JP2007333846A - Heat shrinkable film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat shrinkable film which is used for forming a retardation film and from which the retardation film having excellent balance between the orientation in the machine direction (MD) and that in the transverse direction (TD) can be obtained. <P>SOLUTION: The heat shrinkable film is a biaxially-stretched polypropylene film consisting of a propylene-1-butene copolymer having 0.1-10 wt.% 1-butene content and ≤3% content of a portion soluble in xylene of 20°C and is characterized in that the coefficient of heat shrinkage in the transverse direction (TD) is twice of or more than that of heat shrinkage in the machine direction (MD) at 140°C and the coefficient of heat shrinkage in the transverse direction (TD) is twice of or more than that of heat shrinkage in the machine direction (MD) at 150°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat shrink film. More specifically, it is a heat-shrinkable film used for the production of a retardation film, which can obtain a retardation film with a good balance between the machine direction (MD) orientation and the transverse direction (TD) orientation. The present invention relates to a shrink film.

  The retardation film, for example, by laminating a biaxial polypropylene film on both sides of a polycarbonate film, heating and stretching the film, and shrinking the biaxial polypropylene film in the machine direction (MD) and the transverse direction (TD), The polycarbonate film is produced by orienting in the machine direction (MD) and the transverse direction (TD).

  JP-A-2005-157306 discloses a polypropylene film to be bonded to a polycarbonate film, the ratio of the shrinkage stress in the width direction to the shrinkage stress in the flow direction at 160 ° C. is 2.5 to 5.5, and A biaxially stretched polypropylene film having a shrinkage in the flow direction of 13% or more and a shrinkage in the width direction of 24% or more is described.

JP-A-2005-157306

  However, improvement is demanded for the balance between the orientation in the machine direction (MD) and the orientation in the transverse direction (TD) of the retardation film, and the biaxially stretched polypropylene film described in the above publication is also at a lower temperature. Even in the case of shrinkage, there has been a demand for a heat shrinkable film capable of obtaining a retardation film having a good balance between the orientation in the machine direction (MD) and the orientation in the transverse direction (TD).

  Under the circumstances as described above, an object of the present invention is a heat-shrinkable film used for the production of a retardation film, which has a good balance between the machine direction (MD) orientation and the transverse direction (TD) orientation. The object is to provide a heat shrinkable film capable of obtaining a retardation film.

As a result of intensive studies, the present inventor has found that the present invention can solve the above-described problems, and has completed the present invention.
That is, the present invention
A biaxially stretched polypropylene film comprising a propylene-1-butene copolymer having a 1-butene content of 0.1% by weight to 10% by weight and a 20 ° C. xylene soluble part content of 3% or less, ,
The horizontal direction (TD) heat shrinkage at 140 ° C. is more than twice the vertical direction (MD) heat shrinkage, and
The present invention relates to a biaxially stretched polypropylene film having a heat shrinkage in the transverse direction (TD) at 150 ° C. that is at least twice that in the machine direction (MD).

  ADVANTAGE OF THE INVENTION According to this invention, the heat-shrinkable film which can obtain the retardation film with the favorable balance of the orientation of a vertical direction (MD) and a horizontal direction (TD) can be obtained.

The 1-butene content of the propylene-1-butene copolymer used in the present invention is 0.1 wt% or more and 10 wt% or less, preferably 0.1 wt% or more and 7 wt% or less, more preferably 1 % By weight or more and 5% by weight or less. However, the total weight of the propylene-1-butene copolymer is 100% by weight.
When the 1-butene content is less than 0.1% by weight, the stretchability may be insufficient, the film may be broken during transverse stretching, and is obtained by stretching at a high temperature so that the film does not break. The heat shrinkage rate in the transverse direction (TD) of the film may be small. When 1-butene content exceeds 10 weight%, the heat shrinkage rate of the machine direction (MD) of the heat shrinkable film obtained may become large.

  The propylene-1-butene copolymer has a 20 ° C. xylene-soluble component amount (CXS) of 3 wt% or less, preferably 0.1 wt% or more and 3 wt% or less, more preferably 0.1 wt% or more 2 % By weight or less, more preferably 0.1% by weight or more and 1% by weight or less. When CXS exceeds 3% by weight, the heat shrinkage rate in the machine direction (MD) of the obtained heat shrinkable film may increase.

