JP2005313562A - Easily tearable biaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easily tearable biaxially oriented polyester film which has easy cutting properties and adhesive properties and further, outstanding characteristics of a polyester film such as heat resistance, moistureproofness, transparency and aroma retention. <P>SOLUTION: In the polyester laminated film formed of at least two layers such as a layer substantially without molecular orientation and a layer substantially with molecular orientation, the index of refraction Nz, in the thickness direction, of the polyester laminated film is not lower than 1.480 and the piercing strength of the film is not more than 8.0 N. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an easily tearable biaxially stretched polyester film. More specifically, packaging that maintains the practical characteristics without losing the excellent properties of the stretched polyester film, such as heat resistance, fragrance retention, water resistance, etc. It is related with the easily tearable biaxially-stretched polyester-type film useful as a film for a film.

  Conventionally, cellophane is known as a film having excellent cutting properties. Cellophane is widely used for various packaging materials and adhesive tapes due to its excellent transparency, easy cutting property, twisting property and the like. However, on the other hand, cellophane has a hygroscopic property, and its characteristics fluctuate depending on the season, and it has been difficult to always supply a product of a certain quality. In addition, packaging bags and adhesive tapes using polyethylene terephthalate as the base film are used because of the excellent properties such as toughness, heat resistance, water resistance, and transparency of the stretched polyethylene terephthalate film. Although it has these excellent characteristics, it has disadvantages that it cannot be used for packaging because it is difficult to cut, it is difficult to tear the opening of the packaging bag, and the adhesive tape is difficult to cut. .

As a method for solving the above problems, a uniaxially oriented polyester film laminated with paper, a biaxially oriented polyester film obtained by copolymerizing a large amount of diethylene glycol components, and a low molecular weight polyester resin are mixed and used. Biaxially oriented polyester film, and at least one side of the polyester resin layer (A) has a terephthalic acid crystalline polyester resin (a), a crystalline segment having a melting point of 170 ° C. or higher, and a melting point or softening point of 100 ° C. or lower, molecular weight A laminate in which a polyester resin mixture layer (B) having a melting point of 10 ° C. or more higher than the melting point of the polyester resin layer (A) is laminated, comprising a mixture of block copolymerized polyesters (b) having a soft polymer of 400 to 8000 Polyester films have been proposed (see Patent Documents 1 to 4).
Japanese Patent Publication No.55-8551 Japanese Patent Publication No. 56-50692 Japanese Patent Publication No.55-20514 JP 2002-337290 A

  However, the plastic film obtained by molecular orientation in the uniaxial direction in the above prior art can be easily cut linearly in the alignment direction but difficult to cut in other directions, and a large amount of diethylene glycol component is copolymerized. The obtained polyester film has a disadvantage that the original properties of polyethylene terephthalate are lost by copolymerization. In addition, a polyester film obtained by mixing and using a low molecular weight polyester resin is not practical because troubles of film breakage in the stretching process are likely to occur.

  Furthermore, the polyester film obtained by using a mixture of a terephthalic acid-based crystalline polyester resin and a block copolymerized polyester as a resin constituting the surface layer has a dispersed structure in which the block copolymerized polyester is a crystalline polyester-based resin. In other words, because it has a dispersive sea-island structure, it is easy to tear, but easily peels off at the interface between the crystalline polyester resin and the block copolymer polyester. The cohesive strength of the film was inferior, cohesive failure occurred in the layer, and the laminate strength might deteriorate.

  In view of the above-mentioned conventional problems, the present invention has easy cutting properties and adhesiveness, and further has heat resistance, moisture resistance, transparency, fragrance retaining properties, etc., which are excellent properties of a polyester film. An object is to provide an easily tearable biaxially stretched polyester film.

  In order to achieve the above object, the easily tearable biaxially stretched polyester film of the present invention is a polyester-based laminated film composed of at least two layers of a layer having substantially no molecular orientation and a layer having molecular orientation, The polyester laminated film has a refractive index Nz in the thickness direction of 1.480 or more and a puncture strength of 8.0 N or less.

