TW200407366A - Heat-shrinkable multilayered polyester film for packaging - Google Patents

Abstract

A heat-shrinkable multilayered film for packaging comprises at least three layers and is produced by a coextrusion method, in which the surface layers each comprises as the main component a mixture of a polyester (A) obtained from an acid ingredient comprising more than 80 mole% of terephthalic acid (TA) and either naphthalenedicarboxylic acid (NDC) or isophthalic acid (IA) and a glycol ingredient consisting more than 80 mole% of ethylene glycol (EG) and a polyester (B) obtained from an acid ingredient comprising TA and IA and a glycol ingredient consisting mainly of tetramethylene glycol, and at least one of the core layer(s) comprises as the main component a polyester (C) obtained from an acid ingredient comprising TA and IA and a glycol ingredient consisting mainly of EG. The multilayered film has a shrinkage of 35% or higher in the main shrinkage direction and a shrinkage of 5% or lower in the direction perpendicular thereto. The polyester A is formed of terephthalic acid (TA) and either naphthalenedicarboxylic acid (NDC) or isophthalic acid (IA) in a mole ratio of 95/5 to 80/20. The main diol is ethylene glycol, and the polyester B contains terephthalic acid and isophthalic acid in a mole ratio of 90/10 to 60/40. The main component of diol is tetramethylene glycol, and the polyester C is formed of an acid component consisting of terephthalic acid (TA) and isophthalic acid (IA) in a mole ratio of 95/5 to 80/20. The main ingredient of ethylene glycol is glycol. The invented film can be used as a packaging material due to its excellent properties in endurance, dimensional stability, mechanical strength, oil resistance, solvent resistance, and printability.

Description

200407366 (1) 发明. Description of the invention [Technical field to which the invention belongs] The present invention relates to a heat-shrinkable multilayer polyester film used for packaging articles. More specifically, it relates to a multilayer polyester film having excellent durability, dimensional stability, mechanical strength, and solvent resistance and useful as a shrink packaging material having excellent printability.

[Prior art] In the past, for shrink packaging applications including bottle labels, polyester shrink films or non-polyester shrink films such as polystyrene and polyvinyl chloride have been used. Among these, polyester film shrink films are superior to non-polyester shrink films in terms of solvent resistance, durability, dimensional stability, and mechanical strength. However, although polyester-based shrink films are excellent in shrinkage and solvent adhesion due to the use of amorphous materials, they need to be improved due to their lack of mechanical strength.

