JP4967504B2 - Biaxially stretched polyester film laminate - 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. 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 (A) and a polyester resin (B) The polyester resin (A) is mainly composed of terephthalic acid, the diol component is mainly ethylene glycol, and the polyester resin (B) is mainly composed of terephthalic acid. Polyester film containing cyclohexanedimethanol and having excellent hand cutting properties, wherein the mass ratio A / B between the polyester resin (A) and the polyester resin (B) is 95/5 to 30/70, etc. Have been proposed (for example, Patent Documents 1 to 4). Irradiation).
Japanese Patent Publication No.55-8551 Japanese Patent Publication No. 56-50692 Japanese Patent Publication No.55-20514 JP 2003-155403 A

  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, it is a polyester film comprising a mixture of a polyester resin (A) and a polyester resin (B), wherein the acid component of the polyester resin (A) is mainly terephthalic acid, the diol component is mainly ethylene glycol, and the polyester resin (B ) Is mainly terephthalic acid, contains cyclohexanedimethanol as the diol component, and the mass ratio A / B of the polyester resin (A) to the polyester resin (B) is 95/5 to 30/70. The polyester film excellent in hand cutting characteristics characterized by this is inferior to hand cutting when the ratio of the polyester resin (A) is large, and is manifested when the ratio of the polyester resin (A) is reduced. However, since the polyester resin (B) with poor heat resistance is present throughout the film, Poor heat resistance of things, there are problems such as wrinkles and pitch shift occurs during processing. Or since polyester resin (B) exists on the film surface, there existed a problem of sticking to the heating roll in the longitudinal stretch.

Alternatively, on at least one side of the polyester resin layer (A), the polyester resin layer has a melting point that is higher by 10 ° C. than the melting point of the polyester resin layer (A) and has a thickness of 5% or more and 60% or less with respect to the total thickness. The unstretched laminated film in which (B) is laminated is heat-treated at least at a temperature lower by 10 ° C. than the melting point of the polyester resin layer (A) and at a temperature lower than the melting point of the polyester resin layer (B) after uniaxial stretching. A method for producing a polyester film imparted with tearability and twistability has been proposed (see, for example, Patent Document 5).
Japanese Patent No. 3561919

  However, on at least one side of the polyester resin layer (A), the polyester resin layer has a melting point that is 10 ° C. or more higher than the melting point of the polyester resin layer (A) and has a thickness of 5% or more and 60% or less with respect to the total thickness. The unstretched laminated film in which (B) is laminated is heat-treated at least at a temperature lower by 10 ° C. than the melting point of the polyester resin layer (A) and at a temperature lower than the melting point of the polyester resin layer (B) after uniaxial stretching. When the polyester film imparted with tearing and twisting properties is heat-treated at a temperature lower than the melting point of the polyester resin layer (A), the orientation collapse of the polyester resin layer (A) becomes insufficient, resulting in poor hand cutting properties. When the thickness of the polyester resin layer (B) that bears rigidity is thin, the film is insufficient in rigidity and heat resistance, although it has sufficient hand cutting properties. Wrinkles and elongation is there is a problem or cause to.

  The present invention was made against the background of the problems of the prior art, and in addition to the toughness, heat resistance, water resistance, and transparency that are the characteristics of polyester films, it is a laminate that combines these characteristics with particular attention to processability. It is intended to provide a film.

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 is a laminate obtained by extrusion laminating a melt low density polyethylene between a biaxially stretched polyester film and an aluminum foil, and further extruding and laminating a melt low density polyethylene on the aluminum foil. The polyester film has a three-layer structure of surface layer / intermediate layer / surface layer, the surface layer is formed of polyethylene terephthalate, the intermediate layer is formed of a terephthalic acid-isophthalic acid-ethylene glycol copolymer, and further terephthalic after biaxial stretching. It is a film heat-treated at a temperature not lower than the melting point of acid-isophthalic acid-ethylene glycol copolymer at a temperature of -1 ° C and not higher than a melting point of polyethylene terephthalate at a temperature of -15 ° C. (Μm), ET ² is 400 (GPa · μm ² ) or more The biaxially stretched polyester film laminate is characterized in that both end and tear resistance values in the longitudinal and transverse directions are 70 N or less.

