RU2830427C1 - Thermoplastic polyurethane film and multilayer film - Google Patents

Abstract

FIELD: packaging industry.

SUBSTANCE: present invention relates to a thermoplastic polyurethane film, as well as a multilayer film comprising a surface coating layer formed on one side of the thermoplastic polyurethane film. Thermoplastic polyurethane film contains polyurethane, which is a reaction product obtained using dicyclohexylmethane diisocyanate.

EFFECT: obtained thermoplastic polyurethane film and multilayer film have good stress relaxation property regardless of the type of polyol and have excellent suitability for gluing.

7 cl, 11 dwg, 4 tbl, 11 ex

Description

Field of technology

[0001]

The present invention relates to a thermoplastic polyurethane film suitable for use as a protective sheet for applied paint or a protective sheet for a surface, and to a multilayer film including a surface coating layer formed on one side of the thermoplastic polyurethane film.

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 curved surfaces. For this reason, they are required to have the ability to follow the surface and stretch, and are often based on thermoplastic polyurethane films.

[0003]

These polyurethane films are sticky and when used outdoors where sand, dust or other dirt sticks to the surface, the dirt will settle and cannot be removed, and therefore the above mentioned protective sheets are usually made as multi-layer films by applying layers of dirt-proof coating on the surface of polyurethane films.

[0004]

Meanwhile, the objects to be protected, such as automobiles, have many curved surface parts on the outside, and the films need to be stretched when pasted. Depending on the characteristics of the polyurethane films, the stretching stress of the films may be excessive, or the return stress may be high, which may make it difficult to paste some films. In other words, when pasted on curved surfaces, films that are difficult to stretch or films that are highly elastic when stretched will not conform to the curved surfaces due to the return force, and may cause wrinkling or other problems. Therefore, it is also required that the polyurethane films be easy to stretch and have a low return force.

[0005]

Since this high or low recovery force correlates with the percentage of stress relaxation, the stress relaxation property must be improved to ensure smooth adhesion of the film. In order to obtain such a stress relaxation property, polyurethane films are often defined by the type of polyol, such as polyester-based, polycaprolactone-based, and polycarbonate-based (see, for example, Patent Literature 1-6).

[0006]

In addition, soft polyvinyl chlorides have often been used as such thermoplastic films. This is because, when adding plasticizers to soften them, the loss tangent (tan δ) shows a maximum value (peak value) in an environment with a temperature of 0 to 60°C, which is at and near the normal temperature (see Non-Patent Literature 1), and the stress-strain curve (S-S) is linear and increases smoothly (see Patent Literature 7), resulting in excellent stress relaxation property.

Citation list

Patent literature

[0007]

Patent Literature 1: Japanese Patent Laid-Open No. 2005-272558.

Patent Literature 2: Japanese Translation of PCT International Application Publication No. 2008-539107.

Patent Literature 3: Japanese Patent Laid-Open No. 2015-98574.

Patent Literature 4: Japanese Patent Laid-Open No. 2015-52100.

Patent Literature 5: Japanese Patent Laid-Open No. 2014-166748.

Patent Literature 6: Japanese Patent Laid-Open No. 2018-53193.

Patent Literature 7: Japanese Patent Laid-Open No. 2018-188652.

Non-patent literature

[0008]

Non-Patent Literature 1: “Netto waku porima”, Vol. 32, No. 6, 2011, p. 362-367.

The essence of the invention

Technical task

[0009]

However, when using polyurethane films as in Patent Literatures 1 to 6, it is necessary to check the characteristics of these polyurethanes and determine the type of polyol, and no polyurethane raw material has been proposed that provides the stress relaxation property regardless of the type of polyol.

[0010]

In addition, the surface coating layer also needs to have extensibility to match the polyurethane, but when the extensibility of the surface coating layer is too high, the viscosity is too high, which makes it easy for dirt to stick to the surface, and the extensibility is required in the range that ensures adhesion.

[0011]

On the other hand, the use of soft PVCs is not encouraged by society due to concerns about adverse effects on the human body caused by the dissolution of plasticizers and the formation of dioxin during combustion, and it would also be desirable for thermoplastic films to develop alternative products that exhibit excellent stress relaxation property equivalent to that of soft PVCs.

[0012]

The first object of the present invention is to provide a thermoplastic polyurethane film which is capable of achieving a stress relaxation property regardless of the type of polyol while having good adhesiveness, as well as a multilayer film using the same.

[0013]

In addition, a second object of the present invention is to provide a thermoplastic polyurethane film that exhibits an excellent stress relaxation property equivalent to that of vinyl chloride and can replace vinyl chloride, as well as a multilayer film using the same.

Solution to the problem

[0014]

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

[0015]

That is, the authors concluded that when a thermoplastic polyurethane film is formed by a reaction product obtained using dicyclohexylmethane diisocyanate (H ₁₂ MDI), it has a good stress relaxation property regardless of the type of polyol, has excellent adhesion property, and, even when a surface coating layer is formed thereon, it can be formed into a multilayer film with excellent adhesion property.

[0016]

In addition, the authors came to another conclusion that when the thermoplastic polyurethane film was formed by the reaction product obtained using H ₁₂ MDI, it showed excellent stress relaxation property at the same level as soft PVCs.

[0017]

The present invention is based on these discoveries, and the means for solving the above problems are as follows.

[0018]

<1> A thermoplastic polyurethane film containing thermoplastic polyurethane, which is a reaction product obtained using dicyclohexylmethane diisocyanate (H ₁₂ MDI).

[0019]

<2> A thermoplastic polyurethane film according to <1>, wherein, when the loss tangent value of JIS K7244-4 is measured by raising the temperature from -60°C to a maximum of 60°C, the measured value satisfies conditions (1) and (2):

(1) the maximum value is obtained at an ambient temperature of 15 to 60°C; and

(2) The minimum value is obtained at an ambient temperature of 0°C or below.

