JP2020157740A - Surface protective film - Google Patents

Abstract

To provide a surface protective film having balanced performances of stress relaxation, transparency and scratch resistance.SOLUTION: A surface protective film 10 has (A) a resin layer containing an ethylene-unsaturated carboxylic acid copolymer or an ionomer thereof, and (B) a resin layer that is formed on at least one side of (A) the resin layer and contains an ethylene-polar monomer copolymer.SELECTED DRAWING: Figure 1

Description

The present invention relates to a surface protective film.

As a film for protecting the surface of the vehicle body, a surface protective film using a polyurethane resin is generally used.

Examples of the technique related to the surface protective film include those described in Patent Document 1.
Patent Document 1 includes a base material of an olefin resin having an adhesive function and a top coat layer of a urethane resin supported by the base material, which is a film used for the exterior of an automobile. Described is an automobile exterior film characterized in that it is attached to an automobile exterior component via a base material.

Japanese Unexamined Patent Publication No. 2003-225977

According to the studies by the present inventors, it has been clarified that the surface protective film using the conventional polyurethane resin is excellent in transparency and scratch resistance, but has the following problems.
First, the surface protective film is attached to the surface of the vehicle body using an adhesive while being stretched so as to follow the shape of the vehicle body. However, if the film strength is too strong or the stretched state is not maintained, the film may peel off over time. That is, according to the study by the present inventors, it is clear that when the surface protective film is stretched and bonded to the vehicle body, the bonded film is likely to be peeled off unless the stress applied to the surface protective film is relaxed. became. For this reason, a plurality of skilled workers are required for the construction work, which is difficult in efficiency and economy.
That is, the present inventors have improved the stress relaxation property of the surface protection film using the conventional polyurethane resin while satisfying the transparency and scratch resistance performance required for the surface protection film. , Found that there is room for improvement.

The present invention has been made in view of the above circumstances, and provides a surface protective film having an excellent balance of stress relaxation, transparency and scratch resistance.

The present inventors have made extensive studies to achieve the above problems. As a result, by laminating the resin layer (A) containing the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer and the resin layer (B) containing the ethylene / polar monomer copolymer, stress relaxation property and transparency are achieved. We have found that the performance balance between property and scratch resistance can be improved, and have arrived at the present invention.

That is, according to the present invention, the following surface protective film is provided.

[1]
A resin layer (A) containing an ethylene / unsaturated carboxylic acid copolymer or an ionomer thereof,
A resin layer (B) laminated on at least one surface of the resin layer (A) and containing an ethylene / polar monomer copolymer.
Surface protective film with.
[2]
In the surface protective film according to the above [1],
A surface protective film in which the ethylene / unsaturated carboxylic acid copolymer or its ionomer contains an ethylene / (meth) acrylic acid copolymer or its ionomer.
[3]
In the surface protective film according to the above [1] or [2],
A surface protective film in which the content of the structural unit derived from the unsaturated carboxylic acid in the ethylene / unsaturated carboxylic acid copolymer or its ionomer is 2% by mass or more and 35% by mass or less.
[4]
In the surface protective film according to any one of the above [1] to [3],
According to JIS K7210: 1999, the melt mass flow rate (MFR) of the above ethylene / unsaturated carboxylic acid copolymer or its ionomer measured at 190 ° C. and 2160 g load is 0.01 g / 10 minutes or more and 50 g. / 10 minutes or less surface protection film.
[5]
In the surface protective film according to any one of the above [1] to [4],
The ethylene / polar monomer copolymer is a surface protective film containing at least one copolymer selected from an ethylene / vinyl ester copolymer and an ethylene / unsaturated carboxylic acid ester copolymer.
[6]
In the surface protective film according to the above [5],
The ethylene / polar monomer copolymer is a surface protective film containing an ethylene / vinyl acetate copolymer.
[7]
In the surface protective film according to any one of the above [1] to [6],
According to JIS K7210: 1999, the melt mass flow rate (MFR) of the ethylene / polar monomer copolymer measured at 190 ° C. and a load of 2160 g is 0.1 g / 10 minutes or more and 150 g / 10 minutes or less. Surface protective film.
[8]
In the surface protective film according to any one of the above [1] to [7],
A surface protective film having a haze of 5% or less as measured according to JIS K7136: 2000.
[9]
In the surface protective film according to any one of the above [1] to [8],
A surface protective film having a total light transmittance of 80% or more measured in accordance with JIS K7136: 2000.
[10]
In the surface protective film according to any one of the above [1] to [9],
A surface protective film further comprising a resin layer (C) containing a thermoplastic polyurethane resin in the outermost layer of either one.
[11]
In the surface protective film according to any one of the above [1] to [10],
A surface protective film further provided with an adhesive layer (D) on the outermost layer of either one.
[12]
In the surface protective film according to the above [11],
The pressure-sensitive adhesive layer (D) is composed of at least one type of pressure-sensitive adhesive selected from urethane-based pressure-sensitive adhesives, rubber-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, styrene-based pressure-sensitive adhesives, olefin-based pressure-sensitive adhesives, and acrylic-based pressure-sensitive adhesives. Surface protective film.
[13]
In the surface protective film according to any one of the above [1] to [12],
A surface protection film that is a paint protection film.
[14]
In the surface protective film according to any one of the above [1] to [13],
A surface protective film used so that the surface of the resin layer (A) is on the atmospheric side.

According to the present invention, it is possible to provide a surface protective film having an excellent balance of stress relaxation, transparency and scratch resistance.

