JP6856374B2 - Surface protection sheet - Google Patents

Description

The present invention relates to a surface protective sheet.

In general, a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive; the same applies hereinafter) exhibits a soft solid state (viscoelastic body) in a temperature range near room temperature, and has a property of easily adhering to an adherend by pressure. Taking advantage of these properties, the pressure-sensitive adhesive is widely used in various applications in the form of a single-sided pressure-sensitive adhesive sheet with a base material in which a pressure-sensitive adhesive layer is provided on one surface of the base material. For example, the single-sided adhesive sheet with a base material is preferably used as a surface protection sheet that is attached to a metal plate and protects the surface of the metal plate during drawing, bending, punching, etc. of the metal plate. There is. Patent Documents 1 and 2 are listed as technical documents relating to a surface protective sheet used for processing a metal plate.

Japanese Unexamined Patent Publication No. 8-134415 Japanese Unexamined Patent Publication No. 2012-77226

The surface protective sheet is removed from the adherend at an appropriate timing after achieving the protective purpose. Therefore, for example, a surface protective sheet for processing a metal plate is required to have a property that the surface protective sheet can be easily peeled off and removed from the processed metal plate (work). For example, a surface protective sheet that can maintain light peelability even after a lapse of time after being attached to the adherend is desirable. Further, in this type of surface protection sheet, it is desirable that the surface protection sheet is not torn or torn even if the metal plate is processed (particularly, processing accompanied by deformation of the metal plate). This is because if the surface protective sheet is torn or torn, a part of the surface protective sheet is torn and adheres to the processing apparatus or other work, which may cause a malfunction of the apparatus or a decrease in the processing yield. The tearing or tearing of the surface protective sheet can also be a factor that reduces workability when the surface protective sheet is peeled off and removed from the metal plate.

Therefore, an object of the present invention is to provide a surface protective sheet that is less likely to be torn or torn due to processing of an adherend (protection object) and has good workability for removal from the adherend.

The surface protective sheet disclosed herein includes a base material and an adhesive layer arranged on one surface (first surface) of the base material. The pressure-sensitive adhesive layer has a glass transition temperature (Tg) of the base polymer of −50 ° C. or higher. The surface protective sheet has a tensile elongation at break _{Eb TD} tensile elongation at break _{Eb MD} and the width direction of the flow direction (MD) (TD) is both greater than 200%. According to the surface protection sheet that stretches well with respect to both MD and TD, the stress that can be applied by the processing of the adherend can be absorbed or dispersed by the elongation deformation of the surface protection sheet. As a result, damage (tear, tear, tear, etc.) of the surface protective sheet can be suppressed. Further, when the Tg of the base polymer is equal to or higher than a predetermined value, the pressure-sensitive adhesive exhibits good cohesiveness. As a result, the surface of the pressure-sensitive adhesive (adhesive surface) is less likely to get wet with respect to the surface of the adherend, and an increase in peel strength with time is suppressed. Combined with these effects, a surface protective sheet that is less likely to be damaged by processing the adherend and has good removal workability from the adherend is realized.

The surface protective sheet, neither the tensile break strength _{TS MD} and the width direction (TD) tensile strength _{TS TD} in the flow direction (MD) is preferably higher than 15N / 20 mm. As described above, according to the surface protective sheet exhibiting a tensile breaking strength of a predetermined value or more for both MD and TD, tearing, tearing, and tearing of the surface protective sheet can be suitably suppressed.

The pressure-sensitive adhesive layer preferably has a weight fraction of a toluene-insoluble matter (gel fraction) G _C is 60% or more. By gel fraction G _C is a predetermined value or more, there is a tendency that adhesive residue on the adherend is inhibited. The pressure-sensitive adhesive layer preferably has a weight average molecular weight of toluene-soluble matter (sol molecular weight) S _Mw is 10 × 10 ⁴ or more. When the weight average molecular weight (Mw) of the sol, which has higher mobility than the gel, is equal to or higher than a predetermined value, the adhesive surface is less likely to get wet with the adherend surface, which effectively suppresses the increase in peel strength over time. Can be done.

In a preferred embodiment, the pressure-sensitive adhesive layer has a minimum load L _{min of the} unloading curve in the nanoindenter measurement of less than −2.0 μN. Such an adhesive layer does not easily get wet with respect to the surface of the adherend. As a result, the increase in peel strength with time can be suitably suppressed.

The base polymer is preferably a polymer of a monomer raw material containing a monomer having a Tg of 10 ° C. or higher (hereinafter, also referred to as “monomer H”) of the homopolymer in a proportion of 20% by weight or more of all the monomer components. By using the monomer H in the above ratio, the cohesive force of the pressure-sensitive adhesive is increased, and the pressure-sensitive adhesive surface tends to be less likely to get wet with the adherend surface. As a result, the increase in peel strength with time can be suitably suppressed.

The surface protective sheet disclosed herein can be preferably implemented in an embodiment in which the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer. As the base polymer of the acrylic pressure-sensitive adhesive layer, for example, an acrylic polymer synthesized by emulsion polymerization can be preferably adopted.

In the surface protective sheet according to a preferred embodiment, the thickness of the base material is 100 μm or less. According to the technique disclosed herein, even in a configuration using a base material having a thickness of 100 μm or less, a surface protective sheet in which damage due to processing of the adherend is suppressed can be realized.

As the base material of the surface protective sheet disclosed herein, a base material containing a polyolefin-based resin film can be preferably adopted. In such a configuration, a surface protective sheet that suppresses damage due to processing of the adherend and has good removal workability from the adherend can be preferably realized.

Surface protection sheet according to one preferred embodiment, time peel strength _{P A} measured at 3m / min peel rate after storage 7 days at pasted 60 ° C. in a stainless steel (SUS plate) is 0.70N / 20mm or less Is. A surface protective sheet exhibiting light peelability of a predetermined value or less under the above conditions has good workability for removal from an adherend even after a lapse of time.

Surface protective sheet according to one preferred embodiment, the initial peel strength above aging peel strength P _{A [N} / 20mm] is measured in 3m / min peel rate surface protective sheet adhered to the SUS plate after 15 minutes It is 2.0 times or less of P _{0 [N / 20 mm].} That _is, P A / _{P 0} of 2.0 or less. As described above, the surface protective sheet having a small increase in peel strength with time has good sticking workability to the adherend, protective property of the adherend, and good removal workability from the adherend.

Even if the surface protective sheet disclosed herein is used for an adherend that is deformed by applying a strong stress such as a metal plate that is subjected to drawing processing, it is damaged (torn, torn, etc.) due to the above stress. It is less likely to be torn, etc.) and has excellent workability for removal from the adherend after processing. Therefore, the surface protective sheet disclosed herein is particularly preferably used as a surface protective sheet for a metal plate to be drawn.

It is sectional drawing which shows typically one form example of the surface protection sheet. It is a schematic diagram for demonstrating the unloading curve in nanoindenter measurement and the minimum load in the unloading curve.

Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in the present specification and necessary for the practice of the present invention are based on the teachings regarding the practice of the invention described in the present specification and the common general knowledge at the time of filing. Can be understood by a person skilled in the art. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art.

<Surface protection sheet>
The surface protective sheet disclosed herein has an adhesive layer on a sheet-like base material (supporting base material). The cross-sectional structure of the surface protection sheet according to one embodiment is shown in FIG. The surface protection sheet 10 has a structure in which the pressure-sensitive adhesive layer 2 is provided on one surface 1A of the base material 1, and is used by attaching the surface 2A of the pressure-sensitive adhesive layer 2 to a protective object. The surface protective sheet 10 before use (that is, before sticking to the object to be protected) has the surface (adhesive surface, that is, the sticking surface to the adherend) 2A of the adhesive layer 2 having at least the peeling surface on the adhesive layer side. It may be in a form protected by a release liner (not shown). Alternatively, the other surface (back surface) 1B of the base material 1 is a peeling surface, and the surface protective sheet 10 is wound in a roll shape so that the adhesive layer 2 comes into contact with the other surface and the surface (the surface). Adhesive surface) The surface protective sheet 10 may have a form in which 2A is protected.

As the release liner, a conventional release paper or the like can be used, and the release liner is not particularly limited. For example, a release liner having a release treatment layer on the surface of a liner base material such as a plastic film or paper, a release liner made of a low-adhesive material of a fluorine-based polymer (polytetrafluoroethylene, etc.) or a polyolefin-based resin can be used. it can. The peeling treatment layer may be formed by surface-treating the liner base material with various peeling treatment agents such as silicone-based, long-chain alkyl-based, fluorine-based, and molybdenum sulfide.

The thickness of the surface protective sheet disclosed herein is not particularly limited, but from the viewpoint of handleability, lightness, etc., it is usually set to about 1000 μm or less (typically about 300 μm or less, for example, about 150 μm or less). Appropriate. In one aspect, the thickness of the surface protective sheet can be preferably 110 μm or less, more preferably 90 μm or less, still more preferably 70 μm or less, for example 60 μm or less. The thickness of the surface protective sheet can typically be greater than 20 μm, preferably greater than 30 μm, more preferably greater than 40 μm, for example greater than 45 μm.
In the present specification, the thickness of the surface protective sheet means the thickness from the surface of the adhesive layer (adhesive surface) to the back surface of the surface protective sheet (the surface opposite to the adhesive surface), and is the thickness of the release liner. Does not include.

The thickness of the base material constituting the surface protective sheet disclosed herein is not particularly limited. The thickness of the base material can be, for example, about 800 μm or less (typically about 250 μm or less). In one embodiment, the thickness of the substrate (typically a non-foamed resin film) can be preferably 100 μm or less, more preferably 80 μm or less, still more preferably 65 μm or less, for example 55 μm or less. When the thickness of the base material is reduced, the followability of the surface protective sheet to the adherend shape during the processing process (for example, a processing process including a plurality of sequentially performed pressing processes) and the post-processing is improved, and the floating and peeling is suppressed. It tends to be done. Further, from the viewpoint of handleability and the like, the thickness of the base material can be typically 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, still more preferably 40 μm or more, for example 45 μm or more.

The thickness of the pressure-sensitive adhesive layer constituting the surface protective sheet disclosed herein is not particularly limited. From the viewpoint of preventing adhesive residue on the adherend, the thickness of the pressure-sensitive adhesive layer is usually preferably 15 μm or less, preferably 10 μm or less, and more preferably 7 μm or less (for example, 6 μm or less). The thickness of the pressure-sensitive adhesive layer is usually preferably 1 μm or more, and preferably 2 μm or more. From the viewpoint of suppressing floating and peeling during the processing process and after processing, the thickness of the pressure-sensitive adhesive layer is preferably 3 μm or more, and more preferably 4 μm or more.

(Tension breaking elongation)
The surface protective sheet disclosed herein preferably has an MD tensile elongation at break Eb _MD and a TD tensile elongation at break Eb _TD of 200% or more. According to the surface protection sheet that stretches well with respect to both MD and TD, the stress that can be applied to the surface protection sheet by processing the adherend can be absorbed or dispersed by the elongation deformation of the surface protection sheet. As a result, damage (tear, tear, tear, etc.) of the surface protective sheet can be suppressed.

The tensile elongation at break [%] is measured by the following method.
The surface protection sheet to be measured is cut into a test piece type 2 shape (rectangular shape, width 20 mm) described in JIS K 7127 to prepare a test piece. This test piece, a marked line interval 50 mm, distance between chucks 100 mm, tensile speed of 300 mm / min condition until the test piece is broken subjected to tensile test of stretching, the marked line distance L ₁ when the specimen is broken From the first marked line interval L ₀ (50 mm in this case), the tensile elongation at break is calculated by the following equation: tensile elongation at break [%] = 100 × (L _{1 −} L ₀ ) / L ₀ ;. As the tensile tester, the product name "Autograph AG-10G type tensile tester" manufactured by Shimadzu Corporation can be used. The same method is adopted for the examples described later.

When measuring MD tensile elongation at break Eb _MD , prepare so that the length direction of the test piece coincides with the MD of the surface protection sheet. When measuring the TD tensile elongation at break Eb _TD , prepare so that the length direction of the test piece coincides with the TD of the surface protection sheet.
The MD of the surface protection sheet typically corresponds to the longitudinal direction of the base material constituting the surface protection sheet (in the case of a roll-shaped surface protection sheet, the winding direction). The TD of the surface protection sheet is in the direction orthogonal to the MD of the surface protection sheet.

