Stretched polypropylene film

Abstract

To provide a stretched polypropylene film having good stretchability, heat resistance and dimensional stability while enhancing the rigidity of the film and capable of contributing to the enhancement of production efficiency in secondary processing.SOLUTION: A laminated film includes a base material layer and a surface layer laminated on one surface or both surfaces of the base material layer, in which the base material layer is composed of at least two or more different resin mixtures in which a propylene / ethylene / 1-butene random copolymer is mixed with a polypropylene resin (A) having a mesopentad fraction of 95% or more, and the propylene / ethylene / 1-butene random copolymer is mixed in an amount of 1 to 10% by weight with respect to 100% by weight of the resin mixture.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an oriented polypropylene film. [Background technology]

[0002] Traditionally, oriented polypropylene films have been widely used in a variety of applications, including packaging materials, taking advantage of their excellent transparency, mechanical strength, moisture resistance, rigidity, etc. However, in recent years, in order to reduce the environmental impact, efforts have been made to reduce the amount of polypropylene used, such as by reducing thickness, but users still require the film to maintain its rigidity so as not to impair the feel when used.

[0003] In other words, thin stretched polypropylene films must have significantly improved rigidity compared to conventional stretched polypropylene films. Furthermore, because stretched polypropylene films are subjected to printing and lamination, they must have sufficient heat resistance and dimensional stability while also having improved rigidity.

[0004] To solve these problems, a technique is known in which a polypropylene having high stereoregularity and a narrow molecular weight distribution is used to form a stretched film, thereby providing a film with high-temperature rigidity and heat resistance (see Patent Document 1). However, the polypropylene described in Patent Document 1 has a narrow temperature range in which it can be stretched, requiring strict temperature control in the longitudinal and transverse stretching steps, and furthermore, there is a problem in that uneven stretching occurs, increasing the rate of rejects.

[0005] Also proposed is a stretched film using a polypropylene composition containing two polypropylene components selected from polypropylenes having a pentad fraction of 92% or more, an index of high stereoregularity, with the difference in pentad fraction between the two components being 1 to 5% (see Patent Document 2). However, since a polypropylene with a low pentad fraction is used, the stretchability is improved compared to the film described in Patent Document 1, and the reject rate due to stretching unevenness is reduced, but this is still not fully satisfactory. Furthermore, heat resistance and dimensional stability have not been investigated, leaving room for improvement.

[0006] Furthermore, a method has been proposed in which a polypropylene resin composition is used, which is a propylene polymer composition consisting of a propylene homopolymer and a propylene-α-olefin random copolymer, and which has an α-olefin content of 0.3 to 1.6% by weight, an isotactic pentad index of 0.97 or more, an extractable amount with xylene of 3% or less, and a melt flow rate of 0.5 to 10 (g / 10 min) (see Patent Document 3). This method also has a tendency to produce insufficient stretchability and uneven stretching. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-325327 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-235228 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-323542 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in consideration of the above points, and provides a stretched polypropylene film that improves the rigidity of the film, has good heat resistance and dimensional stability, and has good stretchability, allowing for the efficient production of films of stable quality, while also contributing to improved production efficiency in secondary processing. [Means for solving the problem]

[0009] That is, the first invention relates to a laminated film comprising a base layer and a surface layer laminated on one or both sides of the base layer, wherein the base layer is composed of at least two different resin mixtures in which a propylene-ethylene-1-butene random copolymer is mixed with a polypropylene resin (A) having a mesopentad fraction (mmmm) of 95% or more, and the propylene-ethylene-1-butene random copolymer is mixed in an amount of 1 to 10% by weight relative to 100% by weight of the resin mixture.

[0010] A second invention relates to the stretched polypropylene film of the first invention, wherein the ethylene content of the propylene-ethylene-1-butene random copolymer is 5 to 15 mol % and the butene content is 5 to 20 mol %.

[0011] The third invention relates to either the first or second invention, wherein the laminated film is a stretched polypropylene film having a heat shrinkage rate of 6.5% or less in the MD and TD directions when heated at 150°C for 5 minutes.

[0012] The fourth invention relates to a stretched polypropylene film according to any one of the first to third inventions, wherein the laminated film has a content of the crystalline component (H) with the lowest mobility of 55 to 70% and a content of the amorphous component (S) with the highest mobility of 5 to 11% in a three-component approximation of the free induction decay curve at 70°C, as measured by the solid echo method of pulsed NMR. [Effects of the Invention]

[0013] The first aspect of the present invention provides a stretched polypropylene film, which is a laminated film comprising a base layer and a surface layer laminated on one or both sides of the base layer. The base layer is composed of a mixture of at least two different resins, in which a propylene-ethylene-1-butene random copolymer is mixed with a polypropylene resin (A) having a mesopentad fraction (mmmm) of 95% or more. The propylene-ethylene-1-butene random copolymer accounts for 1 to 10% by weight of the resin mixture (100% by weight). This improves the rigidity of the film, while providing good heat resistance and dimensional stability. The film also has good stretchability, allowing for the efficient production of films of stable quality, and contributing to the efficient production of secondary processing.

[0014] According to the stretched polypropylene film of the second invention, in the first invention, the ethylene content of the propylene-ethylene-1-butene random copolymer is 5 to 15 mol % and the butene content is 5 to 20 mol %, so that the stretchability of the film can be improved while maintaining the dimensional stability and rigidity of the film.

[0015] According to the stretched polypropylene film of the third invention, in either the first or second invention, the laminated film has a heat shrinkage rate of 6.5% or less in the MD and TD directions when heated at 150°C for 5 minutes, so that it has excellent dimensional stability and can contribute to improved productivity.

