JP4839680B2 - Biaxially stretched polyester film with excellent adhesion - Google Patents

Description

  The present invention relates to a 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, scent retention, water resistance, etc., particularly excellent adhesiveness, and even better tearability The present invention relates to a stretched polyester film useful as an industrial film.

  Conventionally, cellophane has been 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 made of polyethylene terephthalate as a base film are used with the excellent properties of stretched polyethylene terephthalate phthalate film such as toughness, heat resistance, water resistance, and transparency. Although it has these excellent characteristics, it is difficult to cut, it is difficult to tear the mouth of the packaging bag, the adhesive tape is difficult to cut, and the twist fixing property is inferior, so it is used for twist packaging. There were drawbacks such as inability to do so.

As a method for solving the above problem, a polyester film oriented in a uniaxial direction, a copolymerized diethylene glycol component, a polyester resin having a low molecular weight, or a polyester resin layer (A) on at least one side At least uniaxially stretched unstretched laminated film having a melting point higher than the melting point of the resin layer (A) by 10 ° C. or more and laminated with a polyester resin layer (B) having a thickness of 5% to 60% of the total thickness A method for producing a polyester film imparted with tearing and twisting, characterized by heat treatment at a temperature lower than the melting point of the polyester resin layer (A) by 10 ° C. or higher and lower than the melting point of the polyester resin layer (B) Has been proposed (see Patent Documents 1 to 3).
Japanese Patent Publication No.55-8551 Japanese Patent Publication No. 56-50692 Japanese Patent Publication No.55-20514

  However, in the above prior art, the method of aligning in the uniaxial direction is easily cut linearly in the alignment direction but difficult to cut in directions other than the alignment direction. The method of copolymerizing a large amount of diethylene glycol component, etc. is polyethylene by copolymerization. It has the disadvantage that the original properties of terephthalate are lost. In addition, the method using a low molecular weight polyester resin is not practical because it easily causes a problem of film breakage in the stretching process.

Further, as an easily tearable polyester film with improved printability, a crystalline polyester containing 80 mol% or more of terephthalic acid having a thickness of 5% to 60% of the previous thickness on at least one side of the polyester resin layer (A). Resin (a) 98 to 70% by weight, block copolymer polyester (b) 2 to 30% by weight comprising 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 A laminated polyester film in which a polyester resin mixture layer (B) having a melting point 10 ° C. higher than the melting point of the polyester resin layer (A) is laminated is proposed.
JP 2003-337290 A

  However, the method of adding the block copolymer polyester to the crystalline polyester resin has a “sea-island structure” in which the block copolymer polyester is dispersed in the crystalline polyester, and the interface between the crystalline polyester and the block copolymer polyester is the same. Peeling easily occurs, and when laminating is performed, the cohesive force in the layer is inferior to the adhesive force, causing cohesive failure in the layer, and the laminate strength may be deteriorated.

  The present invention has been made against the background of the problems of the prior art, and particularly pays attention to easy cutting and adhesiveness, and has these characteristics, and further has excellent properties of polyester film, such as heat resistance, moisture resistance, and transparency. An object of the present invention is to provide a laminated film having a combination of aroma retention and the like.

As a result of intensive studies to solve the above problems, the present inventors have finally completed the present invention. That is, the present invention provides a biaxially stretched polyester film having at least a three-layer structure, wherein each layer comprises at least one type of crystalline polyester resin and at least one type of amorphous polyester resin. The outer layer is a crystalline polyester resin / amorphous polyester resin = a layer having crystallinity mixed at a ratio of 50/50 to 90/10% by weight, and the intermediate layer is a crystalline polyester resin / amorphous polyester resin = It is an easily tearable biaxially stretched polyester film excellent in adhesiveness, comprising a layer having no crystallinity mixed at a ratio of 5/95 to 30/ 70 % by weight.

  The polyester-based resin film according to the present invention is a laminated film having excellent hand cutting properties and excellent adhesiveness while having the inherent properties of polyester such as heat resistance, cold resistance, moisture resistance, transparency, and fragrance retention. It is. By improving the adhesiveness, it is possible to prevent deterioration of the opening property that the laminate peels off at the time of opening and the sealant layer cannot be cut, and it is possible to obtain a good opening property.

