JP2003261727A - Polypropylene resin composition for heat shrinkable film, heat shrinkable film comprising the resin composition - Google Patents

Abstract

(57) [Problem] A heat-shrinkable film having excellent bending whitening resistance, transparency, hot-slip properties, and scratch resistance during film production, and in which an anti-blocking agent does not fall off during film formation or a slitting step. The present invention provides a polypropylene resin composition for use and a heat-shrinkable film obtained by stretching the composition at least in a uniaxial direction. SOLUTION: Crystalline polypropylene resin (a) 10
The weight average particle diameter is 0.5 to 5 μm with respect to 0 parts by weight.
And the content of the styrene derivative monomer unit is 6
0 to 96% by weight, the content of the radical polymerizable monomer unit is 2 to 38% by weight, the content of the crosslinkable monomer unit is 2 to 38% by weight, and the polymer of the radical polymerizable monomer is refracted. A polypropylene-based resin composition for a heat-shrinkable film containing 0.05 to 1 part by weight of crosslinked polymer beads (b) having a ratio of 1.50 or less, and a heat-shrinkable film obtained by stretching it at least in one axis direction.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polypropylene resin composition for a heat shrinkable film, and a heat shrinkable film obtained by stretching the resin composition in at least one axial direction. More specifically, a polypropylene-based resin composition for heat-shrink film, which is excellent in folding whitening resistance during film production, transparency, hot slip resistance, scratch resistance, and does not drop the anti-blocking agent during steps such as film formation or slitting. And a heat-shrinkable film obtained by stretching the resin composition in at least a uniaxial direction.

[0002]

2. Description of the Related Art Generally, a heat-shrinkable film is used by first covering a single object to be packaged or a plurality of objects to be packaged with the heat-shrinkable film and then heating and shrinking the same. By thus heating and shrinking and using it, the object to be packaged can be fixed / held and packaged.

Heat-shrinkable films generally do not whiten when bent during film production (that is, they have excellent resistance to whitening by bending), transparency, hot slip resistance and scratch resistance, and film formation. It is desired that the anti-blocking agent does not fall off during the process such as time or slitting.

As a method for improving the hot slip property of the heat shrink film, for example, Japanese Patent Application Laid-Open No. 8-269265 discloses a method of adding spherical polymethylmethacrylate, and Japanese Patent Application Laid-Open No. 11-199686. Describes a method of adding silicone-based fine particles, and JP-A No. 11-335500 describes a method of adding spherical magnesium silicate particles.

However, in addition to hot-slip properties, further improvement in that the anti-blocking agent does not fall off during the steps of film formation, slitting, etc., during folding whitening resistance, transparency and scratch resistance during film production. Was desired.

[0006]

The object of the present invention is to provide excellent anti-whitening property against bending during film production, transparency, hot slip resistance, and scratch resistance, and an anti-blocking agent during the process of film formation or slitting. It is intended to provide a polypropylene resin composition for a heat-shrinkable film that does not fall off, and a heat-shrinkable film obtained by stretching the resin composition in at least a uniaxial direction.

[0007]

Means for Solving the Problems The inventors of the present invention have made earnest studies in view of such circumstances, and as a result, have a weight average particle diameter within a certain range for a certain weight of a crystalline polypropylene resin, and The content of the derivative monomer unit is in a certain range, the content of the radically polymerizable monomer unit is in a certain range, the content of the crosslinkable monomer unit is in a certain range, the polymer of the radically polymerizable monomer Polypropylene resin composition for heat-shrink film having a refractive index in a certain range and weight in a certain range, and a heat-shrinkable film obtained by stretching the resin composition in at least one axial direction. However, they have found that the above problems can be solved, and have completed the present invention.

That is, in the present invention, the following (requirement 1) is added to 100 parts by weight of the crystalline polypropylene resin (a).
~ Crosslinked polymer beads (b) 0.0 satisfying (Requirement 3)
The present invention relates to a polypropylene resin composition for a heat shrinkable film containing 5 to 1 part by weight. (Requirement 1) The weight average particle diameter is 0.5 to 5 μm. (Requirement 2) The content of the styrene derivative monomer unit is 60 to 96% by weight, the content of the radical polymerizable monomer unit is 2 to 38% by weight, and the content of the crosslinkable monomer unit is 2 to 38% by weight. Is. (However, the total weight of the crosslinked polymer beads is 100% by weight.) (Requirement 3) The refractive index of the polymer of the radically polymerizable monomer is 1.50 or less. The present invention also relates to a heat-shrinkable film obtained by stretching the above polypropylene-based resin composition for heat-shrinkable film in at least a uniaxial direction. Hereinafter, the present invention will be described in detail.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The crystalline polypropylene resin (a) used in the present invention is a propylene homopolymer or a propylene random copolymer. When the propylene-based polymer used in the present invention is a propylene-based random copolymer, propylene is copolymerized with ethylene and / or at least one comonomer selected from α-olefins having 4 to 20 carbon atoms. The propylene random copolymer obtained is mentioned.

