JP2011020299A - Surface protective film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface protective film which has appropriate adhesiveness and adhesion stability and does not cause the minute contamination of the surface of an article to be adhered after peeling or the transfer of irregularity to the surface of the article. <P>SOLUTION: The surface protective film is composed of an adhesive layer (A), a substrate layer (B) and a surface layer (C) laminated in this order. The adhesive layer (A) is based on a mixed resin comprising 5-50 mass% of an amorphous α-olefinic polymer and 50-95 mass% of linear low-density polyethylene (A2) or a mixed resin comprising 5-50 mass% of an amorphous α-olefinic polymer, 40-90 mass% of linear low-density polyethylene and 5-50 mass% of a crystalline ethylene-α-olefin copolymer. The substrate layer (B) is based on a polyethylene type resin containing at least 50 mass% of linear low-density polyethylene. The surface layer (C) contains at least 70 mass% of a polypropylene type resin having a melting point of 120-165°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is applied to the surface of various resin plates, glass plates, metal plates, etc. used in building materials, electrical / electronic fields, etc. for the purpose of protection, storage, transportation and post-processing. The present invention relates to a surface protective film that protects a kimono from scratches and contamination. In particular, after the surface protective film is adhered to the adherend, there is no lifting or peeling from the adherend, contamination such as adhesive residue on the adherend surface after film peeling, or unevenness of the surface protective film. The present invention relates to a surface protective film having no transfer.

  Various resin plates, glass plates, metal plates, etc. used in building materials, electrical / electronic fields, etc. have a surface protection film to protect their surfaces from scratches and dirt during storage, transportation and post-processing. Paste. In particular, when it is used as a heat-molded shape with a surface protective film bonded to various resin plates, it has both heat resistance to the heating temperature and followability to molding, as well as floating and peeling from the adherend. In addition, there is a demand for a surface protective film that has very little adverse effects such as adhesive residue on the surface of the adherend after film peeling and damage to the adherend.

  As a method for improving the above-mentioned problems, a film having a heat-resistant propylene resin as a main component is used as a base material, and an acrylic or rubber adhesive is applied on one side. . However, these surface protective films have problems such that it is difficult to peel off the protective film after heat molding, and there are adhesive residues on the adherend. Moreover, the surface of the polypropylene base material is often roughened in an uneven shape for the purpose of reducing blocking when the protective film is wound. Polypropylene base material is excellent in heat resistance, so there is no melting break at the time of heat molding, and moldability is good, but since it is harder than polyethylene, surface irregularities are present in the surface of the adherend during secondary processing. There was a problem of transferring. In addition, the surface protective film produced by applying a pressure-sensitive adhesive to the film requires a minimum of two steps, ie, a film production process and a pressure-sensitive adhesive coating process. There is a problem that a large amount of solvent needs to be removed in the pressure-sensitive adhesive coating process, which increases the environmental load.

  Further, a self-adhesive surface protective film in which a base film layer and an adhesive layer are simultaneously extruded and laminated by a coextrusion lamination method has been proposed. As such a surface protective film, for example, a low-density polyethylene (LDPE) is used as a base layer, a release layer made of a silicone resin on one side, and an ethylene-vinyl acetate copolymer (EVA) on the other side. ) And an adhesive layer made of a mixed resin of a tackifier made of an aliphatic hydrocarbon resin, or a coextruded laminated film having a three-layer structure, or a specific low-density polyethylene instead of EVA, and / or a specific direct A co-extruded laminated film using a chain low density polyethylene can be mentioned. However, in the surface protective film made of the above-mentioned coextruded laminated film, it is used as a surface base layer for a heating temperature of about 120 to 160 ° C. when thermoforming an acrylic (PMMA) plate or a polycarbonate (PC) plate. There is a problem that the heat resistance of the LDPE to be produced is insufficient and melting breakage occurs, or when EVA is used for the adhesive layer, it becomes difficult to peel off after heating.

  As a protective film for solving these problems, the present inventors have already provided a surface protective film using a crystalline propylene-based polymer as a base layer and a specific mixed resin as an adhesive layer (for example, Patent Documents). 1). The protective film of Patent Document 1 is excellent in heat resistance because it uses a crystalline propylene-based polymer for the base material layer, and has excellent peelability after heat molding by using a specific adhesive layer, and also has an adhesive residue. No. However, as described above, in the case of a polypropylene-based substrate, the surface protective film itself is hard, and there is a problem that surface irregularities are transferred to the adherend.

JP 2008-246947 A

  The subject of this invention is providing the surface protection film which has moderate adhesiveness and adhesion stability, and does not have the trace amount contamination to the to-be-adhered body surface after peeling, and a transcription | transfer of an unevenness | corrugation.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have determined that a specific ratio of an amorphous α-olefin polymer and a linear low-density polyethylene as a resin used for the adhesive layer of the surface protective film. Or a resin obtained by mixing an amorphous α-olefin polymer, a linear low density polyethylene, and a crystalline ethylene-α-olefin copolymer in a specific ratio as a main component, In order to complete the present invention, it has been found that by using a specific polyethylene-based resin as the material layer and a specific polypropylene-based resin for the surface layer, it is possible to prevent contamination and surface irregularities from being transferred to the surface of the adherend. It came.