It is sectional drawing which shows typically an example of the structure of the surface protection film of embodiment which concerns on this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Unless otherwise specified, "X to Y" in the numerical range represents X or more and Y or less. Also, in this embodiment, "(meth) acrylic" means "acrylic, methacrylic or both acrylic and methacrylic".

1. 1. Surface Protective Film FIG. 1 is a cross-sectional view schematically showing an example of the structure of the surface protective film 10 according to the embodiment of the present invention.
The surface protective film 10 according to the present embodiment is laminated on at least one surface of a resin layer (A) containing an ethylene / unsaturated carboxylic acid copolymer or an ionomer thereof and an ethylene layer (A), and is ethylene. A resin layer (B) containing a polar monomer copolymer is provided.

As described above, the present inventors improve the stress relaxation property of the surface protection film using the conventional polyurethane resin while satisfying the transparency and scratch resistance performance required for the surface protection film. From this point of view, we found that there is room for improvement.
The present inventors have made extensive studies to achieve the above problems. By laminating a resin layer (A) containing an ethylene / unsaturated carboxylic acid copolymer or its ionomer and a resin layer (B) containing an ethylene / polar monomer copolymer, stress relaxation property, transparency and scratch resistance are achieved. We have found that the performance balance of attachment can be improved, and have reached the present invention.
That is, according to the present embodiment, it is possible to provide a surface protective film having an excellent balance of stress relaxation property, transparency and scratch resistance.

The resin layer (A) is preferably composed of a single layer containing an ethylene / unsaturated carboxylic acid-based copolymer or an ionomer thereof as a main component, but both ethylene / unsaturated carboxylic acid-based copolymers. It may be composed of a plurality of layers having different types and contents of the polymer or its ionomer.
The "main component" means that the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer is contained in the resin layer (A) in an amount of 50% by mass or more.

Further, the resin layer (B) is preferably composed of a single layer containing an ethylene / polar monomer copolymer as a main component, but the type and content of the ethylene / polar monomer copolymer. It may be composed of a plurality of layers having different characteristics.
The "main component" means that the ethylene / polar monomer copolymer is contained in the resin layer (B) in an amount of 50% by mass or more.

In the present embodiment, the overall thickness of the surface protective film 10 is preferably 10 μm or more and 1000 μm or less from the viewpoint of performance balance of stress relaxation property, flexibility, mechanical strength, transparency, interlayer adhesiveness, and scratch resistance. , More preferably 30 μm or more and 500 μm or less.

In the surface protective film 10 according to the present embodiment, the thickness of the resin layer (A) is preferably from the viewpoint of performance balance of stress relaxation property, flexibility, mechanical strength, transparency, interlayer adhesiveness, and scratch resistance. It is 5 μm or more and 200 μm or less, more preferably 10 μm or more and 100 μm or less, and the thickness of the resin layer (B) is preferably 5 μm or more and 800 μm or less, more preferably 20 μm or more and 400 μm or less.

In the surface protective film 10 according to the present embodiment, the haze measured in accordance with JIS K7136: 2000 is preferably 5% or less, more preferably 4% or less, and preferably 3% or less. Especially preferable. The lower limit of the haze of the surface protective film 10 is not particularly limited, but is, for example, 0% or more.
As a result, the transparency of the surface protective film 10 can be further improved.

In the surface protective film 10 according to the present embodiment, the total light transmittance measured in accordance with JIS K7136: 2000 is preferably 80% or more, more preferably 85% or more, and 90% or more. It is particularly preferable to have. The upper limit of the total light transmittance of the surface protective film 10 is not particularly limited, but is, for example, 100% or less.
As a result, the transparency of the surface protective film 10 can be further improved.

The surface protective film 10 according to the present embodiment is, for example, a paint protection film (PPF) for protecting the vehicle body of an automobile, an aircraft, a ship, a motorcycle, etc. from dirt, scratches, etc .; a light guide plate, a polarizing plate, a retardation plate, etc. Protective film for electronic parts to protect the surface of electronic parts; Protective film to protect the surface of synthetic resin plates, decorative plates, metal plates, etc .; windows, building materials, digital signage, packaging, office supplies, medical care It can be suitably used as a protective film for protecting the surface of equipment and the like. Among these, it can be particularly preferably used as a paint protection film.

When the surface protective film 10 according to the present embodiment is used, the resin layer (A) surface may be on the atmospheric side (the side that comes into contact with the atmosphere), or the resin layer (B) surface may be on the atmospheric side. However, from the viewpoint of improving scratch resistance, it is preferable to use the resin layer (A) so that the surface is on the atmospheric side.

Hereinafter, each layer constituting the surface protective film 10 will be described.

<Resin layer (A)>
The resin layer (A) contains an ethylene / unsaturated carboxylic acid-based copolymer or an ionomer thereof as a main component. The ethylene / unsaturated carboxylic acid-based copolymer according to the present embodiment is a polymer obtained by copolymerizing ethylene with at least one unsaturated carboxylic acid. The ionomer of the ethylene / unsaturated carboxylic acid-based copolymer according to the present embodiment is an ionomer of a polymer obtained by copolymerizing ethylene with at least one of unsaturated carboxylic acids, and both ethylene and unsaturated carboxylic acid-based copolymers. It is a resin in which at least a part of carboxyl groups of a polymer is neutralized with metal ions.
As the ethylene / unsaturated carboxylic acid-based copolymer, a copolymer containing ethylene and an unsaturated carboxylic acid can be exemplified.