Examples of the α-olefin having 4 to 20 carbon atoms include 1-butene, 2-methyl-1-propene, 1-pentene, 2-methyl-1-butene and 3-methyl-1-butene. , 1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1
-Pentene, 3-methyl-1-pentene, 4-methyl-
1-pentene, 3,3-dimethyl-1-butene, 1-heptene, methyl-1-hexene, dimethyl-1-pentene, ethyl-1-pentene, trimethyl-1-butene,
Methylethyl-1-butene, 1-octene, methyl-1
-Pentene, ethyl-1-hexene, dimethyl-1-hexene, propyl-1-heptene, methylethyl-1-
Heptene, trimethyl-1-pentene, propyl-1-
Examples include pentene, diethyl-1-butene, 1-nonene, 1-decene, 1-undecene, 1-dodecene.
Preferably, 1-butene, 1-pentene, 1-hexene, 1-octene, more preferably 1-butene,
1-hexene.

As the propylene-based random copolymer,
For example, a propylene-ethylene random copolymer, a propylene-α-olefin random copolymer, a propylene-ethylene-α-olefin random copolymer and the like can be mentioned. As the propylene-α-olefin random copolymer, for example, propylene-1-butene random copolymer, propylene-1-hexene random copolymer,
Examples thereof include propylene-1-octene random copolymer, and examples of the propylene-ethylene-α-olefin random copolymer include propylene-ethylene-1-.
Butene random copolymer, propylene-ethylene-1-
Hexene random copolymer, propylene-ethylene-1
-Octene random copolymer and the like, and preferably propylene-ethylene random copolymer, propylene-
1-butene random copolymer, propylene-1-hexene random copolymer, propylene-ethylene-1-butene random copolymer and propylene-ethylene-1-hexene random copolymer.

When the propylene-based random copolymer is a propylene-ethylene random copolymer, the content of ethylene is considered from the viewpoint of the stretch processability of the polypropylene resin composition for heat-shrink film and the rigidity of the heat-shrink film. Is preferably 1 to 7% by weight, more preferably 2 to 7% by weight, still more preferably 3 to 5% by weight.

When the propylene-based random copolymer is a propylene-α-olefin random copolymer, from the viewpoint of stretching processability of the polypropylene-based resin composition for a heat shrinkable film and hot slip property of the heat shrinkable film, The content of α-olefin is preferably 1 to 30% by weight, more preferably 2 to 28% by weight, and further preferably 8 to 23% by weight.

When the propylene-based random copolymer is a propylene-ethylene-α-olefin random copolymer, the polypropylene resin composition for heat-shrinkable film obtained can be stretched easily and the heat-shrinkable film can be hot-slipped. Therefore, the content of ethylene is preferably 0.1
-7% by weight, more preferably 2-6% by weight, still more preferably 2-4.5% by weight.

When the propylene-based random copolymer is a propylene-ethylene-α-olefin random copolymer, the polypropylene resin composition for heat-shrinkable film obtained can be stretched and processed, and the heat-shrinkable film can be hot-slipped. Therefore, the α-olefin content is preferably 1 to
30% by weight, more preferably 2 to 10% by weight,
More preferably, it is 3 to 7% by weight.

The melt flow rate (MFR) of the crystalline polypropylene resin (a) used in the present invention is the fluidity of the obtained polypropylene resin composition for stretched film at the time of extrusion processing and the obtained polypropylene for heat shrink film. From the viewpoint of the stretchability of the resin composition, it is preferably 0.3 to 20 g / 10 minutes, more preferably 0.
5 to 10 g / 10 minutes, more preferably 2 to 7 g
/ 10 minutes.

