JP6397644B2 - Surface protection film - Google Patents

Description

  The present invention relates to a surface protective film in which an intermediate layer and an adhesive layer are laminated in this order on a substrate formed of a polyolefin-based resin.

  Conventionally, surface protective films have been used for the purpose of preventing dust adhesion and scratches on the surfaces of synthetic resin plates, decorative plywood, metal plates and the like.

  For example, Patent Document 1 below discloses a surface protective film in which an intermediate layer and an adhesive layer are laminated in this order on a base material layer formed of a thermoplastic resin. The said intermediate | middle layer is formed with the resin composition containing the component which comprises the said base material layer, and the component which comprises the said adhesive layer. The intermediate layer has a thickness of 7 to 20 μm.

  Further, Patent Document 1 describes that the “ear” of the surface protection film that has been conventionally discarded can be used as a collected raw material for the material constituting the intermediate layer. Further, in Patent Document 1, when “ears” are used as the intermediate layer, an intermediate between the heat history received when the resin is once co-extruded and the heat history received during the co-extrusion performed again. It is described that when the layer is too thick, fish eyes are likely to be generated in the surface protective film, and the intermediate layer is likely to be cohesively broken by the peeling force. For these reasons, in Patent Document 1, the thickness of the intermediate layer is limited to 20 μm or less.

Japanese Patent No. 3088190

  In the conventional surface protection film, in order to unwind the surface protection film in a roll state or to bond the surface protection film to the adherend well, the surface protection film is used at the time of unwinding or bonding. You may have to pull with a weak force. For this reason, there exists a problem that the working efficiency at the time of handling a surface protection film is low. Further, the bonded product may be curled after the surface protective film is bonded to the adherend.

  Further, in the surface protective film described in Patent Document 1, the “ear” of the surface protective film that has been conventionally discarded is used as a collected raw material for the intermediate layer. For this reason, the raw material cost of a surface protection film can be held down.

  On the other hand, in a surface protective film provided with an intermediate layer and an adhesive layer, the interlayer strength between the intermediate layer and the adhesive layer is high, and it is required that no peeling occurs between the intermediate layer and the adhesive layer. . For example, when the surface protective film is bonded to the adherend and then peeled off, it is required that no adhesive residue is generated on the adherend. In the surface protective film described in Patent Document 1, although the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer is increased to some extent, it is required to further increase the interlayer strength.

  An object of the present invention is to provide a surface protective film that can increase the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer and is excellent in handleability.

  According to a wide aspect of the present invention, a base material, an intermediate layer laminated on one surface of the base material, and an adhesive layer laminated on the surface of the intermediate layer opposite to the base material side The base material is formed of a polyolefin-based resin, the adhesive layer is formed of a synthetic rubber-based adhesive, and the intermediate layer is 85% by weight or more and 97% by weight or less of the polyolefin resin. And a synthetic rubber-based pressure sensitive adhesive 3 wt% or more and 15 wt% or less.

  On the specific situation with the surface protection film which concerns on this invention, the thickness of the said intermediate | middle layer exceeds 20 micrometers and is 60 micrometers or less.

  On the specific situation with the surface protection film which concerns on this invention, the said synthetic rubber adhesive contained in the said intermediate | middle layer contains a synthetic rubber. The synthetic rubber adhesive contained in the intermediate layer may contain a synthetic rubber and a tackifier resin.

  On the specific situation with the surface protection film which concerns on this invention, in the said synthetic rubber-type adhesive contained in the said intermediate | middle layer, content of the said tackifying resin with respect to 100 weight part of said synthetic rubbers is 5 weight part or more, 50 Less than parts by weight.

  The synthetic rubber is preferably a styrene elastomer. The styrene elastomer is preferably a hydrogenated styrene elastomer. The hydrogenated styrene elastomer is preferably a styrene-ethylene-butylene-styrene copolymer.

  In the surface protective film according to the present invention, a base material, an intermediate layer, and an adhesive layer are laminated in this order, the base material is formed of a polyolefin-based resin, and the adhesive layer is a synthetic rubber. Since the intermediate layer includes 85% by weight or more and 97% by weight or less of the polyolefin resin and 3% by weight or more and 15% by weight or less of the synthetic rubber adhesive, The interlayer strength with the pressure-sensitive adhesive layer can be increased, and the handleability of the surface protective film can be increased.

  Details of the present invention will be described below.

[Surface protection film]
The surface protective film according to the present invention includes a base material, an intermediate layer, and an adhesive layer. The intermediate layer is laminated on one surface of the base material. The said adhesive layer is laminated | stacked on the surface on the opposite side to the said base material side of the said intermediate | middle layer. The intermediate layer is disposed between the base material and the pressure-sensitive adhesive layer. Therefore, the surface protective film according to the present invention has a structure in which the substrate, the intermediate layer, and the pressure-sensitive adhesive layer are laminated in this order.