In the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer, when the total number of the structural units constituting the ethylene / unsaturated carboxylic acid-based copolymer is 100% by mass, the structural unit derived from ethylene is preferably used. It is 65% by mass or more and 98% by mass or less, more preferably 70% by mass or more and 95% by mass or less, and further preferably 75% by mass or more and 92% by mass or less.
When the structural unit derived from ethylene is at least the above lower limit value, the heat resistance, mechanical strength, etc. of the resin layer (A) can be made better. Further, when the structural unit derived from ethylene is not more than the above upper limit value, the transparency, flexibility, adhesiveness and the like of the resin layer (A) can be improved.

In the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer, when the total number of the constituent units constituting the ethylene / unsaturated carboxylic acid-based copolymer is 100% by mass, the constituent unit derived from the unsaturated carboxylic acid is It is preferably 2% by mass or more and 35% by mass or less, more preferably 5% by mass or more and 30% by mass or less, and further preferably 8% by mass or more and 25% by mass or less.
When the structural unit derived from the unsaturated carboxylic acid is at least the above lower limit value, the transparency, flexibility, adhesiveness, etc. of the resin layer (A) can be improved. Further, when the structural unit derived from the unsaturated carboxylic acid is not more than the above upper limit value, the processability of the resin layer (A) can be improved.

Examples of the unsaturated carboxylic acid in the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, and monomethyl maleate. Examples thereof include monoethyl maleate. Among these, at least one selected from acrylic acid and methacrylic acid is preferable from the viewpoint of productivity, hygiene and the like of the ethylene / unsaturated carboxylic acid-based copolymer. That is, the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer is preferably an ethylene / (meth) acrylic acid copolymer or its ionomer.
In addition, these unsaturated carboxylic acids may be used individually by 1 type, and may be used in combination of 2 or more type.

For the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer, preferably 0% by mass or more and 30% by mass or less, more preferably 0% by mass or more and 25% by mass, based on 100% by mass of the total of ethylene and unsaturated carboxylic acid. Percentages or less may contain constituent units derived from other copolymerizable monomers. Other copolymerizable monomers include, for example, vinyl esters such as vinyl acetate and vinyl propionate; methyl (meth) acrylate, ethyl (meth) acrylate, isobutyl (meth) acrylate, n- (meth) acrylate. Examples thereof include unsaturated carboxylic acid esters such as butyl, 2-ethylhexyl (meth) acrylate, dimethyl maleate, and diethyl maleate. It is preferable that the structural unit derived from the other copolymerizable monomer is contained in the above range because the flexibility of the resin layer (A) is improved.

Examples of the metal ion constituting the ionomer of the ethylene / unsaturated carboxylic acid-based copolymer according to the present embodiment include monovalent metal ions such as lithium ion, potassium ion, sodium ion, silver ion, mercury ion and copper ion. Polyvalent metals such as calcium ion, magnesium ion, zinc ion, aluminum ion, barium ion, beryllium ion, strontium ion, copper ion, cadmium ion, mercury ion, tin ion, lead ion, iron ion, cobalt ion and nickel ion. Ions and the like can be mentioned.
Among these, it is preferable to contain one or more selected from lithium ion, potassium ion, sodium ion, calcium ion, magnesium ion, zinc ion, aluminum ion, and barium ion, and potassium ion, sodium ion, and zinc ion. And at least one selected from magnesium ions is more preferred, and at least one selected from sodium ions and zinc ions is particularly preferred.

The degree of neutralization of the ionomer of the ethylene / unsaturated carboxylic acid-based copolymer according to the present embodiment is not particularly limited, but the flexibility, adhesiveness, mechanical strength, processability, etc. of the resin layer (A) are improved. From the viewpoint, 95% or less is preferable, 90% or less is more preferable, 80% or less is further preferable, and 75% or less is even more preferable.
Further, the degree of neutralization of the ionomer of the ethylene / unsaturated carboxylic acid-based copolymer according to the present embodiment is not particularly limited, but from the viewpoint of improving the transparency, heat resistance, water resistance, etc. of the resin layer (A). Therefore, 5% or more is preferable, 10% or more is more preferable, 15% or more is further preferable, and 20% or more is particularly preferable.
Here, the degree of neutralization of the ionomer of the ethylene / unsaturated carboxylic acid-based copolymer is the carboxyl neutralized by metal ions among all the carboxyl groups contained in the ethylene / unsaturated carboxylic acid-based copolymer. Refers to the percentage of groups.

The method for producing the ethylene / unsaturated carboxylic acid-based copolymer according to the present embodiment is not particularly limited, and it can be produced by a known method. For example, it can be obtained by radical copolymerizing each polymerization component under high temperature and high pressure. Further, the ionomer of the ethylene / unsaturated carboxylic acid-based copolymer according to the present embodiment can be obtained by reacting the ethylene / unsaturated carboxylic acid-based copolymer with a metal compound. Further, as the ionomer of the ethylene / unsaturated carboxylic acid-based copolymer, a commercially available one may be used.

In the present embodiment, from the viewpoint of further improving the processing stability, a melt of an ethylene / unsaturated carboxylic acid-based copolymer or an ionomer thereof, which is measured under the conditions of 190 ° C. and 2160 g load according to JIS K7210: 1999. The lower limit of the mass flow rate (MFR) is preferably 0.01 g / 10 minutes or more, more preferably 0.05 g / 10 minutes or more, and the upper limit is preferably 50 g / 10 minutes or less. It is more preferably 30 g / 10 minutes or less, and further preferably 20 g / 10 minutes or less.
When the MFR is at least the above lower limit value, the processability of the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer can be further improved. When the MFR is not more than the above upper limit value, the heat resistance and mechanical strength of the obtained resin layer (A) can be further improved.

