyester urethane resin, cellulose ester resin,
A colored ink containing a resin such as an alkyd resin as a binder and a pigment or dye of an appropriate color as a colorant may be used. As a method for forming the printing layer, a normal printing method such as an offset printing method, a gravure printing method, or a screen printing method may be used. In particular, an offset printing method or a gravure printing method is suitable for performing multicolor printing and gradation expression. In the case of a single color, a coating method such as a gravure coating method, a roll coating method, and a comma coating method can be adopted. The print layer, depending on the pattern you want to express,
It may be provided entirely or partially. The pattern layer 3 may be a metal thin film layer or a combination of a printed layer and a metal thin film layer.

The adhesive layer 4 adheres the above layers to the surface of the molded product 6. The adhesive layer 4 is formed on a portion to be bonded. In other words, if the part you want to bond is all over,
The adhesive layer 4 is formed on the entire surface. If the portion to be bonded is partial, the adhesive layer 4 is partially formed. Adhesive layer 4
As the material, a heat-sensitive or pressure-sensitive resin suitable for the material of the molded product 6 is appropriately used. For example, when the material of the molded product 6 is polyacrylic resin, polyacrylic resin may be used. The material of the molded product 6 is polyphenylene oxide / polystyrene resin, polycarbonate resin,
In the case of a styrene copolymer resin or a polystyrene blend resin, a polyacrylic resin, polystyrene resin, polyamide resin or the like having an affinity for these resins may be used. Further, when the material of the molded product 6 is polypropylene resin, chlorinated polyolefin resin, chlorinated ethylene-vinyl acetate copolymer resin, cyclized rubber and coumarone indene resin can be used. As a method for forming the adhesive layer 4, there are a coating method such as a gravure coating method, a roll coating method, and a comma coating method, and a printing method such as a gravure coating method and a screen printing method.

The structure of the surface protection sheet 5 is not limited to the above-mentioned embodiment, and for example, the molded product 6 is used.
When the surface protection sheet 5 is used only for the surface protection treatment by making the best use of the background pattern and the transparency, the pattern layer 3 can be omitted (see FIG. 2).

An anchor layer may be provided between the layers. The anchor layer is a resin layer for improving the adhesion between the layers and protecting the molded product 6 and the pattern layer 3 from chemicals,
For example, a two-component curable urethane resin, a melamine-based or epoxy-based thermosetting resin, or a vinyl chloride copolymer resin or other thermoplastic resin can be used. As a method for forming the anchor layer, there are a coating method such as a gravure coating method, a roll coating method and a comma coating method, and a printing method such as a gravure printing method and a screen printing method.

The surface protection sheet having the above-mentioned structure is adhered to the surface of the molded product by using the insert molding method and then irradiated with ultraviolet rays to reduce the molded product excellent in abrasion resistance and chemical resistance. It can be obtained at a cost and does not cause cracks in the curved surface of the molded product.

[0030]

According to the present invention, the protective layer of the surface protective sheet is
(Meth) acrylic equivalent 100 to 300 g / eq, hydroxyl value 20 to
500, composed of a cross-linking reaction product of an active energy ray-curable resin composition containing a polymer having a weight average molecular weight of 5000 to 50000 and a polyfunctional isocyanate as an active ingredient, and this protective layer attached to the surface of a molded article. Since it is cured by irradiation with active energy rays in the subsequent step, a molded product having excellent wear resistance and chemical resistance can be obtained, and cracks do not occur in the curved surface of the molded product.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a surface protection sheet according to the present invention.

FIG. 2 is a schematic cross-sectional view showing another embodiment of the surface protective sheet according to the present invention.

[Explanation of symbols]

 1 Base Sheet 2 Protective Layer 3 Picture Layer 4 Adhesive Layer 5 Surface Protective Sheet

Claims (4)

[Claims] 1. A surface protective sheet in which at least a protective layer is provided on one surface of a base sheet and at least an adhesive layer is provided on the opposite surface, wherein the protective layer is a (meth) acrylic equivalent.
100-300 g / eq, hydroxyl value 20-500, weight average molecular weight 5
A surface protection sheet comprising a thermal crosslinking reaction product of an active energy ray-curable resin composition containing 000 to 50,000 polymers and a polyfunctional isocyanate as active ingredients. 2. The surface protective sheet according to claim 1, wherein the polymer is a reaction product obtained by subjecting a glycidyl (meth) acrylate polymer to an addition reaction with an α, β-unsaturated monocarboxylic acid. 3. A glycidyl (meth) acrylate polymer is a glycidyl (meth) acrylate homopolymer,
The surface protective sheet according to claim 2, which is a copolymer composed of glycidyl (meth) acrylate and an α, β-unsaturated monomer having no carboxyl group. 4. The surface protection sheet according to claim 1, wherein a pattern layer is provided between the base sheet and the adhesive layer.