  The base material is formed of a polyolefin resin. The pressure-sensitive adhesive layer is formed of a synthetic rubber pressure-sensitive adhesive. The intermediate layer is formed of a polyolefin resin and a synthetic rubber adhesive. In 100% by weight of the intermediate layer, the content of the polyolefin-based resin is 85% by weight or more and 97% by weight or less, and the content of the synthetic rubber-based pressure-sensitive adhesive is 3% by weight or more and 15% by weight or less.

  In this invention, since said structure is employ | adopted, the interlayer strength of an intermediate | middle layer and an adhesive layer can be raised, and peeling with an intermediate | middle layer and an adhesive layer can be suppressed. Further, by increasing the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer, it is difficult for adhesive residue to occur on the adherend after the surface protective film is peeled off from the adherend. Therefore, the surface protective film according to the present invention is excellent in reliability.

  Furthermore, in the present invention, since the above-described configuration is adopted, the handleability of the surface protective film can be improved. The surface protective film in a roll state can be unwound well, and the surface protective film can be satisfactorily bonded to the adherend. When unrolling a surface protection film in a roll state or pasting the surface protection film to an adherend, even if a certain amount of strong tensile stress is applied to the surface protection film, the surface protection film can be unwound well or stuck together Can go. For this reason, the work efficiency at the time of handling a surface protection film becomes high.

  Furthermore, in the present invention, since the above configuration is employed, the surface protective film is unlikely to shrink when the surface protective film is exposed to a relatively high temperature. For this reason, even after the surface protective film is bonded to the adherend, even if the bonded product is exposed to a relatively high temperature, the bonded product is difficult to curl. As a result, the adherend is also difficult to curl, The protective film is difficult to peel from the adherend.

  Furthermore, in the surface protective film according to the present invention, a polyolefin resin is used for both the base material and the intermediate layer, and a synthetic rubber adhesive is used for both the adhesive layer and the intermediate layer. ing. In the surface protective film according to the present invention, a polyolefin resin and a synthetic rubber pressure sensitive adhesive are used for the intermediate layer, and the polyolefin resin and the synthetic rubber pressure sensitive adhesive as a whole are formed on the base material and the pressure sensitive adhesive layer. Is used. For this reason, in the present invention, a polyolefin resin and a synthetic rubber adhesive are used, and a part or all of a surface protective film provided with a base material and an adhesive layer, or a polyolefin resin and a synthetic rubber. In addition, a part or all of the surface protective film including the base material, the intermediate layer, and the pressure-sensitive adhesive layer can be used as the recovered raw material for the intermediate layer. If the recovered raw material is used, the surface protective film according to the present invention can be manufactured at a low cost. Moreover, if the recovered raw material is used, the environmental load can be reduced.

  Hereinafter, details of each layer constituting the surface protection film will be described.

(Middle layer)
The intermediate layer includes a polyolefin resin and a synthetic rubber adhesive. The composition for forming the said intermediate | middle layer contains polyolefin resin and a synthetic rubber adhesive. The intermediate layer is formed of a polyolefin resin and a synthetic rubber adhesive.

  In the intermediate layer, the content of the polyolefin resin is 85 wt% or more and 97 wt% or less, and the content of the synthetic rubber pressure-sensitive adhesive is 3 wt% or more and 15 wt% or less. When the content of the polyolefin-based resin is not less than the above lower limit and the content of the synthetic rubber-based pressure-sensitive adhesive is not more than the above upper limit, the handleability of the surface protection film is increased, and the curling of the bonded product is less likely to occur. The dimensional stability at a high temperature of the surface protective film is increased. When the content of the polyolefin-based resin is not more than the above upper limit and the content of the synthetic rubber-based adhesive is not less than the above lower limit, the interlayer strength between the intermediate layer and the adhesive layer is increased.

  From the viewpoint of effectively increasing the handleability of the surface protective film and further reducing the curling of the bonded product, the content of the polyolefin resin in the intermediate layer is preferably 86.0% by weight or more, The content of the synthetic rubber-based adhesive is preferably 14.0% by weight or less, the content of the polyolefin-based resin is more preferably 87.0% by weight or more, and the content of the synthetic rubber-based adhesive is more Preferably it is 13.0 weight% or less. From the viewpoint of further increasing the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer, the content of the polyolefin-based resin in the intermediate layer is preferably 96% by weight or less, and the content of the synthetic rubber-based pressure-sensitive adhesive is preferably The content of the polyolefin-based resin is more preferably 95.0% by weight or less, and the content of the synthetic rubber-based pressure-sensitive adhesive is more preferably 5.0% by weight or more.