That is, the present invention is a surface protective film obtained by laminating an adhesive layer (A), a base material layer (B), and a surface layer (C) in the order of (A) / (B) / (C), Linear low-density polyethylene (A2) 50 having an adhesion layer (A) of 5 to 50% by mass of an amorphous α-olefin polymer (A1) and a density of 0.880 to 0.938 g / cm ^3. Linear low-density polyethylene having a mixed resin of ˜95% by mass or an amorphous α-olefin polymer (A1) of 5 to 50% by mass and a density of 0.880 to 0.938 g / cm ^3. (A2) 40 to 90% by mass and a mixed resin of crystalline ethylene-α-olefin copolymer (A3) 5 to 50% by mass, and the base material layer (B) is Mainly composed of a polyethylene resin containing 50% by mass or more of linear low density polyethylene (B1) And than, the surface layer (C) is one in which the melting point is to provide a surface protective film which is characterized in that one containing one hundred twenty to one hundred sixty-five ° C. for polypropylene resin (C1) to 70 wt%. In addition, in this invention, having a specific resin in each layer as a main component means that in the resin composition used in the layer (all including various additives and other resins used in combination as necessary) This means that the resin or mixed resin specified in the present invention is contained in an amount of 65% by mass or more, and preferably that the specific resin or mixed resin is contained in an amount of 85% by mass or more.

  The surface protective film of the present invention is visually observed on the surface of the adherend after peeling, even after being stuck to various resin plates, glass plates, metal plates, etc., and then left for a long time or exposed to a high temperature environment. There is no adhesive residue that can be confirmed, and there is no transfer of surface irregularities. Therefore, the surface protective film of the present invention is useful as a film for protecting the surface of various resin plates, glass plates, metal plates, etc., and is particularly formed by heating while being attached, or secondary such as printing after the protective film is peeled off. It is suitable for applications where processing is performed.

  Hereinafter, the present invention will be described in detail. The surface protective film of the present invention is a coextruded laminated film in which an adhesive layer (A), a base material layer (B), and a surface layer (C) are formed by a coextrusion laminating method.

  The amorphous α-olefin polymer (A1) used in the pressure-sensitive adhesive layer (A) of the surface protective film of the present invention is a polymer containing monomer units based on an α-olefin having 3 to 20 carbon atoms or A copolymer, a melting peak having a heat of fusion of 1 J / g or more and a crystallization peak having a heat of crystallization of 1 J / g or more in a differential scanning calorimeter (DSC) measurement range of −100 to 200 ° C. None of these polymers are observed, and these may be used alone or in combination of two or more.

  The α-olefin having 3 to 20 carbon atoms may be linear or branched, for example, propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1 , Nonene-1, decene-1, undecene-1, dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nanodecene-1, eicosene-1, etc. Linear α-olefin; branched such as 3-methylbutene-1, 3-methylpentene-1, 4-methylpentene-1, 2-ethyl-1-hexene, 2,2,4-trimethylpentene-1, etc. Α-olefins and the like.

  Further, the amorphous α-olefin polymer (A1) is preferably a copolymer having two or more monomer units based on these α-olefins, and a monomer unit based on propylene and a carbon number. A copolymer having at least one monomer unit based on 4 to 20 α-olefin is industrially available, linear low density polyethylene (A2) described later, or crystalline ethylene-α-olefin copolymer. From the viewpoints of compatibility with the polymer (A3), coextrusion moldability and the like, amorphous propylene-butene-1 copolymer and amorphous propylene-ethylene-butene-1 copolymer are most preferable. . The amorphous α-olefin polymer (A1) may have a monomer unit other than the α-olefin. Examples of such monomer units include monomer units based on ethylene, polyene compounds, cyclic olefins, vinyl aromatic compounds, and the like.

  The content of monomer units based on propylene in the amorphous propylene-butene-1 copolymer is selected from the viewpoint of improving the heat resistance of the resulting surface protective film. When the total monomer unit of the polymer is 100% by mass, it is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more.

  As a content rate of the monomer unit based on propylene in the amorphous propylene-ethylene-butene-1 copolymer, from the viewpoint of improving the heat resistance of the obtained surface protective film, amorphous propylene-ethylene- When the total monomer unit of the butene-1 copolymer is 100% by mass, 50% by mass or more is preferable, and more preferably 60% by mass or more. Similarly, the content of monomer units based on ethylene in the amorphous propylene-ethylene-butene-1 copolymer is the same as the total amount of the amorphous propylene-ethylene-butene-1 copolymer. The amount is preferably 10% by mass or more, more preferably 20% by mass or more, based on 100% by mass of the monomer unit. If the content of the monomer unit based on ethylene is within this range, the adhesive layer (B) becomes relatively soft, and even if the adherend surface has irregularities, it adheres in a form that follows the irregularities. Therefore, sufficient adhesive strength can be obtained.

  The intrinsic viscosity [η] of the amorphous α-olefin polymer (A1) is preferably 0.1 to 10.0 dl / g, more preferably 0.7 to 7.0 dl / g. Furthermore, the molecular weight distribution (Mw / Mn) represented by the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) is preferably more than 1 and 4 or less, more preferably 2 to 3. . When the intrinsic viscosity and molecular weight distribution of the amorphous α-olefin polymer (A1) are in this range, the heat resistance, transparency, and adhesiveness are improved, and the adherend having a surface protective film attached thereto is used. Reduces contamination of the adherend due to migration of low molecular weight components in the amorphous α-olefin polymer (A1) to the adherend surface even when stored for a long time or exposed to a high temperature environment. be able to. In addition, since the amorphous α-olefin polymer (A1) is an olefin polymer, as in the case where an ethylene-vinyl acetate copolymer is used as the resin for the adhesive layer, it is possible to remove acetic acid. There is no increase in adhesive strength over time due to resin alteration, and stable adhesive strength can be maintained over a long period of time.

