RU2832562C1 - Multilayer protective film - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to polymer materials and relates to a multilayer protective film which is used on external parts of an automobile to prevent damage caused by abrasion and weather conditions. Film has a thermoplastic polyurethane layer and a surface coating layer, where the thermoplastic polyurethane layer contains one or more layers and the layer adjacent to the surface coating layer contains more than 30 wt.% of thermoplastic polyurethane, which is a reaction product obtained using hexamethylene diisocyanate (HDI-TPU), and has thickness of 5 mcm or more, in which, when the thermoplastic polyurethane layer contains one layer, one layer also contains thermoplastic polyurethane, which is a reaction product obtained using dicyclohexyl-methane diisocyanate (H₁₂MDI-TPU).

EFFECT: invention enables to create a multilayer protective film, which has excellent chemical resistance without changing the appearance and reducing adhesion strength, due to preventing swelling of the thermoplastic polyurethane layer when exposed to a chemical.

7 cl, 10 dwg, 7 tbl

Description

Field of technology

[0001]

The present invention relates to a multilayer film having a thermoplastic polyurethane layer and a surface coating layer.

State of the art

[0002]

Adhesive sheets used as protective sheets for applied paint or protective sheets for surfaces to prevent scratches caused by abrasion and flying stones on the exterior of vehicles such as cars and to prevent damage due to weather conditions, are used to protect painted surfaces, headlights, window glass and other parts of cars, and therefore must be adhered even to volumetric step sections or three-dimensional curved surfaces. Therefore, they are required to have the ability to follow the surface and stretchability, they are often based on thermoplastic polyurethane films and can generally be identified by the type of polyol, such as polyester based, polycaprolactone based and polycarbonate based.

[0003]

These polyurethane films are sticky and when used outdoors where sand, dust or other dirt adheres to the surface, the dirt will settle and cannot be removed, and therefore the above-mentioned protective sheets are usually made into multi-layer films by applying layers of dirt-proof coating on the surface of the polyurethane films (see, for example, Patent Documents 1-6).

[0004]

There have also been numerous studies on such multilayer films. For example, Patent Document 7 proposes using a polyester-based thermoplastic polyurethane having high hardness in the surface protective layer to improve the workability during manufacturing.

Citation list

Patent literature

[0005]

Patent Document 1: Japanese Patent Laid-Open No. 2005-272558;

Patent Document 2: Japanese translation of PCT International Application Publication No. 2008-539107;

Patent Document 3: Japanese Patent Laid-Open No. 2015-98574;

Patent Document 4: Japanese Patent Laid-Open No. 2015-52100;

Patent Document 5: Japanese Patent Laid-Open No. 2014-166748;

Patent Document 6: Japanese Patent Laid-Open No. 2018-53193;

Patent Document 7: Japanese Patent Laid-Open No. 2019-1015.

The essence of the invention

Technical task

[0006]

Chemicals can stick to the protective sheets that are applied to cars. Specifically, these substances are cleaning agents called engine cleaners or engine conditioners and are used to clean various places such as engine compartments and areas adjacent to the wheels. Such a chemical, when attached to the protective sheet, can pass through the coating layer and reach the polyurethane film, so that the film dissolves in the chemical or swells in it and then dries, thereby deteriorating its appearance.

[0007]

When the surface of the polyurethane film is provided with layers of antipollution coating, a coating agent diluted with a solvent is often used in the coating layers. The surface of such a polyurethane film is often coated directly, and in this case, the solvent in the coating agent can penetrate into the polyurethane film and destroy the surface of the polyurethane film on the opposite side without a coating layer. This destruction also makes the closed adhesion strength insufficient when an adhesive is applied to the surface or the surface is glued to an adherend by thermal welding.

[0008]

It is therefore required that there be no change in the appearance without swelling of thermoplastic polyurethane films due to penetration of engine cleaners dripped onto the surface coating layers, and that there be no reduction in adhesion strength during application due to application of adhesives or gluing to other adherends by thermal welding or the like.

[0009]

In this context, Patent Document 7, which mentions thermoplastic polyurethane films having a multilayer configuration, makes no mention or suggestion of chemical resistance.

[0010]

Although Patent Document 3 mentions chemical resistance, this patent document considers organic solvents such as gasoline as chemicals that adhere to surfaces, and does not mention chemicals with high dissolving power such as dichloromethane, which is a component of engine cleaners, nor does it mention a change in appearance when chemicals adhere.

[0011]

The object of the present invention is to provide a multilayer film with excellent chemical resistance.

Solution to the problem

[0012]

As a result of careful research aimed at solving the above-mentioned problems, the authors of the present invention have come to the following conclusions.

[0013]

That is, it has been established that a multilayer film having a thermoplastic polyurethane layer and a surface coating layer can have excellent chemical resistance due to the use of thermoplastic polyurethane, which is a reaction product obtained using hexamethylene diisocyanate, in the thermoplastic polyurethane layer and due to the optimization of its content or layer thickness.

[0014]

The present invention is based on these discoveries made by the applicants and the means for solving the above mentioned problems are as follows.

[0015]

<1> A multilayer film having a thermoplastic polyurethane layer and a surface coating layer, in which the thermoplastic polyurethane layer comprises one layer or a plurality of layers, and a layer adjacent to the surface coating layer contains more than 30% by mass of thermoplastic polyurethane which is a reaction product obtained using hexamethylene diisocyanate (hereinafter referred to as "HDI-TPU"), and has a thickness of 5 μm or more.

[0016]

<2> The multilayer film according to item <1>, wherein when the thermoplastic polyurethane layer comprises one layer, the one layer also comprises a thermoplastic polyurethane which is a reaction product obtained by using dicyclohexylmethane diisocyanate (hereinafter referred to as "H ₁₂ MDI-TPU"("H ₁₂ MDI-TPU")).

[0017]

<3> The multilayer film according to item <1>, wherein, when the thermoplastic polyurethane layer comprises a plurality of layers, the layer other than the layer adjacent to the surface coating layer comprises H ₁₂ MDI-TPU.

[0018]

<4> The multilayer film according to <1> or <3>, wherein, when the thermoplastic polyurethane layer comprises a plurality of layers, the layer adjacent to the surface coating layer comprises 100% by weight of HDI-TPU.

[0019]

<5> A multilayer film according to any one of <1> to <4>, wherein the surface coating layer has a urethane bond.

[0020]

<6> A multilayer film according to any one of <1> to <5>, in which the stress at the time of 10% elongation is 20 N/25 mm or less, and the load (residual stress) 30 s after stopping in the state of 40% elongation is 25 N/25 mm or less.

[0021]

<7> The multilayer film according to any one of <1> to <6>, in which the haze value according to JIS K7136 is 3.0% or less.

[0022]

<8> A multilayer film according to any one of paragraphs <1> to <7>, wherein the multilayer film is used to protect an adherend having a curved surface.

Positive effects of the invention

[0023]

The multilayer film of the present invention can have excellent chemical resistance because the layer adjacent to the surface coating layer in the thermoplastic polyurethane layer contains more than 30 mass% of thermoplastic polyurethane, which is a reaction product obtained by using hexamethylene diisocyanate (hereinafter referred to as "HDI-TPU"), and has a thickness of 5 μm or more.

Brief description of the drawings

[0024]

[Figure 1] FIG. 1 is a cross-sectional view showing an example of one shape of a layer configuration of a multilayer film of the present invention.

[Figure 2] FIG. 2 shows an example of gluing the multilayer film of FIG. 1 onto an adherend.

[Figure 3] FIG. 3 shows another example of gluing the multilayer film of FIG. 1 onto an adherend.

[Figure 4] FIG. 4 is a cross-sectional view showing an example of another shape of a layer configuration of a multilayer film of the present invention.

[Figure 5] FIG. 5 shows an example of gluing the multilayer film of FIG. 4 onto an adherend.

[Figure 6] FIG. 6 shows another example of gluing the multilayer film of FIG. 4 onto an adherend.

[Figure 7] FIG. 7 is a photograph showing the results of resistance to the engine cleaner in Example 1.

[Figure 8] FIG. 8 is a photograph showing the results of resistance to engine cleaner in Comparative Example 2.

[Figure 9] FIG. 9 is a photograph showing the results of suitability for sticking to a car door mirror in Example 22.

[Figure 10] FIG. 10 is a photograph showing the results of adhesion suitability on an uneven painted steel sheet in Example 24.

Description of embodiments

[0025]

The multilayer film of the present invention has at least a thermoplastic polyurethane layer and a surface coating layer.

[0026]

FIG. 1 is a diagram showing an example of one form of the layer configuration of the multilayer film of the present invention, FIG. 2 is a diagram showing an example of adhering the multilayer film of FIG. 1 to an adherend, and FIG. 3 is a diagram showing another example of adhering the multilayer film of FIG. 1 to an adherend. FIG. 4 is a diagram showing an example of another form of the layer configuration of the multilayer film of the present invention, FIG. 5 is a diagram showing an example of adhering the multilayer film of FIG. 4 to an adherend, and FIG. 6 is a diagram showing another example of adhering the multilayer film of FIG. 4 to an adherend.