Hereinafter, the present invention will be described in detail.
The biaxially stretched polyester film in the present invention is a biaxially stretched polyester film having at least a three-layer structure, and each layer has at least one or more types of crystalline polyester resin and at least one or more types of non-stretched polyester films. It is made of a crystalline polyester resin, and both outer layers are made of a layer having crystallinity mixed in a ratio of crystalline polyester resin / amorphous polyester resin = 50/50 to 90/10% by weight, and the intermediate layer is crystalline polyester. a laminated film having a resin / amorphous polyester resin = 5/95 - 30/70% by weight structure obtained by stacking no layer mixed crystallinity ratio.

  Examples of the crystalline polyester resin used in the present invention include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, or a copolymer mainly composed of these components.

Preferably, it is a polyester having 90 mol% or more of terephthalic acid as a main acid component and 90 mol% or more of ethylene glycol as a main glycol component, more preferably 95 mol% or more of terephthalic acid, based on the entire crystalline polyester resin. A crystalline polyester resin composed of 95 mol% or more of ethylene glycol is contained in an amount of 90 wt% or more based on the entire crystalline polyester resin used for mixing, more preferably 98 mol% or more of terephthalic acid and 97 mol% or more of ethylene glycol. The crystalline polyester resin comprising 95% by weight or more based on the whole crystalline polyester resin.

  If the content of terephthalic acid and / or ethylene glycol is less than 95 mol%, it becomes difficult to ensure crystallinity and film rigidity, and transesterification reaction during mixing and extrusion with an amorphous resin. This is not preferable because it tends to be a uniform resin.

  In addition, as the amorphous polyester resin, terephthalic acid such as terephthalic acid-isophthalic acid-ethylene glycol copolymer, terephthalic acid-ethylene glycol-neopentyl glycol copolymer, and the like are mainly composed of terephthalic acid and ethylene glycol, and other acid components. Polyesters containing and / or other glycol components as copolymerization components are preferred. Other acid components include aliphatic dibasic acids (for example, adipic acid, sebacic acid, azelaic acid) and aromatic dibasic acids (for example, isophthalic acid, diphenyldicarboxylic acid, 5-tert-butylisophthalic acid, 2,2,6,6-tetramethylbiphenyl-4,4-dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,1,3-trimethyl-3-phenylindene-4,5-dicarboxylic acid) . Glycol components include aliphatic diols (eg neopentyl glycol, diethylene glycol, propylene glycol, butane diol, hexane diol), alicyclic diols (eg 1,4-cyclohexanedimethanol) or aromatic diols (eg Renglycol, bis (4-β-hydroxyphenyl) sulfone, 2,2- (4-hydroxyphenyl) propane derivative) are used.

  In the present invention. Both outer layers are mixed in a ratio of crystalline polyester resin / amorphous polyester resin = 60/40 to 90/10% by weight, preferably 70/30 to 80/20% by weight. When the ratio of the crystalline polyester resin is less than 60% by weight, the crystallinity of both outer layers becomes insufficient, and the strength, rigidity, and heat resistance of the film become insufficient, which is not preferable.

  Alternatively, when the ratio of the crystalline polyester resin exceeds 90% by weight, it is not preferable because hand cutting properties deteriorate and adhesiveness deteriorates.

In the present invention, the intermediate layer is mixed at a ratio of the crystalline polyester resin / amorphous polyester resin = 5/95 to 30/70 wt%.

  When the ratio of the crystalline polyester resin in the intermediate layer is less than 5% by weight, the rigidity of the intermediate layer is remarkably lowered, and the rigidity of the entire film becomes insufficient. On the other hand, if it exceeds 40% by weight, crystallinity may be exhibited after mixing with the amorphous polyester resin, and the excellent easy tearing characteristic of the present invention cannot be obtained.

Also, if the piercing strength is less than 2.0N, the film becomes brittle, so more attention is required during film formation and processing. For example, the film may break due to fluctuations in tension or slippage of the film during slitting or splicing. It is not preferable because it can be a cause.

  In the present invention, the film is preferably heat-treated at a melting point of −30 ° C. or higher and a melting point of −10 ° C. or lower, more preferably a film melting point of −25 ° C. or higher and a melting point of −15 ° C. or lower. The heat treatment is excellent in that the orientation of the intermediate layer disappears and good tearability is obtained, the crystallization of the crystalline polyester contained in both outer layers proceeds, and the orientation of the amorphous polyester disappears. Adhesiveness, tearability, rigidity, and barrier properties can be obtained.