[0020]

<3> A thermoplastic polyurethane film according to <2>, wherein, when the loss tangent value of JIS K7244-4 is measured by increasing the temperature from -60°C to a maximum of 60°C, the measured value does not become smaller but remains constant or becomes larger when the temperature is increased from 0 to 25°C.

[0021]

<4> A thermoplastic polyurethane film according to any one of <1> to <3>, wherein the load (residual stress) after 30 seconds after stopping in a state of 40% elongation under the condition of a temperature of 23±2°C is 20 N/25 mm or less, and the stress relaxation percentage after 3 minutes after stopping in this state is 25% or more.

[0022]

<5> A thermoplastic polyurethane film according to any one of <1> to <4>, wherein the overall light transmittance according to JIS K7361-1 is 90% or more.

[0023]

<6> The thermoplastic polyurethane film according to any one of <1> to <5>, wherein the haze value according to JIS K7136 is 3.0 or less.

[0024]

<7> A multilayer film comprising a surface coating layer formed on one side of a thermoplastic polyurethane film according to any one of items <1> to <6>.

[0025]

<8> A multilayer film according to <7>, wherein the surface coating layer has a urethane bond.

[0026]

<9> A multilayer film according to <7> or <8>, wherein the overall light transmittance according to JIS K7361-1 is 90% or more.

[0027]

<10> The multilayer film according to any one of <7> to <9>, wherein the haze value according to JIS K7136 is 3.0 or less.

[0028]

<11> A multilayer film according to any one of paragraphs <7> to <10>, wherein the multilayer film is used to protect an adherend having a curved surface.

Positive effects of the invention

[0029]

Since the thermoplastic polyurethane film of the present invention contains a reaction product obtained using dicyclohexylmethane diisocyanate (H ₁₂ MDI), the stress relaxation property can be achieved regardless of the type of polyol, and good adhesion can be obtained.

[0030]

Since the thermoplastic polyurethane film of the present invention is used in the multilayer film of the present invention, good adhesion property can be achieved.

[0031]

In addition, since the thermoplastic polyurethane film of the present invention has a thermoplastic polyurethane layer containing a thermoplastic polyurethane which is a reaction product obtained using H ₁₂ MDI, the temperature range in which the maximum loss tangent value is exhibited and the shape shown by the stress-strain curve are close to the temperature range and the shape of the curve of soft polyvinyl chlorides, the film exhibits an excellent stress relaxation property at the same level as the stress relaxation property of soft polyvinyl chlorides, and can be used as an alternative product thereto.

Brief description of the drawings

[0032]

[Figure 1] FIG. 1 shows one form of the layer configuration of the multilayer film of the present invention.

[Figure 2] FIG. 2 shows an example of gluing a multilayer film of the present invention onto an adherent.

[Figure 3] FIG. 3 shows another example of gluing the multilayer film of the present invention to an adherent.

[FIG. 4] FIG. 4 is a graph showing the data for the loss tangent at a temperature from -60 to 60°C for Examples 1-4.

[Figure 5] FIG. 5 is a graph showing the data for the loss tangent at a temperature of -60 to 60°C for Comparative Examples 1 to 3.

[Figure 6] FIG. 6 is a graph showing the data for the loss tangent at a temperature of -60 to 60°C for Comparative Examples 4 to 6.

[Figure 7] FIG. 7 is a graph showing the stress-strain curves for Examples 1-4.

[Figure 8] FIG. 8 is a graph showing the stress-strain curves for Comparative Examples 1-3.

[Figure 9] FIG. 9 is a graph showing the stress-strain curves for Comparative Examples 4-6.

[Figure 10] FIG. 10 is a photograph showing the results of adhesion suitability for Example 5.

[Figure 11] FIG. 11 is a photograph showing the results of adhesion suitability for Comparative Example 7.

Description of embodiments of the invention

[0033]

Thermoplastic polyurethane film

In the present invention, the thermoplastic polyurethane is a block copolymer obtained by polymerizing a polyisocyanate, a chain extender and a polyol. In the present invention, dicyclohexylmethane diisocyanate (hereinafter referred to as "H ₁₂ MDI"), which is aliphatic, is selected as the polyisocyanate component. It should be noted that H ₁₂ MDI is required to be present only as a main component, and other polyisocyanate components may be present to the extent that they do not affect the effects of the present invention achieved by H ₁₂ MDI.

[0034]

Examples of H ₁₂ MDI include 4,4'-, 2,4'- or 2,2'-dicyclohexylmethane diisocyanate or a mixture or derivative thereof. One of these polyisocyanates may be used alone or a combination of one or more types thereof may be used.

[0035]

Examples of other polyisocyanate components include aliphatic diisocyanates, alicyclic diisocyanates, isocyanate-terminated compounds obtained by the reaction of polyisocyanates with compounds containing groups with an active hydrogen atom, polyisocyanate-modified products obtained by the reaction of polyisocyanates, and polyisocyanates that are partially stabilized by a blocking agent having one active hydrogen atom in the molecule. Examples of aliphatic diisocyanates include dodecane diisocyanate and trimethylhexamethylene diisocyanate. Examples of alicyclic diisocyanates include cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, norbornane diisocyanatomethyl, and 1,4-bis(isocyanatomethyl)cyclohexane. 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.

[0036]

Examples of the chain extender include 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, dipropylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6-hexanediol and 1,4-bis(2-hydroxyethyl)benzene. It should be noted that one of these compounds may be used alone or a combination of two or more types thereof may be used.

[0037]

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

[0038]

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

[0039]

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).

[0040]

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.

[0041]

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.

[0042]

Commercially available thermoplastic polyurethane products include, for example, the series under the trade name "ESTANE (R)" of Lubrizol Corporation, the series under the trade name "Elastollan (R)" of BASF Japan, the series under the trade name "KRYSTALGRAN" of Huntsman Corporation, and others.

