JP5742023B2 - Surface protective film and method for producing the same - Google Patents

Description

  The present invention relates to a film for surface protection and a method for producing the same. More specifically, the present invention is excellent in adherend protection and has little transferability of additives. The present invention relates to a surface protective film excellent in laminating workability and peelability and a method for producing the same.

  In recent years, in order to prevent scratches, dust adhering, and contamination during processing of liquid crystal panels and polarizing plates of personal computers, liquid crystal televisions, etc., synthetic resin removable surface protective films have been used for liquid crystal panels and polarizing plates. It has been practiced to protect by sticking to a plate (for example, see Patent Document 1).

  In particular, polypropylene-based unstretched films have few defects such as gels and are heat resistant, and thus have been widely used in the surface protective film field (see, for example, Patent Document 2).

  The surface protective film is generally used by laminating an adhesive layer on the surface of the base film and fixing the surface of the target article to be protected using the adhesive force of the adhesive layer.

  In recent years, demands for quality and cost reduction have increased along with the expansion of applications, and a base film excellent in adhesive applicability has been demanded. In particular, the processing temperature is increasing for the purpose of increasing the processing speed of adhesive processing, etc., and even when processed at a high temperature, thermal deformation due to the processing temperature is small, and dimensional stability during processing is good, There is a need for dimensional stability at high temperatures (hereinafter also simply referred to as heat-resistant dimensional stability) that suppresses the occurrence of thermal wrinkles during processing.

  As a method for improving the heat-resistant dimensional stability of a film, a polypropylene resin film to which a crystal nucleating agent is added has been proposed (for example, see Patent Document 3).

  However, if this method is adopted, the residence time during extrusion of the resin becomes relatively long in a large-scale production equipment level considering economy, so fish eyes caused by aggregation and decomposition of the crystal nucleating agent in the film. There is a problem that a minute foreign matter called “is generated”. Moreover, when it uses as a film for surface protection, there exists a problem that followable | trackability to a to-be-adhered body is inferior, or peelability is inferior.

  As another method for improving the heat-resistant dimensional stability of the film, a composition in which an aromatic organophosphate metal salt is blended with a polypropylene resin having specific characteristics is extruded at a cooling roll temperature of 40 to 50 ° C. It has been proposed to mold (see, for example, Patent Document 4).

  However, the film obtained by the above method may cause fish eyes due to the aromatic organophosphate metal salt, and many spherulites with large crystal sizes are generated during cooling, resulting in poor transparency. Therefore, the application is limited. Also in this case, the toughness of the film is lowered, and when used as a surface protecting film, there is a problem that followability to an adherend is inferior or peelability is inferior.

  Instead of using various additives as described above, when the molten resin is cast, it is rapidly cooled so that the crystal size does not become large, and then the heat treatment is used to improve the crystallinity and to maintain the mechanical strength while maintaining high transparency. An improvement method has also been proposed (see, for example, Patent Documents 5 and 6).

  However, even with the polypropylene resin film by the above method, the dimensional change and the tensile elastic modulus are large, the applicability of the pressure-sensitive adhesive, the bonding processability to the adherend and the peelability are not sufficient, and there are problems with blocking resistance and appearance. There is.

JP 2005-281328 A Japanese Patent Laid-Open No. 10-309781 JP 2002-146130 A JP-A-10-298367 JP 2003-170485 A JP 2009-12225 A

  The present invention was devised in view of the problems of the prior art, and its purpose is excellent in adherend protection after processing, and less additive transferability, and further the applicability of the adhesive and An object of the present invention is to provide a surface protective film excellent in bonding workability and peelability to an adherend and a method for producing the same.

  In order to achieve the above object, the present inventors have intensively studied a suitable composition of a polypropylene resin substantially free of additives and a suitable physical property of the film, and as a result, the present invention has been completed.

That is, the present invention has the following configurations (1) to (4).
(1) A film for protecting a surface comprising a polypropylene resin substantially free from a crystal nucleating agent, an antiblocking agent, and a lubricant, and containing 70% by weight or more of a block polypropylene resin, wherein the TD direction and MD of the film The tensile modulus of elasticity in the direction is 500 to 650 MPa, the breaking elongation in the TD direction and MD direction of the film is both 500% or more, and the thermal shrinkage rate at 120 ° C. in the TD direction and MD direction of the film is The film for surface protection characterized by being 0 to 1.0% and having a heating elongation in the TD direction and MD direction of 0 to 5.0%.
(2) The surface protecting film according to (1), wherein a surface treatment is applied to at least one surface of the film.
(3) The film for surface protection according to (1), wherein an adhesive layer is provided on at least one side of the film.
(4) The melt-extruded polypropylene resin film is brought into contact with a cooling roll, cooled and solidified, preheated and then heated to 70 to 120 ° C. with a heating roll, and subsequently cooled to 35 ° C. or less with a cooling roll. The manufacturing method of the film for surface protection in any one of (1)-(3).