In the present invention, the difference (Nx−Ny) between the refractive index Nx in the longitudinal direction and the refractive index Ny in the width direction of the intermediate layer is −0.002 or more and 0.002 or less. When it is less than −0.002 and exceeds 0.002 , the disappearance of the orientation of the intermediate layer is insufficient, and the hand cutting property is insufficient.

In the present invention, both outer layers are layers having adhesiveness and easy tearing while maintaining the strength and rigidity of the film, and the intermediate layer is a layer having rigidity while having excellent easy tearing. It plays a role of being. When these are not compatible, for example, when an amorphous polyester resin is not added to both outer layers, the difference between the refractive index in the longitudinal direction and the lateral refractive index of the intermediate layer is −0.002 or more and 0, for example. Even if it is 0.002 or less, the hand cutting property is inferior.

  In the present invention, the ratio of the total thickness of both outer layers to the thickness of the intermediate layer is preferably both outer layers / intermediate layer = 1/4 to 4/1, more preferably 1/2 to 2/1. Yes, more preferably 4/6 to 6/4. When the ratio of the total thickness of both outer layers and the thickness of the intermediate layer is out of the range of both outer layers / intermediate layers = 1/4 to 4/1, the tearing property is excellent but the film strength is inferior, or the tearing is reversed. It is not preferable because the film has insufficient properties.

  In the present invention, an elastomer component can be added to the intermediate layer in order to maintain flexibility during processing such as printing and vapor deposition.

  The elastomer component may be any thermoplastic resin having a glass transition temperature lower than room temperature and dispersed with a sea-island structure with respect to the polyester resin. Specific examples include low-density polyethylene and linear low-density. Polyethylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene-propylene copolymer, ethylene-propylene-butene copolymer, ethylene-acrylic acid copolymer, ethylene-methyl acrylate copolymer, Polyamide elastomers such as ethylene-ethyl acrylate copolymers, polyamides and polyamide-polyethylene oxide block copolymers, polyamide-polytetramethylene oxide block copolymers, polyamide-polyethylene oxide block copolymers, polyester-polyethylene Emissions oxide block copolymers, polyesters - such as polyester elastomer polytetramethylene oxide block copolymer can be increased.

Among these resins, for example, a block copolymer polyester resin made of a soft polymer having a crystal segment having a melting point of 170 ° C. or higher and a melting point or softening point of 100 ° C. or lower and a molecular weight of 400 to 8000 is preferable.

  In addition, the intrinsic viscosity of the polyester resin used for this invention becomes like this. Preferably it is 0.55-1.3 dl / g, More preferably, it is 0.62-0.78 dl / g.

  More preferably, the intrinsic viscosity difference of all the resins is within 0.3. When the intrinsic viscosity of each resin is significantly different, in the present invention, two or more kinds of polyester resin layers selected from the intrinsic viscosities within these ranges are laminated. In the lamination process, a multi-manifold method or a feed block method is used. In use, if the intrinsic viscosity is remarkably different, the flow of the resin becomes non-uniform, and uniform characteristics cannot be obtained in the width direction.

The thickness of the stretched film of the present invention is 12 μ to 30 μm, but is not particularly limited.

  The polyester film of the present invention may be added with various known additives such as lubricants, pigments, antioxidants, antistatic agents, etc., as long as the effects of the present invention are not impaired.

  Next, an example of a method for producing the film of the present invention will be described.

  Vacuum-dried crystalline polyester resin and amorphous polyester resin are used as outer layer mixed raw material and intermediate layer mixed raw material, supplied to two separate extruders, and melt extruded at a temperature above the melting point of crystalline polyester resin. Then, they are laminated by a multi-manifold die method, extruded as two types and three layers, and cooled and solidified to form an unstretched laminated sheet.

  The unstretched laminated sheet thus obtained is stretched 3 to 5 times in the machine direction at a temperature not lower than the glass transition temperature of the crystalline polyester resin and not higher than the glass transition temperature + 30 ° C., and immediately cooled to 20-40 ° C. .

  Next, the film is stretched 3.5 to 4.5 times in the transverse direction at a stretching temperature in the longitudinal direction + 5 ° C. or more and a temperature lower than the cold crystallization temperature of the crystalline polyester resin.