  The method for producing the amorphous α-olefin polymer (A1) is not particularly limited. For example, using a gas phase polymerization method, a solution polymerization method, a slurry polymerization method, a bulk polymerization method, or the like, Examples thereof include a method of polymerizing with a metallocene catalyst. As a more preferable manufacturing method, the manufacturing method disclosed in JP-A-2002-348417 is exemplified.

  The resin used for the adhesive layer (A) in the surface protective film of the present invention is a resin obtained by mixing the amorphous α-olefin polymer (A1) and the linear low density polyethylene (A2), or the amorphous material. This is a resin obtained by mixing an α-olefin polymer (A1), a linear low density polyethylene (A2), and a crystalline ethylene-α-olefin copolymer (A3). By blending the linear low density polyethylene (A2) and the crystalline ethylene-α-olefin copolymer (A3) into the amorphous α-olefin polymer (A1), the surface state of the adherend, Adhesive strength can be adjusted according to the required properties depending on the material and application of the adherend, and contamination on the adherend surface after peeling can be reduced regardless of the strength of the adhesive strength.

The linear low density polyethylene (A2), the density of ones in the range of 0.880~0.938g / cm ^3, the density is more preferably from 0.898~0.925g / cm ^3. The melt flow rate (MFR, based on JIS K7210: 1999, measured at 190 ° C. and 21.18 N) is preferably 0.5 to 30.0 g / 10 min. What is 0-15.0 g / 10min is more preferable. If the density and MFR of the linear low density polyethylene (A2) are within this range, the compatibility with the amorphous α-olefin polymer (A1) described above is good and the film formability of the laminated film is improved. To do.

Examples of the crystalline ethylene-α-olefin copolymer (A3) include an ethylene-propylene copolymer, an ethylene-butene-1 copolymer, and the like, and may be an ethylene-butene-1 copolymer. It is preferable from the viewpoint of easy industrial availability and easy adjustment of the adhesive strength of the resulting surface protective film. As crystalline ethylene-α-olefin copolymer (A3), MFR (value measured at 190 ° C., 21.18 N) is 0.5-30.0 g / 10 min, and density is 0.870-0. Those having a .905 g / cm ³ are preferred, and more preferably those having an MFR of 2.0 to 15.0 g / 10 min and a density of 0.880 to 0.900 g / cm ³ . When the MFR and density of the crystalline ethylene-α-olefin copolymer (A3) are within this range, the compatibility with the amorphous α-olefin polymer (A1) described above is good, and the laminated film is formed. Film properties are improved. Further, from the viewpoint of the effect of preventing contamination of the adherend surface, these resins are more preferably a metallocene catalyst system described later with a small amount of low molecular weight components. The crystallinity is a measurement range of −100 to 200 ° C. of a differential scanning calorimeter (DSC), a melting peak having a heat of fusion of 1 J / g or more, and a crystallization peak having a heat of crystallization of 1 J / g or more. Is a polymer in which any of the above is observed.

  When the mixed resin of the amorphous α-olefin polymer (A1) and the linear low density polyethylene (A2) is used as the main component for the adhesive layer (A), the blending ratio is amorphous α-olefin. The polymer (A1) is 5 to 50% by mass and the linear low density polyethylene (A2) is 50 to 95% by mass, more preferably the component (A1) is 5 to 40% by mass and the component (A2) is 60 to 95% by mass. %. When the blending ratio of the amorphous α-olefin polymer (A1) is less than 5% by mass, sufficient adhesive strength cannot be obtained, and when it exceeds 50% by mass, the adhesive strength is too strong, making it difficult to handle the film. There is a problem. Moreover, by adjusting the blending ratio of the component (A1) and the component (A2) within the above range, the adhesive strength is adjusted to about 0.05 to 5.0 N / 25 mm according to the required adhesive strength. Easy to do.

Further, a resin obtained by mixing an amorphous α-olefin polymer (A1), a linear low density polyethylene (A2), and a crystalline ethylene-α-olefin copolymer (A3) in the adhesive layer (A). When used as the main component, the blending ratio is 5 to 50% by mass of the amorphous α-olefin polymer (A1), and a linear low density polyethylene (0.880 to 0.938 g / cm ³ in density). A2) 40-90 mass%, crystalline ethylene-α-olefin copolymer (A3) 5-50 mass%, more preferably component (A1) 5-30 mass%, component (A2) 40-85 mass %, Component (A3) is 10 to 45% by mass. By adjusting the blending ratio of the component (A1), the component (A2), and the component (A3) within the above range, an adhesive of about 0.1 to 7.0 N / 25 mm depending on the required adhesive strength. It becomes easy to adjust to the force.

  In the present invention, the resin used for the adhesive layer (A) is mainly composed of the above-mentioned mixed resin, but other resins may be used in combination as long as the effects of the present invention are not impaired. Examples of other resins that can be used at this time include propylene homopolymer, propylene-butene-1 copolymer, propylene-butene-1-ethylene terpolymer, butene-1 homopolymer, styrene-butadiene- Styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-ethylene-propylene-styrene copolymer (SEPS), styrene- Butadiene copolymer (SB), styrene-isoprene copolymer (SI), styrene-ethylene-butylene copolymer (SEB), styrene-butadiene rubber (SBR), styrene-ethylene-butylene-ethylene copolymer (SEBC) ) And these hydrogenated products.

  The method for preparing the mixed resin used in the pressure-sensitive adhesive layer (A) of the present invention is not particularly limited, but the amorphous α-olefin polymer (A1) is difficult to handle at room temperature. In view of the above, in order to more easily apply the coextrusion lamination method, the amorphous α-olefin polymer (A1) is previously melted with the linear low density polyethylene (A2) or other crystalline polymer. It is preferable to knead and form pellets that are easy to handle.