The melting point (Tm) of the crystalline polypropylene resin (a) used in the present invention, which is determined from the peak temperature of the melting curve measured by DSC, is said to exhibit good hot slip properties and stretch processability at the same time. From the viewpoint, it is preferably 130 to 145 ° C., more preferably 132 to 143 ° C., and further preferably 133.
~ 142 ° C.

The amount of the cold xylene-soluble part (CXS) of the crystalline polypropylene resin (a) used in the present invention is preferably 0.5 from the viewpoint of simultaneously exhibiting good hot slip property and stretch processability. ˜4% by weight, more preferably 1 to 3.5% by weight, still more preferably 2-3% by weight.

As a method for producing the crystalline polypropylene resin (a) used in the present invention, a known catalyst for stereoregular polymerization of propylene is used.

As a catalyst for stereoregular polymerization of propylene, for example, titanium trichloride catalyst, titanium containing titanium, magnesium, halogen, and an electron donor as essential components are used.
Examples thereof include a catalyst system in which a solid catalyst component such as a Mg-based catalyst is combined with an organoaluminum compound and, if necessary, a third component such as an electron donating compound, and a metallocene catalyst.

Preferably, a solid catalyst component containing magnesium, titanium, halogen and an electron donor as essential components,
The catalyst system is a combination of an organoaluminum compound and an electron donating compound.
The catalyst systems described in JP-A-218606, JP-A-61-287904, JP-A-7-216017 and the like can be mentioned.

The crosslinked polymer beads (b) used in the present invention have a weight average particle diameter of 0.5 to 5 μm, preferably 0.8 to 3 μm. Weight average particle diameter is 0.
If the thickness is less than 5 μm, protrusions having a sufficient height cannot be formed on the surface of the stretched film, and the blocking resistance may be insufficient. If the weight average particle size exceeds 5 μm, voids may occur during stretching the film. The cross-linked polymer beads may scatter light and the transparency of the film may deteriorate.

The content of the styrene derivative monomer unit in the crosslinked polymer beads (b) used in the present invention is 60 to 96% by weight, preferably 70 to 92% by weight. Styrene derivative monomer unit content is 6
If it is less than 0% by weight, voids may be easily generated during stretching of the film or the transparency of the film may be deteriorated. If it is more than 96% by weight, the crosslinked polymer beads scatter light, resulting in transparency of the film. May worsen.

Examples of the styrene derivative monomer used for the crosslinked polymer beads (b) include styrene, methylstyrene, ethylstyrene, butylstyrene, propylstyrene and the like.

The content of the radical-polymerizable monomer unit in the crosslinked polymer beads (b) used in the present invention is 2-38% by weight, preferably 5-28% by weight.
Is. Radical polymerizable monomer unit content is 2
If less than wt%, the cross-linked polymer beads will scatter light,
The transparency of the film may be deteriorated, and if it exceeds 38% by weight, voids may be easily generated during stretching of the film, or the transparency of the film may be deteriorated.

In the crosslinked polymer beads (b) used in the present invention, the refractive index of the polymer of the radical-polymerizable monomer is 1.50 or less. When the refractive index exceeds 1.50, the difference between the refractive index of the crosslinked polymer beads and the refractive index of the crystalline polypropylene-based resin becomes large, and the transparency of the resin composition may be impaired.

The radical-polymerizable monomer used in the crosslinked polymer beads (b) is, for example, Polymer.
r Handbook 3rd. Ed. VI / No. 45
1-461 (J. Brandrup and E.
H. Edited by Immergut, 1989, John Wi
ley & Sons. Inc. ). For example, butyl acrylate, t-butyl methacrylate, vinyl propionate, vinyl acetate, methyl acrylate, isopropyl methacrylate, dodecyl methacrylate, tetradecyl methacrylate, hexadecyl methacrylate,
Vinyl formate, isobutyl methacrylate, vinyl acetal, vinyl butyral, hexyl methacrylate, butyl methacrylate, ethylidene dimethacrylate, propyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, ethyl methacrylate, methyl methacrylate, vinyl alcohol, 4-methylcyclohexyl methacrylate And the like, and particularly preferred are methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, and butyl acrylate.

The content of the crosslinkable monomer unit in the crosslinked polymer beads (b) used in the present invention is 2 to.
38% by weight, preferably 2 to 30% by weight,
More preferably, it is 3 to 20% by weight. When the content of the crosslinkable monomer unit is less than 2% by weight, projections having a sufficient height are not formed on the surface of the stretched film, and blocking resistance may be insufficient. When the content of the crosslinkable monomer unit exceeds 38% by weight, the transparency may be insufficient.