  Since the surface protective film of the present invention is excellent in heat-resistant dimensional stability, for example, it is excellent in suitability for secondary processing such as pressure-sensitive adhesive application, and even when subjected to treatment such as drying at a high temperature around 120 ° C. Generation of thermal wrinkles and film sagging and shrinkage of the film in the width direction are suppressed, so that productivity of secondary processing can be improved and generation of defective products can be suppressed. Moreover, since the film of this invention does not contain an antiblocking agent substantially, it can prevent the dropout of an antiblocking agent. In addition, despite the fact that it contains substantially no lubricant or antiblocking agent, the surface roughness is appropriate, the film is slippery and blocking resistant, and the film is easy to handle. Is excellent. Furthermore, the followability to a to-be-adhered body is favorable, and it is excellent in the secondary processing and the bonding workability and peelability to an to-be-adhered body. Therefore, the film of the present invention is particularly suitable as a surface protective film in various precision products and parts having a strong demand for suppressing contamination and defects, and processing and assembling processes thereof.

It is explanatory drawing of the manufacturing method of the film for surface protections of this invention.

  First, the surface protective film of the present invention will be described. The film for surface protection of the present invention is made of a polypropylene resin that substantially does not contain a crystal nucleating agent, an antiblocking agent, and a lubricant and contains 70% by weight or more of a block polypropylene resin.

  The film for surface protection of the present invention is characterized in that a crystal nucleating agent is not actively added and is substantially not contained. Here, “substantially does not contain” means that the content is 50 ppm or less, preferably 10 ppm or less. If the crystal nucleating agent is present in an amount exceeding 50 ppm, depending on the melt extrusion conditions of the resin, the fish eye in the film increases and a problematic case occurs. Further, it is not preferable because a problem such as a reduction in productivity such as pressure increase due to clogging of a filter provided in an extruder for the purpose of removing foreign substances in the resin occurs.

  In addition, the surface protective film of the present invention is characterized in that an anti-blocking agent such as inorganic and / or organic fine particles is not actively added and is not substantially contained. Here, “substantially does not contain” means that the content is 50 ppm or less, preferably 10 ppm or less. Particularly preferably, the amount of the anti-blocking agent is below the detection limit by a usual quantitative method such as ash or elemental analysis. As a result, the anti-blocking agent is prevented from falling off due to film abrasion in the production and secondary processing steps of the film, so that contamination, failure occurrence, and the like due to the falling off matter are suppressed.

  Furthermore, the film for surface protection of the present invention is characterized in that a lubricant such as polyethylene wax, calcium stearate, erucic acid amide, ethylene biserucic acid amide is not actively added and is substantially not contained. Here, “substantially does not contain” means that the content is 50 ppm or less, preferably 10 ppm or less. Particularly preferably, the amount of the lubricant is below the detection limit in a usual quantitative method such as elemental analysis or extraction method. This prevents migration of the lubricant to the film surface and subsequent contamination of the packaged or protected object due to the transition to the packaged or protected object, and maintains the clarity of the packaged or protected object. The

  The polypropylene resin used for the surface protective film of the present invention needs to contain 70% by weight or more of a block polypropylene resin. Suitable block polypropylene resins include those having a melting point of 150 to 170 ° C. having both flexibility and heat resistance. More preferable block polypropylene resins include those having a rubber component of 5% by weight or more. When only a highly crystalline polypropylene resin such as a polypropylene homopolymer is used, the tensile modulus is high, the blocking resistance is lowered, and fish eyes are easily generated. Even when a low crystalline polyolefin resin, such as a polyolefin-based elastomer, is added to a highly crystalline polypropylene resin such as a polypropylene homopolymer, the fish eye is not improved. As a commercially available block polypropylene resin, for example, F763 manufactured by Prime Polymer Co., Ltd. or BC3HF manufactured by Nippon Polychem Co., Ltd. can be used.

  In addition to the above-mentioned block polypropylene resin, the polypropylene resin may contain other resins, for example, in an amount of less than 30% by weight, for example, cost, improvement of extrusion film formation, improvement of impact resistance, etc. Elastomer components such as polypropylene homopolymer, random polymerized polypropylene resin, ethylene-propylene copolymer rubber, styrene-butadiene copolymer or its hydrogenated product, ethylene-propylene-diene monomer copolymer can be blended. It is. However, if a resin that is poorly compatible with the block polypropylene resin is used, it will peel off at the interface between the resins during bending and cause whitening, cracks, breaks, etc. In addition, it should be noted that the excellent properties of the block polypropylene resin are diminished.

