JP6443334B2 - Heat-sealable polypropylene laminated stretched film - Google Patents

Description

  The present invention relates to a heat-sealable polypropylene laminated stretched film. More specifically, it can be suitably used in various fields that have sufficient heat seal strength for use as a packaging application, good transparency, dimensional stability at high temperatures, and high rigidity. The present invention relates to a biaxially stretched heat-sealable polypropylene laminated stretched film having excellent properties and mechanical properties.

  Conventionally, stretched films using polypropylene have been widely used in a wide range of applications such as packaging of foods and various products, electrical insulation, and surface protection films, but there are applications that require heat sealability. Conventionally, a co-extrusion laminated polypropylene resin film in which a low melting point polyolefin resin is laminated on a polypropylene resin has been used as a heat sealable film. Such heat-sealable films have a shrinkage rate of several tens of percent at 150 ° C., have lower heat resistance than PET and the like, and have low rigidity, and thus have limited applications. For example, if the heat seal temperature can be set high, the line speed in the bag making process can be increased. However, the stretched polypropylene film still has insufficient heat seal properties and heat resistance at high temperatures.

In order to solve these problems, the polypropylene resin constituting the base material layer (A) has a high stereoregularity, and a polypropylene film having a narrow molecular weight distribution is used as a stretched film to obtain a high-temperature rigidity and heat-resistant film. The technique has been known (see, for example, Patent Document 1).
In addition, a technology has been known that can be suitably used as a capacitor film having excellent electrical insulation, mechanical properties and the like by using a polypropylene film having high stereoregularity and having a wide molecular weight distribution as a stretched film ( For example, see Patent Document 2).

Furthermore, a technology for forming a separator film using polypropylene having a low molecular weight and a soluble content of 0 ° C. by a temperature rising fractionation method in a specific range is known. This film has dimensions in a drying process and a printing process. It was also said to be excellent in stability (see, for example, Patent Document 3).
However, Patent Documents 1 to 3 have difficulty in stretchability and inferior mechanical properties such as impact resistance.

  By adding a small amount of long-chain branched or cross-linked polypropylene to medium molecular weight products, it promotes the formation of child lamellae, improves stretchability, and excels in mechanical properties, heat resistance, voltage resistance properties, and uniformity in various physical properties. A technique for forming a film has been known (see, for example, Patent Document 4).

  Also known is a technology that balances rigidity and workability by using polypropylene with a film containing high molecular weight and medium molecular weight materials (substantially low molecular weight), wide molecular weight distribution, and low decalin soluble content. (See, for example, Patent Document 5).

In these patent documents 4 to 5, it cannot be said that the heat resistance at high temperature is sufficient, and a polypropylene film having high heat resistance and excellent impact resistance and transparency has not been known.
That is, they do not exceed the range of conventional polypropylene films, and their uses are limited. For example, no attention has been paid to heat resistance at high temperatures exceeding 150 ° C.

JP-A-8-325327 JP 2004-175932 A JP 2001-146536 A JP 2007-84813 A Special table 2008-540815

  The present invention has been made against the background of such prior art problems. That is, an object of the present invention is to provide a stretched polypropylene laminated film having a low shrinkage comparable to PET at 150 ° C. and capable of being heat-sealed at a high temperature.

As a result of intensive studies to achieve the above object, the present inventors have completed the present invention. That is, the present invention is a film mainly composed of polypropylene resin, having a heat shrinkage rate of 10% or less in the MD direction and TD direction at 150 ° C., an impact strength of 0.6 J or more, and a haze. It is a stretched polypropylene laminated film characterized by being 6% or less.
A stretched film is a film having an orientation stretched by a method such as uniaxial, simultaneous biaxial, sequential biaxial, etc. industrially. The degree of orientation is, for example, a plane orientation coefficient obtained from a refractive index. Etc.

  In this case, it is preferable that the Young's modulus in the MD direction is 2.1 GPa or more and the Young's modulus in the TD direction is 3.7 GPa or more.

  In this case, it is preferable that the polyolefin heat seal resin (B) is laminated with a heat seal layer made of a propylene random copolymer and / or a propylene block copolymer.

According to the present invention, the heat-sealable stretched polypropylene laminated film can have a low shrinkage rate and high rigidity comparable to PET at 150 ° C., and thus can be thinned.
Furthermore, the stretched polypropylene laminate film of the present invention can maintain various physical properties even when exposed to an environment of 150 ° C. or higher, and has not been considered in the base layer (A) of the conventional stretched polypropylene laminate film. It can be used even in high-temperature environments.
For example, by setting the heat seal temperature high, it is possible to increase the line speed in the bag making process, and the productivity is improved. Further, the heat seal strength can be improved by increasing the heat seal temperature. Furthermore, the amount of deformation of the bag can also be suppressed when performing high temperature processing such as retort.

The present invention relates to a heat-sealable stretched polypropylene laminated film. More specifically, it can be suitably used in various fields that have sufficient heat seal strength for use as a packaging application, good transparency, dimensional stability at high temperatures, and high rigidity. The present invention relates to a heat-sealable stretched polypropylene laminated film having excellent properties and mechanical properties. The feature of the stretched polypropylene laminate film of the present invention is the molecular weight distribution of the polypropylene resin used for the base material layer (A).
The present invention is a stretched polypropylene laminated film composed mainly of a polypropylene resin, having a thermal shrinkage of 10% or less in the MD direction and TD direction at 150 ° C., and an impact strength of 0.6 J or more, It is necessary that the haze is 6% or less.

  Here, the MD direction is the film flow direction, and the TD direction is the direction perpendicular to the film flow direction.