The content of the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer in the resin layer (A) according to the present embodiment is, for example, 50% by mass or more when the entire resin layer (A) is 100% by mass. It is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more. When the content of the ethylene / unsaturated carboxylic acid copolymer or its ionomer in the resin layer (A) according to the present embodiment is at least the above lower limit, the processability and interlayer adhesiveness of the resin layer (A) , Transparency, mechanical strength and other performance balance can be further improved.
The upper limit of the content of the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer in the resin layer (A) is not particularly limited, but is, for example, 100% by mass or less.

The resin layer (A) according to the present embodiment may contain various additives as long as the object of the present invention is not impaired. The various additives are not particularly limited, but for example, plasticizers, antioxidants, ultraviolet absorbers, wavelength converters, antistatic agents, surfactants, colorants, light stabilizers, foaming agents, lubricants, crystal nuclei. Agents, crystallization accelerators, crystallization retardants, catalyst deactivators, heat ray absorbers, heat ray reflectors, radiators, ethylene / unsaturated carboxylic acid copolymers and thermoplastic resins other than their ionomers, thermosetting Resins, inorganic fillers, organic fillers, impact resistance improvers, slip agents, cross-linking agents, cross-linking aids, tackifiers, silane coupling agents, processing aids, mold release agents, hydrolysis inhibitors, heat stable Examples thereof include agents, antiblocking agents, antifogging agents, flame retardants, flame retardant aids, light diffusing agents, antibacterial agents, anticorrosion agents, dispersants and other resins. The various additives may be used alone or in combination of two or more.

<Resin layer (B)>
The resin layer (B) is laminated on at least one surface of the resin layer (A) and contains an ethylene / polar monomer copolymer as a main component. The ethylene / polar monomer according to the present embodiment is a polymer obtained by copolymerizing ethylene with at least one polar monomer. In the present embodiment, the polar monomer means a monomer having a functional group.
Examples of the ethylene / polar monomer copolymer according to the present embodiment include at least one polymer selected from an ethylene / vinyl ester copolymer and an ethylene / unsaturated carboxylic acid ester copolymer.

Examples of the ethylene / vinyl ester copolymer according to the present embodiment include an ethylene / vinyl acetate copolymer, an ethylene / vinyl acetate copolymer, an ethylene / vinyl butyrate copolymer, and an ethylene / vinyl stearate copolymer. One or more selected from the above can be used.

The ethylene / unsaturated carboxylic acid ester copolymer according to the present embodiment is a polymer obtained by copolymerizing ethylene with at least one unsaturated carboxylic acid ester.
Specifically, a copolymer composed of ethylene and an alkyl ester of an unsaturated carboxylic acid can be exemplified.

Examples of the unsaturated carboxylic acid in the unsaturated carboxylic acid ester include acrylic acid, methacrylic acid, etaclilic acid, crotonic acid, fumaric acid, maleic acid, maleic anhydride, itaconic acid, and itaconic anhydride.
Examples of the alkyl moiety in the alkyl ester of unsaturated carboxylic acid include those having 1 to 12 carbon atoms, and more specifically, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and secondary butyl. , 2-Ethylhexyl, isooctyl and the like can be exemplified. In the present embodiment, the number of carbon atoms in the alkyl moiety of the alkyl ester is preferably 1 to 8.

Examples of unsaturated carboxylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, isobutyl (meth) acrylate, and (meth) acrylate. It is preferable to contain one or more selected from (meth) acrylic acid esters such as n-butyl, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. These unsaturated carboxylic acid esters may be used alone or in combination of two or more. Among these, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, isobutyl (meth) acrylate, n-butyl (meth) acrylate and the like. It is more preferable to include one or more selected from.

In the present embodiment, the preferred ethylene / unsaturated carboxylic acid ester copolymer is an ethylene / (meth) acrylic acid ester copolymer. Among them, a copolymer composed of one kind of compound is preferable as the (meth) acrylic acid ester. Examples of such copolymers include ethylene / methyl (meth) acrylate copolymer, ethylene / ethyl (meth) acrylate copolymer, ethylene / isopropyl (meth) acrylate copolymer, and ethylene / (meth). N-propyl acrylate copolymer, isobutyl ethylene (meth) acrylate copolymer, n-butyl copolymer (meth) acrylate, isooctyl copolymer (meth) acrylate, ethylene ( Meta) Examples thereof include a 2-ethylhexyl acrylate copolymer.

The ethylene / polar monomer copolymer includes an ethylene / vinyl acetate copolymer, an ethylene / methyl (meth) acrylate copolymer, an ethylene / ethyl (meth) acrylate copolymer, and an isopropyl (meth) acrylate copolymer. One or two selected from a polymer, an ethylene / (meth) acrylate n-propyl copolymer, an ethylene / (meth) acrylate isobutyl copolymer, and an ethylene / (meth) acrylate n-butyl copolymer. It is preferable to include the above, and it is more preferable to include an ethylene / vinyl acetate copolymer.
In this embodiment, the ethylene / polar monomer copolymer may be used alone or in combination of two or more.

