JP5538741B2 - Stretched film and method for producing the same - Google Patents

Description

  The present invention relates to a stretched film containing syndiotactic polypropylene and a method for producing the same.

  A number of techniques have been reported for stretching a polypropylene film (see Patent Documents 1 to 4). However, although syndiotactic polypropylene has high transparency, it was difficult to stretch at a low magnification in order to obtain an optical retardation film.

In contrast, a technique for stretching a syndiotactic polypropylene film has also been reported. ^When a polypropylene resin composition containing syndiotactic polypropylene having a peak intensity of about 0.5 or more observed at about 20 ppm measured by ¹³ C-NMR can be stretched 4 to 10 times at 100 to 160 ° C. Has been reported (see Patent Document 5). In addition, it has been reported that a syndiotactic polypropylene molded article in which a diffraction line is not observed with an interplanar spacing of about 7.1 mm by X-ray diffraction measurement is stretched three times or more (see Patent Document 6). However, the obtained stretched film is not sufficiently transparent, and for example, it may be difficult to apply to an optical film.

  In addition, an optical compensation film such as a retardation film may be used to widen the viewing angle of a liquid crystal display (LCD). As the retardation film, a stretched film of polycarbonate resin (Express Document 7), a film of triacetyl cellulose (Patent Document 8), a stretched film of thermoplastic norbornene resin (Patent Document 9), and the like have been reported. However, both have problems such as a large photoelastic coefficient and inferior phase difference due to stretching.

JP 2007-253377 A JP 2007-286615 A Japanese Patent Laid-Open No. 2001-316489 Japanese Patent Laid-Open No. 2002-248861 JP-A-8-99353 JP-A-3-290228 Japanese Patent Laid-Open No. 9-325216 JP 2002-221629 A JP-A-8-43812

  An object of the present invention is to obtain a stretched film having high thickness uniformity and low haze by uniformly stretching a syndiotactic polypropylene film. Furthermore, it aims at obtaining a desired retardation film by adjusting a draw ratio freely and controlling the phase difference of a stretched film (especially making a phase difference low).

That is, the first of the present invention relates to the stretched film shown below.
<1>: A stretched film comprising a resin (A) having a melting point and a resin (B) having a melting point 5 ° C. lower than the melting point of the resin (A): the resin (A) and the resin At least one of (B) is a syndiotactic polypropylene; a stretched film having a total light transmittance of 90% or more and a dimensional change rate of 10% or less in a heat resistance test at 120 ° C. in air for 120 hours.
<2>: Maximum endothermic peak due to DSC is observed at a temperature lower than the melting point of the resin (A) and higher than the melting point of the resin (B), the melting point of the resin (A), and the resin (B) The stretched film according to <1>, wherein no endothermic peak is observed at the melting point. Here, “the melting point is not observed” means that a crystal melting heat peak with a crystal melting heat of 10 J / g or more is not observed in DSC measurement.
<3>: The stretched film according to <1> or <2>, wherein the resin (A) is a syndiotactic polypropylene having a melting point of 150 ° C. or higher; and the resin (B) is a resin having a melting point of 140 ° C. or lower. .
<4>: The stretched film according to <3>, wherein the resin (B) is syndiotactic polypropylene.
<5>: The stretched film according to <1> to <4>, wherein the melting point of the resin (B) is 100 ° C. or higher; and lower than the melting point of the resin (A) by 20 ° C. or higher.
<6>: The stretched film according to any one of <1> to <5>, wherein the content of the resin (B) is 20% by weight or more and 80% by weight or less.

<7>: A method for producing a stretched film according to any one of <1> to <6>, wherein in the step of preheating the unstretched film containing the resin (A) and the resin (B), Step (1) in which the preheating temperature is higher than the temperature lower by 10 ° C. than the melting point of the resin (B) and lower than the melting point of the resin (A), and the step of stretching the preheated unstretched film (2) The manufacturing method which has.
<8>: The production method according to <7>, wherein the stretching temperature in the step (2) is higher than a temperature lower by 10 ° C. than the melting point of the resin (B) and lower than the melting point of the resin (A). .
<9>: The production method according to any one of <7> or <8>, wherein the draw ratio in the step (2) is 1.1 to 4 times.