[0027]

The multilayer film 10 shown in FIG. 1 is formed by a central thermoplastic polyurethane layer 11 and a surface coating layer 12 formed so as to adjoin its surface.

[0028]

When sticking the multilayer film 10 to the object to be protected, the thermoplastic polyurethane layer 11 and the surface coating layer 12 are used as a base material, and as shown in FIG. 2, an adhesive layer 13 is provided on the opposite side of the thermoplastic polyurethane surface without the surface coating layer and is stuck to the adherent "a". Thus, the film is used to prevent scratches and wear of the protected objects, including the outer parts of vehicles, such as painted surfaces, headlights, window glass and other parts of cars.

[0029]

In addition, since polyurethane is thermoplastic and the adhesive property can also be obtained by thermal melting, the multilayer film 10 can also be glued to the adherent “a” for use in direct thermal melting without creating an adhesive layer, as shown in FIG. 3.

[0030]

On the other hand, the multilayer film 20 shown in FIG. 4 has a two-layer configuration of a first polyurethane layer 22 and a second polyurethane layer 23 in order from the side where the central thermoplastic polyurethane layer 21 adjoins the surface coating layer 12.

[0031]

In the multilayer film 20, which has such a two-layer configuration of the thermoplastic polyurethane layer 21, the second polyurethane layer 23 provides an improvement in the adhesion suitability of the first polyurethane layer 22. The surface coating layer 12 is formed on the surface of the thermoplastic polyurethane layer 21, as in the multilayer film 10 in FIG. 1.

[0032]

The multilayer film 20 is used as the multilayer film 10 of FIG. 1, in such a way that, as shown in FIG. 5, on the opposite side of the thermoplastic polyurethane surface without the surface coating layer, an adhesive layer 13 is provided and glued to the adherent "a". On the other hand, the multilayer film 20 can also be glued to the adherent "a" for use in direct thermal melting without creating an adhesive layer, as shown in FIG. 6.

[0033]

The components of the respective layers constituting the multilayer film of the present invention are described below.

[0034]

Thermoplastic polyurethane layer

In the present invention, the thermoplastic polyurethane means a block copolymer obtained by polymerizing a polyisocyanate, a chain extender and a polyol, and the thermoplastic polyurethane layer means a single layer containing the thermoplastic polyurethane or a laminate containing a plurality of layers.

[0035]

The present invention can provide a film having excellent chemical resistance by using thermoplastic polyurethane (hereinafter referred to as "HDI-TPU"), which is a reaction product obtained by using hexamethylene diisocyanate (hereinafter referred to as "HDI"), as a component constituting a thermoplastic polyurethane layer.

[0036]

The polyisocyanate component HDI-TPU used in the invention preferably consists only of HDI, and other polyisocyanates may be present as polymerizable components without deteriorating the effects of the present invention.

[0037]

The polyisocyanate of thermoplastic polyurethane is not particularly limited as long as HDI is present as a main component in a layer adjacent to the surface coating layer. Examples thereof include aliphatic diisocyanates, alicyclic diisocyanates, isocyanate-terminated compounds obtained by reacting polyisocyanates with compounds containing groups with an active hydrogen atom, polyisocyanate-modified products obtained by reacting polyisocyanates, and polyisocyanates which are partially stabilized by a blocking agent having one active hydrogen atom in a molecule. Examples of aliphatic diisocyanates include dodecane diisocyanate and trimethylhexamethylene diisocyanate. Examples of alicyclic diisocyanate include cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, and norbornane diisocyanatomethyl. Examples of the reaction of polyisocyanates include the carbodiimidation reaction. Examples of the blocking agent having one active hydrogen atom in the molecule include methanol, n-butanol, benzyl alcohol, ethyl acetoacetate, ε-caprolactam, methyl ethyl ketone oxime, phenol and cresol.

[0038]

Examples of the thermoplastic polyurethane chain extender include, but are not particularly limited to, compounds with a molecular weight of 500 or less. Examples of such compounds include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,9-nonanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, N-phenyldiisopropanolamine, monoethanolamine, dipropylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6-hexanediol and 1,4-bis(2-hydroxyethoxy)benzene.

[0039]

There is no particular limitation on the polyol of the thermoplastic polyurethane as long as it is a compound with a molecular weight of about 200 to 10,000 which has two hydroxy groups in one molecule, and examples thereof include polyetherdiols, polyesterdiols and polycarbonatediols.

[0040]

Specific examples of polyetherdiols include polyethylene glycol, polypropylene glycol (PPG), ethylene oxide-propylene oxide copolymers, and polytetramethylene glycol (PTMG).

[0041]

Examples of polyester diols include poly(ethylene adipate) diol, poly(propylene adipate) diol, poly(butylene adipate) diol (PBA), poly(hexamethylene adipate) diol, poly(butylene isophthalate) diol, and poly-ε-caprolactone diol (PCL).

[0042]

Examples of polycarbonate diols include polyhexamethylene carbonate diol (PHC) and co-condensates of polyhexamethylene carbonate diol with other polyester diols, polyether diols, and polyether ether diols.

[0043]

One of these polyisocyanates, chain extenders or polyols may be used alone or a combination of two or more of their types may be used.

[0044]

Thermoplastic polyurethane is synthesized by known methods such as a one-step method and a prepolymer method, and it can be produced in the form of granules by known methods such as a batch reaction method and a continuous reaction method.

[0045]

Commercially available HDI-TPU products that can be used include, for example, products under the trade name "Miractran (R) XN-2000" series from Tosoh Corp., the trade name "Elastollan (R)" series from BASF Japan, and others.

[0046]

The hardness of the film formed by the thermoplastic polyurethane layer is not particularly limited, but is usually in the range of 70 Shore A hardness to 65 Shore A hardness, preferably 80 Shore A hardness to 60 Shore D hardness, and more preferably 85 to 95 Shore A hardness. When the hardness is greater than 65 Shore D hardness, the load (residual stress) of the film after 30 seconds after stopping in a state of 40% elongation and the stress value of the film in a state of 10% elongation are high, and when producing a multilayer film and pasting it, the film may be hard and the ability to conform to a curved surface cannot be obtained. When the Shore A hardness is less than 70, the hardness may be weak and the film may be difficult to handle during pasting. Shore A hardness is a standard for measuring the hardness of ordinary rubbers, and Shore D hardness is a similar standard for rubbers with high hardness exceeding Shore A 95. Both values can be measured using a durometer (a spring-type rubber hardness tester) in accordance with JIS K7311.

[0047]

The thermoplastic polyurethane layer, when it contains only HDI-TPU, that is, 100% by weight of HDI-TPU excluding trace components such as impurities or additives, can have strong elastic properties of rubber. In order to improve the adhesion property of adherends having steps or three-dimensional curved surfaces, it is preferable to mix HDI-TPU with thermoplastic polyurethane with excellent adhesion property without deteriorating chemical resistance.

[0048]

In the case of mixing HDI-TPU with thermoplastic polyurethane with excellent adhesion property, the compounding weight ratio between HDI-TPU and the resin with excellent adhesion property is more than 3:7, preferably 4:6 or more, and more preferably 5:5 or more. That is, the thermoplastic polyurethane layer contains more than 30 mass%, preferably 40 mass% or more, and more preferably 50 mass% or more of HDI-TPU. When 50 mass% or more of HDI-TPU is contained therein, the chemical resistance can be excellent. On the other hand, if the compounding amount of HDI-TPU is 30 mass% or less, its compatibility with the resin is poor, and the appearance cannot be excellent because the haze value of the thermoplastic polyurethane layer mentioned later is more than 3.0%.

[0049]

HDI-TPU and thermoplastic polyurethane with excellent adhesion can adopt a multilayer configuration without deteriorating chemical resistance, so as to improve adhesion to adherents having steps or three-dimensional curved surfaces. In this case, in the present invention, HDI-TPU is used as a component constituting a layer adjacent to the surface coating layer, so as to obtain chemical resistance. The second polyurethane layer 23 shown in FIG. 4 corresponds to such a layer containing thermoplastic polyurethane with excellent adhesion.

[0050]

Suitable examples of thermoplastic polyurethane with excellent adhesiveness include, in addition to the above-mentioned polyisocyanates, a thermoplastic polyurethane which is a reaction product obtained by using dicyclohexylmethane diisocyanate (hereinafter referred to as “H ₁₂ MDI-TPU”).

[0051]

Commercially available H ₁₂ MDI-TPU products that can be used include, for example, products under the trade name of the “ESTANE (R)” series from Lubrizol Corporation, under the trade name of the “Elastollan (R)” series from BASF Japan, under the trade name of the “KRYSTALGRAN” series from Huntsman Corporation, and others.

[0052]

When the thermoplastic polyurethane layer has a plurality of layers, the HDI TPU-containing layer adjacent to the surface coating layer has a thickness of preferably 5 μm or more, and more preferably 10 μm or more. If the thickness is less than 5 μm, the chemical resistance may not be excellent.