In the surface protective sheet according to a preferred embodiment, _{at least one (preferably both) of Eb MD} and Eb _TD is 300% or more, more preferably 350% or more, still more preferably 400% or more, particularly preferably 500% or more, for example. It is 600% or more. When _{at least one (preferably both) of Eb MD} and Eb _TD becomes larger, damage to the surface protective sheet tends to be better prevented during processing of the adherend or the like. The upper limit of Eb _MD and Eb _TD is not particularly limited. From the viewpoint of ease of manufacture, handleability, etc., it is usually _{appropriate that one or both of Eb MD} and Eb _TD is about 1500% or less, and about 1200% or less (for example, about 1000% or less). May be good. The tensile elongation at break of the surface protective sheet can be adjusted by, for example, the selection of the base material type, the manufacturing method (molding method, molding conditions), and the like.

The ratio of _{Eb TD} for _{Eb MD (Eb} TD / Eb _MD ratio) is not particularly limited. From the viewpoint of usability, it is advantageous that the anisotropy in the characteristics of the surface protective sheet is small. From this point of view, the Eb _TD / Eb _MD ratio of the surface protection sheet is usually preferably 5.0 or less, preferably 3.0 or less, more preferably 2.0 or less, and 1.7 or less (for example, 1. 5 or less) is more preferable. For the same reason, the Eb _TD / Eb _MD ratio of the surface protection sheet is preferably 0.2 or more, preferably 0.3 or more, more preferably 0.5 or more, and 0.6 or more (for example, 0.7). The above) is more preferable. In a preferred embodiment, the Eb _TD / Eb _MD ratio can be approximately 1.0 (eg, 0.9 or more and 1.1 or less). The Eb _TD / Eb _MD ratio can be adjusted by, for example, selection of a base material type, a manufacturing method (molding method, molding conditions), and the like.

(Tensile breaking strength)
In the surface protection sheet disclosed herein, _{at least one of MD tensile breaking strength TS MD} and TD tensile breaking strength TS _TD is preferably higher than 15 N / 20 mm, _{and both TS MD} and TS _TD are higher than 15 N / 20 mm. Is more preferable. According to the surface protective sheet exhibiting such tensile breaking strength, damage to the surface protective sheet can be suitably suppressed. The surface protective sheet disclosed herein _{is preferably carried out in an embodiment in which at least one (preferably both) of TS MD} and TS _TD is 17 N / 20 mm or more (more preferably 19 N / 20 mm or more, for example, 20 N / 20 mm or more). Can be done. The upper limit of TS _MD and TS _TD is not particularly limited, but usually 50 N / 20 mm or less (for example, 40 N / 20 mm or less) is suitable, and 35 N / 20 mm or less (for example, from the viewpoint of facilitating both good tensile elongation at break). For example, 30 N / 20 mm or less) may be used. The tensile breaking strength of the surface protective sheet can be adjusted by, for example, selection of a base material type, a manufacturing method (molding method, molding conditions), and the like.

The tensile breaking strength [N / 20 mm] is measured as the strength when the test piece breaks in the measurement of the tensile breaking elongation. The same method is adopted for the examples described later.

The ratio of the _{TS TD} for _{TS MD (TS} TD / TS _MD ratio) is not particularly limited. From the viewpoint of usability, it is advantageous that the anisotropy in the characteristics of the surface protective sheet is small. From this point of view, the TS _TD / TS _MD ratio of the surface protection sheet is usually preferably 3.0 or less, preferably 2.0 or less, more preferably 1.8 or less, and even more preferably 1.5 or less. For the same reason, the TS _TD / TS _MD ratio of the surface protection sheet is preferably 0.3 or more, preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more. In a preferred embodiment, the TS _TD / TS _MD ratio can be approximately 1.0 (eg, 0.9 or more and 1.1 or less). The TS _TD / TS _MD ratio can be adjusted by, for example, selection of a base material type, a manufacturing method (molding method, molding conditions), and the like.

<Base material>
As the base material of the surface protective sheet disclosed herein, a resin film, a rubber sheet, a foam sheet, a composite thereof, or the like can be used. Examples of the rubber sheet include a natural rubber sheet, a butyl rubber sheet and the like. Examples of the foam sheet include a foamed polyurethane sheet, a foamed chloroprene rubber sheet, and the like.

The technique disclosed herein can be preferably applied to a surface protective sheet based on a resin film. The "resin film" referred to here is typically a film formed by molding a resin composition mainly containing a resin component as shown below into a film shape, and is distinguished from so-called non-woven fabrics and woven fabrics. (That is, the concept excluding non-woven fabrics and woven fabrics). A substantially non-foamed resin film is preferred. Here, the non-foaming resin film refers to a resin film that has not been intentionally treated to form a foam, and specifically, the foaming ratio is less than about 1.1 times (for example, 1.05 times). Less than, typically less than 1.01 times) resin film.

Examples of the resin components constituting the resin film include polyolefin resins (polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, etc.) and vinyl chloride resins (typically, soft vinyl chloride resins). ), Vinyl acetate resin, polyurethane resin (ether-based polyurethane, ester-based polyurethane, carbonate-based polyurethane, etc.), urethane (meth) acrylate, thermoplastic elastomer (olefin-based elastomer, styrene-based elastomer, acrylic-based elastomer, etc.), polyester-based Examples thereof include resins (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, etc.), polycarbonate resins, polyamide resins, polyimide resins and the like. These resin components may be used alone or in combination of two or more.

Although not particularly limited, the surface protective sheet according to one embodiment mainly contains one or more resin components selected from the group consisting of polyolefin resins, vinyl chloride resins, polyurethane resins and thermoplastic elastomers. A base material containing as a component (typically, a base material containing such a resin component in a proportion of more than 50% by weight) can be preferably adopted. For example, a base material containing any of these resins in a proportion of more than 50% by weight is preferable. Among the above resin materials, polyolefin resins, polyurethane resins and olefin elastomers are preferable from the viewpoint of thermal stability and light weight, and polyolefin resins and olefin elastomers are particularly preferable from the viewpoint of handleability and the like.

The surface protective sheet disclosed herein can be preferably carried out in a mode including a base material containing a polyolefin-based resin as a main component, that is, a mode in which a polyolefin-based resin film is used as a base material. For example, a polyolefin-based resin film in which 50% by weight or more of the entire base material is a polyethylene (PE) resin or a polypropylene (PP) resin can be preferably adopted. In other words, in the polyolefin resin film, the total amount of the PE resin and the PP resin may occupy 50% by weight or more of the entire base material.

The PP resin may contain various polymers (propylene-based polymers) containing propylene as a constituent monomer as a main component. It may be a PP resin substantially composed of one kind or two or more kinds of propylene-based polymers. The concept of a propylene-based polymer referred to here includes, in addition to homopolypropylene, a random copolymer (random polypropylene) of propylene and another monomer and a block copolymer (block polypropylene). The concept of the propylene-based polymer referred to here includes, for example, the following.
Propylene homopolymer (homopolypropylene). For example, isotactic polypropylene.
Random copolymers (random polypropylene) of propylene with other α-olefins (typically one or more selected from ethylene and α-olefins with 4-10 carbon atoms). Preferably, random polypropylene containing propylene as a main monomer (main constituent monomer, that is, a component accounting for 50% by weight or more of the total monomer).
A copolymer (block polypropylene) obtained by block-copolymerizing propylene with another α-olefin (typically one or more selected from ethylene and α-olefin having 4 to 10 carbon atoms). Preferably, block polypropylene containing propylene as a main monomer (main constituent monomer, that is, a component accounting for 50% by weight or more of the total monomer).

The PE resin may contain various polymers (ethylene-based polymers) containing ethylene as a constituent monomer as a main component. It may be a PE resin substantially composed of one kind or two or more kinds of ethylene-based polymers. The ethylene-based polymer may be a homopolymer of ethylene, and is obtained by copolymerizing ethylene as a main monomer with another α-olefin as a submonomer (random copolymerization, block copolymerization, etc.). May be good. Preferable examples of the α-olefin include 3 to 10 carbon atoms such as propylene, 1-butene (which may be branched 1-butene), 1-hexene, 4-methyl-1-pentene, 1-octene and the like. Α-olefins of. For example, a PE resin containing an ethylene polymer as a main component, in which α-olefin as the submonomer is copolymerized in a proportion of 10% by weight or less (typically 5% by weight or less), can be preferably adopted.

The PE resin also comprises a PE resin containing a copolymer of ethylene and a monomer having another functional group in addition to the polymerizable functional group (functional group-containing monomer), and the functional group-containing monomer copolymerized with an ethylene-based polymer. It may be made of PE resin or the like. Examples of the copolymer of ethylene and the functional group-containing monomer include ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylate copolymer (EMAA), and ethylene-acrylic. Methyl Acid Copolymer (EMA), Ethylene-Ethyl Acrylic Copolymer (EEA), Ethylene-Methyl methacrylate copolymer (EMMA), Ethylene- (meth) acrylic acid (ie, acrylic acid and / or methacrylate) ) Examples thereof include those in which the copolymer is crosslinked with metal ions.

The density of the PE resin is not particularly limited. The concept of PE resin as used herein includes any of high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE). In one embodiment, the density of the PE resin can be, for example, about ^{0.90 to 0.94 g / cm 3.} Preferred PE resins include LDPE and LLDPE. The PE resin may contain one or more LDPEs and one or two or more LLDPEs. The blend ratio of each LDPE or LLDPE and the blend ratio of LDPE and LLDPE are not particularly limited, and can be appropriately set so as to be a PE resin exhibiting desired characteristics. As the base material of the surface protective sheet disclosed herein, an LLDPE film containing LLDPE in a proportion of more than 50% by weight (preferably 75% by weight or more, for example, 90% by weight or more) or LDPE in more than 50% by weight (preferably). A polyethylene-based resin film such as an LDPE film containing 75% by weight or more, for example, 90% by weight or more) can be preferably adopted. A laminated resin film containing such a polyethylene-based resin film as a constituent element may be used.

The resin film (for example, a polyolefin-based resin film) used as the base material of the surface protective sheet disclosed herein may contain an appropriate component that is permitted to be contained in the base material, if necessary. For example, pigments (typically inorganic pigments), fillers, colorants (pigments, dyes), antioxidants, light stabilizers (meaning to include radical scavengers, UV absorbers, etc.), antistatic. Additives such as agents, plasticizers, slip agents, and anti-blocking agents can be appropriately blended. The blending amount of each additive can be, for example, about the same as the usual blending amount in the field of resin films used as a base material for surface protection sheets.

The base material may have a single-layer structure, or may have a multi-layer structure of two layers, three layers or more. In the case of a multilayer structure, at least one layer (preferably all layers) is preferably any of the above-mentioned resin films. For example, a substrate having a thickness of 75% or more (more preferably 90% or more) composed of a single layer or a multilayer (typically a single layer) polyolefin resin film is preferable. The entire base material may be a base material made of a single-layer or multi-layer polyolefin resin film. From the viewpoint of economy, a base material made of a resin film having a single layer structure (for example, LLDPE film, LDPE film, etc.) can be preferably adopted.

The method for producing the base material may appropriately adopt a conventionally known method, and is not particularly limited. For example, when a resin film is used as a base material, a resin film produced by appropriately adopting a conventionally known general film molding method such as inflation molding, extrusion molding, T-die casting molding, or calender roll molding is used. can do.

In a configuration in which at least one surface (the surface on the pressure-sensitive adhesive layer side) of the base material is the surface of the resin film, the surface of the resin film is subjected to corona discharge treatment, plasma treatment, ozone exposure, flame exposure, ultraviolet irradiation treatment, and the like. Conventionally known surface treatments such as acid treatment, alkali treatment, and application of an undercoating agent may be applied. Such a surface treatment may be a treatment for improving the adhesion between the base material and the pressure-sensitive adhesive layer, in other words, the anchoring property of the pressure-sensitive adhesive layer on the base material. In the embodiment in which the polyolefin-based resin film is used as the base material, it is particularly meaningful to perform the above surface treatment.

<Adhesive layer>
The type of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer of the surface protective sheet disclosed herein is not particularly limited. The adhesive is one or more selected from various polymers (adhesive polymers) such as acrylic, polyester, urethane, polyether, rubber, silicone, polyamide, and fluorine. Can be a pressure-sensitive adhesive formed from a pressure-sensitive adhesive composition containing, as a base polymer (a main component in the polymer component, that is, a component accounting for 50% by weight or more). The techniques disclosed herein can be preferably implemented, for example, in the form of a surface protective sheet with an acrylic pressure-sensitive adhesive.

Here, the "acrylic pressure-sensitive adhesive" refers to a pressure-sensitive adhesive using an acrylic polymer as a base polymer. The "acrylic polymer" is a monomer having at least one (meth) acryloyl group in one molecule (hereinafter, this may be referred to as "acrylic monomer") as a main constituent monomer component (main of the monomer). It refers to a polymer as a component (that is, a component that accounts for 50% by weight or more of the total amount of monomers constituting an acrylic polymer). Further, in the present specification, the “(meth) acryloyl group” means to comprehensively refer to an acryloyl group and a methacryloyl group. Similarly, "(meth) acrylate" is meant to comprehensively refer to acrylates and methacrylates.

