JP2021014593A - Surface protective film - Google Patents

Abstract

To provide a surface protective film in which the step on the coating film surface after peeling and removing can be suppressed even when the surface protective film is attached with air entrained.SOLUTION: In a surface protective film including a substrate layer and an adhesive layer provided on one surface of the substrate layer, the tensile elastic modulus at 23°C measured in accordance with JIS K 7161 of the adhesive layer is set in the range of 1.0 to 3.5 MPa, and the tensile elastic modulus at 80°C is set in the range of 0.6 to 2.0 MPa.SELECTED DRAWING: Figure 1

Description

The present invention relates to a surface protective film provided with an adhesive layer, and more particularly to a surface protective film temporarily attached to protect the surface of a coating film such as a coated steel sheet.

When processing or transporting a metal plate, a painted steel plate, a synthetic resin plate, or the like, a surface protective film is attached to protect the surface from damage such as scratches and dirt. Generally, the surface protective film is temporarily attached to the adherend for a certain period of time, and after finishing the role of surface protection, is peeled off and removed from the adherend. Therefore, the surface protective film is required to have good adhesiveness (temporary adhesion) and to have no adhesive residue on the surface of the adherend after use. Surface protective sheets that satisfy such requirements have been proposed (for example, Patent Documents 1 and 2 and the like).

By the way, if the surface protective film is wrinkled when the surface protective film is attached to the adherend, the surface protective sheet may be attached to the adherend in a state of entraining air. Further, depending on the application, the surface protective film is manually attached to the adherend, and it is often difficult to attach the surface protective film without entraining air. In particular, when a surface protection film is attached to a painted steel sheet, if there is a part that entrains air (that is, a part where the surface protection sheet does not adhere to the painted surface), it depends on the storage environment when stored for a long period of time. Is a shrinkage of the surface protective film, and a step is generated on the coating film surface at the boundary between the part where air is entrained and the part where air is not entrained (that is, the part where the surface protective film is in close contact with the painted surface). There was a case that it ended up. Since such a step on the surface of the coating film remains as a mark after the surface protective film is peeled off, improvement has been required.

In response to the above problems, Patent Document 3 proposes a surface protective film that does not cause marks on the coating film by setting the shear storage elastic modulus of the pressure-sensitive adhesive at 10 Hz within a predetermined range.

Japanese Unexamined Patent Publication No. 6-3365777 Japanese Unexamined Patent Publication No. 8-245938 Japanese Unexamined Patent Publication No. 2001-234149

As a result of diligent studies on the above problems, the present inventors have a tensile elastic modulus in the range of 1.0 to 3.5 MPa at 23 ° C. and at 80 ° C. as the pressure-sensitive adhesive layer of the surface protective film. By using an adhesive whose tensile elastic modulus is in the range of 0.6 to 2.0 MPa, even if the surface protective film is attached with air entrained, after peeling and removing. It was found that the level difference on the surface of the coating film can be suppressed. The present invention is based on such findings.

Therefore, an object of the present invention is to provide a surface protective film capable of suppressing a step on the coating film surface after peeling and removing even when the surface protective film is attached with air entrained.

The surface protective film according to the present invention includes a base material layer and an adhesive layer provided on one surface of the base material layer, and the pressure-sensitive adhesive layer is measured at 23 ° C. according to JIS K 7161. The tensile elastic modulus of the above is in the range of 1.0 to 3.5 MPa, and the tensile elastic modulus at 80 ° C. is in the range of 0.6 to 2.0 MPa.

According to the aspect of the present invention, the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer may contain an elastomer component as a main component, and may further contain a pressure-sensitive adhesive and a softening agent.

According to the aspect of the present invention, the tackifier may be contained in a ratio of 1 to 50 parts by mass with respect to 100 parts by mass of the elastomer component.

According to the aspect of the present invention, the softener may be contained in a ratio of 1 to 25 parts by mass with respect to 100 parts by mass of the elastomer component.

According to the aspect of the present invention, the elastomer component may be a styrene-based block copolymer or a hydrogenated product thereof.

According to the aspect of the present invention, the surface protective film may be provided with a release layer on the surface of the base material layer opposite to the surface on which the pressure-sensitive adhesive layer is provided.