[0043]

In the obtained thermoplastic polyurethane film, the load (residual stress) after 30 seconds after stopping in a state of 40% elongation under the condition of a temperature of 23±2°C is usually 20 N/25 mm or less, preferably 18 N/25 mm or less, and more preferably 16 N/25 mm or less. Usually, when producing a multilayer film and sticking it to a curved surface, a part of the film is stuck to an adherent, then while stretching the film with one hand, the film is moved along the curved surface, and the adherent and the film are firmly attached with a squeegee held in the opposite hand. Therefore, if the residual stress is more than 20 N/25 mm, the force of pulling the film back will be large when sticking, which makes it difficult to fix the position of the film with one hand while stretching it, or causes the adhesive to shift, which may make it difficult to move.

[0044]

In the obtained thermoplastic polyurethane film, the stress relaxation percentage after 3 minutes after stopping in a state of 40% elongation under the condition of a temperature of 23±2°C is usually 25% or more, preferably 30% or more, and more preferably 35% or more. If the stress relaxation percentage is less than 25%, the stress that occurs when producing a multilayer film and stretching it for pasting on a curved surface cannot be relaxed, which may cause wrinkles. There is also a risk of "floating" after pasting the multilayer film.

[0045]

It should be noted that the load described above can be measured, for example, by cutting a specimen of suitable size and elongating it by 40% in a commercially available tensile testing apparatus, and the percentage of stress relaxation can be determined by calculating the percentage of the load measured after 3 minutes relative to the load immediately after stopping.

[0046]

In order to obtain such physical properties, when the temperature in the thermoplastic polyurethane film is increased from -60°C to a maximum of 60°C to measure the change in the loss tangent value as a function of temperature, the measured value preferably satisfies the conditions (1) to (3) described below. In this case, the loss tangent is an index (tan δ) of the viscous element and the elastic element of the object based on the relationship between the peak values of the stress and strain phase waveform (sinusoids) and the phase shift (strain lag) on the time axis, and it can be measured in accordance with the K7244-4 standard.

(1) The maximum value (peak value) is obtained at an ambient temperature of 15 to 60°C, preferably 25 to 50°C.

(2) The minimum value is obtained at an ambient temperature of 0°C or below.

(3) The value does not become smaller but remains constant or becomes larger when the temperature increases from 0 to 25°C.

[0047]

When the measured value meets the above conditions, that is, the wave form of tan δ increases smoothly and continuously, the changes in the physical properties of the film under the conditions of the environment in which the gluing operations are carried out are small, and the film will have excellent stress relaxation property. In addition, when the maximum value of tan δ, that is, the glass transition temperature, is in the range of 15 to 60°C, which corresponds to and is near the normal temperature, the mobility of the molecules constituting the film is low under the conditions of the environment in which the gluing operations of the film are carried out, and when the film is stretched, it exhibits low elastic deformation ability, resulting in excellent suitability for gluing.

[0048]

Suitable examples of a polyisocyanate component that provides a loss tangent value of a thermoplastic polyurethane film that satisfies these requirements include the above-mentioned H ₁₂ MDI.

[0049]

In other words, in conventional cases, it has been considered effective to use specific types of thermoplastic polyurethane obtained from a polyol because the stress relaxation property is considered to vary depending on the types of thermoplastic polyurethane due to the polyol used. In contrast, by using H ₁₂ MDI as a diisocyanate component in the present invention, its reaction product, thermoplastic polyurethane, can provide a good stress relaxation property without taking into account the characteristics described above, even in combination with various polyol components.

[0050]

In addition, by using H ₁₂ MDI, the obtained thermoplastic polyurethane film has the maximum loss tangent (tan δ) value in the environment with a temperature of 15 to 60°C as mentioned above, and its stress-strain (SS) curve is linear and increases smoothly and gradually. Such characteristics are similar to those of soft PVC, and thermoplastic polyurethane film can be an alternative product for soft PVC which is not welcomed by society.

[0051]

In the obtained thermoplastic polyurethane film, the stress value of the film in the state of 10% elongation under the condition of a temperature 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 form folds, resulting in poor adhesion.

[0052]

The hardness of the thermoplastic polyurethane film is not particularly limited, but is usually in the range of a hardness of 70 Shore A to a hardness of 65 Shore D, preferably a hardness of 80 Shore A to a hardness of 60 Shore D, and more preferably a hardness of 85 to 95 Shore A. When the hardness is greater than 65 Shore D, 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 multi-layer film and pasting it, the film may be hard and the ability to conform to a curved surface cannot be obtained. When the hardness of Shore A is less than 70, the rigidity may be weak and the film may be difficult to handle during pasting. It should be noted that 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.

[0053]

Regarding the optical characteristics of the thermoplastic polyurethane 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. 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. It should be noted that the measurement 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.

[0054]

The thermoplastic polyurethane film can be formed into layers by known methods such as, for example, 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.

[0055]

When thermoplastic polyurethane film is formed by the flat die clamp method, it can be produced by passing it through a chill roll together with a release agent on one side or both sides of the resin in the molten state that has been extruded from the flat die.

[0056]

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

[0057]

When the release agent cannot be easily separated by peeling from the laminated film of the release agent and thermoplastic polyurethane, it is preferable to use a release agent whose surface has been subjected to a release treatment. Examples of the release treatment method include a method of coating the surface of the 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 treated with a release agent is suitably used. In addition, silicone-based release agents may migrate into the thermoplastic polyurethane layer and interfere with tight adhesion or adhesion with an adhesive or an adherend, and therefore non-silicone release agents are preferable.

[0058]

The thickness of the thermoplastic polyurethane film layer is not particularly limited, but is usually 50 to 500 μm, preferably 100 to 300 μm, and more preferably 100 to 200 μm. When the film is thinner than 50 μm, the film may be difficult to handle and may be easily scratched by flying stones. When the film is thicker than 500 μm, the film may be difficult to stick and may not have the ability to conform to curved surfaces.