[0053]

In this context, the thickness of the thermoplastic polyurethane layer can be measured in accordance with JIS K7130 using a commercially available film thickness gauge. In addition, the thickness of each layer can be measured, for example, by evaluating at 3 places (both ends and the center) on the cross section under a microscope.

[0054]

In the case of such a plurality of layers, the HDI-TPU-containing layer preferably contains only HDI-TPU, i.e., 100% by weight of HDI-TPU excluding trace components such as impurities or additives. In the absence of other resins compounded therewith, the resulting film generally has good haze and can have excellent chemical resistance.

[0055]

The thermoplastic polyurethane layer having a single layer or a plurality of layers can be formed by known methods such as a die casting method, a clamp die forming method, a blow molding method, and a calendering method, and a clamp die method is particularly preferable.

[0056]

A plurality of resin layers with excellent adhesion can be formed by selecting a suitable direct lamination method such as coextrusion, thermal fusion or extrusion lamination, an indirect lamination method using an adhesive such as dry lamination or the like. Of these, it is preferable to form a film having a plurality of layers by coextruding a plurality of resin layers from a flat die.

[0057]

When a thermoplastic polyurethane layer is formed by a flat die with a clamp method, it can be produced by passing it through a cooling roll together with a separator in the form of a film (or in the form of a sheet) on one side or both sides of the thermoplastic polyurethane in a molten state, which has been extruded from a flat die.

[0058]

Examples of the material that forms the separator include polyester-based resins such as polyethylene terephthalate (PET), polyolefin-based resins such as polyethylene (PE) and polypropylene (PP), polyimide (PI), polyetheretherketone (PEEK), and paper.

[0059]

The thermoplastic polyurethane layer is usually obtained by temporarily laminating a thermoplastic polyurethane in a molten state to a release agent, cooling and curing the thermoplastic polyurethane, and then peeling off the release agent. When the release agent cannot be easily peeled off from such a laminated film of a release agent and a thermoplastic polyurethane, it is preferable to use a release agent whose surface has been further subjected to a release treatment. Examples of the release treatment method include a method of coating the surface of a release agent with a silicone, fluorine-containing, acrylic, melamine, alkyd or other release agent, and a method of laminating a polyolefin-based resin such as polyethylene or polypropylene. For example, a polyethylene terephthalate film whose surface has been treated with a release agent is suitably used as a release agent.

[0060]

In the case of applying a film-forming resin composition to form a surface coating layer or an adhesive onto a thermoplastic polyurethane layer in a subsequent step, silicone release agents, if used, may migrate to the surface of the thermoplastic polyurethane layer and interfere with tight adhesion or adhesion between the thermoplastic polyurethane layer and an adherent or other components such as an adhesive, and therefore non-silicone release agents are preferred.

[0061]

The thickness of the thermoplastic polyurethane layer is not particularly limited, and for both a single layer and a plurality of layers, the total thickness of all layers is usually 50 to 500 μm, preferably 100 to 300 μm, and more preferably 100 to 200 μm. When the thickness is thinner than 50 μm, the film may be difficult to handle during pasting and may be easily scratched by flying stones. When the layer is thicker than 500 μm, the film may be difficult to paste and may not have the ability to conform to steps and three-dimensional curved surfaces.

[0062]

With regard to the optical characteristics of the thermoplastic polyurethane layer, in order that the obtained multilayer film does not affect the visibility of the protected object, the overall light transmittance is preferably 90% or more, preferably 92% or more, and the haze value is preferably 3.0% or less, preferably 2.0% or less. When the overall light transmittance is less than 90% and the haze value is greater than 3.0%, the film may appear whitish when it is pasted on glossy painted surfaces such as automobile surfaces. Measurements of the overall light transmittance and the haze value can be performed using a haze meter, and the overall light transmittance and the haze value can be measured according to JIS K7361-1 and JIS K7136, respectively.

[0063]

In the thermoplastic polyurethane layer, the stress value of the film in the state of 10% elongation under the temperature condition of 23±2°C is preferably 20 N/25 mm or less, and more preferably 15 N/25 mm or less. When this stress value is greater than 20 N/25 mm, the film may be hard, difficult to stretch, and wrinkles are formed, resulting in poor adhesion.

[0064]

In the thermoplastic polyurethane layer, the load (residual stress) after 30 seconds after stopping in the state of 40% elongation under the temperature condition of 23±2°C is usually 25 N/25 mm or less, preferably 20 N/25 mm or less, and more preferably 16 N/25 mm or less. When producing a multilayer film and pasting it on steps or a three-dimensional curved surface, a part of the film is pasted on an adherend, then while stretching the film with one hand, the film is moved along the step or the three-dimensional curved surface, and the adherend and the film are firmly attached with a squeegee held in the opposite hand. Therefore, if the residual stress is more than 25 N/25 mm, when pasting, the force of pulling the film back will be large, which makes it difficult to fix the position of the film with one hand while stretching it at the same time, or causes the adhesive to shift, which may make it difficult to handle.

[0065]

These stresses can be measured, for example, by cutting the specimen to the appropriate size and extending it to a specified length in a commercially available tensile testing machine.

[0066]

The thermoplastic polyurethane layer preferably contains an ultraviolet absorber. When the film contains an ultraviolet absorber, damage to the polyurethane layer and deterioration of the adhesive can be reduced when used outdoors in a case where an adhesive or the like is applied to the film for use.

[0067]

There is no particular limitation on the ultraviolet ray absorber as long as it is conventionally known, and, for example, benzotriazole-based, triazine-based and benzophenone-based ultraviolet ray absorbers are preferable.

[0068]

Examples of the benzotriazole-based ultraviolet absorbers include 2-(2'-hydroxy-5'-methylphenyl)-benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)-5,6-dichlorobenzotriazole), 2-(2'-hydroxy-5'-tert-butylphenyl)benzotriazole, 2-(2'-hydroxy-3'-methyl-5'-tert-butylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-5'-phenylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2’-hydroxy-3’-tert-butyl-5’-methylphenyl)-5-chlorobenzotriazole, 2-(2’-hydroxy-3’,5’-di-tert-amylphenyl)benzotriazole, 2-(2’-hydroxy-3’,5’-di-tert-butylphenyl)benzotriazole, 2-(2’-hydroxy-5’-tert-octylphenyl)benzotriazole, 2-{2’-hydroxy-3’-(3”,4”,5”,6”-tetrahydro-phthalimidomethyl)-5’-methylphenyl}benzotriazole and 2-{2-hydroxy-3,5-bis(α,α’-dimethylbenzyl)phenyl}-2-hydroxybenzotriazole, as well as mixtures thereof, modified products, polymerized products and derivatives thereof.

[0069]

Examples of triazine-based ultraviolet absorbers include 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol, 2-[4-[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine and 2,4-bis(2,4-dimethyl-phenyl)-6-(2-hydroxy-4-isooctyloxyphenyl)-s-triazine, as well as mixtures thereof, modified products, polymerized products and derivatives thereof.

[0070]

Examples of benzophenone-based ultraviolet absorbers include 2,3'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, and 2,2',4,4'-tetrahydroxybenzophenone.

[0071]

In the thermoplastic polyurethane layer, it is also preferable to use these ultraviolet absorbers in combination with a light stabilizer or antioxidant.

[0072]

Examples of light stabilizers include hindered amine based light stabilizers such as poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], dimethylsuccinate-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, and bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl)sebacate.

[0073]

As the antioxidant, phenolic antioxidants, phosphoric acid-based antioxidants, sulfur-based antioxidants and others can be used, and examples thereof include sterically hindered phenolic antioxidants such as antioxidants under the trade name Irganox 1010 and Irganox 1076 manufactured by BASF Japan, and phosphorus-based antioxidants such as an antioxidant under the trade name Adekastab PEP8 manufactured by ADEKA Corporation.

[0074]

In the thermoplastic polyurethane layer, the light transmittance calculated in accordance with the JIS S3107 standard from the data measured with a self-recording spectrophotometer in accordance with the JIS R3106 standard is 25% or less for the transmittance at a wavelength of 300 to 380 nm, preferably 15% or less, and more preferably 10% or less. By suppressing the light transmittance in the ultraviolet region in this way, the film can be used as an agricultural film that requires blocking ultraviolet rays, and also as a measure to prevent various damages caused by birds and animals that can visually recognize ultraviolet rays.

[0075]

Surface coating layer

The surface coating layer in the present invention generally contains a urethane bond in the main chain. If the surface coating layer contains a urethane bond, the layer more easily follows the elongation of the thermoplastic polyurethane layer when it is glued to a step or a three-dimensional curved surface, and cracking of the surface coating layer when the film elongates can be prevented.

[0076]

The tensile property of the surface coating layer can be confirmed by elongating the multilayer film. More specifically, the presence of visible cracks in the surface coating layer is confirmed by cutting strips of the multilayer film obtained by forming the surface coating layer on the thermoplastic polyurethane layer, fixing the strip in a tensile testing machine and elongating it. The elongation percentage at which cracks begin to appear in the surface coating layer is defined as the crack elongation of the surface coating layer. The crack elongation of the surface coating layer is not particularly limited, but is usually 60% or more, preferably 80% or more, and more preferably 100% or more.