In order to improve the mechanical strength of the polyester-based shrink film, Japanese Patent Laid-Open No. 08-3 3 3 8 5 3 proposes a method of using a three-layer structure and using a highly crystalline polyester in the core layer. In this proposal, in order to obtain the solvent adhesion of the surface layer polymer, the ratio of the polyethylene terephthalate component is made 80 mol% or less, but due to the difference in crystallinity between the surface and the core layer The resulting interlayer peeling is remarkable, and the purpose of improving the characteristics of the polyester-based shrink film cannot be achieved. This tendency to peel between layers is also noticeable when the polymer seeds of the core layer and the surface-layer are different. (2) (2) 200407366 [Summary of the invention] As a result of intensive research to solve the above-mentioned shortcomings of the polyester-based shrink film, the inventor found that if the polyester used for the surface layer and the polyester used for the core layer are made as much as possible, Copolymers or mixtures thereof close to the proportion of the ethylene terephthalate component can improve the affinity between the surface layer and the core layer and obtain heat-shrinkable polyester films with good mechanical strength and adhesion. In fact, the present invention has finally been completed. The heat-shrinkable multilayer polyester film for packaging according to the present invention is one of the at least three layers of the multilayer film produced by co-extrusion filming (one polyester layer 1) and the other one (polyester layer 2). Based on a molten mixture of polyester A and polyester B as the main component, the terephthalic acid component in the mixture is 80 mol% or more of the total acid component, and the ethylene glycol component is the total glycol component. Above 80 mol%, at least one of the core layers is a multilayer film with a polyester C-based layer (polyester layer 3), and is characterized in that the multilayer film is treated in warm water at 80 ° C. 1 The shrinkage rate in the main shrinkage direction at 0 seconds is 35% or more, and the shrinkage rate in the right-angled direction with respect to the main shrinkage direction is 5% or less. Here, the molar ratio of "terephthalic acid" to "naphthalene dicarboxylic acid or isophthalic acid" in the polyester A-based acid component is composed of a ratio of 95/5 to 80/20, and "Ethylene glycol" is a polyester having a main diol component. Furthermore, the molar ratio of "terephthalic acid" to "isophthalic acid" in the polyester B-based acid component is 95/5 to 60/40, and "tetramethylene glycol" It is a polyester with a main diol component, and the molar ratio of "terephthalic acid" to "isophthalic acid" in the polyester C-based acid component is (3) 200407366 ratio of 95/5 to 80/20 [Polymer] The surface layer (polyester layers 1 and I) of the multilayer polyester film of the present invention with "ethylene glycol" as the main diol component [polyester] The acid component The molar ratio of "terephthalic acid" to "naphthalene dicarboxylic acid or acid" is composed of a ratio of 95/5 to 80/20. The alcohol component is polyester A mainly composed of "ethylene glycol". The molar ratio of "dicarboxylic acid" to "isophthalic acid" and "isophthalic acid" is 90/1 (, and the main component is a molten mixture of glycol ester B mainly composed of "tetramethylene glycol". And the acid in the mixture is more than 80 mole% of the total acid component and more than 80 mole% of the ethylene glycol component. In terms of one state of the polyester A, The polyesters containing terephthalic acid and naphthalenedicarboxylic acid and alcohol as diol components can be prepared by the known ratio, that is, from terephthalic acid and 2.6-naphthalenedicarboxylic acid dimethyl and Ethylene glycol transesterification reaction method with terephthalic acid, 2,6-naphthalenedicarboxylic acid and ethylene glycol directly obtained oligomers, melt polymerization and production, but can also be ineffective It copolymerizes with other components within the range. As for the acid component of such other copolymerization components, aliphatic dicarboxyoxyethanedicarboxylic acids such as azelaic acid, sebacic acid, and decanedicarboxylic acid, Diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid polyester 0 Rhombic ester layer 2) Isophthalic acid and as the two of "paraphenylene I to 60/40 component polyparaxylene is a total glycol is The acid component contains dimethyl oxalate, or the present invention is produced by esterification. Adipic acid; aromatic dicarboxylic acids such as diphenyl, en-carboxy (4), (4) 200407366 acid, etc. As for the diol component, it can be exemplified by aliphatic glycols such as diethylene glycol, propylene glycol, neopentyl glycol, butanediol, pentanediol, and hexanediol; polyethylene Polyethylene glycols such as alcohols, polypropylene glycols, polytetramethylene glycols, etc. These can be used alone or in two or more ways. Here, the amount of naphthalenedicarboxylic acid component in the polyester is the total acid component 5 to 20 mol%, preferably 7 to 18 mol%, more preferably 9 to 15 mol%. If the amount of naphthalenedicarboxylic acid is less than 5 mol%, the The crystallinity is too high, so that the sealability required by the solvent required for shrink packaging will be insufficient. If it exceeds 20 mol%, the melting point will be lowered and the amorphousness will be caused, resulting in drying, manufacturing It is difficult and practical to handle the film. In another state of the polyester A, paradicarboxylic acid and isophthalic acid are contained as the acid component and ethyl is contained as the diol component in the above proportion. Polyesters of diols can be produced by well-known methods, that is, from the transesterification reaction of dimethyl terephthalate and dimethyl isophthalate with ethylene glycol, or from terephthalic acid and isophthalate After the direct esterification of formic acid and ethylene glycol to obtain an oligomer, it can be obtained by melt polymerization, but it can also be used without affecting Effect within the scope of the invention be copolymerized with other components. Examples of the acid component of such other copolymerization components include aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid; 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, anthracenedicarboxylic acid, etc. Family one residual acid and so on. In addition, as for the diol component, diethylene glycol, propylene glycol, neopentyl glycol, butanediol, pentanediol, hexanediol, and the like can be exemplified. 9- (5) 200407366 aliphatic glycol , Polyethylene glycol, polypropylene glycol, polytetramethylene glycol and other polyalkylene glycols. These can be used alone or in a combination of two or more.

