JP2009102629A - Polypropylene-based resin film for surface protection and surface protecting film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene-based resin film which has excellent heat resistant dimensional stability, scarcely contains fisheyes, has suitable transparency, and has good film handleability in spite of substantially not containing a lubricant or an anti-blocking agent, and is suitable as, for example, a base film for a protective film, and to provide a protective film comprising the polypropylene-based resin film and an adhesive layer disposed thereon. <P>SOLUTION: The polypropylene-based resin film is essentially composed of a polypropylene-based resin and contains ≤100 ppm crystal nucleus agent and has 30-65% film crystallinity and birefringence (Δn) of 4×10<SP>-3</SP>to 2.5×10<SP>-3</SP>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface-protective polypropylene-based resin film and a surface protective film, and in particular, has high thermal deformation resistance and flatness at high temperatures, and is excellent in processing suitability such as adhesive processing, and an additive. The present invention relates to a surface-protective polypropylene-based resin film that is suitable for the surface protection of various articles, and a surface-protective film using the surface-protective polypropylene-based resin film. is there.

  Polypropylene-based unstretched films have good transparency and are inexpensive, and are therefore widely used as base materials for surface protection films for the purpose of protecting the surface of various packaging materials such as food packaging and various articles.

For example, even in the surface protection film field, a surface protection film is attached to the surface of a metal plate, decorative plate, resin plate, glass plate, etc. to prevent surface scratches, dirt and rust that tend to occur during transportation and processing. Method (for example, refer to Patent Documents 1 to 3), for example, scratches, dust adhesion, contamination during processing and assembly of electronic, precision products, components and related members such as related materials such as liquid crystal panels and polarizing plates As a coating surface protection film for protecting a coating film on an automobile body from acid rain, dust, dust, etc. during transportation and storage of the vehicle, for example, (For example, see Patent Documents 6 and 7, etc.) For example, as a method of partially plating the connection terminal portion of the flexible printed circuit board, an adhesive film is attached to the non-plated portion and the mask is used. Then, use in plating and etching processes such as a method of plating and a method of protecting a resist film or etching resistance film provided on an unetched surface in an etching process at the time of manufacturing a shadow mask (see, for example, Patent Documents 8 and 9) ), A method for protecting a surface of a semiconductor element by laminating a film on a surface without a circuit of the semiconductor element, and simplifying a process when assembling a semiconductor device (for example, see Patent Documents 10 and 11, etc.) Used in the field.
JP 2003-119435 A JP 2003-213229 A JP 2005-281328 A Japanese Patent Laid-Open No. 10-309781 JP-A-11-165368 JP-A-8-143829 Japanese Patent Laid-Open No. 2001-121661 JP-A-11-291411 Japanese Patent Laid-Open No. 11-302611 JP 2004-63551 A JP 2004-142430 A

  The surface protective film is generally used by laminating an adhesive layer on the surface of a base film and fixing it to the surface of an object to be protected using the adhesive force of the adhesive layer. In recent years, with the expansion of applications, demands for quality and cost reduction have become stronger, and there is a demand for a base film having excellent adhesive processability. 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 demand for dimensional stability at high temperatures (hereinafter, also simply referred to as heat-resistant dimensional stability) that suppresses the occurrence of hot flame during processing.

Regarding the surface protective film, there is no disclosure of the above-mentioned technology for improving the heat-resistant dimensional stability, but a composition in which an aromatic organophosphate metal salt is blended with a specific polypropylene resin has a cooling roll temperature of 40. A polypropylene resin film that is excellent in workability and dimensional stability in secondary processing such as high-speed film formation and metal deposition by extrusion molding at -50 ° C. and suitable for fiber packaging and food applications has been disclosed. (See Patent Document 12).
JP-A-10-298367

In addition, the polypropylene resin film contains minute foreign matter called fish eye. For example, the definition of fish eye is written in Polymer Editorial Board, Polymer Dictionary, Taiseisha, 2000, 6th edition, P337, etc. A fish eye refers to a small spherical shape or the like formed in a film product. The name was given because there are many things that have transparency like fish eyes. There are various types such as unmelted lumps resulting from insufficient kneading of the molding material, lumps due to gelation of a part of the raw material, lumps due to partial deterioration of the material during molding, and those with foreign matter as the core. The fish eye here excludes those with foreign matter as the core. Examples of the foreign matter include cellulose, dust, metal pieces, resin carbide, plastics of different types, lint, and pieces of paper. For example, when packaging with a film containing a large amount of fish eyes, the fish eyes can be seen with the naked eye, which reduces the product image of the package, which is not preferable. With regard to the fish eye, in recent years, market demands have become stricter along with the increasing safety orientation of consumers. For example, even if it is not visible to the consumer under normal conditions, such as when used as an inner layer material for a paper pack, the paper pack will be cut out for collection to the consumer's eyes. As a result, phenomena such as raising anxiety about safety have begun to appear.
In addition, when used as a transparent packaging bag, fish eyes may stand out as foreign matter depending on the color and form of the contents. These market requirements require strict management. Moreover, also in the above-mentioned protective film use, since the said external appearance defect reduces the product image of the goods protected, there exists a strong request of mixing suppression. In particular, for example, in the case of a protective film for plating, if the fish eye is present, a protrusion is formed in a portion where the fish eye is present on the film, and adhesion failure occurs between the protrusion and an object to be protected. A space is created between the object and the object, and the plating solution enters the space and the protective effect is reduced. Therefore, it is necessary to reduce it as much as possible. In the case of a protective film for protecting the LCD panel, the fish eye on the surface of the protective film may be damaged by the unevenness or rubbing of the fish eye when pressed on the surface in contact with the LCD panel. That is a problem. Recently, liquid crystal plates have been inspected with a protective film for protecting the liquid crystal plate. If fish eyes are present, it may be determined that the liquid crystal plate itself is a defect. The development of films such as grades and low fish eye grades is required.

  With respect to the surface protective film, there is no disclosure of a technique for suppressing the above fish eye, but a technique for suppressing the fish eye contamination of the polypropylene resin film is disclosed.