The content of the crosslinked polymer beads in the polypropylene resin composition of the present invention is 0.05 to 1 part by weight, preferably 0.07 to 0.6 part by weight, based on 100 parts by weight of the crystalline polypropylene resin (a). Parts, and more preferably 0.1 to 0.4 parts by weight. When the content of the crosslinked polymer beads is 0.05 to 1 part by weight, it is possible to obtain a heat-shrinkable film having an excellent balance of transparency and hot slip property without deteriorating the appearance.

The concentration of the crosslinked polymer beads in the polypropylene resin composition of the present invention is adjusted by preparing in advance a masterbatch containing 1 to 25 parts by weight of the polypropylene resin in the polypropylene resin and appropriately blending this masterbatch. You may. In this case, with respect to 100 parts by weight of the total crystalline polypropylene resin including the polypropylene resin in the masterbatch,
The final addition concentration of the crosslinked polymer beads is adjusted to be 0.05 to 1 part by weight.

The method for adding the cross-linked polymer beads (b) to the crystalline polypropylene resin (a) of the present invention may be any method in which the cross-linked polymer beads (b) are uniformly dispersed. For example, a ribbon blender, Examples thereof include a method of mixing with a Henschel mixer and the like, and melting and kneading the mixture with an extruder.

An antioxidant may be added to the polypropylene resin composition for a heat shrinkable film of the present invention, if necessary. As the type of antioxidant, generally known ones can be mentioned. For example, phosphorus-based antioxidants, phenol-based antioxidants, sulfur-based antioxidants and the like can be mentioned. These may be used alone or in combination of at least two kinds.

The polypropylene resin composition for heat-shrink film of the present invention may optionally contain a neutralizing agent. The neutralizing agent is generally one that can act on the acidic substance remaining in the polymer to inactivate it. Examples thereof include hydrotalcites, higher fatty acid metal salts, silicates, metal oxides, metal hydroxides and the like. These neutralizing agents may be used alone or in combination of at least two kinds.

Examples of hydrotalcites include:
Examples include water-containing basic carbonates such as magnesium, calcium, zinc, aluminum, and bismuth, and basic carbonates that do not contain water of crystallization. Further, these carbonates which are natural products or those which are synthetic products Is mentioned.
From the viewpoint of bending whitening, DHT-4A (manufactured by Kyowa Chemical Industry Co., Ltd.) and DHT-4C (manufactured by Kyowa Chemical Industry Co., Ltd.) are preferable.

As the higher fatty acid metal salt, for example, magnesium stearate, magnesium laurate, magnesium palmitate, calcium stearate, calcium oleate, calcium laurate, barium stearate, barium oleate, barium laurate, barium arachidate, Barium behenate, zinc stearate, zinc oleate, zinc laurate, lithium stearate, sodium stearate, sodium palmitate, sodium laurate, potassium stearate, potassium laurate, calcium 12-hydroxystearate, calcium montanate, etc. Is mentioned. Preferred are calcium stearate and magnesium stearate.

When the neutralizing agent is used in the present invention, the amount of the neutralizing agent added is usually 0.005 with respect to 100 parts by weight of the propylene-ethylene-α-olefin random copolymer.
To 1.0 part by weight, preferably 0.005 to 0.2
0 parts by weight.

The polypropylene resin composition for heat-shrink film of the present invention contains, if necessary, an ultraviolet absorber, a lubricant, a pigment, an antistatic agent, a copper damage inhibitor, a flame retardant, a foaming agent,
Additives such as a plasticizer, an anti-foaming agent, a cross-linking agent, a flowability improver, and a light resistance stabilizer may be appropriately added.

As the method for molding the heat-shrinkable film of the present invention, known molding methods can be mentioned. For example, there may be mentioned a method in which a raw material film for stretching is molded using a melt extrusion molding machine and the raw material material is stretched.

As a method for forming the original film for stretching,
For example, a T die cast method, a water cooling inflation method and the like can be mentioned.

As a method for stretching the raw film for stretching, for example, a uniaxial stretching method such as a roll stretching method, a roll rolling method, a tenter transverse uniaxial stretching method, a tenter biaxial stretching method, or a tubular biaxial stretching method is used. A biaxial stretching method such as a method may be used.