Polyolefin resin:
The polyolefin resin contained in the intermediate layer is preferably the same as the polyolefin resin contained in the substrate. However, the polyolefin resin contained in the intermediate layer may be different from the polyolefin resin contained in the substrate. The polyolefin resin contained in the intermediate layer may be used alone or in combination of two or more.

  The polyolefin resin contained in the intermediate layer is not particularly limited, but an ethylene homopolymer, an ethylene-α-olefin copolymer, an ethylene- (meth) acrylic acid copolymer, an ethylene- (meth) acrylic acid ester. Polyethylene resins such as copolymers and ethylene-vinyl acetate copolymers; Polypropylene resins such as propylene homopolymers, propylene-α-olefin copolymers, and propylene-ethylene copolymers; Butene homopolymers; Examples include homopolymers or copolymers of conjugated dienes such as butadiene and isoprene. Examples of the polyethylene resin include high density polyethylene and low density polyethylene. The form of copolymerization may be random, block, or terpolymer.

  The polyethylene resin is obtained using ethylene as a main component. The proportion of structural units derived from ethylene is preferably 50% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight or more, in 100% by weight of all the structural units of the polyethylene resin.

  The polypropylene resin is obtained using propylene as a main component. The proportion of structural units derived from propylene is preferably 50% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight or more in 100% by weight of all the structural units of the polypropylene resin.

  From the viewpoint of effectively increasing the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer, effectively improving the handleability of the surface protective film, and further enhancing the dimensional stability of the surface protective film at high temperatures, the intermediate layer described above is used. The polyolefin-based resin contained in is preferably a polypropylene-based resin.

Synthetic rubber adhesive:
The synthetic rubber-based pressure-sensitive adhesive contained in the intermediate layer is preferably the same as the synthetic rubber-based pressure-sensitive adhesive contained in the pressure-sensitive adhesive layer. However, the synthetic rubber pressure sensitive adhesive contained in the intermediate layer may be different from the synthetic rubber pressure sensitive adhesive contained in the pressure sensitive adhesive layer. The said synthetic rubber-type adhesive may be used independently and may use 2 or more types together.

  From the viewpoint of effectively increasing the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer, effectively improving the handleability of the surface protective film, and further enhancing the dimensional stability of the surface protective film at high temperatures, the intermediate layer described above is used. It is preferable that the synthetic rubber-based pressure-sensitive adhesive contained in contains a synthetic rubber and a tackifying resin. The said synthetic rubber may be used independently and may use 2 or more types together. The above tackifying resins may be used alone or in combination of two or more. The tackifying resin may not be used.

  Examples of the synthetic rubber that can be used for the intermediate layer include elastomers such as styrene elastomers and olefin elastomers. The elastomer includes a hydrogenated elastomer.

  Examples of the styrenic elastomer that can be used in the intermediate layer include a block copolymer having a soft segment that is a diene block (diene polymer portion) and a hard segment that is a styrene block (styrene polymer portion). It is done. The diene block may be a block having a random structure of styrene and diene.

  Specific examples of the styrene-based elastomer that can be used for the intermediate layer include styrene-butadiene (SB) copolymer, styrene-butadiene-styrene (SBS) copolymer, styrene-isoprene (SI) copolymer, and styrene. -Isoprene-styrene (SIS) copolymer, styrene-ethylene-butylene (SEB) copolymer, styrene-ethylene-butylene-styrene (SEBS) copolymer, styrene-ethylene-propylene (SEP) copolymer, and Copolymers such as a styrene-ethylene-propylene-styrene (SEPS) copolymer may be mentioned. These copolymers may be block copolymers. These copolymers may be used alone or in combination of two or more.

  From the viewpoint of effectively increasing the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer, effectively improving the handleability of the surface protective film, and further enhancing the dimensional stability of the surface protective film at high temperatures, the intermediate layer described above is used. The synthetic rubber-based pressure-sensitive adhesive contained in is preferably a styrene-based elastomer, more preferably a SEB copolymer, a SEBS copolymer, a SEP copolymer, or a SEPS copolymer, and even more preferably a SEBS copolymer. It is a coalescence.

  From the viewpoint of further improving thermal stability during extrusion, obtaining a homogeneous surface protective film, and effectively increasing the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer, effectively improving the handleability of the surface protective film Furthermore, from the viewpoint of further enhancing the dimensional stability of the surface protective film at high temperature, the synthetic rubber-based pressure-sensitive adhesive contained in the intermediate layer is preferably a hydrogenated styrene elastomer, more preferably hydrogenated. SEB copolymer, hydrogenated SEBS copolymer, hydrogenated SEP copolymer, or hydrogenated SEPS copolymer, more preferably a hydrogenated SEBS copolymer. .