According to the present invention, by forming an adhesive layer having a tensile elastic modulus in a specific range at a predetermined temperature, even when a surface protective film is attached with air entrained, the coating film is peeled off and removed. It is possible to realize a surface protective film capable of suppressing a step on the surface.

FIG. 6 is a schematic cross-sectional view showing an embodiment of a surface protective film according to the present invention. FIG. 6 is a schematic cross-sectional view showing another embodiment of the surface protective film according to the present invention.

The surface protective film according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an embodiment of a surface protective film according to the present invention. The surface protective film 10 includes a base material layer 1 and an adhesive layer 2 provided on one surface of the base material layer 1. When the surface protective film 10 is applied to protect the surface of an adherend (not shown) such as a painted steel plate, the surface protective film 10 is attached so that the adhesive layer 2 adheres to the painted surface. To. Hereinafter, each layer constituting the surface protective film according to the present invention will be described.

[Base layer]
The base material layer plays a role of protecting the adherend from damage such as scratches and dirt, and various materials can be used as the base material layer without particular limitation as long as this purpose can be achieved. However, preferably, a film or sheet made of a thermoplastic resin can be preferably used. Examples of the thermoplastic resin that can be suitably used as the base material layer include polyester resin, polyamide resin, polyolefin resin, polyimide resin, polyvinyl chloride resin, acrylic resin, polyurethane resin, and the like. Polyester-based resins are preferable because they do not generate toxic gas even when incinerated later and have few problems in terms of post-treatment.

Examples of the polyolefin resin include polyethylene, ethylene-α-olefin copolymer, propylene-α-olefin copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, ethylene-n butyl acrylate copolymer, and polypropylene. And so on. As the thermoplastic resin for forming the base material layer, one type may be used alone, or two or more types may be used in combination.

If necessary, the base material layer may contain various additives using the above-mentioned thermoplastic resin as a matrix. For example, a light stabilizer, an ultraviolet absorber, an antioxidant, a filler, a lubricant and the like can be added. These additives are either mixed with the thermoplastic resin and extruded when the thermoplastic resin is formed into a film or sheet, or a master batch in which the additive is kneaded into the thermoplastic resin in advance is extruded. At this time, the base material layer can be formed by mixing with a thermoplastic resin to form a film.

The thickness of the base material layer can be appropriately set according to the intended use of the surface protective film, but is approximately 20 to 100 μm.

[Adhesive layer]
The pressure-sensitive adhesive layer is provided on one surface of the above-mentioned base material layer and has a function of adhering the surface protective film to the adherend. In the present invention, the tensile elastic modulus at 23 ° C. measured according to JIS K 7161 is in the range of 1.0 to 3.5 MPa, and the tensile elastic modulus at 80 ° C. is 0.6 to 2. It is characterized by having an adhesive layer in the range of 0 MPa. When the surface protective film is stored for a long period of time in a state of being attached to the adherend by forming an adhesive layer such that the respective tensile elastic moduli at 23 ° C. and 80 ° C. are within the above-mentioned predetermined ranges. Since the shrinkage stress of the film (base material layer) generated in the above can be relaxed by the pressure-sensitive adhesive layer, it occurs on the surface of the coating film especially when the surface protective film is attached to the coating film in a state where air is entrained. It is possible to suppress the occurrence of traces. If the tensile elastic modulus of the pressure-sensitive adhesive layer exceeds 3.5 MPa at 23 ° C. or 2.0 MPa at 80 ° C., the pressure-sensitive adhesive layer cannot relieve the stress generated when the film shrinks, and the pressure-sensitive adhesive layer cannot be relaxed. The shear stress between the coating film surface and the coating film surface may cause marks on the coating film surface. On the other hand, if the tensile elastic modulus of the pressure-sensitive adhesive layer is less than 1.0 MPa at 23 ° C. or less than 0.6 MPa at 80 ° C., the pressure-sensitive adhesive layer becomes over-adhesive to the adherend. The shrinkage stress directly affects the surface of the coating film, and as a result, marks may also occur on the surface of the coating film. The preferable range of the tensile elastic modulus of the pressure-sensitive adhesive layer is 1.3 to 2.0 MPa at 23 ° C. and 0.8 to 1.7 MPa at 80 ° C. For the tensile elastic modulus in the present invention, a test piece obtained by forming a film of an adhesive layer is prepared, and a tensile test is performed at a predetermined temperature under the condition of a tensile speed of 300 mm / using a tensile tester, and a stress-strain curve Is calculated, and means the value calculated by the following formula from the tensile stress (σ) and the tensile strain (ε _L ) within the tensile proportional limit.
E (MPa) = σ / ε _L