  In this case, a biaxially stretched polyester film comprising a layer made of a crystalline polyester resin having the orientation and a layer made of a polyester resin having substantially no orientation.

  In this case, the biaxially stretched polyester film is characterized in that the dry heat shrinkage rate at 150 ° C. for 30 minutes is 3% or less in both length and width.

  The polyester-based resin film according to the present invention is a stretched polyester having excellent hand cutting properties and excellent processability while having the inherent properties of polyester such as heat resistance, cold resistance, moisture resistance, transparency, and fragrance retention. It is a film. By improving the workability, there is an advantage that a good product can be obtained without causing wrinkles or pitch deviation during printing and laminating.

Hereinafter, the present invention will be described in detail.
The biaxially stretched polyester film in the present invention has an initial elastic modulus E (GPa) and a thickness T (μm) in the longitudinal direction, and ET ² is 400 (GPa · μm ² ) or more. It is an easily tearable biaxially stretched polyester film excellent in workability, characterized in that both end tear resistance values are 70 N or less.

  In the present invention, both the longitudinal and lateral end resistances of the film are 70 N or less, preferably 50 N or less. When it exceeds 70 N, the strength of the film becomes strong and it is difficult to tear by hand, which is not preferable.

  In addition, when the end tear resistance is extremely small, the film becomes brittle, and further caution is required at the time of film formation and processing. For example, it may cause breakage due to fluctuations in tension and displacement of the film during slitting and addition. . Therefore, it is preferable that it is 25N or more practically.

  Although the initial elastic modulus and thickness are characteristics relating to the rigidity of the film, a thin film having a high initial elastic modulus has a low rigidity and is difficult to process. On the contrary, even if the rigidity is low, a thick film can be processed.

In the present invention, ET ² is preferably 400 (GPa · μm ² ) or more in the initial elastic modulus E (GPa) and thickness T (μm) in the longitudinal direction. More preferably, it is 500 (GPa · μm ² ) or more. When ET ² is less than 400 (GPa · μm ² ), wrinkles and elongation occur in processing processes such as printing and laminating, and wrinkles occur in the winding process and slit process of the film forming process. It is easy to do and is not preferable.

  As for the thickness of the stretched film of the present invention, the film thickness used in a packaging bag or the like which is the intended use of the present invention is 12 μm to 35 μm. For example, in the case of 12 μm, the initial elastic modulus in the longitudinal direction is 2 .8 GPa or more, preferably 3.5 GPa or more.

  Examples of the polyester resin of the layer having an orientation 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.

  In the present invention, the melting point of the crystalline polyester resin layer is preferably 245 ° C. or higher. When the melting point is less than 245 ° C., the heat resistance is insufficient, which is not preferable because it causes wrinkles, shrinkage, and pitch deviation in the printing and laminating processes.

  The polyester resin of the layer having substantially no orientation is mainly composed of terephthalic acid such as terephthalic acid-isophthalic acid-ethylene glycol copolymer, terephthalic acid-ethylene glycol-neopentyl glycol copolymer, and ethylene glycol. And polyesters containing other acid components 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.

  Moreover, it is preferable that it is a polyester-type resin whose glass transition temperature is 70 degreeC or more, and aromatic or alicyclic dibasic acid or diol, such as isophthalic acid and 1, 4- cyclohexane dimethanol, as a copolymerization component Is preferably used because it can prevent the glass transition temperature from being lowered. Since a linear dibasic acid or diol has a high degree of freedom of C—C bond in the molecular chain, the glass transition temperature is lowered when used for copolymerization.

  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 0.60-0.74 dl / g. More preferably, the difference in intrinsic viscosity of all resin layers is within ± 0.2 dl / g.

  In the present invention, two or more types of polyester resin layers selected from the intrinsic viscosities within these ranges are laminated. When a multi-manifold method or a feed block method is used in the lamination process, the intrinsic viscosity is remarkably different in each layer. If a different resin is used, the flow of the resin becomes non-uniform and uniformity in the width direction cannot be obtained. That is, due to the difference in viscosity of each resin layer, the flow of resin does not become uniform during lamination, so the thickness ratio of each layer becomes non-uniform depending on the position, film properties such as tearability, breaking strength, breaking elongation This is not preferable because it causes variations in the like.