[0059]

The thermoplastic polyurethane film preferably contains an ultraviolet absorber. When the film contains an ultraviolet absorber, if it is used outdoors, the damage to the polyurethane layer and the deterioration of the adhesive in the case where the adhesive or the like is applied to the film for use can be reduced, and the film can be used as an agricultural film that is necessary for blocking ultraviolet rays, and also as a measure to prevent birds and animals that can visually recognize ultraviolet rays.

[0060]

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.

[0061]

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.

[0062]

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-dimethylphenyl)-6-(2-hydroxy-4-isooctyloxyphenyl)-s-triazine, as well as mixtures thereof, modified products thereof, polymerized products and derivatives thereof.

[0063]

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

[0064]

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

[0065]

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.

[0066]

As the antioxidant, phenolic antioxidants, phosphoric acid-based antioxidants, sulfur-based antioxidants and others can be used, and examples thereof include 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.

[0067]

In the thermoplastic polyurethane film, 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.

[0068]

Multilayer film

The multilayer film of the present invention has at least a layer made of the thermoplastic polyurethane film of the present invention (hereinafter referred to as a "thermoplastic polyurethane layer") and a surface coating layer formed on one side of the thermoplastic polyurethane layer to cover the surface thereof.

[0069]

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 gluing the multilayer film of the present invention to an adherend, and FIG. 3 is a diagram showing another example of gluing the multilayer film of the present invention to an adherend.

[0070]

The multilayer film 10 shown in FIG. 1 is formed by a central layer of thermoplastic polyurethane 11 and a surface coating layer 12 formed on its surface.

[0071]

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 the base material, and as shown in FIG. 2, the adhesive layer 13 is provided on the opposite side of the thermoplastic polyurethane surface without the surface coating layer, and the base material is stuck to the adherent "a". With this approach, it is used to prevent scratches and damage to the protected objects, including, for example, the outer parts of vehicles, such as painted surfaces, headlights, window glass and other parts of cars.

[0072]

In addition, since polyurethane is thermoplastic and adhesiveness can also be obtained by thermal melting, in the case of application, the multilayer film 10 can also be glued to the adherent “a” by directly thermal melting it without creating an adhesive layer, as shown in FIG. 3.

[0073]

Thermoplastic polyurethane layer

The thermoplastic polyurethane layer in the present invention is a thermoplastic polyurethane film of the present invention, and the detailed information has already been provided.

[0074]

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 bonded to a curved surface, and cracks in the surface coating layer can be prevented when the film elongates.

[0075]

The tensile property of the surface coating layer can be confirmed by elongating the multilayer film. More specifically, the tensile property can be 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, elongating it, and then measuring the elongation at which cracks begin to appear in the surface coating layer (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.

[0076]

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.

[0077]

Examples of the isocyanate 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.

[0078]

Examples of the isocyanate 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.

[0079]

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

[0080]

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.

[0081]

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.

[0082]

Conventional known diluents may be added to the film-forming resin composition used for the surface coating layer, if necessary. There is no particular limitation on such diluents, and suitable examples include methyl isobutyl ketone (MIBK), ethyl acetate, butyl acetate, methyl ethyl ketone (MEK), and toluene.

[0083]

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.

[0084]

The surface coating layer can be formed by applying a film-forming resin composition (containing a solvent) to the surface of a thermoplastic polyurethane layer, drying it from the solvent and water, and curing it by known methods.

[0085]

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.

[0086]

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 coaters. There is no particular limitation on the drying method, and any known drying method for the film coating can be used accordingly, for example.

[0087]

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(s) in a known coating machine, and a holding chamber.

[0088]

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 curved surface, causing cracking of the surface coating layer.

[0089]

In order to protect the surface coating layer and make it smooth, it is preferable that a release agent be glued to the surface coating layer.

[0090]

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

[0091]

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

[0092]

It is desirable that the surface of the separator be smooth. The surface roughness Ra of the surface of the separator that is in contact with the surface coating layer is preferably 20 nm or less, and even 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 cars.

[0093]

Whether the film appears whitish after pasting can be checked not only by visual evaluation but also by reflective turbidity. Reflective turbidity can be measured by a surface analyzer "Rhopoint IQ-S" manufactured by Konica Minolta Japan, Inc. or other devices. Reflective turbidity is preferably 2.0 (%) or less, and more preferably 1.5 or less.

[0094]

Adhesive layer

When an adhesive layer is provided in the application, 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.

[0095]

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 filler 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.

[0096]

In order that the optical characteristics of the multilayer film of the present invention do not affect the visibility of the protected object, the total light transmittance is preferably 90% or more, and the haze value is preferably 3.0 or less. It should be noted that the measurements of the total light transmittance and the haze value can be carried out using a turbidimeter, and the total light transmittance and the haze value can be measured according to JIS K7361-1 and JIS K7136, respectively.

[0097]

Since the multilayer film of the present invention uses the thermoplastic polyurethane layer of the present invention, it has an excellent stress relaxation property. 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 allows the film to be smoothly adhered to the protected object.

[0098]

Thus, the multilayer film of the present invention can be widely used for protecting adherents having curved surfaces, not only as protective sheets for applied paint or surface protective sheets 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 curved surface parts of flexible liquid crystals and other devices.

Examples

[0099]

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

[0100]

Study 1. Physical properties of thermoplastic polyurethane layer

First, we study how the physical properties of the resulting thermoplastic polyurethane films change depending on the polyisocyanate component used, as described below.

[0101]

Production of thermoplastic polyurethane film

Example 1

Thermoplastic polyurethane obtained by the copolymerization reaction of dicyclohexylmethane diisocyanate as the H ₁₂ MDI polyisocyanate component and poly-ε-caprolactone diol as the polyol component was 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 were pressed in a state where it was sandwiched between PET films as a spacer, to obtain a thermoplastic polyurethane film (thermoplastic polyurethane layer) of Example 1 as a layer of 150 μm in thickness.

