JP5113991B2 - Surface protection film - Google Patents

Description

  The present invention relates to a surface protective film to be adhered to an adherend surface in order to prevent dust from adhering to the adherend surface and damage to the adherend surface, and more specifically, a rubber on one surface of a polyolefin-based substrate. The present invention relates to a surface protective film in which a PSA layer is laminated.

  In order to protect various articles and members, a surface protective film is often temporarily attached to the surfaces of the articles and members. For example, the surface of various adherends such as synthetic resin plates, metal plates, decorative plywood, painted steel plates, painted resin plates, or various nameplates may be contaminated or scratched during processing and transportation. In order to prevent this, surface protective films are frequently used.

  This type of surface protective film has a structure in which an adhesive layer is laminated on one side of a film substrate. In general, a film substrate made of a thermoplastic resin is used as the film substrate. The surface protective film is affixed to the adherend surface using the adhesive force of the pressure-sensitive adhesive layer to protect the adherend surface. When the adherend is used, the surface protective film is peeled off from the adherend surface. Therefore, the surface protective film is required to have appropriate adhesiveness so that it can be easily temporarily attached to the surface of the adherend, and can be easily peeled off from the adherend surface after use. It is required to have a good releasability. Further, there is a strong demand not to contaminate the adherend surface after peeling with adhesive residue or the like.

  In particular, a surface protective film used for surface protection of a coating film such as a coated steel sheet is generally temporarily attached to the surface of the coating film by hand attachment and finally peeled off. In this case, the temperature of the coating film surface of the coated steel sheet may be 0 ° C. or lower in winter. Therefore, in order to ensure the workability at such a low temperature, the surface protective film is also required to have high toughness at a low temperature.

  On the other hand, the film base material of the surface protective film is required to have a certain degree of waist in consideration of workability. A film substrate made of a polypropylene-based composition is used as a loose film substrate at a normal temperature, that is, at room temperature of about 20 to 25 ° C. However, although the film base material made of the polypropylene-based composition has sufficient rigidity at room temperature, there is a problem that the toughness at a low temperature of 0 ° C. or 0 ° C. or lower is not sufficient.

Therefore, as a solution to such a problem, the following Patent Documents 1 to 4 describe a film having a composition in which polypropylene is blended with an olefin-based elastomer such as low-density polyethylene or ethylene-propylene-rubber (EPR). Substrates have been proposed.
JP 58-1111846 A JP-A-57-73034 Japanese Unexamined Patent Publication No. 57-159841 JP-A 63-4342

  However, toughness at low temperatures may not be sufficiently increased by simply blending low density polyethylene or EPR with polypropylene.

  In view of the current state of the prior art described above, the object of the present invention is that the elastic modulus at room temperature of about 20 to 25 ° C. is sufficiently high, the workability is excellent, and the toughness at a low temperature of 0 ° C. or below 0 ° C. It is to provide a surface protective film having an elevated film substrate.

  According to the present invention, there is provided a surface protective film in which a rubber-based pressure-sensitive adhesive layer is laminated on a polyolefin-based substrate, wherein the polyolefin-based substrate is a sea phase composed of a polypropylene component and an island phase composed of an olefin-based elastomer. The average distance between island phases determined by an electron microscope is 600 nm or less, and the tensile elastic modulus at 23 ° C. measured according to JIS K 7127 is 300 to 2000 MPa. A featured surface protective film is provided.

  In the present invention, preferably, the rubber-based pressure-sensitive adhesive layer includes a rubber-based resin and a tackifier resin, and the rubber-based resin is a styrene-based elastomer.

  Details of the present invention will be described below.

(Polyolefin base material)
Inventors of the present application, as a result of earnestly examining this problem in view of the fact that it may not be possible to sufficiently increase the toughness at low temperatures only by using a polyolefin-based substrate obtained by simply blending an olefin-based elastomer with polypropylene. Rather than simply blending an olefin elastomer with a polypropylene component, if the olefin elastomer is highly dispersed, especially if the olefin elastomer is highly and uniformly dispersed above a certain density. The inventors have found that the toughness at a low temperature can be further reliably increased, and have reached the present invention.

  That is, the present invention is characterized in that it has a sea-island structure in which an island phase composed of an olefin elastomer is dispersed in a sea phase composed of a polypropylene-based component, and the average distance between the island phases is 600 nm or less. It is characterized by using a film base material in which the elastomer is highly dispersed and the tensile elastic modulus at 23 ° C. is in the range of 300 to 2000 MPa, whereby the elastic modulus at room temperature is sufficient, The toughness at a low temperature of 0 ° C. or 0 ° C. or lower is effectively enhanced.