(Film characteristics)
The lower limit of the 150 ° C. heat shrinkage in the MD direction and the TD direction of the stretched film of the present invention is preferably 0.5%, more preferably 1%, still more preferably 1.5%, particularly preferably. 2%, most preferably 2.5%. If it is in the above range, realistic production may be easy in terms of cost or the like, and thickness unevenness may be reduced.
The upper limit of the 150 ° C. heat shrinkage in the MD direction and the TD direction is preferably 10%, more preferably 9%, still more preferably 8%, particularly preferably 7%, and most preferably 6%. It is. When it is in the above range, it is easier to use in applications that may be exposed to a high temperature of about 150 ° C. If the heat shrinkage at 150 ° C. is up to about 2.5%, for example, it is possible to increase the low molecular weight component, adjust the stretching conditions and the fixing conditions, but below that, annealing treatment can be performed offline. preferable.
In the conventional stretched polypropylene laminated film, the 150 ° C. heat shrinkage rate in the MD direction and the TD direction is 15% or more, and the 120 ° C. heat shrinkage rate is about 3%. By setting the heat shrinkage rate within the above range, a stretched polypropylene laminated film having excellent heat resistance can be obtained.

The lower limit of the impact resistance (23 ° C.) of the stretched polypropylene film of the present invention is preferably 0.6 J, more preferably 0.7 J. Within the above range, the film has sufficient toughness and does not break during handling.
The upper limit of the impact resistance is preferably 3J, more preferably 2.5J, even more preferably 2.2J, and particularly preferably 2J from the practical viewpoint. For example, impact resistance tends to decrease when the total molecular weight is low when there are many low molecular weight components, when the total molecular weight is low, or when the molecular weight of the high molecular weight components is low. These components can be adjusted to be within the range.

The lower limit of the haze of the stretched polypropylene laminate film of the present invention is preferably 0.1% as a practical value, more preferably 0.2%, still more preferably 0.3%, particularly preferably 0.8. 4%, most preferably 0.5%.
The upper limit of haze is preferably 6%, more preferably 5%, still more preferably 4.5%, particularly preferably 4%, and most preferably 3.5%. If it is within the above range, it may be easy to use in applications requiring transparency. For example, when the stretching temperature and the heat setting temperature are too high, the haze tends to be worse when the cooling roll (CR) temperature is high and the cooling rate is slow, or when the low molecular weight is too much. I can do it.

(Polypropylene resin)
The polypropylene resin constituting the base material layer (A) of the stretched polypropylene laminate film of the present invention may be a complete homopolypropylene obtained only from a propylene monomer or a copolymer with a copolymerization monomer if it is in a trace amount. Copolymeric monomer species can be ethylene, butene, hexene, octene, and the like.

Although an additive and other resin may be added to the base material layer (A) of the present invention as necessary, it is preferably 30 wt% 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 antiblocking agent, and an inorganic or organic filler. Other resins include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers that are copolymers of α-olefins having 4 or more carbon atoms such as propylene and ethylene, butene, hexene, octene, and various elastomers. Is mentioned.

(Molecular weight distribution of polypropylene resin)
The polypropylene resin constituting the stretched polypropylene laminated film of the present invention is mainly composed of a low molecular weight component having a mass average molecular weight (Mw) of about 100,000, for example, and a high molecular weight component having a very high molecular weight, for example, Mw of about 1,500,000. It is included. Crystallinity can be greatly increased by mainly using a low molecular weight component, and it is considered that a highly-stretched and heat-resistant stretched polypropylene film that has not been conventionally obtained is obtained. On the other hand, a low molecular weight polypropylene resin has a low melt tension when softened by heating and cannot generally be a stretched film. The high molecular weight component is allowed to be stretched by the presence of several percent to several tens of percent, and the high molecular weight component serves as a crystal nucleus, further increasing the crystallinity of the film. It is thought that the effect is achieved.

As an index representing such molecular weight distribution, (Mz + 1) / Mn, which is a ratio of Z + 1 average molecular weight (Mz + 1), which is an average molecular weight focusing on high molecular weight components, and number average molecular weight (Mn), is preferable.
The lower limit of Mz + 1 / Mn is preferably 50, more preferably 60, still more preferably 70, particularly preferably 80, and most preferably 90. If it is less than the above, it may be difficult to obtain the effects of the present application such as a low thermal shrinkage at high temperatures.
The upper limit of Mz + 1 / Mn is preferably 300, more preferably 200. If the above is exceeded, it may be difficult to produce a realistic resin.

When the polypropylene resin having the molecular weight distribution is represented by mass average molecular weight (Mw) / number average molecular weight (Mn), which is generally an index of the molecular weight distribution, naturally, the value becomes large, but Mw / The lower limit of Mn is preferably 5.5, more preferably 6, further preferably 6.5, particularly preferably 7, and most preferably 7.2.
The upper limit of Mw / Mn is preferably 30, more preferably 25, still more preferably 20, particularly preferably 15, and most preferably 13. In addition, these average molecular weights can be obtained by measuring using germanium permeation chromatography (GPC).

The lower limit of Mz + 1 by GPC of the entire polypropylene resin constituting the base material layer (A) of the present invention is preferably 2500000, more preferably 3000000, still more preferably 3300000, particularly preferably 3500000, Preferably it is 3700000. Within the above range, the high molecular weight component is sufficient, and the effects of the present invention are easily obtained.
The upper limit of the total Mz + 1 is preferably 40000000, more preferably 35000000, and even more preferably 30000000. Within the above range, realistic resin production may be easy, stretching may be facilitated, and fish eyes in the film may be reduced.