The content of the polar monomer in the ethylene / polar monomer copolymer according to the present embodiment is preferably 5% by mass or more and 50% by mass or less, more preferably 8% by mass or more and 45% by mass or less, and particularly preferably. Is 10% by mass or more and 32% by mass or less.
When the polar monomer is vinyl acetate, the content of the polar monomer can be measured according to, for example, JIS K7192: 1999. When the polar monomer is an unsaturated carboxylic acid ester, the content of the polar monomer is measured, for example, by the infrared absorption spectrum (IR) attributable to the unsaturated carboxylic acid ester. For example, when the unsaturated carboxylic acid ester is ethyl acrylate (EA), it is determined from the absorbance of 860 cm ^-1 attributable to EA. However, the calibration curve is obtained by determining the EA concentration by nuclear magnetic resonance spectrum (NMR) and correlating it with the absorbance of 860 cm ^-1 of IR.

In the present embodiment, from the viewpoint of further improving the processing stability, the melt mass flow rate of the ethylene / polar monomer copolymer (A) measured under the conditions of 190 ° C. and 2160 g load according to JIS K7210: 1999 (A). MFR) is preferably 0.1 g / 10 minutes or more and 150 g / 10 minutes or less, more preferably 0.2 g / 10 minutes or more and 100 g / 10 minutes or less, and 0.5 g / 10 minutes or more and 50 g / min. It is more preferably 10 minutes or less.
The MFR of the ethylene / polar monomer copolymer may be prepared by blending a plurality of ethylene / polar monomer copolymers having different MFRs.

The method for producing the ethylene / polar monomer copolymer according to the present embodiment is not particularly limited, and the copolymer can be produced by a known method. For example, it can be obtained by radical copolymerizing each polymerization component under high temperature and high pressure. Further, as the ethylene / polar monomer copolymer, a commercially available one may be used.

The content of the ethylene / polar monomer copolymer in the resin layer (B) according to the present embodiment is, for example, 50% by mass or more, preferably 60% by mass, when the whole resin layer (B) is 100% by mass. As mentioned above, it is more preferably 70% by mass or more, further preferably 80% by mass or more, and particularly preferably 90% by mass or more. When the content of the ethylene / polar monomer copolymer in the resin layer (B) according to the present embodiment is at least the above lower limit value, the processability, interlayer adhesion, transparency, and mechanical properties of the resin layer (B) are mechanical. The performance balance such as strength can be further improved.
The upper limit of the content of the ethylene / polar monomer copolymer in the resin layer (B) is not particularly limited, but is, for example, 100% by mass or less.

The resin layer (B) according to the present embodiment may contain various additives as long as the object of the present invention is not impaired. The various additives are not particularly limited, but for example, plasticizers, antioxidants, ultraviolet absorbers, wavelength converters, antistatic agents, surfactants, colorants, light stabilizers, foaming agents, lubricants, crystal nuclei. Agents, crystallization accelerators, crystallization retardants, catalyst deactivators, heat ray absorbers, heat ray reflectors, radiators, thermoplastic resins other than ethylene / polar monomer copolymers, thermosetting resins, inorganic fillers, Organic fillers, impact resistance improvers, slip agents, cross-linking agents, cross-linking aids, tackifiers, silane coupling agents, processing aids, mold release agents, hydrolysis inhibitors, heat stabilizers, anti-blocking agents, Examples thereof include antifogging agents, flame retardants, flame retardant aids, light diffusing agents, antibacterial agents, anticorrosive agents, dispersants and other resins. The various additives may be used alone or in combination of two or more.

<Resin layer (C)>
The surface protective film 10 according to the present embodiment may further include a resin layer (C) containing a thermoplastic polyurethane resin.
The resin layer (C) contains a thermoplastic polyurethane resin as a main component.
The thickness of the resin layer (C) is, for example, 10 μm or more and 1000 μm or less.

The thermoplastic polyurethane resin is not particularly limited, and known ones can be used. For example, block copolymers having polyurethane as a hard segment and polyether as a soft segment; polyester such as adipate polyester and caprolactone polyester; and polycarbonate and the like can be mentioned.
Among these, as the thermoplastic polyurethane resin, a block copolymer having polyurethane as a hard segment and a polyether as a soft segment (also referred to as a polyether-based thermoplastic polyurethane resin) is preferable.
The content of the thermoplastic polyurethane resin in the resin layer (C) is, for example, 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass, when the whole resin layer (C) is 100% by mass. As mentioned above, it is more preferably 80% by mass or more, and particularly preferably 90% by mass or more. When the content of the thermoplastic polyurethane resin in the resin layer (C) according to the present embodiment is at least the above lower limit value, the performance balance such as transparency, flexibility, and mechanical strength of the surface protective film 10 is further improved. Can be good.
The upper limit of the content of the thermoplastic polyurethane resin in the resin layer (C) according to the present embodiment is not particularly limited, but is, for example, 100% by mass or less.

The thermoplastic polyurethane resin constituting the resin layer (C) is not particularly limited, and known ones can be used. For example, block copolymers having polyurethane as a hard segment and polyether; polyester such as adipate-based polyester and caprolactone-based polyester; polycarbonate and the like can be mentioned as soft segments.

The thermoplastic polyurethane resin constituting the resin layer (C) is more specifically a resin formed of a bifunctional polyol, a diisocyanate, and a chain extender and containing a urethane group in its molecular structure. Examples thereof include those having thermoplasticity.

The thermoplastic polyurethane resin may be a block copolymer containing a hard segment formed by a reaction between a chain extender and a diisocyanate and a soft segment formed by a reaction between a bifunctional polyol and a diisocyanate. preferable.

Further, the thermoplastic polyurethane resin is classified according to the type of the bifunctional polyol or the like as a raw material, and examples thereof include a polyether-based thermoplastic polyurethane resin, a polyester-based thermoplastic polyurethane resin, and a polycarbonate-based thermoplastic polyurethane resin. One type of these thermoplastic polyurethane resins may be used alone, or two or more types may be used in combination.

