JP7526459B2 - How to apply decorative sheets - Google Patents

Description

The present invention relates to a method for applying a decorative sheet to a base material for the exterior or interior of a building using a water-based adhesive composition containing a water-dispersible polyurethane.

Decorative sheets made from polyvinyl chloride resins and the like are inexpensive, yet have good chemical and water resistance, and excellent moldability, making them widely used as interior and exterior building materials for walls, ceilings, floors, etc. Decorative sheets are applied to the exterior and interior base materials of buildings to improve the design of the building.

For example, a decorative sheet having a laminated structure with an adhesive layer, in which a top coat layer, a transparent resin layer, an adhesive layer, an ink layer, and a primer layer are laminated from the surface side, may be used. A decorative sheet having an adhesive layer is used by adhering it to a base material via the adhesive layer (Patent Document 1).

However, when replacing decorative sheets with an adhesive layer during renovation of a building, there was a risk that the base material of the building would be damaged, such as by leaving adhesive marks or scratches on the base material. Therefore, when replacing the decorative sheet, workers were required to work carefully, and there was a need to improve work efficiency.

In addition, decorative sheets are sometimes applied to the base material of buildings using hot melt adhesives in which urethane resins and the like are dispersed in an organic solvent. The hot melt adhesive is applied to the base material at the work site, the decorative sheet is aligned in a specified position on the base material, and the hot melt adhesive is heat-treated from the surface of the decorative sheet, thereby applying the decorative sheet to the base material. However, organic solvent-dispersed hot melt adhesives pose problems in terms of work safety and environmental impact, as the organic solvent volatilizes during application. In addition, organic solvent-dispersed hot melt adhesives require sufficient volatilization of the organic solvent, which can cause thermal damage to the decorative sheet during heat treatment, resulting in poor appearance such as wrinkles.

In addition, to ensure work safety and reduce the environmental load, a water-based adhesive composition may be applied to a base material and a decorative sheet may be applied to the base material. However, the adhesive strength of the water-based adhesive composition is not good enough. In addition, the water-based adhesive composition may cause a phenomenon called blistering, in which a part of the decorative sheet peels off from the base material, which may result in poor appearance. In addition, the decorative sheet must be applied before the adhesive composition solidifies due to the moisture in the adhesive composition evaporating or being absorbed by the base material, and there are problems such as the need for skill in applying the sheet to a base with a complex shape such as an external corner or an internal corner, and the adhesive composition cannot be applied all at once to apply the decorative sheet to a large-area base.

JP 2020-37276 A

In view of the above circumstances, the present invention aims to provide a decorative sheet application method that can prevent damage to the base material by simple operations when applying or replacing a decorative sheet, has excellent adhesive strength and appearance, is safe to work with, reduces the environmental load, and allows easy alignment of the decorative sheet without requiring skill in application of the decorative sheet.

The gist of the invention is as follows.
[1] A coating step of coating a water-based adhesive composition containing a water-dispersible polyurethane on a base material;
a drying step of drying the aqueous adhesive composition containing the water-dispersed polyurethane applied onto the base material until the water content of the aqueous adhesive composition containing the water-dispersed polyurethane is 5% by mass or less to form an aqueous adhesive composition layer;
a lamination step of laminating a decorative sheet on the aqueous adhesive composition layer with the rear surface facing the aqueous adhesive composition layer to form a laminate;
a bonding step of subjecting the laminate to a heat treatment to bond the decorative sheet onto a base material;
Including,
A method for applying a decorative sheet, wherein the softening point of the decorative sheet is higher than the softening point of the polyurethane of the aqueous adhesive composition layer, and the temperature of the heat treatment is higher than the softening point of the polyurethane of the aqueous adhesive composition layer and lower than the softening point of the decorative sheet.
[2] The method for applying a decorative sheet according to [1], wherein the softening point of the decorative sheet is at least 50° C. higher than the softening point of the polyurethane of the aqueous adhesive composition layer.
[3] The method for applying a decorative sheet according to [1] or [2], wherein the heat treatment is carried out at a temperature that is at least 20° C. higher than the softening point of the polyurethane of the aqueous adhesive composition layer and at least 10° C. lower than the softening point of the decorative sheet.
[4] The method for applying a decorative sheet according to any one of [1] to [3], wherein the softening point of the polyurethane is 50°C or higher and 170°C or lower.
[5] The method for applying a decorative sheet according to any one of [1] to [4], wherein the softening point of the decorative sheet is 160°C or higher and 220°C or lower.
[6] A method for applying a decorative sheet according to any one of [1] to [5], comprising applying a primer onto the base material, and then applying an aqueous adhesive composition containing the water-dispersible polyurethane.
[7] The method for applying a decorative sheet according to any one of [1] to [6], wherein the base material of the decorative sheet comprises a polyvinyl chloride resin layer.
[8] A method for applying a decorative sheet according to any one of [1] to [7], wherein the base material is a ceramic exterior material for a building.
[9] The method for applying a decorative sheet according to any one of [1] to [8], wherein an aqueous adhesive composition containing the water-dispersible polyurethane is applied to the entire surface of the base material.