Here, the amount of the isophthalic acid component in the polyester A is 5 to 20 mol% 'in the total acid component, preferably 7 to 9 mol%, and more preferably 10 to 18 mol%. If the amount of isophthalic acid is 5 mol% or less, the crystallinity at the time of film formation is too high ', so that the sealability imparted by the solvent required for shrink packaging is insufficient. If it exceeds 20 mol%, the melting point will be lowered, and the amorphous state will be carried out, so that drying and handling during film formation will be difficult and impractical.

The amount of the ethylene glycol component in the polyester A is an amount of the ethylene glycol component in the total glycol component in the mixture with the polyester b to be 80 mol% or more. Therefore, the amount of the ethylene glycol component in polyester A is determined according to the mixing ratio of polyester a and polyester B, but it is preferably 80 mol% or more, and more preferably 90 mol% or more. Particularly preferred is substantially 100 mole%. Substantially 100 mol% means a ratio of a glycol component (for example, diethylene glycol) other than ethylene glycol by-produced in trace amounts during polymerization. The polyester B of the present invention is composed of terephthalic acid and isophthalic acid as the acid component and tetramethylene glycol as the diol component, and can be produced by a well-known method, that is, Transesterification from dimethyl terephthalate and dimethyl isophthalate with tetramethylene glycol, or direct esterification with terephthalic acid and isophthalic acid with tetramethylene glycol After the oligomer is obtained, it is prepared by melt polymerization. Polyester B may be copolymerized with other components as long as it does not affect the effect of the present invention. As for the acid component of such other copolymerization components, adipic acid, aliphatic dicarboxylic acids such as -10- (6) (6) 200407366, azelaic acid, sebacic acid, and decanedicarboxylic acid; Phthalic acid; 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1 '5-naphthalenedicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyl Aromatic dicarboxylic acids such as ether ether dicarboxylic acids and anthracenedicarboxylic acids. Examples of the diol component include aliphatic glycols such as diethylene glycol, propylene glycol, neopentyl glycol, butanediol, pentanediol, and hexanediol; polyethylene glycol and polypropylene glycol , Polytetramethylene glycol and other polybutanediol. These can be used alone or in a combination of two or more. In the acid component of the polyester B, the amount of isophthalic acid is 10 to 40 mol%, preferably 12 to 37 mol%, and more preferably 5 to 33 mol%. If the amount of isophthalic acid is less than 10 mol%, the crystallinity of the surface will be increased, so that the sealability imparted by the solvent required for shrink packaging will be insufficient. If it exceeds 40 mol%, it will be difficult and impractical to handle and dry the film due to the lowering of the melting point and the amorphous state. The amount of the tetramethylene glycol component in the polyester B is an amount of the ethylene glycol component in the total glycol component in the mixture with the polyester a to be 80 mol% or more. Therefore, the amount of the tetramethylene glycol component in the diol component of the polyester B is determined depending on the mixing ratio of the polyester A and the polyester B, but it is preferably 80 mol% or more, more preferably Above 90 mol%, particularly preferred is substantially 100 mol%. Essentially 100 mol% means the proportion of diol components other than tetramethylene glycol by-produced during the polymerization process. The present invention is a multilayer film that is at least one of the core layers On the other hand, polyester layer 3 containing polyester C as a main component was included. This polyester C is known as an acid component of -11-(7) 200407366, with terephthalic acid and isophthalic acid as the main component, and glycol as the diol component. Production method, that is, from dimethyl terephthalate and transesterification reaction of dimethyl isophthalate and ethylene ester, or by direct esterification with terephthalic acid and isophthalic acid and ethylene glycol After the oligomer is obtained, the polymer is obtained by melting the polymer. However, as long as the effect of the present invention is not affected, the polyester C may be copolymerized with other ingredients.

Examples of the acid component of such other copolymerization components include aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid; phthalic acid; 2 '6- Naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, anthracenedicarboxylic acid Aromatic dicarboxylic acids, such as acids. Examples of the diol component include aliphatic glycols such as diethylene glycol, propylene glycol, neopentyl glycol, butanediol, pentanediol, and hexanediol; polyethylene glycol and polypropylene glycol , Polytetramethylene glycol and other polybutanediol. These can be used alone or in combination of two or more.