  As resin used for the base material layer (B) of the surface protection film of this invention, the polyethylene-type resin which contains 50 mass% or more of linear low density polyethylene (B1) is a main component. By using a polyethylene-based resin as the base material layer, the hardness of the obtained surface protective film itself can be adjusted, and as a result, the unevenness on the surface of the surface protective film is prevented from being transferred to the adherend. It becomes possible.

As said linear low density polyethylene (B1), the thing similar to the linear low density polyethylene (A1) used for the above-mentioned adhesion layer (A) can be used. It may be the same as or different from the linear low density polyethylene used for the adhesive layer (A). In particular, those having a density of 0.915 to 0.950 g / cm ³ are more preferable in terms of achieving both flexibility and heat resistance. The melt flow rate (measured at 190 ° C. and 21.18 N) is preferably 0.5 to 30.0 g / 10 minutes, and preferably 2.0 to 15.0 g / 10 minutes. Is more preferable.

  Examples of the polyethylene resin that can be used for the base material layer (B) include low density polyethylene, linear low density polyethylene, medium density polyethylene, and high density polyethylene. These may be used alone or in combination with linear low density polyethylene (B1). Among these, it is preferable to use low density polyethylene (B2) in combination with linear low density polyethylene (B1) from the viewpoint of preventing uneven transfer of the surface protective film to be obtained.

The low density polyethylene (B2) has a density in the range of 0.910 to 0.929 g / cm ³ and a melt flow rate (190 ° C., 21.18 N) of 0.1 to 20 g / 10 min. It is preferable to use a film having a thickness within the range from the viewpoint of preventing uneven transfer and forming a multilayer film.

  In the base material layer (B), when the linear low density polyethylene (B1) and the low density polyethylene (B2) are used in combination, the linear low density polyethylene (B1) is 50% by mass or more. If it is, it will not specifically limit, However, From a viewpoint of preventing the uneven | corrugated transfer to a to-be-adhered body more, it is preferable to use so that a linear low density polyethylene (B1) may be 60 mass% or more.

  It is essential to provide the surface protective film of the present invention with a surface layer (C). As a resin used for the surface layer (C), a polypropylene resin (C1) having a melting point of 120 to 165 ° C. is 70% by mass. It is essential to contain the above. By using such a resin, it retains heat resistance and molding followability when it is subjected to a thermoforming process with the surface protective film adhered, and is stored in a stacked state for a long time while being adhered. In this case, it is possible to improve the prevention of damage to the adherend surface.

  As the polypropylene resin (C1) which is the main component of the surface layer (C), homopolypropylene having a melting point of 120 to 165 ° C., copolymers of propylene and other olefins, etc. can be used. By modifying to a satin finish, it is possible to improve the anti-blocking effect when the surface protective film is rolled up and stored, and in particular, mixing of a copolymer of propylene and ethylene and homopolypropylene Resin can be used suitably.

Here, the propylene-ethylene copolymer is preferably a block copolymer. For example, the propylene-ethylene block copolymer etc. which are obtained by superposing | polymerizing ethylene or superposition | polymerization of ethylene and propylene in presence of a propylene homopolymer are mentioned. Among these, a propylene-ethylene block copolymer having an ethylene-derived component content of 8 to 20% by mass is preferable because the surface is easy to have a satin finish, and the ethylene-derived component content is 10 to 10%. More preferably, it is a 15 mass% propylene-ethylene block copolymer. The melt flow rate (230 ° C., 21.18 N) is preferably 4 to 12 g / 10 minutes from the viewpoint of easy extrusion, and more preferably 6 to 10 g / 10 minutes. Preferably the density is 0.890~0.910g / cm ^3, more preferably 0.895~0.905g / cm ^3.

  Furthermore, as a method for modifying the surface into a satin texture, a method using a combination of the polypropylene resin (C1) and the low density polyethylene (C2) may be used.

The resin that can be used as the low-density polyethylene (C2) has a density in the range of 0.910 to 0.929 g / cm ³ and a melt flow rate (190 ° C., 21.18 N) of 0.1 to 0.13. What is the range of 15 g / 10min is preferable. More preferably, the density is 0.91 to 0.925 g / cm ³ , and the melt flow rate (190 ° C., 21.18 N) is in the range of 0.2 to 8 g / 10 minutes. When the density and the melt flow rate are within these ranges, it is preferable from the viewpoint of the surface-like texture-like modification effect.

  In general, since ethylene resins and propylene resins have low affinity, it is known that peeling occurs between the layers when multilayered by a coextrusion lamination method. However, in the present invention, although an ethylene-based resin is used for the base layer (B) and a propylene-based resin is used for the surface layer (C), each is made of a specific resin as described above. The main feature is that peeling from the adherend is easy.

  Further, by modifying the surface layer (C) to a more satin-like shape, blocking when storing the surface protective film in a roll shape is prevented, which contributes to improving the productivity of consumers. By using the material layer (B), even if the surface layer (C) is modified into a satin finish, the surface of the obtained protective film is not transferred to the adherend.

  The surface protective film of the present invention preferably has a total film thickness of 20 to 120 μm. If the thickness of all the films is in this range, the protective properties and adhesion of the adherend, and workability such as sticking / peeling will be good. Moreover, 3-30 micrometers is preferable and, as for the thickness of the adhesion layer (A), More preferably, it is 5-25 micrometers. If the thickness of the pressure-sensitive adhesive layer (A) is within this range, the pressure-sensitive adhesive property and the film forming property of the laminated film will be good. Furthermore, the thickness of the surface layer (C) of the present invention is preferably from 3 to 35 μm, more preferably from 5 to 25 μm. When the thickness of the surface layer (C) is within this range, the heat resistance and the film formability of the laminated film are good.