The lower limit of Mn obtained by GPC of the entire polypropylene resin constituting the base material layer (A) of the present invention is preferably 20000, more preferably 22000, still more preferably 24000, and particularly preferably 26000. Most preferably, it is 27000. When it is in the above range, there are the advantages that stretching becomes easy, thickness unevenness is reduced, stretching temperature and heat setting temperature are easily raised, and thermal shrinkage rate is lowered.
The upper limit of the total Mn is preferably 65000, more preferably 60000, still more preferably 55000, particularly preferably 53000, and most preferably 52000. Within the above range, the effects of the present application such as a low heat shrinkage rate at high temperature, which is an effect of a low molecular weight substance, may be easily obtained, or stretching may be facilitated.

The lower limit of the mass average molecular weight (Mw) obtained by GPC of the entire polypropylene resin constituting the base material layer (A) of the present invention is preferably 250,000, more preferably 260000, still more preferably 270000, particularly It is preferably 280000, and most preferably 290000. When it is in the above range, there are the advantages that stretching becomes easy, thickness unevenness is reduced, stretching temperature and heat setting temperature are easily raised, and thermal shrinkage rate is lowered.
The upper limit of the total Mw is preferably 500,000, more preferably 450,000, still more preferably 400,000, particularly preferably 380000, and most preferably 370000. Within the above range, the mechanical load may be small and stretching may be easy.

The lower limit of the melt flow rate (MFR) (230 ° C., 2.16 kgf) of the entire polypropylene resin constituting the base material layer (A) of the present invention is preferably 1 g / 10 min, more preferably 1.2 g / 10 min. More preferably 1.4 g / 10 min, particularly preferably 1.5 g / 10 min, and most preferably 1.6 g / 10 min. Within the above range, the mechanical load may be small and stretching may be easy.
The upper limit of the total MFR is preferably 20 g / 10 min, more preferably 17 g / 10 min, still more preferably 15 g / 10 min, particularly preferably 14 g / 10 min, and most preferably 13 g / 10 min. When it is within the above range, stretching may be easy, thickness unevenness may be reduced, and the stretching temperature and heat setting temperature may be easily increased, resulting in a lower thermal shrinkage rate.

When the GPC integration curve of the entire polypropylene resin constituting the film is measured, the lower limit of the amount of the component having a molecular weight of 100,000 or less is preferably 35% by mass, more preferably 38% by mass, and further preferably 40% by mass. Particularly preferably 41% by mass, and most preferably 42% by mass. Within the above range, the effects of the present application such as a low heat shrinkage rate at a high temperature, which is an effect of a low molecular weight substance, may be easily obtained, and stretching may be facilitated.
The upper limit of the amount of the component having a molecular weight of 100,000 or less is preferably 65% by mass, more preferably 60% by mass, still more preferably 58% by mass, particularly preferably 56% by mass, and most preferably 55%. % By mass.

Molecules with a molecular weight of about 10,000 or less do not contribute to the entanglement of the molecular chains, and have the effect of loosening the entanglement between the molecules as a plasticizer. . As a result, it is possible to stretch at a low stretching stress, and as a result, the residual stress is low and the shrinkage rate at high temperature is considered to be low.
The lower limit of the amount of the component having a molecular weight of 10,000 or less is preferably 2% by mass, more preferably 2.5% by mass, still more preferably 3% by mass, particularly preferably 3.3% by mass, Most preferably, it is 3.5 mass%.
The upper limit of the amount of the component having a molecular weight of 10,000 or less in the GPC integration curve is preferably 20% by mass, more preferably 17% by mass, still more preferably 15% by mass, and particularly preferably 14% by mass. Most preferably, it is 13% by mass.

  A high molecular weight component and a low molecular weight component suitable for forming a polypropylene resin having such a molecular weight distribution characteristic will be described, but means for widening the molecular weight distribution is not limited thereto.

(High molecular weight component)
The lower limit of 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. Is 0.005 g / 10 min. If it is in the above range, the production of the resin is practically easy or the fish eye of the film may be reduced.
The MFR at 230 ° C. and 2.16 kgf of the high molecular weight component may be too small to make practical measurement difficult. When expressed in terms of MFR at 10 times the weight (21.6 kgf), the preferred lower limit is 0.1 g / 10 min, more preferably 0.5 g / 10 min, even more preferably 1 g / 10 min, and particularly preferably 5 g / 10 min.
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 min. Most preferably, it is 0.1 g / 10 min. If the amount is in the above range, it is not necessary to use a large amount of polymer component in order to maintain the overall MFR, and the effects of the present application such as a low heat shrinkage rate at a high temperature, which is an effect of a low molecular weight product, can be easily obtained. There is.

The lower limit of Mw of the high molecular weight component is preferably 500,000, more preferably 600,000, still more preferably 700,000, particularly preferably 800,000, and most preferably 1,000,000. If the amount is in the above range, it is not necessary to use a large amount of polymer component in order to maintain the overall MFR, and the effects of the present application such as a low heat shrinkage rate at a high temperature, which is an effect of a low molecular weight product, can be easily obtained. There is.
The upper limit of Mw of the high molecular weight component is preferably 10000000, more preferably 8000000, still more preferably 6000000, and particularly preferably 5000000. If it is in the above range, the production of the resin is practically easy or the fish eye of the film may 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. Within the above range, it is not necessary to increase the molecular weight of the low molecular weight product in order to maintain the overall MFR, and the effects of the present application such as a low heat shrinkage rate at high temperatures may be more easily obtained.
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, and particularly preferably 20% by mass. Within the above range, the effects of the present application such as a low heat shrinkage rate at a high temperature, which is an effect of a low molecular weight substance, may be more easily obtained.
Here, as the high molecular weight component, a polypropylene resin having a long chain branching or a crosslinked structure can be used instead of the linear polypropylene resin, which is known as high melt tension polypropylene, manufactured by Borealis. There are Daploy WB130HMS and WB135HMS.