[0016] According to the fourth invention, in the stretched polypropylene film of any of the first to third inventions, the laminated film has, in measurement by the solid echo method of pulsed NMR, a three-component approximation of the free induction decay curve at 70°C, in which the amount of the crystalline component (H) with the lowest mobility is 55 to 70%, and the amount of the amorphous component (S) with the highest mobility is 5 to 11%, so that it is possible to obtain a film with excellent rigidity and heat resistance while suppressing stretching unevenness. DETAILED DESCRIPTION OF THE INVENTION

[0017] The stretched polypropylene film of the present invention has high rigidity and heat resistance because the base layer is made of polypropylene resin (A) having a mesopentad fraction (mmmm) of 95% or more, and by blending propylene-α-olefin random copolymer (B), the rigidity of the film is maintained while improving the stretchability and dimensional stability, thereby increasing the productivity of films with stable quality and contributing to the improvement of production efficiency in secondary processing.

[0018] The stretched polypropylene film of the present invention is a laminated film that satisfies the following requirements: a dimensional change in the MD direction at 140°C when heated from 30°C to 150°C at a rate of 5°C / min and a load of 0.32 N is applied, as measured using a thermomechanical analyzer (TMA), of 30% or less; and a storage modulus in the TD direction (E') at 120°C of 600 MPa or more and at 140°C of 300 MPa or more, as measured using dynamic viscoelasticity measurement at a heating rate of 3°C / min and a frequency of 1.0 Hz.

[0019] The dimensional change rate in the MD direction at 140°C when the temperature was raised from 30°C to 150°C at a rate of 5°C / min and a load of 0.32 N was applied, as measured using a thermomechanical analyzer (TMA). This is an index that reproduces the elongation of a film when it is heated and dried under tension during secondary processing such as vapor deposition, printing, or lamination of a metal or inorganic oxide layer. A film with this dimensional change rate of 30% or less can contribute to improving production efficiency in secondary processing.

[0020] Dynamic viscoelasticity measurement is a method for measuring the mechanical properties of a sample by applying a time-varying (oscillating) strain or stress to the sample and measuring the resulting stress or strain. It is possible to measure the temperature and frequency dependence of the storage modulus (E'), loss modulus (E"), loss tangent (tanδ (=E" / E')), etc. This allows for the observation of various relaxation phenomena, including glass transition, and provides information on the molecular structure and molecular motion of polymers. The storage modulus (E') is the amount of energy generated by external forces and strains stored within an object. A higher storage modulus at high temperatures (120°C to 140°C) indicates superior elastic modulus, rigidity, and heat resistance in high-temperature environments. A low storage modulus reduces the elastic modulus in high-temperature environments, resulting in poor mechanical properties, a loss of stiffness, and the film becomes more stretchy, which can lead to wrinkling due to deformation. In other words, a film having a storage modulus (E') in the TD direction at 120°C of 600 MPa or more and a storage modulus (E') in the TD direction at 140°C of 300 MPa or more, as measured by dynamic viscoelasticity measurement at a heating rate of 3°C / min and a frequency of 1.0 Hz, exhibits excellent modulus, rigidity, and heat resistance in high-temperature environments.

[0021] In other words, by setting the MD dimensional change rate in TMA measurement and the TD storage modulus in dynamic viscoelasticity measurement within these ranges, a stretched polypropylene film with an excellent balance of rigidity, heat resistance, and dimensional stability can be obtained. In particular, the film has excellent dimensional stability in high-temperature environments, and when processing the stretched polypropylene film, such as vapor deposition, printing, or lamination of a metal or inorganic oxide layer, it exhibits less elongation under high-temperature load, reducing wrinkles and deformation during the vapor deposition process and misregistration during printing. This significantly improves processing efficiency and further reduces wrinkles during lamination, enabling use in higher-temperature environments. This can significantly contribute to improving the production efficiency of secondary processing, such as food packaging films and industrial films.

[0022] The polypropylene resin (A) must have a mesopentad fraction (mmmm) of 95% or more. Use of this polypropylene resin (A) tends to improve crystallinity, resulting in a film with excellent rigidity and heat resistance. Use of a polypropylene resin with a mesopentad fraction of less than 95% tends to reduce the rigidity and heat resistance of the film. There are no particular limitations on the mesopentad fraction (mmmm) as long as it is 95% or more, and polypropylene homopolymers and copolymers with ethylene or α-olefins having 4 or more carbon atoms can be used. Propylene homopolymers that do not contain ethylene or α-olefins having 4 or more carbon atoms are particularly preferred.

[0023] The mesopentad fraction (mmmm) is an index of stereoregularity that can be obtained by high-temperature nuclear magnetic resonance (NMR) measurement. The mesopentad fraction (mmmm) is measured as follows: 13 The measurement can be carried out using C-NMR, and the mesopentad fraction can be calculated by the method described in "Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973)". The pentad fraction, which represents the degree of stereoregularity, is 13 It indicates the proportion of isotactic sequences in pentad units in polypropylene molecular chains measured using C-NMR, and is the fraction (mmmm) of propylene monomers at the center of a chain consisting of five consecutive meso-bonded propylene units. Specifically, 13 The intensity fraction of the mmmm peak among all absorption peaks in the methyl carbon region of the C-NMR spectrum is taken as the isotactic pentad unit.

[0024] The base layer is formed by blending the above-mentioned polypropylene resin (A) with a propylene-α-olefin random copolymer (B) to form a resin mixture. The propylene-α-olefin random copolymer (B) is blended in an amount of 1 to 10% by weight relative to 100% by weight of the resin mixture. Blending these resins in this composition broadens the temperature range in which stretching is possible, reducing the rate of defects due to stretching unevenness and contributing to improved production efficiency. Furthermore, it is easy to adjust the dimensional change rate in the MD direction in TMA measurement and the storage modulus in the TD direction in dynamic viscoelasticity measurement to the above-mentioned values. Note that a masterbatch containing an antistatic agent, antiblocking agent, etc. may be blended into the resin mixture, and resins other than the above-mentioned polypropylene resin (A) and propylene-α-olefin random copolymer (B) may be blended.