  Here, the refractive index is measured by an Abbe refractometer.

  In this case, the melting point of the polyester resin constituting the layer having molecular orientation can be higher than the melting point of the polyester resin constituting the layer having substantially no molecular orientation.

  Further, it is desirable that the layer having molecular orientation does not have a resin dispersion structure.

  Moreover, an adhesive layer can be laminated | stacked on the surface side of the layer which has the molecular orientation of a polyester-type laminated | multilayer film.

  According to the easily tearable biaxially stretched polyester film of the present invention, while having the original characteristics of a polyester film such as heat resistance, cold resistance, moisture resistance, transparency, and fragrance retention, It is a laminated film with excellent adhesiveness, and by improving the adhesiveness, it prevents the opening of the package from deteriorating due to peeling of the laminate part at the time of opening, and exhibits good opening properties. it can.

  Hereinafter, the present invention will be described in detail. The easily tearable biaxially stretched polyester film of the present invention is a polyester-based laminated film composed of a layer having molecular orientation and a layer having substantially no molecular orientation.

  Examples of the polyester-based resin constituting the layer having molecular orientation include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, or a copolymer mainly composed of these components. Such a polyester-based resin is preferably a polyester having terephthalic acid as the main acid component and ethylene glycol as the main alcohol component, more preferably a polyester comprising terephthalic acid of 95 mol% or more and ethylene glycol of 95 mol% or more. Resin.

  Here, the layer having the molecular orientation of the laminated film in the present invention is confirmed by the refractive index Nz in the thickness direction of the laminated film measured using an Abbe refractometer being 1.480 or more. For the following reason. That is, in the heat setting zone after biaxial stretching of the laminated film, the resin layer constituting the layer having molecular orientation proceeds with crystallization, and the refractive index in the longitudinal direction, the transverse direction and the thickness direction, that is, all directions. In contrast, the resin layer constituting the layer having substantially no molecular orientation is in a molten state in the heat setting zone, so that the orientation in the vertical and horizontal directions is generally It disappears and takes a behavior that the orientation in the thickness direction increases remarkably, so that only the orientation in the thickness direction is larger than the orientation of the layer having molecular orientation. As a result, the refractive index in the thickness direction is higher than that of the layer having molecular orientation. The value is shown. The Abbe refractometer has a characteristic of showing refraction of a layer having the lowest refractive index in the measurement direction when layers having different refractive indexes are laminated.

  Polyester resins constituting layers having substantially no molecular orientation include terephthalic acid-isophthalic acid-ethylene glycol copolymer, terephthalic acid-isophthalic acid-butylene glycol copolymer, terephthalic acid-ethylene glycol-neopentyl glycol. Polyesters containing terephthalic acid and glycols as main components, such as copolymers, and other acid components and / or other glycol components as copolymerization components are preferred, and their melting points are polyester systems that constitute layers having molecular orientation. It is preferable that the melting point is lower than the melting point of the resin, particularly 20 ° C. or more. Here, as other acid components, aliphatic dibasic acids (for example, adipic acid, sebacic acid, azelaic acid) and aromatic dibasic acids (for example, isophthalic acid, diphenyldicarboxylic acid, 5-tert-butyl) Isophthalic acid, 2,2,6,6-tetramethylbiphenyl-4,4-dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,1,3-trimethyl-3-phenylindene-4,5-dicarboxylic acid) Is used. Examples of the glycol component include aliphatic diols (for example, neopentyl glycol, diethylene glycol, trimethylene glycol, propylene glycol, butanediol, hexanediol, etc.), alicyclic diols (for example, 1,4-cyclohexanedimethanol, etc.). Alternatively, aromatic diols (for example, xylylene glycol, bis (4-β-hydroxyphenyl) sulfone, 2,2- (4-hydroxyphenyl) propane derivative) and the like are used.