  The method for producing the surface protective film of the present invention is not particularly limited as long as it is a coextrusion lamination method. For example, the resin used for each resin layer is melted by using two or more extruders, Examples include a method of laminating in a molten state by a coextrusion method such as an extrusion die method or a feed block method, and then processing into a film using a method such as inflation or a T-die / chill roll method. In the case of the T-die / chill roll method, the melt-laminated film may be nipped and cooled between a rubber touch roll, a steel belt or the like and the chill roll.

  Furthermore, the surface protective film of the present invention may be stretched in at least one axial direction. As the stretching method, a known method such as longitudinal or lateral uniaxial stretching, sequential biaxial stretching, simultaneous biaxial stretching, or tubular method biaxial stretching can be employed. Further, the stretching process may be inline or offline. The stretching method for uniaxial stretching may be a proximity roll stretching method or a rolling method. The stretching ratio of uniaxial stretching is preferably 1.1 to 80 times, more preferably 3 to 30 times in the longitudinal or transverse direction. On the other hand, the stretch ratio of biaxial stretching is preferably 1.2 to 70 times in terms of area ratio, more preferably 4 to 6 times in length, 5 to 9 times in width, and 20 to 54 times in area ratio.

  In addition, the longitudinal or lateral stretching step is not necessarily limited to one-stage stretching, and may be multi-stage stretching. In particular, in longitudinal uniaxial stretching such as longitudinal uniaxial roll stretching and longitudinal uniaxial rolling stretching in sequential biaxial stretching, it is preferable to perform multistage stretching in view of thickness, uniformity of physical properties, and the like. Further, in the proximity roll stretching, either the flat method or the cross method may be used, but multistage proximity cross stretching that can reduce width shrinkage is more preferable. In the case of uniaxial stretching, the stretching temperature is preferably 80 ° C to 160 ° C in any stretching method, and in the case of using tenter stretching in uniaxial stretching, 90 to 165 ° C is preferable. Moreover, as more preferable extending | stretching temperature, they are 110-155 degreeC and 120-160 degreeC, respectively. On the other hand, in the case of biaxial stretching, the stretching temperature range similar to that in the case of uniaxial stretching is preferable in any method. Moreover, you may provide a pre-heating part before an extending process, and a heat setting part after an extending process suitably. In this case, the temperature of the preheating part is preferably in the range of 60 to 140 ° C, and the temperature of the heat fixing part is preferably in the range of 90 to 160 ° C.

  The surface protective film of the present invention is at least uniaxially stretched and heat-fixed to stabilize the structure, so that the heat resistance is further improved by orientation crystallization of the resin used in each layer, and the adhesive force changes over time. Is preferable.

  In addition, a lubricant, an antiblocking agent, an ultraviolet absorber, a light stabilizer, an antistatic agent, an antifogging agent, and the like may be added as appropriate within the range not impairing the effects of the present invention. May be added to any layer depending on the purpose. As these additives, it is preferable to use various additives for olefin polymers.

  The present invention will be specifically described below with reference to examples and comparative examples.

(Synthesis Example 1)
[Synthesis of Amorphous α-Olefin Polymer (Amorphous Propylene-Butene-1 Copolymer)]
In a 100 L stainless steel polymerization vessel equipped with a stirrer, propylene and butene-1 were continuously copolymerized using hydrogen as a molecular weight regulator to produce amorphous propylene-butene as an amorphous α-olefin polymer. -1 copolymer was obtained. Specifically, hexane as a polymerization solvent is continuously supplied from the lower part of the polymerization vessel at a supply rate of 100 L / hour, propylene at 24.00 kg / hour, and butene-1 at 1.81 kg / hour. From the top of the reaction mixture, the reaction mixture was continuously withdrawn so that the reaction mixture in the polymerization vessel maintained 100 L. Further, from the lower part of the polymerization vessel, dimethylsilyl (tetramethylcyclopentadienyl) (3-t-butyl-5-methyl-2-phenoxy) titanium dichloride is added as a catalyst component at 0.005 g / hour at triphenylmethyl. Tetrakis (pentafluorophenyl) borate was continuously fed at a rate of 0.298 g / hr and triisobutylaluminum was fed at a rate of 2.315 g / hr. The copolymerization reaction was carried out at 45 ° C. by circulating cooling water through a jacket attached to the outside of the polymerization vessel. A small amount of ethanol was added to the reaction mixture continuously extracted from the upper part of the polymerization vessel to stop the polymerization reaction, and after passing through the monomer removal, water washing, and solvent removal steps, the amorphous propylene-butene-1 A polymer was obtained. Subsequently, the obtained copolymer was dried under reduced pressure at 80 ° C. for 24 hours. The content of the propylene monomer unit in the amorphous propylene-butene-1 copolymer was 94.5% by mass, and the content of the butene-1 monomer unit was 5.5% by mass. Moreover, the melting peak in DSC of the copolymer was not observed, the intrinsic viscosity [η] was 2.3 dl / g, and the molecular weight distribution (Mw / Mn) was 2.2.