The amount of isophthalic acid in the polyester C is 5 to 20 mol%, preferably 7 to 17%, and more preferably 10 to 15%. If the amount of isophthalic acid exceeds 20%, it is not suitable because the amorphous strength of the core layer will increase, resulting in a decrease in mechanical strength. When it is 5 mol% or less, crystallization tends to occur, which may cause a drop in tear resistance. The amount of the ethylene glycol component in the polyester C is preferably 80 mol or more, more preferably 90 mol% or more, and particularly preferably substantially 100 mol. /. . In essence, 100 mol% refers to the proportion of a diol component (for example, diethylene glycol) other than ethylene glycol, which is a by-product produced during the polymerization. -12- (8) 200407366

The polyester constituting the polyester layer 1 and the polyester layer 2 of the present invention is a mixture (blend) of polyester A and polyester B. The blending ratio is based on the total acid content of each mixture. The proportion of the dicarboxylic acid component can be more than 80 mol%, and the proportion of the ethylene glycol component in the total diol component can be determined as 80 mol%. When the ratio of the ethylene terephthalate component is 80 mol or less, the affinity with the polyester C constituting the core layer is deteriorated, so that interlayer peeling may occur after solvent adhesion. The mixing ratio of the polyester A and the polyester B is changed according to the composition ratio of the polyester A and the polyester B, but it is preferable that the weight ratio of the polyester A / polyester B is 70/3/3 to 95 / The range of 5 is particularly preferably in the range of 80/20 to 90/10. Here, if the polyester component ratio of the polyester layer 1 and the polyester layer 2 is in the above range, it may be a polyester of the same composition or a different one, but for the purpose of producing multilayer polyester films with high efficiency, Preferably, polyesters having the same composition are used. [Multilayer polyester film] The multilayer polyester film of the present invention has a heat of crystal melting Δ Hm preferably in the range of 20 to 60 J / g, more preferably 25 to 55 J / g, and particularly preferably 30 to 50 0 J / g. . The size of △ Hm can be used as a standard for the amount of crystals in the film (orientation crystallization during film formation and cold crystallization during heating). When Δ Hm is below 30] / g, it means that the film is close to amorphous, and the mechanical strength of the film may be insufficient. On the other hand, if it exceeds 60] / g, the degree of crystallization is too high, and physical properties that are indispensable to the packaging material such as tear resistance may be reduced. In the polyester layer 1 and / or the polyester layer 2 of the present invention, it is preferable that the composition contains a lubricant having an average particle diameter of 2.5 μm or less. Such lubricants may be either inorganic or organic, but inorganic ones are preferred. Examples of the inorganic lubricant include silicon oxide, alumina, titanium dioxide, calcium carbonate, and barium sulfate, and examples of the organic lubricant include silicone particles. It is preferable that the average particle diameters are all 2.5 μm or less. If the average particle size exceeds 2.5 μm, it will not be suitable as a packaging material because it will affect the transparency of the multilayer polyester film.

The above lubricant may be blended in the polyester layer 3. In terms of the haze (haze, haze) of the multilayer polyester film of the present invention, if transparency is required as a packaging material, the thickness is preferably 15% or less, and particularly preferably 10% or less with a thickness of 40 μm. The amount of the above lubricant added varies depending on its particle size, but it can be selected within a range that does not affect the reelability and transparency of the film.