  Examples of the olefin elastomer that can be used in the intermediate layer include a crystalline olefin-ethylene-butene-crystalline olefin (CEBC) copolymer and a styrene-ethylene-butene-crystalline olefin (SEBC) copolymer. It is done. These copolymers may be random copolymers or block copolymers.

  The tackifier resin that can be used in the intermediate layer is not particularly limited, but is an aliphatic copolymer, an aromatic copolymer, an aliphatic / aromatic copolymer, and an alicyclic copolymer. And other petroleum resins, coumarone-indene resins, terpene resins, terpene phenol resins, polymerized rosin and other rosin resins, phenol resins, xylene resins and the like. These resins may be hydrogenated resins. The above tackifying resins may be used alone or in combination of two or more. When the tackifying resin is a hydrogenated resin, the peelability and weather resistance are further enhanced. The tackifying resin in the intermediate layer is preferably a hydrogenated resin.

  From the viewpoint of enhancing the adhesion between the intermediate layer and the base material and the pressure-sensitive adhesive layer, the softening point of the tackifying resin in the intermediate layer is preferably 90 ° C. or higher, and preferably 140 ° C. or lower.

  In the synthetic rubber-based pressure-sensitive adhesive contained in the intermediate layer, the content of the tackifying resin is preferably 5 parts by weight or more, more preferably 20 parts by weight or more, preferably 50 parts with respect to 100 parts by weight of the synthetic rubber. It is 40 parts by weight or less, more preferably 40 parts by weight or less. When the content of the tackifying resin is not less than the above lower limit, the adhesion of the intermediate layer to the base material is further increased, and the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer is further increased. When the content of the tackifying resin is not more than the above upper limit, the flexibility of the intermediate layer is further increased, the handleability of the surface protective film is further increased, and the curling of the bonded product is further less likely to occur. Furthermore, the dimensional stability at a high temperature of the surface protective film is further enhanced.

  It is preferable that the said intermediate | middle layer is formed with the composition containing collection | recovery raw materials. When the intermediate layer is formed from the recovered raw material, the manufacturing cost can be reduced and the environmental load can be reduced. This point will also be described in detail in the column of the method for producing the surface protective film described later. The composition containing the recovered raw material may contain only the recovered raw material, or may contain the recovered raw material and a new raw material (polyolefin resin, synthetic rubber adhesive, etc.).

  The thickness of the intermediate layer is preferably 10 μm or more, more preferably more than 20 μm, still more preferably 21 μm or more, preferably 100 μm or less, more preferably 60 μm or less. When the thickness of the intermediate layer is not less than the above lower limit, the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer is further increased. When the thickness of the intermediate layer is not more than the above upper limit, it becomes difficult to cause a poor appearance of the surface protective film. For example, a defect called fish eye is less likely to occur.

(Base material)
The base material is formed of a polyolefin resin. Examples of the polyolefin resin contained in the substrate include the polyolefin resins exemplified as the polyolefin resin contained in the intermediate layer. The said polyolefin resin may be used independently and may use 2 or more types together.

  From the viewpoint of effectively increasing the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer, effectively improving the handleability of the surface protective film, and further enhancing the dimensional stability of the surface protective film at high temperatures, The polyolefin resin contained in is preferably a polypropylene resin.

  The thickness of the base material is not particularly limited. The thickness of the substrate is preferably 2 μm or more, preferably 55 μm or less. The handleability of a surface protection film becomes it high that the thickness of the said base material is more than the said minimum and below the said upper limit.

(Adhesive layer)
The pressure-sensitive adhesive layer is formed of a synthetic rubber pressure-sensitive adhesive. From the viewpoint of effectively increasing the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer, effectively improving the handleability of the surface protective film, and further enhancing the dimensional stability of the surface protective film at high temperatures, the pressure-sensitive adhesive described above. The synthetic rubber-based pressure-sensitive adhesive contained in the layer preferably contains a synthetic rubber and a tackifying resin. The said synthetic rubber may be used independently and may use 2 or more types together. The above tackifying resins may be used alone or in combination of two or more. The tackifying resin may not be used.

  Examples of the synthetic rubber that can be used for the pressure-sensitive adhesive layer include elastomers such as styrene elastomers and olefin elastomers, acrylic elastomers, urethane elastomers, ester elastomers, and amide elastomers. The elastomer includes a hydrogenated elastomer.

  Examples of the styrenic elastomer that can be used in the pressure-sensitive adhesive layer include a block copolymer having a soft segment that is a diene block (diene polymer portion) and a hard segment that is a styrene block (styrene polymer portion). Can be mentioned. The diene block may be a block having a random structure of styrene and diene.