The processing conditions during the stretching process are known conditions, and the stretching temperature is preferably from room temperature to the melting point of the copolymer or lower, and the stretching ratio is preferably 2 to 2 in both the longitudinal and transverse directions. It is about 10 times. The stretching ratios in the machine direction and the transverse direction may be the same or different, and can be arbitrarily selected according to each application. Moreover, you may heat-set after extending | stretching.

The heat-shrinkable film of the present invention may be used as a single layer, and the polypropylene-based resin composition for heat-shrinkable film is laminated on at least one outermost layer of a base film made of the same or different polyolefin resin. You may use. As the laminating method, a dry laminating method, a coextrusion method, or the like can be applied. From the viewpoint of bending whitening, it is preferable to use the polypropylene resin composition for heat-shrink film laminated on at least one outermost layer of a base film made of the same or different polyolefin resin.

The heat-shrinkage rate of the heat-shrinkable film of the present invention is preferably such that the heat-shrinkage rate obtained in the measurement of immersing the heat-shrinkable film in silicone oil at 110 ° C. for 5 seconds has a value of at least uniaxial value of 5 % Or more,
It is more preferably at least 12%, particularly preferably 15%.
% Or more. The heat shrinkage stress of the film is preferably not more than the deformation strength of the packaged object.

The thickness of the heat shrinkable film of the present invention is usually 2
It is not more than 00 μm, preferably 5 to 100 μm, and more preferably 8 to 50 μm.

[0045]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Physical property values in Examples and Comparative Examples were measured according to the following methods. (1) Melt index (MFR, unit: g / 10
Min) According to JIS K7210, temperature 230 ° C., load 2.
It was measured at 16 kgf.

(2) Melting point (Tm, unit: ° C) Differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer Co., Ltd.)
In advance, a propylene polymer or polypropylene resin composition was hot press molded (preheated at 230 ° C. for 5 minutes, then increased to a pressure of 50 kgf / cm ² over 3 minutes, and held for 2 minutes. 30 kgf / ° C
After cooling at a pressure of cm ² for 5 minutes, 10 mg of a sample taken from the sheet was heat-treated at 220 ° C. for 5 minutes under a nitrogen atmosphere to cool the polymer, and then cooled to 150 ° C. at a temperature lowering rate of 300 ° C./min. Incubate for 1 minute, cool to 50 ° C at a cooling rate of 5 ° C / minute, and incubate for 1 minute at 50 ° C, then increase the temperature from 50 ° C to 180 ° C by 5 ° C /
The melting peak temperature when heated in minutes is the melting point (Tm (° C))
Sought as.

(3) Ethylene content and 1-butene content (unit: wt%) The ethylene content and 1-butene content (wt%) are
The infrared absorption spectrum of the press sheet described in (2) above was measured, and the methyl group (-
CH _3), methylene group (-CH ₂ -) and ethyl (-C
_It was determined by the calibration curve method using the absorbance of the characteristic absorption attributed to ₂ H ₅ ).

(4) Xylene soluble component amount (CXS, unit:% by weight) After dissolving 10 g of a propylene polymer in 1000 ml of boiling xylene, the mixture was gradually cooled to 50 ° C., then immersed in ice water and stirred for 20 times. After cooling to ℃ and leaving at 20 ℃ overnight, the precipitated polymer is filtered off, xylene is evaporated from the filtrate, and dried at 60 ℃ under reduced pressure to recover the polymer soluble in xylene at 20 ℃. It was calculated.

(5) Weight average particle diameter (unit: μm) The weight average particle diameter was measured using a light diffraction scattering particle diameter measuring device (Microtrac FRA) manufactured by Leeds & Northrup.

(6) Film processing (sequential tenter type biaxial stretching machine) The obtained resin composition was heated at a resin temperature of 230 ° C. by a single screw extruder.
And extruded at 25 ℃, cooled with a chill roll at a temperature of 350μ
m sheets were obtained. This sheet was stretched by a tenter type sequential biaxial stretching device under the stretching condition 1 shown below,
A biaxially stretched film having a thickness of 15 μm was obtained. Stretching conditions 1 Stretching machine: Mitsubishi Heavy Industries tenter type sequential biaxial stretching machine Longitudinal stretching temperature: 120 ° C Longitudinal stretching ratio: 4 times Horizontal preheating temperature: 130 ° C Horizontal stretching temperature: 125 ° C Horizontal stretching ratio: 4 times Film winding speed : 14.5m / min

(7) Haze (%) The film obtained under the stretching condition 1 was measured according to ASTM D-1003.

