JP2006341422A - Polyester resin film excellent in adhesiveness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide a polyester stretched film having good tear properties and adhesiveness without losing strength, transparency, heat resistance, barrier properties, etc. and useful as a packaging film, a film for a tape, the opening port of a PTP pack or a beverage pack or an exterior material of gum or candy. <P>SOLUTION: This easy tear biaxially stretched polyester film excellent in adhesiveness is characterized in that its adhesive layer comprises a layer having crystallinity composed of a mixture of a crystalline polyester resin and an amorphous polyester resin and its thrust strength is 2.0-8.0 N. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 is 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 because of the excellent properties such as toughness, heat resistance, water resistance, and transparency of stretched polyethylene terephthalate phthalate films. 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 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 is characterized in that the adhesive layer of the film is a layer having crystallinity composed of a mixture of a crystalline polyester resin and an amorphous polyester resin, and the piercing strength of the film is 2.0 N or more and 8.0 N or less. It is an easily tearable biaxially stretched polyester film excellent in adhesion.

  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.
In the polyester resin film in the present invention, the adhesive layer is composed of a layer having crystallinity composed of a mixture of a crystalline polyester resin and an amorphous polyester resin, and the piercing strength of the film is 2.0 N or more and 8.0 N or less. It is an easily tearable biaxially stretched polyester film excellent in adhesion and characterized by being.

  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 90 mol%, the crystallinity is lowered, making it difficult to ensure the rigidity of the film, and transesterification during mixing and extrusion with an amorphous resin. This is not preferable because it tends to be a uniform resin by reaction.

  The amorphous polyester resin includes terephthalic acid such as terephthalic acid-isophthalic acid-ethylene glycol copolymer, terephthalic acid-ethylene glycol-neopentyl glycol copolymer, or terephthalic acid-ethylene glycol-cyclohexanedimethanol. Polyesters containing ethylene glycol as the main component and other acid components and / or other glycol components as copolymerization components are preferred.

  For example, examples of the acid component include aliphatic dibasic acids (for example, adipic acid, sebacic acid, azelaic acid) and aromatic dibasic acids (for example, 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). Examples of the glycol component include aliphatic diols (for example, diethylene glycol, propylene glycol, butanediol, hexanediol), alicyclic diols (for example, 1,4-cyclohexanedimethanol) or aromatic diols (for example, xylylene glycol, bis). (4-β-hydroxyphenyl) sulfone, 2,2- (4-hydroxyphenyl) propane derivative) are used.

  In the present invention, the puncture strength of the film is 2.0 N or more and 8.0 N or less, preferably 2.5 N or more and 6.0 N or less, and more preferably 3.0 N or more and 5.0 N or less. When it exceeds 8.0 N, the strength of the film becomes strong and it is difficult to tear by hand, which is not preferable.

  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. 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 is insufficient, and the strength, rigidity, and heat resistance of the film are insufficient.

  Or when it exceeds 90 weight%, sufficient adhesiveness will not be acquired and it is unpreferable.

  The principle of improving the adhesion in the present invention is that the amorphous polyester resin is mixed in the adhesive layer, so that the amorphous polyester resin melts when the adhesive is applied, and the polyester resin film and the adhesive resin It is thought that the coagulation with In addition, it is considered that the amorphous polyester resin is melted by the heat treatment in the film forming process, and the orientation in the film thickness direction is remarkably increased. This can prevent cohesive failure inside the film.

  In the present invention, the refractive index Nz in the thickness direction of the film is 1.490 or more, more preferably 1.495 or more. When Nz is less than 1.490, when laminating with an adhesive, the adhesive force between the adhesive and the film surface and the cohesive force in the thickness direction of the film layer are insufficient, causing peeling and cohesive failure in the layer. Cause.

  The refractive index of the present invention is measured using an Abbe refractometer. The Abbe refractometer has a characteristic that, when layers having different refractive indexes are laminated, 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 of the present invention and the layer having molecular orientation is measured, the measured values Nx and Ny in the vertical and horizontal directions are the refraction of the layer having no molecular orientation. Indicates the rate.