[0025] The propylene-α-olefin random copolymer (B) is a random copolymer of propylene and an α-olefin (excluding propylene). Examples of the α-olefin include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. These copolymers may be used alone or in combination. Among the propylene-α-olefin random copolymers, propylene-ethylene random copolymers, propylene-ethylene-1-butene random copolymers, and propylene-1-butene random copolymers are preferred, with propylene-ethylene-1-butene random copolymers being more preferred.

[0026] Furthermore, the propylene-ethylene-1-butene random copolymer preferably has an ethylene content of 1 to 15 mol% and a butene content of 1 to 20 mol%, more preferably an ethylene content of 5 to 15 mol% and a butene content of 5 to 20 mol%, and most preferably an ethylene content of 7 to 14 mol% and a butene content of 7 to 17 mol%. When the contents are within the above ranges, a resin mixture mainly composed of a polypropylene resin with a high pentad fraction can be provided with good stretchability, and good rigidity and heat resistance can be maintained.

[0027] The ethylene and butene contents of the propylene-α-olefin random copolymer (B) are as follows: 13 The ethylene content and butene content can be calculated by a known method from the integrated intensity obtained by C-NMR measurement. The ethylene content and butene content can be calculated by the following formulas (i-1) and (i-2). Ethylene content (mol%) = IE × 100 / (IE + IP + IB) (i-1) Butene content (mol%) = IB × 100 / (IE + IP + IB) (i-2)

[0028] IE, IP and IB are the integrated intensities for ethylene, propylene and butene, respectively, and are calculated by the following formulas (i-3), (i-4) and (i-5). IE=I δδ / 2+I γδ / 4-I ββ +I αγ (P)+I αδ (P)+I αγ (B)+I αδ (B) (i-3) IP = 1 / 3 × [I CH3 (P)+I CH (P)+I αα (PP)+1 / 2×(I αα (PB)+I αγ (P)+I αδ (P)) ···(i-4) IB=1 / 4×(I CH3 (B)+I CH (B)+I 2B2 +I αα (BB))+1 / 2×(I αα (PB)+I αγ (B)+I αδ (B)) ···(i-5)

[0029] The subscript (P) indicates a signal based on a methyl group branch derived from propylene, and similarly (B) indicates a signal based on an ethyl group branch derived from butene. αα (PP) is the signal of the methylene carbon based on the propylene chain, and similarly αα(BB) indicates the signal of methylene carbon based on butene chain, αα (PB) is the signal of the methylene carbon based on the propylene-butene linkage.

[0030] Substitute the following into formulas (i-3), (i-4), and (i-5) to determine the content of each component. I ββ =I 24.8-23.3 I γδ =I 30.0-29.6 I δδ =I 29.6-29.2 I αγ (P)+I αδ (P)=I 38.5-37.2 I αγ (B)+I αδ (B)=I 34.5-33.5 I CH3 (P)=I 22.6-18.0 I CH (P)=I 29.2-27.9 +I 31.1-30.0 +I 33.5-32.2 I αα (PP)=I 48.0-44.8 I CH3 (B)=I 11.5-9.0 I CH (B)=I 35.4-34.5 +I 37.1-36.5 +I 39.5-38.8 I αα (BB)=I 40.2-39.5 I αα (PB)=I 43.7-41.6 I 2B2 =I 26.9-26.0

[0031] The lower limit of the melting temperature (Tm) of the polypropylene resin (A) constituting the base layer, as measured by a differential scanning calorimeter (DSC), is preferably 162°C, more preferably 163°C, and even more preferably 164°C. When the Tm is 162°C or higher, rigidity and heat resistance at high temperatures are likely to be obtained. When the Tm of the propylene-α-olefin random copolymer (B) is in the range of 120 to 165°C, preferably 130 to 165°C, and more preferably 140 to 165°C, an excellent balance of rigidity and heat resistance is achieved.

[0032] The melt flow rate (MFR) (230°C, 2.16 kgf) of the polypropylene resin (A) constituting the base layer is preferably 1 to 15 g / 10 min, more preferably 1.5 to 10 g / 10 min, and even more preferably 2.0 to 8 g / 10 min, from the viewpoint of extrusion moldability. The MFR (230°C, 2.16 kgf) of the propylene-α-olefin random copolymer (B) is preferably 5 to 15 g / 10 min, more preferably 6 to 10 g / 10 min. Within the above ranges, the mechanical load tends to be small, and stretchability tends to be easier.

[0033] The weight-average molecular weight (Mw) of the polypropylene resin (A) constituting the base layer, as measured by gel permeation chromatography (GPC), is not particularly limited, but is preferably from 250,000 to 600,000, and more preferably from 300,000 to 550,000. Furthermore, the molecular weight distribution (Mw / Mn), expressed as the ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), is preferably from 2 to 20, and more preferably from 4 to 10. When the molecular weight is within the above range, the resin fluidity is excellent, stretching during film formation is easy, and thickness unevenness is reduced, thereby contributing to improved productivity. There are no particular limitations on the GPC apparatus used in the GPC method, and a commercially available high-temperature GPC apparatus capable of molecular weight analysis of polyolefins can be used.

[0034] Furthermore, the laminate film of the present invention is a laminate film consisting of a base layer and a surface layer laminated on one or both sides of the base layer, and in the case of the base layer and the surface layer laminated on one side, it may have a one-type two-layer structure or a two-type two-layer structure, and in the case of the base layer and the surface layers laminated on both sides (first surface layer and second surface layer), it may have a one-type three-layer structure, a two-type three-layer structure, or a three-type three-layer structure.