(8) Hot Slip Property (Unit: Sliding Friction Coefficient) The film obtained under the stretching condition 1 is ASTM-D189 at a film temperature of 55 ° C. in a thermostatic chamber with a relative humidity of 65% RH.
The dynamic friction coefficient was measured according to 4-63.

(9) After fixing the film obtained under the stretching condition 1 on the silicon sheet of the measuring stand in which the silicon sheet is laminated on the scratch-resistant flat plate, a load of 2 kg is applied on the fixed measuring film. One film was placed and the other film was slid in one direction 10 times. The scratches on the measurement film fixed on the silicon sheet were visually observed, and the results were judged according to the following criteria. ◯: There was no scratch. X: A streak-like scratch was clearly attached.

(10) Dropping of anti-blocking agent Film formation was continued for 5 minutes under stretching condition 1, and the powder (falling-off anti-blocking agent) adhering to the nip roll immediately before the winding machine was wiped off with a black cloth to remove the powder. The amount of adhesion was visually confirmed. ◯: The anti-blocking agent did not fall off. X: The anti-blocking agent was dropped off.

(11) Bending and whitening The obtained resin composition was heated at a resin temperature of 230 ° C. in a single-screw extruder.
And extruded at 25 ℃, cooled with a chill roll at a temperature of 350μ
m sheets were obtained. After folding the sheet between the roll A and the roll B under the condition 2 shown below, it was stretched under the condition 3 shown below to obtain a biaxially stretched film. The transparency of the stretched film corresponding to the folded portion of the sheet was visually evaluated. ◯: White streaks were not observed. X: White streaks were observed. Condition 2 Roll A: Rubber roll, Roll B: Metal roll Pressure between rolls: 4.5 kg / cm ² Roll take-up speed: 10 m / min Condition 3 Stretching machine: Tabletop biaxial stretching machine manufactured by Toyo Seiki Temperature: 120 ° C Preheating time: 1 Minute draw ratio: 4 × 4 times Stretch speed: 1.8 m / min Heat set time: 30 seconds

Example 1 100 parts by weight of propylene homopolymer powder having a melt index of 2.3 g / 10 minutes was added to Sumitomo Chemical Co., Ltd.
20 parts by weight of styrene / MMA-based crosslinked polymer beads CS30 (weight average particle diameter is 3.0 μm), 0.1 part by weight of calcium stearate as a stabilizer, Irgan
ox1010 (antioxidant manufactured by Ciba-Geigy) 0.15
After mixing 0.1 part by weight of Irgaphos 168 (antioxidant manufactured by Ciba Geigy) with a Henschel mixer, a master batch of crosslinked polymer beads was obtained by granulating and pelletizing with a 40 mmφ extruder. Then
Polypropylene pellets (Sumitomo Noblen, Grade F)
L851G4, melt flow rate: 6.4g / 10
Min, melting point (Tm): 136 ° C, ethylene content: 2.5
%, 1-butene content: 5.3% by weight, xylene soluble component amount: 1.9% by weight), and 1.5 parts by weight of the above master batch of crosslinked polymer beads was added to 98.5 parts by weight. After mixing with a pellet blender, the mixture is put into the skin layer extruder, and the core layer extruder is made of polypropylene pellets (Sumitomo Noblen, grade FL851G4, melt flow rate: 6.4 g / 10 minutes, melting point (Tm): 13
6 ° C, ethylene content: 2.5 wt%, 1-butene content: 5.3 wt%, xylene soluble component amount: 1.9 wt%)
And co-extrude at a resin temperature of 230 ° C.
The thickness is 350 by quenching with a cooling roll at 25 ℃.
After being solidified by cooling into a sheet having a size of μm, and then preheated, the film was stretched at a stretching temperature of 120 ° C. in the longitudinal direction by a roll peripheral speed difference of a longitudinal stretching machine.
Double stretching, and then stretch at a stretching temperature of 12 with a tenter type stretching machine.
It was stretched 4 times in the transverse direction at 5 ° C. to obtain a stretched film in which the thickness of each layer was skin / core / skin = 2/11/2 μm. The evaluation results of the film physical properties are shown in Table 1.