  Prior to the filing of this application, as described in Patent Documents 1 to 4 described above, a polyolefin-based base material obtained by blending an olefin-based elastomer with polypropylene was obtained. As is clear from the comparison between the Examples and Comparative Examples, the toughness at low temperatures could not be sufficiently increased. On the other hand, in the present invention, as described above, the average distance between the island phases is 600 nm or less, that is, since the olefin-based elastomer is highly dispersed, the toughness can be reliably increased at low temperatures. It is possible.

  The tensile elastic modulus at 23 ° C. measured in accordance with JIS K 7127 of the polyolefin-based substrate needs to be in the range of 300 to 2000 MPa. If it is less than 300 MPa, the tensile elastic modulus at normal temperature is low, the polyolefin base material is stretched with a slight external force, and the performance of sticking to an adherend as a surface protective film is lowered. If it exceeds 2000 MPa, the tensile elastic modulus becomes too high, the curved surface followability is lowered, and floating or peeling occurs, so that the pasting operation becomes difficult.

  As described above, the polyolefin-based substrate of the surface protective film of the present invention has a sea phase composed of a polypropylene component and an island phase composed of an olefin-based elastomer.

  The polypropylene component is composed of a propylene homopolymer, a copolymer of propylene, ethylene and / or an α-olefin having 4 to 12 carbon atoms, and a mixture thereof. As the α-olefin having 4 to 12 carbon atoms, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 4-methyl-1-pentene and the like can be used. is there. As for the said ethylene or alpha olefin, only 1 type may be used and 2 or more types may be used.

  However, in this invention, the said polypropylene component shall say that the unit derived from a propylene is 95 mass% or more. Therefore, the content of copolymerization components other than propylene such as ethylene or α-olefin is less than 5% by mass. More preferably, the ratio of the copolymer component other than the propylene is 0.1 to 3.5% by mass. If the content of ethylene and / or α-olefin having 4 to 12 carbon atoms exceeds 5% by mass, the rigidity and heat resistance of the polyolefin-based substrate may be lowered.

  The polypropylene component can be produced by a known polymerization method using, for example, a known Ziegler-Natta catalyst or metallocene catalyst. In the above-mentioned polyolefin base material, when rigidity and heat resistance are particularly required, the polypropylene component is preferably a propylene homopolymer. Further, when impact resistance and transparency are particularly required, the polypropylene component is preferably a copolymer of propylene and ethylene and / or α-olefin.

  In the present invention, the olefin-based elastomer constituting the island phase of the polyolefin-based substrate is not particularly limited, but an olefin-based elastomer of propylene and ethylene and / or an α-olefin having 4 to 12 carbon atoms is used. Preferably used. The α-olefin having 4 to 12 carbon atoms is not particularly limited. For example, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 4-methyl-1- Examples include pentene.

  The olefin-based elastomer preferably refers to those having a unit derived from propylene of 50 to 85% by mass. More preferably, it is 55-85 mass%, More preferably, it is 55-80 mass%. If the unit derived from propylene exceeds 85% by mass, the impact resistance at low temperatures becomes insufficient, and if it is less than 50% by mass, the mechanical strength may be extremely lowered.

  In the polyolefin-based substrate according to the present invention, the ratio of the polypropylene component and the olefin-based elastomer component is not particularly limited, but is preferably 50 to 10% by mass of the olefin-based elastomer with respect to 50 to 90% by mass of the polypropylene component. It is considered as a range. If the ratio of the olefin-based elastomer is less than 10% by mass, the impact resistance may be inferior, and if it exceeds 50% by mass, the rigidity and heat resistance may be inferior. The ratio of the olefin elastomer is preferably in the range of 10 to 45% by mass, more preferably in the range of 15 to 40% by mass.

  Although the thickness of the said polyolefin-type base material changes with purposes of use, 20-100 micrometers is preferable.

(Adhesive composition)
In the surface protective film according to the present invention, a rubber-based pressure-sensitive adhesive layer is laminated on one side of the polyolefin-based substrate. The rubber-based pressure-sensitive adhesive layer preferably contains a rubber-based resin and a tackifier resin. The shear storage modulus of the rubber-based pressure-sensitive adhesive layer at a frequency of 10 Hz is preferably 1 × 10 ⁶ Pa or less at 23 ° C. and 2 × 10 ⁵ Pa or more at 70 ° C.