[0035] From the viewpoint of ensuring the rigidity, heat resistance, and dimensional stability of the laminate film, the pentad fraction of the polypropylene resin used in the surface layer is preferably 90% or more. However, if a low-crystalline resin is used in the surface layer to effectively bleed out antistatic properties or to impart heat-sealing properties, it can be used within a range that does not impair the desired physical properties of the laminate film. Examples of low-crystalline resins include random copolymers of propylene and α-olefins (excluding propylene), such as propylene-ethylene random copolymers, propylene-ethylene-1-butene random copolymers, and propylene-1-butene random copolymers. The overall thickness of the laminate film is preferably 9 to 100 μm, more preferably 10 to 80 μm, even more preferably 12 to 60 μm, and particularly preferably 12 to 50 μm. The thickness of the surface layer can be adjusted within a range that does not impair the desired physical properties of the laminate film.

[0036] As described above, additives may be added to the laminate film as appropriate. Examples of additives include antioxidants, UV absorbers, antistatic agents, lubricants, nucleating agents, adhesives, antifogging agents, flame retardants, antiblocking agents, inorganic or organic fillers, etc. Examples of antistatic agents include aliphatic amine compounds such as lauryl diethanolamine, myristyl diethanolamine, and oleyl diethanolamine, aliphatic amide compounds such as lauryl diethanolamide, myristyl diethanolamide, and oleyl diethanolamide, and polyhydric alcohols. The antistatic agent can be added by a known method. For example, a high-concentration masterbatch may be prepared separately and mixed in any step, or it may be premixed with polyolefin powder or polyolefin pellets. The high-concentration masterbatch can be prepared by, for example, heat-kneading a polyolefin resin and an antistatic agent using a known mixer or extruder, such as a Banbury mixer, Henschel mixer, tumbler mixer, single-screw extruder, or multi-screw extruder.

[0037] The heat shrinkage of the stretched polypropylene film of the present invention at 150° C. is preferably 6.5% or less in both the MD and TD directions, resulting in a film with excellent mechanical properties, heat resistance, and dimensional stability in a high-temperature environment.

[0038] In the stretched polypropylene film of the present invention, when the free induction decay curve at 70°C is measured by the solid echo method of pulsed NMR, the amount of the crystalline component (H), which has the lowest mobility, is preferably 55 to 70% or less, and the amount of the amorphous component (S), which has the highest mobility, is preferably 5 to 11% or less, when three-component approximation is used. It is more preferable that the amount of the crystalline component (H) is 60% or more and 70% or less, and the amount of the amorphous component (S) is 5 to 10% or less. This allows for a laminated film that not only has good stretchability but also has a good balance of rigidity, heat resistance, and dimensional stability.

[0039] If the (H) component of the stretched polypropylene film is less than 55%, the rigidity and heat resistance are poor, and if it is 70% or more, the stretchability deteriorates and productivity tends to decrease. If the (S) component of the stretched polypropylene film is less than 5%, sufficient stretchability cannot be obtained and stretching unevenness tends to occur, and if it is more than 11%, the stretchability is good but the rigidity and heat resistance tend to decrease.

[0040] Pulse NMR is an analytical method for evaluating the mobility of polymer molecular chains as a whole system, and molecular mobility can be evaluated by measuring the relaxation time and the signal intensity at that time. Generally, the lower the mobility of the polymer chain, the shorter the relaxation time, so the signal intensity decays faster, and the relative signal intensity, when the initial signal intensity is taken as 100%, decreases over a short period of time. Furthermore, the higher the mobility of the polymer chain, the longer the relaxation time, so the signal intensity decays slower, and the relative signal intensity, when the initial signal intensity is taken as 100%, decreases gradually over a long period of time. Techniques for separating and analyzing three components using pulse NMR are well known.

[0041] The free induction decay curve at 70°C measured by the solid echo method of pulsed NMR was simultaneously fitted for multiple mixed components (H, M, S) according to the following formula (ii), and the relaxation time T2 for each component was calculated. The relaxation time T2 correlates with molecular mobility; the shorter the relaxation time T2, the lower the molecular mobility, and the longer the relaxation time T2, the higher the molecular mobility. The ratio of each component was calculated according to formulas (iii) to (v). The (M) component is a constrained amorphous component, with a relaxation time between the (H) and (S) components, and its molecular mobility is also between the (H) and (S) components. A (t) =A (0)H ×exp{-(t / T 2H ) WH}+A (0)M ×exp{-(t / T 2M ) WM}+A (0)S ×exp{-(t / T 2S ) WS} (ii) F (H)={A (0)H / (A (0)H +A (0)M +A (0)S )}×100 (iii) F (M) ={A (0)M / (A (0)H +A (0)M +A (0)S )}×100 (iv) F (S) ={A (0)S / (A (0)H +A (0)M +A (0)S)}×100 (v) t: Capture time A (t) : signal intensity at acquisition time t A (0)H : (H) Initial value of the signal intensity of the component (y-axis value when x-axis is 0) A (0)M : (M) Initial signal strength value (y-axis value when x-axis is 0) A (0)S : (S) Initial value of the signal strength of the component (y-axis value when x-axis is 0) T 2H : (H) component relaxation time T2 T 2M : (M) component relaxation time T2 T 2S : (S) component relaxation time T2 W H : Weibull coefficient of (H) component W M : Weibull coefficient of (M) component W S : Weibull coefficient of (S) component F H : (H) Component ratio F M : (M) Component ratio F S : (S) Component ratio

[0042] The method for producing the stretched polypropylene film of the present invention is not particularly limited. For example, it is as follows. The resins constituting each layer are respectively fed into three extruders, and laminated in the order of first surface layer / base layer / second surface layer. The resins are co-extruded through a three-layer T-die set at 200 to 250°C, and cooled and solidified with a cooling roll at 20 to 60°C to obtain a raw sheet. The raw sheet is preferably further placed in a water tank. The cooling temperature is preferably 40°C or less, and a temperature of 30°C or less is preferable in order to not only obtain the transparency of the raw sheet but also to facilitate stretching in the subsequent step and reduce thickness unevenness.