  Even if the block polypropylene resin is sufficiently cooled at the cooling rate of the conventional extrusion molding conditions, even if it is a part that can be crystallized, crystallization can proceed completely to a monoclinic system that is a stable phase. Without being able to do so, it remains in the quasi-hexagonal system which is a metastable phase. Furthermore, it is important to convert the pseudo-hexagonal system part, which is a metastable phase, into a monoclinic crystal composed of crystals with a small crystal size, not a monoclinic crystal containing spherulites with a large crystal size, by making a solid phase transition. is there.

  As a means of increasing crystallinity, spherulite becomes large if a method of simply adding a crystal nucleating agent or a method of gradually cooling at a relatively high temperature when extruding a molten resin into a sheet and cooling and solidifying it is adopted. As the degree of crystallinity increases, the film loses its flexibility and extensibility and whitens.

  The molecular chain in the pseudo hexagonal system has a united structure called nodules. Adjacent nodules have a structure that is easily displaced by stress, and they have a property that behaves like a liquid crystal (smectic liquid crystal) with respect to the stress, so that they can easily follow changes in external shape. The crystal is plastically deformed and can maintain transparency without causing breakage or whitening. Also, when impact stress is applied, the energy of impact is absorbed by the plastic deformation of the crystal. And has good impact resistance. On the other hand, however, there is a problem that the size is easily changed by heating and aging.

  In contrast, monoclinic crystals are packed with the molecular chains of polypropylene resin most closely, and have a crystal structure that is less likely to slip between adjacent lamellae. Even if rubbed, the crystals are resistant to contact stress with hard materials and the crystals are difficult to plastically deform. However, on the other hand, it is difficult to plastically deform the crystal following the change in the outer shape during bending, so in order to follow the change in the outer shape, the interface between the crystals and the interface between the crystal part and the amorphous part Deformation may occur due to occurrence of fine peeling and displacement from each other. In particular, when many spherulites with large crystal sizes exist, when impact stress is applied, the impact energy cannot be sufficiently absorbed by the plastic deformation of the crystals, and There is a problem that whitening, cracks, breakage, and the like are likely to occur due to fine peeling at the interface between the crystal and the crystal part.

  The block polypropylene resin used in the present invention has a melt flow rate (MFR) in the range of 3 to 15 g / 10 min (230 ° C.) and a molecular weight distribution (MWD = Mw / Mn) in the range of 2 to 10. Is preferred. If the melt flow rate is too high, the melt viscosity in the molding process is low, resulting in unstable shape maintenance, and the resin molecule diffusion rate during the crystallization process in the molding process and the phase transition process in the reheating process. Therefore, the average particle diameter of spherulites, the phase transition ratio, etc. tend to be unstable. If the mel flow rate is too small, it may be difficult to extrude the film. In addition, if the molecular weight distribution is small, the moldability tends to deteriorate.

  In the present invention, without adding an additive to the block polypropylene resin, first, it is cooled and solidified under relatively low temperature conditions, and a molded product in which the crystallizable part of the block polypropylene is substantially composed of only a pseudo hexagonal system part. By producing and heat-treating this at a constant temperature of 70 ° C. to 120 ° C. for a certain time, a substantial part of the pseudo hexagonal structure inside the compact is phase-transformed to the monoclinic system, Both the average grain size and amount of the crystals to be generated and the ratio of the pseudo hexagonal system part to the monoclinic system part are controlled independently and precisely, thereby enabling control of physical properties. In other words, by generating a quasi-hexagonal system part and generating a large amount of monoclinic phase by generating a quasi-hexagonal part without generating spherulites as much as possible during cooling and solidification, a certain amount of crystals with a small crystal size can be generated. is important. The crystal size is preferably 200 nm or less which does not scatter visible light.

  The film for surface protection of the present invention controls the molecular orientation of the film during crystallization, so that the thermal shrinkage rate at 120 ° C. in the TD direction and MD direction of the film is 0 to 1.0%. The heating elongation in the TD direction and the MD direction is 0 to 5.0%. If the heat shrinkage rate is less than 0%, the film is stretched and cannot be applied well when an adhesive is applied to the film. On the other hand, if it exceeds 1.0%, the thickness of the film becomes uneven and the coating cannot be performed well. Preferably, the heat shrinkage rate is 0 to 0.8%. When the heating elongation is larger than 5.0%, the film is stretched when the adhesive is applied to the film and cannot be applied well. From the flexibility of the film, the heating elongation is preferably 2 to 4.5%.