(Acrylic polymer)
The acrylic polymer contains, for example, an alkyl (meth) acrylate (hereinafter, also referred to as “monomer A”) and another monomer copolymerizable with the alkyl (meth) acrylate (hereinafter, also referred to as “monomer B”). A polymer of a monomer raw material that can further contain.) Is preferable. The acrylic polymer typically has a copolymer composition corresponding to the composition of the monomer component contained in the monomer raw material.

As the monomer A, an alkyl (meth) acrylate represented by the following general formula (1) can be preferably used.
CH ₂ = C (R ¹ ) COOR ² (1)
^{Here, R 1} in the above formula (1) is a hydrogen atom or a methyl group. Further, R ² is an alkyl group having 1 to 20 carbon atoms. Hereinafter, such a range of the number of carbon atoms may be expressed _{as "C 1-20".} From the viewpoint of polymerization reactivity and polymerization stability, the alkyl (meth) acrylate are preferable ^{R 2} is an alkyl group of _{C 1-16,} ^{R 2} is _{C 1-12} (typically _{C 1-10,} e.g. Alkyl (meth) acrylate, which is an alkyl group of C _{1-8), is more preferable.}

Examples of the alkyl (meth) acrylate in which R ² is a C _1-20 alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, and n-butyl (meth) acrylate. ) Acrylate, isobutyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2 -Ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, n-decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (Meta) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, nonadecil (meth) ) Acrylate, Eikosyl (meth) acrylate and the like can be mentioned. Such alkyl (meth) acrylates can be used alone or in combination of two or more.

Examples of compounds that can be used as monomer B may include the following functional group-containing monomers. Such a functional group-containing monomer can be useful for introducing cross-linking points into the acrylic polymer and enhancing the cohesive force of the acrylic polymer.
Carboxyl group-containing monomer: Ethyloxyunsaturated monocarboxylic acid such as acrylic acid (AA), methacrylic acid (MAA), crotonic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate; itaconic acid, maleic acid , Fumaric acid, citraconic acid and other ethylenically unsaturated dicarboxylic acids.
Acid anhydride group-containing monomer: An acid anhydride such as the above ethylenically unsaturated dicarboxylic acid such as maleic anhydride and itaconic anhydride.
Hydroxy group-containing monomers: For example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate. Hydroxyalkyl (meth) acrylates such as vinyl alcohols, allyl alcohols, 2-hydroxyethyl vinyl ethers, 4-hydroxybutyl vinyl ethers, unsaturated alcohols such as diethylene glycol monovinyl ethers.
Amide group-containing monomers: For example, (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-butyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methylolpropane (meth) acrylamide, N- Monomermethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide.
Imid group-containing monomer: For example, N-isopropylmaleimide, N-cyclohexylmaleimide, itaconimide.
Amino group-containing monomer: For example, aminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, t-butylaminoethyl (meth) acrylate.
Monomers having an epoxy group: for example, glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, allyl glycidyl ether.
Cyanide-containing monomers: for example, acrylonitrile, methacrylonitrile.
Keto group-containing monomers: for example, diacetone (meth) acrylamide, diacetone (meth) acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetoacetate, vinyl acetoacetate.
Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinyl. Pyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholin, N-vinylcaprolactam, N- (meth) acryloylmorpholine, N- (meth) acryloylpyrrolidone.
Alkoxysilyl group-containing monomers: eg 3- (meth) acryloxypropyltrimethoxysilane, 3- (meth) acryloxypropyltriethoxysilane, 3- (meth) acryloxipropylmethyldimethoxysilane, 3- (meth) Acryloxypropylmethyldiethoxysilane.

Other examples of compounds that can be used as monomer B include vinyl ester-based monomers such as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as styrene, substituted styrene (α-methylstyrene, etc.) and vinyltoluene; cyclohexyl (meth). ) Non-aromatic ring-containing (meth) acrylates such as acrylates, t-butylcyclohexyl (meth) acrylates, cyclopentyl (meth) acrylates, isobornyl (meth) acrylates; aryl (meth) acrylates (eg, phenyl (meth) acrylates, benzyls). (Meta) acrylate), aryloxyalkyl (meth) acrylate (eg, phenoxyethyl (meth) acrylate), arylalkyl (meth) acrylate (eg, benzyl (meth) acrylate) and other aromatic ring-containing (meth) acrylates; ethylene , Olefin-based monomers such as propylene, isoprene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride and vinylidene chloride; isocyanate group-containing monomers such as 2- (meth) acryloxyethyl isocyanate; methoxyethyl (meth) acrylate, ethoxyethyl. An alkoxy group-containing monomer such as (meth) acrylate; a vinyl ether-based monomer such as methyl vinyl ether, ethyl vinyl ether, and isobutyl vinyl ether; and the like can be mentioned.

Yet another example of a compound that can be used as monomer B is a polyfunctional monomer. Specific examples of the polyfunctional monomer include 1,6-hexanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, pentaerythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and dipentaerythritol hexa. Examples thereof include compounds having two or more (meth) acryloyl groups in one molecule, such as (meth) acrylate and methylenebisacrylamide. When such a polyfunctional monomer is used, the amount used is not particularly limited, but it is usually appropriate to use 2% by weight or less (more preferably 1% by weight or less) of all the monomer components.

Although not particularly limited, the ratio of the monomer A to the total monomer components can be, for example, about 50% by weight or more, preferably 60% by weight or more, preferably 70% by weight or more. 80% by weight or more is more preferable, and 85% by weight or more is further preferable. By containing the monomer A in a predetermined amount or more, a surface protective sheet with a small increase in peel strength with respect to an adherend (for example, a metal plate) with time can be preferably realized. The technique disclosed herein can be preferably carried out, for example, in a manner in which the proportion of monomer A in the total monomer components is 90% by weight or more. In one aspect, the proportion of monomer A may be 95% by weight or more, or 97% by weight or more. The proportion of monomer A may be 100% by weight. Further, in the embodiment in which the monomer A and the monomer B are used in combination, the ratio of the monomer A to the total monomer components can be, for example, 99.9% by weight or less from the viewpoint of appropriately exerting the effect of the monomer B. Usually, 99.5% by weight or less is preferable, and 99% by weight or less is more preferable.

When the above-mentioned non-aromatic ring-containing (meth) acrylate is copolymerized with the acrylic polymer, the amount of the non-aromatic ring-containing (meth) acrylate used is, for example, the non-aromatic ring-containing (meth) acrylate. The total amount of the (meth) acrylate and the monomer A can be set so as to occupy about 60% by weight or more of all the monomer components constituting the acrylic polymer. By containing a non-aromatic ring-containing (meth) acrylate and the monomer A in a total amount of a predetermined amount or more, a surface protective sheet with a small increase in peel strength with respect to an adherend (for example, a metal plate) with time can be preferably realized. In one embodiment, the ratio of the total amount of the non-aromatic ring-containing (meth) acrylate and the monomer A to the total monomer components may be, for example, 70% by weight or more, 80% by weight or more, or 85% by weight. It may be 90% by weight or more. Further, from the viewpoint of sticking workability, cohesiveness, etc., the ratio of the total amount of the non-aromatic ring-containing (meth) acrylate and the monomer A to the total monomer components is usually 99.9% by weight or less. Is appropriate, 99.5% by weight or less is preferable, and 99% by weight or less is more preferable.
When the above-mentioned functional group-containing monomer is copolymerized with the acrylic polymer, the ratio of the functional group-containing monomer to all the monomer components constituting the acrylic polymer is usually 0.1% by weight or more (typically). It is preferably 0.5% by weight or more, for example, 1% by weight or more, and 40% by weight or less (typically 30% by weight or less, for example, 20% by weight or less). For example, when a carboxyl group-containing monomer is copolymerized with an acrylic polymer, the ratio of the carboxyl group-containing monomer to all the monomer components is usually 0.1% by weight from the viewpoint of sticking workability and cohesiveness. It is preferably 0.3% by weight or more, for example 0.5% by weight or more, and 20% by weight or less (preferably 10% by weight or less, typically 5% by weight or less). For example, it is preferably 3% by weight or less). When the hydroxyl group-containing monomer is copolymerized with the acrylic monomer, the ratio of the hydroxyl group-containing monomer to the above-mentioned previous monomer component is usually 0.001% by weight or more (typically) from the viewpoint of sticking workability and cohesiveness. It is preferably 0.02% by weight or more, for example 0.05% by weight or more, and 10% by weight or less (typically 5% by weight or less, for example 3% by weight or less). Is.

(Tg of base polymer)
In the surface protective sheet disclosed herein, the Tg of the base polymer of the pressure-sensitive adhesive layer (in the case of the acrylic pressure-sensitive adhesive layer, the acrylic polymer) is not particularly limited. The Tg of the base polymer is typically −70 ° C. or higher, for example −60 ° C. or higher. In the surface protective sheet according to a preferred embodiment, the Tg of the base polymer of the pressure-sensitive adhesive layer is −50 ° C. or higher. According to the base polymer having such Tg, a pressure-sensitive adhesive layer suitable for suppressing an increase in peel strength with time can be preferably formed. A better effect can be achieved according to the embodiment in which the Tg of the base polymer is −40 ° C. or higher (more preferably −35 ° C. or higher, further preferably −30 ° C. or higher, for example −27 ° C. or higher). Further, from the viewpoint of sticking workability to the adherend and prevention of displacement during processing, the Tg of the base polymer is usually preferably 0 ° C. or lower, preferably -10 ° C. or lower, and -15 ° C. or lower. Is more preferable. The Tg of the base polymer may be -17 ° C or lower. The Tg of the base polymer can be adjusted by appropriately changing the monomer composition (that is, the type and amount ratio of the monomers used in the synthesis of the polymer).

In the present specification, the Tg of a polymer is a Fox based on the Tg of a homopolymer of each monomer constituting the polymer and the weight fraction (copolymerization ratio based on the weight) of the monomer. The value obtained from the formula of. As shown below, the Fox formula is a relational expression between the Tg of the copolymer and the glass transition temperature Tgi of the homopolymer in which each of the monomers constituting the copolymer is homopolymerized.
1 / Tg = Σ (Wi / Tgi)
In the Fox formula, Tg is the glass transition temperature (unit: K) of the copolymer, Wi is the weight fraction of the monomer i in the copolymer (copolymerization ratio based on the weight), and Tgi is the homopolymer of the monomer i. Represents the glass transition temperature (unit: K) of.

As the Tg of the homopolymer, the value described in the publicly known material shall be adopted. Specifically, for each of the monomers shown in Table 1 below, the values in the table are used as the Tg of the homopolymer.

For Tg of homopolymers of monomers other than those exemplified above, the numerical values described in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. The highest value is adopted for the monomers for which a plurality of types of values are described in this document. When the Tg of the homopolymer is not described in the Polymer Handbook, the value obtained by the measuring method described in JP-A-2007-51271 shall be used.

The base polymer (typically an acrylic polymer) is a copolymer of a monomer (monomer H) having a homopolymer Tg of 10 ° C. or higher and a monomer (monomer L) having a homopolymer Tg of less than 10 ° C. Is preferable. By using the monomer H and the monomer L in combination, the Tg of the base polymer can be suitably adjusted. The monomer H and the monomer L may correspond to the above-mentioned monomer A or may correspond to the monomer B, respectively.

The ratio of monomer H to all monomer components can be, for example, 1% by weight or more, usually 5% by weight or more, preferably 10% by weight or more, and 15% by weight or more. Is more preferable. By containing a large amount of the monomer H, the cohesive force of the pressure-sensitive adhesive is increased, the increase in peel strength with time is suppressed, and the peeling workability tends to be improved. Increasing the proportion of monomer H can also help reduce the value of _{the minimum load L min of the unloading curve described later.} The surface protective sheet disclosed herein can be preferably carried out in an embodiment in which the proportion of the monomer H is 20% by weight or more (more preferably 25% by weight or more, still more preferably 30% by weight or more, for example 35% by weight or more). .. The proportion of monomer H may be 40% by weight or more. Further, the proportion of the monomer H is usually preferably 70% by weight or less, preferably 60% by weight or less, more preferably 60% by weight or less, from the viewpoint of sticking workability to the adherend and prevention of deviation during processing. It is 50% by weight or less. In some embodiments, the proportion of monomer H may be, for example, 45% by weight or less.

Non-limiting examples of monomers that can be preferably used as Monomer H in acrylic polymers include methyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-butyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, and isobol. Nyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, acrylamide and the like can be mentioned.