[0077]

There is no particular limitation on the composition of the film-forming resin used for the surface coating layer as long as it contains a urethane bond, and a two-component curable type obtained by mixing a polyisocyanate compound and a polyol compound at the time of use is preferable, and a thermosetting type is more preferable.

[0078]

Examples of the polyisocyanate compound include aliphatic diisocyanates, cyclic aliphatic diisocyanates, and trifunctional or more functional isocyanate compounds. Examples of aliphatic diisocyanates include lysine diisocyanate, hexamethylene diisocyanate, and trimethylhexane diisocyanate. Examples of cyclic aliphatic diisocyanates include hydrogenated xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2,4-(or 2,6)-diisocyanate, 4,4'-methylenebis-(cyclohexyl isocyanate), and 1,3-(isocyanatomethyl)cyclohexane. Examples of tri- or more functional isocyanate compounds include lysine triisocyanate.

[0079]

Examples of the polyisocyanate compound may also include isocyanate polymers such as so-called isocyanurate products, biuret products, adducts and allophanate products, and isocyanate compounds attached to polyhydric alcohols or low molecular weight polyester resins.

[0080]

It should be noted that the polyisocyanate compound can be in the form of the so-called blocked isocyanate as long as it reacts with the diol.

[0081]

The polyol compound is preferably at least any compound selected from the group consisting of polycaprolactone polyols, polycaprolactam polyols, polycarbonate polyols, polyester polyols, polyether polyols, acrylic polyols and fluorinated polyols.

[0082]

Examples of the film-forming resin composition also include block polymers in which a polyol compound is copolymerized with a fluorine-containing component, a silicone component and other components, graft polymers in which the fluorine-containing component, the silicone component and other components are attached as side chains, and graft block polymers that combine them.

[0083]

An ultraviolet absorber, a light stabilizer or an antioxidant may be added to the film-forming resin composition used for the surface coating layer, if necessary, as in the case of the thermoplastic polyurethane layer.

[0084]

Commercially available products of the coating composition of the film-forming resin used for the surface coating layer are supplied to the market by, for example, Dainichiseika Color & Chemicals Mfg. Co., Ltd., Tokushiki Co., Ltd., Arakawa Chemical Industries, Ltd., etc.

[0085]

The surface coating layer can be formed by appropriately adjusting the viscosity of the film-forming resin composition by diluting with a solvent or water before application, by applying the composition to the surface of the thermoplastic polyurethane layer, and then drying from the solvent and water and curing by known methods.

[0086]

There is no particular limitation on such a diluting solvent, and suitable examples thereof include methyl isobutyl ketone (MIBK), ethyl acetate, butyl acetate, methyl ethyl ketone (MEK), and toluene.

[0087]

Examples of curing methods include thermal curing, light curing, electron beam curing, moisture curing and oxidative curing. In this case, light curing can be carried out by UV curing, which uses ultraviolet rays for curing, but when the multilayer film is used outdoors, it is necessary to use a weathering agent such as an ultraviolet absorber, and therefore the application of UV curing may be limited. Thus, of the above methods, thermal curing, which heats the resin composition to form a crosslinked structure and cures it, is particularly preferable.

[0088]

There is no particular limitation on the application method, and the application can be carried out by known coating applicators such as, for example, rod coaters, spray coaters, air knife coaters, roller coaters, metallizing rod coaters, grooved roller coaters, reverse roller coaters, dip coaters and pressure die coaters. There is no particular limitation on the drying method, and any known drying method for film coating can be used accordingly, for example.

[0089]

The temperature and time in the case of thermal curing can be set appropriately so that the thermoplastic polyurethane layer is not deformed. The temperature is, for example, 40 to 120°C, and the time is, for example, 10 minutes to 1 week. Examples of the thermal curing method may include methods using hot air, a drying chamber (dryer) in a known coating machine, and a holding chamber.

[0090]

There is no particular limitation on the thickness of the surface coating layer, and the thickness is preferably 3 to 50 μm, and more preferably 5 to 20 μm. When the thickness is less than 3 μm, the surface coating layer cannot achieve the desired performance, and when the thickness is greater than 50 μm, the surface coating layer cannot follow the elongation of the thermoplastic polyurethane layer when bonded to a step or a three-dimensional curved surface, which causes cracking of the surface coating layer.

[0091]

In order to protect the surface coating layer and impart smoothness to the surface of the surface coating layer, it is preferable that a release agent in the form of a film (or in the form of a sheet) be adhered to the surface of the film-forming resin composition after the film-forming resin composition forming the surface coating layer is applied.

[0092]

Examples of the material that forms the separator include polyester-based resins such as polyethylene terephthalate (PET), polyolefin-based resins such as polyethylene (PE) and polypropylene (PP), polyimide (PI), polyetheretherketone (PEEK), and paper.

[0093]

It is preferable to use a release agent whose film surface made of the above-mentioned material has been further subjected to release treatment. Examples of release treatment methods include methods of coating the surface with a silicone, fluorine-containing, acrylic, melamine, alkyd or other release agent, and a method of laminating a polyolefin-based resin such as polyethylene or polypropylene onto the surface. For example, a polyethylene terephthalate film whose surface has been treated with a release agent is suitably used as a release agent.

[0094]

It is desirable that the surface of the separator be smooth. The surface roughness Ra (arithmetic mean of roughness) of the surface of the separator which is adjacent to the surface coating layer is preferably 20 nm or less, and still more preferably 15 nm or less. When this surface roughness Ra is greater than 20 nm, the film may appear whitish when pasted on glossy painted surfaces such as automobiles. Whether the film appears whitish after pasting can be checked not only by visual evaluation but also by reflectance turbidity. Reflectance turbidity can be measured by a surface analyzer "Rhopoint IQ-S" manufactured by Konica Minolta Japan, Inc. or other devices. Reflectance turbidity is preferably 2.0% or less, and more preferably 1.5% or less.

[0095]

Adhesive layer

When an adhesive layer is provided for use, known adhesives can be used. As the adhesive, general-purpose adhesives such as acrylic adhesives, rubber-based adhesives, silicone-based adhesives, polyester-based adhesives, and urethane-based adhesives can be used. Of the above, acrylic adhesives are preferable, since they can exhibit suitable adhesive strength, durability, and other properties.

[0096]

In addition, in addition to the above-mentioned components, materials that are conventionally added to the above-mentioned components, such as a flame retardant, a heat resistance enhancing additive, a plasticizer, a lubricant, an antistatic agent, an electrical conductivity imparting agent, a coloring agent, inorganic and organic fillers, a fibrous reinforcing agent and a reaction retarder, may be added to the thermoplastic polyurethane layer, the surface coating layer and the adhesive layer in such an amount that the physical properties are not affected.

[0097]

With respect to the optical characteristics of the obtained multilayer film, the overall light transmittance is 90% or more, preferably 92% or more, and the haze value is 3.0% or less, preferably 2.0% or less, as in the thermoplastic polyurethane layer.

[0098]

In the obtained multilayer film, the stress at the time of 10% elongation is preferably 20 N/25 mm or less, and the load (residual stress) 30 sec after stopping in the state of 40% elongation is preferably 25 N/25 mm or less. When the stress at the time of 10% elongation is 20 N/25 mm or less, and the load (residual stress) 30 sec after stopping in the state of 40% elongation is 25 N/25 mm or less, the thermoplastic polyurethane layer exhibits moderate extensibility, and the surface coating layer has good ability to follow the thermoplastic polyurethane layer, which ensures good adhesion to an object to be protected.

[0099]

By using HDI-TPU in the thermoplastic polyurethane layer, the multilayer film of the present invention has excellent chemical resistance and can prevent change in appearance and decrease in adhesive strength. Moreover, since the multilayer film of the present invention has a surface coating layer containing a urethane bond, moderate stretchability is obtained and good ability to follow the thermoplastic polyurethane layer is achieved, which ensures smooth adhesion to the object to be protected.

[0100]

Thus, the multilayer film of the present invention can be widely used for protecting adherents having steps or three-dimensional curved surfaces, not only as protective sheets for applied paint or protective sheets for a surface for preventing scratches caused by abrasive wear and flying stones on the exterior of vehicles such as automobiles and for preventing damage due to weather conditions, but also as films that are pasted to protect the screen on parts with a curved surface of flexible liquid crystals and other devices.

[0101]

Examples of the present invention are described below, but the present invention is not limited to the examples described below.

[0102]

Study 1. Physical properties when thermoplastic polyurethane layer is single layer and one polyisocyanate component is used separately

First, the physical properties of the thermoplastic polyurethane layer are studied as a function of the polyisocyanate component, as described below, when the thermoplastic polyurethane layer has a single layer (see FIG. 1) and one polyisocyanate component is used separately.