[0043] Next, the raw sheet is preheated at a set temperature of 110°C to 140°C, stretched 4 to 6 times in the MD direction, and then annealed at 130 to 150°C. Note that MD stretching may be performed in two or more stages using three or more stretching rolls. A stretch ratio in the MD direction within the above range facilitates stretching in the TD direction stretching step and improves productivity. Next, the sheet is preheated in a tenter at a set temperature of 170°C to 185°C and stretched 6 to 12 times in the TD direction at a stretching temperature of 155°C to 170°C. The sheet is then annealed in an atmosphere of 160 to 175°C while relaxing by 3 to 10%. While a higher annealing temperature is preferable to reduce heat shrinkage, setting it too high can cause low-molecular-weight components to melt and recrystallize, roughening the film surface and leading to whitening. While increasing the relaxation can reduce heat shrinkage, excessive relaxation can also reduce the film's rigidity. At least one side of the stretched polypropylene film thus obtained is subjected to a corona discharge treatment, and then the film is wound up on a winder to obtain a roll sample of the stretched polypropylene film. [Example]

[0044] [Materials used] The inventors used the following materials to make the stretched polypropylene film:

[0045] <Polypropylene resin (A)> Resin PP-1: Polypropylene resin "FL1105F" manufactured by Japan Polypropylene Corporation, mesopentad fraction (mmmm) = 96.1%, MFR = 3.5 g / 10 min, Tm = 166 °C, Mw / Mn = 4.9 Resin PP-2: Prime Polymer Co., Ltd., polypropylene resin "F133A", mesopentad fraction (mmmm) = 96.0%, MFR = 3.0 g / 10 min, Tm = 166°C, Mw / Mn = 4.8 Resin PP-3: Polypropylene resin "FL100A" manufactured by Japan Polypropylene Corporation, mesopentad fraction (mmmm) = 91.0%, MFR = 3.0 g / 10 min, Tm = 163°C, Mw / Mn = 5.4

[0046] <Propylene-α-olefin random copolymer (B)> Resin PP-4: Mitsui Chemicals, Inc., propylene-α-olefin random copolymer "PN2060", MFR = 6.0 g / 10 min, Tm = 162°C, Mw / Mn = 2.2, ethylene content 11.4 mol%, butene content 7.1 mol% Resin PP-5: Mitsui Chemicals, Inc., propylene-α-olefin random copolymer "PN3560", MFR = 6.0 g / 10 min, Tm = 162°C, Mw / Mn = 2.2, ethylene content 10.5 mol%, butene content 16.1 mol% Resin PP-6: Propylene-α-olefin random copolymer "FW4BA" manufactured by Japan Polypropylene Corporation, MFR=7.0g / 10min, Tm=138℃, Mw / Mn=5.2, ethylene content 2.8mol%, butene content 2.8mol% Resin PP-7: Propylene-α-olefin random copolymer "FX4EA" manufactured by Japan Polypropylene Corporation, MFR = 5.5 g / 10 min, Tm = 131°C, Mw / Mn = 5.0, ethylene content 1.3 mol%, butene content 5.1 mol% Resin PP-8: Mitsui Chemicals, Inc., propylene-α-olefin random copolymer "XM-7070" MFR = 7.0 g / 10 min, Tm = 75°C, Mw / Mn = 2.0, ethylene content 0 mol%, butene content 26.4 mol%

[0047] <Additives> An antistatic masterbatch (resin PP-9) was used as an additive. Resin PP-3 was used as the base, and the antistatic agent concentration was adjusted to 9%.

[0048] [Measurement of physical properties of materials used] <Mesopentad fraction> Using an FT-NMR device (JEOL RESONANCE Co., Ltd., "JNM-ECA400"), 13 C-NMR measurements were performed. 0.6 mL of a mixture of deuterated orthodichlorobenzene and deuterated benzene in an 8:2 (volume ratio) was added to 120 mg of sample, and the mixture was heated to 135°C to dissolve. Measurements were then performed at 135°C. The mesopentad fraction was calculated using the method described in "Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973)," and peak assignments were based on a revised version of the above-mentioned publication described in "Macromolecules, Vol. 8, p. 687 (1975)." Observation kernel: 13 C(100MHz) Measurement mode: Single pulse proton broadband decoupling Pulse interval: 5 seconds Pulse width: 45° Shift reference: solvent-derived signal = 132.39 ppm Accumulation count: 11,000 times

[0049] <Ethylene and butene contents of propylene-α-olefin random copolymer (B)> Using an FT-NMR device (JEOL RESONANCE Co., Ltd., "JNM-ECA400"), 13 C-NMR measurement was performed. 0.6 mL of a mixture of deuterated orthodichlorobenzene and deuterated benzene in an 8:2 (volume ratio) was added to 120 mg of sample, and the mixture was heated to 135°C to dissolve the sample. Measurement was then performed at 135°C. The ethylene and butene contents were calculated by substituting the obtained integrated intensities into equations (i-3), (i-4), and (i-5), as described above. Observation kernel: 13 C(100MHz) Measurement mode: Single pulse proton broadband decoupling Pulse interval: 5 seconds Pulse width: 45° Shift reference: solvent-derived signal = 132.39 ppm Accumulation count: 11,000 times

[0050] <Melting temperature> The melting temperature was determined by differential scanning calorimetry (DSC) according to JIS K 7121 (2012). Measurements were performed using a DSC6200 manufactured by Seiko Instruments Inc. (unit: °C).