When the shear storage modulus at a frequency of 10 Hz is outside the above range, when the surface protective film is temporarily attached to the adherend, the adhesive force may become too high with time and peeling may be difficult. In addition, when used as a surface protective film such as a coated steel plate, it may be exposed to a relatively high temperature for a long time. In such a case, if the shear storage elastic modulus of the pressure-sensitive adhesive layer is higher than 1 × 10 ⁶ Pa at 23 ° C., the film has a shrinkage stress when temporarily attached with air bubbles and wrinkles in the adherend. It cannot be relaxed by the pressure-sensitive adhesive layer. For this reason, the pressure-sensitive adhesive layer is brought into a state where the coating film is drawn at the boundary of the peeling portion, and there is a possibility that traces of bubbles and wrinkles remain as steps on the surface of the coating film after peeling.

  The rubber-based resin used in the present invention is not particularly limited. For example, styrene-based elastomer; polyisobutylene (polymer of isobutylene), butyl rubber (copolymer of isobutylene and isoprene) as a main component, and if necessary Olefin-based elastomers such as those obtained by copolymerization or modification of monomers having a crosslinkable functional group), polybutene (polymer of 1-butene), polychloroprene, nitrile rubber, etc., which are used alone Or two or more of them may be used in combination. Of these, styrenic elastomers are preferable in terms of removability and easy moldability.

  Examples of the styrene elastomer include styrene-conjugated diene block copolymers and styrene isobutylene block copolymers, and those having an aliphatic unsaturated bond are preferably hydrogenated. The weight average molecular weight of the styrene-based elastomer is preferably in the range of 50,000 to 400,000, more preferably 80,000 to 200,000 in terms of polystyrene-converted weight average molecular weight according to the GPC method. When the weight average molecular weight is less than 50,000, the cohesive force of the pressure-sensitive adhesive is reduced, so that adhesive residue may be generated on the adherend during re-peeling. When it exceeds 400,000, the adhesive force is insufficient and the fluidity may be deteriorated.

  The tackifying resin is not particularly limited, and a resin that satisfies the shear storage modulus value when added to the rubber-based resin is preferably used. Examples of such tackifying resins include aliphatic petroleum resins, alicyclic petroleum resins, aromatic petroleum resins, terpene resins, terpene / phenol resins, alkyl / phenol resins, coumarone / indene resins. Examples thereof include resins, rosin resins, and the like. Among them, hydrogenated aliphatic, alicyclic, and aromatic petroleum resins and terpene resins are preferable because of excellent weather resistance. More specifically, for example, hydrogenated alicyclic petroleum resin, manufactured by Arakawa Chemical Co., Ltd., trade name: Archon, terpene resin, Yashara Chemical Co., Ltd., trade name: Clearon, and the like can be mentioned. These may be used independently and 2 or more types may be used together.

  The tackifying resin is preferably blended in the range of 5 to 70 parts by weight, and more preferably 20 to 50 parts by weight with respect to 100 parts by weight of the rubber-based resin. If the amount is less than 5 parts by weight, the shear storage modulus may be too high, and the adhesive force to the adherend may be insufficient. If it exceeds 70 parts by weight, the cohesive force of the pressure-sensitive adhesive is insufficient, and after use as a surface protective film, it may be difficult to peel off from the adherend, and there is a possibility that an adhesive residue may be generated upon peeling.

  In the surface protective film according to the present invention, an ultraviolet absorber, a light stabilizer, an antioxidant, an adhesion progressing preventing agent, or the like may be added to the pressure-sensitive adhesive layer as necessary, as long as the pressure-sensitive adhesive performance is not impaired. Good.

  The ultraviolet absorber is not particularly limited, and examples thereof include commonly used ones such as salicylic acid series, benzophenone series, benzotriazole series, and cyanoacrylate series. Examples of the light stabilizer include hindered amine compounds. It does not specifically limit as antioxidant, For example, what is used normally, such as a phenol type (monophenol type, bisphenol type | system | group, high molecular type phenol type), sulfur type, phosphorus type | system | group, is mentioned. Examples of the adhesion progress preventing agent include fatty acid amides, polyethyleneimine long-chain alkyl grafts, soybean oil-modified alkyd resins (for example, Arakawa Chemical Co., Ltd., trade name “Arachid 251”), tall oil-modified alkyd resins (for example, Arakawa). Chemical name, “Arachid 6300”, etc.).

  The thickness of the rubber-based pressure-sensitive adhesive layer varies depending on the purpose of use, but is preferably in the range of 3 to 50 μm.