[0103]

Example 1

A thermoplastic polyurethane resin obtained by a copolymerization reaction of hexamethylene diisocyanate (hereinafter referred to as "HDI") as a polyisocyanate component and a polycarbonate polyol as a polyol component is fed into an extruder, melted and kneaded, and then extruded from a flat die attached to the tip of the extruder.

Both sides of the extrudate are pressed in a state where it is inserted between polyethylene terephthalate (hereinafter referred to as “PET”) films as a separator, to obtain a thermoplastic polyurethane (hereinafter also referred to as “TPU”) film in the form of a layer (thermoplastic polyurethane layer) of 150 μm in thickness.

[0104]

The PET films on both sides of this manufactured thermoplastic polyurethane film were peeled off, and the hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane film were measured as described below. The results are shown in Table 1. The thermoplastic polyurethane film in this state is composed of 100% by weight of thermoplastic polyurethane, which is a reaction product obtained by using hexamethylene diisocyanate (hereinafter referred to as "HDI-TPU").

[0105]

At the same time, as a coating liquid for the film-forming resin composition of the surface coating layer, a coating liquid is prepared from a fluorine-modified acrylic urethane resin A by compounding a fluorine-modified acrylic polyol (solid content 35%) with an isocyanate-based curing agent (solid content 60%) and ethyl acetate as a diluting solvent in a weight ratio of 39:19:42.

[0106]

The PET film on one side of the manufactured TPU layer was peeled off, and a coating liquid for a surface coating layer was applied thereto so that the thickness after drying was 10 μm, thereby obtaining the multilayer film of Example 1. Its resistance to an engine cleaner was evaluated using chemical resistance as an index, as described below.

[0107]

Measurement of each chemical property

Hardness

Hardness is measured using a durometer (a spring-type rubber hardness tester) in accordance with JIS K7311.

[0108]

Stress relaxation property

A measuring specimen of 25 mm in width and 150 mm in length is cut out and fixed in a tensile testing machine (Autograph AG-X, manufactured by Shimadzu Corporation) so that the distance between the clamps is 100 mm. Then, the specimen is stretched at a speed of 200 mm/min under the condition of a temperature of 23±2°C. The tension is stopped when the distance between the clamps reaches 140 mm and the specimen is in a state of elongation of 40% (the elongated state is 1.4 times the original length), and the load (residual stress) in Newtons (N) is measured 30 s after the stop.

[0109]

Tensile properties

A measuring specimen of 25 mm in width and 100 mm in length is cut out and fixed in a tensile testing machine (Autograph AG-X, manufactured by Shimadzu Corporation) so that the distance between the clamps is 50 mm. Then, the specimen is stretched at a speed of 300 mm/min at a temperature of 23±2°C, and the stress at a state of 10% elongation is measured in Newtons (N).

[0110]

Optical characteristics

When measuring the total light transmittance (%) in accordance with JIS K7361-1:1997, also measure the turbidity (%) in accordance with JIS K7136:2000 using a turbidity meter (NDH7000, manufactured by Nippon Denshoku Industries Co., Ltd).

[0111]

Resistance to engine cleaner

In a graduated cylinder, equal volumes of dichloromethane and methanol are weighed to prepare an engine cleaner, which is used as a mixed liquid for chemical resistance testing. One drop of this mixed liquid is added to the surface coating layer of the measurement specimen, and the resulting object is then left alone until 5 seconds and 60 seconds have passed. Then, the surface with the applied drop is wiped with a paper wiping cloth, and the presence or absence of anomalies in appearance is visually confirmed. The evaluation criteria are as follows.

“Good”, indicated by a circle ○: The appearance does not change after 60 s.

"Satisfactory", indicated by the triangle Δ: The appearance does not change after 5 sec, whereas after 60 sec the appearance changes with the appearance of whitishness.

"Bad", indicated by an X: The appearance changes with a whitish appearance after 5 s.

As examples, a photograph of the results for Example 1 is shown in FIG. 7, and a photograph of the results for Comparative Example 2 is shown in FIG. 8.

[0112]

Examples 2-4

Each thermoplastic polyurethane film (thermoplastic polyurethane layer) and each multilayer film were produced in the same manner as in Example 1, except that a thermoplastic polyurethane resin different in hardness from that in Example 1 was used. The hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 1. The results are shown in Table 1.

[0113]

Example 5

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film of Example 5 were produced in the same manner as in Example 1, except that the polyol component of Example 1 was changed to polycaprolactone polyol. The hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 1. The results are shown in Table 1.

[0114]

Example 6

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film of Example 6 were produced in the same manner as in Example 1, except that the polyol component of Example 1 was changed to polyadipate polyol. The hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 1. The results are shown in Table 1.

[0115]

Example 7

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film of Example 7 were produced in the same manner as in Example 1, except that the polyol component of Example 1 was changed to polyether polyol. The hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 1. The results are shown in Table 1.

[0116]

Reference example 1

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film of Reference Example 1 were produced in the same manner as Example 1, except that the polyisocyanate component of Example 1 was changed to diphenylmethane diisocyanate (MDI) as an aromatic isocyanate and the polyol component of Example 1 was changed to polyether polyol. The hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as Example 1. The results are shown in Table 1.

[0117]

Comparative example 1

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film of Comparative Example 1 were produced in the same manner as in Example 1, except that the polyisocyanate component of Example 1 was changed to dicyclohexylmethane diisocyanate (hereinafter referred to as “H ₁₂ MDI”). The hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 1. The results are shown in Table 2.

[0118]

Comparative example 2

The thermoplastic polyurethane film (thermoplastic polyurethane layer) and the multilayer film of Comparative Example 2 were produced in the same manner as in Example 5, except that the polyisocyanate component of Example 5 was changed to H ₁₂ MDI. The hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 1. The results are shown in Table 2.

[0119]

Comparative examples 3 and 4

Each thermoplastic polyurethane film (thermoplastic polyurethane layer) and each multilayer film were produced in the same manner as in Comparative Example 2, except that a thermoplastic polyurethane resin different in hardness from that in Comparative Example 2 was used. The hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 1. The results are shown in Table 2.

[0120]

Comparative example 5

The thermoplastic polyurethane film (thermoplastic polyurethane layer) and the multilayer film of Comparative Example 5 were produced in the same manner as in Example 6, except that the polyisocyanate component of Example 6 was changed to H ₁₂ MDI. The hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 1. The results are shown in Table 2.

[0121]

Comparative example 6

The thermoplastic polyurethane film (thermoplastic polyurethane layer) and the multilayer film of Comparative Example 6 were produced in the same manner as in Example 7, except that the polyisocyanate component of Example 7 was changed to H ₁₂ MDI. The hardness, stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 1. The results are shown in Table 2.

[0122]

[0123]

[0124]

As is apparent from the results of Tables 1 and 2, the multilayer films having the thermoplastic polyurethane layer, which is the reaction product obtained using HDI in Examples 1 to 7 of the present invention, have excellent chemical resistance without changing the appearance because the engine cleaner dropped onto the surface coating layer does not cause swelling of the thermoplastic polyurethane layer (see FIG. 7). In contrast, the multilayer films of Comparative Examples having the thermoplastic polyurethane layer obtained without using HDI are inferior in chemical resistance because the engine cleaner causes swelling of the thermoplastic polyurethane layer and the appearance changes to whitish (see FIG. 8).

It has been found that a multilayer film provided with a coating layer on the surface of a thermoplastic polyurethane layer can have good chemical resistance without swelling of the thermoplastic polyurethane layer in a chemical such as an engine cleaner, by forming the thermoplastic polyurethane layer using a reaction product obtained using HDI.

In this case, the multilayer film of Reference Example 1 also shows excellent chemical resistance, but is not suitable for the purpose of the present invention as a surface protective sheet or the like because this multilayer film uses aromatic isocyanate (MDI) in the thermoplastic polyurethane layer and therefore turns yellow when exposed to light.

[0125]

The hardness is in the acceptable range for all examples, and the optical properties are also good in all examples with a total light transmittance of 90% or more and a haze value of 2.0% or less.

[0126]

On the other hand, thermoplastic polyurethane layers in some examples have a value of 25 N/25 mm or more as a value indicating the stress relaxation property, and a value of 20 N/25 mm or more as a value indicating the tensile properties. Therefore, further studies are desirable from the viewpoint of suitability for multilayer film bonding.

[0127]

Study 2. Physical properties when thermoplastic polyurethane layer has multiple layers

Next, an evaluation was made of how the physical properties of the thermoplastic polyurethane layer change when the thermoplastic polyurethane layer has a plurality of layers, a layer containing HDI-TPU and a layer containing H ₁₂ MDI-TPU, which is a thermoplastic polyurethane with excellent adhesion property (see FIG. 4), and has a varying thickness so as to obtain good results in adhesion property while obtaining good results in chemical resistance.

[0128]

Example 8

Thermoplastic polyurethane obtained by the copolymerization reaction of HDI as a polyisocyanate component and polycarbonate polyol as a polyol component is fed into an extruder, melted and kneaded, and then extruded from a flat die attached to the extruder tip. Both sides of the extrudate are pressed in a state where it is inserted between a PET film on one side and a matte biaxially oriented polypropylene (hereinafter referred to as "OPP") film on the other side, to obtain a thermoplastic polyurethane film in the form of a layer (first thermoplastic polyurethane layer) with a thickness of 25 μm. The obtained thermoplastic polyurethane film is cured for about 1 day, and only the OPP film is peeled off.