In one aspect, the monomer H preferably comprises one or more monomers selected from alkyl (meth) acrylates and cycloalkyl (meth) acrylates. For example, it is preferable that about 50% by weight or more (more preferably 70% by weight or more, for example 90% by weight or more) of the monomer H is an alkyl (meth) acrylate or a cycloalkyl (meth) acrylate. Methyl methacrylate (MMA) is mentioned as a particularly preferable monomer H. In the present specification, the cycloalkyl (meth) acrylate includes a monocyclic cycloalkyl (meth) acrylate such as cyclohexyl (meth) acrylate and a polycyclic cycloalkyl (meth) acrylate such as isobornyl (meth) acrylate. It is a concept to do.

In the surface protection sheet disclosed herein, a homopolymer having a Tg of 35 ° C. or higher (more preferably 60 ° C. or higher, for example, 80 ° C. or higher) contains 50% by weight or more (more preferably 70% by weight or more) of the monomer H. , For example, 90% by weight or more) can be preferably carried out. A base polymer having such a composition (for example, an acrylic polymer) is suitable for reducing the value of _{the minimum load L min of the unloading curve described later.} In one aspect, from the viewpoint of initial adhesiveness and the like, 50% by weight or more (more preferably 70% by weight or more) of the monomer H is a monomer having a homopolymer Tg of 180 ° C. or less (for example, 150 ° C. or less). Good.

In the surface protection sheet disclosed herein, a monomer having a homopolymer Tg of −25 ° C. or lower (more preferably −35 ° C. or lower, for example, −45 ° C. or lower) is 50% by weight or more (more preferably 70) of the monomer L. It can be preferably carried out in a mode that occupies% by weight or more, for example, 90% by weight or more. As described above, according to the composition containing a large amount of the monomer having a low Tg of the homopolymer, a larger amount of the monomer H can be used at the Tg of a predetermined value or less. This can be advantageous in reducing the value of the minimum load L _{min on the unloading curve.} In a preferred embodiment, 50% by weight or more (more preferably 70% by weight or more, for example, 90% by weight or more) of the monomer L is a monomer having a homopolymer Tg of −50 ° C. or less (for example, BA, 2EHA, n−). One or more selected from octyl acrylate, n-nonyl acrylate, isononyl acrylate and n-hexyl acrylate, preferably one or both of BA and 2EHA), and the Tg of the homopolymer is -60. It may be a monomer (for example, 2EHA) below ° C.

(Synthesis of base polymer)
The method for obtaining the base polymer (for example, an acrylic polymer) is not particularly limited. For example, known polymerization methods such as a solution polymerization method, an emulsion polymerization method, a massive polymerization method, and a suspension polymerization method can be appropriately adopted. Alternatively, photopolymerization performed by irradiating light such as UV (typically performed in the presence of a photopolymerization initiator), radiation polymerization performed by irradiating radiation such as β-rays and γ-rays, and the like. Active energy ray irradiation polymerization may be adopted. As the monomer supply method in the solution polymerization method or the emulsion polymerization method, a batch charging method, a continuous supply (dropping) method, a divided feeding (dropping) method, or the like in which all the monomer raw materials are supplied at once can be appropriately adopted. The polymerization temperature can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, and the like. The polymerization temperature is usually preferably 20 ° C. or higher, preferably 40 ° C. or higher, more preferably 50 ° C. or higher, 60 ° C. or higher, 65 ° C. or higher, and even 70 ° C. or higher. Good. The polymerization temperature is usually 170 ° C. or lower (typically 140 ° C. or lower), preferably 95 ° C. or lower (for example, 85 ° C. or lower). In emulsion polymerization, the polymerization temperature is preferably 95 ° C. or lower (for example, 85 ° C. or lower).

The solvent (polymerization solvent) used for solution polymerization can be appropriately selected from conventionally known organic solvents. For example, aromatic compounds such as toluene (typically aromatic hydrocarbons), acetic acid esters such as ethyl acetate, aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane are preferably used.

The initiator used for the polymerization can be appropriately selected from known or commonly used polymerization initiators according to the type of the monomer and the type of the polymerization method. For example, azo-based polymerization of 2,2'-azobisisobutyronitrile, 2,2'-azobis (2-methylpropionamidine) disulfate, 2,2'-azobis (2-amidinopropane) dihydrochloride, etc. An initiator can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate and ammonium persulfate; peroxide-based initiators such as benzoyl peroxide, t-butyl hydroperoxide and hydrogen peroxide; and phenyl-substituted ethane and the like. Substituted ethane initiators; aromatic carbonyl compounds; and the like. Yet another example of the polymerization initiator is a redox-based initiator that is a combination of a peroxide and a reducing agent. Examples of such redox-based initiators include a combination of a peroxide such as hydrogen peroxide solution and ascorbic acid, a combination of a peroxide such as hydrogen peroxide solution and an iron (II) salt, and a persulfate and sulfite. Examples include a combination with sodium hydrogen peroxide. The polymerization initiator may be used alone or in combination of two or more. The amount of the polymerization initiator used may be a normal amount, for example, about 0.005 to 1 part by weight (typically 0.01 to 1 part by weight) with respect to 100 parts by weight of all the monomer components. You can choose from a range.

The surfactant (emulsifier) used for emulsion polymerization is not particularly limited, and known anionic surfactants, nonionic surfactants and the like can be used. A surfactant having a radically polymerizable functional group may be used. Hereinafter, a surfactant having a radically polymerizable functional group is also referred to as a reactive (polymerizable) surfactant. On the other hand, a general surfactant having no radically polymerizable functional group may be referred to as a non-reactive (non-polymerizable) surfactant. As the surfactant, one type may be used alone or two or more types may be used in combination. The amount of the surfactant used is usually preferably 0.1 part by weight or more (for example, 0.5 part by weight or more) with respect to 100 parts by weight of all the monomer components, and is also preferably with respect to 100 parts by weight of all the monomer components. It is preferably 10 parts by weight or less (for example, 5 parts by weight or less).

Examples of non-reactive surfactants are sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium polyoxyethylene lauryl sulfate, sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkyl phenyl ether sulfate, polyoxy. Anionic emulsifiers such as sodium ethylenealkylphenyl ether sulfate and sodium polyoxyethylene alkyl sulfosuccinate; nonions such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, and polyoxyethylene polyoxypropylene block polymer. System emulsifier; etc.

The reactive surfactant is not particularly limited as long as it has a radically polymerizable functional group. For example, it may be a reactive surfactant having a structure in which a radically polymerizable functional group is introduced into the anionic surfactant or nonionic surfactant as described above. Examples of the radically polymerizable functional group include a vinyl group, a propenyl group, an isopropenyl group, a vinyl ether group (vinyloxy group), an allyl ether group (allyloxy group) and the like. The concept of a propenyl group here includes a 1-propenyl group (CH _3- CH = CH-) and a 2-propenyl group (CH ₂ = CH-CH _2- ; sometimes referred to as an allyl group). included.

Examples of anionic reactive surfactants include polyoxyethylene (allyloxymethyl) alkyl ether sulfate (eg ammonium salt), polyoxyethylene nonylpropenylphenyl ether sulfate (eg ammonium salt), alkylallyl sulfosuccinic acid. Examples thereof include a salt (for example, a sodium salt), a methacryloxypolyoxypropylene sulfate ester salt (for example, a sodium salt), a polyoxyalkylene alkenyl ether sulfate (for example, an ammonium salt having an isopropenyl group at the end of the alkenyl group) and the like. When the anionic reactive surfactant forms a salt, the salt may be, for example, a metal salt such as a sodium salt or a non-metal salt such as an ammonium salt or an amine salt. ..
Examples of nonionic reactive surfactants include polyoxyethylene nonylpropenylphenyl ether and the like.

Commercially available reactive surfactants include the trade names "Aqualon HS-05", "Aqualon HS-10", "Aqualon HS-1025", "Aqualon HS-20", and "Aqualon" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. KH-10, Aqualon KH-1025, Aqualon KH-05, Aqualon BC-0515, Aqualon BC-10, Aqualon BC-1025, Aqualon BC-20, Aqualon BC -2020 "," Aqualon RN-20 "," Aqualon RN-30 "," Aqualon RN-50 ", ADEKA product name" Adecaria Soap SE-10N "," Adecaria Soap SR-1025 ", Kao Product names "Latemuru PD-104", "Latemuru PD-420", "Latemuru PD-430", "Latemuru PD-450", Sanyo Kasei's product names "Ereminol JS-20", "Ereminol RS" -3000 ”, trade name“ Antox MS-60 ”manufactured by Nippon Emulsion Co., Ltd., and the like.

Although not particularly limited, in some embodiments, a reactive surfactant having an oxyethylene chain may be preferably used. Here, the oxyethylene chain refers to a repeating structure of oxyethylene units, that is, a structural portion represented by _{− (C 2} H ₄ O) _{n −.} n indicates the number of repetitions in oxyethylene units. For example, a reactive surfactant having this repetition number n of about 5 to 30 (for example, 8 to 25) is preferable.

From the viewpoint of polymerization stability during emulsion polymerization and the like, a reactive surfactant having a propenyl group can be preferably adopted in some embodiments. Reactive surfactants having a propenyl group and an oxyethylene chain are particularly preferred.

From the viewpoint of emulsification performance and the like, an anionic reactive surfactant (for example, an anionic reactive surfactant having an oxyethylene chain) can be preferably adopted in some embodiments. When the anionic reactive surfactant forms a salt, the salt is preferably a non-metal salt from the viewpoint of preventing traces on the surface of the adherend (for example, the surface of the coating film). Ammonium salts are preferred.
When a nonionic reactive surfactant is used, other surfactants such as anionic reactive surfactant, anionic non-reactive surfactant, nonionic non-reactive surfactant, etc. More favorable results can be achieved by using in combination with.

By emulsion-polymerizing the monomer raw material in the presence of a reactive surfactant having a radically polymerizable functional group, the above reactive surfactant can react and be incorporated into an acrylic polymer. The reactive surfactant incorporated into the acrylic polymer is less likely to bleed out to the surface of the pressure-sensitive adhesive layer because its movement within the pressure-sensitive adhesive layer is restricted. Therefore, the use of the reactive surfactant can suppress the bleeding out of the low molecular weight compound to the surface of the pressure-sensitive adhesive layer. This is preferable from the viewpoint of low contamination of the surface protective sheet. From the viewpoint of achieving better low pollution, a mode in which only a reactive surfactant is used as the surfactant during emulsion polymerization can be preferably adopted.

For emulsion polymerization, various conventionally known chain transfer agents (which can also be grasped as a molecular weight adjuster or a degree of polymerization adjuster) can be used, if necessary. The chain transfer agent may be used alone or in combination of two or more. As the chain transfer agent, mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, and thioglycolic acid can be preferably used. When a chain transfer agent is used, the amount used can be, for example, about 0.01 to 1 part by weight with respect to 100 parts by weight of all the monomer components. The techniques disclosed herein may also be preferably practiced in aspects that do not use chain transfer agents.

<Adhesive composition>
The pressure-sensitive adhesive layer of the surface protective sheet disclosed herein can be a pressure-sensitive adhesive layer formed from various forms of pressure-sensitive adhesive compositions. Examples of the form of the pressure-sensitive adhesive composition include a composition in which a pressure-sensitive adhesive (adhesive component) is contained in an organic solvent (solvent-type pressure-sensitive adhesive composition), and a composition in which the pressure-sensitive adhesive is dissolved or dispersed in an aqueous solvent. A product (water-based pressure-sensitive adhesive composition), a composition prepared to be cured by active energy rays such as ultraviolet rays and radiation to form a pressure-sensitive adhesive (active energy ray-curable pressure-sensitive adhesive composition), and coated in a heat-melted state. Examples thereof include a hot melt type pressure-sensitive adhesive composition that is processed and forms a pressure-sensitive adhesive when cooled to around room temperature.
From the viewpoint of reducing the environmental load, the aqueous pressure-sensitive adhesive composition can be preferably adopted. As a preferred example of such an aqueous pressure-sensitive adhesive composition, an water-dispersed pressure-sensitive adhesive composition containing an acrylic polymer as a base polymer (acrylic water-dispersed pressure-sensitive adhesive composition, typically an acrylic emulsion-type pressure-sensitive adhesive composition). ).

(Crosslinking agent)
In the surface protective sheet disclosed herein, the pressure-sensitive adhesive composition used for forming the pressure-sensitive adhesive layer may contain a cross-linking agent, if necessary. The use of crosslinking agents, gel fraction G _C and sol molecular weight S _Mw can be suitably adjusted. The type of the cross-linking agent used is not particularly limited, and can be appropriately selected from conventionally known cross-linking agents.