  In addition, it is preferable to blend an elastomer component with the polyester-based resin in order to maintain flexibility during processing such as printing and laminating in a layer having substantially no molecular orientation. As the elastomer component, the secondary transition point is lower than that of a polyester resin used for a layer having substantially no molecular orientation, and any thermoplastic resin that forms a sea-island structure and disperses with respect to the polyester resin may be used. Specific examples include, but are not limited to, low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene-propylene copolymer, ethylene-propylene-butene copolymer. Polymer, ethylene-acrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, polyamide and polyamide-polyethylene oxide block copolymer, polyamide-polytetramethylene oxide block copolymer, polyamide- Polyethylene oxide block co-weight Other block copolymer polyester resin such polyamide elastomer body and the like.

  The block copolymer polyester is typically a block copolymer polyester composed of a crystalline segment having a melting point of 170 ° C. or higher and a soft polymer having a melting point or softening point of 100 ° C. or lower and a molecular weight of 400 to 8000. As a polymer with only its components, the melting point is 170 ° C. or higher, for example, residues of aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, Polyesters composed of residues of aliphatic, aromatic, and alicyclic diols such as ethylene glycol, propylene glycol, butanediol, pentamethylene glycol, p-xylene glycol, and cyclohexanedimethanol can be used. It is desirable that the acid residue occupies 80 mol% or more.The soft polyester having a molecular weight of 400 to 8000 has a melting point or softening point of 100 ° C. or less when measured only with the segment constituents. Examples of the low melting point soft polymer include polyethylene oxide glycol, polytetramethylene. Polyethers such as oxide glycol, polypropylene oxide glycol, copolymerized glycol of ethylene oxide and tetrahydrofuran, aliphatic polyesters such as polyneopentyl azelate, polyneopentyl adipate, polyneopentyl separate, poly-ε-caprolactone, etc. Polylactones can be indicated. Preferably, polyethylene oxide glycol, polytetramethylene oxide glycol, and the like are practical. Specific examples of the block copolymer polyester include polyethylene terephthalate-polyethylene oxide block copolymer, polyethylene terephthalate-polytetramethylene oxide block copolymer, polybutylene terephthalate-polyethylene oxide block copolymer, polybutylene terephthalate-polytetra. Methylene oxide block copolymer, polyethylene terephthalate-polyethylene oxide / polypropylene oxide block copolymer, polytetramethylene terephthalate / isophthalate-polytetramethylene oxide block copolymer, polyethylene terephthalate-poly-ε-caprolactone block copolymer, Polyethylene terephthalate-polyneopentyl sebacate block copolymer, etc. It can gel.

  Here, the layer having substantially no molecular orientation of the laminated film in the present invention has a longitudinal refractive index Nx and a lateral refractive index Ny of 1.580 or less as measured with an Abbe refractometer. This is confirmed by the following reason. That is, in the heat setting zone after biaxial stretching of the laminated film, the resin layer constituting the layer having molecular orientation proceeds with crystallization, and the refractive index in the longitudinal direction, the transverse direction and the thickness direction, that is, all directions. In contrast, the resin layer constituting the layer having substantially no molecular orientation is in a molten state in the heat setting zone, so that the orientation in the vertical and horizontal directions is generally From this, the measured values of Nx and Ny indicate the values of the layer having substantially no molecular orientation. The Abbe refractometer has a characteristic of showing refraction of a layer having the lowest refractive index in the measurement direction when layers having different refractive indexes are laminated.

  The intrinsic viscosity of the polyester-based resin constituting the polyester-based laminated film of the present invention is preferably 0.55 to 1.3 dL / g, more preferably 0.60 to 0.74 dL / g, and a layer having molecular orientation The layer having substantially no molecular orientation is preferably a layer made of two or more polyester resins selected from resins having intrinsic viscosities within these ranges.

  Furthermore, the layer constitution of the film of the present invention is such that at least one of the outer layers is formed from film forming properties such as fusion and adhesion to a roll in the longitudinal stretching step, and adhesion to a tenter at the time of breaking in the transverse stretching step. Is preferably composed of a layer having molecular orientation, and more preferably, both outer layers are layers having molecular orientation.