  Further, the refractive index Nz in the thickness direction measures the refractive index of the layer having molecular orientation. That is, all the layers are oriented in the longitudinal direction and the transverse direction by stretching, and the orientation in the thickness direction is remarkably reduced. Next, in the heat setting zone, crystallization of the layer having molecular orientation proceeds, and the refractive index in all the longitudinal, lateral and thickness directions increases. However, the layer with substantially no molecular orientation is in a molten state in the heat setting zone, so that the orientation in the longitudinal and transverse directions almost disappears and the orientation in the thickness direction increases remarkably, so only the orientation in the thickness direction is taken. Becomes larger than the layer having molecular orientation, and the refractive index of the layer having molecular orientation can be measured.

  That is, by measuring using an Abbe's refractive system, it has a state in which the molecular orientation of the layer having substantially no molecular orientation, which is an easy tearing index, is collapsed, and a molecular orientation, which is an adhesiveness index. The crystallinity of the layer can be measured.

  An elastomer component can be added to the polyester resin film layer other than the adhesive layer in order to maintain flexibility during processing such as printing and laminating.

  In addition, the intrinsic viscosity of the polyester is preferably 0.55 to 1.3 dl / g, and more preferably 0.60 to 0.75 dl / g. A polyester resin selected from the intrinsic viscosities within these ranges is preferable from the viewpoint of film forming properties and processability. In addition, it is preferable that the intrinsic viscosities of the respective layers are close when a laminated structure is used, and the intrinsic viscosity difference is 0.3. The following is preferable.

  When the intrinsic viscosity difference is significant between the layers, particularly in the feed block method, the thickness of each layer varies in the width direction, and uniform characteristics may not be obtained.

  Furthermore, the layer structure of the film of the present invention is such that both outer layers are crystallized due to 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. It is preferable to have properties.

  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.

  A crystalline polyester resin and an amorphous polyester resin, which have been vacuum-dried so that the water content is 50 ppm or less, are mixed to obtain a mixed raw material for the outer layer and a mixed raw material for the intermediate layer, which are supplied to two different extruders, The melt-extruded polyester resin is melt-extruded at a temperature of 10 ° C. or higher, laminated by a feed block method, extruded as two layers / three layers comprising an outer layer / intermediate layer / outer layer, and cooled and solidified to form an unstretched laminated sheet.

  The unstretched laminated sheet thus obtained is stretched 3 to 5 times in the longitudinal direction at a temperature in the range of the glass transition temperature of the crystalline polyester resin and the glass transition temperature + 30 ° C., so that crystallization does not proceed. Immediately cool to 20-40 ° C.

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

  The film after biaxial stretching is heat-treated at a temperature not lower than the melting point or softening temperature of the intermediate layer and not higher than the melting point of the outer layer minus -20 ° C. In addition, it is preferable to perform a relaxation treatment during the heat treatment because the dimensional change is eliminated at the time of subsequent processing such as printing and lamination.

  Through the above steps, both outer layers are layers having excellent adhesiveness while maintaining the strength and rigidity of the film, and the intermediate layer is an adhesive layer having excellent easy cutting properties and rigidity. An easily tearable biaxially stretched polyester film having excellent properties can be 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: A refractive index Nz in the thickness direction was determined using an Abbe refractometer.

(B) 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 (manufactured by Shimadzu Corporation, Autograph AGC-1KNG type), the sample is folded in half and sandwiched between chucks so that the length from the chuck is 50 mm. The steel ball having a diameter of 0.7 mm is pierced through the folded portion at a speed of 50 mm / min, and the load when the hole is pierced is obtained. The measurement was performed with n = 5, and the average was obtained from three points excluding the highest value and the lowest value.

