WO2015087990A1

WO2015087990A1 - Polyolefin-based unstretched multilayer film

Info

Publication number: WO2015087990A1
Application number: PCT/JP2014/082906
Authority: WO
Inventors: 直彦倉本; 三輪　和弘; 健二勘田; 陽介村越; 佐藤　豪一
Original assignee: サン・トックス株式会社
Priority date: 2013-12-12
Filing date: 2014-12-05
Publication date: 2015-06-18
Also published as: KR20160096589A; TW201538324A; CN105793037A; JPWO2015087990A1; JP6457402B2

Abstract

The present invention provides a polyolefin-based unstretched multilayer film, which has excellent optical characteristics, blocking resistance, heat sealing properties, hermetic sealing properties, package openability by tearing and easy peeling properties. This polyolefin-based unstretched multilayer film comprises a laminate layer, at least one intermediate layer, and a heat sealing layer. At least one intermediate layer is formed of a polyolefin-based resin containing a long-chain branched LLDPE. The long-chain branched LLDPE in the polyolefin-based resin of the intermediate layer has a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in terms of polystyrene as determined by gel permeation chromatography, namely Mw/Mn of 7.5-15.0 and an amorphous content of 1-4% by weight as determined by a temperature raising elution fractionation method. The long-chain branched LLDPE in the polyolefin-based resin of the intermediate layer has 1.5-5.0 branches, each of which has 8 or more carbon atoms, per 1,000 carbon atoms as determined by ¹³C-NMR.

Description

Polyolefin-based unstretched multilayer film

The present invention relates to a polyolefin-based unstretched multilayer film. Specifically, it has excellent optical properties such as high transparency, high glossiness, high image clarity, blocking resistance, and low temperature heat seal properties.
The present invention relates to a polyolefin-based unstretched multilayer film excellent in heat seal strength when bonded to a base film to form a composite film; sealing performance; tear-opening property or easy peel property of a package.

Polyolefin resin films are widely used as materials for packaging various products. For example, food packaging applications; textile goods / garments daily goods packaging applications; industrial parts packaging applications. In particular, polypropylene resin films are widely used because they are excellent in rigidity and heat resistance, and have a high feeling of elasticity. However, the polypropylene resin film is not sufficient in at least heat sealability, particularly low temperature heat sealability, and impact resistance. Thus, attempts have been made to improve heat sealability and impact resistance by copolymerizing film material polypropylene. However, a significant effect has not been obtained particularly with respect to impact resistance at low temperatures. Also, blocking problems occur when trying to improve heat sealability. For this reason, the above attempts to form a copolymer have not been successful.
In this regard, in Japanese Patent Laid-Open No. 5-147179, a linear ethylene-α-olefin copolymer (LLDPE) is used as an intermediate layer, and the intermediate layer and a polypropylene resin layer as both outer layers are laminated. Has proposed a polyolefin-based multilayer film having improved impact resistance. According to this method, an improvement in impact resistance is certainly observed, but the optical properties (transparency, glossiness, image clarity, etc.) of the laminated film are impaired. Moreover, since the tear strength when the laminated film is bonded to a base film to obtain a composite film becomes very high, the tear-opening property when this is used as a packaging material is significantly impaired.
JP-A-2004-276373 discloses a polyolefin-based multilayer film having improved low-temperature heat sealability and blocking resistance by laminating a specific polypropylene-based polymer as both outer layers and an LLDPE layer as an intermediate layer. Proposed. Even with this technique, the tear strength of the resulting composite film is very high, and the tear-openability when this film is used as a packaging material is not satisfactory.
By the way, in food packaging applications, particularly packaging of snacks, etc., there is a demand to peel off the heat seal portion and open the package in addition to the above-described tear opening at the time of opening. That is, it is a case where it opens by grasping | ascertaining the heat seal part vicinity of each film which comprises a bag body oppositely, pulling this part in the direction spaced apart perpendicularly to a film surface, and peeling a heat seal part. This ease of peeling of the heat seal portion is called “easy peel”.
Even in the case of a packaging material having easy peel properties, it is necessary to maintain hermeticity as long as it is used for food applications. However, in the prior art, there is almost no investigation to improve easy peelability while maintaining the sealing property of the packaging material.

The present invention has been made in view of the present state of the art as described above.
The object of the present invention is excellent in various properties such as optical properties, blocking resistance, low-temperature heat sealability, heat seal strength, and sealability, as well as polyolefin-based non-stretching that is excellent in tear-opening properties and easy peel properties of the package. It is to provide a multilayer film.
According to the present invention, the above objects and advantages of the present invention are:
A polyolefin-based unstretched multilayer film having a laminate layer as an outermost layer, at least one intermediate layer, and a heat seal layer as another outermost layer,
The laminate layer is made of a polyolefin resin,
At least one of the intermediate layers is made of a polyolefin resin containing long-chain branched LLDPE,
The heat seal layer is made of a polyolefin resin containing a polypropylene resin,
The polyolefin resin of the laminate layer has a higher melting point than the polypropylene resin in the heat seal layer,
The long-chain branched LLDPE in the polyolefin-based resin in the intermediate layer is
The ratio Mw / Mn of polystyrene-equivalent weight average molecular weight Mw and number average molecular weight Mn measured by gel permeation chromatography is 7.5 to 15.0,
The amount of non-crystalline components measured by the temperature rising elution fractionation method is 1 to 4% by weight, and the number of branches having 8 or more carbon atoms measured by ¹³ C-NMR is 1.5 per 1,000 carbon atoms. Achieved by the multilayer film, characterized in that it is ~ 5.0.