The pressure-sensitive adhesive layer contains an elastomer component as a main component and further contains a pressure-sensitive adhesive, a softening agent, and the like. By appropriately adjusting the type and blending amount of each of these components, the pressure-sensitive adhesive layer can be adhered. The tensile elastic modulus of the agent layer can be in the above range. Hereinafter, each component constituting the pressure-sensitive adhesive layer will be described.

As the elastomer component which is the main component constituting the pressure-sensitive adhesive layer, a styrene-based block copolymer or a hydrogenated product thereof can be used. The styrene-based block copolymer is generally a block copolymer represented by ABA, or a block copolymer represented by ABA and a block copolymer represented by AB. It may be a mixture with a coalescence (Note that A indicates a styrene polymer block and B indicates another polymer block). The B block constituting the styrene-based block copolymer includes an olefin-based polymer block such as an ethylene polymer block, a propylene polymer block, and a butylene polymer block, and a diene-based weight such as a butadiene polymer block and an isoprene polymer block. Examples include coalesced blocks, diene polymer blocks, and hydrogenated products of these polymers. In order for the pressure-sensitive adhesive layer to be in the above-mentioned range of tensile elastic modulus, the mass ratio of the elastomer component A block to B block is preferably in the range of 5:95 to 50:50.

Specific examples of the above-mentioned ABA type styrene block copolymer include styrene-butadiene-styrene type block copolymer (SBS), styrene-isoprene / styrene type block copolymer (SIS), and the like. Examples thereof include styrene-ethylene / butylene-styrene type block copolymer (SEBS), styrene-ethylene / propylene-styrene type block copolymer (SEPS), styrene-isobutylene-styrene type block copolymer (SIBS) and the like.

Further, as the above-mentioned AB type styrene block copolymer, specifically, a styrene / butadiene type copolymer (SB), a styrene / isoprene type copolymer (SI), and a styrene-ethylene / butylene type. Examples thereof include a copolymer (SEB), a styrene-ethylene / propylene type copolymer (SEP), and a styrene-isobutylene type copolymer (SIB).

Further, as the elastomer component, those other than the above-mentioned ABA type and AB type may be contained. For example, a styrene-based random copolymer such as styrene-butadiene rubber (SBR), an ABC-type styrene-olefin crystal block copolymer such as styrene-ethylene / butylene-olefin crystal (SEBC), and an olefin crystal. Examples thereof include CBC type olefin crystal block copolymers such as -ethylene / butylene-olefin crystals (CEBC), and olefin elastomers.

The weight average molecular weight of the above-mentioned styrene-based block copolymer or its hydrogenated product is preferably in the range of about 30,000 to 400,000. If the weight average molecular weight is too small, the cohesive force of the adhesive becomes small, and adhesive residue may occur when the surface protective film attached to the adherend is peeled off. On the other hand, if a styrene-based block copolymer having an excessively large weight average molecular weight or a hydrogenated product thereof is used, the adhesion of the surface protective film to the adherend may be inferior, and the surface is coextruded as described later. It may interfere with the manufacture of the protective film. In the present invention, the weight average molecular weight means the polystyrene-equivalent weight average molecular weight measured by using GPC.

Commercially available elastomer components may be used as described above. For example, Hybler 5127, 5125, 7125 (all manufactured by Kuraray Corporation), Shibster 102T (manufactured by Kaneka Corporation), S.A. O. E. S1605. S1606, S1611 (all manufactured by Asahi Kasei Co., Ltd.), AR-SC-0, AR-SC-5, AR-SC-15, AR-SC-30 (all manufactured by Aronkasei Co., Ltd.), etc. are preferably used. can do.

The tackifier, which is an optional component constituting the pressure-sensitive adhesive layer, has a function of imparting adhesiveness to the pressure-sensitive adhesive layer. By containing the tackifier, the adhesive strength can be appropriately increased while suppressing the generation of adhesive residue due to the decrease in cohesive force. However, since the tensile elastic modulus of the pressure-sensitive adhesive layer tends to increase when the pressure-sensitive adhesive is contained, it is necessary to add it to the elastomer component so that the tensile elastic modulus of the pressure-sensitive adhesive layer is within the above range.