The amount of the cross-linking agent used is not particularly limited, and can be appropriately set so as to obtain suitable properties after cross-linking in consideration of the composition of the base polymer and the weight average molecular weight. Although not particularly limited, the amount of the cross-linking agent used with respect to 100 parts by weight of the base polymer (typically an acrylic polymer) is, for example, 0.01 parts by weight or more (typically 0.05 parts by weight or more). can do. From the viewpoint of the stability of the peel strength over time, the amount of the cross-linking agent used is usually 15 parts by weight or less (preferably 10 parts by weight or less, for example, 5 parts by weight or less) with respect to 100 parts by weight of the base polymer. It is appropriate to do.

Specific examples of the cross-linking agent include oxazoline-based cross-linking agent, aziridine-based cross-linking agent, isocyanate-based cross-linking agent, epoxy-based cross-linking agent, melamine-based cross-linking agent, peroxide-based cross-linking agent, urea-based cross-linking agent, and metal alkoxide-based cross-linking agent. , Metal chelate-based cross-linking agent, metal salt-based cross-linking agent, carbodiimide-based cross-linking agent, hydrazine-based cross-linking agent, amine-based cross-linking agent, silane coupling agent and the like. These can be used alone or in combination of two or more. For example, it is preferable to use one or more selected from the group consisting of an oxazoline-based cross-linking agent, an aziridine-based cross-linking agent, an isocyanate-based cross-linking agent, and an epoxy-based cross-linking agent. In one embodiment, an oxazoline-based cross-linking agent can be preferably used.

As the oxazoline-based cross-linking agent, one having one or more oxazoline groups in one molecule can be used without particular limitation. In the water-dispersible pressure-sensitive adhesive composition, it is preferable to use an oxazoline-based cross-linking agent that can be dissolved or dispersed in water.
The oxazoline group may be any of a 2-oxazoline group, a 3-oxazoline group, and a 4-oxazoline group. Usually, an oxazoline-based cross-linking agent having a 2-oxazoline group can be preferably used. For example, 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4- A water-soluble copolymer or an aqueous-dispersed copolymer obtained by copolymerizing an addition-polymerizable oxazoline such as methyl-2-oxazoline or 2-isopropenyl-5-ethyl-2-oxazoline with another monomer. , Can be used as an oxazoline-based cross-linking agent.
Examples of commercially available oxazoline-based cross-linking agents include the trade names "Epocross WS-500", "Epocross WS-700", "Epocross K-2010E", "Epocross K-2020E", and "Epocross K-" manufactured by Nippon Shokubai Co., Ltd. 2030E ”and the like.

Examples of the aziridine-based cross-linking agent include trimethylolpropane tris [3- (1-aziridinyl) propionate], trimethylolpropane tris [3- (1- (2-methyl) aziridinyl propionate)], and the like. Be done.

Examples of isocyanate-based cross-linking agents include aromatic isocyanates such as tolylene diisocyanate and xylene diisocyanate; aliphatic isocyanates such as isophorone diisocyanate; aliphatic isocyanates such as hexamethylene diisocyanate; and the like. More specifically, trimethylolpropane / tolylene diisocyanate adduct (manufactured by Toso Co., Ltd., trade name "Coronate L"), trimethylolpropane / hexamethylene diisocyanate adduct (manufactured by Toso Co., Ltd., trade name). Examples thereof include isocyanate adducts such as "Coronate HL") and isocyanurates of hexamethylene diisocyanate (manufactured by Toso Co., Ltd., trade name "Coronate HX"). In the water-dispersible pressure-sensitive adhesive composition, it is preferable to use an isocyanate-based cross-linking agent that can be dissolved or dispersed in water. For example, a water-soluble, water-dispersible or self-emulsifying isocyanate-based cross-linking agent may be preferably adopted. A so-called blocked isocyanate type isocyanate-based cross-linking agent in which the isocyanate group is blocked can be preferably used.

As the epoxy-based cross-linking agent, one having two or more epoxy groups in one molecule can be used without particular limitation. An epoxy-based cross-linking agent having 3 to 5 epoxy groups in one molecule is preferable. In the water-dispersible pressure-sensitive adhesive composition, it is preferable to use an epoxy-based cross-linking agent that can be dissolved or dispersed in water.
Specific examples of the epoxy-based cross-linking agent include N, N, N', N'-tetraglycidyl-m-xylene diamine, 1,3-bis (N, N-diglycidyl aminomethyl) cyclohexane, and 1,6-hexane. Examples thereof include diol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether.
Commercially available epoxy cross-linking agents include Mitsubishi Gas Chemical's product names "TETRAD-X" and "TETRAD-C", DIC's product name "Epicron CR-5L", and Nagase ChemteX's products. Examples thereof include the name "Denacol EX-512" and the product name "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd.

As the carbodiimide-based cross-linking agent, a low molecular weight compound or a high molecular weight compound having two or more carbodiimide groups can be used. In the water-dispersible pressure-sensitive adhesive composition, it is preferable to use a carbodiimide-based cross-linking agent that can be dissolved or dispersed in water. Examples of commercially available carbodiimide-based cross-linking agents include the carbodilite V series (aqueous solution type) such as "carbodilite V-02", "carbodilite V-02-L2", and "carbodilite V-04" manufactured by Nisshinbo. Examples thereof include a carbodilite series such as a carbodilite E series (water-dispersed type) such as "carbodilite E-01", "carbodilite E-02", and "carbodilite E-04".

(Release adjuster)
The pressure-sensitive adhesive layer disclosed herein may contain a release modifier. The peeling adjuster contained in the pressure-sensitive adhesive layer may migrate to the surface of the pressure-sensitive adhesive layer over time to suppress an increase in peeling strength and contribute to improvement in peeling workability. By using the release adjusting agent, it becomes easy to preferably achieve both the adhesion to the adherend at the time of protection and the light release property at the time of removing the protective sheet. The release modifier disclosed herein is typically a compound having a hydrophobic group and a hydrophilic group, and preferred examples thereof include various surfactants such as anionic surfactants and nonionic surfactants. Agents can be mentioned. Fatty acid amide may be used as the exfoliation modifier. The peeling modifier may be used alone or in combination of two or more. The release modifier may be used at the time of polymerization or may be added after the polymerization. In a preferred embodiment, the release modifier can be used during polymerization (eg, during emulsion polymerization). In another aspect, the release modifier can be preferably used in a mode in which the release adjuster is added after polymerization, that is, in a mode in which the release adjuster is added to a pre-synthesized base polymer.

Non-limiting examples of surfactants that can be used as peeling modifiers include, as anionic surfactants, carboxylates, sulfonates, sulfates, phosphates, etc .; as nonionic surfactants, esters. Type, ether type, ester ether type, fatty acid alkanolamide type in which a hydrophobic group and a hydrophilic group are bonded by an amide bond, etc .; as a cationic surfactant, an amine salt type, a quaternary ammonium salt type, etc.; Can be mentioned.

In one aspect of the surface protective sheet disclosed herein, a phosphoric acid ester-based surfactant can be preferably used as the peeling conditioner. Examples of the phosphoric acid ester include alkyl phosphoric acid esters such as lauryl phosphate and lauryl phosphate; polyoxyethylene tridecyl ether phosphoric acid, polyoxyethylene lauryl ether phosphoric acid, polyoxyethylene octadecyl ether phosphoric acid and the like. , Polyoxyethylene alkyl phosphoric acid ester; polyoxyethylene nonylphenyl ether phosphoric acid, polyoxyethylene octylphenyl ether phosphoric acid, polyoxyethylene dinonylphenyl ether phosphoric acid, polyoxyethylene dioctylphenyl ether phosphoric acid, etc. Ethylene alkylaryl phosphate: etc. From the viewpoint of preventing migration to the adherend, in one embodiment, a phosphoric acid ester having a weight average molecular weight of 150 to 5000 can be preferably used. The phosphoric acid ester-based surfactant may contain one of such phosphoric acid esters alone or in combination of two or more. Each phosphoric acid ester contained in the phosphoric acid ester-based surfactant may be a monoester, a diester, or a mixture thereof.

The phosphoric acid ester-based surfactant may be used alone or in combination of two or more. A phosphoric acid ester-based surfactant may be used in combination with another surfactant. Further, the phosphoric acid ester-based surfactant may be used alone or in a salt form (for example, sodium salt, potassium salt, barium salt, triethanolamine salt, etc.), and may be used as a mixture thereof. It may be used.

The amount of the release adjusting agent used is usually about 0.01 to 30 parts by weight with respect to 100 parts by weight of the base polymer. By setting the content of the release adjusting agent to 0.01 parts by weight or more, the removability tends to be improved. Further, when the content of the release adjusting agent is 30 parts by weight or less, the pressure-sensitive adhesive layer tends to adhere well to the adherend and the contamination of the adherend tends to be prevented. The content of the release adjusting agent is preferably 0.1 part by weight or more (for example, 0.5 part by weight or more, typically 1 part by weight or more) with respect to 100 parts by weight of the base polymer, and is 10 parts by weight or less. (For example, 5 parts by weight or less, typically 3 parts by weight or less) is preferable.

The pressure-sensitive adhesive composition may contain a known pressure-sensitive adhesive such as a rosin-based pressure-sensitive adhesive, a terpene-based pressure-sensitive adhesive, and a hydrocarbon-based pressure-sensitive adhesive, if necessary. From the viewpoint of avoiding excessively high peel strength, the amount of the tackifier used is preferably 5 parts by weight or less, more preferably 1 part by weight or less, based on 100 parts by weight of the base polymer. Surface protective sheet disclosed herein, since that can effectively control the adhesive force through the gel fraction G _C and sol molecular weight S _Mw of the adhesive can be preferably implemented in a manner that does not use a tackifier.

The pressure-sensitive adhesive composition may contain, if necessary, a leveling agent, a cross-linking aid, a plasticizer, a softening agent, a filler, an antistatic agent, an antioxidant, an ultraviolet absorber, an antioxidant, a light stabilizer, and the like. It may contain various additives that are common in the field of pressure-sensitive adhesive compositions. As for such various additives, conventionally known ones can be used by a conventional method and do not particularly characterize the present invention, and thus detailed description thereof will be omitted.

<Adhesive layer>
As a method of providing the pressure-sensitive adhesive layer on the base material, a method of directly applying (typically applying) the pressure-sensitive adhesive composition as described above to the base material and curing treatment (direct method), or an appropriate peeling surface By applying the above-mentioned pressure-sensitive adhesive composition on (for example, the surface of a transfer sheet having peelability) and curing treatment, a pressure-sensitive adhesive layer is formed on the peel-off surface, and the pressure-sensitive adhesive layer is bonded to a base material. (Transfer method) or the like can be used. The curing treatment may be one or more treatments selected from drying (heating), cooling, cross-linking, additional copolymerization reaction, aging and the like. For example, a treatment for simply drying the pressure-sensitive adhesive composition containing a solvent (heat treatment, etc.) and a treatment for simply cooling (solidifying) the pressure-sensitive adhesive composition in a heat-melted state are also referred to as the curing treatment here. Can be included. When the curing treatment includes two or more treatments (for example, drying and cross-linking), these treatments may be performed simultaneously or in multiple steps.

The pressure-sensitive adhesive composition can be applied using a conventional coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, or a spray coater. From the viewpoint of promoting the cross-linking reaction and improving the production efficiency, it is preferable that the pressure-sensitive adhesive composition is dried under heating. Although it depends on the type of the object (base material, etc.) to which the pressure-sensitive adhesive composition is applied, for example, a drying temperature of about 40 ° C. to 150 ° C. can be adopted.

(Gel fraction _G C)
In the surface protective sheet disclosed herein, may be a gel fraction G _C of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited, for example, 40% or more (typically 50% or more). In one embodiment, the gel fraction _{G C} of the pressure-sensitive adhesive is suitably 60% or more, preferably 65% or more, more preferably 70% or more, more preferably 75% or more. Gel fraction G _C of the pressure-sensitive adhesive may be for example 80% or more. The increase in the gel fraction G _C, improved cohesiveness of the pressure-sensitive adhesive, tends to adhesive residue on the adherend (i.e., cohesive failure of the adhesive layer during peeling removal) is suppressed. Surface protective sheet disclosed herein may be suitably implemented in a manner which is gel fraction G _C is 85% or more (e.g., 90%). The upper limit of the gel fraction _{G C} is in principle, 100%. In some embodiments, in view of facilitating compatibility between preferred sol molecular weight S _Mw disclosed herein, the gel fraction G _C may be, for example, 98% or less, 95% or less (e.g., 90% The following) may be used. Surface protective sheet disclosed herein may be suitably implemented in a manner which is less than 80% gel fraction G _C (e.g. 70% or less). Gel fraction G _C, for example, can be adjusted composition of the base polymer, polymerization methods and the polymerization conditions of the base polymer, the molecular weight of the base polymer, selection of presence and the kind and amount of use of the crosslinking agent, by such .. Gel fraction G _C is measured by the following method. The same method is adopted for the examples described later.