[0051] <Melt flow rate (MFR)> The melt flow rate (MFR) was measured in accordance with Method A of JIS K 7210-1 (2014).

[0052] <Molecular weight, molecular weight distribution measurement> The molecular weight and molecular weight distribution were measured using "HLC-8321GPC-HT" manufactured by Tosoh Corporation under the following conditions. Column: TSKgel GMHHR-H(20)HT x 3 (7.8mm ID x 300mm x 3) Eluent: 1,2,4-trichlorobenzene (0.05% BHT added) Flow rate: 1.0mL / min Detector: RI detector (polarity: -) Column temperature: 140℃ Injection volume: 300μL Molecular weight standard: Standard polystyrene

[0053] [Preparation of oriented polypropylene film] <Prototype example 1> The base layer was a dry blend of 95% by weight of PP-1 resin (A) and 5% by weight of PP-4 resin (B) as a propylene-α-olefin random copolymer. Resin PP-3 was used for the first and second surface layers. The materials were fed into three extruders, each with a first surface layer / base layer / second surface layer configuration, and coextruded through a three-layer T-die set at 240°C. The extruded material was then contacted with a 30°C cooling roll and then placed directly in a 30°C water bath to obtain a raw sheet. The sheet was then preheated to a set temperature of 135°C, stretched 5 times in the MD direction, and annealed at 140°C. It was then preheated to a set temperature of 182°C in a tenter and stretched 8 times in the TD direction at a stretching temperature of 163°C. It was then annealed at 170°C with a relaxation of 6.5%. One side of the film was then corona-discharge-treated and wound on a winder to obtain the stretched polypropylene film of Prototype Example 1.

[0054] <Prototype example 2> The stretched polypropylene film of Prototype Example 2 was obtained in the same manner as in Prototype Example 1, except that the base layer was made of polypropylene resin (A) containing 87% by weight of resin PP-1, propylene-α-olefin random copolymer (B) containing 3% by weight of resin PP-4, and antistatic agent masterbatch containing 10% by weight of resin PP-9.

[0055] <Prototype example 3> The base layer was made of polypropylene resin (A) containing 84% by weight of resin PP-1, propylene-α-olefin random copolymer (B) containing 6% by weight of resin PP-4, and antistatic masterbatch containing 10% by weight of resin PP-9. The stretched polypropylene film of prototype 3 was obtained in the same manner as prototype 2, except that the TD magnification was 8.7 times and the relaxation was 9.0%.

[0056] <Prototype example 4> The stretched polypropylene film of Prototype Example 4 was obtained in the same manner as in Prototype Example 2, except that the base layer was made of polypropylene resin (A) consisting of 87% by weight of resin PP-1, propylene-α-olefin random copolymer (B) consisting of 3% by weight of resin PP-5, and antistatic masterbatch consisting of 10% by weight of resin PP-9, and the preheating temperature in the TD direction was 184°C.

[0057] <Prototype 5> The stretched polypropylene film of Prototype Example 5 was obtained in the same manner as in Prototype Example 2, except that the base layer was made of polypropylene resin (A) consisting of 84 wt% resin PP-1, propylene-α-olefin random copolymer (B) consisting of 6 wt% resin PP-6, and antistatic masterbatch consisting of 10 wt% resin PP-9, and the preheating temperature in the TD direction was 183°C.

[0058] <Prototype Example 6> The stretched polypropylene film of Prototype Example 6 was obtained in the same manner as in Prototype Example 3, except that the base layer was made of polypropylene resin (A) consisting of 81% by weight of resin PP-1, propylene-α-olefin random copolymer (B) consisting of 9% by weight of resin PP-6, and antistatic masterbatch consisting of 10% by weight of resin PP-9, and the preheating temperature in the TD direction was set to 183°C.

[0059] <Prototype Example 7> The stretched polypropylene film of Prototype Example 7 was obtained in the same manner as in Prototype Example 2, except that the base layer was made of polypropylene resin (A) containing 84% by weight of resin PP-1, propylene-α-olefin random copolymer (B) containing 6% by weight of resin PP-7, and antistatic agent masterbatch containing 10% by weight of resin PP-9.

[0060] <Prototype Example 8> The stretched polypropylene film of Prototype Example 8 was obtained in the same manner as in Prototype Example 2, except that the base layer was made of polypropylene resin (A) containing 84% by weight of resin PP-1, propylene-α-olefin random copolymer (B) containing 6% by weight of resin PP-8, and antistatic agent masterbatch containing 10% by weight of resin PP-9.

[0061] <Prototype Example 9> The stretched polypropylene film of Prototype Example 9 was obtained in the same manner as in Prototype Example 2, except that the base layer was made of polypropylene resin (A) containing 87% by weight of resin PP-2, propylene-α-olefin random copolymer (B) containing 3% by weight of resin PP-4, and antistatic agent masterbatch containing 10% by weight of resin PP-9.

[0062] <Prototype example 10> The base layer was made of polypropylene resin (A) containing 79% by weight of resin PP-1, propylene-α-olefin random copolymer (B) containing 11% by weight of resin PP-4, and antistatic masterbatch containing 10% by weight of resin PP-9. The same procedures as in Prototype 2 were followed, except that the preheating temperature in the TD direction was 183°C, the stretching ratio in the TD direction was 8.7 times, and the relaxation was 9.0%, to obtain the stretched polypropylene film of Prototype 10.