The polyolefin-based unstretched multilayer film of the present invention has a laminate layer that is the outermost layer, at least one intermediate layer, and a heat seal layer that is the other outermost layer.
<Laminate layer>
The laminate layer in the multilayer film of the present invention is made of a polyolefin resin.
The polyolefin resin has a higher melting point than the polypropylene resin in the heat seal layer described later. The melting point of the polyolefin resin is preferably 3 ° C. or higher, more preferably 5 ° C. or higher, and further preferably 15 ° C. higher than the melting point of the polypropylene resin in the heat seal layer. Thereby, sufficient heat resistance can be obtained in the production, lamination, heat sealing, etc. of the multilayer film of the present invention. On the other hand, the difference between the melting point of the polyolefin resin and the melting point of the polypropylene resin in the heat seal layer is preferably kept at 20 ° C. or lower. This is because if the melting point difference becomes excessively large, curling may occur in the multilayer film.
Examples of the polyolefin resin constituting the laminate layer in the present invention include a polypropylene resin, an ethylene homopolymer, an ethylene-α-olefin copolymer, and a thermoplastic elastomer. These may be used alone or in admixture of two or more. These polyolefin resins preferably have a melting point in the range of 120 to 165 ° C. and a melt flow rate MFR in the range of 1 to 30 g / 10 minutes. The melting point is the peak top temperature (Tm) of the maximum endothermic peak in a differential scanning calorimeter (DSC) chart;
The MFR is a value measured according to JIS K 7210 (both melting point and MFR are the same in the present specification).
As said polypropylene resin, the homopolymer of propylene and the copolymer of a propylene and a copolymerization component can be mentioned. As the copolymer component, for example, ethylene and α-olefin are preferable, and specifically, for example, ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene. 4-methyl-1-pentene can be used, and one or more selected from these can be used. The proportion of the copolymer component in this polypropylene resin is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 3 mol% or less.
The said ethylene-alpha-olefin copolymer does not include what corresponds to said polypropylene resin. Examples of the α-olefin which is a copolymerization component in the ethylene-α-olefin copolymer include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1- Examples include decene and 4-methyl-1-pentene, and one or more selected from these can be used. The proportion of the α-olefin component in the ethylene-α-olefin copolymer is preferably 1 to 20 mol%, more preferably 5 to 15 mol%.
The polyolefin resin in the laminate layer of the multilayer film of the present invention preferably contains a polypropylene resin as described above. The laminate layer may consist only of a polypropylene resin, and may contain other polymers together with the polypropylene resin. The other polymer used here is preferably selected from the above-mentioned ethylene homopolymer, ethylene-α-olefin copolymer, and thermoplastic elastomer.
The content of the other polymer is preferably 10% by weight or less, more preferably 5% by weight or less, and most preferably no other polymer based on the whole polyolefin resin. .
[Optional ingredients]
In addition to the polyolefin resin as described above, the laminate layer of the multilayer film of the present invention includes, as an optional additive, for example, a heat stabilizer, a processing stabilizer, a lubricant, a nucleating agent, an antistatic agent, an antifogging agent, An antiblocking agent, antioxidant, a ultraviolet absorber, a pigment etc. can be mentioned. These additives may be added by a method of directly blending with the polymer constituting the polyolefin resin, or may be added by a method of blending these additives as a master batch containing a high concentration. As the base resin for the masterbatch, any of the above polyolefin resins can be used.
The proportion of the optional component as described above is preferably 10% by weight or less, and more preferably 5% by weight or less, based on the entire polyolefin resin. Most preferably, it does not contain such an optional component.
[Thickness of laminate layer]
The thickness of the laminate layer in the multilayer film of the present invention is preferably 1.0 to 30 μm, more preferably 2.5 to 25 μm. By setting the thickness of the laminate layer within this range, the resulting multilayer film and composite film are preferable in that high impact resistance can be obtained without impairing heat resistance and openability.
<Intermediate layer>
At least one of the intermediate layers in the multilayer film of the present invention is made of a polyolefin resin containing long-chain branched LLDPE (B1).
[Long-chain branched LLDPE]
The long chain branched LLDPE (B1) in the present invention is a linear low density polyethylene having a branch having 8 or more carbon atoms.
The LLDPE used in the prior art film is common to the long chain branched LLDPE (B1) and LDPE (low density polyethylene) in the present invention in that it is a low density polyethylene having a branch. However, the long-chain branched LLDPE (B1) in the present invention is different from LLDPE and LDPE in the prior art at least in the content of long-chain branches, Mw / Mn and the amount of non-crystalline components.
The long chain branched LLDPE (B1) in the present invention is ¹³ The number of branches having 8 or more carbon atoms measured by C-NMR is 1.5 to 5.0 per 1,000 carbon atoms. This value is preferably 2.0 to 5.0, and more preferably 2.5 to 4.5. By using LLDPE having such a long chain branch, when the multilayer film of the present invention is used as a package, it is possible to obtain an advantage that both tear opening and easy peel properties are compatible.
In this regard, the LLDPE in the prior art is dominant when the number of carbon atoms in the branch is 6 or less, and even if there is a branch having 8 or more carbon atoms, the amount thereof is small, usually per 1,000 carbon atoms. 1 or less, and at most 2 or less.
On the other hand, LDPE ¹³ In the C-NMR measurement, the number of components detected as branches having 8 or more carbon atoms is more than 5 per 1,000 carbon atoms.
Therefore, the long-chain branched LLDPE (B1) in the present invention is ¹³ It can be distinguished from LLDPE and LDPE in the prior art by the amount of branching of 8 or more carbon atoms measured by C-NMR.
The branched structure of long-chain branched LLDPE (B1) in the present invention and the branched structure of LLDPE in the prior art are: ¹³ The following describes how it is measured on C-NMR. Here, as branch, C of long chain branch LLDPE ₈ Branched (1-decene structure) and LLDPE C in the prior art ₆ We decided to focus on branching (1-octene structure).
The methylene carbon present in the main chain of polyethylene is ¹³ A chemical shift δ = 30 ppm is observed on C-NMR. The methyl carbon at the branch end is C ₈ Branch and C ₆ Both branches appear at the chemical shift δ = 14.06 ppm. However, the chemical shift of each of the second and third methylene carbons from the branch end is C ₈ Branch and C ₆ The branching differs as shown in Table 1 below.

