JP2007160577A - Biaxially stretched polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially stretched polyester film improved in film forming properties, lamination properties and bag making properties. <P>SOLUTION: The biaxially stretched polyester film is constituted by laminating polyester layers (B), each of which has a melting point higher than that of a polyester layer (A) with a melting point of 240°C or lower containing a butylene terephthalate unit, on both sides of the polyester layer (A) and characterized in that the end tear resistance values in the longitudinal and lateral directions of the film are 40 N or below, and the glass transition temperature of the film is 65°C or above. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a film excellent in hand cutting properties and suitable as a packaging material for industrial materials, pharmaceuticals, sanitary materials, foods and the like.

  Conventionally, it has been required that packaging materials for industrial materials, pharmaceuticals, sanitary materials, foods, etc. have good hand cutting properties. For example, in small bag packaging materials such as confectionery, powder medicine, etc. There is a big merit that it is easy. As a material for producing such a hand cutting property, cellophane, a so-called moisture-proof cellophane obtained by coating cellophane with a vinyl chloride-vinyl acetate copolymer, or a film obtained by coating cellophane with vinylidene chloride (K-coated cellophane) is used. .

  However, although cellophane, moisture-proof cellophane, and K-coated cellophane have excellent hand-cutting properties, the characteristics of the film vary depending on the humidity and the printing characteristics are poor. In addition, the cellophane base material is expensive, and there is a concern about supply in the future. Furthermore, K-coated cellophane is difficult to use due to environmental considerations such as the possibility of dioxin generation during combustion.

  Polyester film, on the other hand, is used as a packaging material due to its excellent properties such as mechanical properties, dimensional stability, heat resistance, water resistance, and transparency. Has the problem. As a method for solving this drawback, a polyester film oriented in a uniaxial direction (Patent Document 1), a copolymerized diethylene glycol component (Patent Document 2), or a low molecular weight polyester resin (Patent Document 3). ) Etc. have been proposed.

  However, in the above prior art, the method of aligning in the uniaxial direction is easy to cut linearly in the alignment direction but difficult to cut in other directions, and the method of copolymerizing a large amount of the diethylene glycol component or the like is by copolymerization. It has the disadvantage that the original properties are lost. Furthermore, the method using a low molecular weight polyester resin is not practical because it easily causes troubles in film breakage in the stretching step.

  Also, a method of laminating a copolyester layer having a low melting point and a polyester layer having a high melting point to almost completely collapse the molecular orientation of the low melting point polyester layer (Patent Document 4) or a method of mixing an amorphous polyester (Patent Document) 5) The method of interposing an amorphous polyester layer (Patent Document 6) has been proposed. However, in these methods, if it is attempted to improve the hand-cutting property, the film breaks during film formation or breaks during lamination. The problem remains.

  In order to solve the above problem, a method of interposing a polyester layer containing polybutylene terephthalate (Patent Document 7) has been proposed. Films made by this method have film-forming stability, and when making bags using this film, excellent hand cutting properties are possible without laminating other materials with good hand cutting properties such as aluminum and paper. Have However, when a packaging bag is made using this film, there is a new problem that it tends to be wrinkled due to the process of laminating the sealant layer and the sealing process.

Japanese Patent Publication No.55-8551 Japanese Patent Publication No. 56-50692 Japanese Patent Publication No.55-20514 Japanese Patent Laid-Open No. 5-104618 Japanese Patent Laid-Open No. 2003-155403 Japanese Patent Laid-Open No. 2003-220678 Japanese Patent Laid-Open No. 2004-136447

  This invention is made | formed in view of said subject, Comprising: The solution subject is providing the film with good hand cutting property excellent in film forming property, laminating property, and bag making aptitude.

  As a result of intensive studies on the above problems, the present inventor has found that the above problems can be easily solved by a film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is a film in which a polyester layer (B) having a melting point higher than the melting point of the polyester layer (A) is laminated on both sides of the polyester layer (A) having a melting point of 240 ° C. or less containing a butylene terephthalate unit. In the biaxially stretched polyester film, the end tear resistance value in the longitudinal direction and the width direction of the film is 40 N or less, and the glass transition temperature of the film is 65 ° C. or more.

Hereinafter, the present invention will be described in detail.
The butylene terephthalate unit in the present invention refers to a polymer constituent unit containing an ester group obtained by polycondensation from terephthalic acid as an acid component and 1,4-butanediol as a glycol component. Such a polymer may be a homopolymer or a copolymer of the third component.

  The copolyester is represented by a polyester in which the acid component is terephthalic acid and isophthalic acid, and the glycol component is ethylene glycol. Further, other copolymer components may be copolymerized.