  The film for surface protection of the present invention preferably has a film crystallinity of 30 to 65% according to the measurement method described later. If the crystallinity is less than 30%, the heat-resistant dimensional stability is inferior, and the film is slack or stretched during processing in the subsequent process, resulting in poor flatness. On the other hand, when the crystallinity exceeds 65%, the transparency of the film is significantly deteriorated, which is not preferable. On the other hand, when the degree of crystallinity exceeds 65%, it is generally not practical because it contains a large amount of a crystal nucleating agent and requires a higher heat treatment temperature. The lower limit of the crystallinity of the film is more preferably 40% or more, and most preferably 50% or more from the viewpoint of heat-resistant dimensional stability. On the other hand, the upper limit of the crystallinity of the film is preferably 60% or less from the viewpoint of transparency.

In the surface protective film of the present invention, the number of fish eyes having a maximum diameter of 0.1 mm or more in the film is preferably 10 / m ² or less, and more preferably 5 / m ² or less. Further, the number of fish eyes having a maximum diameter of 0.1 mm or less is preferably 100 / m ² or less, more preferably ^{2 to} 80 / m ² or less, and further preferably ^{2 to} 60 / m ² or less. Thereby, when it uses as a base film of a protective film, for example, when it uses as a base film of a protective film, the disorder | damage | failure generation | occurrence | production by the penetration | invasion to the protection part, etc. of plating solution by adhesion failure can be suppressed.

  The haze value of the surface protective film of the present invention is 40% or less, preferably 35% or less, and more preferably 30% or less. By reducing the haze value, the visibility of the object to be protected is improved, and for example, the object to be protected can be inspected while the surface protective film is still attached. On the contrary, when the haze value is high, the transparency is deteriorated. The lower limit of the haze value is preferably low, but in order to obtain slipperiness, it may be 15% or more, further 20% or more.

  The surface protective film of the present invention is characterized in that the tensile elastic modulus in the TD direction and the MD direction are both 500 to 650 MPa. 550 MPa or more is more preferable, and 600 MPa or more is more preferable. If it is less than 500 MPa, when a film is made into a roll, wrinkles and sagging are likely to occur, and the handleability is lowered, which is not preferable. The upper limit is preferably about 650 MPa from the balance with other characteristics. If it exceeds 650 MPa, the followability to the adherend may be inferior or the peelability may be lowered.

  The film for surface protection of the present invention is characterized in that both the elongation at break in the TD direction and the MD direction are 500% or more. 550% or more is more preferable, and 600% or more is more preferable. If it is less than 500%, the toughness is not sufficient, the film is broken when it is wound or unwound, the followability to the adherend is not sufficient at the time of adhesive processing, and the handling property is lowered, which is not preferable. The upper limit is preferably about 800% from the balance with other characteristics.

  The surface protective film of the present invention preferably has an impact strength at 23 ° C. of 50 Pa or more. 60 Pa or more is more preferable. When the impact strength is high, the reliability with respect to impact resistance when used as a protective film or the like is increased. Therefore, it is preferable that this characteristic is satisfied after the above-described characteristics are given. The upper limit is preferably about 100 Pa from the balance with other characteristics.

  The surface protective film of the present invention preferably has a surface roughness (SRa) on both sides in the range of 0.20 to 0.50 μm. 0.25 to 0.45 μm is more preferable, and 0.30 to 0.45 μm is more preferable. By setting the surface roughness within the above range, the slipperiness between films is improved, and wrinkles are less likely to occur when a roll is formed in combination with the effect of dimensional stability of the film. The blocking resistance of the surface protective film of the present invention is preferably 1 to 10 mN, more preferably 1 to 7 mN, in the evaluation method described later.

  The surface protective film of the present invention preferably has a thickness variation rate of ± (1 to 10)%. When the thickness variation rate is less than 1%, there is no problem in terms of quality, but the time required for adjusting the thickness becomes enormous, so the economical efficiency is remarkably lowered and is not realistic. On the other hand, when the thickness variation rate exceeds 10%, the heat-resistant dimensional stability and transparency vary in proportion to the thickness variation, and the flatness of the film (waving and curling) is deteriorated, which is not preferable. The thickness variation rate is more preferably ± (1.5 to 8)%, and most preferably in the range of ± (2 to 5)%.