  In the present invention, as a method for adjusting the resistance to end tearing, the ratio between the layer having molecular orientation and the layer having substantially no molecular orientation, the crystallinity of the layer having molecular orientation, or substantially Can be used depending on the degree of molecular orientation of the layers having no molecular orientation, the molecular weight of the polyester resin constituting each layer, etc., and preferably a layer having molecular orientation and a layer having substantially no molecular orientation Is the ratio.

  In the present invention, the melting point of a layer made of a polyester resin having substantially no orientation is −3 ° C. or more, and the melting point of a layer made of a crystalline polyester resin having an orientation is −30 ° C. or more, and the melting point is −10 ° C. or less. It is preferable to perform heat treatment at a temperature of, more preferably, a melting point of a layer made of a polyester resin having substantially no orientation is −1 ° C. or more, and a melting point of a layer made of a crystalline polyester resin having an orientation is −25 ° C. or more. The melting point is −15 ° C. or lower. The polyester resin layer substantially free of orientation due to the heat treatment loses the orientation caused by stretching and provides good tearability, and the crystallization of the layer made of crystalline polyester resin having orientation proceeds. Thus, excellent workability, tearability, rigidity, and barrier properties can be obtained.

  In the present invention, the dry heat shrinkage in the vertical and horizontal directions when the polyester film is left in an atmosphere of 150 ° C. for 30 minutes is 3% or less, particularly preferably 2% or less. If the dry heat shrinkage at 150 ° C is greater than 3%, wrinkles or flatness may occur during multicolor printing, laminating, or forming a metal or inorganic vapor deposition layer. In addition, it causes mechanical troubles, and the appearance of the package is deteriorated.

  In the present invention, in order to set the dry heat shrinkage in the longitudinal and transverse directions to 3% or less, the method according to the temperature, magnification and speed at the time of longitudinal stretching and transverse stretching, the heat setting temperature, and the longitudinal and lateral directions. There are methods based on the rate of relaxation treatment and the temperature during the relaxation treatment.

  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.

  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.

  Two types of crystalline polyester resins having different melting points are vacuum-dried so that the water content is 50 ppm or less. Each crystalline polyester resin is supplied to two different extruders, melt extruded at a temperature equal to or higher than the melting point, and laminated by a multi-manifold die method to become a high melting point resin layer / low melting point resin layer / high melting point resin layer. An unstretched laminated sheet is formed by extruding onto a mirror surface roll adjusted to 30 ° C. as two types and three layers and cooling and solidifying.

  The obtained unstretched laminated sheet is stretched 3 to 5 times in the machine direction at a temperature not lower than the glass transition temperature and not higher than the glass transition temperature + 30 ° C. and immediately cooled to 20 to 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 of + 5 ° C. or more and lower than the cold crystallization temperature.

  The obtained biaxially stretched film is heat-treated at a temperature of the melting point of the low-melting polyester resin −1 ° C. or higher and the melting point of the high-melting polyester resin −10 ° C. or lower. In this heat treatment, a relaxation treatment may be performed as necessary, and the relaxation treatment is preferable because the thermal dimensional stability is improved.

  By the above steps, both outer layers maintain the strength and rigidity of the film, and the intermediate layer provides a biaxially stretched polyester film having excellent easy tearability.

  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) Initial elastic modulus: measured in accordance with JIS-K7127.

(B) Thickness: Measured according to JIS-K7130.

(C) End tear resistance value: measured according to JIS-C2318 (1975). The result was the larger value in the longitudinal and width directions.

(D) Workability: Using a single extrusion laminator manufactured by Modern Machinery Co., Ltd., the state of wrinkles when laminated with the film / 15 μm extruded LDPE (L705 manufactured by Sumitomo Chemical Co., Ltd.) / 9 μm aluminum foil was observed.
The processing was performed at a resin temperature of 320 ° C. and a processing speed of 100 m / min.
○: Good without wrinkles △: Wrinkles are not noticeable but not suitable for use ×: Wrinkles are noticeable and cannot be used

(E) Hand cutting property: Performed by a sensory test, extrusion lamination is performed on the aluminum foil side of the laminate obtained above, and the film / 15 μm extrusion LDPE / 9 μm aluminum foil / 35 μm extrusion LDPE is formed. The bag was made with a seal and evaluated by the unsealing property when the seal part was cut by hand. 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 with raised nails

Example 1
Polyethylene terephthalate resin (represented as RE554 manufactured by Toyobo Co., Ltd .: [A]) obtained by adding 2000 ppm spherical silica having a particle size of 2.4 μm to polyethylene terephthalate resin composed of terephthalic acid and ethylene glycol is used as the crystalline polyester resin for the surface layer. It was. The polyethylene terephthalate resin had a melting point of 255 ° C. and an intrinsic viscosity of 0.64 dl / g.