  The obtained biaxially stretched film is heat treated at a temperature of the melting point of the film to -30 ° C or higher and the melting point of -10 ° C or lower. In this heat treatment, a relaxation treatment may be performed as necessary, and the relaxation treatment is preferable because thermal dimensional stability is improved.

Through the above steps, both outer layers become layers having excellent adhesion and easy tearing while maintaining the strength and rigidity of the film, and the intermediate layer is a layer having rigidity while having excellent easy tearing. A biaxially stretched polyester film excellent in easy bendability is obtained.
Thus, an easily tearable biaxially stretched polyester film having excellent adhesion, that is, a layer having rigidity while having excellent easy cutting properties, is obtained.

  Next, the present invention will be specifically described with reference to examples and comparative examples. About the evaluation method in an Example and a comparative example, it carried out by the method of (a)-(d).

(A) Refractive index: Using an Abbe refractometer, the refractive index Nx in the longitudinal direction and the refractive index Ny in the width direction were determined.

(C) Lami strength:
Laminate: Two-component curable polyester-polyurethane adhesive TM590 manufactured by Toyo Morton Co., Ltd. and the same curing agent CAT56 were applied so that the solid content was 3 g / m ² , and then bonded to a sealant at 60 ° C., and then 40 ° C. Measured after curing for 48 hours. In addition, Toyobo Co., Ltd. L6102 40micrometer was used as a sealant.

  Measurement: A strip of 200 mm in the longitudinal direction and 15 mm in the width direction was cut out, and the laminate was peeled off at a rate of 200 mm / min using an autograph manufactured by Shimadzu Corporation, and the strength at that time was measured. . Each sample was measured 5 times and the average was obtained.

Evaluation: Evaluated in the following four stages according to the laminate strength: A: Unpeelable (sealant or substrate breakage)
○: 5 N / 15 mm or more Δ: 3 N / 15 mm or more, less than 2 N / 15 mm x: less than 3 N / 15 mm

(D) Hand-cut property: Performed by a sensory test, laminated with the polyester film / adhesive / 9 μm aluminum foil / 15 μm extruded LDPE to form a laminate, then bag-formed by heat sealing, and the seal part is hand-held It evaluated by the openability when cut | disconnecting by. When holding the bag with both hands, it was carried out in both the longitudinal direction and the width direction with an interval of about 3 mm.
○: Can be easily opened without raising nails △: Can be easily opened by raising nails ×: Cannot be easily opened even when nails are raised

Example 1

  As the crystalline polyester resin, a polyethylene terephthalate resin composed of terephthalic acid and ethylene glycol (referred to as polyester RE553, PES-A manufactured by Toyobo Co., Ltd.) was used. The polyethylene terephthalate resin had a melting point of 255 ° C. and an intrinsic viscosity of 0.64 dl / g.

  As an amorphous polyester resin, terephthalic acid is used as an acid component, and a copolymer polyester resin obtained by copolymerizing 70 mol% of ethylene glycol and 30 mol% of cyclohexanedimethanol as a glycol component (copolyester FP301, PES-B manufactured by Toyobo Co., Ltd.) Used). The copolyester resin had an intrinsic viscosity of 0.74 dl / g and did not show clear crystallization temperature and melting point.

  Both outer layers were used by mixing 70% by weight of PES-A and 30% by weight of PES-B. As the intermediate layer, 30% by weight of PES-A and 70% by weight of PES-B were mixed and used. The melt was melted by a separate extruder at a temperature of 275 ° C., the melt was joined by a multi-manifold die at a residence time of about 3 minutes, extruded, rapidly cooled with a cooling drum adjusted to 30 ° C., and the outer layer / A three-layer unstretched laminated sheet having an intermediate layer / outer layer configuration was obtained.

  The unstretched laminated sheet was stretched 4.0 times at 95 ° C in the longitudinal direction and then 4.1 times at 105 ° C in the transverse direction, and then heat treated at a temperature of 230 ° C while relaxing 2.5%. The post-adhesion layer side was subjected to corona discharge treatment to obtain a 14 μm film having a layer ratio of 2/6/2. The properties of the obtained film are shown in Table 1.

(Example 2)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that 60% by weight of PES-A and 40% by weight of PES-B were mixed in both outer layers. The properties of the obtained film are shown in Table 1.