[Measurement of gel fraction _{G C]}
Approximately 0.1 g of adhesive sample (weight Wg _{1 ) is wrapped in a porous polytetrafluoroethylene film (weight Wg 2} ) having an average pore size of 0.2 μm in a purse-like shape, and the mouth is tied with octopus thread (weight Wg ₃ ). As the porous polytetrafluoroethylene film, the trade name "Nitoflon (registered trademark) NTF1122" (Nitto Denko KK, average pore diameter 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent product thereof is used. This package is immersed in 50 mL of toluene and held at room temperature (typically 23 ° C.) for 7 days to elute only the sol component in the pressure-sensitive adhesive layer out of the film. Next, the package is taken out, the toluene adhering to the outer surface is wiped off, the package is dried at 130 ° C. for 2 hours, and the weight of the package (Wg ₄ ) is measured. By substituting each value into the following equation, it is possible to calculate the gel fraction G _C of the pressure-sensitive adhesive.
Gel fraction _{G C (%) = [(} Wg 4 -Wg 2 -Wg 3) / Wg 1] × 100

PSA sample used in the measurement of the gel fraction G _C may be taken from the pressure-sensitive adhesive layer of the surface protective sheet. Alternatively, a pressure-sensitive adhesive prepared from the pressure-sensitive adhesive composition used for forming the pressure-sensitive adhesive layer may be used as the pressure-sensitive adhesive sample. For example, the pressure-sensitive adhesive composition was dried for 3 minutes at 130 ° C., to form a pressure-sensitive adhesive layer having a thickness of about 35 [mu] m, were taken adhesive samples from the adhesive layer, to measure the gel fraction G _C be able to.

(Sol molecular weight _SMw )
Sol molecular weight S _Mw of adhesive is not particularly limited. From the viewpoint of preventing contamination of the adherend, the sol molecular weight _SMw is usually preferably 1 × 10 ⁴ or more, and ^{preferably 5 × 10 4} or more (for example, 7 × 10 ⁴ or more). .. Surface protective sheet disclosed herein, the sol molecular weight S _Mw of the adhesive can be suitably carried out in a manner at 10 × 10 ⁴ or more. By increasing the Mw of the sol component (toluene-soluble component), which has higher mobility than the gel, it becomes difficult for the adhesive surface to wet the adherend surface, and the increase in peel strength over time is effectively suppressed. There is a tendency. From this point of view, the sol molecular weight _{S Mw} of adhesive, preferably 20 × 10 ⁴ or more, more preferably 30 × 10 ⁴ or more, can be, for example, 40 × 10 ⁴ or more. From the viewpoint of facilitating compatibility between a predetermined or more gel fraction _{G C,} the sol molecular weight _{S Mw} of adhesive, usually, is suitably 100 × 10 ⁴ or less, preferably 80 × 10 ⁴ or less, 70 × more preferably 10 ⁴ or less, for example, be a 65 × 10 ⁴ or less. In some embodiments, the sol molecular weight _{S Mw} of the adhesive can be, for example, less than 40 × 10 ^4, 35 × 10 than ^4, or less than 30 × 10 ^4. The surface protective sheet disclosed herein can be preferably implemented even at _{such a sol molecular weight SMw.}

The sol molecular weight _SMw is such that the surface protective sheet is immersed in toluene for 48 hours at room temperature to extract the toluene-soluble component from the pressure-sensitive adhesive layer, and then the residue obtained by volatilizing the toluene is dissolved in tetrahydrofuran (THF). By performing GPC (gel permeation chromatography) measurement, the weight average molecular weight in terms of standard polystyrene can be obtained. As the GPC measuring device, it is preferable to use the model name "HLC-8320GPC" manufactured by Tosoh Corporation. The measurement conditions should be as follows. The same method is adopted for the examples described later.
[GPC measurement conditions]
Column: TSKgel GMH-H (S), 2 connected Column size: 7.8 mm I. D. × 300 mm
Detector: Differential Refractometer Eluent: THF
Flow velocity: 0.6 mL / min Measurement temperature: 40 ° C
Sample injection volume: 100 μL

Increasing the gel fraction G _C by blending a crosslinking agent to the base polymer, sol molecular weight S _Mw tends to decrease in general. According to the art disclosed herein, by increasing the sol molecular weight S _Mw at a predetermined or more gel fraction G _C, adhesive residue is less likely to occur, and the surface protection sheet over time increase is effectively suppressed in the peel strength is It can be preferably realized.

The sol molecular weight _SMw is, for example, the composition of the base polymer, the polymerization method and polymerization conditions of the base polymer (polymerization temperature, the type and amount of the polymerization initiator used, the type of the polymerization solvent, the supply mode of the monomer, etc.), and the base polymer. It can be adjusted by the molecular weight, the presence or absence of the use of the cross-linking agent, the type thereof, the selection of the amount used, and the like. More specifically, for example, in the synthesis of a base polymer (typically an acrylic polymer), the sol molecular weight _SMw tends to be generally improved by increasing the monomer concentration in the reaction system. As a method for increasing the monomer concentration in the reaction system, for example, in a polymerization mode in which the monomer is continuously supplied to the reaction vessel, a method for increasing the supply rate of the monomer can be adopted. If the temperature in the polymerization reaction system is not properly controlled (for example, if the polymerization temperature becomes excessively high in a part of the reaction system due to insufficient stirring or cooling), the temperature is low. It should be noted that a molecular weight substance may be produced and the sol molecular weight _{SMw may decrease.} Those skilled in the art based on the common general knowledge as of the description and the Applicant of the present specification and specific examples described below, a method of realizing a suitable sol molecular weight S _Mw disclosed herein, where It may understand how to achieve a suitable gel fraction G _C and a suitable sol molecular weight S _Mw disclosed simultaneously.

_{(Minimum load L min of} unloading curve in nanoindenter measurement)
_{The surface protective sheet disclosed herein preferably has a minimum load L min of the} unloading curve of less than −2.0 μN in the nanoindenter measurement of the pressure-sensitive adhesive layer. The fact that the load applied to the indenter at the time of unloading is in the negative direction means that the indenter pushed into the pressure-sensitive adhesive layer is difficult to be pulled out, and thus suggests that the pressure-sensitive adhesive has a high cohesive force. In such an adhesive layer, wetting of the adhesive surface with respect to the adherend surface is difficult to proceed. Therefore, according to the surface protective sheet having such an adhesive layer, the increase in peel strength with time tends to be preferably suppressed.

The minimum load L _min of the unloading curve is measured by nanoindenter measurement in which a minute indenter is pushed from the surface (adhesive surface) of the pressure-sensitive adhesive layer toward the pressure-sensitive adhesive layer and then pulled out. At this time, in the load (pushing) -unloading (pulling) curve obtained by plotting the transition of the load applied to the indenter (vertical axis) with respect to the displacement (horizontal axis) of the indenter with respect to the adhesive surface. It is calculated as the minimum (minimum) load value of the unloading curve. According to the nanoindenter measurement, it is possible to accurately evaluate the behavior of the pressure-sensitive adhesive layer itself by suppressing the influence of the base material to a negligible level even for a thin pressure-sensitive adhesive layer as in the examples described later. it can.

The nanoindenter measurement can be performed, for example, using a Triboindenter manufactured by Hysitron under the following conditions. The same method is adopted for the examples described later.
[Nanoindenter measurement conditions]
Indenter used: Berkovich (triangular pyramid) type diamond indenter Measurement method: Single indentation measurement Measurement temperature: Room temperature (25 ° C)
Push-in depth setting: 300 nm
Pushing speed: 100 nm / sec Pulling speed: 100 nm / sec

In the surface protection sheet according to one aspect, the minimum load L _min of the unloading curve is preferably −2.5 μN or less, more preferably −3.0 μN or less, and further preferably −4.0 μN or less. The minimum load L _min of the unloading curve may be −4.5 μN or less, −5.0 μN or less, for example, −6.0 μN or less. The lower limit of the minimum load L _min of the unloading curve is not particularly limited, but it is usually appropriate to set it to -10 μN or more from the viewpoint of sticking workability to the adherend and protection of the adherend in the above usage mode. Is.

As a method of lowering the minimum load L _min of the unloading curve, for example, a method of increasing the Tg of the base polymer of the pressure-sensitive adhesive layer, increasing the sol molecular weight _SMw , or the like can be effective. Other elements that may be utilized in the regulation of minimum load L _min of unloading curve, gel fraction G _C, the composition of the base polymer (e.g., the type of the monomer component used in the synthesis, the monomer H to the total monomer components Ratio, etc.), polymerization method and polymerization conditions of the base polymer, type of cross-linking agent, addition amount, and the like.

<Characteristics of surface protection sheet>
(Medium speed peel strength)
The surface protective sheet disclosed herein is attached to a stainless steel plate (SUS plate) and stored at 60 ° C. for 7 days, and then measured at a peeling speed of 3 m / min (that is, 50 mm / sec) and a peeling angle of 180 degrees. aging peel strength (hereinafter, also referred to as a time during speed peel strength.) _{P a} is preferably at about 0.70N / 20mm or less. As a result, the surface protective sheet can maintain light peelability from the adherend even if the sticking period to the adherend such as a metal plate is relatively long. Therefore, the load applied to the surface protective sheet during the removal work from the adherend is reduced, and the surface protective sheet is less likely to be torn or torn. This improves the workability of removing from the adherend. According to the surface protecting sheet over time in speed peel strength _{P A} is 0.60N / 20mm or less (more preferably 0.50 N / 20 mm or less), better peeling workability can be realized. In one embodiment, time during speed peel strength _{P A} may be at 0.40 N / 20 mm or less, or even less 0.30 N / 20 mm. Further, during the protection period of the adherend (for example, during processing of the adherend surface protection sheet is attached) peeling floating view of suppressing in, over time in speed peel strength P _A, usually, 0.05 N It is suitable that it is / 20 mm or more, preferably 0.10 N / 20 mm or more, and more preferably 0.15 N / 20 mm or more. Time during speed peel strength P _A is measured by the method described in the examples below.

The surface protective sheet disclosed here has an initial peel strength measured at a peel speed of 3 m / min and a peel angle of 180 degrees 15 minutes after being attached to a SUS plate (hereinafter, also referred to as an initial medium speed peel strength). It _{is preferable that P 0} is 0.50 N / 20 mm or less (more preferably 0.40 N / 20 mm or less, for example 0.30 N / 20 mm or less). Such a surface protective sheet is used such that after being attached to an adherend such as a metal plate, the adherend is processed in a relatively short time and then peeled off from the adherend. Also in the embodiment, good removal workability from the adherend can be exhibited. Further, from the viewpoint of sticking workability to the adherend and protection of the adherend in the above-mentioned usage mode _{, it is usually appropriate that the initial medium-speed peel strength P 0} is 0.05 N / 20 mm or more. It is preferably 0.10 N / 20 mm or more, more preferably 0.15 N / 20 mm or more, and may be 0.20 N / 20 mm or more. The initial medium-speed peel strength P ₀ is measured by the method described in Examples described later.

Although not particularly limited, the surface protective sheet disclosed herein, the ratio of the initial medium speed peel strength _P 0 [N / 20mm] over time in speed peel to strength _P A [N / 20mm] (i.e. _P A / P ₀ ratio) is 5.0 times or less (typically 3.0 times or less, may be, for example, 2.5 times or less). _A small PA / P ₀ ratio means that the peel strength does not increase with time. This makes it possible to achieve both initial adhesiveness and light peelability during peeling work. From this point of _view, the P A / _{P 0} ratio is preferably 2.0 or less, it may be 1.8 or less, 1.5 or less, or even 1.3 or less. _Further, the P A / _{P 0} ratio may typically be in is 0.5 or more, such as 0.7 or more.

(Low speed peel strength)
The surface protective sheet disclosed herein is attached to a SUS plate and stored at 60 ° C. for 7 days, and then has a peeling speed of 0.3 m / min and a peeling strength with time measured at a peeling angle of 180 degrees (hereinafter, low speed with time). It is also referred to as peel strength.) P _B is preferably about 1.5 N / 20 mm or less (more preferably 1.0 N / 20 mm or less, for example 0.80 N / 20 mm or less). Such a surface protective sheet may be less likely to leave adhesive residue on the adherend even if the sticking period on the adherend such as a metal plate is relatively long. It is preferable that the low-speed peel strength P _B with time is low from the viewpoint of improving the workability of removing from the adherend. Further, from the viewpoint of suppressing peeling during the protection period of the adherend (for example, during processing of the adherend to which the surface protection sheet is attached), the low-speed peel strength P _{B with} time is usually 0.05 N /. It is suitable that it is 20 mm or more, preferably 0.10 N / 20 mm or more, and more preferably 0.15 N / 20 mm or more. The low-speed peel strength P _{B with} time is measured by the method described in Examples described later.