  The melt flow rate (MFR) of the propylene-1-butene copolymer is preferably 0.1 to 20 g / 10 min from the viewpoint of obtaining sufficient fluidity during extrusion processing and preventing breakage during stretching. More preferably, it is 0.1-10 g / 10min, More preferably, it is 1-5 g / 10min.

Examples of the method for producing the propylene-1-butene copolymer include a method of copolymerizing propylene and 1-butene using a known polymerization catalyst.
As a known polymerization catalyst, for example,
(1) Ti—Mg-based catalyst comprising a solid catalyst component containing magnesium, titanium and halogen as essential components,
(2) A catalyst system in which a solid catalyst component containing magnesium, titanium and halogen as essential components is combined with an organoaluminum compound and a third component such as an electron donating compound, if necessary, (3) a metallocene catalyst, etc. Can be mentioned.
The catalyst system is preferably a combination of a solid catalyst component containing magnesium, titanium and halogen as essential components with an organoaluminum compound and an electron donating compound.

Examples of solid catalyst components containing magnesium, titanium, and halogen as essential components include catalyst systems described in JP-A-61-218606, JP-A-61-287904, JP-A-7-216017, and the like. Can be mentioned.
Examples of the organoaluminum compound include triethylaluminum, triisobutylaluminum, a mixture of triethylaluminum and diethylaluminum chloride, and tetraethyldialumoxane.
Examples of the electron donating compound include tert-butyl-n-propyldimethoxysilane, tert-butylethyldimethoxysilane, cyclohexylethyldimethoxysilane, and dicyclopentyldimethoxysilane.

  As a method for copolymerizing propylene and 1-butene, a solvent polymerization method using a hydrocarbon such as hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, benzene, toluene, xylene as an inert solvent, a liquid monomer as a solvent Examples thereof include a bulk polymerization method used as a gas phase polymerization method and a gas phase polymerization method performed in a gaseous monomer. The bulk polymerization method or the gas phase polymerization method is preferable because post-treatment is easy.

  The polymerization temperature when propylene and 1-butene are copolymerized is usually 20 to 150 ° C., and preferably 35 to 95 ° C. from the viewpoint of increasing productivity.

  Examples of the method for copolymerizing propylene and 1-butene include a polymerization method using one polymerization reactor, or a multistage polymerization method using at least two polymerization reactors.

  As a post-treatment of copolymerization of propylene and 1-butene, catalyst deactivation, solvent removal, monomer removal, drying, granulation, and the like may be performed as necessary.

If necessary, additives and other resins may be added to the propylene-1-butene copolymer used in the present invention.
Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a nucleating agent, an antifogging agent, and an antiblocking agent.
Examples of the other resins include polyolefin resins, and examples thereof include polyethylene resins and polypropylene resins other than the propylene-1-butene copolymer used in the present invention.

In the biaxially stretched polypropylene film of the present invention, the heat shrinkage in the transverse direction (TD) at 140 ° C. is more than twice the heat shrinkage in the machine direction (MD), and the transverse direction (TD) in 150 ° C. It is a biaxially stretched polypropylene film having a heat shrinkage rate of at least twice that in the machine direction (MD).
The heat shrinkage in the transverse direction (TD) at 140 ° C. is preferably 2 to 5 times, more preferably 2.2 to 4 times as the heat shrinkage in the longitudinal direction (MD). Further, the heat shrinkage in the transverse direction (TD) at 150 ° C. is preferably 2 to 5 times, more preferably 2.2 to 4 times as the heat shrinkage in the longitudinal direction (MD).

  When the heat shrinkage in the transverse direction (TD) at 140 ° C. is less than twice the heat shrinkage in the longitudinal direction (MD), or the heat shrinkage in the transverse direction (TD) at 150 ° C. is heated in the longitudinal direction (MD). When the shrinkage rate is less than twice, the physical properties of the retardation film obtained using the biaxially stretched polypropylene film may be insufficient.

  The horizontal direction (TD) heat shrinkage at 140 ° C. is the longitudinal direction (MD) measuring method, and the horizontal direction (TD) heat shrinkage at 150 ° C. is the vertical direction (MD) heat shrinkage. The measurement method is as follows.

