TW201412779A - Polypropylene film used for in-mold labels - Google Patents

Abstract

Disclosed is a polypropylene film used for in-mold labels. The means provided by the instant disclosure to solve problems is a polypropylene film used for in-mold labels, which is mainly made of polypropylene resin, characterized as: the thermal contraction rates at 150 DEG C along the MD direction and the TD direction are both below 9%, Young's modulus along the MD direction is above 2GPa, Young's modulus along the TD direction is above 4GPa, and the haze is below 6%.

Description

Polypropylene film for in-mold label

The present invention relates to a polypropylene film for an in-mold label excellent in heat resistance and mechanical properties.

The shrinkage ratio of the conventional polypropylene film at 150 ° C is several tens of %, and the heat resistance is lower than that of PET or the like, and the rigidity is also low, and curling is likely to occur due to shrinkage during lamination processing, which causes a defect.

In order to solve these problems, it is known to produce a film having a high-temperature rigidity and heat resistance by using a polypropylene having a high stereoregularity and a narrow molecular weight distribution to form a stretched film (see, for example, Patent Document 1).

In addition, it is known that a stretched film made of polypropylene having a high stereoregularity and a wide molecular weight distribution can be used as a capacitor film excellent in electrical insulating properties and mechanical properties (see, for example, Patent Document 2).

Further, it is known to use a technique of forming a separator by using a low molecular weight, polypropylene having a soluble content of 0 ° C in a specific range according to a temperature rising fractionation method, and the film is excellent in dimensional stability in a drying step and a printing step (refer to, for example, Patent Document 3, etc.).

However, the films described in Patent Documents 1 to 3 are difficult to stretch and have poor mechanical properties.

It is known to add a trace amount of long chain branched or crosslinked polypropylene to The medium molecular weight component promotes the formation of a sub-layer to improve the stretchability, and is excellent in mechanical properties, heat resistance, and withstand voltage characteristics, and is excellent in the uniformity of various physical properties (see, for example, Patent Document 4).

Further, it is known that a film having a substantially equal amount of a high molecular weight component and a medium molecular weight component (having a small molecular weight component), a broad molecular weight distribution, and a low content of decahydronaphthalene soluble matter is formed into a film to achieve rigidity and A technique for balance of workability (see, for example, Patent Document 5).

The films described in Patent Documents 4 to 5 are not sufficiently high in heat resistance at high temperatures, and have high heat resistance, and are excellent in polypropylene film having excellent punching resistance and transparency. That is, they do not exceed the scope of the conventional polypropylene film, and their use is limited, and heat resistance at a high temperature of, for example, higher than 150 ° C is not conspicuous.

When the label is attached to the outside of a resin container such as a polypropylene or a polyethylene container, the in-mold label method attached to the outside of the container while the container is molded is difficult to remove due to the comprehensive sealing. It can be used with a large-area label display, etc., which is excellent in design and can be made thinner by increasing the rigidity of the container by the label.

In the past, paper, synthetic paper, plastic film, and the like have been used as the in-mold label base material (see, for example, Patent Document 6, Patent Document 7, Patent Document 8, and the like).

In the case of a plastic film, in order to perform printing, lamination processing, or subsequent processing, the same plastic film is bonded to each other, and a plastic film of various materials according to the label specifications is bonded to form an in-mold label. As the plastic film, a polypropylene film is often used from the viewpoint of adhesion to a container.

However, the past in-mold labels used polypropylene film, known because of these additions Specifically, the film is stretched or shrunk due to the tension of the film under heating during printing and lamination, and the curl of the label causes many problems after processing as a label (see, for example, Patent Document 9).

In order to suppress the curling, it is necessary to frequently adjust the processing conditions, thicken the thickness of the polypropylene film, and select the center portion in the width direction of the polypropylene film to use the method as the in-mold label substrate in the printing and lamination processing. Make labels at high cost.

[Previous Technical Literature]

[Patent Document]

Patent Document 1 Japanese Patent Laid-Open No. Hei 8-325327

Patent Document 2 Japanese Patent Laid-Open Publication No. 2004-175932

Patent Document 3 Japanese Patent Laid-Open Publication No. 2001-146536

Patent Document 4 Japanese Patent Laid-Open Publication No. 2007-84813

Patent Document 5 Japanese Patent Publication No. 2008-540815

Patent Document 6 Japanese Patent Laid-Open No. 58-69015

Patent Document 7 Japanese Special Fair 02-7814

Patent Document 8 Japanese Patent Publication No. 02-84319

Patent Document 9 Japanese Patent Laid-Open Publication No. 2005-208355

The present invention has been completed in the context of the subject matter of the related art. That is, it is an object of the present invention to provide a polypropylene film suitable for use in in-mold labels.

The inventor of the case, etc., in order to achieve the result of this effort, the end To complete the present invention. That is, the present invention relates to a polypropylene film for an in-mold label, which is a film mainly composed of a polypropylene resin, characterized in that the heat shrinkage ratio in the MD direction and the TD direction at 150 ° C is 9% or less. The Young's modulus in the MD direction is 2 GPa or more, the Young's modulus in the TD direction is 4 GPa or more, and the haze value is 6% or less.

In this case, the lower limit of the isotactic meso pentad fraction of the polypropylene resin constituting the film is preferably 96%, and the lower limit of the surface alignment coefficient of the film is preferably 0.0125.

Further, in this case, the upper limit of the amount of the comonomer of the polypropylene resin constituting the film is preferably 0.1 mol%.

Further, in this case, the content of the normal temperature xylene solubles of the polypropylene resin constituting the film is preferably 7% by mass or less.

Even when a plastic film of various materials is attached to the polypropylene film of the present invention to form an in-mold label, the polypropylene film of the present invention is not easily stretched by the tension at the time of printing and lamination processing, and the bonding can be prevented. The label after the curl is curled.

Fig. 1 is a DSC chart of the polypropylene film described in Example 1 and Comparative Example 1.

[Formation of the Invention]

The present invention relates to a polypropylene film for in-mold labels. The polypropylene film for in-mold label of the present invention is made of polypropylene resin as a main body The film is characterized in that the heat shrinkage ratio in the MD direction and the TD direction at 150 ° C is 9% or less, the Young's modulus in the MD direction is 2 GPa or more, the Young's modulus in the TD direction is 4 GPa or more, and the haze value is 6 %the following.

(film properties)

The lower limit of the heat shrinkage ratio in the MD direction and the TD direction of the polypropylene film of the present invention at 150 ° C is preferably 0.5%, more preferably 1%, still more preferably 1.5%, particularly preferably 2%, most preferably 2.5. %. When the heat shrinkage ratio is 0.5% or more, it is practically easy to manufacture on a cost surface or the like, and the thickness unevenness is small. Wherein the MD direction is the moving direction of the film, and the TD direction is perpendicular to the direction of the film moving direction.

The upper limit of the heat shrinkage ratio at 150 ° C in the MD direction and the TD direction is 9%, preferably 8%, more preferably 7%, still more preferably 6%, most preferably 5%. When the heat shrinkage ratio is 9% or less, a film excellent in heat resistance can be obtained, and it is easier to use it in applications that may be exposed to a high temperature of about 150 °C. In the case where the heat shrinkage ratio at 150 ° C is about 2.5% or more, the tensile condition and the heat setting condition can be adjusted by, for example, increasing a low molecular weight polypropylene having a molecular weight of about 100,000 (hereinafter referred to as a low molecular weight component). However, in the case where it is lower than about 2.5%, it is preferable to carry out annealing treatment offline. Among them, in the conventional polypropylene film, the heat shrinkage rate at 150 ° C in the MD direction and the TD direction was 15% or more, and the heat shrinkage ratio at 120 ° C was about 3%.