In the surface protection sheet disclosed herein, the initial peel strength measured at a peel speed of 0.3 m / min and a peel angle of 180 degrees 15 minutes after being attached to the SUS plate (hereinafter, also referred to as initial low speed peel strength). ) _{It is appropriate that P 1} is about 0.05 N / 20 mm or more. Such a surface protective sheet floats from the adherend even in a usage mode in which the adherend is processed in a relatively short time after being attached to an adherend such as a metal plate. Peeling is unlikely to occur, and good protection performance can be exhibited. In one embodiment, the initial low speed peel strength P ₁ can be 0.10 N / 20 mm or higher (eg 0.15 N / 20 mm or higher). The upper limit of the initial low-speed peel strength P ₁ is not particularly limited, but from the viewpoint of better preventing adhesive residue on the adherend, 0.70 N / 20 mm or less is usually suitable, and 0.50 N / 20 mm or less (for example). 0.40N / 20mm or less) is preferable. The initial low-speed peel strength P ₁ is measured by the same method as the measurement _{of the initial medium-speed peel strength P 0} described in Examples described later, except that the tensile speed is 0.3 m / min.

In the surface protective sheet disclosed herein, _{the ratio of the slow peel strength P B [N / 20 mm] over time to the initial low speed peel strength P 1} [N / 20 mm] (that is, the P _B / P ₁ ratio) is not particularly limited. For example, it can be 5.0 times or less (typically 4.0 times or less). Further, the P _B / P ₁ ratio is typically 0.5 or more, for example, 0.7 or more.

<Use>
Since the surface protective sheet disclosed here has good workability for removing from an adherend, it is attached to the surface of a metal plate, a painted steel plate, a synthetic resin plate, etc. to process or transport them. At that time, it is preferably used as a surface protective sheet for preventing damage (scratches, stains, etc.) on these surfaces. For example, it can be preferably used for protecting a metal plate made of a metal such as stainless steel, aluminum, or iron. Further, the surface protective sheet disclosed here is less likely to be damaged by the processing even if it is applied to an adherend that is significantly deformed, such as a metal plate that is subjected to drawing processing. Therefore, for example, a metal plate It is suitable as a metal plate protective sheet that protects the surface of the metal plate during processing such as drawing. After molding, the metal plate that is subjected to such drawing processing is used as parts for dishwashers and other various home appliances, kitchen sinks and bathtubs, name plates, foil covers, lamps, kitchen utensils (gas range top plates, etc.). Can be done. Further, in the surface protective sheet disclosed herein, since the increase in peel strength with time is suppressed, for example, the protection period of the adherend is relatively long (typically 2 weeks or more, for example 4 weeks or more). ) Even if it becomes, good removal workability can be exhibited. Therefore, for example, it can be suitably used even in a usage mode in which the period from attachment to an adherend (for example, a metal plate) to processing of the adherend can be 2 weeks or more (for example, 4 weeks or more).

Matters disclosed by this specification include:
(1) A surface protective sheet containing a base material and an adhesive layer arranged on one surface of the base material.
MD tensile elongation at break Eb _MD and TD tensile elongation at break Eb _TD are both 200% or more (preferably 500% or more).
The pressure-sensitive adhesive layer is a surface protective sheet in which the Tg of the base polymer is −50 ° C. or higher.
(2) The surface protective sheet according to (1) above, wherein both the MD tensile breaking strength TS _MD and the TD tensile breaking strength TS _{TD are higher than 15 N / 20 mm.}
(3) The pressure-sensitive adhesive layer has a weight average molecular weight _{S Mw} of toluene-soluble matter is the 10 × 10 ⁴ or more, a surface protective sheet according to any one of the above (1) or (2).
(4) The pressure-sensitive adhesive layer, the weight fraction G _C toluene-insoluble matter is 60% or more, the surface protection sheet of any one of (1) to (3).
(5) The surface protective sheet according to any one of (1) to (4) above, wherein the pressure-sensitive adhesive layer has a minimum load L _{min of a unloading curve of less than −2.0 μN in nanoindenter measurement.}
(6) The surface protective sheet according to any one of (1) to (5) above, wherein the Tg of the base polymer is −40 ° C. or higher and −10 ° C. or lower (preferably −30 ° C. or higher and −15 ° C. or lower).

(7) The base polymer contains a monomer having a homopolymer Tg of 10 ° C. or higher (that is, monomer H) in an amount of 10% by weight or more (preferably 20% by weight or more, more preferably 30% by weight or more) of all the monomer components, for example. The surface protection sheet according to any one of (1) to (6) above, which is a polymer of a monomer raw material contained in a proportion of 35% by weight or more).
(8) The base polymer contains a monomer having a Tg of 60 ° C. or higher as a homopolymer in an amount of 10% by weight or more (preferably 20% by weight or more, more preferably 30% by weight or more, for example 35% by weight or more) of all the monomer components. The surface protection sheet according to any one of (1) to (7) above, which is a polymer of a monomer raw material contained in a proportion.

(9) The surface protective sheet according to any one of (1) to (8) above, wherein the base polymer contains an acrylic polymer.
(10) The base polymer contains an alkyl (meth) acrylate having a homopolymer Tg of 10 ° C. or higher in an amount of 10% by weight or more (preferably 20% by weight or more, more preferably 30% by weight or more, for example 35) of all monomer components. The surface protection sheet according to any one of (1) to (9) above, which is a polymer of a monomer raw material contained in a proportion of (% by weight or more).
(11) The base polymer is a polymerization of a monomer raw material containing methyl methacrylate in a proportion of 10% by weight or more (preferably 20% by weight or more, more preferably 30% by weight or more, for example 35% by weight or more) of all the monomer components. The surface protective sheet according to any one of (1) to (10) above, which is a product.
(12) The surface protective sheet according to any one of (1) to (11) above, wherein the pressure-sensitive adhesive composition is a pressure-sensitive adhesive layer formed from an emulsion-type pressure-sensitive adhesive composition.
(13) The surface protective sheet according to (12) above, wherein the emulsion-type pressure-sensitive adhesive composition contains an acrylic polymer synthesized by using a reactive emulsifier.
(14) The surface protective sheet according to any one of (1) to (13) above, wherein the pressure-sensitive adhesive layer contains a release adjusting agent.
(15) The surface protective sheet according to (14) above, wherein the release modifier is a phosphoric acid ester-based surfactant.

(16) The surface protective sheet according to any one of (1) to (15) above, wherein the thickness of the base material is 100 μm or less.
(17) The surface protective sheet according to any one of (1) to (16) above, wherein the base material contains a polyolefin-based resin film.
(18) The surface protective sheet according to any one of (1) to (17) above, wherein the base material contains at least one of an LLDPE film and an LDPE film.

(19) The surface protection sheet over time peel strength _{P A} measured at 3m / min peel rate after storage 7 days with and 60 ° C. adhered to a stainless steel plate is less than 0.70N / 20mm, the (1 )-(18). The surface protective sheet according to any one of (18).
(20) The aging peel strength _P A [N / 20mm], the initial peel strength _P 0 measured at 3m / min peel rate after 15 minutes stuck the surface protective sheet to a stainless steel plate [N / 20 mm] The surface protective sheet according to (19) above, which is 2.0 times or less of the above.

(21) A surface protective sheet containing a base material and an adhesive layer arranged on one surface of the base material.
The pressure-sensitive adhesive layer, the weight fraction G _C toluene-insoluble matter is 60% or more, and is a weight average molecular weight S _Mw of toluene-soluble matter is 10 × 10 ⁴ or more,
The pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer.
The acrylic polymer is a polymer of a monomer raw material containing methyl methacrylate in a proportion of 20% by weight or more of all the monomer components, and the Tg of the acrylic polymer is −40 ° C. or higher and −10 ° C. or lower.
The base material is an LLDPE film or an LDPE film, and the thickness of the base material is 40 μm or more and 100 μm or less.
The surface protection sheet is a surface protection sheet having MD tensile elongation at break Eb _MD and TD tensile elongation at break Eb _TD of 500% or more.

(22) The surface protective sheet according to any one of (1) to (21) above, which is used for a metal plate to be drawn.

Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to those shown in such examples. In the following description, "part" and "%" are based on weight unless otherwise specified.

<Example 1>
(Synthesis of acrylic polymer A1P)
57 parts of 2-ethylhexyl acrylate (2EHA), 41 parts of methyl methacrylate (MMA), 2 parts of acrylic acid (AA), 3 parts of emulsifier (based on solid content) and 42 parts of ion-exchanged water are mixed and mixed by stirring with a homomixer. An aqueous emulsion (monomer emulsion) was prepared. As the emulsifier, a reactive anionic emulsifier (Daiichi Kogyo Seiyaku Co., Ltd., trade name "Aquaron KH-1025") was used.
51.5 parts of ion-exchanged water was placed in a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer and a stirrer, and the mixture was stirred at room temperature for 1 hour or more while introducing nitrogen gas. Then, the temperature of the system was raised to 70 ° C., 0.05 part by weight of ammonium persulfate (APS) as a polymerization initiator was added, and then the monomer emulsion was continuously added over 3 hours with stirring. After the addition of the monomer emulsion was completed, stirring was continued at 75 ° C. for 2 hours, and then the mixture was cooled to 30 ° C. 10% aqueous ammonia was added to the obtained polymerization reaction solution to adjust the pH to 8. In this way, an aqueous dispersion of the acrylic polymer A1P (concentration of the acrylic polymer A1P: 50%) was obtained.

(Preparation of Adhesive Composition A1C)
To the aqueous dispersion of the acrylic polymer A1P, two parts of the cross-linking agent were added to 100 parts of the acrylic polymer A1P contained in the aqueous dispersion, and the mixture was stirred and mixed at 300 rpm at 23 ° C. for 10 minutes to adhere. The agent composition A1C was prepared. As the cross-linking agent, a water-soluble cross-linking agent containing an oxazoline group (Nippon Shokubai Co., Ltd., trade name “Epocross WS-500”, oxazoline group equivalent: 220 g · solid / eq.) Was used.

(Preparation of surface protection sheet)
Two 50 μm-thick resin films F1 made of LLDPE with corona treatment on one side were prepared. The acrylic pressure-sensitive adhesive composition A1C is applied to the corona-treated surface of the first resin film F1 and dried at 90 ° C. for 1 minute to form a pressure-sensitive adhesive layer having a thickness of 5 μm, and a surface protective sheet having a total thickness of 55 μm is formed. Obtained. The second resin film F1 was used as a release liner by adhering its non-corona-treated surface (second surface) to the pressure-sensitive adhesive layer.

<Example 2>
The amount of emulsifier used for the preparation of the monomer emulsion was 2 parts, the addition time of this monomer emulsion was 2 hours, and the phosphate ester-based surfactant as a peeling conditioner at the time of polymerization (SOLVAY, polyoxyethylene). Tridecyl ether phosphate, trade name "RHODAFAC RS710-E") was used for 100 parts by weight of the monomer raw material, except that 1 part was used for the acrylic polymer A2P in the same manner as in the synthesis of the acrylic polymer A1P. An aqueous dispersion was obtained. The pressure-sensitive adhesive composition A2C was prepared in the same manner as in the preparation of the pressure-sensitive adhesive composition A1C except that this aqueous dispersion was used.
Two sheets of a resin film F2 having a thickness of 50 μm made of LLDPE and having corona treatment on one side were prepared. A surface protective sheet according to this example was obtained in the same manner as in Example 1 except that the pressure-sensitive adhesive composition A2C and the resin film F2 were used instead of the pressure-sensitive adhesive composition A1C and the resin film F1.

<Example 3>
An aqueous dispersion of the acrylic polymer A3P was obtained in the same manner as in the synthesis of the acrylic polymer A2P except that the amounts of 2EHA and MMA used were changed to 61 parts and 37 parts, respectively. The pressure-sensitive adhesive composition A3C was prepared in the same manner as in the preparation of the pressure-sensitive adhesive composition A1C except that this aqueous dispersion was used.
Two sheets of a resin film F3 having a thickness of 50 μm made of LLDPE, which had been subjected to corona treatment on one side, were prepared. A surface protective sheet according to this example was obtained in the same manner as in Example 1 except that the pressure-sensitive adhesive composition A3C and the resin film F3 were used instead of the pressure-sensitive adhesive composition A1C and the resin film F1.