(Example 3)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that 85% by weight of PES-A and 15% by weight of PES-B were mixed in both outer layers. The properties of the obtained film are shown in Table 1.

Example 4
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that 10% by weight of PES-A and 90% by weight of PES-B were mixed in the intermediate layer. The properties of the obtained film are shown in Table 1.

(Example 5)
As an amorphous polyester resin, 78 mol% terephthalic acid and 22 mol% isophthalic acid as an acid component, and a copolymerized polyester resin copolymerized with ethylene glycol as a glycol component (denoted as copolymer polyesters RN100A and PES-C manufactured by Toyobo Co., Ltd.) A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that it was used. The properties of the obtained film are shown in Table 1. The polyethylene-tere / iso-phthalate resin had an intrinsic viscosity of 0.74 dl / g and did not show clear crystallization temperature and melting point.

(Example 6)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that the layer ratio of the film was set to 1/8/1. The properties of the obtained film are shown in Table 1.

(Example 7)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that the layer ratio of the film was changed to 4/2/4. The properties of the obtained film are shown in Table 1.

(Comparative Example 1)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that only PES-A was used for both outer layers. The properties of the obtained film are shown in Table 2.

(Comparative Example 2)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that only PES-A was used for the intermediate layer. The properties of the obtained film are shown in Table 2.

(Comparative Example 3)
When both layers were formed in the same manner as in Example 1 except that 40% by weight of PES-A and 60% by weight of PES-B were mixed and used, the film was melted by heat treatment and a film was not obtained.

(Comparative Example 4)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that the same raw material in which 70% by weight of PES-A and 30% by weight of PES-B were mixed in each extruder was used. The properties of the obtained film are shown in Table 2.

(Comparative Example 5)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that the heat treatment temperature was 190 ° C. The properties of the obtained film are shown in Table 2.

  Table 1 shows the evaluation results of the films obtained in Examples 1 to 7 and Comparative Examples 1 to 5.

  As is clear from Examples 1 to 7 and Comparative Examples 1 to 5, in the biaxially stretched polyester film having at least three layers, each layer is composed of at least one crystalline polyester resin and at least one. It is composed of more than one kind of amorphous polyester resin, and both outer layers are composed of layers having crystallinity mixed in a ratio of crystalline polyester resin / amorphous polyester resin = 60/40 to 90/10% by weight, and an intermediate layer Is composed of a layer having no crystallinity mixed in a ratio of crystalline polyester resin / amorphous polyester resin = 5/95 to 30/70% by weight. It can be seen that the stretched polyester film has excellent hand cutting properties and adhesiveness.

  The polyester-based resin film of the present invention has excellent hand cutting properties and adhesiveness, and is used as a packaging bag film and tape film, as an opening for PTP packaging and beverage packs, or as a packaging material for gum or candy. It can be used in a wide range of application fields and contributes greatly to the industrial world.

Claims (4)

In the biaxially stretched polyester film having at least three layers, each layer is composed of at least one crystalline polyester resin and at least one amorphous polyester resin, and both outer layers are crystalline polyester. Resin / amorphous polyester resin = a layer having crystallinity mixed in a ratio of 60/40 to 90/10% by weight, and the intermediate layer is crystalline polyester resin / amorphous polyester resin = 5/95 to 30 / 70 wt% of non-crystalline layers mixed and the difference (Nx−Ny) between the refractive index Nx in the longitudinal direction and the refractive index Ny in the width direction is −0.002 or more and 0.002 An easily tearable biaxially stretched polyester film excellent in adhesiveness, characterized by being:   The easily tearable biaxially stretched polyester film according to claim 1, wherein the crystalline polyester resin is heat-treated at a temperature ranging from a melting point of -50 ° C to a melting point of -10 ° C after stretching in at least a uniaxial direction. Easily tearable biaxially stretched polyester film with excellent adhesion.   The easily tearable biaxially stretched polyester film according to claim 1 or 2, wherein the ratio of the total thickness of both outer layers to the thickness of the intermediate layer is both outer layers / intermediate layer = 1/4 to 4/1. Easily tearable biaxially stretched polyester film with excellent adhesion.   The easily tearable biaxially stretched polyester film according to claim 1, 2, or 3, wherein the crystalline polyester resin used is composed of 90 mol% or more of terephthalic acid and 90 mol% or more of ethylene glycol. Easy tearable biaxially stretched polyester film with excellent adhesion.