[0063] <Prototype Example 11> The stretched polypropylene film of Prototype Example 10 was obtained in the same manner as in Prototype Example 10, except that the base layer was made of polypropylene resin (A) containing 78% by weight of resin PP-1, propylene-α-olefin random copolymer (B) containing 12% by weight of resin PP-6, and antistatic agent masterbatch containing 10% by weight of resin PP-9.

[0064] <Comparative Example 1-1> The same procedures as in Prototype Example 1 were carried out except that the base layer was made of polypropylene resin (A) containing 100% by weight of resin PP-1, the TD stretching temperature was 165°C, and the TD annealing temperature was 168°C, and a stretched polypropylene film of Comparative Example 1-1 was obtained.

[0065] <Comparative Example 1-2> A stretched polypropylene film of Comparative Example 1-2 was obtained in the same manner as in Comparative Example 1-1, except that the preheating temperature in the TD direction was 185°C and the stretching temperature in the TD direction was 163°C.

[0066] <Comparative Example 1-3> A stretched polypropylene film of Comparative Example 1-3 was obtained in the same manner as in Comparative Example 1-1, except that the preheating temperature in the TD direction was 180°C and the stretching temperature in the TD direction was 165°C.

[0067] <Comparative Example 1-4> The same procedures as in Comparative Example 1-1 were conducted except that the preheating temperature in the TD direction was 178°C and the stretching temperature in the TD direction was 168°C, to obtain a stretched polypropylene film of Comparative Example 1-4.

[0068] <Comparative Example 2> A stretched polypropylene film of Comparative Example 2 was obtained in the same manner as in Prototype Example 1, except that the base layer was made of polypropylene resin (A) containing 100% by weight of resin PP-3, the preheating temperature in the TD direction was 181°C, the stretching temperature in the TD direction was 164°C, and the annealing temperature in the TD direction was 168°C.

[0069] <Comparative Example 3> The stretched polypropylene film of Comparative Example 3 was obtained in the same manner as in Prototype Example 1, except that the base layer was made of polypropylene resin (A) with a composition of 90% by weight of resin PP-3 and 10% by weight of resin PP-9 as the antistatic agent masterbatch, the preheating temperature in the TD direction was 181°C, the stretching temperature in the TD direction was 164°C, and the annealing temperature in the TD direction was 168°C.

[0070] Tables 1 to 3 show the resin compositions and film-forming conditions for the intermediate layer and surface layer of each prototype and comparative example.

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] [Performance evaluation of oriented polypropylene film] To evaluate the stretched polypropylene films of each prototype and comparative example, the dimensional change rate, storage modulus, heat shrinkage rate, pulse NMR, tensile modulus, and haze were measured. Additionally, the thickness of each film was measured, and the appearance of the film was evaluated visually. The results are summarized in Tables 4 to 6. Note that Comparative Examples 1-2 to 1-4 had severe stretching unevenness during production, and some of the measurements could not be performed, so they are omitted from the tables. Comparative Example 1-2 had stretching unevenness and whitening, resulting in a decrease in transparency. Comparative Example 1-3 had even worse stretching unevenness. Comparative Example 1-4 had stretching unevenness at the same level as Comparative Example 1-3.

[0075] <Dimensional change rate> The dimensional change rate (%) was measured using a thermomechanical measuring device (TA Instruments Japan, Model No. Q400) as the TMA measurement device. Each of the prototype and comparative examples of oriented polypropylene films was cut into 8 mm x 4 mm test pieces. The MD direction of the test pieces was set as the tensile direction, and the test pieces were fixed to the probe of the TMA device. A load of 0.32 N was applied to the test pieces, and the initial length (L0) of the test pieces was measured. The test pieces were heated from 30°C to 150°C at a heating rate of 5°C / min, and the length (L1) of the test pieces after heating to 140°C was measured. During the heating process, a load of 0.32 N was applied to the test pieces in the MD direction. The lengths (L0) and (L1) of the test pieces before and after heating were then substituted into the following equation (vi), and the dimensional change rate (%) was calculated from the relationship between the initial test piece length and the amount of change. The stretched polypropylene film of Comparative Example 2 was elongated to the measurement limit before the test piece reached 140°C, making it impossible to calculate the dimensional change rate, and was therefore deemed unmeasurable and indicated as "-" in the table. At this time, the dimensional change rate calculated from the elongation (L1) at the measurement limit was 43.4%. Dimensional change rate (%) = {(L1-L0) / L0} × 100 (vi)

[0076] <Storage modulus> The storage modulus (MPa) was measured in the TD direction at 120°C and 140°C under the following conditions using a DVA-225 manufactured by IT Measurement and Control Co., Ltd. Deformation mode: tension Temperature range: -60℃~150℃ Heating rate: 3℃ / min Frequency: 1Hz Environment: Under Air

[0077] <Heat shrinkage rate> The heat shrinkage (%) was measured in accordance with JIS Z 1712 (2009). Test pieces measuring 15 mm in the TD direction and 200 mm in the MD direction were cut out from the stretched polypropylene film of each prototype and comparative example, and marks were made 50 mm from both ends to determine the test length (l0) before heating. The test pieces were then hung in a hot air oven at 150°C and heated for 5 minutes. The test pieces were then removed and cooled at room temperature, and the length after heating was measured. The test length after heating was designated as (l1) and substituted into the following formula (vii) to determine the heat shrinkage. Heat shrinkage rate (%) = {(l0-l1) / l0} × 100 (vii)

[0078] <Pulse NMR> Pulse NMR (%) was measured using a pulse NMR device (manufactured by Bruker, "the minispec mq20") under the following conditions: Test pieces of the stretched polypropylene films of each prototype and comparative example were cut with scissors and placed in sample tubes. Weibull coefficient W H uses values ​​between 1.76 and 2.00, and W M and W S The value of 1 was used for the Weibull coefficient W H was used as a variable in the fitting, and the values ​​were changed to accurately match the free induction decay curve. Observation kernel: 1 H (resonance frequency: 20MHz) Measurement temperature: 70℃ Measurement method: Solid Echo method 90° pulse width: 3.26 μs Pulse interval: 0.008 ms Capture time: 2 ms Repeat time: 1s Number of times accumulated: 1024

[0079] <Tensile modulus> The tensile modulus (GPa) was measured in the MD and TD directions using a tensile testing machine (manufactured by A&D Co., Ltd., "RTF-1310"), in accordance with JIS K 7127 (1999), under conditions of a chuck distance of 100 mm and a pulling speed of 200 mm / min, by cutting out test pieces of 15 mm width x 200 mm from the stretched polypropylene film of each prototype and comparative example.