  In order for the polyester-based laminated film to exhibit good tearability and to obtain stable productivity, it is necessary to have both a layer having substantially no molecular orientation and a layer having molecular orientation. The degree of molecular orientation of the layer having the molecular orientation of the polyester-based laminated film of the present invention can be confirmed by a known method such as measurement of birefringence or measurement of absorbance in IR analysis. It can be determined by the resistance at the time, the degree of anisotropy, and the strength at the time of piercing a pencil or the like.

  In order to obtain a laminated structure of the polyester-based laminated film of the present invention, a resin having the lowest melting point is obtained by stretching an unstretched laminated film in which two or more types of polyester resins having different melting points are laminated and then heat-treating. A method of leaving the molecular orientation of the layer made of a resin having a high melting point by eliminating the molecular orientation of the layer made of or laminating an unstretched film that becomes a layer showing the lowest melting point on a stretched film that becomes a layer showing the highest melting point It can depend on the method.

  In the polyester-based laminated film of the present invention, the refractive index Nz in the thickness direction of the laminated film is 1.480 or more, more preferably 1.485 to 1.492. When Nz is less than 1.480, when the adhesive layer is laminated on the polyester laminated film using an adhesive, the adhesive force between the adhesive and the polyester laminated film surface of the present invention or the adhesive layer film surface and the film layer The cohesive force in the thickness direction is insufficient, causing peeling and cohesive failure in the layer.

  It is practically preferable to further laminate an adhesive layer using an adhesive on the surface side of the layer having molecular orientation of the polyester-based laminated film of the present invention. Such an adhesive layer is not particularly limited, but is usually an unstretched film, and as a resin constituting such a layer, low density polyethylene (LDPE), polypropylene, ethylene propylene copolymer, linear A low density polyethylene (LLDPE) etc. can be illustrated. In addition, the adhesive layer may be formed on the surface of the polyester-based laminated film by extrusion extrusion after the resin constituting the adhesive layer is extruded, and any method such as laminating the adhesive layer film by the dry lamination method. Can be.

  In the present invention, the refractive index of the film is measured using an Abbe refractometer. The Abbe refractometer has a characteristic that, when layers having different refractive indexes are stacked, the refraction of the layer having the lowest refractive index is shown in the measurement direction.

  Therefore, when the laminate of the layer having substantially no molecular orientation and the layer having molecular orientation of the present invention is measured, the measured values Nx and Ny in the vertical and horizontal directions are the values of the layer having substantially no molecular orientation. Refractive index is shown. The refractive index Nz in the thickness direction indicates the refractive index of the layer having molecular orientation.

  This will be described in relation to the manufacturing process of the present invention. That is, in producing a polyester-based laminated film, all the layers are oriented in the longitudinal direction and the transverse direction in the stretching step, and the orientation in the thickness direction is remarkably reduced.

  Next, in the heat setting zone, the resin layer constituting the layer having molecular orientation is crystallized, and the refractive index in the longitudinal direction, the lateral direction and the thickness direction, that is, all directions is increased and the layer has molecular orientation. It becomes. However, the resin layer constituting the layer having substantially no molecular orientation is in a molten state in the heat setting zone, so that the orientation in the longitudinal direction and the transverse direction generally disappears, and the orientation in the thickness direction increases remarkably. Therefore, only the orientation in the thickness direction is larger than the orientation of the layer having molecular orientation. As a result, the refractive index in the thickness direction indicates the value of the layer having molecular orientation.

  Thus, by measuring using an Abbe refractometer, it has a state in which the molecular orientation of the layer having substantially no molecular orientation that is an index of easy tearing has collapsed and a molecular orientation that is an index of adhesion The crystallinity of the layer can be measured.