As the tackifier, any known tackifier may be used as long as the above object can be achieved. For example, a rosin resin, a terpene resin, an aliphatic petroleum resin, or an alicyclic petroleum-based resin can be used. Known tackifiers such as resins and aromatic resins can be preferably used.

The blending amount of the tackifier may be appropriately set in consideration of the adhesive performance required according to the use of the surface protective film, but is preferably about 1 to 50 parts by mass with respect to 100 parts by mass of the elastomer component. , More preferably 1 to 30 parts by mass, and particularly preferably 1 to 20 parts by mass.

The softener, which is an optional component constituting the pressure-sensitive adhesive layer, is added in order to adjust the adhesive strength of the pressure-sensitive adhesive layer by using it in combination with the above-mentioned pressure-sensitive adhesive. As the softener, for example, a low molecular weight rubber-based material, procel oil (paraffin-based oil), petroleum-based softener, epoxy-based compound and the like are preferably used. These softeners may be used alone or in combination of two or more.

When the softener is contained, the blending amount may be appropriately set in consideration of the adhesive performance required according to the use of the surface protective film, but it is about 1 to 25 parts by mass with respect to 100 parts by mass of the elastomer component. It is preferably 5 to 25 parts by mass, and particularly preferably 5 to 15 parts by mass.

In addition to the above-mentioned components, the pressure-sensitive adhesive layer may contain additives such as an ultraviolet inhibitor, an antioxidant, a filler, and a lubricant, if necessary.

[Manufacturing method of surface protective film]
Next, an example of a method for producing a surface protective film according to the present invention will be described. First, the mixture of the above components and the thermoplastic resin forming the base material layer are separately supplied to the extrusion molding machine. Specifically, the above-mentioned pressure-sensitive adhesive layer component is supplied to an extrusion molding machine for forming a film of a pressure-sensitive adhesive layer, and a thermoplastic resin is supplied to an extrusion molding machine for forming a film of a base material layer. Each material is co-extruded from one die by a two-layer co-extrusion method. By adopting such a manufacturing method, a surface protective film 10 having a base material layer 1 and an adhesive layer 2 provided on one surface of the base material layer 1 as shown in FIG. 1 can be obtained. Be done.

When supplying the above-mentioned pressure-sensitive adhesive layer component to an extrusion molding machine for forming a pressure-sensitive adhesive layer, a masterbatch of a mixture of an elastomer component and a pressure-sensitive adhesive is prepared in advance, and the masterbatch is prepared. And an elastomer component or other additives may be mixed and supplied to the extruder. In addition to the two-layer coextrusion method, an adhesive layer may be formed on one surface of a long film forming a base material layer by an extrusion molding method. Further, the surface protective film may be produced by laminating the film constituting the base material layer and the pressure-sensitive adhesive layer (film) formed as described above.

The thickness of the base material layer 1 in the obtained surface protective film can be, for example, 20 to 100 μm. The thickness of the pressure-sensitive adhesive layer 2 in the obtained surface protective film can be, for example, 2 to 50 μm.

The obtained surface protective film is usually wound in a roll shape for convenience of use. When the surface protective film is stored in a roll shape, the adhesive layer on the inner layer side may be in close contact with the base material layer on the outer layer side, making it difficult for the surface protective film to be developed from the roll. Therefore, as shown in FIG. 2, the surface protective film may be provided with the release layer 3 on the surface opposite to the surface on which the pressure-sensitive adhesive layer 2 is provided. The release layer is not particularly limited as long as it is a material having releasability, but for example, silicone resin, organic resin modified silicone resin, fluororesin, aminoalkyd resin, melamine resin, acrylic resin, polyester resin and the like. Can be mentioned. In addition, a release aid may be added to the pressure-sensitive adhesive layer in order to improve the releasability. Examples of the peeling aid include silicone-based peeling aids, paraffin-based peeling aids, polyethylene waxes, acrylic polymers and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not intended to be construed as being limited to the embodiments shown in the following Examples.