In the case where the polypropylene film is a biaxially stretched film, the lower limit of the Young's modulus (23 ° C) in the MD direction is 2 GPa, preferably 2.1 GPa, more preferably 2.2 GPa, still more preferably 2.3 Gpa, most preferably 2.4GPa. The upper limit of the Young's modulus in the MD direction is preferably 4 GPa, more preferably 3.7 Gpa, and even more preferably 3.5GPa, especially good for 3.4Gpa, the best is 3.3GPa. When the Young's modulus in the MD direction is 2 GPa or more and 4 GPa or less, it is easy to manufacture in reality, and the MD-TD balance becomes good.

In the case where the polypropylene film is a biaxially stretched film, the lower limit of the Young's modulus (23 ° C) in the TD direction is 4 GPa, more preferably 4.2 GPa, still more preferably 4.3 GPa. The upper limit of the Young's modulus in the TD direction is preferably 8 GPa, more preferably 7.5 GPa, still more preferably 7 GPa, and particularly preferably 6.5 GPa. If the Young's modulus in the TD direction is 3.8 GPa or more and 8 GPa or less, it is easy to manufacture in reality, and the MD-TD balance becomes good.

Among them, the Young's modulus can be increased by increasing the stretching ratio, and the TD can be increased by setting the stretching ratio in the MD direction to a low value and increasing the stretching ratio in the TD direction in the case of MD-TD stretching. Young's coefficient of direction.

The lower limit of the practical value of the haze value of the polypropylene film of the present invention is preferably 0.1%, more preferably 0.2%, still more preferably 0.3%, particularly preferably 0.4%, most preferably 0.5%. The upper limit of the haze value of the film is 6%, preferably 5%, more preferably 4.5%, still more preferably 4%, most preferably 3.5%. By allowing the haze value to be 6% or less, it is easy to use for applications requiring transparency. When the haze value is too high, for example, when the stretching temperature or the heat setting temperature is too high, the temperature of the cooling roll is high, the cooling rate is slow, and the amount of low molecular weight components is too large, there is a tendency that the haze value is increased by adjusting the items. It is set within the above range.

The upper limit of the crimp amount of the polypropylene film of the present invention is preferably 15 mm, more preferably 14 mm, still more preferably 13 mm, most preferably 12 mm. When the amount of crimping is 15 mm or less, the occurrence of film defects due to curling can be suppressed. Among them, the method of measuring the amount of curling will be described later.

(polypropylene resin)

The polypropylene resin constituting the film of the present invention has a characteristic broad molecular weight distribution. A polypropylene-based resin used in the present invention, for example, mass average molecular weight (M _w) of about 100,000 low molecular weight polypropylene (low molecular weight component) as a main component, further comprising e.g. M _w of about 1.5 million of very high molecular weight High molecular weight polypropylene (hereinafter referred to as a high molecular weight component) is preferred. By using a low molecular weight component as a main component, it is considered that the crystallinity can be greatly improved, and a polypropylene film having high rigidity and high heat resistance which has not been obtained in the past can be obtained. On the other hand, the low molecular weight polypropylene resin has a low melt tension after heat softening, and it is generally difficult to form a stretched film. The stretching can be carried out by the presence of a high molecular weight component of several to tens of %, and the crystallinity of the film can be further improved by the role of the high molecular weight component as a crystal nucleus, and it is considered that the polypropylene of the present invention can be easily obtained. film.

Examples of the parameter indicating the molecular weight of the polymer include a number average molecular weight (M _n ), a mass average molecular weight (M _w ), a Z average molecular weight (M _z ), a Z+1 average molecular weight (M _z+1 ), and a peak molecular weight. (M _p) and the like, which is based molecular weight to the number of molecules (M _i) of the (N _i) as hereinafter defined.

Number average molecular weight: M _n = Σ (N _i .M _i ) / ΣN _i

Mass average molecular weight: M _w = Σ (N _i .M _i ² ) / Σ (N _i .M _i )

Z average molecular weight: M _z = Σ (N _i .M _i ³ ) / Σ (N _i .M _i ² )

Z+1 average molecular weight: M _z+1 = Σ (N _i .M _i ⁴ ) / Σ (N _i .M _i ³ )

Peak molecular weight: M _p (molecular weight of the peak position of the gel permeation chromatography (GPC) curve)

Further, as a parameter indicating the molecular weight distribution, the ratio of these average molecular weights is generally used, and examples thereof include M _w /M _n , M _z+1 /M _n and the like, and molecular weights characteristic of the polypropylene resin usable in the present invention are used. Distribution, M _z+1 /M _{n is} appropriate. As a method of measuring such a molecular weight and a molecular weight distribution, GPC is generally used.

The lower limit of M _z+1 /M _n is preferably 50, more preferably 60, still more preferably 70, particularly preferably 80, and most preferably 90. When M _z+1 /M _{n is} less than 50, the effect of the present invention such as a low heat shrinkage rate at a high temperature is not easily obtained. The upper limit of M _z+1 /M _n is preferably 300, more preferably 200. If M _z+1 /M _{n is} more than 300, it is practically difficult to manufacture a resin.

The lower limit of M _z+1 of the entire polypropylene resin constituting the film is preferably 2,500,000, more preferably 3,000,000, still more preferably 3,300,000, particularly preferably 3,500,000, and most preferably 3,300,000. When M _z+1 is 2,500,000 or more, the high molecular weight component is sufficient, and the effect of the present invention can be easily obtained. The upper limit of M _z+1 of the entire polypropylene resin constituting the film is preferably 40,000,000, more preferably 35,000,000, still more preferably 30,000,000. When M _z+1 is 4,000,000 or less, it is easy to manufacture a resin in reality, it is easy to stretch, and fisheye in a film is reduced.

The lower limit of the polypropylene resin constituting the entire film is preferably a M _n of 20,000, more preferably 22,000, and still more preferably 24,000, particularly preferably 26,000, most preferably 27,000. When M _n is 20,000 or more, the stretching is easy, the thickness unevenness is small, and the stretching temperature and the heat setting temperature are easily increased to lower the heat shrinkage rate. The upper limit of M _n of all the films constituting the polypropylene resin is preferably from 65,000, more preferably 60,000, and still more preferably 55,000, particularly preferably 53,000, most preferably 52,000. When M _n is 65,000 or less, the effect of a low molecular weight component is easily exhibited, and it is easy to obtain a low heat shrinkage rate at a high temperature, and it is easy to stretch.

The lower limit of the M _w of the entire polypropylene resin constituting the film is preferably 250,000, more preferably 260,000, still more preferably 270,000, particularly preferably 280,000, and most preferably 290,000. When the M _w is 250,000 or more, the stretching is easy, the thickness unevenness is small, and the stretching temperature and the heat setting temperature are easily increased to lower the heat shrinkage rate. The upper limit of the M _w of the entire polypropylene resin constituting the film is preferably 500,000, more preferably 450,000, still more preferably 400,000, particularly preferably 380,000, and most preferably 370,000. When the M _w is 500,000 or less, the mechanical load is small and it is easy to stretch.

Further, the lower limit of M _w /M _n is preferably 5.5, more preferably 6, more preferably 6.5, particularly preferably 7, and most preferably 7.2.

The upper limit of M _w /M _n is preferably 30, more preferably 25, still more preferably 20, particularly preferably 15, and most preferably 13.