[0102]

Example 2

The thermoplastic polyurethane film (thermoplastic polyurethane layer) of Example 2 was prepared in the same manner as in Example 1, except that the polyol component was changed to polyhexamethylene carbonate diol (PHC).

[0103]

Example 3

The thermoplastic polyurethane film (thermoplastic polyurethane layer) of Example 3 is prepared in the same manner as in Example 1, except that the polyol component is changed to polyethylene glycol.

[0104]

Example 4

The thermoplastic polyurethane film (thermoplastic polyurethane layer) of Example 4 was prepared in the same manner as in Example 1, except that the polyol component was changed to poly(ethylene adipate) diol.

[0105]

Comparative example 1

The thermoplastic polyurethane film (thermoplastic polyurethane layer) of Comparative Example 1 was prepared in the same manner as in Example 1 except that the polyisocyanate component was changed to hexamethylene diisocyanate (HDI).

[0106]

Comparative example 2

The thermoplastic polyurethane film (thermoplastic polyurethane layer) of Comparative Example 2 was prepared in the same manner as in Example 3, except that the polyisocyanate component was changed to hexamethylene diisocyanate (HDI).

[0107]

Comparative example 3

The thermoplastic polyurethane film (thermoplastic polyurethane layer) of Comparative Example 3 was prepared in the same manner as in Example 2, except that the polyisocyanate component was changed to hexamethylene diisocyanate (HDI).

[0108]

Comparative example 4

The thermoplastic polyurethane film (thermoplastic polyurethane layer) of Comparative Example 4 was prepared in the same manner as in Example 1 except that the polyisocyanate component was changed to 1,4-hydrogenated xylylene diisocyanate (1,4H ₆ XDI).

[0109]

Comparative example 5

The thermoplastic polyurethane film (thermoplastic polyurethane layer) of Comparative Example 5 was prepared in the same manner as in Example 3 except that the polyisocyanate component was changed to 1,4-hydrogenated xylylene diisocyanate (1,4H ₆ XDI).

[0110]

Comparative example 6

The thermoplastic polyurethane film (thermoplastic polyurethane layer) of Comparative Example 6 was prepared in the same manner as in Example 2 except that the polyisocyanate component was changed to 1,4-hydrogenated xylylene diisocyanate (1,4H ₆ XDI).

[0111]

Measurement of various physical properties

For each of the specimens of the manufactured thermoplastic polyurethane film, the physical properties described below are measured. It should be noted that the hardness is measured using a durometer (a spring-type rubber hardness tester) in accordance with the JIS K7311 standard as mentioned above. The results are shown in Table 1 and Table 2. In addition, the changes in the loss tangent as a function of temperature are shown in the graphs of FIGS. 4-6. Also, the stress-strain curves are shown in the graphs of FIGS. 7-9.

[0112]

Tangent of loss angle

A measuring specimen of 3 cm in length and 5 mm in width is cut out, and the loss tangent tan δ is measured while increasing the temperature in the range of -60°C to a maximum of 60°C using a dynamic viscoelasticity measuring instrument (DMAQ850, manufactured by TA Instruments Japan Inc.). In detail, the storage modulus (E') and the loss modulus (E") are measured in accordance with JIS K7244-4 at a temperature increasing rate of 3°C/min, at a frequency of 3 Hz in a tensile mode, and the loss tangent tan δ is calculated based on the expression represented as " loss tangent tan δ=(E")/(E')" . In addition, the maximum value and the minimum value at this time and the temperatures (peak temperatures) at which they occur are recorded. Moreover, for Examples 1-4 and Comparative Example 6, the numerical value obtained by dividing the maximum value by the minimum value and the temperature difference between the temperature at which the maximum value is obtained and the temperature at which the minimum value is obtained are recorded.

[0113]

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.

In addition, the load is also measured in the same way 3 minutes after stopping and the percentage is calculated relative to the load immediately after stopping.

[0114]

Tensile properties

A measurement 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 under the temperature condition of 23±2°C, and the stress at the state of 10% elongation is measured in Newtons (N).

A stress-strain (S-S) curve is also generated for the range in which the displacement (strain) (in %) of the clamp distance is from 0 to 200%.

[0115]

Optical characteristics

When measuring the total light transmittance (%) according to JIS K7361-1:1997, the turbidity value (%) is also measured according to JIS K7136:2000 using a turbidity meter (NDH7000, manufactured by Nippon Denshoku Industries Co., Ltd.

[0116]

Table 1

Example 1 Example 2 Example 3 Example 4 Configuration Thermoplastic polyurethane layer Isocyanate - H ₁₂ MDI H ₁₂ MDI H ₁₂ MDI H ₁₂ MDI Polyol - Caprolactone Polycarbonate Ether Adipat Hardness According to Shore A 95 90 88 90 Thickness microns 150 150 150 150 Physical properties of thermoplastic polyurethane layer Tangent of loss angle Tan δ max value (temperature) -/℃ 0.31 (44) 0.29 (45) 0.25 (46) 0.34 (29) Tan δ min. value (temperature) -/℃ 0.07 (-50) 0.03 (-60) 0.13 (-60) 0.03 (-59) Max value at 0-60℃/Min value at -60-60℃ - 4.4 9.7 1.9 11.3 Temperature difference between max value and min value ℃ 94 105 106 88 Stress relaxation property 40% and 3 min % 39.3 52.6 44.1 42.1 40% and 30 sec H/25 mm 14.5 10.2 9.4 7.4 Tensile properties 10%Mo H/25 mm 14.9 11.5 7.9 5.4 Optical characteristics Total light transmittance % 92.30 92.05 92.36 91.96 Turbidity % 1.37 1.70 1.54 1.35