In the present invention, attention is paid to the second methylene carbon from the branch end, and it is determined whether or not the number of branched carbons is 8 or more by the chemical shift.
In actual calculation, the relative value of the peak area appearing at the chemical shift δ = 22.87 ppm to the peak area appearing at the chemical shift δ = 30 ppm attributed to the methylene carbon of the main chain is evaluated.
As above ¹³ The C-NMR measurement can be performed under the following conditions using an appropriate nuclear magnetic resonance analyzer such as a model “JNM-ECS400” manufactured by JEOL.
Solvent: Mixed solvent of trichlorobenzene / heavy benzene (75/25% by volume)
Sample concentration: 80 mg / 2.5 mL solution
Measurement mode: 1H-complete decoupling
Measurement temperature: 120 ° C
Pulse width: 90 degree pulse
Pulse repetition time: 9 seconds
Integration count: 9,000 times
The content of long chain branching in the present invention is
C ₈ The peak area of the second carbon from the end of the branch (chemical shift δ = 22.87 ppm) is
It is expressed as a relative value when the peak area of methylene carbon (chemical shift δ = 30 ppm) constituting the polymer chain is 1,000. The unit is (pieces / 1,000 C).
The long chain branched LLDPE (B1) in the present invention has a ratio Mw / Mn (molecular weight distribution) of the weight average molecular weight Mw and the number average molecular weight Mn in terms of polystyrene measured by gel permeation chromatography (GPC) of 7.5 to 15.0. This value is preferably 8.5 to 14.5, and more preferably 9.5 to 13.5. By using a long-chain branched LLDPE having such a molecular weight distribution, when the multilayer film of the present invention is used as a package, it is possible to obtain an advantage that both tear opening and easy peelability are compatible. .
The long-chain branched LLDPE (B1) in the present invention has a polystyrene-equivalent weight average molecular weight Mw measured by GPC of preferably 80,000 to 150,000, more preferably 90,000 to 140,000. preferable.
The long-chain branched LLDPE (B1) in the present invention has an amorphous component amount of 1 to 4% by weight measured by a temperature rising elution fractionation method.
In the temperature rising elution fractionation method, a solution obtained by dissolving a polymer sample in a predetermined solvent at a high temperature is supplied to a TREF (Temperature Rising Elution Fractionation) column, and then cooled to precipitate and adsorb the polymer sample in the column. Then, the column temperature is gradually raised and the eluted fraction is analyzed. In the present invention, after the column after the sample is supplied is cooled to 0 ° C., the supply of the solvent is started, and the fraction eluted during the period in which the column temperature is maintained at 0 ° C. is used as an amorphous component. Is evaluated as the amount of non-crystalline component. The amount of the amorphous component of the long chain branched LLDPE is preferably 1.5 to 3.0% by weight.
Such a temperature rising elution fractionation method can be performed, for example, using an appropriate temperature rising elution fractionation (TREF) apparatus such as a special TREF apparatus manufactured by Senshu Kagaku Co., Ltd.
By using the long-chain branched LLDPE having the crystallinity as described above, it is possible to obtain the advantage of ensuring the blocking resistance and the back feeling (elasticity) of the multilayer film of the present invention.
For reference, the above-mentioned various parameters are shown in Table 2 below for typical commercially available polyethylene.