For example, a method for reducing the fish eye content in the raw resin has been disclosed (see, for example, Patent Documents 13 to 15). Although this method is effective as a method for reducing fish eyes, since fish eyes are also produced by a melt extrusion process or the like, it may be difficult to meet market demands only with this method.
JP-A-6-93061 JP 7-233291 A JP 2003-62954 A

In addition, the present inventors have disclosed a technique for reducing fish eyes by melt extrusion at a low temperature (see Patent Documents 16 and 17). Although the method of the present invention is an effective method for reducing fish eyes, there is a problem that it is necessary to use a limited film-forming machine in order to suppress the deterioration of thickness unevenness of the film obtained by low-temperature extrusion. Have.
JP 2005-178250 A JP-A-2005-179552

Moreover, the polypropylene resin composition which can reduce a fish eye is disclosed by using a phenolic antioxidant and sulfur type antioxidant as antioxidant (refer patent document 18). The method of the present invention is also an effective method for reducing fish eyes, but as shown in the examples, it is intended for fish eyes having a size of 0.2 mm or more, and the number of fish is 15 to 20 / m ² . Fisheye is included and further improvements are needed to meet the high demands of the market in recent years. For example, in the protective film for plating disclosed in Patent Document 8 and the like, the number of fish eyes of 0.2 mm or more is required to be substantially 0 as the number per area, and Small fisheye reduction is required.
JP 2003-268172 A

Also, a polypropylene-based resin film with a large amount of crystal nucleating agent added has been proposed for the purpose of improving the heat-resistant dimensional stability of the film (Patent Document 19). Since the residence time during extrusion of the resin becomes relatively long, there is an effect of improving the crystallinity when the resin is cooled, but fish eyes are generated due to aggregation and decomposition of the crystal nucleating agent in the film. Not practical.
Japanese Patent Application No. 2006-98227

Further, a technique combining the technique approximated to Patent Document 12 and the technique approximated to Patent Document 18, that is, a polypropylene resin composition containing a crystal nucleating agent and two kinds of antioxidants, and a molding formed by molding the same A body is disclosed (see Patent Documents 20 and 21).
JP 2000-109519 A JP 2000-248147 A

  In the technique disclosed in Patent Document 20, improvement of the heat distortion temperature is shown. Further, in the technique disclosed in Patent Document 21, an effect of improving impact resistance at low temperatures is shown. However, no mention is made of the effects intended by the present invention. For example, although the fish eye is not mentioned at all, the composition of the antioxidant that greatly affects the suppression of the fish eye is similar to the technique of Patent Document 18, and the fish described above is similar to the technique of Patent Document 18. It is assumed that it does not meet the high market demand for eye.

In recent years, attention has been focused on the fact that acrylate-based antioxidants exhibit a good antioxidant effect when added in a small amount (for example, see 22 to 25).
JP 58-84835 A Japanese Patent Laid-Open No. 1-168643 Japanese Patent Laid-Open No. 2001-114953 JP 2002-302579 A

In the above-mentioned Patent Document 24, regarding a biaxially stretched polypropylene resin film using a homopolypropylene resin, two types of antioxidants, an acrylate antioxidant and a phenol antioxidant, or an acrylate antioxidant, Examples are disclosed in which three types of antioxidants, a phenolic antioxidant and a phosphorus antioxidant, are used in combination, but an acrylate type is used as compared with the case of using a phenolic antioxidant or a phosphorus antioxidant. The use of an antioxidant only shows the effect of suppressing polymer degradation.
In addition, in the above-mentioned Patent Document 25, an example in which two types of antioxidants, an acrylate-based antioxidant and a phosphorous acid-based antioxidant are used in combination, is disclosed, but when a phenol-based antioxidant is used In contrast, the use of acrylate antioxidants only shows the effect of suppressing odor.

  The present invention is excellent in heat-resistant dimensional stability and flatness at the production level, has small thickness unevenness, has little fish eye at the production level, and has good transparency. For example, for surface protection suitable as a base film of a protective film An object of the present invention is to provide a protective film in which an adhesive layer is provided on a polypropylene resin film and the surface protecting polypropylene resin film.

  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.

That is, the present invention is a surface-protective polypropylene-based resin film containing a polypropylene-based resin as a main component, wherein a crystal nucleating agent is added in an amount of 100 ppm or less, and the crystallinity of the film is 30 to 65. %, The birefringence (Δn) is 0.4 × 10 ^{−3 to} 2.5 × 10 ⁻³ , and the thickness variation rate of the film is 1 to 10%.
In this case, the thickness variation rate of the film is preferably 1 to 10%.
In this case, the content of the antiblocking agent in the film is preferably 50 ppm or less, and the blocking resistance is preferably 10 mN or less.
In this case, the number of fish eyes having a maximum diameter of 0.2 mm or more in the film is 0 / m ² and the number of fish eyes having a maximum diameter of 0.1 mm or more and less than 0.2 mm is 100 / m ^2. The following is preferable.
In this case, it is preferable that the Young's modulus in the vertical direction at 23 ° C. of the film is 500 Mpa or more.
In this case, the impact strength at 23 ° C. of the film is preferably 0.6 J or more.
Further, in this case, it is preferable that at least one acrylate-based antioxidant and at least one antioxidant selected from a phosphorus-based antioxidant and a phenol-based antioxidant are included.
Furthermore, in this case, the film is made of a polypropylene random copolymer resin having an α-olefin content of 5% by mass or less and a block copolymer polypropylene tree having a 20 ° C. xylene soluble part amount of 3 to 50%. Is preferred.
Moreover, this invention is a surface protection film which provides an adhesive layer in the at least single side | surface of said polypropylene resin film for surface protection.

Since the polypropylene resin film for surface protection of the present invention is excellent in heat-resistant dimensional stability, for example, it is suitable for secondary processing such as adhesive processing, and is particularly subjected to treatment such as drying at a high temperature around 130 ° C. In addition, since the occurrence of hot stagnation and film sagging is suppressed, the productivity of the secondary processing can be improved, and the generation of defective products due to hot sag and film sagging can be suppressed.
Moreover, it is preferable that the polypropylene resin film of the present invention does not substantially contain an antiblocking agent. For example, when a film containing an antiblocking agent is run, the antiblocking agent falls off due to wear or the like. Therefore, the contamination and the occurrence of troubles due to the fallout are suppressed. In addition, despite the fact that it contains substantially no lubricant or antiblocking agent, the surface roughness is appropriate, the film has excellent slipperiness and blocking resistance, and is excellent in rigidity. Is excellent.
Moreover, it is preferable that the polypropylene resin film for surface protection of the present invention does not substantially contain a lubricant. For example, when used as a base film for a packaging bag or a protective film, the surface-protected polypropylene resin film is to be packaged or protected. Since there is no transfer of the lubricant, contamination of these packages and protected objects is suppressed.
Moreover, since it is excellent in transparency, it is excellent in the visibility of a to-be packaged object or a to-be-protected body. In addition, since the fish eye is highly mixed, the appearance failure due to the fish eye, for example, when used as a base film of a protective film, penetration of the plating solution due to the above-mentioned adhesion failure to the protective part It is possible to suppress the occurrence of such troubles. In addition, despite the improved heat-resistant dimensional stability described above, it has excellent impact strength, and the impact resistance added by being made of block polypropylene resin is maintained. High reliability when used as a film. Therefore, it can be suitably used as a packaging for articles such as foods and precision parts, which are apt to be contaminated by films, and as a protective film for various precision parts.
Moreover, since the protective film of the present invention is based on the above-mentioned polypropylene resin film for surface protection, a protective film utilizing the characteristics of the above-mentioned base film can be obtained. It can be suitably used as a protective film in various precision products and parts that are strongly required to be suppressed and in the processing and assembly processes of the products and parts.