  Next, the manufacturing method of the surface protection film of this invention is demonstrated. For example, as shown in FIG. 1, the surface protective film of the present invention is obtained by bringing a polypropylene resin film melt-extruded from a die 1 into contact with a cooling roll 2 to cool and solidify, and then passing through a preheating roll 3 and a heating roll 4. It is manufactured by heating to ˜120 ° C. and again contacting the cooling rolls 5 and 6 for cooling.

As film forming conditions for melt-extruding a polypropylene resin containing a block polypropylene resin, a die temperature of 200 ° C. to 270 ° C., a cooling roll temperature of 10 ° C. to 50 ° C., and a cooling time of 0.5 seconds to 5 seconds are preferable. At this time, it is preferable to adjust the draft ratio in the drawing process after melt extrusion to the range of 0.4-3.0. The draft ratio is calculated according to the following film forming conditions.
Draft ratio = (film take-up speed / die exit melt resin speed) / air gap The air gap means the distance (cm) from the die exit to the take-up (cooling) roll contacting the melt resin.
Although the film forming speed depends on the production apparatus, it is preferably 80 to 120 m / min. If the film forming speed is low, the film tends to stretch even after heat treatment.

  Under the above-mentioned film forming conditions, if the cooling roll temperature exceeds 50 ° C., it is not preferable because a pseudo hexagonal system part is hardly generated. In addition, if the cooling time is less than 0.5 seconds, the cooling effect is insufficient, and thus it is not preferable because a pseudo hexagonal system part is hardly generated. On the other hand, the lower limit of the cooling roll temperature and the upper limit of the cooling time are not particularly limited from the viewpoint of the crystallinity of the film, but are preferably 10 ° C. and 5 seconds, respectively, from the viewpoints of economy and productivity.

  The film after the melted resin is extruded into a sheet and rapidly cooled and solidified is heated by bringing the film into contact with a heating roll heated to a predetermined temperature. One heating roll may be used, but a film may be passed between the two heating rolls, and one surface may be sequentially heated with each heating roll.

  The lower limit of the heating temperature is preferably 70 ° C., more preferably 80 ° C., which is the temperature at which the pseudo hexagonal crystal of the block polypropylene resin undergoes solid phase transition to monoclinic crystal. If it is less than 70 degreeC, a solid phase transition does not generate | occur | produce and a problem arises in heating dimensional stability. On the other hand, the block polypropylene resin has a melting point of 150 ° C. to 170 ° C., preferably 155 ° C. to 162 ° C., and the block polypropylene resin has a solid phase transition from pseudo hexagonal to monoclinic at 70 ° C. Considering that the temperature is higher than or equal to ° C., the upper limit of the heating temperature is preferably 120 ° C. from the viewpoint of tensile modulus and elongation at break.

  When heating with a roll of film, adhesion failure due to heat shrinkage of the film may occur. In that case, it is preferable to use a nip roll or a suction roll. However, since the heated film is soft and there is a concern about transfer not only to the heating roll but also to the nip roll or suction roll surface shape film, selection and management of the roll material and surface roughness are important.

  The surface roughness (SRa) of the heating roll is preferably 0.4 μm or more and 1.8 μm or less. More preferably, it is 0.5 μm or more and 1.5 μm or less. If it is less than 0.4 μm, the adhesion of the film becomes too high and sticks, and an appearance defect due to stick-slip may occur at the time of peeling. If the thickness exceeds 1.8 μm, the surface shape may be transferred when it comes into close contact, resulting in poor appearance. Examples of the heating roll satisfying such surface roughness include a roll coated with a fluororesin or the like and a roll formed with a satin-like unevenness on the surface.

  The heating time is preferably 1 second or longer. The adjustment of the heating time is performed by adjusting the contact time with the heating roll, and can be controlled by the traveling speed of the film, the diameter of the heating roll, and the holding angle of the film on the roll. Furthermore, it is possible to use three or more heating rolls in order to increase the heating time. The upper limit of the heating time is not particularly limited as long as there is no problem with a series of film production facilities, but there is no difference in the effect even if the treatment is performed for more than 1 to several seconds where the phase transition is considered to be completed. From the viewpoint of economic constraints of the apparatus, 20 seconds is preferable, 10 seconds is particularly preferable, and 5 seconds is particularly preferable. If the heating roll is held unnecessarily long, transfer of the surface of the scratch or the heating roll may occur.

  It is preferable to install a preheating device immediately before the heating roll and preheat the film temperature to less than 100 ° C. and Tt (heat treatment temperature) −25 ° C. or more and Tt−15 ° C. or less before the heat treatment with the heating roll. The preheating temperature is more preferably less than 100 ° C., and Tt (heat treatment temperature) −20 ° C. or more and Tt−15 ° C. or less. In the above temperature range, so-called heat shock is unlikely to occur during heat treatment, and streaks in the flow direction due to film floating are unlikely to occur. The preheating time is preferably 0.5 seconds to 5 seconds in consideration of productivity.