[0117]

Table 2

Compare example 1 Compare example 2 Compare
example 3 Compare example 4 Compare example 5 Compare example 6 Configuration Thermoplastic polyurethane layer Isocyanate - HDI HDI HDI 1.4H ₆ XDI 1.4H ₆ XDI 1.4H ₆ XDI Polyol - Capro-lactone Ether Polycarbonate Capro-lactone Ether Polycarbonate Hardness According to Shore A 90 90 85 95 85 95 Thickness microns 150 150 150 150 150 150 Physical properties of thermoplastic polyurethane layer Tangent of loss angle Tan δ max value (temperature) -/℃ 0.26 (-21) 0.23 (-45) 0.65 (-8) 0.23 (-2) 0.37 (-43) 0.24 12) Tan δ min. value at
-60-60℃ (temperature) -/℃ 0.02 (-60) 0.04 (59) 0.02 (-45) 0.02 (-55) 0.04 (44) 0.02 (-41) Max value at 0-60℃/Min value at
-60-60℃ - - - - - - 12.0 Temperature difference between max value and min value ℃ - - - - - 53 Stress relaxation property 40% and 3 min % 26.5 24.2 17.4 28.4 22.8 33.0 40% and 30 sec H/25 mm 27.0 21.9 12.0 30.2 12.9 21.8 Tensile properties 10%Mo H/25 mm 24.1 16.9 7.9 24.5 8.7 16.6 Optical characteristics Total light transmittance % 91.85 92.13 92.62 92.13 92.67 92.38 Turbidity % 1.74 1.49 1.39 1.36 1.30 1.53

[0118]

As shown in Table 1 and Table 2, in the claimed thermoplastic polyurethane layers of Examples 1 to 4, the percentage (%) of the load after 3 minutes relative to the load immediately after stopping is 39% or more, which corresponds to a value of approximately 1.2 to 3 times higher than the numerical values of the thermoplastic polyurethane layers of Comparative Examples. Thus, it is found that when H ₁₂ MDI is used as a polyisocyanate component, it does not matter which polyol component is combined with it, and their reaction product, polyurethane, has an excellent stress relaxation property.

[0119]

In addition, both the residual stress amount in the stress relaxation property and the stress amount in the tensile characteristics are 15 N/25 mm or less in the case of the present invention, while many of the comparative examples exceed 20 N/25 mm, and it can be assumed that the present invention provides good adhesion even when a surface coating layer is formed for producing a multilayer film. It should be noted that the hardness is in an acceptable range for all the examples, and the optical properties are also good in all the examples, with a total light transmittance of 90% or more and a haze of 2.0 or less.

[0120]

Moreover, as shown in FIG. 4, for all the thermoplastic polyurethane layers of Examples 1 to 4, the value of tan δ, the loss tangent, shows a maximum value at a temperature near the normal temperature in the range of 15 to 60°C, or more specifically in the range of 25 to 50°C, and also shows a minimum value at 0°C or lower, resulting in a wave form that smoothly increases continuously. In contrast, as shown in FIG. 5 and FIG. 6, many of the thermoplastic polyurethane layers of Comparative Examples show a maximum value at 0°C or lower, and even in Comparative Example 6, which has the highest peak temperature at which the maximum value was shown, it still remains at 12°C.

From the above, it can be concluded that the thermoplastic polyurethane film of the present invention shows a maximum value of loss tangent at a temperature around normal temperature in the range of 15 to 60°C, shows a minimum value at 0°C or lower, and this value does not become smaller but remains constant or becomes larger when the temperature is increased from 0 to 25°C, which results in excellent stress relaxation property regardless of the combination with the polyol component.

[0121]

In addition, for Examples 1 to 4 and Comparative Example 6, which show a maximum value in the range from 0 to 60°C and also show a minimum value at 0°C or lower, when comparing the numerical value obtained by dividing the maximum value by the minimum value and the temperature difference between the temperature at which the maximum value appears and the temperature at which the minimum value appears, the numerical value obtained by dividing the maximum value by the minimum value is smaller for Examples 1 to 4, while the temperature difference between the temperature at which the maximum value appears and the temperature at which the minimum value appears is larger for Examples 1 to 4. Thus, it can be concluded that while the change in the tan δ value is small, the temperature difference between the maximum value and the minimum value is large, indicating a tendency for the tan δ value to increase smoothly, and as a result, contributes to a good stress relaxation property.

[0122]

Moreover, as shown in FIGS. 7-9, for the claimed thermoplastic polyurethane layers of Examples 1-4, the S-S curve shows a shape that is more linear and gradually smoothly increasing than the curve in the case of the comparative examples.

In this case, for soft polyvinyl chlorides, which are known to have an excellent stress relaxation property, it is also known that when the loss tangent is measured at an ambient temperature of approximately -60 to 60°C, the maximum value appears at a temperature around the normal temperature in the range of 0 to 60°C, and its value differs slightly from the minimum value (see, “Netto waku porima”, Vol. 32, No. 6, (2011), p. 363, FIG. 6). It is also known that when an S-S curve is obtained, it has a shape that is linear and gradually increases smoothly (see, Japanese Patent Laid-Open No. 2018-188652, FIG. 3).

Based on the above, it can be concluded that the thermoplastic polyurethane film of the present invention can exhibit excellent stress relaxation property at the same level as soft polyvinyl chlorides while reducing the effects on the human body, and can be used as an alternative product thereto.

[0123]

Study 2. Physical properties of multilayer film

Next, an evaluation was made of how the physical properties changed depending on the polyisocyanate component used when a surface coating layer was additionally formed to produce a multilayer film (base material layer), as described below.

[0124]

Obtaining a multilayer film

Example 5

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

The PET film is peeled off on one side of the thermoplastic polyurethane layer obtained in Example 1, the above-described coating liquid for the surface coating layer is applied thereto so that the thickness after drying is 10 μm, and the multilayer film (base material layer) of Example 5 is obtained.