(Low molecular weight component)
The lower limit of the low molecular weight component MFR (230 ° C., 2.16 kgf) 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, it is 200 g / 10 min. Within the above range, the crystallinity is improved, and the effects of the present application such as a low thermal shrinkage rate at a high temperature may be more easily obtained.
The upper limit of the MFR of the low molecular weight component is preferably 2000 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. is there. Within the above range, the overall MFR can be easily maintained, and the film forming property may be excellent.

The lower limit of the Mw of the low molecular weight component is preferably 50000, more preferably 53000, still more preferably 55000, particularly preferably 60000, and most preferably 70000. Within the above range, the overall MFR can be easily maintained, and the film forming property may be excellent.
The upper limit of the Mw of the low molecular weight component is preferably 150,000, more preferably 140000, still more preferably 130,000, particularly preferably 120,000, and most preferably 110,000. Within the above range, the crystallinity is improved, and the effects of the present application such as a low thermal shrinkage rate at a high temperature may be more easily obtained.

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. Within the above range, the effects of the present application such as a low heat shrinkage rate at a high temperature, which is an effect of a low molecular weight substance, may be more easily obtained.
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, and particularly preferably 95% by mass. Within the above range, it is not necessary to increase the molecular weight of the low molecular weight product in order to maintain the overall MFR, and the effects of the present application such as a low heat shrinkage rate at high temperatures may be more easily obtained.

The lower limit of the MFR of the low molecular weight component / the MFR ratio of the high molecular weight component is preferably 500, more preferably 1000, still more preferably 2000, and particularly preferably 4000. Within the above range, the effects of the present application such as a low heat shrinkage at high temperatures may be more easily obtained.
The upper limit of the MFR ratio of the low molecular weight component / the MFR ratio of the high 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 resins corresponding to each component, and the blending amount in that case is a total amount.
In addition to the high molecular weight component and low molecular weight component in the above range, a component having a molecular weight other than the low molecular weight component and high molecular weight component of the present invention may be added in order to adjust the MFR as a whole polypropylene resin. In order to ease the entanglement of the molecular chains and to adjust the stretchability, a polypropylene resin having a low molecular weight component or less, particularly a molecular weight of about 30,000 or less, and further a molecular weight of about 10,000 or less may be added.

  In order to obtain a preferable molecular weight distribution state of a polypropylene resin using a high molecular weight component and a low molecular weight component, for example, when the molecular weight of the low molecular weight component to be used is low, the molecular weight of the high molecular weight component is increased. The distribution state can be adjusted, for example, by increasing, and the MFR can be adjusted to be easy to produce as a stretched film.

(Regularity of polypropylene resin)
The lower limit of the mesopentad fraction ([mmmm]%) of the polypropylene resin constituting the base material layer (A) of the present invention is preferably 96%, more preferably 96.5%, still more preferably 97%. is there. When it is within the above range, the crystallinity may be improved, and the thermal shrinkage rate at a high temperature may be lower.
The upper limit of the mesopentad fraction ([mmmm]%) is preferably 99.5%, more preferably 99.3%, and even more preferably 99%. In the above range, realistic production may be easy.

In the polypropylene resin constituting the base material layer (A) of the present invention, it is preferable that heterogeneous bonds such as head-to-head bonds are not observed. In addition, not being recognized here means that a peak is not seen by ¹³ C-NMR.

The lower limit of the meso average chain length of the polypropylene resin constituting the base material layer (A) of the present invention is preferably 100, more preferably 120, and still more preferably 130. When it is in the above range, the crystallinity may be improved, and the thermal shrinkage at high temperatures may be reduced.
The upper limit of the meso average chain length is preferably 5000 from a practical aspect.

The lower limit of the xylene soluble content of the polypropylene resin constituting the base material layer (A) of the present invention is preferably 0.1% by mass from a practical aspect.
The upper limit of the xylene-soluble content is preferably 7% by mass, more preferably 6% by mass, and further preferably 5% by mass. When it is in the above range, the crystallinity may be improved, and the thermal shrinkage at high temperatures may be reduced.

  The polypropylene resin constituting the substrate layer (A) of the present invention is most preferably a complete homopolypropylene obtained only from a propylene monomer, but may be a copolymer with a copolymerization monomer as long as it is in a trace amount. As the copolymerization monomer species, ethylene and butene are preferable.

  The upper limit of the amount of the comonomer is preferably 0.1 mol%, more preferably 0.05 mol%, still more preferably 0.01 mol%. When it is in the above range, the crystallinity may be improved, and the thermal shrinkage at high temperatures may be reduced.

  In addition, perfect homopolypropylene has a very narrow range of conditions that can be stretched, such as high crystallinity and a rapid drop in melt tension after melt softening. % Of copolymerization component (mainly ethylene) was added. However, the polypropylene resin having a molecular weight distribution as described above has a moderate decrease in tension after melt softening even if there is little or no copolymerization component, and industrial stretching is possible.