  Other copolymer components include acid components such as adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid and other aliphatic dicarboxylic acids, phthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1 , 5-naphthalene dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, anthracene dicarboxylic acid, and other aromatic carboxylic acids. Examples of the alcohol component include aliphatic diols such as diethylene glycol, propylene glycol, neopentyl glycol, butanediol, pentanediol and hexanediol, and polyalkylene glycols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol. . These may be used alone or in combination of two or more.

  The film of the present invention is a film in which a polyester layer (B) having a melting point higher than the melting point of the polyester layer (A) is laminated on both sides of a polyester layer (A) having a melting point of 240 ° C. or less containing a butylene terephthalate unit, The butylene terephthalate unit of the polyester layer (A) is usually in the range of 5 to 100% and preferably in the range of 10 to 100%. The melting point of the polyester layer (A) is preferably designed to be 235 ° C. or lower, more preferably 200 to 235 ° C.

  The polyester layer (B) in the present invention refers to a polymer containing an ester group obtained by polycondensation from a dicarboxylic acid and a diol or from a hydroxycarboxylic acid. Examples of dicarboxylic acids include terephthalic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and diols include ethylene glycol and 1,4-butane. Examples include diol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol and the like, and examples of hydroxycarboxylic acid include p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. be able to. As the production method, for example, a transesterification reaction is carried out between a lower alkyl ester of an aromatic dicarboxylic acid and a glycol, or an aromatic dicarboxylic acid and a glycol are directly esterified to form a substantially aromatic compound. A method is employed in which a bisglycol ester of a dicarboxylic acid or a low polymer thereof is formed and then polycondensed by heating under reduced pressure. The melting point of the polyester layer (B) is higher than that of the polyester layer (A), and preferably 10 ° C. or higher.

  Typical examples of such a polymer include polyethylene terephthalate and polyethylene-2,6-naphthalate. These polymers may be homopolymers or may be a copolymer of the third component.

  The polyester layer (B) is preferably laminated on both sides of the polyester layer (A) so that the total thickness of the polyester layer (B) is 8 μm or less or 50% or less of the total thickness. It is preferable to make it 30% or less.

  In order to improve workability in the film winding process, coating process, vapor deposition process, and the like, it is desirable that the polyester film in the present invention contains fine particles. These fine particles include inorganic particles such as calcium carbonate, magnesium carbonate, calcium sulfate, barium sulfate, lithium phosphate, magnesium phosphate, calcium phosphate, lithium fluoride, aluminum oxide, silicon oxide, kaolin, acrylic resin, guanamine resin, etc. Although there may be mentioned organic particles and precipitated particles obtained by making catalyst residuals into particles, the present invention is not limited to these. The particle size and amount of these particles can be appropriately determined according to the purpose. The fine particles to be contained may be a single component, or two or more components may be used simultaneously.

  The method of blending each particle with the raw material polyester is not particularly limited, and for example, a method of adding each particle to the polyester polymerization step or a method of melt-kneading the raw material polyester and each particle is suitable. In addition, various stabilizers, lubricants, antistatic agents, and the like can be added as appropriate.

  The polyester film of the present invention is melted by supplying the above-described polyester raw material to a known melt extrusion apparatus represented by an extruder, and heating to a temperature equal to or higher than the melting point of the polymer. Next, while extruding the molten polymer from the slit-shaped die, it is rapidly cooled and solidified so that it is in the form of a rotary cooling drum or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. This sheet is obtained by stretching in a biaxial direction to form a film and heat-setting. In this case, the stretching method may be sequential biaxial stretching or simultaneous biaxial stretching. Moreover, you may extend | stretch longitudinally and / or a horizontal direction again before or after performing heat setting as needed. In the present invention, in order to obtain sufficient dimensional stability and waist as a packaging material, the draw ratio is 9 times or more, preferably 12 times or more as the area magnification.

  In the present invention, the heat treatment temperature after stretching the film is preferably not less than the melting start temperature of the polyester layer (A), more preferably not less than the melting point. If the heat treatment is performed at a temperature lower than the melting start temperature of the polyester layer (A), sufficient tearability may not be obtained after lamination with the sealant layer.

  The end tear resistance in the longitudinal direction and the width direction of the polyester film of the present invention is 40 N or less, preferably 30 N or less. Moreover, it is preferable to design so that the end tear resistance value in the longitudinal direction is smaller than the end tear resistance value in the width direction.

  The glass transition temperature of the polyester film of the present invention needs to be 65 ° C. or higher, and if it is lower than 65 ° C., the bag is stretched and wrinkled in the process of laminating the sealant layer and the sealing process.