The long-chain branched LLDPE (B1) in the present invention as described above may be synthesized by any method as long as it satisfies the above requirements. For example, it can be produced by a method using a known Ziegler-Natta catalyst, preferably together with an appropriate donor compound; a method using a Phillips catalyst; a method using a metallocene catalyst. Among these, the method using a metallocene catalyst is preferable in that a polymer having the above characteristics can be easily obtained.
The metallocene catalyst is a catalyst comprising a metallocene-type transition metal compound having at least one, preferably two, substituted or unsubstituted cyclopentadienyl ligands and a co-catalyst. Examples of the cocatalyst include organoaluminum compounds; complexes of organoboron compounds and cations; ion-exchange silicates and the like, and one or more selected from these can be used. . The metallocene catalyst may be supported on a suitable inorganic substance. Metallocene catalysts are already known in the art, and those skilled in the art can appropriately select and use an appropriate metallocene catalyst according to the purpose.
[Other polymers]
The at least one layer of the intermediate layer in the multilayer film of the present invention may contain other polymers in addition to the long-chain branched LLDPE (B1) as described above.
Examples of other polymers that can be used here include polypropylene resin (B2), polyethylene (B3) other than long-chain branched LLDPE (B1), and thermoplastic elastomer.
As the polypropylene resin (B2), for example, a resin similar to the resin described above can be used for the polypropylene resin as the polyolefin resin constituting the laminate layer.
Examples of polyethylene (B3) other than long-chain branched LLDPE (B1) include HDPE, LLDPE, and LDPE.
At least one resin selected from the group consisting of polyethylene (B3) other than the polypropylene-based resin (B2) and the long-chain branched LLDPE (B1) among the other polymers described above is used as the intermediate layer in the multilayer film of the present invention. By containing, the easy peel strength when the multilayer film is used as a package can be adjusted, which is preferable.
From the above viewpoint, the polyolefin resin in the at least one layer of the intermediate layer of the multilayer film of the present invention is:
Consists of long-chain branched LLDPE (B1) only, or
Long-chain branched LLDPE (B1);
It is preferable to consist of at least one resin selected from the group consisting of polypropylene (B2) and polyethylene (B3) other than the long-chain branched LLDPE (B1) as described above.
The at least one layer of the intermediate layer of the multilayer film of the present invention preferably comprises only the polyolefin resin as described above and does not contain any other resin.
The polyolefin resin in the at least one layer of the intermediate layer of the multilayer film of the present invention preferably contains the above resins in the following proportions.
Long chain branched LLDPE (B1): preferably 40% by weight or more, more preferably 50% by weight or more
Polypropylene resin (B2): preferably 30% by weight or less, more preferably 25% by weight or less, and
Polyethylene (B3) other than long-chain branched LLDPE (B1): preferably 50% by weight or less, more preferably 30% by weight or less
In the above, the total of the polyethylene (B3) other than the long chain branched LLDPE (B1), the polypropylene resin (B2) and the long chain branched LLDPE (B1) is 100% by weight.
[Optional ingredients]
The intermediate layer of the multilayer film of the present invention may contain additives as described as optional components of the laminate layer in the same manner.
[Mode of intermediate layer]
The intermediate layer in the multilayer film of the present invention may consist of only one layer, or may be a laminate of two or more layers. In the latter case, each layer constituting the intermediate layer is selected from the polyolefin resins as described above. The polyolefin resin constituting each layer may be the same in the type of polyolefin resin, the presence or absence of other optional polymers and additives, and the type and content thereof. One or more of may be different.
The thickness of the intermediate layer is preferably 5 to 80 μm, more preferably 10 to 50 μm. By setting the intermediate layer to a thickness in this range, it is preferable in terms of obtaining high impact resistance and excellent image clarity in the obtained multilayer film and composite film without impairing rigidity when a multilayer film is obtained. .
When the intermediate layer is composed of a laminate of polyolefin resin, the number of layers is preferably 2 to 4 layers, and more preferably 2 to 3 layers. The polyolefin resin in each layer may be the same or different. The thickness of the laminate is preferably within the above range as the thickness of the intermediate layer. The thickness of each layer constituting the laminate is preferably 2 to 40 μm, and more preferably 5 to 25 μm.
<Heat seal layer>
The heat seal layer in the multilayer film of the present invention is made of a polyolefin resin containing a polypropylene resin.
This polypropylene resin preferably contains a polypropylene resin containing 70% by weight or more of the propylene-ethylene copolymer (C). The polymer in the polypropylene resin of this heat seal layer may consist only of the propylene-ethylene copolymer (C), and contains other polymers together with the propylene-ethylene copolymer (C). May be.
The composition of the propylene-ethylene copolymer (C) in the polypropylene resin of the heat seal layer is such that the resulting multilayer film and composite film have blocking resistance, low temperature heat seal property, heat seal part strength and heat seal part resistance. Contributes to improved pinhole properties. When the proportion of the propylene-ethylene copolymer (C) in the polypropylene resin of the heat seal layer is less than 70% by weight, the degree of the above effect is insufficient, which is not preferable. The proportion of the propylene-ethylene copolymer (C) in the polypropylene resin of the heat seal layer is preferably 80% by weight or more, more preferably 90% by weight or more.
The propylene-ethylene copolymer (C) preferably has a molecular weight distribution Mw / Mn represented by a ratio of the weight average molecular weight Mw to the number average molecular weight Mn, preferably 1.5 to 3.5, more preferably 1 8 to 3.2, and more preferably 2.0 to 3.0. If the Mw / Mn of the propylene-ethylene copolymer (C) is less than 1.5, the melt tension becomes too low and the film forming property tends to be inferior. On the other hand, it is preferable that Mw / Mn is 3.5 or less from the viewpoint of securing blocking resistance when a multilayer film is formed and securing optical properties in the multilayer film and the composite film. The propylene-ethylene copolymer (C) preferably has a Mw of 450,000 to 100,000, more preferably 400,000 to 200,000.
The propylene-ethylene copolymer (C) preferably has a melt flow rate MFR measured at 230 ° C. and a load of 2.16 kg in accordance with JIS K 7210, preferably 1 to 30 g / 10 minutes, more preferably 5 ~ 15 g / 10 min. If the MFR is less than 1 g / 10 min, the melt viscosity is too high, so that the pressure in the film forming machine (for example, an extruder) becomes excessively high during the production of the multilayer film, and the productivity is reduced. It may cause poor appearance such as uniformity and melt fracture. On the other hand, if the MFR exceeds 30 g / 10 min, the film thickness of the outer layer becomes non-uniform due to an excessive difference in melt viscosity with the resin of the intermediate layer, and the resistance to resistance when a multilayer film is formed. The blocking property may be impaired.
The propylene-ethylene copolymer (C) preferably has a melting point of 120 to 140 ° C, more preferably 120 to 135 ° C. The propylene-ethylene copolymer (C) having a melting point at a temperature in this range is excellent in balance between heat resistance when producing a multilayer film and transparency when formed into a multilayer film or a composite film. This is preferable.
The content of ethylene units in the propylene-ethylene copolymer (C) is preferably 1 to 10 mol%, more preferably 2 to 5 mol%. By setting the content ratio of the ethylene unit within this range, the resulting multilayer film can exhibit excellent blocking resistance without impairing transparency, which is preferable.
The propylene-ethylene copolymer (C) is preferably polymerized using a metallocene catalyst, and the propylene-ethylene copolymer (C) polymerized using a metallocene catalyst is a multilayer obtained. The film is preferable in that it exhibits a high degree of blocking resistance and exhibits excellent optical properties when formed into a multilayer film and a composite film.
The metallocene catalyst is a catalyst comprising a metallocene-type transition metal compound having at least one, preferably two, substituted or unsubstituted cyclopentadienyl ligands and a co-catalyst. Examples of the cocatalyst include organoaluminum compounds; complexes of organoboron compounds and cations; ion-exchange silicates and the like, and one or more selected from these can be used. . The metallocene catalyst may be supported on a suitable inorganic substance. Metallocene catalysts are already known in the art, and those skilled in the art can appropriately select and use an appropriate metallocene catalyst according to the purpose.
[Other polymers]