  According to the present invention, in the stretched film of syndiotactic polypropylene, not only thickness uniformity and low haze, but also the stretch ratio is freely adjusted from low to high. Therefore, application to various optical films is expected. In particular, since the phase difference can be freely adjusted, it is also suitably used as a phase difference film.

The shape of the sample for extending | stretching used in the Example and the comparative example is shown. It is a graph which shows the relationship between the draw ratio of a uniaxially stretched film, and a phase difference.

1. Stretched film of the present invention The stretched film of the present invention is a resin film containing the resin (A) and the resin (B); at least one of the resin (A) and the resin (B) is syndiotactic polypropylene. Preferably the resin (A) is syndiotactic polypropylene; more preferably, both the resin (A) and the resin (B) are syndiotactic polypropylene.

  The stretched film of the present invention is characterized by being uniformly stretched even though it contains syndiotactic polypropylene, which is generally difficult to stretch; it is particularly uniformly stretched even at a low stretch ratio. It is characterized by. This is because the stretched film of the present invention contains a resin (A) and a resin (B) having different melting points.

  That is, both the resin (A) and the resin (B) contained in the stretched film of the present invention have a melting point, and the melting point of the resin (B) is 5 ° C. or more lower than the melting point of the resin (A), It is preferable that the temperature is lower by at least ° C. It is for improving the uniform stretchability of the film containing resin (A) with a high melting point.

  The melting point of the resin (B) is preferably 100 ° C. or higher, and more preferably 120 ° C. or higher. This is to sufficiently increase the heat resistance of the stretched film.

  When the resin (A) is syndiotactic polypropylene, the melting point is preferably 140 ° C. or higher, and can be 150 ° C. or higher. In general, films containing higher melting syndiotactic polypropylene are more difficult to stretch uniformly; although the stretched films of the present invention include higher melting syndiotactic polypropylene, It is stretched uniformly.

  The melting point of the resin (A) and the melting point of the resin (B) can be measured by the DSC method. In DSC measurement, the temperature at which the maximum endothermic peak of each resin occurs can be regarded as the melting point of the resin. The stretched film of the present invention contains the resin (A) and the resin (B), but it is preferable that no endothermic peak by DSC measurement is observed in the melting point of the resin (A) and the melting point of the resin (B). Furthermore, it is preferable that the maximum endothermic peak due to DSC is observed between the melting point of the resin (A) and the melting point of the resin (B). If there is an endothermic peak at the same temperature as the melting point of the resin (A) and the resin (B), the resin (A) and the resin (B) are not completely compatible with each other, resulting in stretching unevenness and a decrease in heat resistance. Sometimes.

  The content of the resin (B) in the stretched film of the present invention is preferably 20 to 80% by weight and preferably 30 to 70% by weight with respect to the total amount of the resin (A) and the resin (B). Is preferable, and it is more preferable that it is 40 to 60 weight%. This is to maintain physical properties as syndiotactic polypropylene; and to facilitate stretching of a film containing the resin (A) that is difficult to stretch by adding the resin (B).

  Either one of the resin (A) and the resin (B) may be a resin other than syndiotactic polypropylene or, of course, syndiotactic polypropylene. Examples of resins other than syndiotactic polypropylene include propylene / α-olefin copolymers such as syndiotactic propylene ethylene rubber and syndiotactic propylene butene rubber (preferably having a structural unit derived from propylene of less than 90 mol%) And other α-olefin copolymers such as syndiotactic butene ethylene rubber.

  The syndiotactic polypropylene constituting at least one of the resin (A) and the resin (B) is not particularly limited as long as it includes a structural unit derived from propylene and has a high syndiotacticity. In the following, particularly preferred embodiments of the syndiotactic polypropylene constituting the resin (A) will be described.

  Syndiotactic polypropylene contains 90 mol% to 100 mol% of structural units derived from propylene, and 0 mol% to 10 mol% of structural units derived from one or more selected from ethylene and an α-olefin having 4 to 20 carbon atoms. Polypropylene containing (however, 100 mol% in total) is preferable.