In the above embodiment [1], the aqueous adhesive composition containing the aqueous polyurethane dispersion is applied to the base material, and then the surface of the decorative sheet is heat-treated to adhere the decorative sheet to the base material, so that the aqueous adhesive composition containing the aqueous polyurethane dispersion is used as a hot melt adhesive. In addition, the "softening point" in this specification means the softening temperature measured by inserting a transparent quartz pin (tip diameter: 0.5 mm) into the test object at a pressure of 9.8 mN in an air atmosphere at a temperature range of 30°C to 350°C at a heating rate of 10°C/min using a thermomechanical analyzer.

According to an aspect of the present invention, the softening point of the decorative sheet is higher than that of the polyurethane in the aqueous adhesive composition layer, so that when replacing the decorative sheet, the aqueous adhesive composition layer is softened by heating the decorative sheet above the softening point of the polyurethane in the aqueous adhesive composition layer and below the softening point of the decorative sheet, so that the decorative sheet can be peeled off by a simple operation without damaging the base material. Also, according to an aspect of the present invention, the softening point of the decorative sheet is higher than that of the polyurethane in the aqueous adhesive composition layer, and the temperature of the heat treatment is higher than the softening point of the polyurethane in the aqueous adhesive composition layer and below the softening point of the decorative sheet, so that excellent adhesive strength is imparted between the decorative sheet and the base material, while preventing the decorative sheet from being thermally damaged during the bonding process, and maintaining an excellent appearance.

In addition, according to an aspect of the present invention, since an aqueous adhesive composition containing a water-dispersible polyurethane is used, the evaporation of organic solvents can be avoided, so that the work is safe and the environmental load can be reduced. In addition, according to an aspect of the present invention, the aqueous adhesive composition containing a water-dispersible polyurethane is dried to form an aqueous adhesive composition layer, so that the decorative sheet can be easily aligned and no skill is required to apply the decorative sheet.

In addition, according to an embodiment of the present invention, the softening point of the decorative sheet is at least 50°C higher than the softening point of the polyurethane in the aqueous adhesive composition layer, which facilitates temperature control during the bonding process while reliably maintaining excellent adhesive strength between the decorative sheet and the base material and excellent appearance of the decorative sheet.

In addition, according to an embodiment of the present invention, by carrying out the heat treatment in the adhesion step at a temperature that is at least 20°C higher than the softening point of the polyurethane in the aqueous adhesive composition layer and at least 10°C lower than the softening point of the decorative sheet, it is possible to impart even better adhesive strength between the decorative sheet and the base material while more reliably maintaining the decorative sheet's excellent appearance.

In addition, according to an embodiment of the present invention, the softening point of the polyurethane is 50°C or higher and 170°C or lower, so that even during high temperatures such as summer, the aqueous adhesive composition layer can be prevented from softening due to the outside air temperature, which would otherwise cause a decrease in adhesive strength, while still reliably maintaining excellent adhesive strength between the decorative sheet and the base material and excellent appearance of the decorative sheet.

The application method of the decorative sheet of the present invention is described in detail below. The application method of the decorative sheet of the present invention includes: (a) a coating step of coating a base material with an aqueous adhesive composition containing a water-dispersed polyurethane; (b) a drying step of drying the aqueous adhesive composition containing the water-dispersed polyurethane coated on the base material until the water content of the aqueous adhesive composition containing the water-dispersed polyurethane is reduced by 50% by mass or more to form an aqueous adhesive composition layer; (c) a lamination step of laminating a decorative sheet with its back surface facing the aqueous adhesive composition layer; and (d) an adhesion step of applying a heat treatment to the surface of the decorative sheet to adhere the decorative sheet to the base material.