As said other polymer, as long as the effect of this invention is not inhibited, it can select and use without a restriction | limiting especially. However, when considering the improvement of the tear-opening property of the packaging material, which is one of the main features of the present invention, as the other polymer, a polypropylene resin other than the propylene-ethylene copolymer (C) ( A1) is preferably used. In the polypropylene resin (A1), the molecular weight distribution Mw / Mn represented by the ratio of the weight average molecular weight Mw and the number average molecular weight Mn is preferably 4 or more, more preferably 4.5 to 10, and still more preferably. Is 5-8. When the Mw / Mn of the polypropylene resin (A1) is smaller than 4, the tear strength of the resulting multilayer film and the composite film produced using the multilayer film is excessively high, and there is an effect of improving the tear openability in the packaging material. It will be difficult to express. This is considered to be due to the fact that when Mw / Mn is less than 4, melt orientation hardly occurs during the production of the multilayer film. On the other hand, it is preferable that Mw / Mn be 10 or less from the viewpoint of securing the melt resistance during the production of the multilayer film within an appropriate range and ensuring the blocking resistance when the multilayer film is formed. The polypropylene resin (A1) preferably has a Mw of 450,000 to 100,000, more preferably 400,000 to 200,000.
The weight average molecular weight Mw and the number average molecular weight Mn are both values in terms of polystyrene measured by gel permeation chromatography (GPC).
The polypropylene resin (A1) preferably has a melt flow rate MFR measured at 230 ° C. under a load of 2.16 kg in accordance with JIS K 7210 at 1 to 30 g / 10 minutes, and 5 to 15 g / 10 minutes. It is more preferable. If the MFR is less than 1 g / 10 min, the melt viscosity is too high, so that the pressure in the film forming machine (for example, an extruder) becomes excessively high during the production of the multilayer film, resulting in a decrease in productivity and a decrease in film thickness. It may cause poor appearance such as uniformity and melt fracture. On the other hand, if the MFR exceeds 30 g / 10 min, the film thickness of the outer layer becomes non-uniform due to an excessive difference in melt viscosity with the resin of the intermediate layer, and the resistance to resistance when a multilayer film is formed. The blocking property may be impaired.
The polypropylene resin (A1) preferably has a melting point of 120 to 150 ° C, more preferably 130 to 145 ° C. The polypropylene resin (A1) exhibiting a melting point at a temperature within this range is preferable in that the balance between the heat resistance when producing the multilayer film and the transparency when formed into the multilayer film and the composite film is excellent. . Here, the melting point of the resin means the peak top temperature (Tm) of the maximum endothermic peak in the differential scanning calorimeter (DSC) chart.
The polypropylene resin (A1) may be a propylene homopolymer or a copolymer of propylene and a copolymer component. As the copolymerization component used here, ethylene and α-olefin are preferable. Specifically, for example, ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 4-methyl-1-pentene and the like can be mentioned, and one or more selected from these can be used. The proportion of the copolymer component in the polypropylene resin (A1) is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 3 mol% or less.
It is preferable that a heat seal layer consists only of the said propylene-ethylene copolymer (C), or consists only of a propylene-ethylene copolymer (C) and a polypropylene resin (A1).
[Optional ingredients]
The heat seal layer of the multilayer film of the present invention may contain additives as described as optional components of the laminate layer in the same manner.
[Thickness of heat seal layer]
The thickness of the heat seal layer in the multilayer film of the present invention is preferably 2 to 30 μm, more preferably 2.5 to 25 μm. By setting the heat seal layer to a thickness in this range, the resulting multilayer film and composite film are preferable in that high impact resistance can be obtained without impairing low-temperature heat sealability and pinhole resistance.
<Thickness of polyolefin-based unstretched multilayer film>
The thickness of the polyolefin-based unstretched multilayer film of the present invention can be appropriately set depending on the use mode and application. Here, the use mode is a selection of whether to use the multilayer film of the present invention as it is as a packaging material, or to use it as a composite film by laminating with a film substrate,
The use refers to the type and weight of the contents of the packaging material.
The thickness of the polyolefin-based unstretched multilayer film of the present invention can be, for example, 10 to 200 μm, preferably 15 to 150 μm, and more preferably 18 to 100 μm.
<Method for producing polyolefin-based unstretched multilayer film>
The multilayer film of the present invention can be produced by any method as long as the method does not substantially involve stretching. “Substantially no stretching” does not mean that even a slight orientation occurs in the film manufacturing process, but means that the film does not go through an explicit stretching process. Therefore, for example, it should be understood that a slight orientation in the extrusion direction is allowed when an extrusion process under the conditions normally employed is employed.
As a method for producing the multilayer film of the present invention, an appropriate method such as an extrusion method or a casting method can be employed. The resin constituting each layer of the multilayer film of the present invention has an appropriate MFR, and is highly compatible with a melt-type film forming machine. It is preferable because it can be expressed to the limit. As the die for the extrusion method, a T die, an annular die, or the like can be used. However, from the viewpoint of precisely controlling the thickness of the layer to obtain excellent optical characteristics, it is not preferable to use an annular die, and it is preferable to use a T die or the like.
Since the multilayer film of the present invention has a laminate layer, at least one intermediate layer, and a heat seal layer, it has a multilayer structure composed of at least three layers. As a method for multilayering the film, a known method such as a co-extrusion method or an in-line laminating method can be employed. Examples of the coextrusion method include a multi-manifold method and a feed block method. Of these, the coextrusion method is preferably used because the thickness of each layer can be uniformly controlled in the width direction.
The multilayer film of the present invention is expected to be applied as a packaging material as it is or in the form of a composite film obtained by laminating it with a film substrate. Therefore, in the former case, printing may be performed on the outermost layer surface in order to clearly indicate the origin of the product or to develop a design effect,
In the latter case, the film base material is affixed on the outermost layer surface, usually on the surface of the laminate layer. In such a case, for the purpose of improving the affinity or adhesion with the ink or the adhesive, a surface treatment may be performed inline or offline on the outermost layer surface, usually on the surface of the laminate layer. Examples of the surface treatment include corona discharge treatment, flame or flame treatment.
<Composite film>
The composite film of the present invention is obtained by sticking the multilayer film as described above on a film substrate with the laminate layer side of the multilayer film as the sticking surface. The composite film of the present invention is excellent in low temperature heat sealability, heat seal strength, and pinhole resistance of the heat seal portion, and is also excellent in tear openability when used as a packaging material.
[Film substrate]
As a material which comprises the film base material in the composite film of this invention, it can determine suitably according to the use of a packaging material. Examples thereof include a resin selected from the group consisting of a polypropylene resin, a polyethylene resin, a polyethylene terephthalate resin, and a polyamide resin, or a metal. The film substrate can be a layer containing one or more materials selected from these, or can be a laminate comprising a plurality of such layers.
The thickness of the film substrate is arbitrary depending on the use of the packaging material, but can be, for example, 5 to 75 μm, and preferably 10 to 50 μm.
[Thickness of composite film]
The total thickness of the composite film of the present invention can be arbitrarily set according to the use of the packaging material, but can be, for example, 15 to 250 μm, preferably 20 to 200 μm, more preferably 23 to 150 μm. It is.
<Production method of composite film>
The manufacturing method of a composite film will not be specifically limited if it is a method which can affix the multilayer film of this invention on the film base material by using the lamination layer side as a sticking surface.
Adhesion between the film substrate and the laminate layer of the multilayer film may be performed by an appropriate adhesive or thermocompression bonding. As the adhesive used here, a commercially available adhesive may be used, or a molten resin such as a molten polyethylene resin may be used. Examples of the method for applying the adhesive include transfer means such as gravure, gravure reverse, and offset; scraping means such as a bar and a comma bar.
Examples of the method of laminating the film base material and the multilayer film with an adhesive layer as required include a dry lamination method and a thermal lamination method.