The polypropylene-based resin film of the present invention contains a polypropylene-based resin as a main component. Preferably, the film preferably contains 70% by weight or more of polypropylene-based resin, and more preferably 80% by weight or more.
The polypropylene resin used in the present invention can be used by mixing one or two of homopolypropylene resin, random copolymerized polypropylene resin copolymerized with ethylene and other α-olefins, and block copolymerized polypropylene resin. .
From the viewpoint of transparency, it is preferable to use a homopolypropylene resin or a random copolymerized polypropylene resin copolymerized with ethylene or other α-olefin. In order to improve impact resistance and slipperiness, particularly blocking resistance, it is preferable to use a block copolymer polypropylene resin in combination with these various polypropylene resins, and the mixing ratio is homopolypropylene resin, ethylene or other α-olefin. It can adjust arbitrarily with respect to the copolymerized random copolymer weight.

Although it does not specifically limit regarding the composition of said polypropylene-type resin, If it is a homo polypropylene resin or a random copolymer polypropylene resin, alpha-olefin content will be 5 mass% or less from a heat resistant dimensional stability viewpoint. Polypropylene random copolymer resins are preferred.
Moreover, if it is block copolymerization polypropylene resin, what is 3 to 50% of 20 degreeC xylene soluble part is preferable from a viewpoint of impact resistance, slipperiness, and blocking resistance. Furthermore, the range of 5 to 30% is preferable.

A small amount of ethylene copolymer elastomer, ionomer, and other master batches may be added for various purposes.
Examples of the ethylene copolymer elastomer include an ethylene-propylene copolymer elastomer.
The intrinsic viscosity of the whole polypropylene resin is 1.5 to 4.0, the intrinsic viscosity of the 20 ° C. xylene soluble part is 1.0 to 4.0, and the intrinsic viscosity of the 20 ° C. xylene insoluble part is 1.0 to 4. Those that are zero are preferred. The melt flow rate of the polypropylene resin used in the present invention is preferably 2 to 20 g / 10 min at 230 ° C.

  The xylene-soluble content of the entire polypropylene resin is preferably 10% by weight or less, more preferably 7% by weight or less.

  The polypropylene resin film for surface protection of the present invention can contain a crystal nucleating agent at 100 ppm or less. If the content exceeds 00 ppm of the crystal nucleating agent, depending on the melt extrusion conditions of the resin, the fish eye in the film tends to increase, which causes a problem. 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.

  Examples of the crystal nucleating agent include, but are not limited to, a crystal nucleating agent mainly composed of a metal salt of rosin, a sorbitol-based crystal nucleating agent, and a crystal nucleating agent composed of an aromatic organophosphate metal salt.

  In addition, the polypropylene resin film for surface protection of the present invention may be a polypropylene resin film that has reached a desired crystallinity (30 to 65%) by a production method without containing any crystal nucleating agent. The manufacturing method may be achieved by raising the temperature of the cooling roll when the molten resin is taken and cooled and solidified, or by heat treatment (annealing).

The surface-protective polypropylene resin film of the present invention has a film crystallinity of 30 to 65% according to a measurement method described later. If the crystallinity is less than 30%, the heat-resistant dimensional stability is inferior, and it is not preferable because the film is liable to be flat when it is processed in a later step, resulting in poor flatness. On the other hand, when the crystallinity exceeds 65%, the transparency of the film is remarkably deteriorated. 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.

Moreover, the polypropylene resin film for surface protection of the present invention has a birefringence (Δn) of 0.4 × 10 ^{−3 to} 2.5 × 10 ⁻³ . When the birefringence is less than 0.4 × 10 ⁻³ , the film is likely to be damaged or stretched, and thus the flatness becomes poor and the heat-resistant dimensional stability is inferior. On the other hand, when the birefringence index exceeds 2.5 × 10 ⁻³ , the impact resistance is remarkably lowered and the mechanical properties of the film itself are deteriorated. From the viewpoint of maintaining heat-resistant dimensional stability and flatness, the birefringence of the film is preferably 0.6 × 10 ⁻³ or more, and more preferably 0.8 × 10 ⁻³ or more. On the other hand, from the viewpoint of maintaining the mechanical properties of the film, the birefringence of the film is preferably 2.3 × 10 ⁻³ or less, and more preferably 2.2 × 10 ⁻³ or less.

  Moreover, the polypropylene resin film for surface protection of this invention is the range whose thickness fluctuation rate of a film is 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 and the economy is significantly reduced, which 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%.

  Moreover, it is preferable that the content of antiblocking agents, such as inorganic and / or organic microparticles | fine-particles, in the film for surface protection polypropylene resin films of this invention is 50 ppm or less. The content of the anti-blocking agent is more preferably 10 ppm or less, and particularly preferably the detection limit or less by a usual quantitative method such as ash or elemental analysis. That is, it is preferable not to contain an antiblocking agent substantially. Here, substantially not containing an antiblocking agent has the same meaning as in the case of the above-mentioned lubricant. By this measure, the anti-blocking agent is prevented from falling off due to film abrasion in the film production and secondary processing steps, so that contamination, troubles, and the like due to the fall-off are suppressed.

  It is important that the polypropylene resin film for surface protection of the present invention has a content of a lubricant such as polyethylene wax, calcium stearate, erucamide, ethylenebiserucamide in the film of 50 ppm or less. The content of the lubricant is more preferably 10 ppm or less, and particularly preferably the detection limit or less by a usual quantitative method such as elemental analysis or extraction method. That is, it is preferable that substantially no lubricant is contained. Here, “substantially containing no lubricant” means forming a film without positively adding the lubricant. The above range is to include that there is a case where a minute amount is mixed due to brand switching or the like at the time of manufacturing a raw material polymer or film without positively adding a lubricant, and it is a preferable embodiment that substantially does not contain a lubricant. is there. In the method of blending the lubricant and improving the slipperiness of the film due to the countermeasure, the migration of the lubricant to the film surface and the contamination of the packaged object or the protected object due to the subsequent transfer to the packaged object or the protected object occur. It is blocked and the clarity of the article to be packaged and the object to be protected is maintained.

In the present invention, the polypropylene resin film for surface protection of the present invention preferably has 0 fisheye / m ² having a maximum diameter of 0.2 mm or more in the film. Furthermore, it is preferable that the fisheye having a maximum diameter of 0.1 mm or more and less than 0.2 mm is 100 pieces / m ² or less. The number of fish eyes having a maximum diameter of 0.1 mm or more and less than 0.2 mm is most preferably 0 / m ² or less, but the above range is preferable in view of economic efficiency, market demand, and the like. 2-80 pieces / m ² or less is more preferable, and 2-60 pieces / m ² or less is more preferable. By this correspondence, when it is used as a base film of a protective film, for example, when it is used as a base film of a protective film, it is possible to suppress the occurrence of troubles due to the penetration of the plating solution into the protective part due to the above-mentioned poor adhesion.