  The thickness of the polyester film in this invention is 9-50 micrometers normally, Preferably it is 12-38 micrometers.

  The tensile strength at break of the polyester film in the present invention is usually 40 to 170 MPa, preferably 50 to 140 MPa.

  The film that has been printed on the polyester film of the present invention to enhance the design and then laminated with the sealant layer can be used as a packaging material with good hand cutting properties. As a typical example, for example, a medicine sachet can be mentioned.

  Moreover, the gas barrier film obtained by providing the polyester film of the present invention with a barrier layer made of metal or metal oxide by vapor deposition or coating an existing barrier layer is used as a gas barrier packaging material with good hand cutting properties. be able to. A laminate with an aluminum foil can also be used as a gas barrier packaging material with good hand cutting properties.

  ADVANTAGE OF THE INVENTION According to this invention, the polyester film with the good hand cutting property excellent in film forming property, laminating property, and bag making aptitude can be provided, The industrial value is high.

  EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In addition, the evaluation method and the processing method of a sample in an Example and a comparative example are as follows. Further, “parts” in Examples and Comparative Examples represents “parts by weight”.

(1) Method for Measuring Intrinsic Viscosity [η] (dl / g) of Polymer 1 g of polymer is dissolved in 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio), and 30 ° C. using an Ubbelohde viscometer. Measured with

(2) Method for measuring film thickness Ten films were stacked and the thickness was measured by a micrometer method, and the average value was obtained by dividing the measured value by 10 to obtain the film thickness.

(3) Method for measuring the thickness of the laminated polyester layer The film piece was fixed with an epoxy resin and then cut with a microtome, and the cross section of the film was observed with a transmission electron micrograph. Two of the cross-sections are observed almost in parallel with the film surface, and the interface is observed by contrast. The distance between the two interfaces and the film surface was measured from 10 photographs, and the average value was defined as the laminated thickness.

(4) Measurement Method of Melting Start Temperature and Melting Point Melting start temperature (Tim) and melting point (Tpm) were measured using a differential scanning calorimeter DSC7 manufactured by PerkinElmer. The DSC measurement conditions are as follows. 6 mg of the sample film was set in a DSC apparatus, the sample was heated from 0 ° C. to 300 ° C. at a rate of 10 ° C./min, and the melting point was detected according to the reading of the DSC curve of JIS K7121.

(5) Measuring method of glass transition temperature The glass transition temperature (Tg) was measured using a Perkin-Elmer differential scanning calorimeter DSC7 type. 6 mg of the sample film was set in a DSC apparatus, and the sample was heated from 0 ° C. to 300 ° C. at a rate of 10 ° C./min, held at 300 ° C. for 5 minutes, and then rapidly cooled with liquid nitrogen. The rapidly cooled sample was heated from 0 ° C. at a rate of 10 ° C./min, and the glass transition temperature was detected according to how to read the DSC curve of JIS K7121.

(6) Measuring method of tensile breaking strength Using a tensile tester model 2001 type manufactured by Intesco Corporation, the length (between chucks) is 50 mm and the width is 15 mm in a room adjusted to a temperature of 23 ° C. and a humidity of 50% RH. A sample sample was pulled at a strain rate of 200 mm / min, the load at the time of film breakage was measured, and the tensile breakage rate was determined by the following formula.
Tensile strength at break (MPa) = Load during cutting (N) / Cross-sectional area of sample film (mm ² )

(7) Measuring method of end tear resistance The average value obtained by the measuring method of JISC2318-1975 was used as end row resistance value.

(8) Measuring method suitable for bag making Pillow using an anchor coating agent (EL510 made by Toyo Morton Co., Ltd.), extruding low density polyethylene to a thickness of 25 μm, extrusion laminating, and laminating the film A packaging bag was prepared and evaluated for properness according to the following criteria.
Evaluation ○: A packaging bag can be created without wrinkles. Evaluation ×: Wrinkles occur when laminating or sealing.

(9) Measuring method of tearability It evaluated on the following reference | standard whether a film and the pillow bag created by said method could be torn smoothly by hand, without making a notch | incision. For the film, the bag was evaluated for the seal portion and the edge portion in the longitudinal direction (MD) and the width direction (TD), respectively.
Evaluation A: Can be easily torn by hand Evaluation B: Can be relatively easily torn by hand Evaluation C: Can not be easily torn by hand

The polyester raw materials used in the following examples and comparative examples were produced by the following method.
<Method for producing polyester 1>
Using terephthalic acid as the dicarboxylic acid component and 1.4 butanediol as the polyhydric alcohol component, polybutylene terephthalate was produced by a conventional melt condensation polymerization method. The intrinsic viscosity ([η]) of this polyester raw material was 0.80 dl / g. The polyester film obtained from the raw material had a melting start temperature (Tim) of 213 ° C. and a melting point (Tpm) of 222 ° C.