Hereinafter, the present invention will be described with reference to examples and comparative examples, but the present invention is not limited to these examples.
Each evaluation in the following examples and comparative examples was performed according to the following procedure.
<Evaluation of multilayer film>
(1) Haze As a transparency index, a haze meter (model number: NDH5000) manufactured by Nippon Denshoku Industries Co., Ltd. was used, and haze was measured based on JIS K7136.
(2) Gloss Gloss was measured according to JIS K 7105 using a gloss meter (model number: UGV-5D) manufactured by Suga Test Instruments Co., Ltd. as an index of gloss. The evaluation of the gloss was performed on both the laminate layer side surface and the heat seal layer side surface of the multilayer film.
(3) Image clarity As an index of image clarity, Suga Test Instruments Co., Ltd., image clarity measuring instrument (model number: ICM-1DP) was used, and the slit width of the optical comb was 0.125 mm in accordance with JIS K 7105. As a result, the image clarity was measured.
(4) Blocking strength As an index of blocking resistance, blocking strength was examined by the following tensile test.
10 layers of multilayer films cut into 120 mm × 120 mm squares are stacked so that the laminating layer and the heat seal layer are in contact with each other between adjacent films, and a temperature of 10 kg is applied to the entire top surface of the multilayer film. It was stored for 3 days or 72 hours in a constant temperature and humidity machine at 40 ° C. and a humidity of 70% RH. Of the multilayer film after storage, 2 sheets of the upper layer and 2 sheets of the lower layer were removed to take 6 sheets in the middle, and 2 adjacent sheets were peeled off as a pair to obtain 3 pairs. In each pair, two multilayer films are pressure-bonded under the above conditions with the laminate layer and the heat seal layer in contact. Each pair was cut into a 30 mm × 120 mm rectangle to obtain three test pieces. The test piece was peeled off from one end of the short side of the test piece so that the pressure-bonded portion remained with a length of 40 mm. The pressure-bonded portion 30 mm × 40 mm remaining on each test piece is a blocking resistance measurement region.
Then, using an autograph (model number: AG-500D) manufactured by Shimadzu Corporation, the layer of the peeled portion of the test piece was sandwiched between two chucks, respectively, and the measurement temperature was 23 ° C. atmosphere and the tensile speed was 50 mm / min. A tensile test was performed under the conditions, and the maximum value of stress until the specimen was completely peeled was examined. The average value (kPa) of the maximum value was taken with n being 3, and this was taken as the blocking strength.
(5) Impact strength As an index of impact resistance, a film impact tester manufactured by Toyo Seiki Co., Ltd. was used, and impact strength was measured under the following conditions.
Test piece dimensions: 120 mm x 120 mm
Measurement temperature: 23 ° C. atmosphere and 0 ° C. atmosphere (6) Tear strength (trouser tear method)
As an index of tear resistance, tear strength was measured under the following conditions using an autograph (model number: AG-500D) manufactured by Shimadzu Corporation in accordance with JIS K 7128-1.
Test piece dimensions: Long side (vertical) 100 mm, short side (horizontal) 50 mm
Slit: 20 mm long notch provided parallel to the long side at the center of one short side of the test piece (position 25 mm from the long side) Tensile speed: 500 mm / min Measuring temperature: 23 ° C. atmosphere <composite film Evaluation>
(7) Heat seal strength As an index of heat sealability, the heat seal layers of two composite films were brought into contact with each other, and the strength when heat sealed at each temperature was examined by the following tensile test.
The composite film is cut into a 15 mm × 200 mm rectangle, and the two sheets are stacked together so that the heat seal layers are in contact with each other, and heated under the following conditions using a YSS heat sealer manufactured by Yasuda Seiki Seisakusho Co., Ltd. A test piece was obtained by sealing.
Seal bar width: 5mm
Seal pressure: 0.1 MPa
Sealing time: 1.0 second Sealing temperature: Variable to 150 ° C., 160 ° C. and 170 ° C. The area of 5 mm × 15 mm, which is the heat seal part of the test piece obtained above, becomes the measurement area of each heat seal strength. . Here, the case where the long side of the rectangle coincides with the extrusion direction of the film is referred to as a “longitudinal” direction test piece, and the case where the long side of the rectangle is orthogonal to the film extrusion direction is referred to as a “lateral” direction test piece. Test pieces of 2 types × 3 temperatures = 6 types for each type of composite film were prepared.
Using an autograph (model number: AG-500D) manufactured by Shimadzu Corporation, open the unsealed part of the test piece after heat sealing at each temperature, and sandwich it between the two chucks, respectively. A tensile test was performed under the condition of minutes, and the maximum value of the stress was examined.
If the maximum value of the stress is 3 N / 15 mm or more, it can be evaluated that sufficient heat seal strength is obtained at the temperature;
If it is 13 N / 15 mm or less, it can be evaluated that it has easy peel properties.
(8) Easy peel (sensory test)
In order to examine the easy peel property, a sensory test was conducted in which the package was opened by human hands.
Using a vertical pillow packaging machine (model “TWX1N”, manufactured by Tokyo Automatic Machinery Co., Ltd.), the heat seal layers of the composite film are heat-sealed under the following conditions to obtain a 120 mm long and 100 mm wide package. It was.
Heat seal temperature 120 ℃
Heat sealing time 0.6 seconds Heat sealing pressure 0.5 MPa
In the portion of the package obtained above 30 mm away from the upper part of the heat-sealed bag mouth, each of the facing composite film surfaces without being heat-sealed is held by the fingertips of the right hand and the left hand, respectively. Opened.
The feel (peeling feeling) at this time was evaluated according to the following criteria and used as an easy peel property index.
A: When easily and smoothly peeled off (very good)
B: When there was slight resistance but it was easily peeled off (good)
C: When the resistance was slightly high but could be peeled off (possible)
D: When it cannot peel or when parts other than a heat seal part are destroyed (defect)
(9) Tear-openability The tear-openability after heat-sealing the heat-seal layers of two composite films was examined.
The composite film is cut into a rectangle of 150 mm × 100 mm, and the two sheets are superposed so that the heat seal layers are in contact with each other. Using a YSS heat sealer manufactured by Yasuda Seiki Seisakusho, 4 The sides were heat-sealed to obtain a pseudo bag-making body. The four sides of the pseudo bag-making body are heat-sealed to the ends.
Heat sealing temperature: 160 ° C
Seal pressure: 0.1 MPa
Heat sealing time: 1.0 seconds Seal width: 5 mm
A cut of 10 mm is made in the vertical direction from the end portion using a cutter in a piece of the heat seal portion of the obtained pseudo bag-making body, and the cut portion is formed in the lateral direction (parallel to the surface of the pseudo-bag-making body and the cut). Tearing by hand in the direction perpendicular to the direction), the force required for the tearing and the state of the tearing portion were examined, judged according to the following criteria, and evaluated by the following calculation formula.
Lightly cut straight from the cut line, no film stretch or fuzz: A (very good)
I feel a little heavy when tearing, but cut straight: B (good)
It feels very heavy when tearing, and the cut film is stretched and fluffy: C (defect)
The film extends from the cut and does not break: D (very poor)
The test was performed by three testers with 10 test pieces each, and the percentage of the total 30 test pieces that was “A” judgment was expressed as a percentage by the following formula (1) and evaluated. .
“A” judgment ratio (%) = (number of “A” judgments ÷ 30) × 100 (1)
(10) Pinhole resistance The flaw detection test of the heat seal part was done as a parameter | index of the pinhole resistance of a heat seal part.
The composite film was cut into a rectangle of 150 mm × 100 mm and folded back into two at the center of the short side so that the heat seal layer was inside. One side of the short side part is left as an opening, and the remaining two sides (one side part and the long side of the short side) are manufactured by Yasuda Seiki Seisakusho Co., Ltd., using a YSS heat sealer. Heat sealed under conditions to obtain an envelope-like pseudo bag-making body.
Heat sealing temperature: 160 ° C
Seal pressure: 0.1 MPa
Heat sealing time: 1.0 seconds Seal width 5mm
From the opening of this pseudo bag-making body, Taseto Co., Ltd., dyeing penetrant flaw detection agent, “permeating liquid FP-S standard type” is sprayed, and the liquid leakage state from the seal part is visually observed. Evaluated by criteria.
No liquid leakage from the heat seal part: ○ (Good pinhole resistance)
Liquid leakage from heat seal part: × (Poor pinhole resistance)
Example 1
<Manufacture of multilayer film>
Three types consisting of a total of three extruders: one single-screw extruder with a screw diameter of 75 mm for the intermediate layer and two single-screw extruders with a screw diameter of 50 mm for both outer layers (laminate layer and heat seal layer) Resin was supplied to each extruder as follows using a three-layer T-die film-forming apparatus.
Extruder for intermediate layer; b-LLDPE-1 (manufactured by Sumitomo Chemical Co., Ltd., product number: CU7004, melting point = 108 ° C., MFR = 3.0 g / 10 min (190 ° C.), Mw / Mn = 11.9, density = 0.924 g / cm ³ , amorphous component = 2.5 wt%, long chain branch content = 4.12 pieces / 1,000 C) 100 parts by weight Laminate layer extruder; PP-1 (Nippon Polypro ( Co., Ltd., product number: WFX4TA, melting point = 126 ° C., MFR = 7.0 g / 10 min (230 ° C., Mw / Mn = 3.0) 70 parts by weight and PP-2 (manufactured by Nippon Polypro Co., Ltd., product number) : FW3GT, melting point = 148 ° C., MFR = 7.0 g / 10 min (230 ° C.), Mw / Mn = 5.3) 30 parts by weight of mixture Heat-seal layer extruder; PP-1 (Nippon Polypro Co., Ltd.) Product number: WFX4TA, melting point = 126 ° C., MFR = 7.0 g / 10 min (230 ° C), Mw / Mn = 3.0) 100 parts by weight Each of the three extruders was subjected to a resin temperature of 220 ° C, a residence time of 1 minute, and a T-die temperature of 230 ° C. Extruded from a T-die, the three layers were combined to obtain a multilayer film through a 25 ° C. cooling roll. This multilayer film had a three-layer configuration, a total thickness of 30 μm, and a three-layer thickness configuration of approximately 1: 2: 1.
Next, a corona discharge treatment was applied so that the wet tension of the surface on the laminate layer side of this multilayer film was 42 mN / m, and further aging at 40 ° C. for 24 hours to obtain a polyolefin-based unstretched multilayer film.
Using the polyolefin-based unstretched multilayer film, the evaluations (1) to (6) were performed. The evaluation results are shown in Table 5.
<Manufacture of composite film>
The laminate layer surface of the above polyolefin-based unstretched multilayer film was attached to a biaxially stretched polypropylene film to produce a composite film.
Adhesive for dry lamination (manufactured by Toyo Morton Co., Ltd.) on the corona-treated surface of a biaxially stretched polypropylene film (product number: Santox-OP PA20, thickness: 20 μm, single-sided corona-treated product) manufactured by Sun Tox Co., Ltd. The main agent (product number: TM-595) 15 g, a curing agent (product number: CAT-56) 2.7 g and a solution obtained by mixing 36.8 g of ethyl acetate were applied with an applicator (2 mil setting), 80 Dry at 1 ° C. for 1 minute. Next, a laminate film of the polyolefin-based unstretched multilayer film obtained above was laminated on this adhesive layer while pressing with a hand roller, and then aged at 40 ° C. for 3 days to obtain a composite film. . The unit “mil” means 0.001 inch, and 1 mil corresponds to about 25.3999 μm.
Using the composite film obtained above, the above (7) to (10) were evaluated. The evaluation results are shown in Table 5.
Examples 2 to 10 and Comparative Examples 1 to 4
In Example 1 above, the polyolefin-based unstretched multilayer was prepared in the same manner as in Example 1 except that the type and amount of resin supplied to the extruder for each layer were as shown in Table 3 and Table 4, respectively. Films and composite films were produced and evaluated respectively.
The evaluation results are shown in Tables 5 and 6.