  The syndiotactic polypropylene may be a homopolypropylene, a random copolymer of propylene and an α-olefin having 2 to 20 carbon atoms (excluding propylene), or a propylene block copolymer. Preferred is a homopolypropylene or a random copolymer of propylene and an α-olefin having 2 to 20 carbon atoms (excluding propylene). Here, examples of the α-olefin having 4 to 20 carbon atoms include 1-butene, 3-methyl-1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene and the like are included.

  Syndiotactic polypropylene usually has 90 to 100 mol% of structural units derived from propylene and 0 to 10 mol% of structural units derived from an α-olefin having 2 to 20 carbon atoms (excluding propylene). (Wherein the total of structural units is 100 mol%); preferably, the structural unit derived from propylene is 91 mol% or more and 100 mol% or less and an α-olefin having 2 to 20 carbon atoms (excluding propylene). Polypropylene containing 0 to 9 mol% of derived structural units (provided that the total of structural units is 100 mol%); more preferably 92 to 100 mol% of structural units derived from propylene, and the number of carbon atoms The structural unit derived from 2 to 20 α-olefin (excluding propylene) is 0 mol% or more and 8 mol%. Polypropylene and a lower (provided that the total of the structural units is 100 mol%) is.

  When the syndiotactic polypropylene is a propylene / α-olefin random copolymer, the structural unit derived from propylene is 92.0 to 99.9 mol%, and the α-olefin having 2 to 20 carbon atoms (propylene). From 0.1 to 8.0 mol%, preferably from 93.0 to 99.9 mol% of a structural unit derived from propylene, and an α-olefin having 2 to 20 carbon atoms ( 0.1 to 7.0 mol% of structural units derived from (except for propylene); more preferably 94.0 to 99.9 mol% of structural units derived from propylene, and α- It contains 0.1 to 6.0 mol% of structural units derived from olefins (excluding propylene). Of the syndiotactic polypropylene, homopolypropylene is more preferable from the viewpoint of heat resistance and the like.

Further, the syndiotactic polypropylene preferably satisfies the following requirements [1] and [2].
[1] The syndiotactic pentad fraction (rrrr fraction) measured by ¹³ C-NMR is 85% or more.
[2] The amount of n-decane soluble part is 1 (wt%) or less.

Requirement [1]
The syndiotactic pentad fraction (rrrr fraction, pentad syndiotacticity) measured by NMR method of the syndiotactic propylene in the present invention is 85% or more, preferably 90% or more, more preferably 93%. More preferably, it is 94% or more. Although there is no restriction | limiting in particular in the upper limit of rrrr fraction, Usually, it is less than 100%, Preferably it is 99% or less.

  By controlling the rrrr fraction of syndiotactic polypropylene, it is excellent in moldability, heat resistance, transparency and mechanical properties, and it is easy to obtain properties as crystalline polypropylene.

The syndiotactic pentad fraction (rrrr fraction) is Prrrr in the ¹³ C-NMR spectrum (absorption intensity derived from the third unit methyl group at the site where 5 units of propylene units are continuously syndiotactically bonded). And it is calculated | required by following formula (1) from the absorption intensity of Pw (absorption intensity derived from all the methyl groups of a propylene unit).
rrrr fraction (%) = 100 × Prrrr / Pw (1)

The NMR measurement is performed as follows, for example. A 0.35 g sample is dissolved by heating in 2.0 ml of hexachlorobutadiene. After this solution is filtered through a glass filter (G2), 0.5 ml of deuterated benzene is added and charged into an NMR tube having an inner diameter of 10 mm. And ¹³ C-NMR measurement is performed at 120 degreeC using the JEOL GX-500 type | mold NMR measuring apparatus. The number of integration is 10,000 times or more.

Requirement [2]
The amount of the n-decane soluble part of the syndiotactic polypropylene is 1 (wt%) or less, preferably 0.8 (wt%) or less, and more preferably 0.6 (wt%) or less. This amount of n-decane soluble part is an indicator closely related to the blocking characteristics of syndiotactic polypropylene or a molded product obtained therefrom. Usually, a small amount of n-decane soluble part means a small amount of low crystalline component. That is, the composition containing syndiotactic polypropylene that satisfies the requirement [2] has very good anti-blocking properties.