[0129]

Thermoplastic polyurethane obtained by the copolymerization reaction of H ₁₂ MDI as a polyisocyanate component and polycaprolactone polyol as a polyol component is fed into an extruder, melted and kneaded, and then extruded from a flat die attached to the extruder tip so that the thickness is 125 μm (the second thermoplastic polyurethane layer). Both sides of the extrudate are pressed in a state where it is inserted between a PET film on one side and a thermoplastic polyurethane film corresponding to the first thermoplastic polyurethane layer mentioned above on the other side, to obtain a thermoplastic polyurethane film (thermoplastic polyurethane layer) with a total thickness of 150 μm. This manufactured thermoplastic polyurethane film is composed of PET/HDI-TPU 25μm/H ₁₂ MDI-TPU 125μm/PET (symbol "/" is displayed between layers, and PET and TPU can be peeled off manually). The first thermoplastic polyurethane layer in this state is 100% by weight HDI-TPU.

[0130]

As for the thickness of the HDI-TPU layer before lamination and the thermoplastic polyurethane film (HDI-TPU 25μm/H ₁₂ MDI-TPU 125μm) after lamination, the thickness is measured at 10 places in the width direction in the obtained film having a width of 300 mm according to the JIS K7130 standard using a constant pressure thickness gauge "FFA-1 1.25N" manufactured by Ozaki MFG. Co., Ltd., and their average value is taken as the thickness.

[0131]

The PET films were peeled off from this manufactured thermoplastic polyurethane film, and the stress relaxation property, tensile properties, and optical properties of the thermoplastic polyurethane layer were measured in the same manner as in Example 1. The results are shown in Table 3. The hardness of the first thermoplastic polyurethane layer in the table is given as the value measured in Study 1 (the same is true for the subsequent examples and comparative examples).

[0132]

The PET film on the HDI-TPU side of the produced thermoplastic polyurethane layer was peeled off, and a coating liquid of the fluorine-modified acrylic urethane resin A of Example 1 was applied to the surface of the HDI-TPU so that the thickness after drying was 10 μm, to obtain a multilayer film of Example 8. The cross section of this multilayer film was observed under a microscope (VHX-6000 digital microscope: manufactured by Keyence Corp.) to confirm that the HDI-TPU layer was 25 μm. The resistance to engine cleaner was evaluated in the same manner as in Example 1 near the position where the cross section was cut off. The results are shown in Table 3.

[0133]

Example 9

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film were produced in the same manner as in Example 8, except that the thickness of the HDI-TPU layer of the first thermoplastic polyurethane layer of Example 8 was changed to 20 μm, while the thickness of the H ₁₂ MDI-TPU layer of the second thermoplastic polyurethane layer of Example 8 was changed to 130 μm. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 8. The results are shown in Table 3.

[0134]

Example 10

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film were produced in the same manner as in Example 8, except that the thickness of the HDI-TPU layer of the first thermoplastic polyurethane layer of Example 8 was changed to 15 μm, while the thickness of the H ₁₂ MDI-TPU layer of the second thermoplastic polyurethane layer of Example 8 was changed to 135 μm. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 8. The results are shown in Table 3.

[0135]

Example 11

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film were produced in the same manner as in Example 8, except that the thickness of the HDI-TPU layer of the first thermoplastic polyurethane layer of Example 8 was changed to 10 μm, while the thickness of the H ₁₂ MDI-TPU layer of the second thermoplastic polyurethane layer of Example 8 was changed to 140 μm. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 8. The results are shown in Table 3.

[0136]

Example 12

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film were produced in the same manner as in Example 8, except that the thickness of the HDI-TPU layer of the first thermoplastic polyurethane layer of Example 8 was changed to 5 μm, while the thickness of the H ₁₂ MDI-TPU layer of the second thermoplastic polyurethane layer of Example 8 was changed to 145 μm. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 8. The results are shown in Table 3.

[0137]

Example 13

The thermoplastic polyurethane film (thermoplastic polyurethane layer) and the multilayer film of Example 13 were produced in the same manner as Example 8, except that the polyol component of Example 8 was changed to polycaprolactone polyol. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as Example 8. The results are shown in Table 3.

[0138]

Example 14

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film were produced in the same manner as in Example 13, except that the thickness of the HDI-TPU layer of the first thermoplastic polyurethane layer of Example 13 was changed to 20 μm, while the thickness of the H ₁₂ MDI-TPU layer of the second thermoplastic polyurethane layer of Example 13 was changed to 130 μm. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 8. The results are shown in Table 3.

[0139]

Example 15

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film were produced in the same manner as in Example 13, except that the thickness of the HDI-TPU layer of the first thermoplastic polyurethane layer of Example 13 was changed to 15 μm, while the thickness of the H ₁₂ MDI-TPU layer of the second thermoplastic polyurethane layer of Example 13 was changed to 135 μm. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 8. The results are shown in Table 3.

[0140]

Example 16

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film were produced in the same manner as in Example 13, except that the thickness of the HDI-TPU layer of the first thermoplastic polyurethane layer of Example 13 was changed to 10 μm, while the thickness of the H ₁₂ MDI-TPU layer of the second thermoplastic polyurethane layer of Example 13 was changed to 140 μm. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 8. The results are shown in Table 3.

[0141]

Comparative example 7

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film were produced in the same manner as in Example 8, except that the thickness of the HDI-TPU layer of the first thermoplastic polyurethane layer of Example 8 was changed to 4 μm, while the thickness of the H ₁₂ MDI-TPU layer of the second thermoplastic polyurethane layer of Example 8 was changed to 146 μm. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 8. The results are shown in Table 4.

[0142]

Comparative example 8

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film were produced in the same manner as in Example 8, except that the thickness of the HDI-TPU layer of the first thermoplastic polyurethane layer of Example 8 was changed to 2 μm, while the thickness of the H ₁₂ MDI-TPU layer of the second thermoplastic polyurethane layer of Example 8 was changed to 148 μm. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 8. The results are shown in Table 4.

[0143]

[0144]

[0145]

As is apparent from the results of Tables 3 and 4, the multilayer films having an HDI-TPU layer thickness of 5 µm or more in Examples 8 to 16 of the present invention have excellent chemical resistance without changing the appearance because the engine cleaner dropped on the surface coating layer does not cause swelling of the HDI-TPU. In contrast, the multilayer films of Comparative Examples having an HDI-TPU layer thickness of less than 5 µm are inferior in chemical resistance because the appearance changes to whitish in a short time. The HDI-TPU layer of 5 µm or less makes it difficult to stably form a film having a width exceeding 1 m, and therefore, its production is problematic.

It has been found that a multilayer film having a thermoplastic polyurethane layer comprising a plurality of layers, an HDI-TPU layer and an H ₁₂ MDI-TPU layer should have an HDI-TPU layer of 5 μm or more in thickness and therefore can have good chemical resistance without swelling of the thermoplastic polyurethane layer in a chemical such as an engine cleaner.

[0146]

In the multilayer films of Examples 8 to 16 having a thermoplastic polyurethane layer comprising a plurality of layers, an HDI-TPU layer and an H ₁₂ MDI-TPU layer, the thermoplastic polyurethane layer has a relatively lower value indicative of the stress relaxation property than that of Examples 1 to 7 having a thermoplastic polyurethane layer comprising a single layer. For example, from a comparison of Example 1 with Examples 8 to 12 or Example 5 with Examples 13 to 16, in which the HDI-TPU is obtained using the same combination of HDI and a polyol component, the stress relaxation property in Examples 8 to 12 is about 50 to 71% relative to Example 1, and the stress relaxation value in Examples 13 to 16 is about 46 to 51% relative to Example 5.

Similarly, in the multilayer films of Examples 8-16, the thermoplastic polyurethane layer has a relatively lower value indicative of tensile properties than that of Examples 1-7. For example, from a comparison of Example 5 with Examples 13-16, in which HDI-TPU is obtained using the same combination of HDI and a polyol component, the tensile properties of Examples 13-16 are about 51-57% relative to Example 5.

Thus, it can be assumed that the multilayer films of Examples 8 to 16 were improved in terms of stress relaxation property and have excellent suitability for being adhered to an object protected by the multilayer film due to having a multilayer configuration of the HDI-TPU layer and the H ₁₂ MDI-TPU layer in combination.

[0147]

Optical performance is good in all examples with overall light transmittance of 92% or greater and haze values of 2.0% or less.

[0148]

Study 3. Physical properties when thermoplastic polyurethane layer is single layer and has combination of HDI-TPU as polyisocyanate component and H ₁₂ MDI-TPU as thermoplastic polyurethane with excellent adhesiveness

Next, it was examined how the physical properties of the thermoplastic polyurethane layer changed depending on the content of HDI-TPU and H ₁₂ MDI-TPU when the thermoplastic polyurethane layer had a single layer (see FIG. 1) and HDI-TPU was used in combination with H ₁₂ MDI-TPU as a thermoplastic polyurethane with excellent adhesiveness to obtain good results in adhesiveness while obtaining good results in chemical resistance.