[0080] <Haze> The haze (%) was measured in accordance with JIS K 7136 (2000) using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., "NDH-5000").

[0081] <Thickness> The thickness (μm) of the film was measured using a thickness measuring device (manufactured by Toyo Seiki Seisakusho, Ltd., "B-1") to determine the total layer thickness (μm).

[0082] <Film appearance evaluation> The appearance of the film was visually evaluated according to the following criteria: A film with almost no unevenness in stretching and good appearance was rated as "◯", and a film with unevenness in stretching and poor appearance was rated as "X".

[0083] [Table 4]

[0084] [Table 5]

[0085] [Table 6]

[0086] [Results and Discussion] The prototypes 1 to 9 have small dimensional change rates in the MD direction at high temperatures and high storage moduli in the TD direction, which results in excellent rigidity, heat resistance, and dimensional stability. Furthermore, the film appearance is free of stretching irregularities and has excellent stretchability, which results in good production efficiency.

[0087] The film made of only polypropylene resin (A) with a high mesopentad fraction in Comparative Example 1-1 had excellent rigidity, heat resistance, and dimensional stability, but exhibited stretching irregularities, making it unsuitable for commercial use. As in Comparative Example 1-1, the stretching irregularities could not be improved even in Comparative Examples 1-2 to 1-4, in which only polypropylene resin (A) with a high mesopentad fraction was used and the film-forming conditions were changed. This indicates that blending a propylene-α-olefin random copolymer (B) into the base layer can improve the stretchability of the film and suppress the occurrence of stretching irregularities.

[0088] In addition, in the films made from polypropylene resins with low mesopentad fractions in Comparative Examples 2 and 3, although they had excellent stretchability and no stretching unevenness occurred, they were poor in rigidity, heat resistance, and dimensional stability, and no films with the desired physical properties were obtained.

[0089] Furthermore, it was shown that films made using polypropylene resin (A) with a high mesopentad fraction and increased amounts of propylene-α-olefin random copolymer (B) as in Prototypes 10 and 11 exhibited poor dimensional change rates, making them difficult to use in high-temperature environments. Furthermore, Prototype 11, which contained a higher amount of propylene-α-olefin random copolymer (B) than Prototype 10, also exhibited poor heat shrinkage, indicating that excessively increasing the amount of propylene-α-olefin random copolymer (B) reduces rigidity, heat resistance, and dimensional stability, potentially reducing production efficiency.

[0090] As shown above, in Prototypes 1 to 9, the base layer was composed of a resin blend containing a polypropylene resin (A) with a mesopentad fraction (mmmm) of 95% or more and a propylene-α-olefin random copolymer (B), and the propylene-α-olefin random copolymer (B) was blended in an amount of 1 to 10% by weight relative to 100% by weight of the resin blend. While maintaining good rigidity, heat resistance, and dimensional stability, the stretchability was improved, reducing the reject rate due to stretching unevenness, thereby contributing to the efficiency of film production. Furthermore, because of the excellent dimensional stability at high temperatures, stretched polypropylene films are less likely to elongate under load under high temperatures, even when subjected to processes such as vapor deposition, printing, and lamination of metal or inorganic oxide layers. This reduces wrinkles and deformation during the vapor deposition process, misregistration during printing, and wrinkles during lamination. This allows the film to be used in higher temperature environments, significantly improving processing efficiency. Therefore, it can also greatly contribute to improving the efficiency of production in secondary processing, such as films for food packaging and industrial use. [Industrial Applicability]

[0091] The stretched polypropylene film of the present invention has good stretchability, heat resistance, and dimensional stability while improving the rigidity of the film. That is, the stretched polypropylene film of the present invention can improve the productivity of films of stable quality while maintaining good rigidity, and also has good dimensional stability even under high-temperature conditions, which can contribute to improving the production efficiency in secondary processing.

Claims

1. A laminated film comprising a base layer and a surface layer laminated on one or both sides of the base layer, the base layer is composed of a mixture of at least two different resins, in which a propylene-ethylene-1-butene random copolymer is mixed with a polypropylene resin (A) having a mesopentad fraction (mmmm) of 95% or more; The propylene-ethylene-1-butene random copolymer is mixed in an amount of 1 to 10% by weight with respect to 100% by weight of the resin mixture. Stretched polypropylene film.

2. 2. The stretched polypropylene film according to claim 1, wherein the propylene-ethylene-1-butene random copolymer has an ethylene content of 5 to 15 mol % and a butene content of 5 to 20 mol %.

3. 3. The stretched polypropylene film according to claim 1, wherein the laminated film has a heat shrinkage rate of 6.5% or less in both the MD and TD directions when heated at 150°C for 5 minutes.

4. 4. The stretched polypropylene film according to claim 1, wherein, in measurement by a solid echo method of pulsed NMR, the laminated film has a three-component approximation of a free induction decay curve at 70°C, in which the amount of the crystalline component (H) with the lowest mobility is 55 to 70%, and the amount of the amorphous component (S) with the highest mobility is 5 to 11%.

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