<Comparative example 1>
65 parts of ethyl acrylate (EA), 20 parts of 2EHA, 10 parts of MMA, 5 parts of acrylonitrile (AN), 3 parts of emulsifier (based on solid content) and 42 parts of ion-exchanged water are mixed and mixed by stirring with a homomixer to form an aqueous emulsion (monomer). Emulsion) was prepared. As the emulsifier, a reactive anionic emulsifier (Daiichi Kogyo Seiyaku Co., Ltd., trade name "Aquaron KH-1025") was used. The addition time of this monomer emulsion was 5 hours. In other respects, an aqueous dispersion of the acrylic polymer A4P was obtained in the same manner as in the synthesis of the acrylic polymer A1P. The pressure-sensitive adhesive composition A4C was prepared in the same manner as in the preparation of the pressure-sensitive adhesive composition A1C except that this aqueous dispersion was used.
Two sheets of a resin film F4 having a thickness of 50 μm made of LDPE, which had been subjected to corona treatment on one side, were prepared. A surface protective sheet according to this example was obtained in the same manner as in Example 1 except that the pressure-sensitive adhesive composition A4C and the resin film F4 were used instead of the pressure-sensitive adhesive composition A1C and the resin film F1.

<Measurement and evaluation (1)>
It relates to the aforementioned Examples 1-3 and Comparative Example 1, by the method described above, the gel fraction G _C, the sol molecular weight S _Mw, tensile elongation at break was measured minimum load L _min of tensile strength and unloading curves. Furthermore, the following peel strength measurement and drawing test were performed. The results obtained are shown in Table 2 together with the schematic configuration of the surface protection sheet according to each example.

(Initial medium speed peel strength P ₀ )
A test piece was prepared by cutting the surface protection sheet to be measured into strips having a width of 20 mm and a length of 100 mm. Under a standard environment of 23 ° C. and 50% RH, this test piece was pressure-bonded to a stainless steel plate (SUS430BA plate) as an adherend by reciprocating a 2 kg rubber roller twice. After holding the samples for 15 minutes under the standard environment, under the standard environment, using a universal tensile testing machine, pulling rate of 3m / min, under conditions of a peeling angle of 180 degrees, the initial medium speed peel strength P _O [N / 20 mm] was measured.

(Time during speed peel strength _P A)
A test piece was prepared by cutting the surface protection sheet to be measured into strips having a width of 20 mm and a length of 100 mm. Under a standard environment of 23 ° C. and 50% RH, this test piece was pressure-bonded to a stainless steel plate (SUS430BA plate) as an adherend by reciprocating a 2 kg rubber roller twice. This sample was stored in an environment of 60 ° C. for 7 days, then kept in a standard environment of 23 ° C. and 50% RH for 1 hour, and then in the standard environment, a tensile speed of 3 m / m / using a universal tensile tester was used. min, under conditions of a peeling angle of 180 degrees was measured over time in speed peel strength _P a [N / 20mm].

(Slow peeling strength over time P _B )
Except that the tensile speed was 0.3 m / min in the same manner as the measurement of the time during speed peel strength P _A, to measure the time slow peel strength P _B.

(Drawing test)
A disk-shaped BA-finished stainless steel plate (SUS304BA plate) having a thickness of 0.6 mm and a diameter of 93 mm was prepared. A surface protective sheet according to each example having a size larger than that of the stainless steel plate was pressure-bonded to the stainless steel plate by reciprocating a 2 kg rubber roller twice. After storing this in an environment of 60 ° C. for 24 hours, a measurement sample was prepared by cutting a portion of the surface protection sheet protruding from the end face of the stainless steel plate along the end face. This measurement sample was subjected to drawing processing to form a cup having a diameter of 45 mm and a depth of 20 mm at the center of the sample (cup test). For the measurement sample after drawing, the total length of the broken portion of the surface protection sheet on the outer peripheral portion was measured. The measurement was performed three times (n = 3), and the fracture prevention property was evaluated according to the following criteria based on the average value thereof.

E: No breakage of the surface protection sheet was observed. Alternatively, a strip-shaped fractured portion of the surface protective sheet was observed along the outer circumference of the measurement sample, but the total length of the fractured portion was less than 5 mm in total (excellent fracture prevention property).
G: A strip-shaped fractured portion of the surface protective sheet was observed along the outer circumference of the measurement sample, but the total length of the fractured portion was 5 mm or more and 10 mm or less (practically sufficiently good). Has excellent breakage prevention properties).
P: A strip-shaped fractured portion of the surface protective sheet was observed along the outer circumference of the measurement sample, and the total length of the fractured portion was more than 10 mm (poor fracture prevention property).

As can be seen from Table 2, the surface protective sheets of Examples 1 to 3 in which the Tg of the base polymer is −50 ° C. or higher and the Eb _MD and Eb _TD are both 200% or higher are good in the drawing test. It showed breakage prevention. On the other hand, _{the surface protective sheet of Comparative Example 1 in which Eb MD} and Eb _TD were less than 200% was clearly inferior in fracture prevention property as compared with Examples 1 to 3. In addition, the surface protective sheets of Examples 1 to 3 showed good light peelability even after a lapse of time.

<Examples 4 to 6>
The pressure-sensitive adhesive compositions A5C, A6C, and A7C were prepared in the same manner as the preparation of the pressure-sensitive adhesive compositions A1C, A2C, and A3C, except that the amount of the cross-linking agent used for 100 parts of the acrylic polymer was changed to 4 parts. The surface protective sheets according to Examples 4 to 6 were obtained in the same manner as in Examples 1 to 3 except that the pressure-sensitive adhesive compositions A5C, A6C, and A7C were used.

<Example 7>
2 The acrylic polymer A5P was synthesized in the same manner as the acrylic polymer A1P, except that the amounts of 2EHA and MMA used were changed to 54 parts and 44 parts, respectively, and the addition time of the monomer emulsion was set to 4 hours. An aqueous dispersion was obtained. The pressure-sensitive adhesive composition A8C was prepared in the same manner as the preparation of the pressure-sensitive adhesive composition A1C except that the aqueous dispersion was used and the amount of the cross-linking agent used for 100 parts of the acrylic polymer was 1 part. ..
Two sheets of a resin film F5 having a thickness of 50 μm made of LDPE, which had been subjected to corona treatment on one side, were prepared. A surface protective sheet according to this example was obtained in the same manner as in Example 1 except that the pressure-sensitive adhesive composition A8C and the resin film F5 were used instead of the pressure-sensitive adhesive composition A1C and the resin film F1.

<Example 8>
The pressure-sensitive adhesive composition A9C was prepared in the same manner as the preparation of the pressure-sensitive adhesive composition A8C except that the amount of the cross-linking agent used for 100 parts of the acrylic polymer was changed to 2 parts. A surface protective sheet according to this example was obtained in the same manner as in Example 7 except that the pressure-sensitive adhesive composition A9C was used.

<Example 9>
Water dispersion of acrylic polymer A6P in the same manner as the synthesis of acrylic polymer A2P except that the composition of the monomer raw material was changed to 66 parts of n-butyl acrylate (BA), 32 parts of isobornyl acrylate (IBXA) and 2 parts of AA. Obtained liquid. The pressure-sensitive adhesive composition A10C was prepared in the same manner as the preparation of the pressure-sensitive adhesive composition A2C except that this aqueous dispersion was used.
Two sheets of a resin film F6 having a thickness of 50 μm made of LLDPE and having corona treatment on one side were prepared. A surface protective sheet according to this example was obtained in the same manner as in Example 1 except that the pressure-sensitive adhesive composition A10C and the resin film F6 were used instead of the pressure-sensitive adhesive composition A1C and the resin film F1.

<Example 10>
The pressure-sensitive adhesive composition A11C was prepared in the same manner as the preparation of the pressure-sensitive adhesive composition A10C except that the amount of the cross-linking agent used for 100 parts of the acrylic polymer was changed to 4 parts. A surface protective sheet according to this example was obtained in the same manner as in Example 9 except that the pressure-sensitive adhesive composition A11C was used.

<Measurement and evaluation (2)>
With respect to Examples 4 to 10, the same measurements and evaluations as in Examples 1 to 3 and Comparative Example 1 described above were performed. The results obtained are shown in Table 3 together with the schematic configuration of the surface protection sheet according to each example.

As can be seen from Table 3, the surface protective sheets of Examples 4 to 10 in which the Tg of the base polymer is −50 ° C. or higher and the Eb _MD and Eb _TD are both 200% or higher are good in the drawing test. It was confirmed that it showed breakage prevention. Particularly good results were obtained in Examples 4 to 6, 9 and 10 in which both Eb _MD and Eb _{TD were 500% or more.} In addition, the surface protective sheets of Examples 4 to 10 showed good light peelability even after a lapse of time.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above.

1: Base material 1A: One surface 1B: The other surface 2: Adhesive layer 2A: Adhesive surface 10: Surface protection sheet

Claims (13)

A surface protective sheet containing a base material and an adhesive layer arranged on one surface of the base material.
The tensile elongation at break Eb _{MD in the} flow direction and the tensile elongation Eb _{TD in the} width direction are both 200% or more.
The pressure-sensitive adhesive layer has a glass transition temperature of the base polymer Ri der -50 ° C. or higher, minimum load L _min of unloading curve in a nano indenter measurement is less than -2.0MyuN, surface protective sheet. The pressure-sensitive adhesive layer, the weight fraction G _C toluene-insoluble matter is 60% or more, and a weight average molecular weight S _Mw of toluene-soluble matter is 10 × 10 ⁴ or more, the surface protection according to claim 1 Sheet. The surface protection sheet according to claim 1 or 2 , wherein the base polymer is a polymer of a monomer raw material containing a monomer having a glass transition temperature of 10 ° C. or higher as a homopolymer in a proportion of 20% by weight or more of all the monomer components. .. The surface protective sheet according to any one of claims 1 to 3 , wherein the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer. The surface protective sheet according to any one of claims 1 to 4 , wherein the thickness of the base material is 100 μm or less. The surface protective sheet according to any one of claims 1 to 5 , wherein the base material contains a polyolefin-based resin film. Aging peel strength P _A measured at 3m / min peel rate after the surface protective sheet was stored for 7 days with and 60 ° C. adhered to a stainless steel plate is less than 0.70N / 20mm, of claims 1-6 The surface protection sheet according to any one item. The time peeling strength _{P A} (unit; N / 20 mm) is, the initial peel strength _{P 0} (units measured at 3m / min peel rate the surface protective sheet 15 minutes after paste to a stainless steel plate; N / 20 mm ) Is 2.0 times or less, the surface protective sheet according to claim 7. The surface protective sheet according to any one of claims 1 to 8 , which is used for a metal plate to be drawn. A surface protective sheet containing a base material and an adhesive layer arranged on one surface of the base material.
Tension fracture elongation Eb in the flow direction _MD And tensile fracture elongation Eb in the width direction _TD Are all over 200%,
In the pressure-sensitive adhesive layer, the glass transition temperature of the base polymer is −50 ° C. or higher, and the weight fraction G of the toluene insoluble component is G. _C Is 60% or more, and the weight average molecular weight S of the toluene-soluble component is S. _Mw Is 10x10 ⁴ That's all, the surface protection sheet. A surface protective sheet containing a base material and an adhesive layer arranged on one surface of the base material.
Tension fracture elongation Eb in the flow direction _MD And tensile fracture elongation Eb in the width direction _TD Are all over 200%,
The pressure-sensitive adhesive layer has a glass transition temperature of the base polymer of −50 ° C. or higher.
The base polymer is a surface protection sheet which is a polymer of a monomer raw material containing a monomer having a glass transition temperature of 10 ° C. or higher as a homopolymer in a proportion of 20% by weight or more of all the monomer components. A surface protective sheet containing a base material and an adhesive layer arranged on one surface of the base material.
The tensile elongation at break Eb _{MD in the} flow direction and the tensile elongation Eb _{TD in the} width direction are both 200% or more.
Aging peel strength P _A measured at 3m / min peel rate after the surface protective sheet was stored for 7 days with and 60 ° C. adhered to a stainless steel plate is not more than 0.70N / 20mm,
The pressure-sensitive adhesive layer is a surface protective sheet having a glass transition temperature of the base polymer of −50 ° C. or higher. Peeling strength over time P _A [N / 20 mm] is the initial peel strength P measured at a peel rate of 3 m / min 15 minutes after the surface protection sheet is attached to the stainless steel plate. ₀ The surface protective sheet according to claim 12, which is 2.0 times or less of [N / 20 mm].

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