  The means for achieving the above characteristics is not limited, but the antioxidant may be optimally blended as described later.

  In the present invention, the polypropylene resin film for surface protection of the present invention preferably has a Young's modulus in the longitudinal direction at 23 ° C. of 650 Mpa or more. 680 Mpa or more is more preferable, and 720 Mpa or more is more preferable. 650 Mpa is not preferable because the handleability of the film is lowered. By this measure, it is possible to suppress a decrease in the handleability of the film due to the absence of the above-mentioned lubricant or antiblocking agent. The upper limit is preferably about 1000 Mpa from the balance with other characteristics.

  In the present invention, the surface-protective polypropylene resin film of the present invention preferably has an impact strength at 23 ° C. of 0.6 J or more. 0.7J or more is more preferable. In general, when the rigidity and heat-resistant dimensional stability described above are improved, the impact strength moves in a decreasing direction. When the impact strength is reduced, the reliability of the impact resistance during use when used as a packaging bag, a protective film or the like is lowered. Therefore, it is preferable to satisfy the above-mentioned characteristics while giving the above-mentioned characteristics. The upper limit is preferably about 1.0 J from the balance with other characteristics.

  The method for imparting the impact strength is not limited, but is greatly affected by the above-described ethylene content. It is preferably achieved as the overall effect of the preferred embodiments described herein including the ethylene content.

In the present invention, as described above, it is preferable not to add a lubricant or an anti-blocking agent that is carried out in a normal polypropylene resin film, but in that case, it is necessary to suppress deterioration of the slipperiness and blocking property of the film. is there. The correspondence is preferably carried out by the above-described resin composition, in particular, film surface protrusions with a sea / island structure made of a block copolymer resin or an ethylene copolymer elastomer.
At this time, it is preferable that it is 10 mN or less by the evaluation mentioned later as an anti-blocking characteristic of the film of this invention. More preferably, it is 7 mN or less.
On the other hand, the formation of film surface protrusions due to the sea / island structure with the block copolymer resin causes a decrease in transparency of the film. Therefore, in this method, the effect of improving slipperiness and blocking resistance due to the formation of surface protrusions and transparency Ensuring sex is a contradictory phenomenon. Therefore, the haze value of the film is an important factor. For example, the use of a block copolymer resin having a high ethylene content as disclosed in Patent Document 20 is effective in improving the above-described slipping property and blocking resistance. This is not preferable because the value is increased and the transparency is deteriorated, and the visibility of the article to be packaged or the object to be protected is lowered.
Therefore, in the present invention, it is important to set the haze value of the film to 40% or less. 35% or less is preferable and 30% or less is more preferable. By making the haze value 40% or less, the visibility of the article to be packaged or the object to be protected is improved, and when used as a packaging bag material, the contents of the article to be packaged can be easily confirmed. Further, when used as a material for a surface protective film, for example, it is possible to inspect an object to be protected while the surface protective film is adhered. On the other hand, when the haze value exceeds 40%, the transparency is deteriorated and the visibility of the article to be packaged or the object to be protected is lowered, which is not preferable. On the other hand, the lower limit of the haze value is preferable because the transparency is improved. However, 5% or more is preferable and 10% or more is more preferable in terms of imparting slipperiness by the above method.

  The acrylate antioxidant of the present invention is an antioxidant having a phenol derivative containing an acrylate residue in the molecule. Examples of the acrylate compound include 2,4-di-t-amyl-6- [1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl] phenyl acrylate, 2,4-di-t. -Amyl-6- [1- (3,5-di-t-amyl-2-hydroxyphenyl) butyl] phenyl acrylate, 2,4-di-t-amyl-6- [1- (3,5-di -T-amyl-2-hydroxyphenyl) propyl] phenyl acrylate, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, and the like.

  Preferably, 2,4-di-t-amyl-6- [1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl] phenyl acrylate and 2-t-butyl-6- (3- t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate.

  As said acrylate compound, it can select from a commercially available thing suitably and can be used. For example, Sumitizer GM (registered trademark) manufactured by Sumitomo Chemical Co., Ltd., which is 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2,4 -Sumitizer GS (registered trademark) manufactured by Sumitomo Chemical Co., Ltd., which is di-t-amyl-6- [1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl] phenyl acrylate Can do. In particular, it is preferable to use a Sumilizer GS (registered trademark).

Although the compounding quantity of the said acrylate antioxidant in this invention is not limited, The range of 100-1000 ppm is preferable with respect to the above-mentioned all polypropylene resin composition. 200 to 800 ppm is more preferable, and 300 to 700 ppm is more preferable. When it exceeds 1000 ppm, the contamination of the cooling roll increases in the film forming step, which is not preferable. The film is also unfavorable because it dyes a pale yellow color unique to antioxidants. On the contrary, if it is less than 100 ppm, the combined effect described later is decreased, which is not preferable. It is preferable to lower the upper limit of the blending amount of the acrylate antioxidant alone than the above two kinds of antioxidants. The acrylate antioxidant is a polypropylene resin rubber compared to other antioxidants. Due to the high solubility in the component, it is more distributed to the rubber component in the film, and the rubber component portion has a slower crystallization rate by the cooling roll than the base resin, so that the rubber is in contact with the cooling roll. It is surmised that the above-mentioned acrylate antioxidant distributed to the components easily migrates to the cooling roll, and thus is caused by increasing the contamination degree of the cooling roll.
For example, this is a unique phenomenon that occurs in the present invention that does not occur in the film formation using the homopolypropylene resin disclosed in Patent Document 23 and the like described above.