  In the polyester-based laminated film of the present invention, the puncture strength of the laminated film is 8.0 N or less, preferably 2.0 to 6.0 N. When the puncture strength exceeds 8.0 N, the strength of the laminated film is increased and it is difficult to tear by hand, which is not preferable. Further, when the piercing strength is less than 2.0 N, the strength of the film is too weak, which is not preferable because it causes breakage in the film winding process and the printing / laminating process.

  In order to set the piercing strength of the polyester-based laminated film of the present invention to 8.0 N or less, the adjustment of the layer thickness ratio of the layer having substantially no molecular orientation and the layer having molecular orientation and the layer having no molecular orientation It can be adjusted by the degree of disappearance of the molecular orientation, the resin composition ratio of the polyester resin in the layer having the molecular orientation, the thickness thereof, and the like.

  For example, in the layer having substantially no molecular orientation and the layer having molecular orientation, the contribution rate to the puncture strength is large in the layer having molecular orientation, so the puncture strength is the orientation of the layer having substantially no molecular orientation. Is determined by the layer thickness of the layer having molecular orientation. At this time, the thickness of the layer having molecular orientation is preferably about 1 to 8 μm. In addition, since Nz of the laminated film is controlled by the layer having molecular orientation, the melting point of the layer having substantially no molecular orientation is set to about -25 ° C. of the layer having molecular orientation, and the melting point of the layer having molecular orientation. Heat treatment is preferably performed at a temperature lower by 20 to 23 ° C.

  Here, for example, as a method of adjusting the easy tearability, there is a method of controlling the degree of collapse of the orientation of the layer having substantially no molecular orientation, but the degree of orientation collapse shows a significant change in the vicinity of the melting point. It is not practical and most of the orientations have collapsed, that is, it is preferable to control Nx and Ny to 1.580 or less and to control by the above method. Further, regarding the lower limit, Nx and Ny do not become lower than the unstretched sheet even when the orientation is completely collapsed, and it is not necessary to manage the lower limit.

In the polyester-based laminated film of the present invention, in order to improve the printability of the layer having molecular orientation, the polyester resin constituting the layer having molecular orientation is incompatible with resins such as polyolefin, polyamide, polybutene terephthalate-poly A small amount of a tetramethylene glycol copolymer or the like can be blended. However, when a sealant film or the like is laminated as an adhesive layer on a layer having a molecular orientation, a layer having a molecular orientation is formed even if the adhesive force between the layer having the molecular orientation and the adhesive that bonds the adhesive layer is strong. Considering that the cohesive force at the interface between the polyester-based resin and the incompatible resin is extremely small, causing cohesive failure inside the layer with molecular orientation, resulting in a film with low laminate strength. There is a need to.
For this reason, the layer having molecular orientation does not have a dispersed structure even when a small amount of incompatible resin such as polyolefin, polyamide, polybutene terephthalate-polytetramethylene glycol copolymer is blended, that is, a sea-island structure in which the layer is dispersed. It is preferable not to have. As a result, peeling is unlikely to occur at the interface between the polyester resin and the incompatible resin, and the cohesive force in the layer is not inferior to the adhesive force between the layers when laminating, and cohesive failure occurs in the layer. Since it does not occur, the laminate strength does not deteriorate.

  Moreover, the thickness of the polyester-based laminated film of the present invention is about 10 to 30 μm when used for a packaging bag which is the main use of the film of the present invention, and has a layer having no molecular orientation and a molecular orientation. The thickness ratio of the layers (the total when both outer layers have molecular orientation) is 95: 5 to 40:60, preferably about 85:15 to 65:35, but is not particularly limited.

  The polyester-based laminated film of the present invention may be blended with various known compounding agents such as lubricants, pigments, antioxidants, antistatic agents and the like as long as the effects of the present invention are not impaired.

  Below, an example of the manufacturing method of the polyester-type laminated | multilayer film of this invention is demonstrated.

  Two kinds of polyester resins with different melting points, dried in vacuum, are supplied to two different extruders, melt extruded at a temperature equal to or higher than the melting point of each polyester resin, passed through a composite adapter, and two layers of three kinds An unstretched laminated film is formed by extruding from the die as (high melting point / low melting point / high melting point) and solidifying by cooling.