  In the present invention, the resin used for the heat seal layer (B) is preferably a low-melting-point propylene random copolymer having a melting point of 150 ° C. or lower or a propylene block copolymer containing an elastomer component. Can be used as a mixture. As the comonomer, it is preferable to use one or more selected from ethylene or an α-olefin having 3 to 10 carbon atoms such as butene, pentene, hexene, octene, and decene.

Furthermore, the melting point of the propylene random copolymer forming the heat seal layer (B) is preferably 60 to 150 ° C. Thereby, sufficient heat seal intensity | strength can be given to a stretched polypropylene resin laminated | multilayer film. When the melting point of the propylene random copolymer forming the heat seal layer (B) is less than 60 ° C, heat resistance of the heat seal portion is poor, and when it exceeds 150 ° C, improvement in heat seal strength cannot be expected. The melting point of the elastomer component contained in the propylene block copolymer is also preferably 150 ° C. or lower.
Moreover, MFR is 0.1-100 g / 10min, Preferably it is 0.5-20 g / 10min, More preferably, the thing of the range of 1.0-10 g / 10min can be illustrated.

(Production method of polypropylene resin)
Polypropylene is obtained by polymerizing propylene as a raw material using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. Among them, in order to eliminate the heterogeneous bond, it is preferable to use a Ziegler-Natta catalyst and a catalyst capable of highly regular polymerization.
As a polymerization method of propylene, a known method may be used, a method of polymerizing in an inert solvent such as hexane, heptane, toluene, xylene, a method of polymerizing in liquid propylene or ethylene, a gas in propylene or ethylene. Examples thereof include a method of adding a catalyst and polymerizing in a gas phase state, or a method of polymerizing by combining these.
The high molecular weight component and the low molecular weight component may be mixed after being polymerized separately, or may be produced in a series of plants in a multistage reactor. In particular, a method is preferred in which a plant having a multi-stage reactor is used, and a high molecular weight component is first polymerized and then a low molecular weight component is polymerized in the presence thereof.

(Additive)
If necessary, additives and other resins may be added to the film-forming resin composition of the present invention. 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 antiblocking agent, and an inorganic or organic filler. Examples of the other resins include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers that are copolymers of propylene and ethylene and / or α-olefins having 4 or more carbon atoms, and various elastomers. These can be blended with polypropylene resin and a Henschel mixer, or master pellets prepared using a melt kneader in advance can be diluted with polypropylene to a predetermined concentration, or the total amount can be melt-kneaded in advance. Also good.

  By using a polypropylene resin having such a characteristic molecular weight distribution for the base material layer (A), it becomes possible to stretch polypropylene mainly composed of low molecular weight, which has been impossible to sufficiently stretch in the past. It is considered that a high heat setting temperature can be adopted, and the heat shrinkage rate at a high temperature can be lowered by a synergistic effect of high crystallinity and strong heat setting.

(Film physical properties)

When the heat-sealable polypropylene laminated stretched film of the present invention is a biaxially stretched film, the lower limit of the Young's modulus (23 ° C.) in the MD direction is preferably 1.8 GPa, more preferably 1.9 GPa, and still more preferably Is 2.0 GPa, particularly preferably 2.1 GPa, and most preferably 2.2 GPa.
The upper limit of the Young's modulus in the MD direction is preferably 3.7 GPa, more preferably 3.6 GPa, still more preferably 3.5 GPa, particularly preferably 3.4 GPa, and most preferably 3.3 GPa. is there. Within the above range, realistic manufacturing may be easy, and the MD-TD balance may be improved.

When the heat-sealable polypropylene laminated stretched film of the present invention is a biaxially stretched film, the lower limit of the Young's modulus (23 ° C.) in the TD direction is preferably 3.7 GPa, more preferably 3.8 GPa, even more preferably Is 3.9 GPa, particularly preferably 4.0 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 it is in the above range, realistic production may be easy, and the MD-TD balance may be improved.
The Young's modulus can be increased by increasing the draw ratio. In the case of MD-TD stretching, the MD stretch ratio is set lower, and the Young's modulus in the TD direction is increased by increasing the TD stretch ratio. Can do.

The lower limit of the thickness uniformity of the stretched polypropylene laminated film of the present invention is preferably 0%, more preferably 0.1%, still more preferably 0.5%, and particularly preferably 1%.
The upper limit of thickness uniformity is preferably 20%, more preferably 17%, still more preferably 15%, particularly preferably 12%, and most preferably 10%. If it is in the above range, defects are unlikely to occur during post-processing such as coating and printing, and it is easy to use for applications that require precision.

(Method for producing polypropylene film)
The stretched polypropylene laminate 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, sequential biaxial stretching or simultaneous biaxial stretching may be used.
By using a stretched film, a film having a low thermal shrinkage can be obtained even at 150 ° C., which could not be expected with a conventional stretched polypropylene laminated film.

A method for producing a film of sequential biaxial stretching of longitudinal stretching and transverse stretching, which is the most preferable example, will be described below.
First, the base material layer (A) is melt-extruded from one extruder, the heat-seal layer (B) is melt-extruded from the other extruder, and the polypropylene resin layer (A) and the heat are heated in a T-die. It laminates | stacks so that it may become a seal layer (B), it cools and solidifies with a cooling roll, and an unstretched sheet is obtained. The melt extrusion conditions are such that the resin temperature is 200 to 280 ° C., the sheet is extruded from a T-die and cooled and solidified with a cooling roll having a temperature of 10 to 100 ° C. Next, the film is stretched 3 to 7 times in the length (MD) direction with a stretching roll at 120 to 165 ° C., and subsequently at a temperature of 155 ° C. to 175 ° C., preferably 158 ° C. to 170 ° C. in the width (TD) direction. Stretch 6-12 times.
Further, heat treatment is performed at an ambient temperature of 165 to 175 ° C., preferably 166 to 173 ° C. while allowing relaxation of 1 to 15%.
If necessary, a roll sample can be obtained by performing corona discharge treatment on at least one surface and then winding it with a winder.