In addition, the abbreviation of the resin raw material in Table 3 and Table 4 has the following meaning, respectively.
b-LLDPE-1: manufactured by Sumitomo Chemical Co., Ltd., product number “CU7004”
b-LLDPE-2: manufactured by Sumitomo Chemical Co., Ltd., product number “GT140”
b-LLDPE-3: manufactured by Sumitomo Chemical Co., Ltd., product number “GH051”
LLDPE-1: Ube Maruzen Polyethylene Co., Ltd., product number “1540F”
LLDPE-2: Ube Maruzen Polyethylene Co., Ltd., product number “2040FC”
LLDPE-3: manufactured by Dow Chemical Japan Co., Ltd., product number “KC8852G”
LDPE-1: manufactured by Sumitomo Chemical Co., Ltd., product number “L405”
PP-1: manufactured by Nippon Polypro Co., Ltd., product number “WFX4TA”
PP-2: manufactured by Nippon Polypro Co., Ltd., product number “FW3GT”
The parameters of the resin raw material are shown in Table 7 below.
The numerical value in the MFR column of Table 7 is the melt flow rate measured at a load of 2.16 kg in accordance with JIS K 7210. The measurement temperature was 190 ° C. for the polyethylene resin and 230 ° C. for the polypropylene resin.
The melting point is the peak temperature of the melting point measured by a differential scanning calorimeter (DSC).
The content of the long chain branch shown in the “long chain branch” column is the number of carbon atoms per 1,000 carbon atoms, calculated according to the following formula (2) from the result of ¹³ C-NMR measured under the following conditions: The number of branches of 8 or more.
[ ^13C -NMR measurement conditions]
Measuring device: Model “JNM-ECS400” manufactured by JEOL Ltd.
Solvent: Mixed solvent of trichlorobenzene / heavy benzene (75/25% by volume)
Sample concentration: 80 mg / 2.5 mL solution Measurement mode: 1H-complete decoupling Measurement temperature: 120 ° C.
Pulse width: 90 degree pulse Pulse repetition time: 9 seconds Integration number: 9,000 times Long chain branch content (pieces / 1000C) = A ÷ B × 1,000 (2)
(In Formula (2), A is the peak area of chemical shift δ = 22.87 ppm, and B is the peak area of chemical shift δ = 30 ppm.)
In the temperature rising elution fractionation method under the following conditions, the amorphous component content is measured during the period in which the column supply after the sample supply is cooled to 0 ° C. and then the supply of the solvent is started and the column temperature is maintained at 0 ° C. This is the weight ratio of the fraction eluted in the total fraction.
Measuring equipment: Model number "TREF equipment special type", manufactured by Senshu Kagaku Co., Ltd.
Column: Internal diameter 10mm x 300mm
Filler: Chromosolv P NAW (manufactured by GL Sciences, 30/60 mesh)
Sample solution concentration: 5 mg / mL
Sample solution injection volume: 2 mL
Solvent: Orthodichlorobenzene Flow rate: 1 mL / min
Sample injection temperature: 140 ° C
Temperature drop rate: 5 ° C / h
Cooling arrival temperature: 0 ° C
Maintenance time at cooling temperature: 30 minutes Temperature increase rate: 5 ° C / h
Detector: Infrared detector Measurement wave number: 3.42 μm