(Synthesis Example 2)
[Synthesis of Amorphous α-Olefin Polymer (Amorphous Propylene-Ethylene-Butene-1 Copolymer)]
A 2 L separable flask reactor equipped with a stirrer, thermometer, dropping funnel and reflux condenser was decompressed and purged with nitrogen, and then 1 L of dry toluene was introduced as a polymerization solvent. Here, ethylene 2 NL / min, propylene 4 NL / min, and butene-1 1 NL / min were continuously supplied at normal pressure, and the solvent temperature was set to 30 ° C. After adding 0.75 mmol of triisobutylaluminum (hereinafter referred to as TIBA) to the polymerization tank, 0.0015 mmol of dimethylsilyl (tetramethylcyclopentadienyl) (3-t-butyl-5-methyl-2-phenoxy) titanium dichloride was added. Added to the polymerization vessel. 15 seconds later, 0.0075 mmol of triphenylmethyltetrakis (pentafluorophenyl) borate was added to the polymerization tank, and polymerization was carried out for 10 minutes. As a result, an amorphous propylene-butene-1-ethylene copolymer was obtained. In this amorphous propylene-ethylene-butene-1 copolymer, the content of propylene monomer units was 61.5% by mass, the content of ethylene monomer units was 21.0% by mass, butene-1 unit The content of the monomer unit was 17.5% by mass. Moreover, the melting peak in DSC of this copolymer was not observed, the intrinsic viscosity [η] was 1.69 dl / g, and the molecular weight distribution (Mw / Mn) was 2.0.

(Preparation Example 1)
[Preparation of Amorphous α-Olefin Polymer Composition (1)]
To the amorphous propylene-butene-1 copolymer obtained above, a crystalline propylene-butene-1 copolymer [density 0.900 g / cm ³ , MFR (230 ° C., 21.18 N) 10.0 g / 10 minutes, DSC maximum melting peak 126 ° C.] was blended so that amorphous propylene-butene-1 copolymer / crystalline propylene-butene-1 copolymer = 60/40 (mass ratio), Furthermore, an aromatic phosphite antioxidant (Irgafos 168 manufactured by Ciba Specialty Chemicals) and a hindered phenol antioxidant (Irganox 1010 manufactured by Ciba Specialty Chemicals) )) Is blended at 2000 ppm each, melt-kneaded with a twin screw extruder, and then amorphous α-olefins with a granulator. A pellet of the polymer polymer composition (1) was obtained.

(Preparation Example 2)
[Preparation of Amorphous α-Olefin Polymer Composition (2)]
Amorphous Propylene-Butene-1 Copolymer / Crystalline Propylene-Butene-1 Copolymer = Amorphous α in the same manner as in Preparation Example 1 except that the blend was made to be 95/5 (mass ratio). -The pellet of the olefin polymer composition (2) was obtained.

(Preparation Example 3)
[Preparation of Amorphous α-Olefin Polymer Composition (3)]
To the amorphous propylene-ethylene-butene-1 copolymer obtained above, a crystalline propylene-butene-1 copolymer [density 0.900 g / cm ³ , MFR (230 ° C., 21.18 N)] 10. 0 g / 10 min, maximum melting peak in DSC of 126 ° C.] is amorphous propylene-ethylene-butene-1 copolymer / crystalline propylene-butene-1 copolymer = 60/40 (mass ratio). In addition, aromatic phosphite antioxidants (“Irgafos 168” manufactured by Ciba Specialty Chemicals Co., Ltd.) and hindered phenol antioxidants (“Irgafos Co., Ltd.” manufactured by Ciba Specialty Chemicals Co., Ltd.). 2000 ppm of each of Irganox 1010 "), melt-kneaded with a twin screw extruder, and then granulator Give more amorphous α- olefin polymer composition pellets (3).

(Adjustment example 4)
[Preparation of Amorphous α-Olefin Polymer Composition (4)]
Amorphous propylene-ethylene-butene-1 copolymer / crystalline propylene-butene-1 copolymer = Amorphous in the same manner as in Preparation Example 1 except that the blend was made to be 95/5 (mass ratio). Pellets of the hydrophilic α-olefin polymer composition (4) were obtained.

Example 1
As a resin for the surface layer, a propylene homopolymer [melting point: 160 ° C., density: 0.90 g / cm ³ , MFR (230 ° C., 21.18 N): 8 g / 10 min; hereinafter referred to as “HOPP”. ] And propylene-ethylene block copolymer [melting point: 160 ° C., density: 0.90 g / cm ³ , MFR (230 ° C., 21.18 N): 8 g / 10 min; hereinafter referred to as “BCOPP”. Are mixed so as to have a mass ratio of 70/30, and a linear low-density polyethylene [density: 0.938 g / cm ³ , MFR (190 ° C., 21.18 N): 5 g / 10 min; hereinafter referred to as “LLDPE (1)”. ] As an adhesive layer resin, 30 parts by mass of the amorphous α-olefin polymer composition (1) prepared above and linear low density polyethylene [density: 0.920 g / cm ³ , MFR ( 190 ° C., 21.18 N): 3.0 g / 10 min; hereinafter referred to as “LLDPE (2)”. ] Using a mixture of 70 parts by mass, each was supplied to an extruder for a base layer (caliber 50 mm) and an extruder for an adhesive layer (caliber 40 mm), and the surface layer was formed from a T-die at an extrusion temperature of 250 ° C. by a coextrusion method. Extruded so that the thickness of the substrate is 18 μm, the thickness of the base material layer is 54 μm, and the thickness of the adhesive layer is 18 μm, and after cooling with a 40 ° C. water-cooled metal cooling roll, it is wound on a roll to obtain a surface protective film It was. The obtained film was aged in a aging room at 35 ° C. for 48 hours in order to stabilize physical properties.

(Example 2)
The surface of Example 2 was the same as Example 1 except that linear low-density polyethylene (density: 0.913 g / cm ³ ; hereinafter referred to as “LLDPE (3)”) was used as the base layer resin. A protective film was obtained.