[0149]

Example 17

HDI-TPU (50 parts by mass) produced by the copolymerization reaction of HDI as a polyisocyanate component and polycarbonate polyol as a polyol component, and H ₁₂ MDI-TPU (50 parts by mass) produced by the copolymerization reaction of H ₁₂ MDI as a polyisocyanate component and polycaprolactone polyol as a polyol component are fed into an extruder, melted and kneaded, and then extruded from a flat die attached to the tip of the extruder. Both sides of the extrudate are pressed in a state where it is inserted between PET films as a spacer, to obtain a thermoplastic polyurethane film in the form of a layer (thermoplastic polyurethane layer) with a thickness of 150 μm.

[0150]

PET films were peeled off from this manufactured thermoplastic polyurethane film, and the stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane film were measured in the same manner as in Example 1. The results are shown in Table 5. The thermoplastic polyurethane film in this state contains 50% by weight of HDI-TPU.

[0151]

The PET film on one side of the produced thermoplastic polyurethane layer was peeled off, and a coating liquid of the fluorine-modified acrylic urethane resin A of Example 1 was applied thereto so that the thickness after drying was 10 μm, to obtain a multilayer film of Example 17. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 1. The results are shown in Table 5.

[0152]

Example 18

A thermoplastic polyurethane film (thermoplastic polyurethane layer) and a multilayer film of Example 18 were produced in the same manner as in Example 17, except that the amount of HDI-TPU and H ₁₂ MDI-TPU compounded in Example 17 was changed to 40 parts by mass and 60 parts by mass, respectively. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 17. The results are shown in Table 5. In this example, the thermoplastic polyurethane film contained 40 mass % of HDI-TPU.

[0153]

Comparative example 9

The thermoplastic polyurethane film (thermoplastic polyurethane layer) and the multilayer film of Comparative Example 9 were produced in the same manner as in Example 17, except that the amounts of HDI-TPU and H ₁₂ MDI-TPU compounded in Example 17 were changed to 30 parts by mass and 70 parts by mass, respectively. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 17. The results are shown in Table 5. In this example, the thermoplastic polyurethane film contained 30 mass % of HDI-TPU.

[0154]

Comparative example 10

The thermoplastic polyurethane film (thermoplastic polyurethane layer) and the multilayer film of Comparative Example 10 were produced in the same manner as in Example 17, except that the amounts of HDI-TPU and H ₁₂ MDI-TPU compounded in Example 17 were changed to 20 parts by mass and 80 parts by mass, respectively. The stress relaxation property, tensile properties and optical properties of the thermoplastic polyurethane layer and the engine cleaner resistance of the multilayer film were measured in the same manner as in Example 17. The results are shown in Table 5. In this example, the thermoplastic polyurethane film contained 20 mass % of HDI-TPU.

[0155]

[0156]

As is evident from the results of Table 5, all the multilayer films having a combination of HDI-TPU and H ₁₂ MDI-TPU in Examples 17 and 18 and Comparative Example 9 have chemical resistance with a change in appearance to such an extent that it is insignificant even when a drop of engine cleaner is applied to the surface coating layer. However, it was found that in order to obtain excellent chemical resistance without a change in appearance with respect to exposure to engine cleaner for a long time, it is desirable to compound the HDI-TPU resin in a ratio of 5:5 or more, that is, 50 mass% or more, as in Example 17.

[0157]

In the multilayer films having a combination of HDI-TPU and H ₁₂ MDI-TPU in Examples 17 and 18, the thermoplastic polyurethane layer has a relatively lower value indicating the stress relaxation property than that in Examples 1 to 7 having a thermoplastic polyurethane layer containing only HDI-TPU. For example, from a comparison of Example 1 with Examples 17 and 18 in which HDI-TPU is obtained with the same combination of HDI and a polyol component, the stress relaxation property in Examples 17 and 18 is about 51 to 54% relative to Example 1.

Similarly, in the multilayer films of Examples 17 and 18, the thermoplastic polyurethane layer has a relatively lower value indicating tensile properties than that of Examples 1 to 7. For example, from a comparison of Example 1 with Examples 17 and 18, in which HDI-TPU is obtained with the same combination of HDI and a polyol component, the tensile properties of Examples 17 and 18 are about 76-77% relative to Example 1.

Thus, it can be assumed that the multilayer films of Examples 17 and 18 have an improved stress relaxation property and have excellent suitability for being glued to an object protected by the multilayer film by combining the HDI-TPU resin with the H ₁₂ MDI-TPU resin.

[0158]

The optical properties are good in all the examples with a total light transmittance of 90% or more, although the haze value is as good as 3.0% or less in Examples 17 and 18, but greatly exceeds 3.0% in Comparative Examples 9 and 10. Therefore, it is found that for good optical properties, it is desirable to blend HDI-TPU with H ₁₂ MDI-TPU in a ratio of more than 3:7, that is, more than 30 mass% of HDI-TPU, and it is more preferable to blend HDI-TPU in a ratio of 5:5 or more, that is, 50 mass% or more.

[0159]

Study 4. Adhesive strength

The surface opposite to the surface coating layer of the thermoplastic polyurethane layer may be damaged due to the solvent that penetrates into the thermoplastic polyurethane layer when applying the film-forming resin composition for the surface coating layer. Therefore, the effect of good or poor chemical resistance on the adhesive strength was investigated as described below.

[0160]

Example 19

As a coating liquid for forming a film coating of the surface coating layer, a coating liquid is prepared from a modified acrylic urethane resin by compounding a modified acrylic polyol (solid content 50%) with an isocyanate-based curing agent (solid content 45%) and butyl acetate as a diluting solvent in a weight ratio of 32:20:48.

[0161]

Then, the PET film on the side of the HDI-TPU thermoplastic polyurethane layer produced in Example 16 was peeled off, and the coating liquid of the modified acrylic urethane resin of Example 1 was applied to the surface of the HDI-TPU so that the thickness after drying was 10 μm, to obtain a multilayer film of Example 19. This multilayer film was evaluated by the adhesive force of the tape as an index of the adhesive strength, as described below. The results are shown in Table 6.

[0162]

Adhesive strength of tape

A 30 mm wide and 100 mm long specimen for measurement is cut out from the manufactured multilayer film. The PET film is peeled off on the side opposite to the surface coating layer of the thermoplastic polyurethane layer, and a 25 mm wide and 120 mm long tape having a 20 μm acrylic adhesive layer and a 150 μm thermoplastic polyurethane layer is press bonded using a rubber roller to the thermoplastic polyurethane surface on the peeling side. Immediately after the press bonding, the tape is attached to the upper clamp of a tensile testing machine (Autograph AG-X: manufactured by Shimadzu Corporation), while the specimen is attached to its lower clamp. Then, the press bonded portion is peeled off at a speed of 300 mm/min, and when the clamp is moved a distance of 160 mm, the peeling load in Newtons (N) is measured, the average of the measured values is taken as the adhesive force of the tape. However, this average of the measured values excludes the measurement value in the area corresponding to the first 25 mm of clamp travel.

[0163]

Example 20

The multilayer film of Example 20 was produced in the same manner as in Example 19, except that the thermoplastic polyurethane layer of Example 19 was replaced with the film produced in Example 11. The tape adhesive force of this multilayer film was measured in the same manner as in Example 19. The results are presented in Table 6.

[0164]

Example 21

The multilayer film of Example 21 was produced in the same manner as in Example 19, except that the thermoplastic polyurethane layer of Example 19 was replaced with the film produced in Example 12. The tape adhesive force of this multilayer film was measured in the same manner as in Example 19. The results are presented in Table 6.

[0165]

Comparative example 11

The multilayer film of Comparative Example 11 was produced in the same manner as in Example 19, except that the thermoplastic polyurethane layer of Example 19 was replaced with the film produced in Comparative Example 2. The tape adhesive force of this multilayer film was measured in the same manner as in Example 19. The results are shown in Table 6.

[0166]

[0167]

As can be seen from the data in Table 6, the multilayer films of Examples 19 to 21 of the present invention have high adhesive strength with a tape adhesive force of 10 N/25 mm or more, which is 1.29 to 1.46 times higher than the tape adhesive force of the multilayer film of Comparative Example 11, respectively. This is probably due to the fact that the diluting solvent present in the formation of the surface coating layer does not penetrate into the thermoplastic polyurethane layer, and the obtained multilayer films of Examples 19 to 21 have excellent chemical resistance and do not show a decrease in adhesive strength caused by the chemical.

For comparison, the adhesive force of the tape made of the H ₁₂ MDI-TPU layer of 150 μm thickness without the surface coating layer formed thereon was estimated in the same manner as above, and it was exactly 12.2 N/25 mm. The multilayer films of Examples 19 to 21 showed a value equivalent to this value. Thus, it is obvious that the diluting solvent present in the formation of the surface coating layer does not penetrate into the thermoplastic polyurethane layer.