The lower limit of the MD draw ratio is preferably 3 times, more preferably 3.5 times. If it is less than the above, film thickness unevenness may occur.
The upper limit of the MD draw ratio is preferably 8 times, more preferably 7 times. If the above is exceeded, it may be difficult to carry out TD stretching.

The lower limit of the MD stretching temperature is preferably 120 ° C, more preferably 125 ° C, and even more preferably 130 ° C. If it is less than the above, the mechanical load may be increased, the thickness unevenness may be increased, or the film may be roughened.
The upper limit of the MD stretching temperature is preferably 160 ° C, more preferably 155 ° C, and even more preferably 150 ° C. A higher temperature is preferable for lowering the thermal shrinkage, but may adhere to the roll and fail to stretch.

The lower limit of the stretching ratio of TD is preferably 4 times, more preferably 5 times, and further preferably 6 times. If it is less than the above, thickness unevenness may occur.
The upper limit of the TD stretch ratio is preferably 20 times, more preferably 17 times, and even more preferably 15 times. If the above is exceeded, the thermal shrinkage rate may increase or the film may break during stretching.

  The preheating temperature in TD stretching is preferably set to be higher by 10 to 15 ° C. than the stretching temperature in order to quickly raise the film temperature in the vicinity of the stretching temperature.

The TD stretching is performed at a higher temperature than the conventional heat-sealable polypropylene laminated stretched film.
The lower limit of the TD stretching temperature is preferably 157 ° C, more preferably 158 ° C. If it is less than the above, it may break without being sufficiently softened, or the thermal shrinkage rate may be increased.
The upper limit of the TD stretching temperature is preferably 170 ° C, more preferably 168 ° C. In order to lower the thermal shrinkage rate, the temperature is preferably higher. However, if the temperature is exceeded, the low molecular component may be melted and recrystallized, resulting in surface roughness or whitening of the film.

The stretched film is heat-set. The heat setting can be performed at a higher temperature than the conventional polypropylene film. The lower limit of the heat setting temperature is preferably 165 ° C, more preferably 166 ° C. If it is less than the above, the thermal shrinkage rate may increase. In addition, a long time is required to lower the heat shrinkage rate, and productivity may be inferior.
The upper limit of the heat setting temperature is preferably 175 ° C, more preferably 173 ° C. If the above is exceeded, the low molecular components may melt and recrystallize, resulting in surface roughness and whitening of the film.

It is preferable to relax at the time of heat setting. The lower limit of relaxation is preferably 2%, more preferably 3%. If it is less than the above, the thermal shrinkage rate may increase.
The upper limit of relaxation is preferably 10%, more preferably 8%. When the above is exceeded, the thickness unevenness may increase.

Further, in order to reduce the thermal shrinkage rate, the film produced in the above process can be once wound up into a roll and then annealed offline.
The lower limit of the offline annealing temperature is preferably 160 ° C., more preferably 162 ° C., and further preferably 163 ° C. If it is less than the above, the effect of annealing may not be obtained.
The upper limit of the offline annealing temperature is preferably 175 ° C., more preferably 174 ° C., and further preferably 173 ° C. When the above is exceeded, the transparency may be lowered, and the thickness unevenness may be increased.

The lower limit of the offline annealing time is preferably 0.1 minutes, more preferably 0.5 minutes, and even more preferably 1 minute. If it is less than the above, the effect of annealing may not be obtained.
The upper limit of the offline annealing time is preferably 30 minutes, more preferably 25 minutes, and further preferably 20 minutes. If the above is exceeded, productivity may be reduced.

  Although the thickness of a film is set according to each use, the minimum of film thickness becomes like this. Preferably it is 2 micrometers, More preferably, it is 3 micrometers, More preferably, it is 4 micrometers. The upper limit of the film thickness is preferably 300 μm, more preferably 250 μm, still more preferably 200 μm, particularly preferably 100 μm, and most preferably 50 μm.

  The polypropylene film thus obtained is usually formed as a roll having a width of 2000 to 12000 mm and a length of 1000 to 50000 m, and is wound up into a roll. Furthermore, it is slit according to each application and is provided as a slit roll having a width of about 300 to 2000 mm and a length of about 500 to 5000 m.

The stretched polypropylene laminated film of the present invention has excellent characteristics as described above which are not present in the prior art.
When used as a packaging film, it is highly rigid and can be thinned, thereby reducing costs and weight.
In addition, since it has high heat resistance, it can be dried at a high temperature when drying a coating or printing, and it is possible to use a coating agent, an ink, a laminating adhesive, or the like, which has been difficult to be used in production, or has been conventionally used. Since there is no need for a laminating process using an organic solvent or the like, it is preferable from the viewpoint of the influence on the global environment economically.

  The present invention will be described in detail below based on examples, but the present invention is not limited to such examples. The measuring method of the physical property in an Example is as follows.

1) Melt flow rate (MFR, g / 10 min)
It was measured at a temperature of 230 ° C. in accordance with JIS K7210.