  Specific examples of the phosphorus antioxidant include a heat stabilizer containing a trivalent phosphorus atom in the molecule, and the phosphorus atom has at least one P—O—C bond. For example, tributyl phosphite, trioctyl phosphite, trilauryl phosphite, tristearyl phosphite, tridecyl phosphite, tricresyl phosphite, tricyclohexyl phosphite, triphenyl phosphite, trilauryl thiophosphite, tris ( 2-ethylhexyl) phosphite, tris (isodecyl) phosphite, tris (tridecyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, tris (butoxyethyl) phosphite, tris (nonylphenyl) Phosphite, tris (3,5-di-t-butyl-4-hydroxyphenyl) phosphite, tris [4,4′-isopropylidenebis (2-t-butylphenol)] phosphite, tris (1,3- Gieste (Royloxyisopropyl) phosphite, 2-ethylhexyl diphenyl phosphite, decyl diphenyl phosphite, phenyl di-2-ethyl hexyl phosphite, phenyl didecyl phosphite, phenyl diisodecyl phosphite, phenyl di (tridecyl) phosphite, diphenyl nonyl phosphite, Diphenyl isooctyl phosphite, diphenyl isodecyl phosphite, diphenyl mono (tridecyl) phosphite, dibutyl hydrogen phosphite, 4,4′-isopropylidene diphenol alkyl (C12 to C15) phosphite, 4,4′-butylidenebis ( 3-methyl-6-tert-butylphenyl) di-tridecyl phosphite, 2,2-methylenebis (4,6-di-tert-butylphenyl) octyl Sufite, 2,2'-ethylidenebis (4,6-di-t-butylphenol) fluorophosphite, bis (2,4-di-t-butyl-6-methylphenyl) .ethyl phosphite, 4,4 ' -Isopropylidenebis (2-t-butylphenol) di (nonylphenyl) phosphite, distearyl pentaerythritol diphosphite, di (nonylphenyl) pentaerythritol diphosphite, diphenylpentaerythritol diphosphite, phenyl 4, 4'-isopropylidenediphenol pentaerythritol diphosphite, bis (4,6-di-t-butylphenyl) pentaerythritol diphosphite, bis (2,6-di-t-butyl-4-methylphenyl) Pentaerythritol diphosphite, phenyl -Bisphenol A pentaerythritol diphosphite, tetraphenyldipropylene glycol diphosphite, tetra (tridecyl) -1,1,3-tris (2-methyl-5-tert-butyl-4-hydroxyphenyl) butanediphos Phyto, tetra (C12-C15 mixed alkyl) -4,4′-isopropylidene diphenyl diphosphite, tetra (tridecyl) -4,4′-butylidenebis (3-methyl-6-tert-butylphenol) diphosphite, tetrakis (4 , 6-Di-t-butylphenyl) -4,4′-biphenylene diphosphonite, tetrakis (2-methyl-4,6-di-t-butylphenyl) -4,4′-biphenylene diphosphonite Bis (octylphenyl) -bis [4,4′-butylidenebis (3-methyl) 6-t-butylphenol)] • 1,6-hexanediol diphosphite, hydrogenated-4,4′-isopropylidene diphenol polyphosphite, 9,10-di-hydro-9-oxa-9-oxa- 10-phosphaphenanthrene-10-oxide, 2-[{2,4,8,10-tetrakis (1,1-dimethylethyl) dibenzo (D, F) (1,3,2) -dioxaphos Fephin-6-yl} oxy] -N, N-bis [2-[{2,4,8,10-tetrakis (1,1-dimethylethyl) dibenzo (D, F) (1,3,2) -Dioxaphosphine-6-yl} oxy] ethyl] ethanamine, 1,1,3-tris (2-methyl-4-di-tridecylphosphite-5-t-butylphenyl) butane, 3,4 , 5,6-Tetraben Like 1,2-oxa phosphane-2-oxide.

  Preferably, those having no pentaerythritol skeleton, tris (2,4-di-t-butylphenyl) phosphite, tris (3,5-di-t-butyl-4-hydroxyphenyl) phosphite, Bis (2,4-di-t-butyl-6-methylphenyl) .ethyl phosphite, tetrakis (2-methyl-4,6-di-t-butylphenyl) -4,4'-biphenylenediphosphonite It is.

  Commercially available products can also be used as the phosphorus-based antioxidant used in the present invention. For example, Irgafos 168 (manufactured by Ciba Specialty Chemicals), Irgafos 38 (manufactured by Ciba Specialty Chemicals), GSY- P101 (manufactured by Yoshitomi Fine Chemicals), Ultranox 641 (manufactured by GE Specialty Chemicals), and the like.

  Although the compounding quantity of the said phosphorus antioxidant in this invention is not limited, The range of 500-5000 ppm is preferable with respect to the above-mentioned all polypropylene resin composition. 1000 to 4000 ppm is more preferable, and 1500 to 3000 ppm is more preferable. If it is less than 500 ppm, the effect of using an antioxidant described later decreases, which is not preferable. On the other hand, if it exceeds 5000 ppm, the effect of using an antioxidant described later is saturated, causing film whitening due to the migration of the antioxidant to the film surface, contamination of the cooling roll in the film forming process, and the like. It is not preferable.

  The phenolic antioxidant used in the present invention is an antioxidant having a phenol derivative in the molecule, such as 2,6-di-t-butyl-4-methylphenol, 2,6-di-t. -Butyl-4-ethylphenol, 2,6-dicyclohexyl-4-methylphenol, 2,6-di-t-amyl-4-methylphenol, 2,6-di-t-octyl-4-n-propylphenol 2,6-dicyclohexyl-4-n-octylphenol, 2-isopropyl-4-methyl-6-t-butylphenol, 2-t-butyl-2-ethyl-6-t-octylphenol, 2-isobutyl-4-ethyl -6-t-hexylphenol, 2-cyclohexyl-4-n-butyl-6-isopropylphenol, dl-α-tocopherol, t-butyl Droquinone, 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 4,4'-butylidenebis (3-methyl-6-tert-butylphenol), 4,4'-thiobis (3-methyl-6) -T-butylphenol), 2,2-thiobis (4-methyl-6-t-butylphenol), 4,4'-methylenebis (2,6-di-t-butylphenol), 2,2'-methylenebis [6- (1-methylcyclohexyl) -p-cresol], 2,2′-ethylidenebis (4,6-di-t-butylphenol), 2,2′-butylidenebis (2-t-butyl-4-methylphenol), 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy-3,5 -Di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, triethylene Glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5-di-tert-butyl-4-hydroxy) Phenyl) propionate], 2,2-thiodiethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], N, N′-hexamethylenebis (3,5-di-t -Butyl-4-hydroxy-hydrocinnamide), 3,5-di-t-butyl-4-hydroxybenzylphosphonate-diethyl ester, tris (2,6-dimethyl) 3-hydroxy-4-t-butylbenzyl) isocyanurate, tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate, tris [(3,5-di-t-butyl-4-hydroxy Phenyl) propionyloxyethyl] isocyanurate, tris (4-t-butyl-2,6-dimethyl-3-hydroxybenzyl) isocyanurate, 2,4-bis (n-octylthio) -6- (4-hydroxy-3) , 5-Di-t-butylanilino) -1,3,5-triazine, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, 2,2′-methylenebis (4-Methyl-6-tert-butylphenol) terephthalate, 1,3,5-trimethyl-2,4,6-tris (3,5-di- t-butyl-4-hydroxybenzyl) benzene, 3,9-bis [1,1-dimethyl-2- {β- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy} ethyl]- 2,4,8,10-tetraoxaspiro [5,5] undecane, 2,2-bis [4- (2- (3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy)) ethoxy Phenyl] propane, β- (3,5-di-t-butyl-4-hydroxyphenyl) propionic acid stearyl ester, and the like.