The normal decane soluble part amount can be measured as follows.
To 5 g of sample, 200 ml of n-decane is added and dissolved by heating at 145 ° C. for 30 minutes. Allow to cool to 20 ° C. over about 3 hours and let stand for 30 minutes. Thereafter, the precipitate (n-decane insoluble part) is filtered off. The filtrate is put into about 3 times the amount of acetone, and the components dissolved in n-decane are precipitated. The precipitate is filtered off from acetone and then dried. The amount of n-decane soluble part is determined by the following formula.
n-decane soluble part amount (wt%) = [precipitate weight / sample weight] × 100

  The stretched film of the present invention may contain an optional component in addition to the resin (A) and the resin (B). Examples of optional components include propylene / α-olefin (co) polymers. The propylene / α-olefin (co) polymer has a constitutional unit derived from propylene of 50 mol% to 100 mol% and one or more constitutional units selected from ethylene and an α-olefin having 4 to 20 carbon atoms. A propylene-based polymer containing 50 mol% (however, a total of 100 mol%). Examples of the α-olefin having 4 to 20 carbon atoms include the α-olefin described in the description of the syndiotactic polypropylene. The propylene / α-olefin copolymer (B) may be, for example, a polymer as described in WO 2006/123759; or a propylene / α-olefin copolymer having an isotactic structure or an atactic structure. An α-olefin copolymer may be used.

  The film of the present invention contains 100 to 50 parts by weight of syndiotactic polypropylene, preferably 100 to 70 parts by weight, more preferably 100 to 90 parts by weight; and further 0 to 50 parts by weight of a propylene / α-olefin copolymer. Part, preferably 0 to 30 parts by weight, more preferably 0 to 20 parts by weight. [However, the sum of the syndiotactic polypropylene and the propylene / α-olefin copolymer is 100 parts by weight].

  The stretched film of the present invention has a weather resistance stabilizer, heat resistance stabilizer, antistatic agent, anti-slip agent, anti-blocking agent, anti-fogging agent, transparent nucleating agent, lubricant, pigment, as long as the object of the present invention is not impaired. Additives such as dyes, plasticizers, anti-aging agents, hydrochloric acid absorbents and antioxidants may be blended. Further, for the purpose of imparting moldability to the film of the present invention, a nucleating agent which is a specific optional component may be included. Examples of the nucleating agent include dibenzylidene sorbitol-based nucleating agent, phosphate ester-based nucleating agent, rosin-based nucleating agent, benzoic acid metal salt-based nucleating agent and the like. Although the compounding quantity of an additive or a nucleating agent does not have a restriction | limiting in particular, It is about 0.1-1 weight part normally with respect to 100 weight part of resin components.

  The film of the present invention may contain polyethylene, isotactic polypropylene, or a styrenic elastomer as necessary. The compounding amount in that case is usually 30 parts by weight or less, preferably 20 parts by weight or less with respect to 100 parts by weight of the resin component.

  The stretched film of the present invention may be a uniaxially stretched film or a biaxially stretched film.

  The stretch ratio of the stretched film of the present invention is not particularly limited as long as it exceeds 1 time, but can be 1.1 to 4 times. Since ordinary syndiotactic polypropylene has a yield point, a conventional syndiotactic polypropylene film cannot be a stretched film having high thickness uniformity unless the stretching ratio is increased.

  On the other hand, as described later, the stretched film of the present invention includes a syndiotactic polypropylene, but has a yield point or a resin film that has no yield point or is reduced, so that the stretch ratio is low. Regardless, it can be a stretched film with high thickness uniformity.

  The stretched film of syndiotactic polypropylene can be used as a retardation film. The phase difference is related to the draw ratio. The greater the draw ratio, the greater the phase difference. As described above, the stretched film of the conventional stretched film has a large stretch ratio, so the retardation of the film has to be large; however, the stretched film of the present invention has a low stretch ratio, so that the retardation of the film can be reduced. Can be reduced.