2) Molecular weight and molecular weight distribution The molecular weight and molecular weight distribution were determined on the basis of monodisperse polystyrene using gel permeation chromatography (GPC).
The columns and solvents used in the GPC measurement are as follows.
Solvent: 1,2,4-trichlorobenzene Column: TSKgel GMH _HR- H (20) HT × 3
Flow rate: 1.0 ml / min
Detector: RI
Measurement temperature: 140 ° C
The number average molecular weight (Mn), the mass average molecular weight (Mw), and the Z + 1 average molecular weight (Mz + 1) are determined by the molecular number (Ni) of the molecular weight (Mi) at each elution position of the GPC curve obtained through the molecular weight calibration curve. It is defined by the following formula.
Number average molecular weight: Mn = Σ (Ni · Mi) / ΣNi
Mass average molecular weight: Mw = Σ (Ni · Mi ² ) / Σ (Ni · Mi)
Z + 1 average molecular weight: Mz + 1 = Σ (Ni · Mi ⁴ ) / Σ (Ni · Mi ³ )
Molecular weight distribution: Mw / Mn, Mz + 1 / Mn
The molecular weight at the peak position of the GPC curve was defined as Mp.
When the baseline is not clear, the baseline should be set in a range up to the lowest position on the high molecular weight side of the elution peak closest to the elution peak of the standard substance.
The peak separation was performed on two or more components having different molecular weights from the obtained GPC curve. The molecular weight distribution of each component is assumed to be a Gaussian function, and Mw / Mn = 4 so as to be the same as the molecular weight distribution of ordinary polypropylene. Each average molecular weight was calculated from the obtained curve of each component.

3) Stereoregularity The mesopentad fraction ([mmmm]%) and meso average chain length were measured using ¹³ C-NMR. The mesopentad fraction was determined according to the method described in Zambelli et al., Macromolecules, Vol. 6, 925 (1973). C. It was calculated according to the method described in Randall, “Polymer Sequence Distribution”, Chapter 2 (1977) (Academic Press, New York).
¹³ C-NMR measurement was carried out at 110 ° C. using AVANCE 500 manufactured by BRUKER, and dissolving 200 mg of a sample in an 8: 2 mixture of o-dichlorobenzene and heavy benzene at 135 ° C.

4) Cold xylene soluble part (CXS, mass%)
Dissolve 1 g of polypropylene sample in 200 ml of boiling xylene, allow to cool, recrystallize in a constant temperature water bath at 20 ° C. for 1 hour, and calculate the ratio of the mass dissolved in the filtrate to the original sample amount by CXS (mass%) It was.

5) Thermal shrinkage (%)
Measurement was performed in accordance with JIS Z 1712.
(The stretched film was 20 mm wide and 200 mm long, cut in the MD and TD directions, suspended in a hot air oven at 150 ° C. and heated for 5 minutes. The length after heating was measured, and the shrinkage relative to the original length was measured. (The heat shrinkage rate was obtained at the ratio of the lengths obtained.)

6) Impact resistance It measured at 23 degreeC using the Toyo Seiki film impact tester.

7) Young's modulus (unit: GPa)
The Young's modulus in the MD and TD directions was measured at 23 ° C. in accordance with JIS K 7127.

8) Haze (Unit:%)
It measured according to JIS K7105.

9) Heat seal strength Under the conditions of a heat seal temperature of 140 ° C., a pressure of 1 kg / cm ² , and a heat seal time of 1 second, the heat seal layer (B) surfaces of the laminated stretched film are overlapped to perform hot plate sealing. A test piece was prepared. The 180-degree peel strength of this test piece was measured and set as a heat seal strength (N / 15 mm).

10) Curling property The curl degree of the laminated stretched film of the film obtained in the evaluation of 9) was measured visually.
○: No curling △: Slightly curling ×: Remarkable curling

11) Thickness unevenness A square sample having a length of 1 m was cut out from the wound film roll, and divided into 10 parts each in the MD direction and the TD direction to prepare 100 measurement samples. The thickness was measured with a contact-type film thickness meter at the approximate center of the measurement sample.
The average value of the 100 points of data obtained was obtained, the difference between the minimum value and the maximum value (absolute value) was obtained, and the value obtained by dividing the absolute value of the difference between the minimum value and the maximum value by the average value was obtained. It was.

12) Appearance of heat seal Heat-sealing is performed by stacking the produced film and PYLEN Film-CTP P1128 manufactured by Toyobo Co., Ltd. and holding it at 170 ° C. and a load of 2 kg for 1 second using a test sealer manufactured by Seibu Machinery Co. It was. The degree of change in appearance due to shrinkage of the film after heat sealing was evaluated visually. A case where the deformation amount of the heat seal portion is small and does not affect the use is indicated by ○, and a case where the heat shrinkage is large and the deformation amount is large is indicated by ×.

Example 1
Using two melt extruders, in the first extruder, as polypropylene resin, Mw / Mn = 7.7, Mz + 1 / Mn = 140, MFR = 5.0, [mmmm] = 97.3% A propylene homopolymer (manufactured by Nippon Polypro Co., Ltd .: Novatec PP “SA4L”) was used as a base layer (A), and in a second extruder, a propylene-ethylene-butene random copolymer (Pr-Et— Bu) (density 0.89 g / cm ³ , MFR 4.6 g / 10 min, melting point 128 ° C.) 85% by weight, propylene-butene random copolymer (Pr—Bu) (density 0.89 g / cm ³ , MFR 9. The mixed resin having a weight of 0 g / 10 minutes and a melting point of 130 ° C. of 15% by weight is used as the heat seal layer (B), and the substrate layer (A) / heat seal layer (B) is formed in the die. (A), heat seal layer After melt coextrusion in the form of a sheet from a T die at 250 ° C. in the order of (B), after cooling and solidifying with a 30 ° C. cooling roll, it is stretched 4.5 times in the length direction at 135 ° C. Next, both ends were sandwiched between clips, guided into a hot air oven, preheated at 170 ° C., stretched 8.2 times in the transverse direction at 160 ° C., and then heat treated at 168 ° C. while relaxing 6.7%. Thereafter, one side of the film was subjected to corona treatment and wound up with a winder. Thus, the thickness of the film obtained was 20 micrometers, and the laminated stretched film whose thickness of a base material layer and a heat seal layer is 18 micrometers and 2 micrometers, respectively was obtained. As shown in Table 1, Table 2, and Table 3, the obtained laminated stretched film satisfies the requirements of the present invention, has a low heat shrinkage, and has sufficient heat seal strength, low back feeling, and curl resistance. It was a thing.