<(a) Coating step>
In the coating step, the aqueous adhesive composition containing the water-dispersed polyurethane is applied onto the base material to form a coating film. The aqueous adhesive composition containing the water-dispersed polyurethane is preferably applied uniformly over the entire surface of the area to which the decorative sheet is to be bonded. The thickness of the coating film of the aqueous adhesive composition containing the water-dispersed polyurethane is not particularly limited, but the lower limit is preferably 0.1 mm, and more preferably 0.2 mm, from the viewpoint of reliably imparting adhesive strength. On the other hand, the upper limit of the thickness of the coating film of the aqueous adhesive composition containing the water-dispersed polyurethane is preferably 1.5 mm, and more preferably 1 mm, from the viewpoint of the appearance after bonding of the decorative sheet.

Any known method can be used to apply the water-based adhesive composition containing the water-dispersed polyurethane, such as roll coating, spray coating, brush coating, etc.

Examples of substrates to which the aqueous adhesive composition containing the water-dispersible polyurethane is applied include the exterior and interior of buildings, such as floors, ceilings, exterior walls, and interior walls. Of these, ceramic exterior materials used for the exterior of buildings are preferred as substrates to which the composition is applied.

<(b) Drying step>
In the drying step, the coating film of the aqueous adhesive composition containing the aqueous dispersion polyurethane applied to the base material is dried until the water content of the aqueous adhesive composition containing the aqueous dispersion polyurethane becomes 5% by mass or less compared to the water content at the time of application, thereby forming an aqueous adhesive composition layer on the base material. The water content of the aqueous adhesive composition layer after the drying step is not particularly limited as long as it is 5% by mass or less, but from the viewpoint of reliably imparting adhesive strength, it is preferably 3% or less, and particularly preferably 1% or less.

When drying is sufficient, the tackiness of the surface of the aqueous adhesive composition layer is sufficiently reduced, and therefore the aqueous adhesive composition layer is dry to the touch.

For the reasons mentioned above, it is preferable that the surface of the aqueous adhesive composition layer is dried to the extent that it loses tack.

The drying method is not particularly limited, and examples include leaving the layer in the open air at ambient temperature and drying with warm air in the open air. In the aqueous adhesive composition layer after drying, the polyurethane derived from the aqueous dispersion polyurethane is a thermoplastic resin.

<(c) Lamination step>
In the lamination step, the back surface of the decorative sheet is placed on the dried aqueous adhesive composition layer to form a laminate of the base material and the decorative sheet. The lamination step is a step of bonding the decorative sheet to the base material. When bonding the decorative sheet to the base material, it is preferable to align the edge of the decorative sheet to be bonded to a predetermined position on the base material and temporarily fix it with a tacker before starting bonding. In addition, when proceeding with the bonding work, it is preferable to perform the bonding while aligning the decorative sheet and temporarily fixing it with a tacker so that wrinkles do not occur from the top to the bottom.

By attaching the back side of the decorative sheet to the base material, the outer surface of the base material becomes decorated with the design of the decorative sheet.

<(d) Bonding step>
In the bonding step, the laminate is heat-treated to bond the decorative sheet onto the base material. In the present invention, the aqueous adhesive composition containing the water-dispersed polyurethane is used as a hot melt adhesive. By heat-treating the laminate, the polyurethane derived from the water-dispersed polyurethane, which is a thermoplastic resin, i.e., the polyurethane of the aqueous adhesive composition layer, receives heat through the decorative sheet and softens. The method for heating the laminate is not particularly limited, and examples thereof include a method for heating the surface of the decorative sheet, a method for heating the surface of the base material, and a method for heating the aqueous adhesive composition layer.

In the present invention, the decorative sheet and the polyurethane of the aqueous adhesive composition layer have a relationship in which the softening point of the decorative sheet is higher than the softening point of the polyurethane of the aqueous adhesive composition layer. Furthermore, in the present invention, the temperature of the heat treatment is set in a range above the softening point of the polyurethane of the aqueous adhesive composition layer and below the softening point of the decorative sheet.