  The heat resistance of the stretched film of the present invention can be increased as necessary. High heat resistance means that when the stretched film is left in air at 120 ° C. for 120 hours, the dimensional change rate is 10% or less (there is no direction in which the dimensional change rate is 10% or more). . Furthermore, it is preferable that the stretched film of the present invention has no change in transmittance, haze, and does not become brittle when left under the above conditions. In order to improve heat resistance, for example, it is preferable to use syndiotactic polypropylene having a high melting point.

  The haze of the stretched film of the present invention can be lowered as necessary, for example, the total light transmittance can be increased. Specifically, the components of the resin (A) and the resin B (B) may be selected as appropriate.

2. Production Method of Stretched Film of the Present Invention The stretched film of the present invention can be produced by any production method as long as the effects of the present invention are obtained. According to a preferred production method, 1) Resin (A) and Resin (B) And 2) a step of stretching a preheated unstretched film.

  The unstretched film may contain an optional additive in addition to the above-described resin (A) and resin (B), and these are as described above. The unstretched film may be produced by forming a resin composition containing the resin (A), the resin (B), and an optional additive into a film by, for example, melt extrusion molding. The method for forming a film by melt extrusion molding is not particularly limited, and any method may be used.

  Although the thickness of an unstretched film is not specifically limited, Although it sets suitably according to a draw ratio and the thickness of the desired stretched film, it is the range of 30-200 micrometers normally.

  The resulting unstretched film is preheated before being stretched. By stretching after preheating, the yield point of the film disappears or is reduced. The preheating temperature is preferably higher than the “temperature lower by 10 ° C. than the melting point of the resin (B)”.

  On the other hand, the preheating temperature is preferably lower than the melting point of the resin (A). This is because if the preheating temperature is equal to or higher than the melting point of the resin (A), the unstretched film is dissolved and the film shape may change.

  The preheating time may be set so that the yield point of the film can be eliminated or reduced, and is not particularly limited.

  Next, the preheated unstretched film is stretched. The stretching temperature is preferably set to a temperature at which the yield point once disappeared or reduced by preheating is not generated or increased again. Therefore, the stretching temperature is preferably higher than the “temperature lower by 10 ° C. than the melting point of the resin (B)”. On the other hand, when the stretching temperature is too high, the strength of the stretched film is lowered, and the film may be cut during stretching. Therefore, the temperature is preferably lower than the melting point of the resin (A). Since stretching is performed after the resin (B) is sufficiently fluidized by preheating, the stretching temperature may be lower than the preheating temperature.

  The stretching ratio may be selected according to the use of the stretched film, but one of the features of the present invention is that the resin film that is difficult to stretch uniformly can be uniformly stretched even at a low magnification. Therefore, the present invention is particularly effective when performing low magnification stretching. Low magnification stretching is, for example, 1.1 to 4 times stretching. The stretching may be uniaxial stretching or biaxial stretching. Although it may be selected according to the use of the stretched film, it is preferable to use uniaxial stretching when obtaining a retardation film.

  Two types of syndiotactic polypropylene (high melting point sPP and low melting point sPP) were prepared. Table 1 shows the melting point, the glass transition temperature Tg, the molecular weight Mw, and the molecular weight distribution Mw / Mn of the prepared syndiotactic polypropylene.

The high melting point sPP was produced according to the following Production Example 1. The low melting point sPP is a commercial product.
(Production Example 1)
To a glass autoclave with an internal volume of 500 ml sufficiently purged with nitrogen, 250 ml of toluene was charged, propylene gas was circulated in an amount of 150 liters / hour, and kept at 25 ° C. for 20 minutes. On the other hand, a magnetic stirrer was placed in a 30-ml branch flask with a sufficient nitrogen substitution, and 5.00 mmol of a toluene solution of methylaluminoxane (Al = 1.53 mol / l) and then dibenzylmethylene (cyclopenta). Toluene solution (5.0 μmol) of (dienyl) (2,7-diphenyl-3,6-di-tert-butylfluorenyl) zirconium dichloride was added and stirred for 20 minutes. This solution was added to toluene in a glass autoclave in which propylene had been circulated, and polymerization was started.
Propylene gas was continuously supplied at a rate of 150 liters / hour, polymerization was carried out at 50 ° C. for 10 minutes under normal pressure, and then a small amount of methanol was added to stop the polymerization. The polymer solution was added to a large excess of methanol to precipitate the polymer and dried under reduced pressure at 80 ° C. for 12 hours. As a result, 6.95 g of polymer was obtained. The properties of the obtained polymer are shown in Table 1.