  Specific examples of the styrene-based elastomer that can be used for the pressure-sensitive adhesive layer include the above-described styrene-based elastomer that can be used for the intermediate layer.

  From the viewpoint of effectively increasing the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer, effectively improving the handleability of the surface protective film, and further enhancing the dimensional stability of the surface protective film at high temperatures, the pressure-sensitive adhesive described above. The synthetic rubber-based pressure-sensitive adhesive contained in the layer is preferably a styrene-based elastomer, more preferably a SEB copolymer, SEBS copolymer, SEP copolymer, or SEPS copolymer, and still more preferably a SEBS copolymer. It is a polymer.

  From the viewpoint of further improving thermal stability during extrusion, obtaining a homogeneous surface protective film, and effectively increasing the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer, effectively improving the handleability of the surface protective film Further, from the viewpoint of further improving the dimensional stability of the surface protective film at high temperature, the synthetic rubber-based pressure-sensitive adhesive contained in the pressure-sensitive adhesive layer is preferably a hydrogenated styrene-based elastomer, more preferably hydrogen. SEB copolymer added, hydrogenated SEBS copolymer, hydrogenated SEP copolymer, or hydrogenated SEPS copolymer, more preferably hydrogenated SEBS copolymer. is there.

  Examples of the olefin elastomer that can be used in the pressure-sensitive adhesive layer include a crystalline olefin-ethylene butene-crystalline olefin (CEBC) copolymer, and a styrene-ethylene butene-crystalline olefin (SEBC) copolymer. Etc. In addition, these copolymers may be random copolymers or block copolymers.

  Examples of the tackifier resin that can be used in the pressure-sensitive adhesive layer include the above-described tackifier resins that can be used in the intermediate layer. The tackifier resin in the pressure-sensitive adhesive layer is preferably a hydrogenated resin.

  From the viewpoint of enhancing the adhesion between the intermediate layer and the pressure-sensitive adhesive layer, the softening point of the tackifying resin in the pressure-sensitive adhesive layer is preferably 90 ° C. or higher, and preferably 140 ° C. or lower.

  In the synthetic rubber-based pressure-sensitive adhesive contained in the pressure-sensitive adhesive layer, the content of the tackifying resin is preferably 5 parts by weight or more, more preferably 20 parts by weight or more, preferably 100 parts by weight of the synthetic rubber. 50 parts by weight or less, more preferably 40 parts by weight or less. When the content of the tackifying resin is not less than the above lower limit, the adhesiveness of the pressure-sensitive adhesive layer to the adherend is further increased, and the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer is further increased. When the content of the tackifying resin is not more than the above upper limit, the flexibility of the pressure-sensitive adhesive layer is further enhanced, the handleability of the surface protective film is further enhanced, and the curling of the bonded product is further less likely to occur. Furthermore, the dimensional stability at a high temperature of the surface protective film is further enhanced.

  The thickness of the pressure-sensitive adhesive layer is not particularly limited. The thickness of the pressure-sensitive adhesive layer is preferably 2 μm or more, preferably 15 μm or less. When the thickness of the pressure-sensitive adhesive layer is not less than the above lower limit, a pressure-sensitive adhesive layer having a more uniform thickness is formed. When the thickness of the pressure-sensitive adhesive layer is not more than the above upper limit, the handleability of the surface protective film is further enhanced.

(Other details of surface protection film)
Each layer in the surface protective film, in particular, the intermediate layer and the base material are within the range that does not impair the object of the present invention, such as an antioxidant such as phenol, phosphorus, amine, or sulfur, benzotriazole, or hydroxy UV absorbers such as phenyltriazines, metal damage inhibitors, halogenated flame retardants such as hexabromobiphenyl ether or decabromodiphenyl ether, flame retardants such as ammonium polyphosphate or trimethyl phosphate, fillers, antistatic agents, stabilizers In addition, additives such as pigments may be included. These additives may be used independently and may use 2 or more types together.

  Each layer in the surface protective film, in particular, the intermediate layer and the pressure-sensitive adhesive layer are within the range not impairing the object of the present invention, for the purpose of controlling the adhesive force, etc. It may contain known additives such as an agent and an adhesion progress inhibitor. These additives may be used independently and may use 2 or more types together.

  The softening agent is not particularly limited, but a low molecular weight diene polymer, polyisobutylene hydrogenated polyisoprene, hydrogenated polybutadiene, paraffinic process oil, naphthenic process oil, aromatic process oil, castor oil, tall oil, Examples thereof include natural oil, liquid polyisobutylene resin, polybutene and hydrogenated products thereof.