(C) Lamination strength: Laminate: Using a two-component curable polyester-polyurethane adhesive TM590 manufactured by Toyo Morton Co., Ltd. and the same curing agent CAT56, the solid content was 3 g / m ^2, and then a sealant at 60 ° C. And measured after curing at 40 ° C. 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 peeled off at a rate of 200 mm / min in such a manner that the laminate part was bent to the sealant side 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 with raised nails

Example 1
As the crystalline polyester resin, a polyethylene terephthalate resin (represented by Toyobo Co., Ltd. RE553, PES-A) composed of terephthalic acid and ethylene glycol 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, a terephthalic acid is used as an acid component, and a copolymerized polyester resin (designated as FP301, PES-B manufactured by Toyobo Co., Ltd.) obtained by copolymerizing 70 mol% of ethylene glycol and 30 mol% of cyclohexanedimethanol as a glycol component. Using. 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 an intermediate layer, 20% by weight of PES-A and 80% 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 225 ° 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)
As an intermediate layer, 85 mol% terephthalic acid, 15 mol% isophthalic acid as an acid component, and a copolymerized polyester resin copolymerized with ethylene glycol as a glycol component (copolymerized polyester RN105 manufactured by Toyobo Co., Ltd., referred to as PES-C) are used. Obtained a film having a thickness of 14 μm in the same manner as in Example 1. The properties of the obtained film are shown in Table 1. The polyethylene tele / isophthalate resin had a melting point of 217 ° C. and an intrinsic viscosity of 0.64 dl / g.

Example 4
Other than using amorphous polyester resin as copolymerized polyester resin (copolymer polyester RN100A manufactured by Toyobo Co., Ltd., PES-D) composed of 78 mol% terephthalic acid as acid component, 22 mol% isophthalic acid and ethylene glycol as glycol component Obtained a film having a thickness of 14 μm in the same manner as in Example 1. The properties of the obtained film are shown in Table 1. The copolyester resin had an intrinsic viscosity of 0.72 dl / g and did not show clear crystallization temperature and melting point.

(Example 5)
A film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that 80% by weight of PES-A and 20% by weight of PES-B were mixed in both outer layers. 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 the same raw material in which 20% by weight of PES-A and 80% by weight of PES-B were mixed was used in each extruder, a film was not obtained by melting in the heat treatment process. When the thermal characteristics of the unstretched laminated sheet of the film were confirmed by DSC, clear crystallization peaks and melting peaks were not observed.

(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 mixed with 80% by weight of PES-A and 20% by weight of PES-B was used for each extruder. 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 only PES-A was used for both outer layers and only PES-C was used for the intermediate layer. 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 5 and Comparative Examples 1 to 5.

  As is clear from Examples 1 to 5 and Comparative Examples 1 to 4, the adhesive layer of the film is a layer having crystallinity composed of a mixture of a crystalline polyester resin and an amorphous polyester resin, and the piercing strength of the film is 2. It can be seen that the easily tearable biaxially stretched polyester film having excellent adhesiveness, characterized by having an N of 0.0N or more and 8.0N or less, 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.

It is explanatory drawing of the jig | tool for a puncture strength measurement of this invention, and a measuring method.

Claims (3)

  A film comprising at least two layers of a base material layer and an adhesive layer, wherein the adhesive layer of the film comprises a layer having crystallinity composed of a mixture of a crystalline polyester resin and an amorphous polyester resin, and the piercing strength of the film is 2 An easily tearable biaxially stretched polyester film excellent in adhesiveness, characterized in that the refractive index Nz in the thickness direction of the adhesive layer is 1.490 or more and is 0.0N or more and 8.0N or less.   2. The biaxially stretched polyester film according to claim 1, wherein at least the ratio of the crystalline polyester resin to the amorphous polyester resin of the adhesive layer is crystalline polyester resin / amorphous polyester resin = 60/40 to 90 /. An easily tearable biaxially stretched polyester film excellent in adhesion, characterized by being mixed at a ratio of 10% by weight and having crystallinity.   3. A biaxially stretched polyester film according to claim 1 or 2, wherein the biaxially stretched polyester film comprises at least three layers, and the intermediate layer comprises a polyester resin layer having no orientation. Stretched polyester film.

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