  Preferably, β- (3,5-di-t-butyl-4-hydroxyphenyl) propionic acid stearyl ester, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] Methane, tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4- Hydroxybenzyl) benzene, dl-α-tocopherol, tris (2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate, tris [(3,5-di-tert-butyl-4-hydroxyphenyl) ) Propionyloxyethyl] isocyanurate, 3,9-bis [1,1-dimethyl-2- {β- (3-tert-butyl-4-hydroxy-5-methyl) Butylphenyl) propionyloxy} ethyl] -2,4,8,10-tetra-oxa-spiro [5,5] undecane.

  Commercially available products may be used as the phenolic antioxidant used in the present invention, for example, Irganox 1010 (manufactured by Ciba Specialty Chemicals), Irganox 1076 (manufactured by Ciba Specialty Chemicals), Irganox 1330 (manufactured by Ciba Specialty Chemicals), Irganox 3114 (manufactured by Ciba Specialty Chemicals), Irganox 1425WL (manufactured by Ciba Specialty Chemicals) and the like.

  Although the compounding quantity of the said phenolic antioxidant in this invention is not limited, The range of 500-5000 ppm is preferable with respect to the above-mentioned all polypropylene resin composition. 1000 to 4000 ppm is more preferable, and 1500 to 3000 ppm is more preferable. If it is less than 500 ppm, the effect of using an antioxidant described later decreases, which is not preferable. On the other hand, if it exceeds 5000 ppm, the effect of using an antioxidant described later is saturated, causing film whitening due to the migration of the antioxidant to the film surface, contamination of the cooling roll in the film forming process, and the like. It is not preferable.

  In the present invention, as described above, it comprises at least two antioxidants selected from at least one selected from the group consisting of acrylate antioxidants, phosphorus antioxidants and phenolic antioxidants. However, it is a more preferable embodiment that three types of acrylate antioxidant, phosphorus antioxidant and phenolic antioxidant are used in combination.

  The above three kinds of antioxidants are not limited to one type each. Two or more of each type may be used in combination, and in addition to the above three types of antioxidants, for example, an antioxidant having another structure such as a sulfur-based antioxidant may be further used in combination.

  By using a plurality of the above-mentioned antioxidants in combination, a high level of fisheye mixing suppression effect that cannot be obtained by a combination of conventionally known antioxidants is exhibited.

  Phenol-based antioxidants and phosphorus-based antioxidants have little selectivity for the antioxidant effect with respect to each component of the raw material resin composition described above, but acrylate-based antioxidants are used with the rubber part of the polypropylene-based block copolymer. It is known that the affinity is strong and the tendency to preferentially suppress the deterioration of the rubber part. On the other hand, regarding the generation of fish eyes, the contribution of the deterioration of the rubber part is large. Therefore, it is presumed that the combined use of the above-mentioned plurality of antioxidants led to a significant reduction in fish eyes.

  The method for preparing the polypropylene resin composition containing the antioxidant and the crystal nucleating agent used in the present invention is not particularly limited, and examples thereof include known methods. Examples thereof include a method of heat-melt kneading using a kneader such as a kneader, a Banbury mixer, or a roll, and a method of heat-melt kneading using a single screw or twin screw extruder. Various resin pellets may be dry blended. In the method for preparing the composition, the antioxidant and the crystal nucleating agent may be added directly to the respective powders, or may be added as a master batch previously mixed with the polypropylene resin. When adding as a masterbatch, it may be prepared for each additive or may be prepared by mixing two or more. Moreover, you may implement combining the commercially available resin in which the said additive was mix | blended well. In addition, the composition may be prepared in advance to be supplied to a film forming process and supplied to a film forming extruder, or the components constituting the composition may be supplied to the film forming extruder. It may be supplied and prepared to form a film.

The feature of the method for producing the surface-protective polypropylene resin film of the present invention is as follows:
-Controlling the crystallinity in controlling the cooling conditions of the molten resin-Controlling the draft ratio during taking up of the molten resin and cooling and solidification.

[Control of crystallinity in cooling condition control]
The extruded film of the present invention is an unstretched film formed by a T-die method, and the thickness of the film is not particularly limited, but is generally 1 to 500 μm, and a film having a preferred thickness is necessary. Selected.
Film forming conditions for using the polypropylene resin composition of the present invention as an extruded film are preferably performed at a die temperature of 200 ° C to 250 ° C and a cooling roll temperature of 40 to 65 ° C. 45-60 degreeC is more preferable. If the cooling roll temperature is less than 40 ° C., a crystallinity sufficient for heat-resistant dimensional stability cannot be obtained, which is not preferable. Conversely, when the temperature exceeds 65 ° C., a touch roll mark of the cooling roll is generated, which is not preferable, and the transparency may be extremely lowered. Moreover, although it does not specifically limit about cooling time, The range for 0.5 second or more is preferable. If the cooling time is less than 0.5 seconds, the cooling effect is insufficient, and a touch roll mark of the cooling roll is generated, which is not preferable. On the other hand, the upper limit of the cooling time is not particularly limited from the viewpoint of the crystallinity of the film, but is preferably 5 seconds or less from the viewpoint of economy and productivity.
When a crystal nucleating agent is used in combination as a means for arbitrarily adjusting the degree of crystallinity, it is necessary to add 100 ppm or less because there is a concern about an increase in fish eye of the film as described above. Therefore, the inventors found the control of the crystallinity by controlling the cooling conditions of the molten resin according to the cooling conditions.

[Draft ratio control]
In the extruded film of the present invention, the birefringence of the film can reach a predetermined range by adjusting the draft ratio in the drawing step after melt extrusion to a range of 0.4 to 3.0. It is generally known that 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.
When the draft ratio is less than 0.4, the thickness unevenness of the film increases, and the flatness of the film is deteriorated during the adhesive processing, which is not preferable. On the other hand, when the draft ratio exceeds 3.0, the birefringence exceeds the predetermined range, the impact resistance is remarkably lowered, and the mechanical properties of the film itself are deteriorated.
The conventional unstretched polypropylene film tends to increase the film take-up speed (by reducing the draft ratio) for the purpose of improving the heat-resistant dimensional stability. A polypropylene resin film for surface protection with a good balance of heat-resistant dimensional stability, film flatness, and impact resistance by controlling the degree of conversion and controlling the draft ratio during film formation and take-up within a certain range. I was able to provide it.

  The extruded film of the present invention can be subjected to surface treatment such as corona discharge treatment or flame treatment by a method generally employed industrially.