The lower limit of the melt flow rate (MFR) (230 ° C, 2.16 kgf) of the entire polypropylene resin constituting the film is preferably 1 g/10 min, more preferably 1.2 g/10 min, still more preferably 1.4 g/10 min. It is preferably 1.5g/10 minutes, and most preferably 1.6g/10 minutes. When the MFR is 1 g/10 minutes or more, the mechanical load is small and it is easy to stretch. The upper limit of the MFR of the entire polypropylene resin constituting the film is preferably 11 g/10 min, more preferably 10 g/10 min, still more preferably 9 g/10 min, and particularly preferably 8.5 g/10 min. When the MFR is 11 g/10 minutes or less, stretching is easy, thickness unevenness is small, and the stretching temperature and the heat setting temperature are easily increased to lower the heat shrinkage rate.

Determination of gel permeation chromatography of the entire polypropylene resin constituting the film In the cumulative curve of (GPC), the lower limit of the ratio of the molecular weight of 10,000 or less components in the entire polypropylene resin is preferably 2% by mass, more preferably 2.5% by mass, still more preferably 3% by mass, and particularly preferably 3.3% by mass. The best is 3.5% by mass. When the ratio of the component having a molecular weight of 10,000 or less is 2% by mass or more, the effect of the present application, such as a low heat-shrinkage ratio at a high temperature, which is more effective in obtaining a low molecular weight product, is more easily obtained, and the film is easily stretched.

The upper limit of the ratio of the molecular weight of 10,000 or less in the entire polypropylene resin in the GPC accumulation curve is preferably 20% by mass, more preferably 17% by mass, still more preferably 15% by mass, particularly preferably 14% by mass, most preferably It is 13% by mass. When the ratio of the component having a molecular weight of 10,000 or less is 20% by mass or less, the stretching is easy, and the thickness unevenness is small, and the stretching temperature and the heat setting temperature are easily increased to lower the shrinkage ratio.

A molecule having a molecular weight of 10,000 or less does not contribute to entanglement of molecular chains, and has an effect of entanglement of molecules caused by a plasticizer. By containing a specific amount of a component having a molecular weight of 10,000 or less, the entanglement of the molecule during stretching is easily released, and it can be stretched with a low tensile stress. As a result, it is considered that the residual stress is low and the shrinkage at a high temperature can be lowered.

The lower limit of the ratio of the molecular weight of 100,000 or less in the entire polypropylene resin in the GPC accumulation curve is preferably 35 mass%, more preferably 38 mass%, still more preferably 40 mass%, particularly preferably 41 mass%, and most preferably It is 42% by mass. When the component ratio of the molecular weight of 100,000 or less is 35 mass% or more, the effect of a low molecular weight substance is easily exhibited, and it is easy to obtain a low heat shrinkage rate at a high temperature, and it is easy to stretch.

The molecular weight of the polypropylene resin in the GPC accumulation curve is 100,000 The upper limit of the ratio of the lower component is preferably 65 mass%, more preferably 60 mass%, still more preferably 58 mass%, particularly preferably 56 mass%, and most preferably 55 mass%. When the ratio of the component having a molecular weight of 100,000 or less is 65 mass% or less, the stretching is easy, the thickness unevenness is small, and the stretching temperature and the heat setting temperature are easily increased to easily lower the heat shrinkage rate.

In the past, polypropylene which is mainly composed of low molecular weight components cannot be sufficiently stretched, but by using a polypropylene resin having a molecular weight distribution having such characteristics, even polypropylene which is mainly composed of a low molecular weight component can be stretched, and can be used. The high heat setting temperature is considered to reduce the heat shrinkage rate at a high temperature by the synergistic effect of high crystallinity and strong heat fixation.

The high molecular weight component and the low molecular weight component which are preferably used in order to obtain a polypropylene resin having such a molecular weight distribution are explained below.

(high molecular weight component)

The lower limit of the MFR (230 ° C, 2.16 kgf) of the high molecular weight component is preferably 0.0001 g/10 min, more preferably 0.0005 g/10 min, still more preferably 0.001 g/10 min, particularly preferably 0.005 g/10 min. . When the MFR of the high molecular weight component is 0.0001 g/10 min or more, it is practically easy to produce a resin, and the fish eye of the film can be reduced.

Among them, the MFR of the high molecular weight component at 230 ° C and 2.16 kgf is too small, and it is difficult to measure it in reality. Preferably, the lower limit is 0.1 g/10 min, more preferably 0.5 g/10 min, more preferably 1 g/10 min, even more preferably 5 g/, expressed as MFR at a load of 10.6 kgf (21.6 kgf). 10 minutes.

The upper limit of the MFR of the high molecular weight component is preferably 0.5 g/10 min, more preferably 0.35 g/10 min, still more preferably 0.3 g/10 min, and particularly preferably 0.2 g/10 Minutes, the best is 0.1g/10 minutes. When the MFR of the high molecular weight component is 0.5 g/10 minutes or less, it is not necessary to contain a large amount of high molecular weight component in order to maintain the MFR of the entire polypropylene resin, and it is easy to exhibit the effect of a low molecular weight component, and it is easier to obtain a low heat shrinkage rate at a high temperature. .

The lower limit of M _w of the high molecular weight component is preferably 500,000, more preferably 600,000, still more preferably 700,000, particularly preferably 800,000, most preferably 1,000,000. M _w molecular weight component if it is more than 500,000, it is not necessary in order to maintain MFR of the whole polypropylene resin composition containing a large amount of polymer, readily exhibit the effect of the low molecular weight component, more readily available at a low temperature of the heat shrinkage and the like.

The upper limit of the M _w of the high molecular weight component is preferably 10,000,000, more preferably 8,000,000, still more preferably 6,000,000, and particularly preferably 5,000,000. When the M _{w of the} high molecular weight component is 10,000,000 or less, it is practically easy to manufacture a resin, and the fish eye of the film can be reduced.

The lower limit of the amount of the high molecular weight component is preferably 2% by mass, more preferably 3% by mass, still more preferably 4% by mass, and particularly preferably 5% by mass. When the amount of the high molecular weight component is 2% by mass or more, it is not necessary to increase the molecular weight of the low molecular weight component in order to maintain the MFR of the entire polypropylene resin, and it is easier to obtain the effect of the present invention such as a low heat shrinkage rate at a high temperature.

The upper limit of the amount of the high molecular weight component is preferably 30% by mass, more preferably 25% by mass, still more preferably 22% by mass, particularly preferably 20% by mass. When the amount of the high molecular weight component is 30% by mass or less, the effect of the low molecular weight component is easily exhibited, and it is easier to obtain a low heat shrinkage rate at a high temperature. Wherein, the ratio of the high molecular weight component to the entire polypropylene resin constituting the film, The peak separation was carried out from a molecular weight distribution curve measured by GPC, and other components such as low molecular weight components to be described later were also obtained.

Among them, the high molecular weight component may also use a polypropylene resin having a long-chain branching or cross-linking structure instead of a linear polypropylene resin, which is known as a high-melting tensile polypropylene, such as Daploy "WB130HMS" manufactured by Borealis Co., Ltd., WB135HMS" and so on.

(low molecular weight component)

The lower limit of the MFR (230 ° C, 2.16 kgf) of the low molecular weight component is preferably 70 g/10 min, more preferably 80 g/10 min, still more preferably 100 g/10 min, particularly preferably 150 g/10 min, most preferably 200g/10 minutes. When the MFR of the low molecular weight component is 70 g/10 minutes or more, the crystallinity is improved, and it is easier to obtain a low heat shrinkage rate at a high temperature.