[Preparation of unstretched film]
The resin composition in which the high melting point sPP and the low melting point sPP were mixed at various ratios was formed into a film by a melt extrusion method to obtain unstretched films AD. The relationship between the unstretched film and the resin composition is as follows.
Unstretched film A: high melting point sPP / low melting point sPP = 10/0
Unstretched film B: high melting point sPP / low melting point sPP = 8/2
Unstretched film C: high melting point sPP / low melting point sPP = 5/5
Unstretched film D: high melting point sPP / low melting point sPP = 0/10

  The melt extrusion was performed using a melt extruder (die width: 20 mm) manufactured by Thermo Plastic Industry Co., Ltd., and a film was formed at a molding temperature of 200 ° C. and a cooling roll temperature of 40 ° C. The film thickness of the molded film was 150 μm.

[Stress strain curve]
A sample having the shape shown in FIG. 1 was punched from the obtained unstretched films A to D. The obtained sample was subjected to the preheating temperature and stretching temperature shown in Table 1 using a tensile tester with a thermostatic bath (tensile tester: AGS-500B, thermostatic bath: TCR1-200, Shimadzu Corporation) with a strain rate of 200% / Measurement was performed by stretching 4 times in min.

  The presence or absence of a yield point was confirmed from the stress strain curve. Further, by observing the stretched state, the case where uniform stretching was possible was evaluated as “◯”, the case where there was a non-uniform portion in part, “Δ”, and the case where uniform stretching was not possible was evaluated as “X”. The results are shown in Table 1.

[Uniaxial stretching]
The obtained unstretched films A to D were punched out to 85 mm □, and the obtained sample was attached to a batch stretching machine (KAROIV Brookner) while being chucked only in the MD direction, and strained at the preheating temperature and stretching temperature shown in Table 1. Uniaxial stretching was performed at a rate of 200% / min so that the film thickness was doubled (the film thickness was 1/2).

[Measurement of phase difference]
The phase difference of the sample stretched twice by uniaxial stretching was measured with an optical material inspection apparatus RETS-100 (Otsuka Electronics Co., Ltd.) and converted to a film thickness of 50 μm. Table 1 shows the numerical values after conversion.

[Measurement of total light transmittance]
The total light transmittance of the sample stretched twice by uniaxial stretching was measured with a fully automatic haze meter TC-HIIIDPK (Tokyo Denshoku Co., Ltd.). The measurement results are shown in Table 1.

[Evaluation of heat resistance]
A sample stretched twice by uniaxial stretching was cut to 50 mm □. The obtained sample was put into an oven (air atmosphere) at 120 ° C. for 120 hours. Subsequent dimensional changes were confirmed. The case where there was no direction in which the dimensional change was 10% or more was evaluated as “◯”, and the case where the dimensional change was 10% or more in one direction was evaluated as “X”. The evaluation results are shown in Table 1.

[Biaxial stretching]
From the obtained unstretched films A to D, a sample of 85 mm □ was punched out. The obtained sample was attached to a batch stretching machine (KAROIV Bruckner) at the preheating temperature and stretching temperature shown in Table 1, and simultaneous biaxial stretching of MD × TD = 2 × 2 was performed. When observing the stretched state, “○” indicates that the film has been uniformly stretched, “○” indicates that there is only a partially uneven portion, and “△” indicates that there is a partially uneven portion. The case where it was not possible was evaluated as "x".

Comparative Examples 1 to 3 in which the film A containing only the high melting point sPP was stretched could not be uniformly stretched due to the yield point, or were broken during stretching because of excessive heat. .
On the other hand, Comparative Examples 4 to 5 in which the film D containing only the low melting point sPP was stretched could eliminate or reduce the yield point by heating, but the film had insufficient heat resistance and was practical. Not a film. Further, the film was cut during stretching due to excessive heating (Comparative Example 6).

  On the other hand, when the film B or film C containing the high melting point sPP and the low melting point sPP is stretched, the yield point can be eliminated or reduced by adjusting the preheating temperature and the stretching temperature, It can be seen that uniform stretching can be realized.