  In the present invention, it is important that the surface protective film is a surface protective film in which an adhesive layer is provided on at least one surface of the above-described surface protective polypropylene-based resin film. By the correspondence, the characteristics of the polypropylene resin film of the present invention described above can be effectively utilized, and the applicability in a wide field as a protective film is improved. In particular, for example, applications that prevent scratches, adhesion of dirt, contamination, etc. during the processing and assembly of electronic and precision products such as liquid crystal panels and polarizing plates, precision products, parts and related members, and connection of flexible printed circuit boards As a method of partially plating the terminal part, etc., a mask is formed by sticking an adhesive film to the non-plated part and then plating, or a resist film or etching resistance provided on the non-etched surface in the etching process when manufacturing the shadow mask Use in plating and etching processes such as methods for protecting the film, methods for protecting the surface of the semiconductor element by laminating a film on the surface without the circuit of the semiconductor element, and simplifying the process when assembling the semiconductor device, etc. Protection of various precision products and parts that are particularly demanding to suppress contamination and defects, and addition of such products and parts It can be suitably used as a protective film in and assembly process. Further, the polypropylene resin 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, the occurrence of hot stagnation and film sagging is suppressed. It becomes possible to increase the productivity of adhesive processing. Moreover, generation | occurrence | production suppression of the inferior goods resulting from a hot bath or film sagging can be suppressed.

  The kind, thickness, adhesive strength, and the like of the pressure-sensitive adhesive layer are not limited. What is necessary is just to select suitably by market demand. Moreover, the lamination method of this adhesive layer is not limited. Any of the coating method and the extrusion laminating method may be used.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, but may be implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all included in the technical scope of the present invention.

  The measurement and evaluation methods employed in this specification are as follows.

・ Melt flow rate [MFR]
According to JIS K7210, the method of Condition-14 (load 2.16 kg, temperature 230 ° C.
Measured with

(2) Ethylene content The ethylene content was measured by ¹³ C-NMR method according to the method described on page 616 of Polymer Handbook (published by Kinokuniya Shoten in 1995).

(3) 20 ° C. xylene solubles After 5 g of sample is completely dissolved in 500 cc of boiling xylene, the temperature is lowered to 20 ° C. and left for 15 hours. Thereafter, this was separated into a precipitate and a solution, and the filtrate and the precipitate were respectively placed under reduced pressure and dried at 70 ° C. The dried product of the filtrate was taken as a 20 ° C. xylene soluble component, and the ratio was determined.

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

(5) Crystallinity degree of film It measured using the wide-angle essence line diffraction transmission method (RIGAKU RINT2500).

(6) Birefringence (Δn)
Using an Abbe refractometer, the refractive index Nx in the film flow direction and the refractive index Ny in the direction perpendicular to the film flow direction were measured and calculated using the following formula.
Δn = | Nx−Ny |

(7) Thickness fluctuation rate One film sample having a width of 1 m was measured at a pitch of 3 cm in the width direction, and an average thickness was calculated. Next, either the maximum value or the minimum value among the measured film samples was calculated by the following calculation formula using either one having a large difference from the average thickness.
Thickness variation rate (%) = | (average thickness) − (maximum value or minimum value) | / (average thickness) × 100

(8) Blocking resistance In accordance with ATM-D1893-67, a load of 90N was applied to the area of A4 size and left for 2 hours in an atmosphere of 60 ° C. The measurement was performed under the condition of 100 mm / min.

(9) Young's modulus In accordance with JIS K7127, the sample shape conforms to No. 1 type test piece (sample length 200 mm, sample width 15 mm, chuck distance 100 mm), and the crosshead speed is 500 mm / min. The MD direction (film longitudinal direction) was measured at 23 ° C.

(10) Impact strength In accordance with ASTM D3420, the sample is cut to 55 to 60 cm in the vertical direction and 9 to 10 cm in the horizontal direction. Read the strength value when punched using an impact tester in a 23 ° C room to the first decimal place. The operation is repeated 10 times, and the average value is obtained.

(11) Fisheye Cut the molded film 33.3 cm in the flow direction × 30 cm in the direction transverse to the flow direction, place it on the plate irradiated with a fluorescent lamp from under the film, and visually observe it with transmitted light. Measure fish eyes 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.

(12) Resistance to thermal deformation The molded film is cut out in a direction of 5 cm in the flow direction and 25 cm in the direction transverse to the flow direction, and the film piece is horizontally held in a dry heat oven at 120 ° C. with both ends held by a metal frame. And heat-treated for 5 minutes. Immediately after the heat treatment, the film was taken out from the oven and allowed to cool at room temperature for 30 minutes, and then the sag (elongation) state due to the weight of the film itself was visually observed in the following range.
○: No dripping or almost no dripping.
(Triangle | delta): A drooping state is observed slightly.
X: A hanging state is observed.

(13) Workability The occurrence of wrinkles and tarmi was visually observed when the molded film was rolled up into a roll with a width of 1300 mm and a film length of 100 m was wound with a slitter (SXR-140, manufactured by Toshin Co., Ltd.).
○: Wrinkles and tarmi are not generated during running and winding.
Δ: Slight wrinkles and tarmi were observed during running or winding.
X: Wrinkles and tarmi were clearly observed during running or winding.

(Example 1)
Homopolypropylene resin containing 100 parts by weight of a random copolymer polypropylene resin (MFR = 7) having an ethylene content of 0.5% by mass and 5% by weight of Sumizer GS (manufactured by Sumitomo Chemical Co., Ltd.), which is an acrylate antioxidant. 2 parts by weight of a masterbatch resin containing an acrylate antioxidant comprising (MFR = 7) is melt-extruded by a T-die film forming machine, and cooled at a cooling roll temperature of 60 ° C. for 2.0 seconds (film forming speed of 60 m). / Min), and the draft ratio at the time of taking the molten resin is 0.64 (die slip gap: 0.5 mm, die slip outlet molten resin speed: 4.8 m / min, air gap: 8 cm). A 40 μm unstretched film was obtained. The resin temperatures in the supply zone, kneading zone and metering zone of the extruder were set to 230, 240 and 235 ° C, respectively. The results are shown in Table 1.
As shown in Table 1, the polypropylene resin film obtained in this example was good in both the heat distortion heat resistance and the processability, and was high quality.

(Example 2)
30 parts by weight of a random copolymer polypropylene resin (MFR = 7) having an ethylene content of 0.5% by mass, and 0.22 mass of Irgafos 168 (manufactured by Ciba Specialty Chemicals Co., Ltd.) as a phosphorus-based antioxidant % And a rubber component amount containing 0.28% by mass of Irganox 1010 (manufactured by Ciba Specialty Chemicals Co., Ltd.) as a phenolic antioxidant, and an ethylene content of 3.2% A polypropylene resin film of Example 2 was obtained in the same manner as in Example 1 except that 70 parts by weight of block copolymerized polypropylene resin (MFR = 2) was blended. The results are shown in Table 1.
The polypropylene resin film obtained in this example had the same properties as the polypropylene resin film obtained in Example 1 and was of high quality.