The upper limit of the MFR of the low molecular weight component is preferably 2,000 g/10 min, more preferably 1800 g/10 min, still more preferably 1600 g/10 min, particularly preferably 1500 g/10 min, most preferably 1500 g/10 min. When the MFR of the low molecular weight component is 2,000 g/10 minutes or less, the MFR of the entire polypropylene resin is easily maintained, and the film formability is excellent.

The lower limit of the M _w of the low molecular weight component is preferably 50,000, more preferably 53,000, still more preferably 55,000, particularly preferably 60,000, most preferably 70,000. When the M _{w of the} low molecular weight component is 50,000 or more, the MFR of the entire polypropylene resin is easily maintained, and the film formability is excellent.

The upper limit of the M _w of the low molecular weight component is preferably 170,000, more preferably 165,000, still more preferably 160,000, particularly preferably 155,000, and most preferably 150,000. M _w of low molecular weight component when 170,000 or less, the crystallinity becomes better, easier to obtain low heat shrinkage at high temperatures.

The lower limit of the amount of the low molecular weight component is preferably 40% by mass, more preferably 50% by mass, still more preferably 55% by mass, and particularly preferably 60% by mass. When the amount of the low molecular weight component is 40% by mass or more, it is easier to obtain a low heat-shrinkage ratio at a high temperature due to the effect of the low molecular weight component.

The upper limit of the amount of the low molecular weight component is preferably 98% by mass, more preferably 97% by mass, still more preferably 96% by mass, particularly preferably 95% by mass. When the amount of the low molecular weight component is 98% by mass or less, it is not necessary to increase the molecular weight of the low molecular weight component in order to maintain the MFR of the entire polypropylene resin, and it is easier to obtain a low heat shrinkage rate at a high temperature.

The lower limit of the MFR ratio of the MFR/high molecular weight component of the low molecular weight component is preferably 500, more preferably 1,000, still more preferably 2,000, and particularly preferably 4,000. When the MFR ratio of the MFR/high molecular weight component of the low molecular weight component is 500 or more, the effect of the present invention such as a low heat shrinkage rate at a high temperature is more easily obtained. The upper limit of the MFR ratio of the MFR/high molecular weight component of the low molecular weight component is preferably 1,000,000.

The high molecular weight component and the low molecular weight component may be a mixture of two or more kinds of the respective components, and the blending amount in this case is a total amount.

Further, in addition to the above-described high molecular weight component and low molecular weight component, in order to adjust the MFR of the entire polypropylene resin, a component having a molecular weight other than the low molecular weight component and the high molecular weight component of the present invention may be added. For example, polypropylene (hereinafter referred to as a medium molecular weight component) having a Mw larger than a low molecular weight component and smaller than a high molecular weight component may be contained. Further, in order to easily entangle the molecular chain to adjust the stretchability and the like, it is preferred to add a polypropylene having a M _{w of} less than 50,000, more preferably a polypropylene resin having a M _{w of} 30,000 or less, particularly preferably M _w Polypropylene resin of less than 10,000.

The lower limit of the ratio of the medium molecular weight component of the entire polypropylene resin constituting the film depends on the M _w of the molecular weight component used, but is preferably 5% by mass, more preferably 10% by mass, and even more preferably 13% by mass, particularly preferably 15% by mass, most preferably 16% by mass. When the ratio of the medium molecular weight component is 5% by mass or more, the fish eye can be reduced and stretched easily.

The upper limit of the ratio of the medium molecular weight component to the entire polypropylene resin constituting the film is preferably 58% by mass, more preferably 56% by mass, still more preferably 54% by mass, particularly preferably 52% by mass, most preferably 50%. quality%. When the ratio of the medium molecular weight component is 58% by mass or less, the stretching is easy, the thickness unevenness is small, and the stretching temperature and the heat setting temperature are easily increased to lower the heat shrinkage rate.

The lower limit of the ratio of the polypropylene having a _{Mw of} less than 50,000 to the entire polypropylene resin constituting the film is preferably 0% by mass, more preferably 1% by mass, still more preferably 2% by mass, particularly preferably 3% by mass. The best is 4% by mass. By adding a polypropylene having a _{Mw of} less than 50,000, it is easier to obtain the effect of the present invention such as a low heat shrinkage rate at a high temperature.

The upper limit of the ratio of the polypropylene having a _{Mw of} less than 50,000 to the entire polypropylene resin constituting the film is preferably 20% by mass, more preferably 18% by mass, still more preferably 17% by mass, particularly preferably 16% by mass. The best is 15% by mass. When the ratio of the polypropylene having a M _{w of} less than 50,000 is 20% by mass or less, the stretching is easy and the thickness unevenness is small.

A polypropylene molecule having a M _{w of} less than 50,000 is less likely to form entanglement of molecular chains with each other, and has an effect of entanglement of molecules caused by a plasticizer. By containing a specific amount of a component of polypropylene having a _{Mw of} less than 50,000, the entanglement of the molecule during stretching is easily solved, and it can be stretched with a low tensile stress, and as a result, it is considered that the residual stress is low and the shrinkage at a high temperature can be lowered. rate.

In order to use a high molecular weight component and a low molecular weight component, the molecular weight distribution of a polypropylene resin is preferable. For example, when the molecular weight of the low molecular weight component used is low, the molecular weight of a high molecular weight component can be increased, the amount of a high molecular weight component can be increased, etc., and molecular weight distribution can be adjusted. The state is adjusted to become an MFR which is easy to manufacture a stretched film.

(stereoregularity of polypropylene resin)

The lower limit of the isotactic pentad fraction (hereinafter also referred to as mmmm) of the stereoregularity index of the polypropylene resin constituting the film is preferably 96%, more preferably 96.5%, still more preferably 97%. . When the mmmm is 96% or more, the crystallinity is improved, and the heat shrinkage rate at a high temperature is lower.

The upper limit of mmmm is preferably 99.5%, more preferably 99.3%, still more preferably 99%. If the mmmm is 99.5% or less, it is easy to manufacture in reality.

In the polypropylene resin constituting the film, it is preferred that a heterojunction bond such as a head-to-head bond of a propylene monomer is not detected. Here, "undetected heterojunction" means that no peak was observed in ¹³ C-NMR.

The lower limit of the isotactic meso-average chain length (hereinafter referred to as meso-average chain length) of the polypropylene resin constituting the film is preferably 100, more preferably 120, still more preferably 130. When the mesogenic average chain length is 100 or more, the crystallinity is improved, and the heat shrinkage rate at a high temperature is small. The upper limit of the meso-average chain length of the polypropylene resin constituting the film is preferably 5,000 from the practical side.

The lower limit of the xylene soluble fraction of the polypropylene resin constituting the film is from reality The surface is preferably 0.1% by mass. The upper limit of the xylene soluble fraction is preferably 7% by mass, more preferably 6% by mass, still more preferably 5% by mass. When the xylene soluble fraction of the propylene resin is 7% by mass or less, the crystallinity is improved, and the heat shrinkage rate at a high temperature is small.

The polypropylene resin constituting the film is preferably a propylene homopolymer (completely homo-polypropylene) obtained only from a propylene monomer, but may also be a copolymer of a propylene monomer and a trace amount of a monomer other than the propylene monomer. The monomer type (comonomer type) other than the propylene monomer may be ethylene, butene, hexene, octene or the like.

The upper limit of the proportion of the monomer other than the propylene monomer is preferably 0.1 mol%, more preferably 0.05 mol%, still more preferably 0.01 mol%. When the ratio of the monomer other than the propylene monomer is 0.1 mol% or less, the crystallinity is improved, and the heat shrinkage rate at a high temperature is small.