(Method for producing surface protective film)
The manufacturing method of the surface protection film which concerns on this invention is not specifically limited. For example, a method of laminating and integrating a pressure-sensitive adhesive composition that constitutes a rubber-based pressure-sensitive adhesive layer and a composition that constitutes a polyolefin-based substrate, or rubber on a film-formed polyolefin-based substrate For example, a method of laminating and laminating a PSA adhesive may be used.

  As a method for laminating and integrating the polyolefin-based substrate and the rubber-based pressure-sensitive adhesive by coextrusion, known methods such as an inflation method and a T-die method can be used. As a method of laminating a rubber-based adhesive on a polyolefin-based substrate, a solution coating method for applying an adhesive solution, a dry lamination method, an extrusion coating method using a T die, or the like is used. Among these, a co-extrusion method using a T-die is preferable because quality can be improved and economical production can be achieved. In the case of the solution coating method, it is preferable to subject the polyolefin base material to a surface treatment such as primer application in advance in order to increase the bonding strength between the base material layer and the pressure-sensitive adhesive layer.

  In the surface protective film according to the present invention, in a configuration in which a rubber-based pressure-sensitive adhesive layer is laminated on a polyolefin-based substrate, the polyolefin-based substrate includes a sea phase composed of a polypropylene component and an island phase composed of an olefin-based elastomer. It has a sea-island structure, and in this sea-island structure, the average distance between the island phases is 600 nm or less, and thus the olefin elastomer is highly dispersed. Therefore, the toughness of the polyolefin base material at a low temperature of 0 ° C. or 0 ° C. or less is effectively enhanced. Therefore, a surface protective film excellent in workability can be provided at low temperatures such as in winter. Moreover, since the tensile elastic modulus of the polyolefin-based substrate at normal temperature is 300 to 2000 MPa, the elastic modulus is sufficiently high at normal temperature, so that it can be easily attached to and peeled off from the adherend.

  That is, according to the present invention, it is possible to provide a surface protective film excellent in toughness at low temperatures while maintaining a high elastic modulus at room temperature.

  When the rubber-based resin constituting the rubber-based pressure-sensitive adhesive layer is a styrene-based elastomer, a surface protective film excellent in workability and weather resistance can be obtained.

In particular, when the shear storage modulus at a frequency of 10 Hz of the rubber-based pressure-sensitive adhesive layer is 1 × 10 ⁶ Pa or less at 23 ° C. and 2 × 10 Pa or more at 70 ° C., a sufficient adhesive force is exhibited at the time of application, and Since it is difficult for the adhesive force to increase with time, the surface protective film can be peeled off from the adherend without difficulty after use.

  Hereinafter, the present invention will be clarified by giving specific examples and comparative examples of the present invention. In addition, this invention is not limited to a following example.

Example 1
Rubber system consisting of 100 parts by weight of hydrogenated styrene-butadiene block copolymer (Clayton Japan, product number: G1657) and 20 parts by weight of tackifier resin (trade name: Alcon P125, manufactured by Arakawa Chemical Co., Ltd.) A pressure-sensitive adhesive composition was prepared.

  On the other hand, the rubber-based pressure-sensitive adhesive composition and the polypropylene-based resin composition (manufactured by Sun Allomer, product number: PB170A) are co-extruded by a T-die method, and the thickness is 10 μm on one side of a 50 μm-thick polyolefin base material. A surface protective film having a rubber-based pressure-sensitive adhesive layer laminated and integrated was obtained. The product number: PB170A manufactured by Sun Allomer, which is a polypropylene-based resin composition used as a polyolefin-based substrate, is a block polypropylene. The rubber content in this block polypropylene and the types of polypropylene contained are described below. Determined by the method.

(Example 2 and Comparative Examples 1 and 2)
The same rubber-based pressure-sensitive adhesive composition as in Example 1 was used except that the polypropylene-based resin composition for constituting the polyolefin-based substrate was changed as shown in Table 1 below. In the same manner as above, a surface protective film was obtained.

  In Example 2, as is clear from Table 1, the polypropylene resin composition comprises 70 parts by weight of FLX80E4 (homopolypropylene) manufactured by Sumitomo Chemical Co., Ltd., and 30 parts by weight of C200F (block polypropylene) manufactured by Sun Allomer. It is a composition containing. Moreover, in the comparative example 1, it consists of Mitsui Chemicals, J715 (block polypropylene). Furthermore, in Comparative Example 2, the polypropylene resin composition is PB270A (block polypropylene) manufactured by Sun Allomer.

  In Examples 1 and 2 and Comparative Examples 1 and 2, the rubber content and the type of polypropylene in the resin composition constituting the polyolefin base material were determined as follows.