  The unstretched laminated film thus obtained was stretched 2 to 4 times in the machine direction at a temperature of the secondary transition point to the secondary transition point + 30 ° C. of the polyester resin on the high melting point side, and immediately 20 to 40 ° C. Cool down.

  Next, the film is stretched 3 to 4.5 times in the transverse direction at a stretching temperature in the longitudinal direction +10 to + 40 ° C.

  The biaxially stretched film thus obtained is at a temperature at which the layer made of the polyester resin on the low melting side melts and lower than the melting point of the layer made of the polyester resin on the high melting point side. Heat treatment is performed according to temperature. More preferably, the melting point of the layer made of the polyester resin on the low melting point side is + 2 ° C. or higher and the melting point of the layer made of the polyester resin on the high melting point side is −10 ° C. or lower. That is, since the degree of orientation collapse shows a remarkable change near the melting point of the melting point, in order to stabilize the characteristics, the melting point of the layer composed of the polyester resin on the low melting point side is preferably + 2 ° C. or higher. In the vicinity of the melting point of the layer made of the polyester-based resin on the side, since the orientation of the high melting point layer is relaxed similarly to the low melting point layer, the film forming property becomes unstable. In this heat treatment, a relaxation treatment may be performed as necessary.

  By selecting such heat treatment conditions, a film having a refractive index Nz in the thickness direction, which is a constituent requirement of the polyester-based laminated film of the present invention, of 1.480 or more can be obtained.

  As described above, the polyester-based laminated film of the present invention has an easily tearable layer in which molecular orientation is almost destroyed by heat treatment in the film-forming process, and maintains the molecular orientation while maintaining the original characteristics of polyester. In addition to the advantage that the desired film properties can be set in a wide range by the balance of the tearing layer, the layer having the molecular orientation has the advantage that the trouble of breaking in the film formation can be prevented.

  Such a polyester-based laminated film of the present invention has a puncture strength of 8.0 N or less, so that it is a film excellent in production / workability and excellent in tearability.

  Next, the present invention will be specifically described with reference to Examples and Comparative Examples. The evaluation of the characteristic values in the present invention was based on the following.

(1) Secondary transition point, melting point Using a DSC-60 differential scanning calorimeter manufactured by Shimadzu Corporation, measurement was performed at a temperature rising rate of 20 ° C / min. The secondary transition point (Tg) was measured as the tangential intersection of displacement, and the melting point (Tm) was measured as the peak temperature of the melting peak.

(2) Refractive index It calculated | required about Nx, Ny, and Nz using the Abbe refractometer in 23 degreeC atmosphere.

(3) Confirmation of dispersion structure A sample of 10 mm in the longitudinal direction and 5 mm in the width direction was cut out, the film was embedded in an epoxy resin, and then trimmed and surfaced using a microtome in the width direction of the film. The exposed epoxy block was placed in RuO ₄ vapor and dyed for 16 hours. An ultrathin section was prepared from this block, placed on a transmission electron microscope observation mesh, and subjected to carbon deposition to obtain an observation sample. The observation was performed using a transmission electron microscope (JEM2010 manufactured by JEOL Ltd.) to confirm whether the layer having molecular orientation in the film had a dispersed structure at 50000 times. Evaluation was based on the following.
Y: Dispersed structure cannot be confirmed
×: having a dispersed structure

(4) Puncture strength A sample having a longitudinal direction of 200 mm and a width direction of 20 mm is cut out. Using a tensile tester (Autograph AGC-1KNG type manufactured by Shimadzu Corporation), the upper end of the measurement jig shown in FIG. 1 (a) is attached to the upper chuck of the tensile tester as shown in FIG. 1 (b). Hold it. On the other hand, the sample is folded in the longitudinal direction to be 100 mm × 20 mm, and the crease part is applied to a steel ball having a diameter of 0.7 mmφ of the center rod of the measuring jig shown in FIG. The opposite end is pierced below the measuring jig and is sandwiched between the lower chuck at a position where the distance from the tip of the rod is 50 mm. Next, the chuck is pulled at a speed of 50 mm / min so that the two folds of the sample sample pierce a steel ball having a diameter of 0.7 mm at the tip of the rod, and the load when the hole is opened by piercing the sample is obtained. It was. The measurement was performed at n = 5, and an average value of three points excluding the highest value and the lowest value was used.