(Example 3)
95 parts by weight of a random copolymerized polypropylene resin (MFR = 7) having an ethylene content of 0.5% by mass, 5 parts by weight of an ethylene-propylene copolymer elastomer (Tafmer P0480 manufactured by Mitsui Chemicals), a cyclic organophosphate compound 1% by weight of bis (2,2′-methylene-bis (4,6-di-tert-butylphenyl) phosphate) -aluminum hydroxide salt (Adeka Stub NA-21, manufactured by Asahi Denka Kogyo Co., Ltd.) 1 part by weight of a masterbatch resin (M-1) containing a crystal nucleating agent made of a homopolypropylene resin (MFR = 7) and 5% by weight of Sumizer GS (manufactured by Sumitomo Chemical Co., Ltd.) which is an acrylate antioxidant Contains 1 part by weight of a masterbatch resin containing an acrylate antioxidant made of homopolypropylene resin (MFR = 7) Then, melt extrusion is performed with a T-die film forming machine, a cooling roll temperature of 45 ° C., a cooling time of 3.0 seconds (film forming speed of 40 m / min), a draft ratio of 1.60 at the time of taking the molten resin (die slip) An unstretched film having a thickness of 100 μm was obtained under the film forming conditions of gap: 0.5 mm, die slip outlet molten resin speed: 8.0 m / min, air gap: 8 cm. The resin temperatures in the supply zone, kneading zone and metering zone of the extruder were set to 230, 240 and 235 ° C, respectively. The results are shown in Table 1.
The polypropylene resin film obtained in this example had the same properties as the polypropylene resin film obtained in Example 1 and was of high quality.

(Comparative Example 1)
In the method of Example 2, the polypropylene resin film of Comparative Example 1 was obtained in the same manner as in Example 2 except that the cooling roll temperature was changed to 20 ° C. The results are shown in Table 2.
The polypropylene-based resin film obtained in this comparative example had good transparency, but the crystallinity of the film was lowered, and the quality was poor with poor heat deformation heat resistance.

(Comparative Example 2)
In the method of Example 2, a polypropylene resin film of Comparative Example 2 was obtained in the same manner as in Example 2 except that the cooling roll temperature was changed to 80 ° C. The results are shown in Table 2.
The polypropylene-based resin film obtained in this comparative example was of low quality such that transparency and impact strength were lowered due to extreme crystallization. Moreover, due to heat loss at the time of film formation, touch roll marks are generated or the flatness of the film itself is deteriorated, resulting in a decrease in film quality.

(Comparative Example 3)
In the method of Example 2, a polypropylene resin film of Comparative Example 3 was obtained in the same manner as in Example 2 except that 5 parts by weight of the master batch resin (M-1) containing a crystal nucleating agent was added. The results are shown in Table 2.
The polypropylene resin film obtained in this comparative example had a low quality because the fish eye increased significantly compared to the polypropylene resin film obtained in Example 2.

(Comparative Example 4)
In the method of Example 3, the film forming speed was 16 m / min, the draft ratio when taking the molten resin was 0.25 (die slip gap: 2.0 mm, die slip outlet molten resin speed: 8 m / min, air A polypropylene resin film of Comparative Example 2 was obtained in the same manner as in Example 2 except that the gap was changed to 8 cm. The results are shown in Table 2.
The polypropylene-based resin film obtained in this comparative example has a low quality because the thickness variation rate is deteriorated, the flatness of the film is lowered, the birefringence is smaller than the lower limit, the elongation is easier, and the processability is inferior. It was.

  The results are shown in Tables 1 and 2.

Since the polypropylene-based resin film of the present invention is excellent in heat-resistant dimensional stability, for example, it is excellent in proper secondary processing such as adhesive processing. Since generation | occurrence | production is suppressed, the improvement of productivity of this secondary processing and generation | occurrence | production suppression of the inferior goods resulting from hot metal or a film slack can be suppressed.
In addition, since the polypropylene resin film of the present invention does not substantially contain an antiblocking agent, for example, when a film containing an antiblocking agent is run, the antiblocking agent falls off due to wear or the like. Can be avoided, so that contamination, failure, etc. due to the fallout are suppressed. Moreover, although the lubricant and the antiblocking agent are not substantially contained, the slipperiness of the film is good and the rigidity is excellent, so that the handleability of the film is excellent.
In addition, since the polypropylene resin film of the present invention does not substantially contain a lubricant, for example, when used as a base film for a packaging bag or a protective film, the lubricant is transferred to an article to be packaged or an object to be protected. As a result, the contamination of these objects to be packaged and the objects to be protected is suppressed.
Moreover, since it has moderate transparency, it is excellent in the visibility of a to-be packaged object or a to-be-protected body. In addition, since the fish eye is highly mixed, the appearance failure due to the fish eye, for example, when used as a base film of a protective film, penetration of the plating solution due to the above-mentioned adhesion failure to the protective part It is possible to suppress the occurrence of such troubles. In addition, despite the improved heat-resistant dimensional stability described above, it has excellent impact strength, and the impact resistance added by being made of block polypropylene resin is maintained. High reliability when used as a film. Therefore, it can be suitably used as a packaging for articles such as foods and precision parts, which are apt to be contaminated by films, and as a protective film for various precision parts.
Moreover, since the protective film of the present invention is based on the polypropylene resin film, a protective film utilizing the characteristics of the base film can be obtained. It can be suitably used as a protective film in various kinds of strong precision products and parts and the processing and assembly processes of the products and parts. Therefore, it is important to contribute to the industry.

Claims (9)

A polypropylene resin film containing a polypropylene resin as a main component, having a crystal nucleating agent of 100 ppm or less, a crystallinity of 30 to 65%, and a birefringence (Δn) of 0. 4 × 10 ^{−3 to} 2.5 × 10 ⁻³ .   2. The polypropylene resin film for surface protection according to claim 1, wherein the thickness variation rate of the film is 1 to 10%.   The surface-protective polypropylene resin film according to claim 1, wherein the content of the antiblocking agent in the film is 50 ppm or less and the blocking resistance is 10 mN or less. The number of fish eyes having a maximum diameter of 0.2 mm or more in the film is 0 / m ² , and the number of fish eyes having a maximum diameter of 0.1 mm or more and less than 0.2 mm is 100 / m ² or less. The polypropylene resin film for surface protection according to claim 1, wherein   2. The polypropylene resin film for surface protection according to claim 1, wherein the film has a longitudinal Young's modulus at 23 ° C. of 500 Mpa or more.   The polypropylene resin film for surface protection according to claim 1, wherein the impact strength of the film at 23 ° C. is 0.6 J or more.   The film comprises at least an acrylate antioxidant and at least one antioxidant selected from a phosphorus antioxidant and a phenolic antioxidant. The polypropylene resin film for surface protection according to 1.   2. The film according to claim 1, wherein the film is made of a polypropylene random copolymer resin having an α-olefin content of 5% by mass or less and a block copolymer polypropylene tree having a 20 ° C. xylene soluble part content of 3 to 50%. A polypropylene resin film for surface protection as described in 1.   A surface protective film comprising a pressure-sensitive adhesive layer on at least one surface of the surface-protective polypropylene resin film according to claim 1.