[0125]

Example 6

As a coating liquid for forming a film coating of the surface coating layer, a coating liquid is prepared from a fluorine-modified acrylic urethane resin B by adding an isocyanate-based curing agent (solid content 60%) and methyl isobutyl ketone (MIBK) as a diluting solvent to a fluorine-modified acrylic polyol (solid content 30%) and mixing them in a weight ratio of 44:20:36.

The PET film is peeled off on one side of the thermoplastic polyurethane layer obtained in Example 1, the above-described coating liquid for the surface coating layer is applied thereto so that the thickness after drying is 10 μm, and the multilayer film (base material layer) of Example 6 is obtained.

[0126]

Example 7

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

The PET film is peeled off on one side of the thermoplastic polyurethane layer obtained in Example 1, the above-described coating liquid for the surface coating layer is applied thereto so that the thickness after drying is 10 μm, and the multilayer film (base material layer) of Example 7 is obtained.

[0127]

Example 8

As a coating liquid for forming a film coating of a surface coating layer, a coating liquid is prepared from a silicone-modified acrylic urethane resin by adding an isocyanate-based curing agent (solid content 75%) and methyl ethyl ketone (MEK) as a diluting solvent to a silicone-modified acrylic polyol (solid content 33%) and mixing them in a weight ratio of 55:9:36.

The PET film is peeled off on one side of the thermoplastic polyurethane layer obtained in Example 1, the above-described coating liquid for the surface coating layer is applied thereto so that the thickness after drying is 10 μm, and the multilayer film (base material layer) of Example 8 is obtained.

[0128]

Example 9

As a coating liquid for forming a film coating of a surface coating layer, a coating liquid is prepared from a silicone-fluorine-containing copolymer resin by adding an isocyanate-based curing agent (solid content 75%) to a silicone-fluorine-containing copolymer resin having a functional group (solid content 10%) and mixing them in a weight ratio of 93:7.

The PET film is peeled off on one side of the thermoplastic polyurethane layer obtained in Example 1, the above-described coating liquid for the surface coating layer is applied thereto so that the thickness after drying is 10 μm, and the multilayer film (base material layer) of Example 9 is obtained.

[0129]

Example 10

The multilayer film (base material layer) of Example 10 was prepared in the same manner as in Example 5, except that the coating liquid for the surface coating layer in Example 5 was applied to the thermoplastic polyurethane layer obtained in Example 3.

[0130]

Example 11

The multilayer film (base material layer) of Example 11 was prepared in the same manner as in Example 5, except that the coating liquid for the surface coating layer in Example 5 was applied to the thermoplastic polyurethane layer obtained in Example 4.

[0131]

Comparative example 7

The multilayer film (base material layer) of Comparative Example 7 was prepared in the same manner as in Example 5, except that the coating liquid for the surface coating layer in Example 5 was applied to the thermoplastic polyurethane layer obtained in Comparative Example 4.

[0132]

Comparative example 8

The multilayer film (base material layer) of Comparative Example 8 was prepared in the same manner as in Example 5, except that the coating liquid for the surface coating layer in Example 5 was applied to the thermoplastic polyurethane layer obtained in Comparative Example 6.

[0133]

Comparative example 9

The multilayer film (base material layer) of Comparative Example 9 was prepared in the same manner as in Example 5, except that the coating liquid for the surface coating layer in Example 5 was applied to the thermoplastic polyurethane layer obtained in Comparative Example 1.

[0134]

Comparative example 10

The multilayer film (base material layer) of Comparative Example 10 was prepared in the same manner as in Example 5, except that the coating liquid for the surface coating layer in Example 5 was applied to the thermoplastic polyurethane layer obtained in Comparative Example 2.

[0135]

Measurement and evaluation of various physical properties

For each of the samples of the base material layer of the manufactured multilayer film, the stress relaxation property, tensile properties and optical properties are measured in the same way as for the above-mentioned thermoplastic polyurethane films, and in the case of tensile properties, the crack elongation of the surface coating layer is measured, which is an index of crack resistance. In addition, the suitability for gluing the multilayer film to the protected object is assessed, as described below. The results are presented in Table 3 and Table 4. It should be noted that in the case of hardness, the tables show the values that were known at the time of obtaining the thermoplastic polyurethane layers.

[0136]

Extension of cracks in the surface coating layer

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 under the temperature condition of 23±2°C, and the elongation at which cracks begin to appear in the surface coating layer (crack elongation of the surface coating layer) is measured.

[0137]

Suitability for gluing

Each of the prepared multilayer film samples is cut into 10 pieces of 30 mm in width and 100 mm in length. The PET on the thermoplastic polyurethane layer side is peeled off and acrylic adhesive is applied, and then three people are asked to stick the piece on the curved surface of the car door mirror as the protected object. When all three people stick the sample smoothly without wrinkles, the sample is rated as “Good”, and when even one person cannot stick the sample smoothly without wrinkles, he is rated as “Bad”.

It should be noted, as an example, that FIG. 10 shows a photograph after pasting of Example 5 whose suitability for pasting was rated as "Good", and a photograph after pasting of Comparative Example 7 whose suitability for pasting was rated as "Poor" is shown in FIG. 11.