According to an aspect of the present invention, the softening point of the decorative sheet is higher than that of the polyurethane in the aqueous adhesive composition layer, and the temperature of the heat treatment is higher than the softening point of the polyurethane in the aqueous adhesive composition layer and lower than the softening point of the decorative sheet. This allows the decorative sheet to maintain an excellent appearance by preventing the decorative sheet from being thermally damaged during the bonding process while providing excellent adhesive strength between the decorative sheet and the base material when the decorative sheet is applied. In addition, according to an aspect of the present invention, the softening point of the decorative sheet is higher than that of the polyurethane in the aqueous adhesive composition layer, and the aqueous adhesive composition layer is softened by heating the decorative sheet to a temperature higher than the softening point of the polyurethane in the aqueous adhesive composition layer and lower than the softening point of the decorative sheet when replacing the decorative sheet. This allows the decorative sheet to be peeled off by simple operations without damaging the base material.

In addition, according to an aspect of the present invention, since an aqueous adhesive composition containing a water-dispersible polyurethane is used, the evaporation of organic solvents can be avoided, so that work safety is ensured and the environmental burden can be reduced. In addition, according to an aspect of the present invention, an aqueous adhesive composition layer is formed by drying an aqueous adhesive composition containing a water-dispersible polyurethane until it loses tack, so that the decorative sheet can be easily aligned on the base material and does not require skill in application of the decorative sheet.

As long as the softening point of the decorative sheet is higher than the softening point of the polyurethane in the aqueous adhesive composition layer, the relationship between the softening point of the decorative sheet and the softening point of the polyurethane in the aqueous adhesive composition layer is not particularly limited. For example, in order to facilitate temperature control in the bonding process while reliably maintaining excellent adhesive strength between the decorative sheet and the base material and excellent appearance of the decorative sheet, it is preferable that the softening point of the decorative sheet is at least 50°C higher than the softening point of the polyurethane in the aqueous adhesive composition layer, and it is particularly preferable that the softening point is at least 70°C higher.

The heat treatment temperature is not particularly limited as long as it is in the range above the softening point of the polyurethane in the aqueous adhesive composition layer and below the softening point of the decorative sheet. For example, the heat treatment temperature is preferably in the range of 20°C or more higher than the softening point of the polyurethane in the aqueous adhesive composition layer and 10°C or more lower than the softening point of the decorative sheet, from the viewpoint of imparting even better adhesive strength between the decorative sheet and the base material while more reliably maintaining an excellent appearance of the decorative sheet, and is particularly preferably in the range of 30°C or more higher than the softening point of the polyurethane in the aqueous adhesive composition layer and 20°C or more lower than the softening point of the decorative sheet.

The softening point of the polyurethane in the water-based adhesive composition layer is not particularly limited as long as it is a temperature lower than the softening point of the decorative sheet, but the lower limit of the softening point of the polyurethane in the water-based adhesive composition layer is preferably 50°C, and more preferably 55°C, from the viewpoint of preventing the water-based adhesive composition layer from softening due to the outside air temperature and reducing the adhesive strength even in hot seasons such as summer. On the other hand, the upper limit of the softening point of the polyurethane in the water-based adhesive composition layer is preferably 170°C, and more preferably 150°C, from the viewpoint of reliably maintaining excellent adhesive strength between the decorative sheet and the base material and excellent appearance of the decorative sheet.

The softening point of the decorative sheet is not particularly limited as long as it is higher than the softening point of the polyurethane in the aqueous adhesive composition layer, but the lower limit is preferably 160°C, and particularly preferably 170°C, in order to reliably maintain the excellent appearance of the decorative sheet. On the other hand, the higher the upper limit of the softening point of the decorative sheet, the better, and an example of this is 220°C.

The melting point of the decorative sheet is higher than the melting point of the polyurethane in the aqueous adhesive composition layer. For example, the melting point of the decorative sheet is preferably at least 50°C higher than the melting point of the polyurethane in the aqueous adhesive composition layer, and is particularly preferably at least 70°C higher, in order to facilitate temperature control during the bonding process while reliably maintaining excellent adhesive strength between the decorative sheet and the base material and excellent appearance of the decorative sheet.

The temperature of the heat treatment is in the range above the melting point of the polyurethane in the aqueous adhesive composition layer and below the melting point of the decorative sheet. For example, in order to provide even better adhesive strength between the decorative sheet and the base material while more reliably maintaining an excellent appearance for the decorative sheet, a temperature range of 20°C or more higher than the melting point of the polyurethane in the aqueous adhesive composition layer and 10°C or more lower than the melting point of the decorative sheet is preferred, and a temperature range of 30°C or more higher than the melting point of the polyurethane in the aqueous adhesive composition layer and 20°C or more lower than the melting point of the decorative sheet is particularly preferred.