  Furthermore, it turns out that the retardation of the uniaxially stretched film of the film C is low compared with other uniaxially stretched films. 2A to 2D are graphs showing the relationship between the draw ratio and the phase difference of the uniaxially stretched films A to D. Specifically, FIG. 2A shows the phase difference of a stretched film obtained by uniaxially stretching film A at 120 ° C. (Comparative Example 2) or 130 ° C. (Comparative Example 3); The retardation of the stretched film uniaxially stretched in Example 1 is shown; FIG. 2C shows the retardation of the stretched film uniaxially stretched at 120 ° C. (Example 3) or 130 ° C. (Example 4). FIG. 2D shows the retardation of a stretched film obtained by uniaxially stretching the film D at 80 ° C. (Comparative Example 4) or 100 ° C. (Comparative Example 5).

  It can be seen that the phase difference of the film C can be easily controlled by the stretching ratio as compared with the film A and the film B.

[DSC measurement]
Resin of unstretched film A (high melting point sPP alone), resin of unstretched film D (low melting point sPP alone), and resin of unstretched film C (1: 1 mixture of high melting point sPP and low melting point sPP) Were respectively measured by DSC. The maximum endothermic peak of the unstretched film A resin was observed at 160 ° C., and the maximum endothermic peak of the resin of the unstretched film D was observed at 128 ° C. On the other hand, for the resin of the unstretched film C, no endothermic peak was observed at 160 ° C. and 128 ° C., and a maximum endothermic peak was observed at 155 ° C.

  In the unstretched film C, neither an endothermic peak corresponding to the high melting point sPP alone nor an endothermic peak corresponding to the low melting point sPP alone was observed, so that it was confirmed that both were completely compatible.

  In addition, in the resin of the unstretched film D (low melting point sPP alone), a small endothermic peak was observed even at 115 ° C., and this is presumed to be a factor causing the dimensional change in the 120 ° C. heat resistance test.

  The stretched film provided by the present invention has thickness uniformity and low haze while containing syndiotactic polypropylene, and the stretch ratio is freely adjusted from low to high. Therefore, application to various optical films, in particular, the retardation can be freely adjusted, so that it can be applied as a retardation film.

Claims (6)

A stretched film comprising a resin composition comprising a resin (A) having a melting point and a resin (B) having a melting point lower by 5 ° C. than the melting point of the resin (A),
The resin (A) and the resin (B) are both syndiotactic polypropylene,
The syndiotactic polypropylene contains 91 to 100 mol% of structural units derived from propylene,
The amount of the resin (B) relative to the total weight of the resin (A) and the resin (B) is 20 to 80% by weight,
Total light transmittance of 90% or more, and Ri der dimensional change of not more than 10% in the heat resistance test at 120 ° C. 120 hours in air,
The resin composition has a maximum endothermic peak due to DSC at a temperature lower than the melting point of the resin (A) and higher than the melting point of the resin (B), and the melting point of the resin (A) and the above The melting point of the resin (B) does not have an endothermic peak due to DSC.
Stretched film. The stretched film according to claim 1, wherein the resin (A) is a syndiotactic polypropylene having a melting point of 150 ° C or higher, and the resin (B) is a syndiotactic polypropylene having a melting point of 140 ° C or lower. The melting point of the resin (B) is at 100 ° C. or higher, and lower 20 ° C. or higher than the melting point of the resin (A), the stretched film according to claim 1 or 2. It is a manufacturing method of the stretched film as described in any one of Claims 1-3 ,
In the step of preheating an unstretched film containing the resin (A) and the resin (B), the preheating temperature is higher than a temperature lower by 10 ° C. than the melting point of the resin (B), and the resin (A) Step (1) having a temperature lower than the melting point of
And a step (2) of stretching the preheated unstretched film. The manufacturing method according to claim 4 , wherein a stretching temperature in the step (2) is higher than a temperature lower by 10 ° C from a melting point of the resin (B) and lower than a melting point of the resin (A). The production method according to claim 4 or 5 , wherein a draw ratio in the step (2) is 1.1 to 4 times.

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