  As said antioxidant, a phenolic antioxidant, sulfur type antioxidant, phosphorus antioxidant, etc. are mentioned, for example. Examples of the phenolic antioxidant include monophenolic antioxidants, bisphenolic antioxidants, and polymeric phenolic antioxidants.

  Examples of the adhesion progress preventing agent include fatty acid amide, polyethyleneimine long chain alkyl graft product, soybean oil-modified alkyd resin, tall oil, and modified alkyd resin.

  The thickness of the surface protective film (total thickness of the base material, the intermediate layer, and the pressure-sensitive adhesive layer) is not particularly limited. The thickness of the surface protective film is preferably 25 μm or more, and preferably 130 μm or less. When the thickness of the surface protective film is not less than the above lower limit, the handleability of the surface protective film is further enhanced, and the dimensional stability at a high temperature of the surface protective film is further enhanced. When the thickness of the pressure-sensitive adhesive layer is not more than the above upper limit, the handleability of the surface protective film is further enhanced.

(Method for producing surface protective film)
The surface protective film according to the present invention comprises a polyolefin resin constituting a base material, a composition comprising a polyolefin resin constituting an intermediate layer and a synthetic rubber adhesive, and a synthetic rubber adhesive constituting an adhesive layer. The agent can be simultaneously extruded by co-extrusion and the layers can be laminated. The method for producing the surface protective film is not limited to the coextrusion molding method. The surface protective film can be produced by various known methods. You may form an intermediate | middle layer and an adhesive layer on a base material.

  In the manufacturing method by the co-extrusion molding method, the intermediate layer and the pressure-sensitive adhesive layer are manufactured in this order on the base material. The end portion of the surface protective film produced by the coextrusion molding method is usually thick due to a neck-in phenomenon. For this reason, the end portion of the surface protective film, that is, the “ear” of the surface protective film is often cut and discarded.

  In this invention, an intermediate | middle layer can be comprised from the raw material currently used for the polyolefin base material and the adhesive layer. For this reason, the "ear" etc. of the surface protection film conventionally cut and discarded can be reused as a collected raw material. Thus, when the recovered raw material is reused, the manufacturing cost can be reduced and the environmental load can be reduced.

  Examples of the collected raw materials include unnecessary portions (ears) at both ends that are generated in the production process of the surface protective film, unnecessary unnecessary portions that are generated in the production process of the surface protective film, and the surface protective film that is used before or after use. Some or all of them are listed.

  The recovered raw material may be a raw material derived from a surface protective film having a two-layer structure of a base material and an adhesive layer, or derived from a surface protective film having a three-layer structure of a base material, an intermediate layer and an adhesive layer. It may be a raw material.

  Specifically, for example, a part or all of a surface protective film including a base material formed of a polyolefin-based resin and an adhesive layer formed of a synthetic rubber-based adhesive is used as a recovered material for the intermediate layer. be able to. Furthermore, a part of a surface protection film comprising a base material formed from a polyolefin-based resin, an intermediate layer formed from a polyolefin-based resin and a synthetic rubber-based adhesive, and an adhesive layer formed from a synthetic rubber-based adhesive, or All of them can be used as a raw material for recovering the intermediate layer. Furthermore, part or all of the surface protective film according to the present invention can also be used as the recovered raw material for the intermediate layer.

  Hereinafter, the present invention will be described in more detail based on specific examples. The present invention is not limited to the following examples.

Example 1
Preparation and preparation of materials for each layer:
A polyolefin resin (polypropylene, “S135” manufactured by Prime Polymer Co., Ltd.) was prepared as a material for forming the base material.

  100 parts by weight of a synthetic rubber (styrene elastomer which is a styrene-ethylene-butadiene-styrene copolymer, “Dynalon 8300P” manufactured by JSR) and 20 parts by weight of a tackifier resin (“Alcon P100” manufactured by Arakawa Scientific) A composition for forming an intermediate layer using a mixture of 3% by weight of a synthetic rubber-based pressure-sensitive adhesive obtained by mixing and 97% by weight of a polyolefin-based resin (polypropylene, “S135” manufactured by Prime Polymer Co., Ltd.) Got.

  100 parts by weight of a synthetic rubber (styrene elastomer which is a styrene-ethylene-butadiene-styrene copolymer, “DYNARON 8300P” manufactured by JSR) and 20 parts by weight of a tackifier resin (“Alcon P100” manufactured by Arakawa Chemical Co., Ltd.) A synthetic rubber pressure-sensitive adhesive for forming a pressure-sensitive adhesive layer was obtained using the mixed mixture.