The bifunctional polyol is not particularly limited, and examples thereof include a polyether-based polyol, a polyester-based polyol, and a polycarbonate-based polyol.
One type of these bifunctional polyols may be used alone, or two or more types may be used in combination.

Examples of the polyether polyol include polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol and the like. These polyether polyols may be polycondensed with 1,2-ethanediol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, etc., or ethylene oxide, propylene oxide, tetrahydrofuran, etc. It can be obtained by ring-opening polymerization of the cyclic ether of.
Examples of the polyester-based polyol include polyester polyols obtained by polycondensation of dibasic acids such as adipic acid, sebacic acid and terephthalic acid with low molecular weight polyols, polycaprolactone glycol and the like.
Examples of the polycarbonate-based polyol include a polycarbonate polyol obtained by polycondensing a dialkyl carbonate such as dimethyl carbonate and diethyl carbonate, phosgene, chloroformate, diallyl carbonate, alkylene carbonate and the like with a low molecular weight polyol. ..

Examples of the diisocyanate include toluene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), polypeptide MDI, tolylene diisocyanate, p-phenylenediocyanis, naphthalenediocyanis, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate hydrogenated MDI and the like. Can be mentioned.

Examples of the chain extender include polyoxyethylene glycol, polyoxypropylene glycol, 1,4-butanediol, trimethylolpropane, bishydroxyethoxybenzene and the like.

The resin layer (C) according to the present embodiment can contain various additives as long as the object of the present invention is not impaired. The various additives are not particularly limited, but for example, plasticizers, antioxidants, ultraviolet absorbers, wavelength converters, antioxidants, surfactants, colorants, light stabilizers, foaming agents, lubricants, crystal nuclei. Agents, crystallization accelerators, crystallization retardants, catalyst deactivators, heat ray absorbers, heat ray reflectors, heat dissipation agents, thermoplastic resins, thermosetting resins, inorganic fillers, organic fillers, impact resistance improvers , Slip agent, cross-linking agent, cross-linking aid, tackifier, silane coupling agent, processing aid, mold release agent, hydrolysis inhibitor, heat stabilizer, anti-blocking agent, antifogging agent, flame retardant, flame retardant Auxiliary agents, light diffusers, antibacterial agents, anti-crosslinking agents, dispersants, water repellents, oil repellents and other resins can be mentioned. The various additives may be used alone or in combination of two or more.

<Adhesive layer (D)>
It is preferable that the surface protective film 10 according to the present embodiment further includes an adhesive layer (D) on one of the outermost layers. From the viewpoint of improving the scratch resistance of the surface protective film 10, the pressure-sensitive adhesive layer (D) is preferably provided on the outermost layer on the resin layer (B) side, but is not limited thereto.
The pressure-sensitive adhesive layer (D) can be formed, for example, by applying a pressure-sensitive adhesive to the resin layer (A) side or the resin layer (B) side. It may be formed directly on the surface of the resin layer, or may be laminated with the resin layer via another layer.
The pressure-sensitive adhesive used for the pressure-sensitive adhesive layer is not particularly limited, and examples thereof include acrylic pressure-sensitive adhesives, rubber-based pressure-sensitive adhesives, urethane-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, styrene-based pressure-sensitive adhesives, and olefin-based pressure-sensitive adhesives. Acrylic adhesives are preferable because they are excellent in heat resistance and weather resistance.
The layer thickness of the pressure-sensitive adhesive layer (D) can be, for example, 3 to 100 μm, preferably 5 to 50 μm, and more preferably 10 to 30 μm.
The layer in contact with the pressure-sensitive adhesive layer (D) can be subjected to surface treatment such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and application of an undercoat agent.

<Other layers>
Further, the surface protective film 10 according to the present embodiment may be composed of only the resin layer (A) and the resin layer (B), and if necessary, the resin layer (C) and / or the pressure-sensitive adhesive layer ( D) may be further provided, and from the viewpoint of imparting various functions to the surface protective film 10, layers other than the resin layer (A) and the resin layer (B) (hereinafter, also referred to as other layers). May have. Examples of other layers include a base material layer, an inorganic material layer, a gas barrier layer, an antistatic layer, a hard coat layer, an adhesive layer, an antireflection layer, an antifouling layer, a sealant layer, an undercoat layer, an adhesive layer and the like. Can be done. The other layers may have one layer alone, or may have two or more layers in combination.

2. 2. Method for Producing Surface Protective Film The method for producing the surface protective film 10 according to the present embodiment is not particularly limited, and a molding method generally used for thermoplastic resins can be applied. For example, it can be carried out by a known method using a T-die extruder, an inflation molding machine, or the like.
For example, the resin composition for forming the resin layer (B) is supplied from the hopper of the T-die extruder, and the resin layer (B) is extruded into a film from the tip of the T-die onto the resin layer (A). Can be obtained by doing. Alternatively, it can also be obtained by forming the resin layer (A) and the resin layer (B) into a film by coextrusion with a multilayer T-die extruder.

Further, in the method for producing the surface protective film 10 according to the present embodiment, a commonly used method for forming a multilayer film can be applied. For example, it can be carried out by a known method using a multi-layer T-die extruder, a multi-layer inflation molding machine, or the like.
For example, the resin composition for forming the resin layer (A) and the resin composition for forming the resin layer (B) can be obtained from the main extruder of the multilayer T-die extruder and the hopper of the slave extruder. It can be obtained by feeding and coextruding from the tip of the T-die into a sheet.
When forming the resin layer (C) or the pressure-sensitive adhesive layer (D), the resin layer (C) or the pressure-sensitive adhesive layer (D) is extruded on one of the obtained multilayer films by a T-die extruder. The method or all the components can be coextruded into a sheet.