  The preheating method is not particularly limited, and examples thereof include a method of contacting a heating roll and a method of heating a running film in a non-contact manner with a heater or the like. Moreover, heat shock can be reduced by performing preheating in steps.

  The heat treatment can be performed by once winding the cooling film in a roll shape and then unwinding it again. However, it is preferable that the heat treatment is performed in a series of film production steps without winding after film formation.

  When cooling the heat-treated film, it is preferable to use two or more rolls and gradually cool, and the upper limit of the roll temperature is 35 ° C., which is a problem of wrinkles and sagging when winding. It is preferable in reducing the amount. The lower limit of the roll temperature is not particularly limited, but is preferably 10 ° C. from the viewpoint of economy and productivity. The cooling time is preferably 0.5 seconds to 5 seconds.

  Although the thickness of the film for surface protection of this invention is not specifically limited, Generally, it is 10-500 micrometers. From the viewpoint of pastability, the thickness is preferably in the range of 20 to 100 μm.

  The surface protective film of the present invention can be subjected to surface treatment such as corona discharge treatment or flame treatment on at least one surface by a method usually employed industrially.

  Moreover, the film for surface protection of this invention can provide an adhesive layer at least on one side. Thereby, the characteristic of the film of this invention mentioned above can be utilized effectively, and the applicability in a wide field | area as a protective film improves. The type, thickness, adhesive strength, and the like of the pressure-sensitive adhesive layer are not particularly limited, and may be appropriately selected according to market requirements. Moreover, the lamination | stacking method of an adhesive layer is not limited, either. For example, any of an application method and an extrusion laminating method may be used.

  The surface protective film of the present invention is used to prevent scratches, dust adhesion, contamination, etc. during processing and assembly of electronic and precision products such as liquid crystal panels and polarizing plates and other related materials, parts and related members. Or, as a method of partially plating the connection terminal part of a flexible printed circuit board, etc., a method of plating with an adhesive film on the non-plated part and then plating, or on the non-etched surface in the etching process during shadow mask manufacturing Can be suitably used as a protective film in plating and etching processes such as a method for protecting a resist film or an etching resistance film provided on the substrate.

  Further, the surface protective film of the present invention is excellent in heat-resistant dimensional stability, and in the above-mentioned adhesive processing, for example, even if the drying temperature in the drying process is increased, generation of thermal wrinkles and film sagging is suppressed, so Processing productivity can be increased. Moreover, generation | occurrence | production of the inferior goods resulting from a heat wrinkle or film sagging can be suppressed.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and is implemented with appropriate modifications within a range that can be adapted to the gist of the present invention. It is possible. The characteristic value evaluation method employed in this specification is as follows.

(1) Melt flow rate [MFR]
Based on JIS-K-7210, the method of Condition-14 (measured at a load of 2.16 kg and a temperature of 230 ° C.).

(2) Haze value Based on JIS-K-6714, it measured using "Haze Tester J" made by Toyo Seiki Seisakusho.

(3) Blocking resistance In accordance with ATM-D1893-67, a load of 90 N was applied to the A4 size area of the film, and after leaving for 2 hours in a 60 ° C. atmosphere, the load was removed, and then the peeling resistance with a φ5 aluminum rod was measured. The measurement was performed under the condition of a moving speed of 100 mm / min.

(4) Tensile modulus / breaking elongation In accordance with JIS-K-7127, the sample shape conforms to No. 1 type test piece (sample length 200 mm, sample width 15 mm, distance between chucks 100 mm), cross It measured at 23 degreeC about MD direction (film longitudinal direction) on the conditions of head speed 500mm / min.

(5) Fisheye Cut the molded film 33.3 cm in the flow direction x 30 cm in the direction transverse to the flow direction, place it on the plate irradiated with a fluorescent lamp from below the film, and visually observe it with transmitted light. Measure fish eyes with a maximum diameter of 0.1 mm or more. Next, if the counted fish eye is immersed in liquid nitrogen and hardened, it is cut in half with a razor and the cross section of the fish eye is observed with a microscope at 50 to 300 times. For example, if there is no foreign matter such as cellulose, it is an unmelted lump, a lump due to gelation of a part of the raw material, or a gel-induced fish such as lump due to partial deterioration of the material during molding. Judged as eye. If there is a nucleus, it is judged as a fish eye caused by a foreign object and excluded from the count.