  As the crystalline polyester resin for the intermediate layer, terephthalic acid and isophthalic acid were used as the acid component and a copolymerized polyester resin (RN103C manufactured by Toyobo Co., Ltd .: [B]) made of ethylene glycol as the glycol component was used. The copolymer polyester resin had a melting point of 231 ° C. and an intrinsic viscosity of 0.64 dl / g.

  The melt was melted by a separate extruder at a temperature of 275 ° C., and the melt was joined with a multi-manifold die at a residence time of about 3 minutes. The melt was extruded and rapidly cooled with a cooling drum adjusted to 30 ° C. A three-layer unstretched laminated sheet having an intermediate layer / surface layer configuration was obtained.

  The unstretched laminated sheet was stretched 3.9 times at 95 ° C. in the longitudinal direction and then 4.2 times at 105 ° C. in the transverse direction, and then heat treated at a temperature of 232 ° C. while relaxing 3%. Corona discharge treatment was performed on the layer side to obtain a 14 μm film having a layer ratio of 15/70/15. 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 the layer ratio was set to 5/90/5. The properties of the obtained film are shown in Table 1.

(Example 2)
A film was obtained in the same manner as in Example 1 except that the layer ratio was 10/80/10 and the thickness was 16 μm. The properties of the obtained film are shown in Table 1.

(Example 3)
A film was obtained in the same manner as in Example 1 except that the layer ratio was 20/60/20 and the thickness was 12 μm. The properties of the obtained film are shown in Table 1.

(Comparative Example 2)
A film was obtained in the same manner as in Example 1 except that the thickness was 12 μm. The properties of the obtained film are shown in Table 1.

(Comparative Example 3)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that the layer ratio was 25/50/25. The properties of the obtained film are shown in Table 1.

(Comparative Example 4)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that the polyester resin [ A ] was used for all layers. The properties of the obtained film are shown in Table 1.

  Table 1 shows the evaluation results of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 4.

As is clear from Examples 1 to 3 and Comparative Examples 1 to 4, ET ² is 400 (GPa · μm ² ) or more in the initial elastic modulus E (GPa) and thickness T (μm) in the longitudinal direction. It can be seen that the easily tearable biaxially stretched polyester film excellent in workability characterized by having an end tear resistance value in the longitudinal and lateral directions of 70 N or less has excellent hand cutting properties and workability.

  The polyester resin film of the present invention has excellent hand cutting properties and processability, 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)

A laminate obtained by extrusion laminating a melt low density polyethylene between a biaxially stretched polyester film and an aluminum foil, and further extruding and laminating a melt low density polyethylene on the aluminum foil, the biaxially stretched polyester film, It consists of a three-layer structure of surface layer / intermediate layer / surface layer, the surface layer is formed of polyethylene terephthalate, the intermediate layer is formed of terephthalic acid-isophthalic acid-ethylene glycol copolymer, and after biaxial stretching, terephthalic acid-isophthalic acid- A film heat-treated at a temperature not lower than the melting point of ethylene glycol copolymer −1 ° C. and not higher than a melting point of polyethylene terephthalate −15 ° C., and has an initial elastic modulus E (GPa) and thickness T (μm) in the longitudinal direction. ET ² is 400 (GPa · μm ² ) or more, and ends in the vertical and horizontal directions A biaxially stretched polyester film laminate having both crack resistance values of 70 N or less. 2. The biaxially stretched polyester film laminate according to claim 1, wherein the biaxially stretched polyester film has both longitudinal and lateral end tear resistance values of 25 N or more. The biaxially stretched polyester film laminate according to claim 1 or 2, wherein the biaxially stretched polyester film has a dry heat shrinkage of 150% at 30 ° C of 3% or less in both length and width. The biaxially stretched polyester film laminate according to any one of claims 1 to 3, wherein the biaxially stretched polyester film has a thickness of 12 to 16 µm .