[Effects of the Invention] According to the present invention, there is no polyolefin-based resin that is excellent in various properties such as optical properties, anti-blocking properties, low-temperature heat sealability, heat seal strength, and sealability, as well as tear-opening properties and easy peel properties of packaging. A stretched multilayer film is provided.
The package formed from the multilayer film of the present invention can be particularly suitably used for food packaging applications, for example.

Claims

A polyolefin-based unstretched multilayer film having a laminate layer as an outermost layer, at least one intermediate layer, and a heat seal layer as another outermost layer,
The laminate layer is made of a polyolefin resin,
At least one of the intermediate layers is made of a polyolefin resin containing long-chain branched LLDPE,
The heat seal layer is made of a polyolefin resin containing a polypropylene resin,
The polyolefin resin of the laminate layer has a higher melting point than the polypropylene resin in the heat seal layer,
The long-chain branched LLDPE in the polyolefin-based resin in the intermediate layer is
The ratio Mw / Mn of polystyrene-equivalent weight average molecular weight Mw and number average molecular weight Mn measured by gel permeation chromatography is 7.5 to 15.0,
The amount of non-crystalline components measured by the temperature rising elution fractionation method is 1 to 4% by weight, and the number of branches having 8 or more carbon atoms measured by 13 C-NMR is 1.5 per 1,000 carbon atoms. The multilayer film as described above, wherein the number is ~ 5.0.
The long chain branched LLDPE in the polyolefin resin in the intermediate layer is
The density is 0.90 to 0.94 g / cm 3 ,
The multilayer film according to claim 1, wherein the melt flow rate MFR measured at 190 ° C and a load of 2.16 kg in accordance with JIS K 7210 is 0.1 to 20 g / 10 min.
The polyolefin resin in the intermediate layer is
40% by weight or more of the long chain branched LLDPE,
3. The multilayer film according to claim 1, comprising 30% by weight or less of polypropylene resin and 50% by weight or less of LLDPE (excluding the long-chain branched LLDPE).
The polypropylene resin in the heat seal layer has a molecular weight distribution Mw / Mn of 1.5 to 3.5, and a melt flow rate MFR measured at 230 ° C. and a load of 2.16 kg according to JIS K 7210 is 1. The multilayer according to claim 1 or 2, which has a melting point of 120 to 140 ° C and 70% by weight or more of a propylene-ethylene copolymer polymerized using a metallocene catalyst. the film.
A composite film comprising a laminate of the multilayer film according to any one of claims 1 to 4 stuck on a film substrate.
A package comprising the composite film according to claim 5.