Production of surface protective film:
Using an extruder, prepare the material for forming the base material layer, the composition for forming the obtained intermediate layer, and the synthetic rubber-based pressure-sensitive adhesive for forming the obtained pressure-sensitive adhesive layer. The surface protective film in which the intermediate layer and the pressure-sensitive adhesive layer were laminated in this order on the base material was obtained by co-extrusion. Regarding the thickness of each layer in the obtained surface protective film, the thickness of the polypropylene substrate was 6 μm, the thickness of the intermediate layer was 28 μm, and the thickness of the pressure-sensitive adhesive layer was 6 μm.

(Examples 2 to 8)
As shown in Table 1 below, the compounding ratio of the polyolefin resin used for the intermediate layer and the synthetic rubber adhesive is set as shown in Table 1 below, and the thicknesses of the substrate, the intermediate layer, and the adhesive layer are shown in Table 1 below. A surface protective film was obtained in the same manner as in Example 1 except that it was set to.

( Reference Example 9)
The intermediate layer and the pressure-sensitive adhesive layer were prepared without using a tackifying resin, the compounding ratio of the polyolefin-based resin used for the intermediate layer and the synthetic rubber-based pressure-sensitive adhesive was set as shown in Table 1 below, and A surface protective film was obtained in the same manner as in Example 1 except that the thicknesses of the base material, the intermediate layer and the pressure-sensitive adhesive layer were set as shown in Table 1 below.

(Comparative Example 1)
A polyolefin resin (polypropylene, “S135” manufactured by Prime Polymer Co., Ltd.) was prepared as a material for forming the intermediate layer.

  A surface protective film was obtained in the same manner as in Example 1 except that the intermediate layer was formed using the material for forming the intermediate layer.

(Comparative Examples 2 to 5)
As shown in Table 1 below, the compounding ratio of the polyolefin resin used for the intermediate layer and the synthetic rubber adhesive is set as shown in Table 1 below, and the thicknesses of the substrate, the intermediate layer, and the adhesive layer are shown in Table 1 below. A surface protective film was obtained in the same manner as in Example 1 except that it was set to.

(Evaluation)
About the obtained surface protection film, the following evaluation items were evaluated.

(1) Decrease rate of elastic modulus Surface protective film so that the dimension in the MD direction (flow direction) during extrusion is 110 mm, and the dimension in the TD direction (direction perpendicular to the MD direction and thickness direction) during extrusion is 10 mm. Was cut to obtain a test piece. Using a Tensilon tensile tester (“STA1255” manufactured by A & D Co., Ltd.), the elastic modulus was measured by pulling in the MD direction (flow direction) under the conditions of a tensile speed of 300 mm / min, 23 ° C. and a relative humidity of 50% RH. did. The decreasing rate of the elastic modulus was calculated using the following formula.

Decrease rate of elastic modulus (%) = (1- (each elastic modulus of Examples 1 to 8, Reference Example 9 or Comparative Examples 2 to 5) / (elastic modulus of Comparative Example 1)) × 100

  The surface protective film of Comparative Example 1 does not have to be pulled with a weak force when unrolling the surface protective film in a roll state or when the surface protective film is attached to the adherend. It was easy and no curling occurred in the bonded product. In the surface protective film of Comparative Example 1, the interlayer strength between the intermediate layer and the adhesive layer is low. With the elastic modulus of the surface protective film of Comparative Example 1 as a reference, the lower the elastic modulus, the lower the surface modulus of the rolled surface protective film, or when the surface protective film is attached to the adherend, it is pulled with a weak force. Therefore, it is difficult for the operator to handle and the bonded product tends to be curled. The rate of decrease in elastic modulus was determined according to the following criteria.

[Criteria for rate of decrease in elastic modulus]
A: Decreasing rate of elastic modulus is 20% or less O: Decreasing rate of elastic modulus is greater than 20%, 25% or less X: Decreasing rate of elastic modulus is greater than 25%

(2) Heat shrinkage rate The surface protective film is cut so that the dimension in the MD direction (flow direction) during extrusion is 100 mm, and the dimension in the TD direction (direction perpendicular to the MD direction and the thickness direction) during extrusion is 100 mm. A test piece was obtained. The obtained test piece was heated at 75 ° C. for 30 minutes, and the shrinkage in the MD direction and the TD direction from the dimension after heating was measured using the following formula. Moreover, the heat shrinkage rate was determined according to the following criteria.