Example 2 Using styrene / MMA type crosslinked polymer beads CS30 (weight average particle diameter 1.8 μm) manufactured by Sumitomo Chemical Co., Ltd. as the crosslinked polymer beads, the crosslinked polymer beads were prepared in the same manner as in Example 1. Other than making a masterbatch,
A stretched film was obtained in the same manner as in Example 1. The results of evaluation of the film properties of the obtained stretched film are shown in Table 1.

Comparative Example 1 Eposter MA1002 (a crosslinked methyl methacrylate polymer having a weight average particle diameter of 2.3 μm) manufactured by Nippon Shokubai Co., Ltd. was used as the crosslinked polymer beads in the same manner as in Example 1. A stretched film was obtained in the same manner as in Example 1 except that a masterbatch of crosslinked polymer beads was prepared in the above manner. The results of evaluation of the film properties of the obtained stretched film are shown in Table 1.

Comparative Example 2 As a substitute for the cross-linked polymer beads, JC20 (spherical aluminosilicate having a weight average particle size of 2 μm) manufactured by Mizusawa Chemical Industry Co., Ltd. was used, and spherical particles were formed in the same manner as in Example 1. A stretched film was obtained in the same manner as in Example 1 except that a master batch of aluminosilicate was prepared. The results of evaluation of the film properties of the obtained stretched film are shown in Table 1.

Comparative Example 3 Tospearl 120 (spherical silicone beads, manufactured by Toshiba Silicone Co., Ltd., was used as an alternative to the crosslinked polymer beads.
The weight average particle diameter was 2 μm. ) Example 1
A stretched film was obtained in the same manner as in Example 1 except that a master batch of spherical silicone beads was prepared in the same manner as in. The results of evaluation of the film properties of the obtained stretched film are shown in Table 1.

[0061]

[Table 1]

Examples 1 and 2 satisfying the requirements of the present invention
It is understood that is excellent in folding whitening resistance, transparency, hot slip resistance and scratch resistance during film production, and that the anti-blocking agent does not fall off during film formation or in steps such as slitting.

On the other hand, in Comparative Example 1 in which the crosslinked polymer beads containing the styrene derivative monomer unit were not used in the crosslinked polymer beads which is a requirement of the present invention,
The anti-blocking agent dropped off significantly. Also,
In Comparative Example 2 in which the spherical aluminosilicate was used instead of the crosslinked polymer beads which is a requirement of the present invention, the scratch resistance of the antiblocking agent was significantly deteriorated. And
In Comparative Example 3 in which spherical silicone beads were used instead of the crosslinked polymer beads which is a requirement of the present invention, the scratch resistance of the antiblocking agent was significantly deteriorated.

[0064]

As described above in detail, according to the present invention, it is excellent in folding whitening resistance during film production, transparency, hot slip resistance, scratch resistance, and anti-blocking during film forming or slitting process. It is possible to obtain a polypropylene-based resin composition for a heat-shrinkable film in which the agent does not fall off, and a heat-shrinkable film obtained by stretching the resin composition in at least a uniaxial direction.

Continued front page    F term (reference) 3E067 AC01 AC03 BB14A BB25A                       BB26A CA01 CA13 CA21                       EC28 FB01                 4F071 AA20 AA22 AD06 AE11 AF61                       AH04 BB07 BC01                 4F210 AA11 AA13 AB07 AB24 AE01                       AG01 AG03 AH54 RA03 RC02                       RG02 RG04 RG43                 4J002 BB121 BB141 BB151 BC072                       FA082 GG02

Claims (2)

[Claims] 1. A crystalline polypropylene resin (a) 100.
A polypropylene resin composition for a heat shrinkable film, which comprises 0.05 to 1 part by weight of crosslinked polymer beads (b) satisfying the following (Requirement 1) to (Requirement 3) with respect to parts by weight. (Requirement 1) The weight average particle diameter is 0.5 to 5 μm. (Requirement 2) The content of the styrene derivative monomer unit is 60 to 96% by weight, the content of the radical polymerizable monomer unit is 2 to 38% by weight, and the content of the crosslinkable monomer unit is 2 to 38% by weight. Is. (However, the total weight of the crosslinked polymer beads is 100% by weight.) (Requirement 3) The refractive index of the polymer of the radically polymerizable monomer is 1.50 or less. 2. A heat-shrinkable film obtained by stretching the polypropylene resin composition for a heat-shrinkable film according to claim 1 in at least a uniaxial direction.