[Method of measuring heat shrinkage]
A4 size film is sampled so that the long axis is parallel to the machine direction (MD), and 20 cm marked lines are drawn in the machine direction (MD) and the transverse direction (TD), respectively, and the specified temperature (140 ° C. or 150 ° C.) is drawn. The sample is hung in an oven kept at (° C.) and held for 15 minutes, after which the film is taken out and cooled at room temperature for 30 minutes, and then the marked line length of the test piece is measured. The heat shrinkage rate in each direction is calculated from the following formula.
Heat shrinkage (%) = {(20−marked length after heating) / 20} × 100

  As the heat shrinkage rate of the biaxially stretched polypropylene film of the present invention, from the viewpoint of the physical properties of the retardation film obtained using the biaxially stretched polypropylene film, the heat shrinkage rate in the machine direction (MD) is preferably 10% or less. Yes, the heat shrinkage in the transverse direction (TD) is 20% or more.

As a method for producing the biaxially stretched polypropylene film of the present invention, at least one of a method of forming a film alone and stretching it biaxially using a commonly used T-die method or the like, or a multilayer configuration with different resins is used. Examples thereof include a method of forming a film as a layer and stretching it biaxially.
Examples of the method for multilayering the biaxially stretched polypropylene film of the present invention with a different resin include commonly used extrusion laminating methods, thermal laminating methods, dry laminating methods and the like.

Further, a method of producing a biaxially stretched polypropylene film of the present invention by stretching a film or sheet obtained by molding in advance is exemplified. Examples of the stretching method include a roll stretching method, a tenter stretching method, a tubular method. Examples thereof include a biaxial stretching method such as a stretching method. From the viewpoint of improving the balance of the heat shrinkage rate of the obtained film, a method of successively biaxially stretching by roll stretching and tenter stretching is preferable.
The stretching temperature is 125 ° C to 160 ° C when stretching in the machine direction (MD), and the temperature when stretching in the transverse direction (TD) is 145 to 165 ° C. The temperature when stretching in the transverse direction (TD) is preferably 20 ° C. or less, more preferably 16 ° C. or less, which is the temperature when stretching in the longitudinal direction (MD).

  The biaxially stretched polypropylene film of the present invention can be used for a heat shrink film for producing a retardation film. It can also be used for shrink label films, food packaging films, and the like.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The sample preparation methods and physical property measurement methods used in Examples and Comparative Examples are shown below.

(1) 1-butene content (unit: wt%)
The IR spectrum measurement described on page 619 of the Polymer Analysis Handbook (1995, published by Kinokuniya) was performed to determine the 1-butene content.

(2) 20 ° C. xylene-soluble component amount (CXS, unit: wt%)
After 1 g of the sample was completely dissolved in 100 ml of boiling xylene, the temperature was lowered to 20 ° C. and left for 4 hours. Thereafter, this was separated into a precipitate and a solution, and the filtrate was dried and dried at 70 ° C. under reduced pressure to obtain a residue. The weight of the obtained residue was measured to determine the 20 ° C. xylene-soluble component amount (CXS).

(3) Intrinsic viscosity ([η], unit: dl / g)
The measurement was performed in 135 ° C. tetralin using an Ubbelohde viscometer.

(4) Melt flow rate (MFR, unit: g / 10 minutes)
According to JIS K7210, the measurement was performed at a temperature of 230 ° C. and a load of 21.18 N.

(5) Heat shrinkage rate (unit:%)
A4 size film is sampled so that the long axis is parallel to the machine direction (MD), and 20 cm marked lines are drawn in the machine direction (MD) and the transverse direction (TD), respectively, and the specified temperature (140 ° C. or 150 ° C.) is drawn. And kept in an oven kept at 15 ° C. for 15 minutes. Thereafter, the film was taken out and cooled at room temperature for 30 minutes, and then the marked line length of the test piece was measured. The heat shrinkage rate in each direction was calculated from the following calculation formula.
Heat shrinkage (%) = {(20−marked length after heating) / 20} × 100