(6) Thermal shrinkage rate at 120 ° C. in the TD direction and MD direction of the film The shrinkage rate of the film heat treated at 120 ° C. for 30 minutes was measured according to JIS-K-7133.

(7) Heat elongation in the TD direction and MD direction of the film The molded film is cut into 40 mm × 210 mm in each direction, and marked lines are placed at intervals of 150 mm in the film. Paste both ends of the film to the metal frame slightly, place a 75g weight on the center of the film, heat at 125 ° C for 1 minute, take out the sample, cool with the weight on for 30 seconds, Was measured, and the amount of change was measured.

(8) Wrinkles and sagging of the roll The wound film is rolled up into a roll with a width of 1300 mm with a slitter (SXR-140 type manufactured by Toshin Co., Ltd.), and wrinkles and sagging of the roll surface of the product are wound. The state of occurrence was visually observed. Evaluation was performed immediately after winding.
○: No wrinkle or sagging occurs.
X: Wrinkles and sagging were clearly observed.

(9) Contamination After sticking the tape on the sample film surface, it was stored at 40 ° C. × 92% RH for 1 week and then peeled off. The adhesive surface of the tape was visually observed to confirm the presence or absence of dirt.
○: Dirt is not visually observed.
X: Dirt is observed visually.

(10) Adhesive application property The wound film is cut into 5 cm in the flow direction and 25 cm in the horizontal direction with respect to the flow direction, and acrylic adhesive (viscosity 30 × 10 ⁻³ Pa · s) by hand coating with a Meyer bar. ), The film piece was horizontally heat treated in a dry heat oven at 120 ° C. for 5 minutes while holding both ends with a metal frame. Immediately after the heat treatment, the film was taken out of the oven and allowed to cool at room temperature for 30 minutes, and then the sagging (elongation) state due to the weight of the film itself and the shrinkage in the width direction were visually observed.
○: There is no or almost no sag, and there is no contraction in the width direction. X: Sag sag and contraction in the width direction are observed.

(11) Bonding property / peelability of adhesive film The adhesive film obtained above was measured by the following method in accordance with JIS-Z-0237 (2000) adhesive tape / adhesive sheet test method.
As an adherend, an acrylic plate (Mitsubishi Rayon Co., Ltd .: Acrylite 3 mm thick) 50 mm × 150 mm is prepared, and a test piece is 25 mm in the winding direction at the time of film production and 180 mm in the direction perpendicular thereto. A piece was cut out, and using a rubber roll having a mass of 2000 g (with a spring hardness of 80 Hs on the roller surface and a width of 45 mm and a diameter (including the rubber layer) of 95 mm, covered with a rubber layer having a thickness of 6 mm), The test piece was reciprocated once at a speed of 5 mm / sec.
・ Adhesiveness Evaluates workability when adhering to an acrylic board. ○: The film has sufficient waist and can be easily attached. No wrinkling or lifting occurs when bonding.
×: The film has a low waist and tends to wrinkle and float when bonded.
-Peelability ○: Easily peelable ×: The film stretches at the time of peeling and peeling is difficult. Film whitening that takes time to peel

Example 1
100% by weight of block polypropylene resin (manufactured by Prime Polymer Co., Ltd., F763, melt flow rate (MFR) 3) is melt-extruded with a T-die film forming machine, die slip gap: 0.5 mm, draw of molten resin An unstretched film having a thickness of 40 μm was obtained under the film forming conditions of a draft ratio of 0.64, a cooling roll temperature of 30 ° C., a cooling time of 2.4 seconds, and a film forming speed of 100 m / min. The resin temperatures of the feeding zone, kneading zone and metering zone of the extruder were 240, 250 and 250 ° C, respectively. Thereafter, the unstretched film is preheated by bringing it into contact with a preheating roll at 80 ° C. for 3 seconds, and immediately after that, it is brought into contact with a heating roll at 100 ° C. for 1.5 seconds, followed by heat treatment, and further with a cooling roll at 30 ° C. The mixture was cooled for 1.5 seconds with a cooling roll at 30 ° C. for 1.5 seconds. The production conditions and evaluation results of the film of Example 1 are shown in Table 1.

(Example 2)
A film was obtained in the same manner as in Example 1 except that the heating temperature on the heating roll was 80 ° C. The production conditions and evaluation results of the film of Example 2 are shown in Table 1.

(Example 3)
A film was obtained in the same manner as in Example 1 except that the heating temperature on the heating roll was 90 ° C. The production conditions and evaluation results of the film of Example 3 are shown in Table 1.

Example 4
A film was obtained in the same manner as in Example 1 except that the heating temperature on the heating roll was changed to 110 ° C. The production conditions and evaluation results for the film of Example 4 are shown in Table 1.