In the case of the conventional polypropylene film, if a propylene homopolymer is used, since the crystallinity is high and the melt tension is rapidly lowered after melting and softening, the range of stretching conditions is very narrow, and industrially difficult to form a film, and usually 0.5 mol is added. About 0.0% of the copolymerization component (mainly ethylene). However, the polypropylene resin having a molecular weight distribution state as described above can be stretched industrially even if it contains almost no copolymerization component or contains no copolymerization component at all, and the tension after melting and softening is stabilized.

(Method for producing polypropylene resin)

The polypropylene resin can be obtained by polymerizing a propylene raw material using a known catalyst such as a 戚Geller-nano catalyst or a metallocene catalyst. Among them, a catalyst which is less likely to have a heterogeneous bond and which is capable of high stereoregular polymerization, such as a Zigler-Natta catalyst, is preferably used.

As a polymerization method of propylene, a known polymerization method can be used, and a method of polymerizing in an inert solvent such as hexane, heptane, toluene or xylene; a method of polymerizing in liquid propylene or ethylene; in propylene or A method in which a catalyst is added to an ethylene gas, and it is polymerized in a gas phase state; or a polymerization method in which these methods are combined.

The method for realizing the polypropylene having the molecular weight distribution of the present invention is not particularly limited, but it is necessary to substantially contain a high molecular weight component and a low molecular weight component. For example, it may be mixed after separately polymerizing a high molecular weight component or a low molecular weight component, or may be produced by a series of apparatuses in a multistage reactor. In particular, in the case of using a device having a multistage reactor, it is preferred to polymerize the high molecular weight component and then polymerize the low molecular weight component in the presence thereof.

In the resin composition for forming a polypropylene film of the present invention, an additive or other resin may be added as needed in addition to a polypropylene resin or the like, but the mass thereof is preferably 30% by mass or less. Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a nucleating agent, an adhesive, an antifogging agent, a flame retardant, an anti-caking agent, an inorganic or organic filler, and the like. Examples of the other resin include a polypropylene resin other than the polypropylene resin used in the present invention, a random copolymer of a copolymer of propylene and ethylene and/or an α-olefin having 4 or more carbon atoms, and various elastomers. Examples of the α-olefin having 4 or more carbon atoms include butene, hexene, and octene. They can be blended with a polypropylene resin in a Hansai mixer, and the masterbatch prepared by using a melt mixer can be diluted to a specific concentration with polypropylene, or the total amount can be melted and mixed in advance.

(film properties)

The lower limit of the surface alignment coefficient of the polypropylene film of the present invention is preferably 0.0125, more preferably 0.0126, still more preferably 0.0127, and particularly preferably 0.0128. The upper limit of the surface alignment coefficient of the polypropylene film of the present invention is preferably 0.015, more preferably 0.0150, still more preferably 0.0148, and particularly preferably 0.0145. The surface alignment coefficient can be adjusted by adjusting the stretching ratio in the MD direction and the TD direction. When the surface alignment coefficient of the film is 0.0125 or more and 0.0155 or less, the thickness unevenness of the film is also good.

The lower limit of the refractive index (N _x ) of the polypropylene film of the present invention in the MD direction is preferably 1.502, more preferably 1.503, still more preferably 1.504. The upper limit of Nx is preferably 1.520, more preferably 1.517, still more preferably 1.515.

The lower limit of the refractive index (Ny) of the polypropylene film of the present invention in the TD direction is preferably 1.523, more preferably 1.525. The upper limit of Ny is preferably 1.535, more preferably 1.532.

The lower limit of the refractive index (Nz) of the polypropylene film of the present invention in the thickness direction is preferably 1.480, more preferably 1.489, still more preferably 1.501. The upper limit of Nz is preferably 1.510, more preferably 1.507, and even more preferably 1.505.

(film crystallinity)

The polypropylene film of the present invention has the following characteristics of high crystallinity.

The lower limit of the degree of crystallization of the polypropylene film of the present invention is preferably 55%, more preferably 56%, still more preferably 57%, particularly preferably 58%, most preferably 59%. When the degree of crystallization of the film is less than 55%, the heat shrinkage rate at a high temperature becomes large. The upper limit of the degree of crystallization of the polypropylene film of the present invention is preferably 85%, more preferably 80%, still more preferably 79%, particularly preferably 78%, most preferably 77%. When the degree of crystallization of the film is more than 85%, it is practically difficult to manufacture. The degree of crystallization of the film can be adjusted by reducing or eliminating comonomers and increasing the low molecular weight. The composition is set such that the stretching temperature and the heat setting temperature are set to a high temperature.

The lower limit of the melting peak temperature of the polypropylene film of the present invention is preferably 168 ° C, more preferably 169 ° C. When the melting peak temperature of the film is 168 ° C or higher, the heat shrinkage rate at a high temperature becomes small. The upper limit of the melting peak temperature of the polypropylene film of the present invention is preferably 180 ° C, more preferably 177 ° C, still more preferably 175 ° C. When the melting peak temperature of the film is 180 ° C or lower, it is practically easy to manufacture. The adjustment of the melting peak temperature can be carried out by reducing or eliminating comonomer, increasing the low molecular weight component, and setting the stretching temperature and the heat setting temperature to a high temperature.

In the case of the conventional polypropylene film, for example, when the melting peak temperature is present at around 170 ° C, a peak (beginning to melt) occurs from about 140 ° C in the case of measurement by a differential scanning calorimeter (hereinafter also referred to as DSC). Even if heat resistance at 140 ° C is expected, the heat shrinkage rate at 150 ° C is rapidly increased. However, the polypropylene film of the present invention did not exhibit a peak even at 150 ° C, and the polypropylene film of the present invention was considered to have low heat shrinkability even at 150 ° C.

The polypropylene film of the present invention can maintain various physical properties even when exposed to an environment of 150 ° C or higher, and can be used even in a high-temperature environment in which a conventional polypropylene film cannot be imagined. Among them, the beginning of melting can be obtained by the DSC chart.

The lower limit of the degree of crystallization at 150 ° C is preferably 48%, more preferably 49%, still more preferably 50%, and particularly preferably 51%. When the degree of crystallization at 150 ° C is 48% or more, the heat shrinkage rate at a high temperature becomes small. The upper limit of the degree of crystallization at 150 ° C is preferably 85%, more preferably 80%, more preferably from the actual side. 79%, especially good 78%. The degree of crystallization at 150 ° C can be set within the range by reducing or eliminating comonomer, increasing the low molecular weight component, setting the stretching temperature, and the heat setting temperature to a high temperature.

The melting peak temperature (Tmp), the degree of crystallization of the film, and the degree of crystallization at 150 ° C can be determined using a differential scanning calorimeter (DSC).

The temperature of the melting endothermic peak obtained when the temperature was raised from room temperature to 230 ° C at a rate of 20 ° C / minute was defined as Tmp. Then, the heat of fusion is obtained from the endothermic peak area, and the degree of crystallization can be obtained by dividing the heat of fusion by 209 J/g of the heat of complete crystallization of polypropylene. Further, among the endothermic peak areas, the heat of fusion is obtained from an endothermic peak area of 150 ° C or more, and the heat of fusion is divided by 209 J/g of the heat of complete crystallization of polypropylene to obtain a total of 150 ° C. The degree of crystallization in the sample. Among them, the heat of fusion of the complete crystallization of polypropylene is the value described in H. Bu, SZDCheng, B. Wunderlich et al., Makromoleculare Chemie, Rapid Communication, Vol. 9, p. 75 (1988), in the examples described later. The same value is also used.