Example 1
[Synthesis of solid catalyst]
After replacing an SUS reaction vessel with an internal volume of 200 L with a stirrer with nitrogen, 80 L of hexane, 6.55 mol of tetrabutoxytitanium, 2.8 mol of diisobutyl phthalate and 98.9 mol of tetrabutoxysilane were added to obtain a homogeneous solution. did. Next, 51 L of a diisobutyl ether solution of butyl magnesium chloride having a concentration of 2.1 mol / L was gradually added dropwise over 5 hours while maintaining the temperature in the reaction vessel at 5 ° C. After completion of the dropwise addition, the mixture was further stirred at room temperature for 1 hour, then solid-liquid separation was performed at room temperature, and washing was repeated 3 times with 70 L of toluene.
Next, after extracting toluene so that the slurry concentration becomes 0.6 kg / L, a mixed solution of 8.9 mol of n-butyl ether and 274 mol of titanium tetrachloride was added, and 20.8 mol of phthalic acid chloride was further added. In addition, the reaction was carried out at 110 ° C. for 3 hours. After completion of the reaction, washing was performed twice with toluene at 95 ° C.
Next, after adjusting the slurry concentration to 0.6 kg / L, 3.13 mol of diisobutyl phthalate, 8.9 mol of di-n-butyl ether and 137 mol of titanium tetrachloride were added, and the reaction was carried out at 105 ° C. for 1 hour. . After completion of the reaction, the solid and liquid were separated at the same temperature, and then washed twice with 90 L of toluene at 95 ° C.
Next, after adjusting the slurry concentration to 0.6 kg / L, 8.9 mol of di-n-butyl ether and 137 mol of titanium tetrachloride were added, and the reaction was performed at 95 ° C. for 1 hour. After completion of the reaction, solid-liquid separation was performed at the same temperature, and washing was performed 3 times with 90 L of toluene at the same temperature.
Next, after adjusting the slurry concentration to 0.6 kg / L, 8.9 mol of di-n-butyl ether and 137 mol of titanium tetrachloride were added, and the reaction was performed at 95 ° C. for 1 hour.
After completion of the reaction, solid-liquid separation was performed at the same temperature, followed by washing with 90 L of toluene three times at the same temperature, and further washing with 90 L of hexane three times, followed by drying under reduced pressure to obtain 11.0 kg of a solid catalyst component.
The solid catalyst component contains 1.89% by weight of titanium atom, 20% by weight of magnesium atom, 8.6% by weight of phthalate ester, 0.05% by weight of ethoxy group and 0.21% by weight of butoxy group. It had a good particle property.

[Preactivation of solid catalyst]
Fully dehydrated and degassed 1.5 L of n-hexane, 37.5 mmol of triethylaluminum, 3.75 mmol of t-butyl-n-propyldimethoxysilane, and the above solid catalyst in a SUS autoclave with an internal volume of 3 L and equipped with a stirrer After 15 g of propylene was added, 15 g of propylene was continuously supplied over 30 minutes while preserving the temperature in the tank at 5 to 15 ° C. and preactivation was performed, the resulting solid catalyst slurry was equipped with a 200 L internal stirrer It was transferred to a SUS autoclave, diluted with 140 L of liquid butane, and stored at a temperature of 5 ° C. or lower.

[Polymerization of propylene-1-butene copolymer]
In a gas phase fluidized bed reactor with a stirrer having an internal volume of 1 m ^3, the amount of polymer retained in the fluidized bed is 80 kg, the polymerization temperature is 80 ° C., the polymerization pressure is 1.9 MPa, the hydrogen concentration in the gas phase is 1.7 vol%, The preactivated solid catalyst component was 0.93 g / hour, triethylaluminum 48 mmol under the condition that propylene, hydrogen and 1-butene were fed so as to keep the 1-butene concentration at 1.1 parts by volume. Propylene-1-butene copolymer 23.3 kg / hour was obtained by performing continuous gas phase polymerization while supplying 6 mmol / hour of t-butyl-n-propyldimethoxysilane / hour. The obtained polymer had a 1-butene content of 2.5% by weight, [η] of 2.0 dl / g, and CXS of 0.4% by weight.

Reference example 1
[Propylene-1-butene copolymer pellets]
Hydrotalcite 0.01 part by weight, Irganox 1010 (manufactured by Ciba Specialty Chemicals) 0.15 part by weight, Irgaphos 168 (Ciba Specialty) with respect to 100 parts by weight of the resulting propylene-1-butene copolymer powder 0.10 parts by weight were mixed and melt-kneaded to obtain pellets. The physical properties of the pellets are shown in Table 1.

[Create biaxially stretched film]
The pellet obtained in Reference Example 1 was melt-extruded at 260 ° C. using a T-die extruder having a 65 mmφ screw, and then rapidly cooled with a cooling roll at 30 ° C. to obtain a sheet. While this sheet was heated at 145 ° C., it was stretched 4.45 times in the machine direction due to the difference in the peripheral speed of the roll of a longitudinal stretching machine, and then stretched 8 times in the transverse direction at a stretching temperature of 157 ° C. in a heating furnace. 3% relaxation treatment was performed (the longitudinal stretching line speed was 3.3 m / min, and the transverse stretching line speed was 14.7 m / min) to obtain a 40 μm biaxially stretched film. The physical properties of the film are shown in Table 2.