(Example 2)
For the base material layer (A), 10 parts by weight of low molecular weight polypropylene having a molecular weight of 10,000 (high wax “NP105” manufactured by Mitsui Chemicals, Inc.) is added to 100 parts by weight with respect to 90 parts by weight of “SA4L”. Both were dry blended and then melt kneaded in a 30 mm twin screw extruder to obtain pellets of the mixture. By using this pellet as a base material layer (A), a laminated film was obtained in the same manner as in Example 1. The physical properties of the obtained film are shown in Table 1, Table 2, and Table 3.

Example 3
A laminated film was obtained in the same manner as in Example 1 except that the preheating temperature in the transverse stretching was 173 ° C., and the stretching temperature and the heat treatment temperature were 167 ° C. The physical properties of the obtained film are shown in Table 1, Table 2, and Table 3.

(Example 4)
A laminated film was obtained in the same manner as in Example 2 except that the film was stretched 5.5 times in the length direction and 12 times in the transverse direction. The physical properties of the obtained film are shown in Table 1, Table 2, and Table 3.

(Example 5)
The laminated film produced in Example 1 was subjected to heat treatment at 170 ° C. for 5 minutes in a tenter hot air oven. The physical properties of the obtained film are shown in Table 1, Table 2, and Table 3.

(Example 6)
For the base material layer (A), as the polypropylene resin, polypropylene alone having Mw / Mn = 8.9, Mz + 1 / Mn = 110, MFR = 3.0 g / 10 min, mesopentad fraction [mmmm] = 97.1% A stretched polypropylene laminate film was prepared in the same manner as in Example 1 except that a polymer (“HU300” manufactured by Samsung Sumtal Co., Ltd.) was used, the preheating temperature for transverse stretching was 171 ° C., and the heat treatment temperature after transverse stretching was 170 ° C. Obtained. The thickness of the obtained film was 20 μm, and the physical properties were as shown in Table 1, Table 2, and Table 3.

(Comparative Example 1)
For the base material layer (A), as a polypropylene resin, Sumitomo Chemical Co., Ltd. Sumitomo Nobrene “FS2011DG3” (Mw / Mn = 4, Mz + 1 / Mn = 21, MFR = 2.5 g / 10 min, “mmmm”) = 97.0%, ethylene amount = 0.6 mol%), and the same method as in Example 1 except that the preheating temperature in transverse stretching was 168 ° C, the stretching temperature was 155 ° C, and the heat treatment temperature was 163 ° C. A laminated film was obtained. The physical properties of the obtained film are shown in Table 1, Table 2, and Table 3.

(Comparative Example 2)
A laminated film was produced in the same manner as in Comparative Example 1, except that the preheating temperature was 171 ° C, the stretching temperature was 160 ° C, and the heat treatment temperature was 165 ° C. The physical properties of the obtained film are shown in Table 1, Table 2, and Table 3.

(Comparative Example 3)
For the base material layer (A), as a polypropylene resin, a propylene homopolymer having MFR = 0.5 g / 10 min, Mw / Mn = 4.5, Mz + 1 / Mn = 10 was used, and a film was formed in the same manner as in Comparative Example 2. Was made. The physical properties of the obtained film are shown in Table 1, Table 2, and Table 3.

(Comparative Example 4)
For the base material layer (A), as a polypropylene resin, Novatec PP “SA03” (MFR = 30 g / 10 min) manufactured by Nippon Polypro Co., Ltd. was used, and biaxial stretching was attempted in the same manner as in Example 1. It was not possible to obtain a film by breaking by transverse stretching.

  Since the stretched polypropylene film of the present invention has high heat resistance, it can be dried at a high temperature when drying a coating or printing, which contributes significantly to the efficiency of the processing process. In addition, it can be widely used for packaging applications and industrial applications. However, since it has particularly high rigidity, it can be thinned, and can be reduced in weight and cost.

Claims (3)

Configured base layer mainly of polypropylene resin and (A), a laminated film Do that because the heat seal layer and (B) a polyolefin laminated on one surface or both surfaces of the substrate layer,
The polypropylene resin constituting the base material layer (A) has a lower limit of 35% by mass of a component having a mass average molecular weight of 100,000 or less, and a lower limit of a mesopentad fraction is 96%.
The laminated film, MD and TD directions of the heat shrinkage ratio at 0.99 ° C. is not more than 10%, impact strength Ri der least 0.6 J, stretching haze characterized der Rukoto most 6% Polypropylene laminated film.   The stretched polypropylene laminated film according to claim 1, wherein Young's modulus in the MD direction is 2.1 GPa or more and Young's modulus in the TD direction is 3.7 GPa or more.   The stretched polypropylene laminated film according to claim 1 or 2, wherein the polyolefin heat seal resin (B) comprises a propylene random copolymer and / or a propylene block copolymer.