The lower limit of the thickness unevenness of the polypropylene film of the present invention is preferably 0%, more preferably 0.1%, still more preferably 0.5%, particularly preferably 1%. The upper limit of the thickness unevenness of the polypropylene film of the present invention is preferably 20%, more preferably 17%, still more preferably 15%, particularly preferably 12%, most preferably 10%. When the thickness unevenness of the film is 0% or more and 20% or less, it is less likely to cause defects during post-processing such as coating or printing, and it is easy to use for applications requiring precision.

The lower limit of the density of the polypropylene film of the present invention is preferably 0.910 g/cm ³ , more preferably 0.911 g/cm ³ , still more preferably 0.912 g/cm ³ , and particularly preferably 0.913 g/cm ³ . When the density of the film is 0.910 g/cm ³ or more, the crystallinity is high and the heat shrinkage rate is small.

The upper limit of the density of the polypropylene film of the present invention is preferably 0.925 g/cm ³ , more preferably 0.922 g/cm ³ , still more preferably 0.920 g/cm ³ , and particularly preferably 0.918 g/cm ³ . When the density of the film is 0.925 g/cm ³ or less, it is practically easy to manufacture. The density of the film can be increased by increasing the draw ratio or temperature, increasing the heat setting temperature, and performing off-line annealing.

(Method for producing polypropylene film)

The polypropylene film of the present invention may be a uniaxially stretched film in the longitudinal direction (MD direction) or the transverse direction (TD direction), but is preferably a biaxially stretched film. In the case of biaxial stretching, it may be a sequential biaxial stretching or a simultaneous biaxial stretching.

By forming a polypropylene film by stretching, it is possible to obtain a film which is unpredictable in the past polypropylene film even at a heat shrinkage rate of 150 °C.

The method for producing the sequential biaxially stretched film of the longitudinal stretching-transverse stretching of the preferred embodiment will be described below, but the method for producing the polypropylene film is not limited thereto.

First, the melted polypropylene resin was heated by a uniaxial or biaxial extruder and extruded onto a cooling roll to obtain an unstretched sheet. The melt extrusion conditions are such that the resin temperature reaches 200 to 280 ° C, extruded into a sheet shape by a T-die, and cooled and solidified by a cooling roll having a temperature of 10 to 100 ° C. Then, the film is stretched 3 to 8 times in the longitudinal direction (MD direction) by a stretching roll at 120 to 160 ° C, and then continued in the width direction (TD direction) at 155 ° C to 175 ° C, preferably 157 ° C to 170 ° C. The temperature is stretched 4 to 15 times.

Next, at 165~175 ° C, preferably 166 ~ 173 ° C ambient temperature The heat treatment (heat setting) was applied while applying 1 to 15% relaxation.

The polypropylene film obtained in this manner is subjected to a corona discharge treatment on at least one side as needed, and then taken up to a film roll by a coiler.

The lower limit of the stretching ratio in the MD direction is preferably 3 times, more preferably 3.5 times. If the draw ratio in the MD direction is less than 3 times, the thickness is uneven. The upper limit of the stretching ratio in the MD direction is preferably 8 times, more preferably 7 times. If the stretching ratio in the MD direction is more than 8 times, subsequent TD stretching is not easily performed.

The lower limit of the temperature at the time of stretching in the MD direction (hereinafter referred to as stretching temperature) is preferably 120 ° C, more preferably 125 ° C, still more preferably 130 ° C. When the stretching temperature in the MD direction is less than 120 ° C, the mechanical load becomes large, the thickness unevenness becomes large, and the surface of the film is rough. The upper limit of the stretching temperature in the MD direction is preferably 160 ° C, more preferably 155 ° C, still more preferably 150 ° C. The high stretching temperature in the MD direction is advantageous for the reduction of the heat shrinkage rate, but it adheres to the roll and cannot be stretched.

The film is preferably preheated prior to stretching in the TD direction. In order to rapidly raise the film temperature to the stretching temperature in the TD direction, it is preferable to set the preheating temperature (hereinafter referred to as preheating temperature) to be 10 to 15 ° C higher than the stretching temperature in the TD direction.

The lower limit of the stretching ratio in the TD direction is preferably 4 times, more preferably 5 times, still more preferably 6 times. If the stretching ratio in the TD direction is less than 4 times, the thickness is uneven. The upper limit of the stretching ratio in the TD direction is preferably 15 times, more preferably 14 times, still more preferably 13 times. If the stretching ratio in the TD direction is more than 15 times, then The heat shrinkage rate becomes high and it breaks when stretched.

The stretching in the TD direction can be carried out at a higher temperature than the conventional polypropylene film, and the lower limit of the stretching temperature in the TD direction is preferably 155 ° C, more preferably 157 ° C. When the stretching temperature in the TD direction is less than 155 ° C, the film may not be sufficiently softened and cracked, and the heat shrinkage rate may become high. The upper limit of the stretching temperature in the TD direction is preferably 175 ° C, more preferably 170 ° C. In order to lower the heat shrinkage rate, the temperature is preferably higher, but if the stretching temperature in the TD direction is more than 175 ° C, the low molecular component melts and recrystallizes, resulting in surface roughness and film whitening.

The stretched film is preferably heat-set by heat treatment. The heat setting can be carried out at a higher temperature than the conventional polypropylene film, and the lower limit of the heat treatment temperature (hereinafter referred to as heat setting temperature) for heat setting is preferably 165 ° C, more preferably 166 ° C. When the heat setting temperature is less than 165 ° C, the heat shrinkage rate becomes high. In order to reduce the heat shrinkage rate, it takes a long time and the productivity is deteriorated. The upper limit of the heat setting temperature is preferably 175 ° C, more preferably 173 ° C. When the heat setting temperature is more than 175 ° C, the low molecular component is melted and recrystallized to cause surface roughness and film whitening.

It is preferable to make it relax when heat is fixed. The lower limit of the relaxation rate is preferably 1%, more preferably 2%. When the relaxation rate is less than 1%, the heat shrinkage rate becomes high. The upper limit of the relaxation rate is preferably 15%, more preferably 10%. If the relaxation rate is more than 15%, the thickness unevenness becomes large.

Further, in order to reduce the heat shrinkage rate, the film produced in the above step may be wound up in a roll and then annealed off-line.

The lower limit of the temperature at which annealing is performed offline (hereinafter referred to as offline annealing temperature) is preferably 160 ° C, more preferably 162 ° C, still more preferably 163 ° C. Offline annealing If the temperature is less than 160 ° C, the effect of annealing cannot be obtained. The upper limit of the off-line annealing temperature is preferably 175 ° C, more preferably 174 ° C, still more preferably 173 ° C. When the off-line annealing temperature is more than 175 ° C, the transparency is lowered and the thickness unevenness is increased.

The lower limit of the time for performing the off-line annealing (hereinafter referred to as offline annealing time) is preferably 0.1 minute, more preferably 0.5 minute, still more preferably 1 minute. If the off-line annealing time is less than 0.1 minutes, the effect of annealing cannot be obtained. The upper limit of the off-line annealing time is preferably 30 minutes, more preferably 25 minutes, still more preferably 20 minutes. If the off-line annealing time is more than 30 minutes, the productivity is lowered.

The thickness of the film is set for each application, but the lower limit of the film thickness is preferably 2 μm, more preferably 3 μm, still more preferably 4 μm. The upper limit of the film thickness is preferably 300 μm, more preferably 250 μm, still more preferably 200 μm, particularly preferably 150 μm, and most preferably 100 μm.