The melting point of the polyurethane in the aqueous adhesive composition layer is a temperature lower than the melting point of the decorative sheet. For example, the lower limit of the melting point of the polyurethane in the aqueous adhesive composition layer is preferably 45°C, and more preferably 50°C, from the viewpoint of preventing the aqueous adhesive composition layer from softening due to the outside air temperature and reducing the adhesive strength even in hot seasons such as summer. On the other hand, the upper limit of the melting point of the polyurethane in the aqueous adhesive composition layer is preferably 170°C, and more preferably 150°C, from the viewpoint of reliably maintaining the excellent adhesive strength between the decorative sheet and the base material and the excellent appearance of the decorative sheet.

The melting point of the decorative sheet is a temperature higher than the melting point of the polyurethane in the aqueous adhesive composition layer, and in order to reliably maintain the excellent appearance of the decorative sheet, the lower limit is preferably 160°C, and particularly preferably 170°C. On the other hand, the higher the upper limit of the melting point of the decorative sheet, the more preferable it is, for example, 220°C. In this specification, the "melting point" is a value measured in accordance with JIS K7121-1987.

When the surface of the decorative sheet is heated as a method for heating the laminate, a method of applying a predetermined pressure and heat from the decorative sheet side can be mentioned. Specific examples include a heating roller, an iron, etc. Among these, a heating roller is preferred from the viewpoint of reliably improving the adhesive strength by heating while applying pressure to the surface of the decorative sheet. The pressure when applying pressure to the surface of the decorative sheet can be, for example, in the range of 50 to 150 g/ ^cm2 .

Next, the water-based adhesive composition and decorative sheet containing the water-dispersible polyurethane having the above softening point will be described below.

<Water-based adhesive composition containing water-dispersible polyurethane>
The aqueous adhesive composition used in the present invention contains a water-dispersed polyurethane. The water-dispersed polyurethane is an aqueous polyurethane emulsion, and has a chemical structure in which an organic polyisocyanate and a polymer polyol are reacted.

Organic polyisocyanates are compounds that have two or more isocyanate groups in one molecule. Examples of organic polyisocyanates include aromatic polyisocyanates in which the isocyanate groups are bonded to aromatic hydrocarbons, aromatic aliphatic polyisocyanates in which the isocyanate groups are bonded to aliphatic hydrocarbon groups, and aliphatic polyisocyanates consisting only of aliphatic hydrocarbon groups.

Examples of polymer polyols include polyester polyols, polycarbonate polyols, polyoxyalkylene polyols, hydrocarbon polyols, poly(meth)acrylic polyols, animal and vegetable polyols, copolyols thereof, and mixtures of two or more of the above polyols. Note that "polymer" means that the number average molecular weight calculated as polystyrene by gel permeation chromatography is 1,000 or more. Note that "(meth)acrylic" means "acrylic and/or methacrylic".

The water content of the aqueous adhesive composition containing the water-dispersed polyurethane is not particularly limited, but may be, for example, 40% by mass or more and 70% by mass or less. The viscosity at 23°C may be, for example, 40 mPa·s or more and 1000 mPa·s or less.

<Decorative sheet>
In the present invention, any decorative sheet that is in general use can be applied. The decorative sheet includes, as a substrate, for example, a concealing thermoplastic resin layer, a pattern layer, and a transparent thermoplastic resin layer.

Examples of the resin system of the opaque thermoplastic resin layer include polyvinyl chloride, polyvinylidene chloride, polypropylene, polyethylene, ethylene and (meth)acrylic ionomers, polyethylene terephthalate, etc. Among these, polyvinyl chloride resin is preferred from the viewpoint of weather resistance. The thickness of the opaque thermoplastic resin layer is not particularly limited, but is preferably, for example, 20 μm or more and 200 μm or less from the viewpoints of ease of printing decorative patterns, shape retention when applied to a base material, and ease of application to a base material. In addition, it is preferable that the opaque thermoplastic resin layer is colored with opaqueness capable of concealing the lower layer by adding or coating an opaque colorant or an opaque pigment such as titanium oxide, zinc oxide, iron oxide, carbon black, or metal powder to the resin system of the resin layer.

As the printing pigment for the design layer, organic pigments and inorganic pigments with excellent weather resistance are preferred. Examples of yellow pigments include anthraquinone, monoazo, disazo, benzimidazolone, isoindolinone, anthraquinone, iron oxide, and mixtures thereof. Examples of red pigments include diketopyrrolopyrrole, polyazo, monoazo, quinacridone, iron oxide, and mixtures thereof. Examples of indigo pigments include phthalocyanine and cobalt blue. Examples of black pigments include carbon black and iron oxide.