Comparative Example 1
[Create biaxially stretched film]
Using the pellets used in Example 1, melt extrusion was performed at 260 ° C. using a T-die extruder having a 65 mmφ screw, and then rapidly cooled with a cooling roll at 30 ° C. to obtain a sheet. While this sheet was heated at 145 ° C., it was stretched 5 times in the machine direction due to the difference in the roll peripheral speed of the longitudinal stretching machine, and then stretched 8 times in the transverse direction at a stretching temperature of 162 ° C. in a heating furnace, and then 13% at 165 ° C. (Line speed of longitudinal stretching was 3.0 m / min, line speed of lateral stretching was 15.0 m / min), and a 40 μm biaxially stretched film was obtained. The physical properties of the film are shown in Table 2.

Comparative Example 2
[Polymerization of propylene-ethylene copolymer]
For the synthesis of the solid catalyst and the preactivation of the solid catalyst, the solid catalyst was synthesized by the same method as in Example 1 and preactivated by the same method.
In a gas phase fluidized bed reactor with a stirrer having an internal volume of 1 m ^3, the amount of polymer retained in the fluidized bed is 80 kg, the polymerization temperature is 80 ° C., the polymerization pressure is 1.8 MPa, the hydrogen concentration in the gas phase is 0.65% by volume, the gas phase Under the condition that propylene, hydrogen, and ethylene were supplied so as to keep the ethylene concentration at 0.51% by volume, 0.71 g / hour of the preactivated solid catalyst component, 40 mmol / hour of triethylaluminum, t Propylene-ethylene copolymer 19.7 kg / hour was obtained by carrying out continuous gas phase polymerization while supplying 4 mmol / hour of -butyl-n-propyldimethoxysilane. The obtained copolymer had an ethylene content of 0.3% by weight, [η] of 2.39 dl / g, and CXS of 1.1% by weight.

Reference example 2
[Propylene-ethylene copolymer pellets]
Propylene-ethylene copolymer pellets were obtained in the same manner as in Reference Example 1 using the obtained propylene-ethylene copolymer powder. The physical properties of the pellets are shown in Table 1.

[Create biaxially stretched film]
Biaxial stretching was performed using the pellets of Reference Example 2 under the same conditions as in Example 1. However, due to poor stretchability, undrawn portions were generated or film cracking occurred and could not be stretched. .

[Comparative Example 3]
[Create biaxially stretched film]
The pellets used in Comparative Example 2 were used, melt extrusion was performed at 260 ° C. using a T-die extruder having a 65 mmφ screw, and then rapidly cooled with a 30 ° C. cooling roll to obtain a sheet. While this sheet was heated at 145 ° C., it was stretched 4.45 times in the machine direction due to the difference in the roll peripheral speed of the longitudinal stretching machine, and then stretched 8 times in the transverse direction at a stretching temperature of 164 ° C. in a heating furnace. 3% relaxation treatment was performed (the longitudinal stretching line speed was 3.3 m / min, and the transverse stretching line speed was 14.7 m / min) to obtain a 40 μm biaxially stretched film. The physical properties of the film are shown in Table 2.

The biaxially stretched polypropylene film of Example 1 that satisfies the requirements of the present invention is a heat-shrinkable film that can obtain a retardation film having a good balance between the machine direction (MD) orientation and the transverse direction (TD) orientation. It is.
In contrast, the biaxially stretched polypropylene films of Comparative Example 1 and Comparative Example 3 that do not satisfy the requirements of the present invention have a good balance between the machine direction (MD) orientation and the transverse direction (TD) orientation. It is a heat shrinkable film from which a film cannot be obtained.
Since the comparative example 2 did not use the propylene-1-butene copolymer which is a requirement of the present invention, a biaxially stretched polypropylene film could not be obtained.

Claims (2)

A biaxially stretched polypropylene film comprising a propylene-1-butene copolymer having a 1-butene content of 0.1% by weight to 10% by weight and a 20 ° C. xylene soluble part content of 3% or less, ,
The horizontal direction (TD) heat shrinkage at 140 ° C. is more than twice the vertical direction (MD) heat shrinkage, and
A biaxially stretched polypropylene film having a heat shrinkage in the transverse direction (TD) at 150 ° C. that is at least twice the heat shrinkage in the machine direction (MD).   The biaxially stretched polypropylene film according to claim 1, wherein the heat shrinkage in the machine direction (MD) is 10% or less and the heat shrinkage in the transverse direction (TD) is 20% or more.