The polypropylene film thus obtained is usually formed into a roll having a width of 2,000 to 12,000 mm and a length of about 1,000 to 50,000 m, and is wound into a roll. Next, it is cut for use in various applications, and is supplied in a slit roll having a width of 300 to 2000 mm and a length of 500 to 5000 m.

The polypropylene film of the present invention has excellent characteristics which have not been conventionally obtained as described above.

When the polypropylene film of the present invention is used as a film for an in-mold label, heat resistance is high, and shrinkage of the film due to heat during in-mold processing is not observed, and the appearance is good and the curl is also reduced. In addition, since the rigidity is high, the operability in the in-mold processing can be improved.

[Examples]

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited thereto. These embodiments. The measurement method of the physical properties in the examples is as follows.

1) Melt flow rate (MFR, g/10 min)

According to JIS K 7210, the temperature was measured at 230 ° C and a load of 2.16 kgf.

2) Molecular weight and molecular weight distribution

The molecular weight and molecular weight distribution were determined by gel permeation chromatography (GPC) on a monodisperse polystyrene basis.

The column and solvent used in the GPC measurement are as follows: Solvent: 1,2,4-trichlorobenzene

Column: TSKgel GMH _HR -H(20)HT×3

Flow rate: 1.0ml/min

Detector: RI

Measuring temperature: 140 ° C

The number average molecular weight (M _n ), the mass average molecular weight (M _w ), the Z average molecular weight (M _z ), and the Z+1 average molecular weight (M _z+1 ) are respectively dissolved in the GPC curve obtained by the molecular weight correction curve. The number of molecules (N _i ) of the molecular weight (M _i ) of the position is defined by the following formula.

Number average molecular weight: M _n = Σ (N _i .M _i ) / ΣN _i

Mass average molecular weight: M _w = Σ (N _i .M _i ² ) / Σ (N _i .M _i )

Z average molecular weight: M _z = Σ (N _i .M _i ³ ) / Σ (N _i .M _i ² )

Z+1 average molecular weight: M _z+1 = Σ (N _i .M _i ⁴ ) / Σ (N _i .M _i ³ )

Molecular weight distribution: M _w /M _n , M _z+1 /M _n

Further, the molecular weight at the peak position of the GPC curve is M _p .

When the baseline is not clear, the baseline is set to the lowest position of the peaks and valleys on the high molecular weight side of the precipitation peak closest to the high molecular weight side of the precipitation peak of the standard substance. The range to the end.

From the obtained GPC curve, peak separation of two or more kinds of components having different molecular weights was carried out. The molecular weight distribution of each component is assumed to be a Gaussian function, and each peak width is set to M _w /M _n =4. The average molecular weight was calculated from the curves of the obtained components.

Then, the ratio of the ratio of the component having a molecular weight of 10,000 or less and the component having a molecular weight of 100,000 or less in the entire polypropylene resin constituting the film was determined from the GPC curve of the entire polypropylene resin constituting the film.

3) Stereo regularity

The measurement of mmmm and meso average chain length was carried out using ¹³ C-NMR. The mmmm is based on the method described by Zambelli et al. in Macromolecules, Vol. 6, p. 925 (1973). The meso-average chain length is described in JC and Alld in "Polymer Sequence Distribution" Chapter 2 (1977) (Academic Press, New The method of York) is calculated.

For the NMR measurement, AVANCE 500 manufactured by BRUKER Co., Ltd. was used, and 200 mg of the sample was dissolved in an 8:2 mixture of o-dichlorobenzene and heavy benzene at 135 ° C, and the mixture was applied at 110 ° C.

4) Density (g/cm ³ )

The density of the film was measured by a density gradient tube method in accordance with JIS K7112.

5) Melting peak temperature (Tmp, °C)

The thermal measurement was performed using a DSC-60 differential scanning calorimeter manufactured by Shimadzu Corporation. Approximately 5 mg of the film was cut out from the film as a sample, and the sample was sealed in an aluminum pan for measurement. The temperature was raised from room temperature to 230 ° C in a ratio of 20 ° C / minute, and the melting peak temperature of the sample was set to Tmp.

6) Crystallization degree

The heat of fusion (ΔHm, J/g) was obtained from the area of the endothermic peak in the DSC melting curve, and the degree of crystallization was determined by dividing the value of ΔHm by the heat of fusion of 640 J/g of the complete crystal of polypropylene.

Then, the heat of fusion (ΔHm', J/g) is obtained from the area of the endothermic peak at 150 ° C or higher in the DSC melting curve, and the value of ΔHm' is divided by the heat of fusion of 209 J/g of the complete crystal of polypropylene. The degree of crystallization in the full sample at 150 ° C was determined.

7) Cold xylene soluble fraction (CXS, mass%)

1 g of the polypropylene sample was dissolved in 200 ml of boiling xylene, allowed to cool, and then recrystallized in a constant temperature water bath at 20 ° C for 1 hour, and the ratio of the mass dissolved in the filtrate to the amount of the original sample was CXS (mass %).

8) Thermal shrinkage rate (%)

Measured in accordance with JIS Z 1712. That is, the polypropylene film was cut in a length of 20 mm and 200 mm in the MD and TD directions, respectively, and heated in a hot air oven for 5 minutes. The length after heating was measured, and the heat shrinkage ratio was determined in proportion to the original length of the shrinkage length.

9) Young's coefficient (GPa)

The Young's modulus in the MD and TD directions was measured at 23 ° C according to JIS K 7127.

10) Fog value (%)

Measured in accordance with JIS K 7105.

11) Refractive index

It was measured using an Abe refractometer manufactured by ATAGO. Will follow MD, TD The refractive indices in the directions are Nx and Ny, respectively, and the refractive index in the thickness direction is Nz.

12) Surface alignment coefficient

From the Nx, Ny, and Nz measured in the above 11), the plane alignment coefficient (P) was calculated by the following formula.

P=[(Nx+Ny)/2]-Nz

13) Uneven thickness

A square sample having a length of 1 m was cut out from the wound film roll, and 10 pieces were equally divided in the MD direction and the TD direction to prepare 100 samples for measurement. The thickness was measured at a substantially central portion of the sample for measurement by a contact film thickness gauge.

The average value of the obtained data of 100 points is obtained, and then the difference (absolute value) between the minimum value and the maximum value is obtained, and the absolute value of the difference between the minimum value and the maximum value is divided by the average value to obtain a film. The thickness is uneven.

(Example 1)

Propylene homopolymer using M _w /M _n =7.7, M _z+1 /M _n =140, MFR=5.0/10 min, mmmm=97.3% (made by Japan Polypropylene Co., Ltd.: NOVATEC (registered trademark) PP "SA4L") (hereinafter referred to as "PP-1") is used as a polypropylene resin. Using a 60 mm extruder, extruded into a sheet shape at 250 ° C in a T-die, cooled and solidified by a cooling roll at 30 ° C, and then stretched 4.5 times in the longitudinal direction (MD direction) at 135 ° C, and then the ends were clipped. After fixing, it was introduced into a hot air oven, preheated at 170 ° C, and then stretched 8.2 times in the transverse direction (TD direction) at 160 ° C, and then heat-treated at 168 ° C while relaxing at a relaxation rate of 6.7%. Then, one side of the film was subjected to corona treatment and taken up by a winder. The thickness of the film thus obtained was 20 μm, the properties of the polypropylene resin and the like are shown in Tables 1 and 2, and the film formation conditions are shown in Table 3. As shown in Table 5, a film having a low heat shrinkage rate and a high Young's modulus was obtained. A DSC chart of the stretched propylene film of Example 1 is shown in FIG.