  Heat shrinkage rate (%) = (dimension before heating−dimension after heating) × 100

[Criteria for heat shrinkage]
○: Heat shrinkage in both MD and TD directions is within ± 2% ×: Heat shrinkage in either MD or TD is outside ± 2%

(3) Interlayer strength between the intermediate layer and the adhesive layer The dimension in the MD direction (flow direction) during extrusion is 100 mm, and the dimension in the TD direction (direction perpendicular to the MD direction and thickness direction) during extrusion is 25 mm. The surface protective film was cut to obtain a test piece. In an environment of room temperature 23 ° C. and relative humidity 50%, the two test pieces were bonded so that the pressure-sensitive adhesive layers faced each other, thereby obtaining a bonded sample. The bonded samples were left for 30 minutes at room temperature of 23 ° C. and 50% relative humidity, and at room temperature of 50 ° C. and 50% relative humidity, respectively. Thereafter, the film was peeled in the 180 ° direction at a tensile speed of 300 mm / min, and the peeled surface after peeling was observed. The interlayer strength between the intermediate layer and the adhesive layer was determined according to the following criteria.

[Judgment criteria for interlayer strength between intermediate layer and adhesive layer]
○: In both the bonded sample left under the 23 ° C environment and the bonded sample left under the 50 ° C environment, peeling occurred between the pressure-sensitive adhesive layer and the pressure-sensitive adhesive layer, and a change in the surface state of the pressure-sensitive adhesive layer was observed. △: A pasted sample left in a 23 ° C environment, peeled off between the pressure-sensitive adhesive layer and the pressure-sensitive adhesive layer, and no change was observed in the surface state of the pressure-sensitive adhesive layer, but it was left in a 50 ° C environment. Peeled between the intermediate layer and the pressure-sensitive adhesive layer in the bonded sample. ×: The bonded sample left in an environment at 23 ° C. and peeled between the intermediate layer and the pressure-sensitive adhesive layer.

(4) Number of fish eyes It was visually observed whether or not there was a fish eye of 0.1 mm or more per 1 m ^{2 of the} surface protective film. The smaller the number of fish eyes, the fewer the defects and the better the appearance of the surface protective film. The number of fish eyes was determined according to the following criteria.

[Criteria for the number of fish eyes]
○: Less than 5 pieces / m ² Δ: 5 pieces / m ² or more, less than 10 pieces / m ² ×: 10 pieces / m ² or more

  Details and results are shown in Table 1 below.

In addition, the specific Example and reference example which formed the surface protection film using the novel raw material for the intermediate | middle layer were shown. It was confirmed that the same effects as those of the present example and the reference example were obtained even when the surface protective film was formed using the recovered raw material instead of the new raw material in the intermediate layer.

Moreover, in Examples 1-3, although the evaluation result of the interlayer strength between an intermediate | middle layer and an adhesive layer is all "(circle)", the surface protection film of Example 3 is more than the surface protection film of Examples 1,2. The surface protective film of Example 2 can be peeled more smoothly between the pressure-sensitive adhesive layer and the pressure-sensitive adhesive layer, and the surface protective film of Example 2 can be peeled more smoothly between the pressure-sensitive adhesive layer and the pressure-sensitive adhesive layer than the surface protective film of Example 1. I was able to. Moreover, in Example 6 and Reference Example 9, the evaluation results of the interlayer strength between the intermediate layer and the adhesive layer are both “Δ”, but the surface protective film of Example 6 is more than the surface protective film of Reference Example 9. Was able to be peeled off more smoothly between the pressure-sensitive adhesive layer and the pressure-sensitive adhesive layer.

Claims (6)

A substrate;
An intermediate layer laminated on one surface of the substrate;
A pressure-sensitive adhesive layer laminated on the surface opposite to the base material side of the intermediate layer,
The base material is formed of a polypropylene-based resin;
The pressure-sensitive adhesive layer is formed of a synthetic rubber-based pressure-sensitive adhesive,
The intermediate layer contains polypropylene resin 85% by weight or more and 97% by weight or less, and synthetic rubber adhesive 3% by weight or more and 15% by weight or less,
The synthetic rubber-based pressure-sensitive adhesive contained in the intermediate layer includes a synthetic rubber and a tackifying resin,
The surface protection film whose thickness of the said intermediate | middle layer is 10 micrometers or more and 100 micrometers or less.   The surface protective film according to claim 1, wherein the intermediate layer has a thickness of more than 20 μm and 60 μm or less. In the synthetic rubber adhesive contained in the intermediate layer, the content of the tackifier resin to the synthetic rubber 100 parts by weight, 5 parts by weight or more, 50 parts by weight or less, according to claim 1 or 2 Surface protective film. The synthetic rubber is a styrene-based elastomer, a surface protective film according to any one of claims 1 to 3. The surface protective film according to claim 4 , wherein the styrene elastomer is a hydrogenated styrene elastomer. The surface protective film according to claim 5 , wherein the hydrogenated styrene elastomer is a styrene-ethylene-butylene-styrene copolymer.