(Example 3)
As the resin for the base layer, linear low density polyethylene [density: 0.948 g / cm ³ ; hereinafter referred to as “LLDPE (4)”. )] Was used to obtain a surface protective film of Example 3 in the same manner as in Example 1.

Example 4
As a resin for the base layer, 80 parts by mass of LLDPE (4), low density polyethylene [density: 0.920 g / cm ³ , MFR (190 ° C., 21.18 N): 2.0 g / 10 min; hereinafter referred to as “LDPE (1 ) ". The surface protective film of Example 4 was obtained in the same manner as in Example 1 except that 20 parts by mass of the mixture was used.

(Example 5)
As a resin for the base layer, 50 parts by weight of LLDPE (4), medium density polyethylene [density: 0.937 g / cm ³ , MFR (190 ° C., 21.18 N): 8.0 g / 10 min; hereinafter referred to as “MDPE” . Example 1 except that 50 parts by weight of the mixture was used and a mixture of 30 parts by mass of the amorphous α-olefin polymer composition (2) and 70 parts by mass of LLDPE (2) was used as the adhesive layer resin. Similarly, the surface protective film of Example 5 was obtained.

(Example 6)
As the resin for the surface layer, HOPP and low-density polyethylene [density: 0.920 g / cm ³ , MFR (190 ° C., 21.18 N): 2.0 g / 10 min; hereinafter referred to as “LDPE (1)”. Are mixed so that the mass ratio is 80/20, LLDPE (1) is used as the base layer resin, and the amorphous α-olefin polymer prepared above is used as the adhesive layer resin. Composition (3) 30 parts by mass, LLDPE (2) 50 parts by mass and ethylene-butene-1 copolymer rubber [density: 0.895 g / cm ³ , MFR (190 ° C., 21.18 N): 3.0 g / 10 minutes; hereinafter referred to as “EBR”. ] Using 20 parts by mass of the mixture, each was supplied to an extruder for base material layer (caliber 50 mm) and an extruder for adhesive layer (caliber 40 mm), and the surface layer from the T-die at an extrusion temperature of 250 ° C. by co-extrusion method. After extruding to a thickness of 15 μm, a base layer thickness of 25 μm, and an adhesive layer thickness of 10 μm, and cooling with a 40 ° C. water-cooled metal cooling roll, it is wound on a roll to obtain a surface protective film It was. The obtained film was aged in a aging room at 35 ° C. for 48 hours in order to stabilize physical properties.

(Example 7)
Example 6 except that the mixture of the amorphous α-olefin polymer composition (4) prepared above, 40 parts by mass, LLDPE (2) 50 parts by mass, and EBR 10 parts by mass was used as the adhesive layer resin. Similarly, the surface protective film of Example 7 was obtained.

(Comparative Example 1)
A mixture of 70 parts by weight of HOPP and 30 parts by weight of BCOPP is used as the resin for the surface layer, HOPP is used as the resin for the base layer, 30 parts by mass of the amorphous α-olefin polymer composition (1) as the resin for the adhesive layer, and A surface protective film of Comparative Example 1 was obtained in the same manner as in Example 1 except that a mixture of 70 parts by weight of LLDPE (2) was used.

(Comparative Example 2)
MDPE is used as the resin for the surface layer and the resin for the base layer, and 30 parts by weight of ethylene-vinyl acetate copolymer (vinyl acetate content 15% by weight, MFR 4.0 g / 10 min,) as the resin for the adhesive layer, LLDPE (3) A surface protective film of Comparative Example 2 was obtained in the same manner as in Example 1 except that 70 parts by weight of the mixture was used.

(Comparative Example 3)
HOPP is used as the resin for the surface layer, 35 parts by weight of LLDPE (4) as the resin for the base layer, and low density polyethylene [density: 0.919 g / cm ³ , MFR (190 ° C., 21.18 N): 7.0 g / 10 minutes; hereinafter referred to as “LDPE (2)”. Example 1 except that 65 parts by weight of the mixture was used and a mixture of 30 parts by weight of the amorphous α-olefin polymer composition (2) and 70 parts by weight of LLDPE (2) was used as the adhesive layer resin. In the same manner, a surface protective film of Comparative Example 3 was obtained.

(Comparative Example 4)
In all extruders, 85 parts by weight of HOPP and low density polyethylene [density: 0.923 g / cm ³ , MFR (190 ° C., 21.18 N): 1.0 g / 10 min; hereinafter referred to as “LDPE (3)”. An adhesive coating film was obtained in the same manner as in Example 1 except that 15 parts by weight of the mixture was used and the total thickness was 40 μm. An acrylic pressure-sensitive adhesive was applied to one side of the obtained film so as to have a thickness of 5 μm, and a surface protective film of Comparative Example 4 was obtained.

  Using the surface protective films obtained in Examples 1 to 7 and Comparative Examples 1 to 4, the following measurements and evaluations were performed.

(1) Evaluation of transferability to adherend Five test pieces each having a surface protective film bonded to both surfaces of a polycarbonate (PC) plate having a thickness of 1 mm, a length of 15 cm, and a width of 5 cm are stacked. A hot press machine manufactured by Tester Sangyo is heated to 30 ° C., pressurized so that a load corresponding to 500 kgf is applied to the five stacked test pieces, and left for 24 hours. After 24 hours, the protective film bonded to both sides of the PC board was peeled off, and an indoor fluorescent lamp was projected on the surface of the PC board, and the uniformity of reflected light was visually compared to evaluate transferability.
PC board before pressing: The reflected fluorescent lamp has a clear outline and the reflected light appears uniform.
○: No change in the state of reflected light compared to the PC plate before pressing.
X: Compared with the PC board before pressing, the reflected light is extremely light and wavy and appears uneven.