(5) Laminate strength (a) Sample preparation: Using a two-component curable polyester adhesive (TM590 made by Toyo Morton) and the same curing agent (CAT56 made by Toyo Morton), the solid content becomes 3 g / m ^2. After coating, the film was pasted with a sealant at 60 ° C. and measured after curing at 40 ° C. for 48 hours. In addition, LLDPE film 40micrometer (L6102 by Toyobo Co., Ltd.) was used as a sealant.

(B) Measurement: A sample having a longitudinal direction of 200 mm and a width direction of 15 mm was cut out, and peeled at a rate of 200 mm / min using an autograph manufactured by Shimadzu Corporation so as to form a T shape, and the strength at that time was measured. Each sample was measured 5 times and the average was obtained.
It calculated | required by the average of 3 points | pieces remove | excluding the highest value and the lowest value.

(C) Evaluation: The laminate strength was evaluated in the following three stages.
○: 2N / 15mm or more
Δ: More than 1N / 15mm and less than 2N / 15mm
×: Less than 1N / 15mm

(6) Easy tearing The sensory test was used. An aluminum foil (9 μm) was laminated to the laminated film obtained in each example via an adhesive, and LDPE was melt extruded and laminated (15 μm) on the aluminum foil side to obtain a laminate. Subsequently, the bag was made by the heat seal method (longitudinal direction / width direction = 15/10 cm), and the sealability was evaluated by the openability when cut by hand. In addition, when holding the edge part of a bag with both hands, the space | interval of about 3 mm was taken and evaluation was performed with respect to both the longitudinal direction of a film, and the width direction.
○: Can be opened easily without raising nails
Δ: Can be easily opened by raising nails
×: Cannot be easily opened even when nails are raised

Example 1
As an intermediate layer, (1) 97% by weight of a polyester resin composed of terephthalic acid-isophthalic acid-ethylene glycol having a secondary transition point of 72 ° C., a melting point of 228 ° C., and an intrinsic viscosity of 0.64 dL / g, and (2) terephthalic acid A resin composition composed of 3% by weight of a polyester-based elastomer having a secondary transition point of −80 ° C., a melting point of 170 ° C., and an intrinsic viscosity of 0.76 dL / g composed of ethylene glycol-polytetramethylene glycol was used. As the outer layer a and the outer layer b, a polyester resin composed of terephthalic acid-ethylene glycol and having a secondary transition point of 75 ° C., a melting point of 265 ° C., and an intrinsic viscosity of 0.62 dL / g was used.

  Each polyester resin was melted by a separate extruder at a temperature of 285 ° C., the melted polymer was joined by a composite adapter, extruded from a T die, and rapidly cooled by a cooling drum adjusted to 20 ° C. An unstretched laminated film having a three-layer structure of (outer layer a / intermediate layer / outer layer b) was obtained.

  The unstretched laminated film was stretched 3.8 times in the machine direction at 100 ° C. and then 4.2 times in the transverse direction at 110 ° C., and then heat treated at 230 ° C. while relaxing 2.5%. A laminated film having a total thickness of 16.0 μm in which the total thickness of both outer layers was 3.0 μm was obtained. The properties of the obtained film are shown in Table 1.

(Example 2)
Using the same raw materials and method as in Example 1, the total thickness of both outer layers was changed to 6.0 μm to obtain a laminated film having a total thickness of 16.0 μm. The properties of the obtained film are shown in Table 1.