[0138]

Table 3

Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Configuration Surface coating layer Fluorine Modified Acrylic Urethane Resin A Fluorine Modified Acrylic Urethane Resin B Modified acrylic urethane resin Silicone modified acrylic urethane resin Silicone fluorine copolymer resin Fluorine Modified Acrylic Urethane Resin A Fluorine Modified Acrylic Urethane Resin A Thermoplastic polyurethane layer Isocyanate - H ₁₂ MDI H ₁₂ MDI H ₁₂ MDI Polyol - Caprolactone Ether Adipat Hardness According to Shore A 95 88 90 Thickness microns 150 150 125 150 150 150 150 Physical properties of the base material layer (surface coating layer/TPU layer) Stress relaxation property 40% 3 min % 38.2 36.6 35.3 36.5 38.7 35.9 34.2 40% 30 sec H/25 mm 16.5 16.2 14.2 17.7 17.9 15.4 13.1 Tensile properties 10%Mo H/25 mm 14.0 11.5 10.8 16.1 14.6 12.5 8.6 Extension of cracks in the covering layer % 103 96 122 101 82 88 100 Optical characteristics Total light transmittance % 92.29 92.27 92.46 92.25 94.50 92.32 92.11 Turbidity % 1.00 1.30 0.92 1.79 34.41 2.09 1.19 Grade Suitability for gluing - Fine Fine Fine Fine Fine Fine Fine

[0139]

Table 4

Comparative example 7 Comparative example 8 Comparative example 9 Comparative example 10 Configuration Surface coating layer Fluorine Modified Acrylic Urethane Resin A Fluorine Modified Acrylic Urethane Resin A Fluorine Modified Acrylic Urethane Resin A Fluorine Modified Acrylic Urethane Resin A Thermoplastic polyurethane layer Isocyanate - 1,4H6XDI 1,4H6XDI HDI HDI Polyol - Caprolactone Polycarbonate Caprolactone Ether Hardness According to Shore A 95 95 90 90 Thickness microns 150 150 150 150 Physical properties of the base material layer (surface coating layer/TPU layer) Stress relaxation property 40% 3 min ％ 28.3 30.2 22.9 23.5 40% 30 sec H/25 mm 32.8 28.7 35.6 30.0 Tensile properties 10％Mo H/25 mm 25.8 21.7 26.5 21.8 Extension of cracks in the covering layer % 97 103 88 80 Optical characteristics Total light transmittance % 92.10 92.25 91.68 92,00 Turbidity % 1.00 1.28 1.46 1.57 Grade Suitability for gluing - Badly Badly Badly Badly

[0140]

As shown in Table 3 and Table 4, in the claimed base material layers of the multilayer films of Examples 5 to 11, the percentage (%) of the load after 3 minutes relative to the load immediately after stopping is 34% or more, which corresponds to a value of approximately 1.13 to 1.69 times higher than the numerical values of the thermoplastic polyurethane films of the comparative examples. Thus, it was found that the multilayer film having a thermoplastic polyurethane layer containing polyurethane which is a reaction product of H ₁₂ MDI as a polyisocyanate component has an excellent stress relaxation property as a base material layer due to the excellent stress relaxation property of the thermoplastic polyurethane layer.

[0141]

In addition, the base material layers of Examples 5-11 can be smoothly adhered to the protected object by all three people, whereas the base material layers of the comparative examples could not be smoothly adhered. When examining the photographs of FIG. 10 and FIG. 11, it can be seen that in FIG. 10, the sample of Example 5 is smoothly adhered to the door mirror without forming wrinkles, whereas for the comparative example 7 in FIG. 11, large wrinkles are visible.

[0142]

Here, in the base material layers of Examples 5 to 11, both the residual stress value in the stress relaxation property and the stress value in the tensile characteristics are 20 N/25 mm or less, while these values for the base material layers of Comparative Examples 8 to 10 are more than 20 N/25 mm. Therefore, it can be concluded that for Examples 5 to 11, even when the surface coating layer is formed, the adhesion property is good. In addition, since all the surface coating layers have a urethane bond, no cracks are observed in the coating layers and they follow the thermoplastic polyurethane film. It can be noted that the optical properties are good in all the examples, with a total light transmittance of 90% or more and a haze of 3.0 or less.

[0143]

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

Industrial applicability

[0144]

The present invention can be used for protecting adherents having curved surfaces, not only as protective sheets for applied paint or surface protective sheets for preventing scratches caused by abrasive wear and flying stones on the outer parts of vehicles such as cars 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 liquid crystals and other devices. These films can also be used as an alternative film for soft polyvinyl chloride films.

List of reference positions

[0145]

10 - Multilayer film

11 - Thermoplastic polyurethane layer (thermoplastic polyurethane film)

12 - Surface coating layer

13 - Adhesive layer

"a" - Adherent

Claims (10)

1. A thermoplastic polyurethane film containing a thermoplastic polyurethane which is a reaction product obtained using dicyclohexylmethane diisocyanate (H ₁₂ MDI), wherein when the loss tangent value of JIS K7244-4 is measured by increasing the temperature from -60°C to a maximum of 60°C, the measured value satisfies conditions (1) and (2) below: (1) the maximum value is obtained at an ambient temperature of 15 to 60°C; and (2) the minimum value is obtained at an ambient temperature of 0°C or below, and the load (residual stress) after 30 seconds after stopping in a state of 40% elongation under the condition of a temperature of 23±2°C is 20 N/25 mm or less, and the stress relaxation percentage after 3 minutes after stopping in this state is 25% or more. 2. The thermoplastic polyurethane film according to claim 1, wherein, when the loss tangent value according to JIS K7244-4 is measured by increasing the temperature from -60°C to a maximum of 60°C, the measured value does not become smaller but remains constant or becomes larger when the temperature is increased from 0 to 25°C. 3. The thermoplastic polyurethane film according to claim 1, wherein the overall light transmittance according to JIS K7361-1 is 90% or more. 4. The thermoplastic polyurethane film according to claim 1, wherein the haze value according to JIS K7136 is 3.0 or less. 5. A multilayer film comprising a surface coating layer formed on one side of a thermoplastic polyurethane film according to any one of claims 1 to 4. 6. A multilayer film according to claim 5, wherein the surface coating layer has a urethane bond. 7. A multilayer film according to claim 5 or 6, in which the multilayer film is used to protect an adherent having a curved surface.

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