According to the composition shown in Table 1 below, the composition containing each component is kneaded with a kneader and then molded by hot pressing to a thickness of about 1 mm to obtain an adhesive sheet (the "adhesive" in the present invention). (Equivalent to "layer") was obtained. All the numerical values in Table 1 represent parts by mass. The details of each component in Table 1 are as follows.
-Hybler 7125: Block copolymer of styrene and vinyl-polyisoprene hydrogenated with vinyl-polyisoprene block (manufactured by Kuraray Co., Ltd.)
-Sibster 102T: Styrene-isobutylene-styrene block copolymer (manufactured by Kaneka Corporation)
・ S. O. E. S1606: Hydrogenated styrene-butadiene block copolymer (manufactured by Asahi Kasei Corporation)
-AR-SC-5: Styrene-ethylene / butylene-styrene type block copolymer (manufactured by Aronkasei Co., Ltd.)
・ Clearon P115: Hydrogenated terpene resin (manufactured by Yasuhara Chemical Co., Ltd.)
・ Clearon P150: Hydrogenated terpene resin (manufactured by Yasuhara Chemical Co., Ltd.)
・ HYCOAL K350: Liquid paraffin (manufactured by Kaneda)

Each of the obtained adhesive sheets was punched into a test piece shape (CW2) conforming to JIS K 7139, and used as a test piece. For each test piece, the tensile elastic modulus was calculated in both atmospheres of 23 ° C. (65% RH) and 80 ° C. using a tensile tester (A & D Co., Ltd., Tencilon) in accordance with JIS K 7161. .. The initial distance between chucks was 1.8 mm, and the tensile speed was 300 mm / min. The tensile elastic modulus of each sample piece obtained by the measurement was as shown in Table 1 below.

Further, the pressure-sensitive adhesive sheet obtained above is superposed on the mold-released surface of the polyethylene phthalate film whose surface has been mold-released, and then pressed by hot pressing so that the thickness of the pressure-sensitive adhesive sheet is 10 μm. A surface protective film was obtained. Subsequently, the obtained surface protective film is transferred to a polypropylene film (corresponding to the "base material" in the present invention) obtained by extruding a polypropylene resin by the T-die method so that the adhesive surfaces face each other. As a result, a surface protective film having a layer structure in which a polypropylene film having a thickness of about 40 μm, an adhesive film having a thickness of about 10 μm, and a polyethylene terephthalate film were sequentially laminated was produced.

Subsequently, a test panel (a test plate for paint conforming to JIS K 5600, manufactured by Nippon Test Panel Co., Ltd.) for evaluation with coating film marks was prepared, and polyethylene was obtained from each surface protective film obtained as described above. After peeling off the terephthalate film, it was attached to a test panel and left in an environment of 80 ° C. for 7 days.

After leaving the test panel for 7 days, the surface protective film was peeled off, and it was visually confirmed whether or not there was a coating film mark on the surface of the test panel. The evaluation criteria are as follows.
◯: Traces could not be visually confirmed ×: Traces could be visually confirmed The evaluation results were as shown in Table 1 below.

1 Base material layer 2 Adhesive layer 3 Release layer 10 Surface protection sheet

Claims (6)

A base material layer and an adhesive layer provided on one surface of the base material layer are provided.
The pressure-sensitive adhesive layer has a tensile elastic modulus in the range of 1.0 to 3.5 MPa at 23 ° C. measured in accordance with JIS K 7161 and a tensile elastic modulus of 0.6 to 2 at 80 ° C. A surface protective film, characterized in that it is in the range of 0.0 MPa. The surface protective film according to claim 1, wherein the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer contains an elastomer component as a main component, and further contains a pressure-sensitive adhesive and a softening agent. The surface protective film according to claim 2, wherein the tackifier is contained in a ratio of 1 to 50 parts by mass with respect to 100 parts by mass of the elastomer component. The surface protective film according to claim 2 or 3, wherein the softener is contained in a ratio of 1 to 25 parts by mass with respect to 100 parts by mass of the elastomer component. The surface protective film according to any one of claims 1 to 4, wherein the elastomer component is a styrene-based block copolymer or a hydrogenated product thereof. The surface protective film according to any one of claims 1 to 5, wherein a release layer is provided on a surface of the base material layer opposite to the surface on which the pressure-sensitive adhesive layer is provided.