[0168]

Study 5. Suitability for gluing

In addition, the suitability for gluing is confirmed and examined as described below when the thermoplastic polyurethane layer has a single layer (HDI-TPU layer) or multiple layers (HDI-TPU layer and H ₁₂ MDI-TPU layer).

[0169]

Example 22

As a coating liquid for forming a coating film of a surface coating layer, a coating liquid of fluorine-modified acrylic urethane resin B is prepared by compounding a fluorine-modified acrylic polyol (solid content of 30%) with an isocyanate-based curing agent (solid content of 60%) and methyl isobutyl ketone (MIBK) as a diluting solvent in a weight ratio of 38:23:39.

[0170]

Then, the PET film on the HDI-TPU side of the first thermoplastic polyurethane layer of the thermoplastic polyurethane layer produced in Example 13 was peeled off, and a coating liquid of fluorine-modified acrylic urethane resin B was applied to the surface of the HDI-TPU so that the thickness after drying was 10 μm, and the multilayer film of Example 22 was obtained.

[0171]

The PET film on the H ₁₂ side of the MDI-TPU multilayer film produced was peeled off, and the stress relaxation property, tensile properties, and optical properties of the multilayer film were measured in the same manner as in Example 1. The engine cleaner resistance was evaluated in the same manner as in Example 1, and the adhesion suitability was evaluated as described below. The results are shown in Table 7.

[0172]

Suitability for gluing

A sample of A4 size is cut out from the manufactured multilayer film. The PET on the thermoplastic polyurethane layer side is peeled off and acrylic adhesive is applied. Then, observers are asked to stick the sample on each object of the curved surface of the car door mirror and the uneven painted steel sheet as the protected objects. Since the door mirror with a three-dimensional curved surface has a higher level of difficulty in sticking than the uneven painted steel sheet, the evaluation criteria are as follows.

"Good", marked with a circle: The sample can be pasted on the car door mirror without forming folds in the multilayer film.

"Satisfactory", indicated by a triangle: Although folds are formed when pasted on a car door mirror, the sample can be pasted on an uneven painted steel sheet without folds.

"Bad", indicated by an X: Wrinkles also form when gluing onto uneven painted steel sheet.

As an example, a photograph of the results of suitability for adhesion to an automobile door mirror in Example 22 is shown in FIG. 9, and a photograph of the results of suitability for adhesion to an uneven painted steel sheet in Example 24 is shown in FIG. 10.

[0173]

Example 23

The multilayer film of Example 23 was produced in the same manner as in Example 22, except that the thermoplastic polyurethane layer of Example 22 was replaced with the film produced in Example 16. The stress relaxation property, tensile properties, and optical properties of this multilayer film were measured in the same manner as in Example 22, and the engine cleaner resistance and adhesion suitability of the multilayer film were also evaluated. The results are shown in Table 7.

[0174]

Example 24

The multilayer film of Example 24 was produced in the same manner as Example 22, except that the thermoplastic polyurethane layer of Example 22 was replaced with the film produced in Example 5. The stress relaxation property, tensile properties, and optical properties of this multilayer film were measured in the same manner as Example 22, and the engine cleaner resistance and adhesion suitability of the multilayer film were also evaluated. The results are shown in Table 7.

[0175]

Example 25

The multilayer film of Example 25 was produced in the same manner as Example 22, except that the thermoplastic polyurethane layer of Example 22 was replaced with the film produced in Example 7. The stress relaxation property, tensile properties, and optical properties of this multilayer film were measured in the same manner as Example 22, and the engine cleaner resistance and adhesion suitability of the multilayer film were also evaluated. The results are shown in Table 7.

[0176]

Comparative example 12

The multilayer film of Comparative Example 12 was produced in the same manner as in Example 22, except that the thermoplastic polyurethane layer of Example 22 was changed to the film produced in Comparative Example 6. The stress relaxation property, tensile properties, and optical properties of this multilayer film were measured in the same manner as in Example 22, and the engine cleaner resistance and adhesion suitability of the multilayer film were also evaluated. The results are shown in Table 7.

[0177]

Comparative example 13

The multilayer film of Comparative Example 13 was produced in the same manner as in Example 22, except that the thermoplastic polyurethane layer of Example 22 was changed to the film produced in Comparative Example 5. The stress relaxation property, tensile properties, and optical properties of this multilayer film were measured in the same manner as in Example 22, and the engine cleaner resistance and adhesion suitability of the multilayer film were also evaluated. The results are shown in Table 7.

[0178]

Comparative example 14

The multilayer film of Comparative Example 14 was produced in the same manner as in Example 22, except that the thermoplastic polyurethane layer of Example 22 was changed to the film produced in Comparative Example 2. The stress relaxation property, tensile properties, and optical properties of this multilayer film were measured in the same manner as in Example 22, and the engine cleaner resistance and adhesion suitability of the multilayer film were also evaluated. The results are shown in Table 7.

[0179]

[0180]

As can be seen from the data in Table 7, all the multilayer films of Examples 22-25 according to the present invention have excellent chemical resistance.

However, in Examples 22 and 23, no fold is formed in the multilayer film adhered to any object among the door mirror of the automobile and the uneven painted steel sheet (see FIG. 9). In contrast, in Examples 24 and 25, folds are formed when adhered to the door mirror of the automobile, although no folds are formed when adhered to the uneven painted steel sheet (see FIG. 10).

Therefore, to obtain chemical resistance as well as excellent suitability for gluing, it is desirable to combine HDI-TPU with H ₁₂ MDI-TPU, as in Examples 22 and 23.

[0181]

On the other hand, the multilayer films of Comparative Examples 12 to 14 having thermoplastic polyurethane containing only H ₁₂ MDI-TPU have excellent adhesiveness but are inferior in chemical resistance. Thus, although H ₁₂ MDI can contribute to improving adhesiveness, HDI is necessary for excellent chemical resistance.

[0182]

The multilayer films of Examples 22 and 23 have a value indicating the stress relaxation property of actually 25 N/25 mm or less and a value indicating the tensile properties of actually 20 N/25 mm or less, while the multilayer films of Examples 24 and 25 have a value of 30 N/25 mm or more as a value indicating the stress relaxation property and more than 20 N/25 mm as a value indicating the tensile properties. Thus, it was found that these stress values within the desired ranges and moderate stretchability of the film are necessary for achieving excellent adhesion, and it is desirable to combine HDI-TPU with H ₁₂ MDI-TPU as in Examples 22 and 23.

[0183]

Optical performance is good in all examples with overall light transmittance of 92% or greater and haze values of 3.0% or less.

[0184]

Although the above embodiments and examples of the present invention are described in detail, the multilayer film of the present invention is not limited to the above embodiments and may include any technical ideas provided within the scope of the present invention.

Industrial applicability

[0185]

The present invention can be used to protect adherents having steps or three-dimensional curved surfaces, not only as protective sheets for applied paint or protective sheets for a surface for preventing scratches caused by abrasive wear and flying stones on the exterior of vehicles such as automobiles and for preventing damage due to weather conditions, but also as films that are pasted to protect the screen on parts with a curved surface of flexible liquid crystals and other devices.

List of reference positions

[0186]

10, 20 - Multilayer film

11, 21 - Thermoplastic polyurethane layer

12 - Surface coating layer

13 - Adhesive layer

22 - First thermoplastic polyurethane layer

23 - Second thermoplastic polyurethane layer

"a" - Adherent.

Claims (9)

1. A multilayer protective film having a thermoplastic polyurethane layer and a surface coating layer, where the thermoplastic polyurethane layer comprises one layer or multiple layers and a layer adjacent to the surface coating layer contains more than 30% by weight of thermoplastic polyurethane which is a reaction product obtained using hexamethylene diisocyanate (HDI-TPU) and has a thickness of 5 μm or more, wherein, when the thermoplastic polyurethane layer comprises one layer, the one layer also contains thermoplastic polyurethane which is a reaction product obtained using dicyclohexyl methane diisocyanate (H ₁₂ MDI-TPU). 2. The multilayer film according to claim 1, wherein, when the thermoplastic polyurethane layer comprises a plurality of layers, the layer other than the layer adjacent to the surface coating layer comprises H ₁₂ MDI-TPU. 3. A multilayer film according to claim 1 or 2, wherein, when the thermoplastic polyurethane layer comprises a plurality of layers, the layer adjacent to the surface coating layer comprises 100 wt.% HDI-TPU. 4. A multilayer film according to any one of claims 1 to 3, wherein the surface coating layer has a urethane bond. 5. The multilayer film according to any one of claims 1 to 4, wherein the stress during 10% elongation is 20 N/25 mm or less and the load (residual stress) 30 s after stopping in the state of 40% elongation is 25 N/25 mm or less. 6. The multilayer film according to any one of claims 1 to 4, wherein the haze value according to JIS K7136 is 3.0% or less. 7. A multilayer film according to any one of claims 1 to 6, wherein the multilayer film is used to protect an adherent having a curved surface.