(Example 5)
A film was obtained in the same manner as in Example 1 except that the film forming speed was 90 m / min. The production conditions and evaluation results for the film of Example 5 are shown in Table 1.

(Example 6)
A film was obtained in the same manner as in Example 1, except that the block polypropylene resin was changed to BC3HF (melt flow rate (MFR) 8.5) manufactured by Nippon Polychem Co., Ltd. The production conditions and evaluation results of Example 6 film are shown in Table 1.

(Example 7)
A film was obtained in the same manner as in Example 1 except that 100% by weight of the block polypropylene resin was changed to 90% by weight of the block polypropylene resin and 10% by weight of polypropylene homopolymer (WF836DG3, manufactured by Sumitomo Chemical Co., Ltd.). . The production conditions and evaluation results for the film of Example 7 are shown in Table 1.

(Comparative Example 1)
A film was obtained in the same manner as in Example 1 except that the preheating with the preheating roll was not performed and the heating temperature with the heating roll was changed to 30 ° C. The production conditions and evaluation results of the film of Comparative Example 1 are shown in Table 1.

(Comparative Example 2)
A film was obtained in the same manner as in Example 1 except that the preheating with the preheating roll was 60 ° C. and the heating temperature with the heating roll was 65 ° C. The production conditions and evaluation results of the film of Example 2 are shown in Table 1.

(Comparative Example 3)
A film was obtained in the same manner as in Example 1 except that the cooling temperature with the cooling roll was 70 ° C. and the heating temperature with the heating roll was 30 ° C. The production conditions and evaluation results of the film of Comparative Example 3 are shown in Table 1.

(Comparative Example 4)
A film was obtained in the same manner as in Example 1 except that 100% by weight of the block polypropylene resin was changed to 10% by weight of the block polypropylene resin and 90% by weight of the polypropylene homopolymer (WF836DG3, manufactured by Sumitomo Chemical Co., Ltd.). It was. The production conditions and evaluation results for the film of Comparative Example 4 are shown in Table 1.

(Comparative Example 5)
A film was obtained in the same manner as in Example 1 except that 100% by weight of the block polypropylene resin was changed to 40% by weight of the block polypropylene resin and 60% by weight of the polypropylene homopolymer (WF836DG3, manufactured by Sumitomo Chemical Co., Ltd.). It was. The production conditions and evaluation results of the film of Comparative Example 5 are shown in Table 1.

  As is clear from Table 1, the films of Examples 1 to 7 satisfied all the constituent requirements of the present invention, so that good results were obtained in all evaluation items. On the other hand, since the film of Comparative Example 1 has a thermal shrinkage rate in the MD direction outside the range of the present invention, the adhesive coating property is inferior, and the film of Comparative Example 2 has a heating elongation rate in the MD direction of the present invention. Since the film of Comparative Example 3 is out of the range of the present invention, the tensile elasticity modulus in the MD and TD directions and the heat shrinkage rate in the TD direction are outside the range of the present invention. The films of Comparative Examples 4 and 5 were inferior in releasability, and the content of the block polypropylene resin and the tensile elastic modulus in the MD and TD directions were outside the scope of the present invention, and therefore inferior in lamination and releasability. In the film of Comparative Example 4, wrinkles on the rolls were also generated.

  The surface protective film of the present invention is excellent in adherend protection after processing, has little transferability of additives, and is excellent in adhesive applicability and adhesion processability and peelability to adherends. Therefore, it is extremely useful as a protective film in various fields.

Claims (4)

  A film for protecting a surface comprising a polypropylene resin substantially containing no crystal nucleating agent, antiblocking agent, and lubricant and containing 70% by weight or more of a block polypropylene resin, wherein the film has a tensile force in the TD direction and MD direction. Both the elastic modulus is 500 to 650 MPa, the breaking elongation in the TD direction and the MD direction of the film is both 500% or more, and the thermal shrinkage rate at 120 ° C. in the TD direction and the MD direction of the film is 0 to 1. The film for surface protection characterized by being 0.0% and having a heating elongation in the TD direction and MD direction of 0 to 5.0%.   The surface protective film according to claim 1, wherein at least one surface of the film is subjected to a surface treatment.   The surface protective film according to claim 1, wherein an adhesive layer is provided on at least one side of the film.   The melt-extruded polypropylene resin film is brought into contact with a cooling roll to be cooled and solidified, preheated, then heated to 70 to 120 ° C. with a heating roll, and subsequently cooled to 35 ° C. or less with a cooling roll. The manufacturing method of the film for surface protection in any one of claim | item 1-3.

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