(2) Evaluation of heat resistance A surface protective film is bonded to both surfaces of an acrylic plate (mirror finish, “Acrylite” manufactured by Mitsubishi Rayon Co., Ltd.) having a thickness of 1 mm, a length of 30 cm, and a width of 30 cm to obtain a test piece. Using a vacuum molding machine manufactured by Sanwa Kogyo Co., Ltd., heating is performed indirectly from both sides of the test piece at a heater temperature of 370 ° C. for 30 seconds, and vacuum molding is performed with a hemispherical female mold. The appearance change of the surface protective film after taking out from the mold was visually evaluated.
○: The film is not melted and torn, and the film is not lifted or peeled off.
X: The film was observed to be melt-ruptured and floated or peeled off.

(3) Measurement of adhesive strength after heating In a thermostatic chamber at 23 ° C. and 50% RH, a surface protective film cut out to a width of 25.4 mm and a length of 18 cm in accordance with the adhesive strength evaluation method of JIS Z0237: 2000, It was bonded to the center of a 2 mm thick acrylic plate (mirror finish, “Acrylite” manufactured by Mitsubishi Rayon Co., Ltd.). The acrylic plate on which the film was bonded was heated at 160 ° C. for 30 minutes, then cooled at 23 ° C. for 24 hours, and 180 ° at a rate of 300 mm / min using a tensile tester (manufactured by A & D Co., Ltd.). The initial adhesive strength was measured after peeling in the ° direction.
○: When the adhesive strength after heating is less than 3 times the initial value ×: When the adhesive strength after heating exceeds 3 times the initial value

(4) Evaluation of adhesive residue After cooling the test piece obtained in (2) at 23 ° C. for 24 hours, the film is peeled off at high speed, and the state of contamination on the surface of the molded product is visually confirmed. Evaluation of adhesive residue was performed.
○: There is no dirt such as cloudy, white streaks or foreign matter on the acrylic plate surface.
X: The acrylic plate surface has any dirt such as cloudy, white streaks or foreign matters.

(5) Measurement of adhesive strength In a thermostatic chamber at 23 ° C. and 50% RH, the obtained surface protective film was applied to a 2 mm thick acrylic plate (mirror finish, Mitsubishi, in accordance with the adhesive strength evaluation method of JIS Z0237: 2000. It was attached to “Acrylite” manufactured by Rayon Co., Ltd.). After leaving the acrylic plate with the film attached in a constant temperature room at 23 ° C. for 30 to 60 minutes, using a tensile tester (manufactured by A & D Co., Ltd.) in the direction of 180 ° at a speed of 300 mm / min. It peeled and the initial adhesive force was measured.

  From Examples 1 to 7, the surface protective film obtained in the present invention has an appropriate adhesive strength, does not float from the adherend, does not peel off, and remains of adhesive on the adherend surface after film peeling. It was confirmed that there was no contamination or transfer of irregularities on the surface protective film.

  On the other hand, in the surface protection film of the comparative example 1, since the polypropylene resin was used for the base material layer, it was confirmed that transferability was deteriorated.

  Comparative Example 2 is an example in which EVA is used for the adhesive layer, and it has been confirmed that the heat resistance is insufficient. Furthermore, although the polyethylene-type resin is used for the base material layer in the comparative example 3, since the content rate of the linear low density polyethylene contained in it is low, it delaminated between the surface layers. Comparative Example 4 is an example in which an acrylic pressure-sensitive adhesive was used as the pressure-sensitive adhesive layer. Both the adhesive residue on the adherend and the transferability were inferior to the surface protective film of the present invention.

  The surface protective film of the present invention has a wide range of adhesive strength from the optimum fine adhesion to a medium adhesion level, and does not cause the occurrence of lifting or peeling after being attached to a substrate even when it is subjected to a heat molding process. . Also, when peeling the film from the attached substrate, no contamination such as cloudiness, streaks or foreign matter can be visually confirmed, and there is no transfer of irregularities to the adherend surface after peeling the surface protective film. Therefore, it is suitable for applications in which secondary processing such as printing is performed after the surface protective film is peeled off.

Claims (5)

An adhesive layer (A), a base material layer (B), and a surface layer (C) are laminated on the surface protective film in the order of (A) / (B) / (C), and the adhesive layer (A) ,
Mixing of amorphous α-olefin polymer (A1) 5 to 50% by mass and linear low density polyethylene (A2) 50 to 95% by mass having a density of 0.880 to 0.938 g / cm ³ Resin, or
Amorphous α-olefin polymer (A1) 5 to 50% by mass, linear low density polyethylene (A2) 40 to 90% by mass having a density of 0.880 to 0.938 g / cm ³ , crystals Mixed resin with 5 to 50% by mass of conductive ethylene-α-olefin copolymer (A3),
Is the main component,
The base material layer (B)
The main component is a polyethylene-based resin containing 50% by mass or more of linear low-density polyethylene (B1),
The surface layer (C) is
A surface protective film comprising 70% by mass or more of a polypropylene resin (C1) having a melting point of 120 to 165 ° C. The surface protective film according to claim 1, wherein the amorphous α-olefin polymer (A1) is an amorphous propylene-butene-1 copolymer or an amorphous propylene-ethylene-butene-1 copolymer. The surface protective film according to claim 1 or 2, wherein the crystalline ethylene-α-olefin copolymer (A3) is a crystalline ethylene-butene-1 copolymer. The surface protective film according to any one of claims 1 to 3, further comprising a low-density polyethylene (B2) in the base material layer (B). The surface protective film according to any one of claims 1 to 4, further comprising low-density polyethylene (C2) in the surface layer (C).