<Method for producing polyester 2>
It was produced by a conventional melt condensation polymerization method using isophthalic acid and terephthalic acid as the dicarboxylic acid component and ethylene glycol as the polyhydric alcohol component, respectively. The isophthalic acid content in the dicarboxylic acid component was 15 mol%. The intrinsic viscosity ([η]) of this polyester raw material was 0.69 dl / g. The polyester film obtained from this raw material had a melting start temperature (Tim) of 198 ° C. and a melting point (Tpm) of 220 ° C.

<Method for producing polyester 3>
Intrinsic viscosity containing terephthalic acid as the dicarboxylic acid component and ethylene glycol as the polyhydric alcohol component, and containing 0.18 parts of amorphous silica having an average particle size of 2.5 μm by a conventional melt condensation polymerization method A polyester chip having ([η]) of 0.70 dl / g was obtained. The polyester film obtained from this raw material had a melting start temperature (Tim) of 242 ° C. and a melting point (Tpm) of 254 ° C.

<Method for producing polyester 4>
It was obtained by blending 20 parts of polyester 1 and 80 parts of polyester 2. The amount of polybutylene terephthalate contained in polyester 4 was 20%, and the isophthalic acid content in the dicarboxylic acid component was 12 mol%. The polyester film obtained from this raw material had a melting start temperature (Tim) of 195 ° C. and a melting point (Tpm) of 217 ° C.

<Method for producing polyester 5>
A blend of 30 parts of polyester 1 and 70 parts of polyester 2 was obtained. The amount of polybutylene terephthalate contained in the polyester 5 was 30%, and the content of isophthalic acid in the dicarboxylic acid component was 11 mol%. The polyester film obtained from this raw material had a melting start temperature (Tim) of 195 ° C. and a melting point (Tpm) of 216 ° C.

Example 1:
Polyester 3 and polyester 4 pellets are melted in separate extruders, and using a laminated die, polyester 3 (layer B) / polyester 4 (layer A) / polyester 3 (layer B), two types and three layers The laminated polyester resin was extruded onto a cooling drum having a surface temperature of 30 ° C. and rapidly cooled to obtain an unstretched film having a thickness of about 250 μm. Next, the film was stretched 3.6 times in the longitudinal direction at 75 ° C., and then subjected to a preheating step in the tenter, transversely stretched 4.3 times at 85 ° C., and heat-treated at 235 ° C. for 5 seconds to form a laminate having a thickness of 16 μm. A polyester film was obtained. The thickness configuration of the B layer / A layer / B layer was 1 μm / 14 μm / 1 μm. The properties of the obtained film are shown in Table 1 below.

Example 2:
A laminated polyester film was prepared in the same manner as in Example 1 except that polyester 5 was used as the raw material for the A layer, and the thickness configuration of the B layer / A layer / B layer was changed to 2 μm / 12 μm / 2 μm. The properties of the obtained film are shown in Table 1 below.

Comparative Example 1:
A laminated polyester film was prepared in the same manner as in Example 1 except that polyester 5 was used as the raw material for the A layer. The properties of the obtained film are shown in Table 2 below.

Comparative Example 2:
A laminated polyester film was prepared in the same manner as in Example 2 except that the thickness constitution of B layer / A layer / B layer was 2.5 μm / 11 μm / 2.5 μm. The properties of the obtained film are shown in Table 2 below.

Comparative Example 3:
A laminated polyester film was prepared in the same manner as in Example 1 except that polyester 2 was used as the raw material for the A layer. The properties of the obtained film are shown in Table 2 below. In this film, the film was easily broken in the film-forming winding process, and it was difficult to form the film.

  In the above table, PET means polyethylene terephthalate, PBT means polybutylene terephthalate, IPA means isophthalic acid, MD means the longitudinal direction, and TD means the width direction.

  The film of the present invention can be suitably used as a packaging material for industrial materials, pharmaceuticals, sanitary materials, foods, and the like.

Claims (1)

A polyester layer (B) having a melting point higher than the melting point of the polyester layer (A) is laminated on both sides of the polyester layer (A) having a melting point of 240 ° C. or less containing a butylene terephthalate unit, and the longitudinal direction of the film A biaxially stretched polyester film having an end tear resistance value in the width direction of 40 N or less and a glass transition temperature of the film of 65 ° C. or more.