The surface protective film 10 according to the present embodiment can be irradiated with an electron beam, for example, for the purpose of improving the film strength and resilience. The electron beam irradiation may be performed after the laminated film of the resin layer (A) and the resin layer (B) is prepared, or may be treated after the resin layer (C) is further laminated.
The irradiation intensity of the electron beam is preferably in the range of 10 to 300 kGy, more preferably in the range of 20 to 200 kGy.

Although the embodiments of the present invention have been described above with reference to the drawings, these are examples of the present invention, and various configurations other than the above can be adopted.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Details of the components used to prepare the surface protective film are as follows.

<Ethylene / unsaturated carboxylic acid copolymer or its ionomer>
EMAA1: Ethylene / methacrylic acid: Acrylic acid ester copolymer (ethylene unit content: 80% by mass, methacrylic acid unit content: 11% by mass, acrylic acid ester unit content: 9% by mass, MFR (JIS) K7210: 1999, 190 ° C, 2160 g load): 10 g / 10 minutes)
Ionomer 1: Zn neutralized product of ethylene / methacrylic acid copolymer (ethylene unit content: 80% by mass, methacrylic acid unit content: 10% by mass, acrylic acid butyl ester unit content: 10% by mass, Zn neutralization degree: 70%, MFR (JIS K7210: 1999, 190 ° C., 2160 g load): 1.0 g / 10 minutes)
Ionomer 2: Zn neutralized product of ethylene / methacrylic acid copolymer (ethylene unit content: 85% by mass, methacrylic acid unit content: 15% by mass, Zn neutralization degree: 23%, MFR (JIS K7210:) 1999, 190 ° C, 2160 g load): 5 g / 10 minutes)

<Ethylene / polar monomer copolymer>
EVA1: Ethylene-vinyl acetate copolymer (ethylene content: 81% by mass, vinyl acetate content: 19% by mass, MFR (JIS K7210: 1999, 190 ° C., 2160 g load): 2.5 g / 10 minutes)
EVA2: Ethylene-vinyl acetate copolymer (ethylene content: 75% by mass, vinyl acetate content: 25% by mass, MFR (JIS K7210: 1999, 190 ° C., 2160 g load): 2.5 g / 10 minutes)

<Thermoplastic polyurethane resin>
TPU1: Polycarbonate-based thermoplastic polyurethane resin (manufactured by Tosoh Corporation, Miractran XN2004S, hardness 96A, softening point: 102 ° C.)

[Example 1]
Ionomer 1 and EVA1 were co-extruded at 220 ° C. and a processing speed of 8 m / min using a 40 mmφ3 type 3-layer cast molding machine. At this time, the thickness of the resin layer (A) made of ionomer 1 is 30 μm, the thickness of the resin layer (B) made of EVA1 is 120 μm, the thickness of the entire film is 150 μm, and the outermost layers on both sides are PET films having a thickness of 25 μm. Was laminated to obtain a laminated film 1. In the evaluation, the PET film was peeled off for evaluation.

[Example 2]
Ionomer 1 and EVA2 were co-extruded at 220 ° C. and a processing speed of 8 m / min using a 40 mmφ3 type 3-layer cast molding machine. At this time, the thickness of the resin layer (A) made of ionomer 1 is 30 μm, the thickness of the resin layer (B) made of EVA2 is 120 μm, the thickness of the entire film is 150 μm, and the outermost layers on both sides are PET films having a thickness of 25 μm. Was laminated to obtain a laminated film 2. In the evaluation, the PET film was peeled off for evaluation.

[Example 3]
Ionomer 2 and EVA2 were co-extruded at 220 ° C. and a processing speed of 8 m / min using a 40 mmφ3 type 3-layer cast molding machine. At this time, the thickness of the resin layer (A) made of ionomer 2 is 30 μm, the thickness of the resin layer (B) made of EVA2 is 120 μm, the thickness of the entire film is 150 μm, and the outermost layers on both sides are PET films having a thickness of 25 μm. Was laminated to obtain a laminated film 3. In the evaluation, the PET film was peeled off for evaluation.

[Example 4]
EMAA1 and EVA2 were co-extruded under the conditions of 220 ° C. and a processing speed of 8 m / min using a 40 mmφ3 type 3-layer cast molding machine. At this time, the thickness of the resin layer (A) made of EMAA1 is 30 μm, the thickness of the resin layer (B) made of EVA2 is 120 μm, the thickness of the entire film is 150 μm, and a PET film having a thickness of 25 μm is formed on the outermost layers on both sides. Each was laminated to obtain a laminated film 4. In the evaluation, the PET film was peeled off for evaluation.

[Example 5]
Ionomer 1 and EVA1 were co-extruded at 220 ° C. and a processing speed of 8 m / min using a 40 mmφ3 type 3-layer cast molding machine. At this time, the thickness of the resin layer (A) made of ionomer 1 is 50 μm, the thickness of the resin layer (B) made of EVA1 is 100 μm, the thickness of the entire film is 150 μm, and the outermost layers on both sides are PET films having a thickness of 25 μm. Was laminated to obtain a laminated film 5. In the evaluation, the PET film was peeled off for evaluation.