For example, acrylic resin or polyolefin resin with a weather-resistant formulation (benzotriazole-based, benzophenone-based, triazine-based ultraviolet absorbers, hindered amine-based light stabilizers, hindered phenol-based antioxidants, etc.) is used for the transparent thermoplastic resin layer. Of these, acrylic resins are preferred from the standpoint of design properties such as transparency and gloss.

<Other embodiments>
Next, another embodiment of the present invention will be described. Before the coating process of coating the aqueous adhesive composition containing the water-dispersed polyurethane, a primer may be coated on the base material in advance. By coating the base material with a primer, it is possible to prevent interfacial peeling between the base material and the aqueous adhesive composition layer, and to further improve the adhesive strength between the base material and the decorative sheet.

An example of the primer is an aqueous primer composition. An example of the aqueous primer composition is an aqueous primer composition containing an anionic group-containing polyurethane resin (A) obtained by reacting an organic isocyanate compound (a) with an active hydrogen-containing compound (b) containing an active hydrogen-containing (meth)acrylic polymer (b-1) and an active hydrogen-containing compound (b-2) having an anionic group to synthesize an isocyanate group-containing urethane prepolymer (U) having an anionic group, and further reacting the resulting mixture with a chain extender (c).

Examples of the organic isocyanate compound (a) include organic polyisocyanate compounds and organic monoisocyanate compounds. Examples of the active hydrogen-containing (meth)acrylic polymer (b-1) include hydroxyl group-containing (meth)acrylic polyols. Examples of the active hydrogen-containing compound (b-2) having an anionic group include active hydrogen-containing compounds having a carboxyl group and active hydrogen-containing compounds having a sulfone group. The chain extender (c) is a compound that has active hydrogen (groups) in it, and reacts (chain extends) with the isocyanate group of the urethane prepolymer (U) to polymerize the urethane prepolymer (U). Examples of the chain extender (c) include amine compounds such as ethylenediamine, 1,4-tetramethylenediamine, 2-methyl-1,5-pentanediamine, 1,4-butanediamine, 1,6-hexamethylenediamine, 1,4-hexamethylenediamine, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, 1,3-bis(aminomethyl)cyclohexane, xylylenediamine, piperazine, adipoylhydrazide, hydrazine (including hydrates), 2,5-dimethylpiperazine, diethylenetriamine, and triethylenetetramine.

The following describes examples of the present invention, but the present invention is not limited to the embodiments.

<Water-based adhesive composition containing water-dispersible polyurethane>
Water-dispersed polyurethane emulsion WU-1
In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen seal tube, and a heating/cooling device, 344 g of polytetramethylene ether glycol (PTG 2000, number average molecular weight 2,000, manufactured by Hodogaya Chemical Co., Ltd.), 126 g of isophorone diisocyanate (IPDI), and 0.03 g of dibutyltin dilaurate (DBTDL) were charged while flowing nitrogen gas, and reacted for 2 hours at 80° C. Next, after cooling this reaction liquid to 50° C., 23.5 g of dimethylolpropionic acid (DMPA), 17.7 g of triethylamine (TEA), and 194 g of acetone were added and reacted for 3 hours. Further, 216 g of acetone was added to this reaction liquid and cooled to 30° C., 8.5 g of 3-aminopropyltriethoxysilane was added and stirred, a mixed liquid consisting of 10 g of hydrazine monohydrate, 103 g of isopropyl alcohol (IPA) and 778 g of water was added and stirred at high speed, and the acetone and IPA were distilled off from this liquid to obtain an aqueous polyurethane emulsion WU-1. The obtained aqueous polyurethane emulsion WU-1 had a solid content of 41% by mass, a viscosity at 25° C. of 110 mPa·s and an average particle size of 78 nm.