As the polymer for the surface layer of the polyester layer 1 and the polyester layer 2 of the present invention, for example, the polyester layer 3 (core layer) may be used by mixing the above-mentioned polyester A and polyester B particles with an automatic blender. For polymers, polyester C is used. Polyester A, polyester B, and polyester C are melted in an extruder after being dried, and discharged from the die to form a multilayer film, which can be stretched and fixed to form a multilayer polymer. Ester film. The heat-fixing temperature of the film is preferably selected in the vicinity of the higher Tg among the Tg (glass transition temperature) of the polyester constituting the polyester layer 1 and the polyester layer 2. If the heat-fixing temperature is too high, the thermal shrinkage of the product film becomes small, so that it loses its original function as a heat-shrinkable packaging. The multilayer polyester film of the present invention needs to be treated in warm water at 80 ° C for 10-14-( 10) (10) The shrinkage rate in the main soup of the main contraction direction at the time of 200,407,366 seconds is more than 35%, and the contraction rate to the right direction of the main contraction direction is less than 5%. If the shrinkage is within this range, the characteristics when used for heat shrinkable packaging will be improved. Here, the shrinkage is measured in accordance with JIS-Z 1 7 09 in the plane direction of the film. In addition, among the longitudinal direction of the film and the wide direction perpendicularly intersecting the film, the direction in which the shrinkage rate is the largest is taken as the main shrinkage direction. The shrinkage rate in the main shrinkage direction in warm water at 80 ° C is preferably 35 to 55%. The shrinkage rate in the main shrinkage direction in warm water at 70 ° C is preferably 5 to 30%. The shrinkage of the multilayer polyester film is ideally caused by the thermal shrinkage of the shrinkage rate only in either the length direction or the width direction, but in fact, it becomes a right angle to the main shrinkage direction (length direction or width direction). There will also be some heat shrinkage in the direction. The thermal contraction in a direction perpendicular to the main contraction direction needs to be 5% or less. In order to make this kind of uniaxial shrinkage, uniaxial stretching in the main shrinking direction is most suitable. However, because the uniaxially stretched film is subject to the orientation characteristics of the polymer, the tear resistance is reduced. Depending on the application, it will be better if it is stretched slightly to the right direction of the main contraction direction. At this time, it is better to stretch the main contraction direction to a right-angle direction by at most 2 times. Depending on the application or required characteristics, it can be appropriately selected from the range of .0 times to 2.0 times. The thickness of the multilayer polyester film of the present invention is preferably 20 to 70 μm, more preferably 30 to 60 μm, and particularly preferably 35 to 55 μm. If the thickness is too thin (for example, less than 20 μm), the deformation resistance (rigidity) of the film becomes weak, and it may bend or produce defective products when the label is attached. On the other hand, if the thickness is too thick (for example, 70 μm or more), the deformation resistance of the film is too strong, and -15 · (11) (11) 200407366 is difficult to handle during processing. The layer structure of the multilayer polyester film of the present invention is preferably a three-layer structure that is laminated in the order of polyester layer 1 / polyester layer 3 / polyester layer 2. With this structure, the solvent-resistant layer can sandwich the core layer, thereby improving the solvent resistance of the core layer. Since such a laminated structure can be formed by a co-extrusion method using two extruders and a multi-manifold die or a feed block, it is suitable from the viewpoint of productivity. [Evaluation method] (1) Using a dotting type film thickness meter for film thickness and layer composition, 50 places where the continuous film formation direction of the film becomes a vertical width direction, and the film width is The thickness was measured at 50 locations in the continuous film-forming direction near the center, and the average thickness of all 100 locations was taken as the film thickness. However, the thickness of the measured film is not uniform in the width direction and the length direction, and it is based on the premise that the thickness is within +20 to -20% of the average thickness. The layer structure was obtained by embedding a thin film in an epoxy resin, cutting it into thin slices using a glass blade, and observing the cross section under a polarizing microscope. (2) Heat of crystallization melting (△ Hm) 20 mg of thin sample is sealed in a pan made of aluminum, and read using a differential scanning calorimeter (SEIKO DSC SSC / 5200 manufactured by Seiko Co., Ltd.) The rate of crystallization melting peak when the sample was heated to 280 ° C at a rate of 20 ° C / min to obtain the heat of crystal melting. A total of -16-(12) 200407366 was measured five times, and the average 値 was used as the measurement heat of crystal melting. (3) Polyethylene terephthalate content (PET unit amount)

From the compounding ratio, molecular weight, and individual copolymerization ratio of the polymer for the surface layer, the mole numbers of each acid component and each diol component in the surface layer polymer are calculated. Among the calculated acid components and diol components, the molar number of the combination of the terephthalic acid (TA) component and the ethylene glycol (EG) component is calculated as the polyethylene terephthalate component amount. . That is, it can be confirmed that the terephthalic acid component is 80 mol% or more in the total acid component and the ethylene glycol component is 80 mol% or more in the total glycol component. (4) Solvent-tightness Two 10 cm x 20 cm film sheets were prepared as samples. On the surface of one prepared film sheet, a dioxolane was coated by swabbing with a cotton rod impregnated with 1-3 dioxolane. The sheet after quasi-distribution of dioxolane was immediately bonded to another sheet of film and pressed with a roller. After lamination, the adhesion of the two thin films was evaluated according to the following criteria. 〇: The two film pieces are firmly adhered (good solvent-tightness). △ ·· The two film pieces are not sufficiently adhered and peel off over time (the solvent-tightness is slightly better). X: The two film sheets are not adhered at all (the solvent sealability is poor). (5) Thermal shrinkage -17- (13) (13) 200 407 366 JI S-Z 1 7 0 9 ， Measured in 80 ° C warm water for 10 seconds and 70 ° C warm water 1 〇 The main contraction direction in seconds and the thermal shrinkage rate during warm boiling which becomes a right angle to the main contraction direction. The average value of the number of measurement points (N) = 3 was used as the measurement value. Here, the continuous film-making direction of the film (longitudinal direction for short) and the direction of the wide width direction (horizontal direction) that intersects perpendicularly are measured in the plane direction of the film, and the direction of maximum shrinkage is taken as the main shrinking direction.