[Comparative Example 1]
A resin layer made of EVA1 having a thickness of 150 μm was extruded under the conditions of 220 ° C. and a processing speed of 8 m / min using a 40 mmφ3 type 3 layer cast molding machine. At this time, the thickness of the entire film was set to 150 μm, and PET films having a thickness of 25 μm were laminated on the outermost layers on both sides to obtain a laminated film 6. In the evaluation, the PET film was peeled off for evaluation.

[Comparative Example 2]
A resin layer made of TPU1 having a thickness of 150 μm was extruded under the conditions of 220 ° C. and a processing speed of 8 m / min using a 40 mmφ3 type 3 layer cast molding machine. At this time, the thickness of the entire film was set to 150 μm, and PET films having a thickness of 25 μm were laminated on the outermost layers on both sides to obtain a laminated film 7. In the evaluation, the PET film was peeled off for evaluation.

<Evaluation>
(1) Measurement of modulus strength With respect to the obtained laminated film, using an autograph (manufactured by Shimadzu Corporation), according to JIS-K7127: 1999, the test piece width is 10 mm, the distance between chucks is 100 mm, and the tensile speed is 200 mm / min. Under the conditions, 5%, 10%, 20%, 50%, 100% and 300% modulus intensities were measured. Here, the modulus strength was measured in the MD direction of the laminated film. It was judged that there is no practical problem if the 300% modulus strength (MD) is 7.5 MPa or more.

(2) Stress relaxation rate In the measurement of modulus strength, it was stopped at 100% elongation and maintained in that state for 10 minutes. Then, the modulus intensity after holding for 10 minutes was measured. Here, the modulus strength was measured in the MD direction of the laminated film. If the 100% elongation modulus strength after holding for 10 minutes was 4.5 MPa or less, it was judged that there was no practical problem.

(3) Haze and total light transmittance With respect to the obtained laminated film, the haze and total light transmittance were measured according to JIS-K7136: 2000 using a haze meter (manufactured by Suga Test Instruments Co., Ltd.), and the transparency of the laminated film was measured. Gender was evaluated. It was judged that there is no practical problem if the total light transmittance is 80% or more. In addition, Haze judged that there was no practical problem if it was 5% or less.

(4) Scratch resistance The scratch resistance of the obtained laminated film was evaluated from the degree of scratches formed on the surface of the laminated film by reciprocating steel wool with a load of 1 kg on the surface of the laminated film 5 times. In addition, Examples 1 to 5 were carried out from the ionomer surface side or the EMAA side.
⊚: Almost no scratches ○: Slight scratches are seen, but the permeability is not significantly reduced ×: Clearly whitened and the permeability is reduced.

The surface protective film of the example was excellent in the performance balance of stress relaxation property, transparency and scratch resistance. On the other hand, the surface protective film of the comparative example was inferior in the performance balance of stress relaxation property, transparency and scratch resistance.

A Resin layer B Resin layer 10 Surface protective film

Claims (14)

A resin layer (A) containing an ethylene / unsaturated carboxylic acid copolymer or an ionomer thereof,
A resin layer (B) laminated on at least one surface of the resin layer (A) and containing an ethylene / polar monomer copolymer.
Surface protective film with. In the surface protective film according to claim 1,
A surface protective film in which the ethylene / unsaturated carboxylic acid copolymer or its ionomer contains an ethylene / (meth) acrylic acid copolymer or its ionomer. In the surface protective film according to claim 1 or 2.
A surface protective film in which the content of the structural unit derived from the unsaturated carboxylic acid in the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer is 2% by mass or more and 35% by mass or less. In the surface protective film according to any one of claims 1 to 3,
According to JIS K7210: 1999, the melt mass flow rate (MFR) of the ethylene / unsaturated carboxylic acid-based copolymer or its ionomer measured at 190 ° C. and a load of 2160 g is 0.01 g / 10 minutes or more and 50 g. / 10 minutes or less surface protection film. In the surface protective film according to any one of claims 1 to 4,
The ethylene / polar monomer copolymer is a surface protective film containing at least one copolymer selected from an ethylene / vinyl ester copolymer and an ethylene / unsaturated carboxylic acid ester copolymer. In the surface protective film according to claim 5,
The ethylene / polar monomer copolymer is a surface protective film containing an ethylene / vinyl acetate copolymer. In the surface protective film according to any one of claims 1 to 6,
According to JIS K7210: 1999, the melt mass flow rate (MFR) of the ethylene / polar monomer copolymer measured at 190 ° C. and a load of 2160 g is 0.1 g / 10 minutes or more and 150 g / 10 minutes or less. Surface protective film. In the surface protective film according to any one of claims 1 to 7.
A surface protective film having a haze of 5% or less as measured according to JIS K7136: 2000. In the surface protective film according to any one of claims 1 to 8.
A surface protective film having a total light transmittance of 80% or more measured in accordance with JIS K7136: 2000. In the surface protective film according to any one of claims 1 to 9,
A surface protective film further comprising a resin layer (C) containing a thermoplastic polyurethane resin. In the surface protective film according to any one of claims 1 to 10.
A surface protective film further provided with an adhesive layer (D) on the outermost layer of either one. In the surface protective film according to claim 11,
The pressure-sensitive adhesive layer (D) is composed of at least one type of pressure-sensitive adhesive selected from urethane-based pressure-sensitive adhesives, rubber-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, styrene-based pressure-sensitive adhesives, olefin-based pressure-sensitive adhesives, and acrylic-based pressure-sensitive adhesives. Surface protective film. In the surface protective film according to any one of claims 1 to 12,
A surface protection film that is a paint protection film. In the surface protective film according to any one of claims 1 to 13.
A surface protective film used so that the surface of the resin layer (A) is on the atmospheric side.

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