Dispercol U42, a water-dispersible polyurethane available on the market (manufactured by Sumika Covestro Urethane Co., Ltd., has a minimum heat activation temperature (melting point) of 80°C to 100°C)
Dispercol U56 (manufactured by Sumika Covestro Urethane Co., Ltd., minimum heat activation temperature (melting point) is 55℃ to 65℃

<Primer>
Water-based primer P-1
Into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen seal tube, and a heating/cooling device, 96.1 g of dimethyl carbonate, 53.5 g of acrylic polyol (ARUFONUH-2041, manufactured by Toagosei Co., Ltd., hydroxyl value 120 mg KOH/g, number average molecular weight 1,320, the number of hydroxyl groups calculated from the hydroxyl value and number average molecular weight is an average of 2.8 per molecule), 5.0 g of oxypropylene triadduct of bisphenol A (BAP-3G, manufactured by Nippon Nyukazai Co., Ltd., hydroxyl value 280 mg KOH/g), 71.5 g of isophorone diisocyanate (IPDI), hexamethyldisiloxane (DMDS), 1.0 g of dimethyl carbonate, ... 17.9 g of an isocyanurate modified polyisocyanate (isocyanurate trimer, Sumidur N3300, manufactured by Sumika Bayer Urethane Co., Ltd., isocyanate group content 21.8%, NCO equivalent 193) and 0.1 g of stannous octylate as a reaction catalyst were charged, and the mixture was gradually heated to 70°C while being careful not to generate heat, and the reaction was continued until the isocyanate group content in the reaction system was 10.3 mass% or less. Then, 18.0 g of 2,2-dimethylolpropionic acid and 12.9 g of triethylamine were added and further reacted to obtain an isocyanate group-containing urethane prepolymer solution having an anionic group. The isocyanate group content of the isocyanate group-containing urethane prepolymer solution having an anionic group was 5.0 mass%. Next, 546.8 g of water was added to emulsify and disperse the isocyanate group-containing urethane prepolymer having an anionic group, and then a mixed solution of 253.8 g of water, 16.7 g of N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane (aminosilane coupling agent KBM-602, manufactured by Shin-Etsu Silicones Co., Ltd.) and 3.8 g of hydrazine monohydrate was added and a chain extension reaction was carried out at 30° C. Furthermore, dimethyl carbonate was distilled off from this solution to obtain an aqueous primer composition P-1 (theoretical resin component 19.8% by mass) containing a polyurethane resin having an anionic group.

<Decorative sheet>
Bonlex BE (BE-701): manufactured by Takiron C.I. Co., Ltd., softening point 182°C
RENOPLAS (HSE47516): manufactured by Takiron C.I. Co., Ltd., softening point 204°C

<Base material>
Mortar board measuring 70mm x 150mm and 10mm thick

<Test Method>
(1) 90 degree peel adhesion strength The peel adhesion strength of the aqueous adhesive composition containing water-dispersible polyurethane was measured by applying water-based primer P-1 as necessary to the above-mentioned base material using each of the above-mentioned decorative sheets in accordance with JIS A 5536:2015 6.3.3b)2) at 23 ° C., 50% RH atmosphere, and then curing for 30 minutes, and then applying WU-1 and the above-mentioned commercially available water-dispersible polyurethane, and curing for 7 days. Then, a 200 mm × 25 mm decorative sheet was pressed at a pressure of 100 g / cm 2 for 10 seconds at each temperature shown in Table 1 below using a tabletop test press (SA-302, manufactured by Tester Sangyo Co., Ltd.) to prepare a test specimen, which was then left to stand for ¹ day in an atmosphere of 23 ° C. and 50% RH, and then 90 degree peeling was performed in accordance with JIS A 5536:2015 6.3.3e)1). An adhesive strength of 10.0 [N/25 mm] or more was considered to be acceptable.

(2) Breakage State The breakage state of the test specimens subjected to the 90 degree peel adhesion strength test was evaluated according to the following criteria.
AF: Interfacial peeling between the decorative sheet and the adhesive GA: Interfacial peeling between the base material and the adhesive F: Destruction of the decorative sheet The numbers to the right of AF, GA, and F indicate the proportion of the evaluation as a percentage (%).

(3) Sheet Surface The surface condition of the decorative sheet was visually observed, and a sheet with at least a few wrinkles was rated as passing.

(4) Softening Point A square frame was made on a release paper using a 2 mm thick square backer, and WU-1 and a commercially available water-dispersible polyurethane were poured into the frame. Excess sample was removed with a spatula, the surface was smoothed, and the sample was aged for 7 days in an atmosphere of 23°C and 50% RH to obtain a sheet for measuring the softening point.