(Comparative Example 1)
By using the same raw materials and method as in Example 1, the total thickness of both outer layers was changed to 12.0 μm to obtain a laminated film having a total thickness of 16.0 μm. The properties of the obtained film are shown in Table 1.

(Comparative Example 2)
As an intermediate layer of Example 1, 97% by weight of a polyester resin composed of terephthalic acid-isophthalic acid-ethylene glycol and having a secondary transition point of 73 ° C., a melting point of 240 ° C., and an intrinsic viscosity of 0.64 dL / g, and terephthalic acid-ethylene Heat treatment at a temperature of 230 ° C. using a resin composition consisting of glycol-polytetramethylene glycol and having a secondary transition point of −80 ° C., a melting point of 170 ° C., and 3% by weight of a polyester elastomer having an intrinsic viscosity of 0.76 dL / g A laminated film having a total thickness of 16.0 μm was obtained in the same manner as in Example 1 except that The properties of the obtained film are shown in Table 1.

(Comparative Example 3)
As an intermediate layer of the film in Example 1, 97% by weight of a polyester resin composed of terephthalic acid-isophthalic acid-ethylene glycol having a secondary transition point of 71 ° C., a melting point of 210 ° C., and an intrinsic viscosity of 0.62 dL / g, and terephthalic acid -A resin composition consisting of ethylene glycol-polytetramethylene glycol and having a secondary transition point of -80 ° C, a melting point of 170 ° C, and an intrinsic viscosity of 0.76 dL / g, 3% by weight of a polyester elastomer, 210 ° C A film having a total thickness of 16.0 μm was obtained in the same manner as in Example 1 except that the heat treatment was performed at the temperature of The properties of the obtained film are shown in Table 1.

(Comparative Example 4)
Polyethylene terephthalate-polytetramethylene glycol comprising polyester resin as both outer layers of Example 1, 100 mol% terephthalic acid as dicarboxylic acid component, 85 mol% butanediol as diol component, and 15 mol% polytetramethylene glycol having a molecular weight of 1000 A film having a total thickness of 16.0 μm was obtained in the same manner as in Example 1 except that 3% by weight of the copolymer was used. The properties of the obtained film are shown in Table 1.

  As described above, the easily tearable biaxially stretched polyester film of the present invention has been described based on a plurality of examples. However, the present invention is not limited to the configuration described in the above examples, and is described in each example. The configurations can be appropriately changed without departing from the gist of the configurations, for example, by appropriately combining the configurations.

  Since the easily tearable biaxially stretched polyester film of the present invention has properties of excellent tearability and adhesiveness, it can be suitably used for packaging film and adhesive tape applications. It can also be used for the opening of PTP packaging and beverage packs.

(A) A puncture strength measuring jig is shown, and (b) a puncture strength measuring method is shown. (A) shows one example of a sectional view of the easily tearable biaxially stretched polyester film of the present invention, and (b) shows another example of a sectional view of the easily tearable biaxially stretched polyester film of the present invention. , (C) shows still another example of a cross-sectional view of the easily tearable biaxially stretched polyester film of the present invention.

Explanation of symbols

1 layer having molecular orientation 2 layer having substantially no molecular orientation 3 adhesive layer

Claims (4)

  A polyester-based laminated film comprising at least two layers of a layer having substantially no molecular orientation and a layer having molecular orientation, wherein the refractive index Nz in the thickness direction of the polyester-based laminated film is 1.480 or more, and the piercing strength is Easily tearable biaxially stretched polyester film characterized by being 8.0 N or less.   The easily tearable biaxially stretched polyester according to claim 1, wherein the melting point of the polyester resin constituting the layer having molecular orientation is higher than the melting point of the polyester resin constituting the layer having substantially no molecular orientation. Film.   The easily tearable biaxially stretched polyester film according to claim 1 or 2, wherein the layer having molecular orientation does not have a dispersed structure.   The easily tearable biaxially stretched polyester film according to claim 1, 2 or 3, wherein an adhesive layer is laminated on the surface side of the layer having molecular orientation.

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