  Homopolypropylene: After the pellet was dyed with ruthenium tetroxide, it was sliced to a thickness of about 0.05 μm using a microtome, and the cross section was measured using a transmission electron microscope (JEM-1200EX II, manufactured by JEOL Ltd.). When a photograph is taken at a magnification of 5000 times, the phase separation structure cannot be confirmed, and when the DSC is measured according to JIS K 7121, the melting point is 158 ° C. or higher.

  Block polypropylene: After the pellet was dyed with ruthenium tetroxide, it was sliced to a thickness of about 0.05 μm using a microtome, and the cross section was measured using a transmission electron microscope (JEM-1200EX II, manufactured by JEOL Ltd.). A phase separation structure can be confirmed when a photograph is taken at a magnification of 5000 times, and a melting point is 158 ° C. or higher when DSC is measured according to JIS K 7121.

  Random polypropylene: a melting point of 150 ° C. or lower when DSC is measured according to JIS K7121.

  Rubber content: Block polypropylene and random polypropylene pellets are dyed with ruthenium tetroxide, etc., and then sliced to a thickness of about 0.05 μm using a microtome, and the cross section is taken with a transmission electron microscope (JEM, JEM) It was determined by the area ratio of the phase separation structure when the photograph was taken at a magnification of about 5000 times using -1200EX II).

  The rubber content of the base material used and the type of polypropylene are shown in Table 2 below.

(Evaluation of Examples 1 and 2 and Comparative Examples 1 and 2)
For the surface protective films of Examples 1 and 2 and Comparative Examples 1 and 2 obtained as described above, (1) the mechanical properties of the film and (2) the distance between island phases made of olefin elastomer were measured.

(1) Mechanical properties of the film The film was cut out in parallel to the extrusion direction (MD) of the surface protective film to obtain a test piece having a width of 20 mm and a length of 250 mm. Next, using a tensile tester (Orientec, Tensilon UTA-500), the elastic modulus and elongation of the surface protective film at room temperature (23 ° C.) were measured at a tensile speed of 300 mm / min in accordance with JIS K 7127. did. Next, at −20 ° C., the tensile modulus and elongation were measured in the same manner under the condition of a tensile speed of 300 mm / min. The results are shown in Table 1 below.

(2) Measurement of distance between island phases made of olefin-based elastomer After the surface protective film is dyed with ruthenium tetroxide, the film is sliced to a thickness of about 0.05 μm using a microtome so as to be parallel to the MD of the film. And the cross section which appeared by the slice was photographed at a magnification of about 5000 times using a transmission electron microscope (JEM-1200EX II, manufactured by JEOL Ltd.).

  FIG. 1 shows an electron micrograph taken as described above for the polyolefin-based substrate of the surface protective film produced in Example 1. As is apparent from FIG. 1, it is understood that a dispersed phase made of an olefin elastomer, that is, an island phase is dispersed in a sea phase made of a polypropylene resin component. A straight line was drawn arbitrarily from one point in the approximate center of the photograph, and the distance between adjacent island phases was measured in a plurality of island phases on the straight line. Ten straight lines were drawn, and the total average value of the distances between the island phases determined on the ten straight lines was determined. The total average value thus determined was defined as the distance between olefin elastomers, that is, the distance between island phases. The results are shown in Table 1 below.

  As is clear from Table 1, in Comparative Examples 1 and 2, the distance between the olefin elastomers, that is, the distance between the island phases was as large as 1200 nm or more, so the elongation at −20 ° C. was very small as 22% or 54%. . On the other hand, in Examples 1 and 2, the distance between the island phases is as small as 420 or 476 nm, and the island phases are highly dispersed, so the elongation at −20 ° C. is as high as 300 and 146%. I understand. That is, it is understood that not only the elastic modulus at normal temperature (23 ° C.) is sufficiently large, but also the elongation at low temperature is large and the toughness at low temperature is excellent.

The electron micrograph which shows the sea-island structure which appeared in the cross section of the polyolefin-type base material produced in Example 1. FIG.

Claims (2)

A surface protective film in which a rubber-based pressure-sensitive adhesive layer is laminated on a polyolefin-based substrate,
The polyolefin base material has a sea-island structure composed of a sea phase composed of a polypropylene component and an island phase composed of an olefin elastomer, the average distance between island phases determined by an electron microscope is 600 nm or less, and JIS K A surface protective film having a tensile modulus of elasticity at 23 ° C. measured in accordance with 7127 of 300 to 2000 MPa. The surface protection film according to claim 1, wherein the rubber-based pressure-sensitive adhesive layer includes a rubber-based resin and a tackifier resin, and the rubber-based resin is a styrene-based elastomer.