Using a thermomechanical analyzer (TMA8310, manufactured by Rigaku Corporation), the softening point of the softening point temperature measurement sheet was measured by inserting a transparent quartz pin (tip diameter: 0.5 mm) into the softening point temperature measurement sheet at a pressure of 9.8 mN in an air atmosphere at a temperature range of 30°C to 350°C at a heating rate of 10°C/min. The softening point of the decorative sheet was also measured in the same manner as the softening point temperature measurement sheet. The measurement results of the softening point of the decorative sheet are as described above.

The test results are shown in Table 1 below.

As can be seen from Table 1 above, Dispercol U42 and Dispercol U56, in which the softening point of the polyurethane in the aqueous adhesive composition layer is lower than that of the decorative sheet, had excellent adhesive strength by satisfying the condition that the heating temperature in the bonding process was 120°C and 180°C, respectively, which was higher than the softening point of the polyurethane in the aqueous adhesive composition layer and lower than the softening point of the decorative sheet, and also suppressed the occurrence of wrinkles due to thermal damage, allowing the decorative sheet to maintain an excellent appearance during the bonding process. Furthermore, the adhesive strength of Dispercol U42 and Dispercol U56 was further improved by applying a primer.

On the other hand, when the heating temperature in the bonding process was set to 210°C, which is higher than the softening point of the decorative sheet, wrinkles occurred due to heat damage, and an excellent appearance could not be maintained. In addition, when bonlex BE was used as the decorative sheet and WU-1 was used as the aqueous adhesive composition containing water-dispersible polyurethane, the softening point of the polyurethane in the aqueous adhesive composition layer was higher than that of the decorative sheet, so even if the heating temperature in the bonding process was set to 120°C or 180°C, which is lower than the softening point of the decorative sheet, no adhesive strength was obtained. In addition, when RENOPLAS was used as the decorative sheet and WU-1 was used as the aqueous adhesive composition containing water-dispersible polyurethane, if the heating temperature in the bonding process was set to 120°C or 180°C in order to suppress the occurrence of wrinkles due to heat damage, the heating temperature in the bonding process was lower than the softening point of the polyurethane in the aqueous adhesive composition layer, so no adhesive strength was obtained.

The decorative sheet application method of the present invention can prevent damage to the base material by simple operations when applying or replacing the decorative sheet, and has excellent adhesive strength and appearance, is safe to work with, and reduces the environmental burden, so it can be used with decorative sheets of various materials and can be particularly used in fields where a wide variety of decorative sheets are used as base materials for the exterior and interior of buildings.

Claims (8)

A coating step of coating a water-based adhesive composition containing a water-dispersible polyurethane on a base material;
a drying step of drying the aqueous adhesive composition containing the water-dispersed polyurethane applied onto the base material until the water content of the aqueous adhesive composition containing the water-dispersed polyurethane is 5% by mass or less to form an aqueous adhesive composition layer;
a lamination step of laminating a decorative sheet on the aqueous adhesive composition layer with the rear surface facing the aqueous adhesive composition layer to form a laminate;
a bonding step of subjecting the laminate to a heat treatment to bond the decorative sheet onto a base material;
Including,
a softening point of the decorative sheet is higher than a softening point of the polyurethane of the aqueous adhesive composition layer, the temperature of the heat treatment is higher than the softening point of the polyurethane of the aqueous adhesive composition layer and lower than the softening point of the decorative sheet, and the heat treatment is carried out at a temperature that is at least 20°C higher than the softening point of the polyurethane of the aqueous adhesive composition layer and at least 10°C lower than the softening point of the decorative sheet. The decorative sheet application method according to claim 1, wherein the softening point of the decorative sheet is at least 50°C higher than the softening point of the polyurethane of the aqueous adhesive composition layer. 3. The method for applying a decorative sheet according to claim 1, wherein the softening point of said polyurethane is from 50° C. to 170° C. 4. The method for applying a decorative sheet according to claim 1, wherein the softening point of the decorative sheet is 160° C. or higher and 220° C. or lower. 5. The method for applying a decorative sheet according to claim 1, further comprising applying a primer onto the base material, and then applying an aqueous adhesive composition containing the water-dispersible polyurethane. 6. The method for applying a decorative sheet according to claim 1, wherein the substrate of the decorative sheet comprises a polyvinyl chloride resin layer. 7. The method for applying a decorative sheet according to claim 1, wherein the base material is a ceramic exterior material for a building. 8. The method for applying a decorative sheet according to claim 1, further comprising applying an aqueous adhesive composition containing said water-dispersible polyurethane to the entire surface of said base material.