(6) Mechanical strength As an evaluation index of the strength of the film, the measurement of the elastic modulus is carried out according to JI S-K 7 1 2 7. The average value of the number of measurement points (N) = 5 was used as the measurement value. 〇: 20 OMP a or more in the continuous film formation direction and 4 5 OMP a or more in a direction perpendicular to the continuous film formation direction. X: Other than the above. (7) Peelability of the surface layer It is carried out at the same time when the layer structure is observed. That is, the film was embedded in an epoxy resin, cut into thin slices using a glass blade, and the cross-section was observed under a polarizing microscope, and the surface peelability was evaluated according to the following criteria. 〇: No peeling was confirmed (good surface peelability) X: The peeling of the surface layer was very strong due to the impact during sectioning. △: Some peeling of the surface layer can be confirmed (the peelability of the surface layer is slightly better -18- (14) 200407366 [Embodiment] [Examples 1 to 11 and Comparative Examples 1 to 14]

Preparation of polyester A: dimethyl terephthalate, 2,6-dimethylnaphthalenedicarboxylic acid, dimethyl isophthalic acid, ethylene glycol as raw materials, and tetrabutyl titanate as ester The exchange catalyst, germanium dioxide is used as a polymerization catalyst, and phosphono acid is used as a stabilizer, and a copolymerized polyethylene terephthalate is produced according to a conventional method. The composition of each component is shown in Table 1. Polyurethane B's g system: using dimethyl terephthalic acid, dimethylphthalic acid, and tetramethylene glycol as raw materials, and also using tetrabutyl titanate as transesterification catalyst and germanium dioxide as polymerization The catalyst and phosphorous acid are used as stabilizers, and copolymerized polybutylene terephthalate is produced by a conventional method. The composition of each component is shown in Table 1.

Preparation of polyester C: using dimethyl terephthalic acid, dimethyl iso-p-benzenecarboxylic acid, ethylene glycol as raw materials, tetrabutyl titanate as vinegar exchange catalyst, and germanium dioxide as polymerization catalyst 2. Phosphorous acid is used as a stabilizer, and a copolymerized polyethylene terephthalate is produced according to a conventional method. The composition of each component is shown in Table 1. Here, the component symbols shown in Table 1 are TA for terephthalic acid, NDC for 2,6-naphthalenedicarboxylic acid, IA for isophthalic acid, EG for ethylene glycol, and TMG for tetradent. Methyl glycol and CHO was cyclohexanedimethanol, and the obtained polyester A and polyester B were blended in the proportion shown in the table to prepare a polymer for the surface layer. Polyester C was used as a polymer for the core layer. Surface Polymerization -19 · (15) 200407366

Polyester c for material and core layer, each dried at 150 ° C for 6 hours, and then supplied to the surface layer. The core layer is used in two compression press buckets, which are melted at a melting temperature of 280 to 300 ° C, using a manifold The die was extruded in a cooling wave tube with a surface temperature of 20 t: quenching to obtain a multilayer unstretched film with a thickness of 180 μm. The multilayer unstretched film thus obtained was stretched only in a direction perpendicular to the continuous film formation direction (lateral direction) under the conditions shown in Table 2 and heat-fixed. In this way, a multilayer polyester film composed of three layers each having a thickness of 4 μm and a core layer of 42 μm was prepared. The characteristics of the film thus obtained are shown in Table 2. As can be seen from the results shown in Table 2, the films of Examples 1 to 11 were all useful as heat-shrinkable packaging materials. On the other hand, the thin films of Comparative Examples 1, 3, 4, 10, and 11 were those in which the surface layer had poor adhesion because a material with high crystallinity was blended. In addition, the films of Comparative Examples 2, 7, and 9 are inferior in affinity between the surface layer and the core layer, and the films of Comparative Examples 8 and 14 are inferior in strength due to the increased amorphousness of the core layer. . In addition, Comparative Examples 5, 6, and