On one surface of the polypropylene film of Example 1, an adhesive (TM-386 manufactured by Toyo Morton Co., Ltd.) was applied, and a laminate film composed of a polypropylene film/adhesive/polypropylene film was formed by further superposing a polypropylene film thereon. .

This lamination processing condition was carried out using a gravure laminator, with a tension of 50 N/m, a take-up tension of 55 N/m, an adhesive application amount of 0.6 g/m ² , a drying temperature of 90 ° C, and a drying time of 10 seconds. The laminated product was heated and cooked at an ambient temperature of 40 ° C for 24 hours, and then cut into a short book having a size of 5 cm in the moving direction (MD direction) and 10 cm in the vertical direction (TD direction). Then, the booklet was adjusted in an environment of 23 ° C and 65% Rh, and the amount of curl was measured on a water platform. The amount of crimping is such that the film which is initially applied with the adhesive is placed on the upper side, and the amount floated from the water platform to the upper side is read in centimeters, and the average value of the four corners of the label is taken as the amount of curl.

(Example 2)

10 parts by weight of a low molecular weight polypropylene (Hi-WAX "NP105" manufactured by Mitsui Chemicals Co., Ltd.) having a molecular weight of 10,000 was added to 90 parts by weight of the above "PP-1", and 100 parts by weight in total was melted by a 30 mm twin screw extruder. The mixture was mixed to obtain a pellet of the mixture "PP-2". This pellet was obtained in the same manner as in Example 1 to obtain a film. The properties and the like of the polypropylene resin are shown in Tables 1 and 2, and the film formation conditions are shown in Table 3. The physical properties of the obtained film and the amount of curl of the label are shown in Table 5.

(Example 3)

For 70 parts by weight of the above "PP-1", 30 parts by weight of propylene homopolymer having _Mw / M _n = 4.6, M _z+1 / M _n = 22, MFR = 120 g/10 min, mmmm = 98.1% was added. Dry blending was carried out to obtain a mixture "PP-3". A film was obtained in the same manner as in Example 1 using "PP-3". The properties and the like of the polypropylene resin are shown in Tables 1 and 2, and the film formation conditions are shown in Table 3. The physical properties of the obtained film and the amount of curl of the label are shown in Table 5.

(Example 4)

Using the above-mentioned "PP-1", a film was obtained in the same manner as in Example 1 except that the preheating temperature was 173 ° C, the stretching temperature in the TD direction, and the heat setting temperature were 167 ° C. The properties and the like of the polypropylene resin are shown in Tables 1 and 2, and the film formation conditions are shown in Table 3. The physical properties of the obtained film and the amount of curl of the label are shown in Table 5.

(Example 5)

A film was obtained in the same manner as in Example 2 except that the film was stretched 5.5 times in the longitudinal direction and 12 times in the transverse direction. The properties and the like of the polypropylene resin are shown in Tables 1 and 2, and the film formation conditions are shown in Table 3. The physical properties of the obtained film and the amount of curl of the label are shown in Table 5.

(Example 6)

Using the film produced in Example 1, heat treatment (offline annealing) was performed at 170 ° C for 5 minutes in a tenter type hot air oven. The properties and the like of the polypropylene resin are shown in Tables 1 and 2, and the film formation conditions are shown in Table 3. The physical properties of the obtained film and the amount of curl of the label are shown in Table 5.

(Example 7)

Except for the use of propylene homopolymer ("SAN300" manufactured by SANSUNTOTAL) with M _w /M _n =8.9, M _z+1 /M _n =110, MFR=3.0 g/10 min, mmmm=97.1% (below) The term "PP-4" is the same as that of the first embodiment except that the preheating temperature is 171 ° C, the stretching temperature in the TD direction is 161 ° C, and the heat setting temperature is 170 ° C. The method gave a polypropylene film. The properties and the like of the polypropylene resin are shown in Tables 1 and 2, and the film formation conditions are shown in Table 3. The physical properties of the obtained film and the amount of curl of the label are shown in Table 5.

(Comparative Example 1)

Sumitomo NOBLEN (registered trademark) "FS2011DG3" manufactured by Sumitomo Chemical Co., Ltd., except _Mw / M _n = 4, M _z+1 / M _n = 21, MFR = 2.5 g/10 min, and ethylene content = 0.6 mol%. (hereinafter referred to as "PP-5") as a polypropylene resin, the MD stretching temperature is set to 125 ° C, the preheating temperature is 168 ° C, the stretching temperature in the TD direction is 155 ° C, and the heat setting temperature is set. A film was obtained in the same manner as in Example 1 except for 163 °C. The properties and the like of the polypropylene resin are shown in Tables 1 and 2, and the film formation conditions are shown in Table 4. The physical properties of the obtained film and the amount of curl of the label are shown in Table 6. The DSC chart of the stretched propylene film of Comparative Example 1 is shown in Fig. 1.

(Comparative Example 2)

A film was produced in the same manner as in Comparative Example 1, except that the preheating temperature was 171 ° C, the stretching temperature in the TD direction was 160 ° C, and the heat setting temperature was 165 ° C. The properties and the like of the polypropylene resin are shown in Tables 1 and 2, and the film formation conditions are shown in Table 4. The physical properties of the obtained film and the amount of curl of the label are shown in Table 6.

(Comparative Example 3)

As the polypropylene, a propylene homopolymer (hereinafter referred to as "PP-6") having M _w /M _n =4.3, M _z+1 /M _n =28, MFR=0.5 g/10 min, mmmm=97.0% was used. A resin was obtained under the same conditions as in Example 7 as a resin. The properties and the like of the polypropylene resin are shown in Tables 1 and 2, and the film formation conditions are shown in Table 4. The physical properties of the obtained film and the amount of curl of the label are shown in Table 6.

(Comparative Example 4)

NOVATEC PP "SA03" manufactured by Japan POLYPRO Co., Ltd. using M _w /M _n =2.8, M _z+1 /M _n =9.2, MFR=30 g/10 min, mmmm=97.9% propylene homopolymer The "PP-7" was used as the polypropylene resin, and biaxial stretching was attempted in the same manner as in Example 1. However, when it was stretched in the transverse direction, it was broken, and the film could not be obtained. The properties and the like of the polypropylene resin are shown in Tables 1 and 2, and the film formation conditions are shown in Table 4.

[Industry Utilization]

The polypropylene film of the present invention is suitable for use as an in-mold label because of its low heat resistance and rigidity, and it is not necessary to use a film having a large thickness in order to prevent curling, and it is not necessary to use an intermediate product, and it is also expected to be used as a label. Cost reduction and other advantages.

Claims (4)

A polypropylene film for in-mold label, which is a film mainly composed of a polypropylene resin, characterized in that the heat shrinkage ratio in the MD direction and the TD direction at 150 ° C is 9% or less, and the Young's modulus in the MD direction When it is 2 GPa or more, the Young's modulus in the TD direction is 4 GPa or more, and the haze value is 6% or less. The polypropylene film according to claim 1, wherein the lower limit of the isotactic meso pentad fraction of the polypropylene resin constituting the film is 96%, and the lower limit of the surface alignment coefficient of the film is 0.0125. . The polypropylene film according to claim 1 or 2, wherein the upper limit of the amount of the comonomer of the polypropylene resin constituting the film is 0.1 mol%. The polypropylene film according to any one of claims 1 to 3, wherein the polypropylene resin constituting the film has a room temperature xylene soluble fraction of 7 mass% or less.