The films of 1,2,3 are too amorphous for the surface layer raw materials, and agglomerate during drying after the stretching process, making film formation difficult and cannot be evaluated. -20- 200407366 1 6 Table-u— 00 003

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-21-(17) 200407366 Table 2

\ Tensing conditions Heat-fixing temperature (° C) Heat shrinkage (%) △ Hm (J / g) Surface peelability Solvent sealability I Mechanical strength test Stretch ratio Stretch temperature (° C) 7 0 ° C 8 or Vertical and horizontal example 1 3.7 76 ΊΊ 3 10 2 50 40 〇〇〇 2 3 10 2 50 45 〇〇3 3 10 2 50 40 〇〇 4 3 10 2 50 39 〇 05 3 10 2 50 42 〇 〇〇3 3 10 2 50 40 〇〇7 3 10 2 50 38 〇〇8 3 10 2 50 43 〇〇9 3 10 2 50 38 〇〇10 3 10 2 50 37 〇〇11 3 10 2 50 49 〇〇〇 Comparative Example 1 3.7 76 77 3 10 2 50 58 〇X 〇2 3 10 2 50 38 △ 〇〇3 3 10 2 50 43 〇 △ 〇4 3 10 2 50 37 〇 △ 〇5 6 — Failed to evaluate 7 77 3 10 2 50 33 X 〇〇8 71 72 3 18 4 52 5 〇X 9 76 77 3 10 2 50 36 △ 〇〇10 3 10 2 50 41 〇 △ 〇 11 3 10 2 50 36 〇 △ 〇12 13 — Failure to evaluate 14 71 72 3 18 4 52 4 〇〇X-22- (18) 200407366 Possibility of industrial utilization The multilayer polyester film is useful as a shrink packaging material because it has excellent durability, dimensional stability, mechanical strength, and solvent resistance, and also has excellent printability. -twenty three-

Claims (1)

(1) (1) 200,407,366, patent application scope 1 · A multilayer polyester film for heat shrink packaging, which is a multilayer film of at least 3 layers continuously filmed by co-extrusion film making method, any one The surface layer on the side is mainly composed of a molten mixture of polyester A and polyester B. The terephthalic acid component in the mixture constituting the surface layer is 80 mol% or more of the total acid component, and the ethylene glycol component is total glycol. At least 80 mol% of the composition, at least one of the core layers is a multilayer film having a layer of polyester C as the main component. The multilayer film has a main shrinkage direction when it is treated in warm water at 80 ° C for 10 seconds. The shrinkage ratio is 35% or more, and the shrinkage ratio is 5% or less with respect to the main shrinkage direction. However, the "terephthalic acid" and "naphthalene dicarboxylic acid or isobenzene" in the polyester A-based acid component The molar ratio of "dicarboxylic acid" is composed of a ratio of 95/5 to 80/20. The main diol component is "ethylene glycol", while the "terephthalic acid" and "isophthalic acid" of polyester B-based acid components are The molar ratio of "phthalic acid" is 90/10/10 to 60/40, and the main diol component is "tetramethylene glycol" And the molar ratio of "terephthalic acid" to "isophthalic acid" of the polyester C-based acid component is 95/5 to 80/20, and the main diol component is "ethylene glycol" . 2 · The multilayer polyester film according to item 1 of the scope of patent application, wherein the multilayer film has a crystal melting heat ΔHm of 20 to 60 (J / g) measured by DSC (differential scanning calorimeter). 3. The multi-layer polyester film according to item 1 of the scope of patent application, wherein the multi-layer film 'is composed of only three layers of the surface layer on both sides and the core layer sandwiched by the surface layer. -24- 200407366 柒, (I), the designated representative of this case is: No picture (II), the representative symbols of this representative diagram are simply explained: No, if there is a chemical formula in this case, please disclose the one that can best show the characteristics of the invention Chemical formula: