Flame-retardant heat shrinkable polyester film

Abstract

The present invention provides a flame-retardant polyester-based heat shrinkable film that has excellent shrinkage ratio at 80°C which is required at the time of coating, has sufficient flame retardancy even when used for a coating material application, has excellent mechanical strength that leads to good initial rupture, is not likely to tear even after coating, and has an excellent appearance that is free from distortion and sagging. A flame-retardant heat shrinkable polyester film according to the present invention is characterized by being obtained by molding a polyester resin that contains at least one flame retardant, and by satisfying the following requirements (1) to (3). (1) The heat shrinkage ratio in the main shrinkage direction after being immersed in hot water at 80°C for 10 seconds is 30% to 80% inclusive. (2) The shrinkage stress in the main shrinkage direction as measured in hot air at 90°C is 2.0 MPa to 15 MPa inclusive. (3) After aging the film in an atmosphere at 30°C and 85% RH for 672 hours, the initial rupture is found in 2 or less samples.

Description

Flame-retardant heat-shrinkable polyester film

[0001] The present invention relates to a flame-retardant heat-shrinkable polyester film, and more particularly to a flame-retardant heat-shrinkable polyester film that has excellent flame retardancy and is superior in shrinkability and mechanical properties to conventional flame-retardant polyester heat-shrinkable films, and is suitable for use in covering objects, as well as a covering material and a package using the same.

[0002] Polyester resins have excellent mechanical properties, heat resistance, and chemical resistance, and are therefore widely used as materials for magnetic tapes, photographic films, packaging films, films for electronic components, electrical insulating films, films for metal lamination, and protective films.

[0003] In recent years, with the enforcement of the Product Liability Act, there has been a strong demand for flame-retardant resins to ensure fire safety. Flame retardancy is particularly required for electrical insulating materials, and flame retardancy is increasingly required for heat-shrinkable films used for coatings and other applications. While conventionally used halogen-based flame retardants, such as organic halogen compounds and halogen-containing organic phosphorus compounds, have a high flame-retardant effect, they have been reported to release halogens during molding and processing, generating corrosive hydrogen halide gases that can corrode molding and processing equipment and potentially worsen the working environment. Furthermore, these flame retardants have been reported to generate gases such as hydrogen halide gases during fires and other combustion events. Therefore, there has been a strong demand for halogen-free flame retardants to replace halogen-based flame retardants. Various phosphorus-based compounds have been investigated as a method for imparting flame retardancy using halogen-free flame retardants. However, flame retardation methods using, for example, phosphate ester compounds, have been found to increase bleed-out and lower melting points when added in large amounts to polyester.

[0004] Patent Document 1 proposes that the use of polyethylene terephthalate copolymerized with a phosphine oxide compound of formula (1) exhibits excellent flame retardancy, and since it is halogen-free, it is possible to provide a flame-retardant film that is excellent in terms of the environment and film-forming process. However, the addition or copolymerization of a phosphine oxide compound reduces the heat shrinkage rate, and therefore, when used to cover an object, sagging and gaps occur, making it impossible to properly cover and hold the object.

[0005] Patent Document 2 proposes that adding a phosphate ester-based flame retardant to a polyester resin copolymerized with an acid component other than terephthalic acid and a glycol component other than ethylene glycol results in sufficient flame retardancy and heat shrinkability, thereby providing a polyester film that combines flame retardancy and heat shrinkability. However, the heat shrinkability evaluation disclosed in the examples of Patent Document 2 involves immersion in 80°C hot water for one minute. Since the current technical level of heat shrinkability required is much higher than that required at the time (details of heat shrinkability evaluation are provided below), the polyester film proposed in Patent Document 2 has insufficient heat shrinkability when used for coating applications. Furthermore, Patent Document 2 uses an amorphous raw material copolymerized with a flame retardant, which reduces mechanical strength and worsens initial breakage, potentially leading to breakage after coating.

[0006] Patent No. 5785067 Patent No. 3741394

[0007] The present invention aims to solve the problems of the prior art as described above. That is, an object of the present invention is to provide a flame-retardant polyester heat-shrinkable film that has an excellent shrinkage rate at 80°C required for coating, sufficient flame retardancy even when used for coating materials, and excellent mechanical strength, resulting in good initial breakage, and an excellent appearance without distortion or sagging.

[0008] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by the following means, and have arrived at the present invention. That is, the present invention comprises the following features. [1] A flame-retardant heat-shrinkable polyester film, which is molded from a polyester resin containing at least one flame retardant and satisfies the following requirements (1) to (3): (1) A heat shrinkage rate in the main shrinkage direction after immersion in 80°C hot water for 10 seconds is 30% to 80%; (2) A shrinkage stress in the main shrinkage direction measured in 90°C hot air is 2.0 MPa to 15 MPa; and (3) The number of initial breaks after aging the film for 672 hours in an atmosphere of 30°C and 85% RH is 2 or less. [2] The flame-retardant heat-shrinkable polyester film according to [1], which has a heat shrinkage rate in the direction perpendicular to the main shrinkage direction after immersion in 80°C hot water for 10 seconds is -15% to 15%. [3] A density of 1.20 g / cm ３ 1.35g / cm or more ３[4] The flame-retardant heat-shrinkable polyester film according to [1] or [2], characterized in that it has an intrinsic viscosity of 0.6 dl / g or more and 1.0 dl / g or less. [5] The flame-retardant heat-shrinkable polyester film according to any one of [1] to [3], characterized in that it contains a phosphorus-based compound as a flame retardant, and the phosphorus atom concentration in the polyester film is 0.3 wt% or more and 2.0 wt% or less, based on the weight of the polyester film. [6] The flame-retardant heat-shrinkable polyester film according to any one of [1] to [5], wherein the polyester is composed primarily of terephthalic acid or a derivative thereof as a polycarboxylic acid component and ethylene glycol as a polyhydric alcohol component. [7] The flame-retardant heat-shrinkable polyester film according to [6], wherein the polyester constituting the flame-retardant heat-shrinkable polyester film contains 50 mol% or more of ethylene terephthalate units relative to 100 mol% of the total resin components. [8] The flame-retardant heat-shrinkable polyester film according to [6], wherein terephthalic components account for 70 mol% or more of the dicarboxylic acid components constituting the polyester. [9] The flame-retardant heat-shrinkable polyester film according to [6], wherein ethylene glycol components account for 50 mol% or more of the diol components constituting the polyester.

[10] The flame-retardant heat-shrinkable polyester film according to [6], wherein the polyhydric alcohol component comprises at least one selected from the group consisting of 1,4-butanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol.

[11] A covering material obtained by heat-shrinking the flame-retardant heat-shrinkable polyester film according to any one of [1] to

[10] to adhere the film to at least a part of an object.

[12] A package at least a part of which is covered with the covering material according to

[11] .

[0009] The polyester heat-shrinkable film of the present invention has excellent flame retardancy, low-temperature shrinkability, and mechanical properties, and when used as a coating film, it is possible to provide a film for coating applications that is resistant to combustion, has a taut feel, has an excellent appearance without distortion or sagging, and is resistant to tearing.

[0010] The flame-retardant polyester heat-shrinkable film of the present invention will be described below. The flame-retardant polyester heat-shrinkable film of the present invention has the following properties.

[0011] 1. Properties of Flame-Retardant Heat-Shrinkable Film 1.1. Heat Shrinkage Ratio The flame-retardant heat-shrinkable film of the present invention is a heat-shrinkable polyester film cut into a 10 cm x 10 cm square and immersed in 80°C hot water for 10 seconds. The heat shrinkage ratio in the main shrinkage direction, between the machine direction (also referred to as the longitudinal direction, or MD direction) and the width direction (also referred to as the transverse direction or TD direction), must be 30% to 80%. The heat shrinkage ratio in the present invention affects the appearance and binding strength when used as a covering material. That is, when the film of the present invention is heated to attach it to an object as a covering material, heat shrinkage eliminates slack in the covering material, giving it a taut feel, resulting in a beautiful appearance and enabling the object to be bound without slippage. The heat shrinkage ratio is a value calculated by the following formula (1): Heat shrinkage ratio (%) = (dimension before heating - dimension after heating) / dimension before heating x 100 (1)

[0012] If the heat shrinkage rate of the film in the main shrinkage direction is less than 30%, the film will not adhere to the object when it is shrunk to cover it, resulting in poor appearance and poor bundling, which is undesirable. A more preferred heat shrinkage rate is 32% or more, even more preferably 35% or more, and particularly preferably 40%. A heat shrinkage rate of more than 80% is undesirable because the heat shrinkage stress is likely to exceed 15 MPa. That is, the heat shrinkage rate of the film in the main shrinkage direction is 30 to 80%, preferably 32 to 80%, and more preferably 35 to 80%.

[0013] 1.2. Heat Shrinkage Stress The flame-retardant heat-shrinkable film of the present invention must have a heat shrinkage stress in the main shrinkage direction measured in hot air at 90°C of 2.0 MPa or more and 15.0 MPa or less. Like the heat shrinkage percentage, the heat shrinkage stress of the present invention affects the appearance and binding strength when used as a covering material and heated. A heat shrinkage stress of less than 2.0 MPa is undesirable because the binding strength is insufficient when the film is applied to an object, resulting in poor binding. On the other hand, a heat shrinkage stress of more than 15.0 MPa is undesirable because excessive thermal deformation of the covering material when attached to the object makes it more likely to deform the object. The heat shrinkage stress is more preferably 3.0 MPa or more and 14.0 MPa or less, and even more preferably 4.0 MPa or more and 13.0 MPa or less. That is, the heat shrinkage stress in the main shrinkage direction is 2.0 to 15.0 MPa, preferably 3.0 to 14.0 MPa, and more preferably 4.0 to 13.0 MPa.

[0014] 1.3. Initial Breakage Furthermore, the flame-retardant heat-shrinkable film of the present invention must have an initial breakage rate of 2 or less out of 10 samples after aging the film for 672 hours in an atmosphere of 30°C and 85% RH. The initial breakage rate in the present invention affects the durability of the film when used as a coating material. The fewer the number of initial breakages, the better, as the film is less likely to break and has excellent durability. On the other hand, if the number of initial breakages exceeds 2, the film is more likely to break when used as a coating material, resulting in a film with insufficient durability. The initial breakage rate is preferably 1 or less, more preferably 0. Generally, when amorphous polyethylene terephthalate, which is used as a raw material for heat-shrinkable films, is used, the initial breakage rate tends to increase. Furthermore, when a flame retardant is added to exhibit flame retardancy, the intrinsic viscosity decreases, which may further worsen the initial breakage rate due to a decrease in mechanical strength. According to a preferred production method of the present invention, by lowering the moisture content of the polyethylene terephthalate raw material in the drying process compared to ordinary polyethylene terephthalate, a high intrinsic viscosity can be maintained even when a flame retardant is added, and a film with excellent mechanical strength and no early rupture can be provided. Furthermore, according to a preferred production method of the present invention, by using highly crystalline and hard polyethylene terephthalate as the raw material, a film with no early rupture can be provided. Furthermore, according to a preferred production method of the present invention, even when amorphous polyethylene terephthalate is used, excellent mechanical strength can be achieved by increasing the crystallinity and orientation in the film-forming process. Methods for lowering the moisture content of the raw material and methods for improving the crystallinity and mechanical strength will be described below in the explanations of the raw materials constituting the film and the film production method.

[0015] 1.4. Density The flame-retardant heat-shrinkable film of the present invention has a density of 1.20 g / cm ３ 1.35g / cm or more ３ The density in a preferred embodiment of the present invention contributes to improving flame retardancy. The flame retardant contained in the film of the present invention contributes to the formation of a carbonized coating when the film is burned, and this carbonized coating blocks oxygen in the air, thereby exhibiting flame retardancy. ３If the density is less than 1.35 g / cm, the number or size of microvoids increases, hindering the formation of a carbonized coating during combustion and deteriorating the flame retardancy, which is not preferable. ３ If the density exceeds 1.21 g / cm, the heat shrinkage rate when immersed in 80°C hot water for 10 seconds will be less than 30%, which is not preferable. ３ 1.34g / cm or more ３ More preferably, it is 1.22 g / cm or less. ３ 1.33g / cm or more ３ It is more preferable that the density is not more than 100%. Thus, in order to achieve excellent flame retardancy, it is important to maintain a high density. The means for achieving this will be described in the explanation of the film-forming method below.

[0016] 1.5. Intrinsic Viscosity The flame-retardant heat-shrinkable film of the present invention preferably has an intrinsic viscosity of 0.6 dl / g or more and 1.0 dl / g or less. In a preferred embodiment of the present invention, the intrinsic viscosity contributes to improved flame retardancy and initial breakage. When the intrinsic viscosity is less than 0.6 dl / g, the film falls to the ground before a large fire pool forms during a combustion test, increasing flame retardancy, but this is undesirable because mechanical strength may decrease and initial breakage may worsen. On the other hand, when the intrinsic viscosity exceeds 1.0 dl / g, the mechanical strength increases, improving initial breakage, but this is undesirable because flame retardancy may decrease. Furthermore, the melt viscosity of the polyester becomes too high, increasing resin pressure and potentially deforming the filter in the melt line, which is undesirable. As described above, there is a trade-off between flame retardancy and initial breakage, and in order to achieve both, the intrinsic viscosity is preferably 0.60 dl / g or more and 1.0 dl / g or less, more preferably 0.65 dl / g or more and 0.95 dl / g or less, and even more preferably 0.70 dl / g or more and 0.90 dl / g or less.

[0017] 1.6. Thickness The thickness of the film of the present invention is not particularly limited, but is preferably 5 μm or more and 100 μm or less. A film thickness of less than 5 μm is not preferred because the strength of the film itself is insufficient and there is a risk of it breaking when used as a coating material. Furthermore, a film thickness of more than 100 μm is not preferred because the chemical cost increases. The film thickness is more preferably 7 μm or more and 98 μm or less, and even more preferably 9 μm or more and 96 μm or less.

[0018] 2. Raw Materials Constituting the Film 2.1. Polyester Raw Materials The polyester component in the raw material composition used for the flame-retardant heat-shrinkable polyester film of the present invention preferably contains ethylene terephthalate units as the main component. A main component containing ethylene terephthalate units means that, based on 100 mol% of all resin components constituting the polyester, ethylene terephthalate units account for preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and even more preferably 75 mol% or more. In a preferred embodiment of the present invention, the polyester contains a polycarboxylic acid component, preferably a dicarboxylic acid component, more preferably terephthalic acid or a derivative thereof, as the main component, and a polyhydric alcohol component, preferably an aliphatic polyhydric alcohol having 4 or less carbon atoms, more preferably a diol component, and even more preferably ethylene glycol, as the main component. In a preferred embodiment, the dicarboxylic acid component suitable for the polycarboxylic acid component may be any of aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids, in addition to terephthalic acid constituting the ethylene terephthalate units. Examples of aromatic dicarboxylic acids include benzenecarboxylic acids such as isophthalic acid, orthophthalic acid, 5-tert-butylisophthalic acid, and 5-sodiumsulfoisophthalic acid; naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid; dicarboxybiphenyls such as 4,4'-dicarboxydiphenyl and 2,2,6,6-tetramethylbiphenyl-4,4'-dicarboxylic acid; 1,1,3-trimethyl-3-phenylindene-4,5-dicarboxylic acid and substituted products thereof; and 1,2-diphenoxyethane-4,4'-dicarboxylic acid and substituted products thereof. Examples of aliphatic carboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, pimelic acid, suberic acid, undecanoic acid, dodecanedicarboxylic acid, brassylic acid, tetradecanedicarboxylic acid, thapsic acid, nonadecanedicarboxylic acid, docosanedicarboxylic acid, and substituted products thereof, 4,4'-dicarboxycyclohexane, and substituted products thereof.Examples of alicyclic dicarboxylic acids include 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methyltetrahydrophthalic acid, etc. When two or more dicarboxylic acids are used in combination, the terephthalic acid component preferably accounts for 70 mol % or more, more preferably 80 mol % or more, even more preferably 90 mol % or more, and still more preferably 95 mol % or more of the polycarboxylic acid component (100 mol %) constituting the polyester.

[0019] An example of a suitable diol component as the polyhydric alcohol component of the polyester contained in the raw material composition is ethylene glycol, which constitutes the polyethylene terephthalate unit. Furthermore, aliphatic diols, alicyclic diols, and aromatic diols can all be used as diol components other than ethylene glycol. That is, in the present invention, ethylene glycol alone may be used as the diol component, or ethylene glycol may be used in combination with a diol component other than ethylene glycol. Examples of diol components other than ethylene glycol are as follows. Examples of aliphatic diols include diethylene glycol, propylene glycol, butanediol, 1,6-hexanediol, 1,10-decanediol, neopentyl glycol, 2-methyl-2-ethyl-1,3-propanediol, 2-diethyl-1,3-propanediol, and 2-ethyl-2-n-butyl-1,3-propanediol. Examples of alicyclic diols include 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol. Examples of aromatic diols include ethylene oxide adducts of bis(4'-β-hydroxyethoxyphenyl)sulfone and other bis(4'-β-hydroxyethoxyphenyl)sulfone compounds; xylylene glycol; and the like. Polyalkylene glycols such as polyethylene glycol and polypropylene glycol can also be used as diol components. Diols used in combination with ethylene glycol are preferably aliphatic diols and alicyclic diols. More preferred aliphatic diols are 1,4-butanediol and neopentyl glycol. More preferred alicyclic diols are 1,4-cyclohexanedimethanol. It is also a preferred embodiment that the polyhydric alcohol component contained in the polyester includes, in addition to ethylene glycol, at least one selected from the group consisting of 1,4-butanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol.

[0020] When two or more diol components are used in combination, the ethylene glycol component is preferably 50 mol % or more, more preferably 60 mol % or more, even more preferably 70 mol % or more, and particularly preferably 80 mol % or more, based on 100 mol % of the polyhydric alcohol components constituting the polyester.

[0021] The polyester contained in the raw material composition is composed of the acid component and diol component. To improve the properties of a heat-shrinkable film, it is preferable to use a combination of one or more acid components or diol components to prepare the polyester. The type and content of the combined monomer components may be determined appropriately based on the desired film properties, economic efficiency, and the like. The raw material composition also contains one or more polyesters. When only one polyester is contained, it may be a homopolyester (homopolymer) containing an ethylene terephthalate unit, or a copolymer polyester (copolymer). When two or more polyesters are mixed, it may be a mixture of copolymer polyesters, or a mixture of a copolymer polyester and a homopolyester with a desired composition. Copolymer polyesters generally have low melting points, which can make them difficult to handle during drying. Therefore, it is preferable to melt-blend a homopolyester (e.g., polyethylene terephthalate, polyethylene naphthalate, poly(1,4-cyclohexene diethylene terephthalate)) with a copolymer polyester. In a preferred embodiment of the present invention, when a heat-shrinkable polyester film is produced, it is preferred that the aliphatic dicarboxylic acid unit accounts for 1 to 2 mol % of the total polyester. By controlling the content within this range, the onset temperature of heat shrinkage can be controlled within a preferred range.

[0022] The method for melt-blending two or more different polyesters is not particularly limited, and known methods such as an extruder or a heated mixer can be used. Among these, a method using an extruder equipped with a barrel and a screw is preferred. When using an extruder, two or more polyesters are charged and melt-blended by heating from the inside of the barrel and by heating due to friction between the barrel wall and the screw wall. The resulting mixture is then passed through a discharge device such as a melt line and a strand die to obtain a single polyester raw material. In a preferred embodiment of the present invention, before heating and melting the polyester, it is preferable to dry the polyester to a moisture content of 90 ppm or less using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer. Typically, the addition of a flame retardant reduces the intrinsic viscosity. In a preferred embodiment of the present invention, drying the polyester to a moisture content lower than usual allows a high intrinsic viscosity to be maintained even when a flame retardant is added. A moisture content of the polyester exceeding 90 ppm is undesirable because hydrolysis during melting of the polyester occurs due to interaction with the flame retardant, making it difficult to maintain an intrinsic viscosity IV of 0.6 dL / g or higher, resulting in increased initial breakage. The moisture content is more preferably 80 ppm or less, and even more preferably 70 ppm or less. The lower limit of the moisture content is 0 ppm, and the lower the better, but a practical lower limit of about 30 ppm is sufficient. When the polyester used is amorphous, the drying temperature is preferably 40°C or higher and 70°C or lower. A drying temperature of less than 40°C is undesirable because it is difficult to reduce the moisture content of the polyester to 90 ppm or less. On the other hand, a drying temperature exceeding 70°C is undesirable because not only does the polyester fuse in the dryer, but the polyester resins may fuse together and cause blocking. The drying temperature is more preferably 61°C or higher and 69°C or lower, and even more preferably 62°C or higher and 68°C or lower. The drying time is preferably 72 hours or longer. A drying time of less than 72 hours is undesirable because it may be difficult to reduce the moisture content of the polyester resin to 90 ppm or less. The drying time is more preferably 84 hours or higher, and even more preferably 96 hours or higher. The lower the drying temperature, the longer the drying time must be, but if it is too long, the productivity will decrease, which is not preferable.When the polyester used is crystalline, the drying temperature is preferably 100°C or higher and 180°C or lower. Drying temperatures below 100°C are undesirable because it is difficult to reduce the moisture content of the polyester to 90 ppm or less. Drying temperatures above 180°C are undesirable because the polyester may decompose. The drying temperature is more preferably 110°C or higher and 170°C or lower, and even more preferably 120°C or higher and 160°C or lower. Furthermore, the drying time in the dryer is preferably 3 hours or longer. Drying times of less than 3 hours are undesirable because it may be difficult to reduce the moisture content of the polyester resin to 90 ppm or less. Drying times of 4 hours or higher are more preferable, and 5 hours or higher are even more preferable. As with amorphous polyesters, drying times that are too long are undesirable because they reduce productivity. Regarding crystalline polyesters and amorphous polyesters, for example, polyesters that show a clear endothermic peak temperature in melting point measurement using a differential scanning calorimeter may be considered crystalline polyesters, and polyesters that do not show a clear endothermic peak temperature in melting point measurement may be considered amorphous polyesters. Alternatively, a polyester containing an amorphous component may be used as the amorphous polyester.

[0023] The heating temperature (melting temperature) during melt blending is preferably 200°C or higher and 280°C or lower. A heating temperature lower than 200°C is undesirable because not only does transesterification not proceed sufficiently, but the melt viscosity of the polyester becomes too high, increasing the resin pressure and deforming the filter in the melt line. A heating temperature higher than 280°C is preferable because transesterification is promoted, but it promotes interaction with the flame retardant and thermal decomposition of the polyester, making it difficult to achieve an intrinsic viscosity IV of 0.6 dL / g or higher. In addition to controlling the moisture content during drying as described above as a preferred embodiment of the present invention, melting the melt blend at a temperature lower than that of ordinary polyester resins is effective in increasing the intrinsic viscosity. The heating temperature is more preferably 205°C or higher and 275°C or lower, and even more preferably 210°C or higher and 270°C or lower. The residence time in the melt line is preferably 1 minute or higher and 15 minutes or lower. A residence time of less than 1 minute is undesirable because transesterification does not proceed sufficiently. A residence time of more than 15 minutes is undesirable because it will cause the thermal decomposition of the polyester to proceed, and the intrinsic viscosity IV will tend to become less than 0.6 dL / g. The operation of melting two or more polyesters to proceed with transesterification as described above may be carried out not only once but also twice or more times, and can be freely set within a range in which the degree of transesterification is 25% or less and the intrinsic viscosity IV is 0.6 dL / g or more as a guide.

[0024] The polyesters in the raw material compositions can be produced by conventional methods. For example, polyesters can be prepared by a direct esterification method in which a dicarboxylic acid and a diol are directly reacted, or a transesterification method in which a dicarboxylic acid dimethyl ester is reacted with a diol. The preparation can be carried out by either a batch method or a continuous method.

[0025] 2.2. Flame Retardant The flame retardant is not particularly limited as long as it imparts flame retardancy. For example, phosphorus-based flame retardants, metal hydroxide-based flame retardants, antimony-based flame retardants, and metal phosphinate-based flame retardants can be used. It is preferable to use a halogen-free flame retardant. Among these, phosphorus-based flame retardants, metal phosphinate-based flame retardants, or mixtures thereof are more preferred because they can suppress roll contamination during the manufacturing process. These flame retardants can be incorporated into the film by blending them with the film raw materials, thereby achieving the excellent flame retardancy desired by the present invention.

[0026] For example, phosphorus-based flame retardants include phosphine oxide compounds, phosphonate compounds, and phosphate ester compounds. Metal hydroxide-based flame retardants include magnesium hydroxide, calcium hydroxide, and aluminum hydroxide. Antimony-based flame retardants include antimony trioxide, antimony pentoxide, and sodium antimonate. Metal phosphinate-based flame retardants include aluminum phosphinate compounds, calcium dimethylphosphinate, calcium methylethylphosphinate, calcium diethylphosphinate, calcium phenylphosphinate, calcium biphenylphosphinate, magnesium dimethylphosphinate, magnesium methylethylphosphinate, magnesium diethylphosphinate, magnesium phenylphosphinate, magnesium biphenylphosphinate, aluminum dimethylphosphinate, aluminum methylethylphosphinate, aluminum diethylphosphinate, aluminum phenylphosphinate, and aluminum biphenylphosphinate. Flame retardants may be used alone or in combination of two or more.

[0027] The preferred amount of phosphorus-based or metal phosphinate-based flame retardants is, based on 100% by mass of the polyester film raw material composition, preferably 1.3 to 8.7% by weight, more preferably 1.5 to 8.5% by weight, and particularly preferably 2.0 to 8.0% by weight. In a preferred embodiment, a flame retardant amount of 1.3% by weight or more provides sufficient flame retardancy when used as a coating material, achieving a VTM-2 or higher in the UL94-VTM test, which is the objective of the present invention. On the other hand, a flame retardant amount exceeding 8.7% by weight is undesirable because the intrinsic viscosity of the film falls below 0.60 dl / g, reducing mechanical strength and increasing initial breakage. Furthermore, the thermal shrinkage rate also decreases, resulting in poor appearance and poor bundling after coating, which is undesirable.

[0028] 2.3. Phosphorus Atom Concentration In a preferred embodiment of the present invention, a phosphorus-based compound is contained as a flame retardant, and the phosphorus atom concentration in the polyester film of the present invention is preferably 0.3 wt% or more and 2.0 wt% or less, based on 100 wt% of the weight of the polyester film. The lower limit of the phosphorus atom concentration is more preferably 0.4 wt%, and even more preferably 0.5 wt%. Meanwhile, the upper limit of the phosphorus atom concentration is more preferably 1.96 wt%, and even more preferably 1.84 wt%. A phosphorus atom concentration below 0.3 wt% is not preferred because flame retardancy is not exhibited. Meanwhile, a phosphorus atom concentration above 2.0 wt% is not only less than 0.6 dl / g intrinsic viscosity, but also less than 1.20 g / cm. ３ This is undesirable because it deteriorates the initial breakage and does not exhibit flame retardancy.

[0029] 2.4. Additives Other Than Flame Retardants In addition to the polyester and flame retardant, various known additives may be added to the raw material composition as needed. Examples of additives include inert particle lubricants, such as inorganic particles of silica, titania, mica, talc, calcium carbonate, etc., and organic particles of polymethyl methacrylate (PMMA), styrene-divinylbenzene, formaldehyde resin, silicone resin, polyamideimide, benzoguanamine, etc., as well as surface-treated versions of these. However, this tends to reduce the transparency of the film due to surface irregularities, so it is recommended to adjust the amount added appropriately depending on the desired transparency. In addition, preferred organic lubricants include paraffin wax, microwax, polypropylene wax, polyethylene wax, ethylene acrylic wax, stearic acid, behenic acid, 12-hydroxystearic acid, stearic acid amide, oleic acid amide, erucic acid amide, methylene bisstearic acid amide, ethylene bisstearic acid amide, ethylene bisoleic acid amide, butyl stearate, stearic acid monoglyceride, pentaerythritol tetrastearate, hydrogenated castor oil, stearyl stearate, siloxane, higher alcohol polymers, stearyl alcohol, calcium stearate, zinc stearate, magnesium stearate, and lead stearate. Among these, the addition of low-molecular-weight polyethylene wax is expected to improve lubricity by smoothing the layer surface and preventing sticking. In addition to the above, ultraviolet absorbers and colorants (dyes, etc.) can also be added depending on the purpose.

[0030] 3. Film Production Conditions 3.1. Melt Extrusion The film of the present invention can be obtained by melt-extruding a raw material resin composition obtained by mixing the polyester raw material described in 2.1. "Polyester Raw Material" above and a flame retardant using an extruder to form an unstretched film, and then stretching the unstretched film by the following predetermined method.

[0031] For example, the polyester resin can be obtained by polycondensing a dicarboxylic acid component and a diol component and selecting their types and amounts so as to contain an appropriate amount of a monomer other than ethylene terephthalate, as described above. Also, two or more types of polyester chips can be mixed and used as a raw material for the polyester-based resin layer.

[0032] As a method for melt-extrusion of the raw material resin, a known method similar to that described in 3.1. "Types of Polyester Raw Materials" above can be used, with a method using an extruder equipped with a barrel and a screw being preferred. The polyester raw material for each layer is preferably dried in advance using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer, until the moisture content is 90 ppm or less, more preferably 80 ppm or less, and even more preferably 70 ppm or less. The moisture content is measured using a Karl Fischer moisture meter (manufactured by Mitsubishi Chemical Corporation, Model CA-100) with a sample weight of 1 g at 200°C. After drying the polyester raw material for each layer in this manner, it is melted and extruded into a laminated film using an extruder at a temperature of 200 to 280°C. Any known extrusion method, such as a T-die method or a tubular method, can be used. The extrusion temperature is preferably 200°C or higher and 280°C or lower. If the extrusion temperature is less than 200°C, not only will the transesterification not proceed sufficiently, but the melt viscosity of the polyester resin will become too high, increasing the extrusion pressure and causing deformation of the filter in the melt line, which is undesirable. If the heating temperature exceeds 280°C, the transesterification is promoted, which is preferable, but the interaction with the flame retardant and the thermal decomposition of the resin will proceed, making it difficult to achieve a melt viscosity IV of 0.60 dL / g or more. The extrusion temperature is more preferably 205°C or higher and 275°C or lower, and even more preferably 210°C or higher and 270°C or lower. The residence time in the melt line is preferably 1 minute or higher and 15 minutes or lower. If the residence time is less than 1 minute, the transesterification will not proceed sufficiently, which is undesirable. If the residence time exceeds 15 minutes, the thermal decomposition of the polyester resin will proceed, making it easier for the IV to become less than 0.60 dL / g, which is undesirable.

[0033] Thereafter, the film melted by extrusion can be rapidly cooled to obtain an unstretched film. A suitable method for rapidly cooling the molten resin is to cast the molten resin from a die onto a rotating drum and rapidly solidify it to obtain a substantially unoriented resin sheet. The film can be produced by either uniaxial stretching (stretching in at least one of the longitudinal (length) direction and the transverse (width) direction) or biaxial stretching. From the viewpoints of mechanical strength, productivity, and shrinkage finish, biaxial stretching is preferred. The following description will focus on transverse uniaxial stretching; sequential biaxial stretching in which longitudinal stretching is followed by transverse stretching; longitudinal uniaxial stretching; and sequential biaxial stretching in which longitudinal stretching is followed by transverse stretching. However, simultaneous biaxial stretching, in which stretching is performed simultaneously in the longitudinal and transverse directions, may also be used.

[0034] The stretching process will be described below for the cases where the main shrinkage direction of the film is the transverse direction and the longitudinal direction.

[0035] 3.2. When the Main Shrinkage Direction is the Transverse Direction Either transverse uniaxial stretching or biaxial stretching (transverse stretching after longitudinal stretching) is possible. 3.2-1. Transverse Uniaxial Stretching Stretching in the first direction (transverse or width direction) is preferably performed in a tenter with both ends of the film in the width direction (the direction perpendicular to the longitudinal direction) held with clips at 65°C to 90°C, at a stretching rate of 5% / sec to 13% / sec, and at a stretch ratio of approximately 3.0 to 5.0. The flame retardant used in the present invention has poor compatibility with polyethylene terephthalate resin, and during stretching, microvoids are formed from the flame retardant portion, resulting in a decrease in density. In a preferred embodiment of the present invention, void formation is suppressed by slowing the stretching speed compared to that of ordinary polyethylene terephthalate, allowing high density to be maintained even when a flame retardant is contained, thereby demonstrating excellent flame retardancy. As described below, the appropriate stretching speed ranges differ between transverse and longitudinal stretching. During transverse stretching, a stretching speed exceeding 13% / sec is undesirable because it promotes void formation, reducing density and potentially impairing flame retardancy. On the other hand, a speed below 5% / sec is undesirable because it results in insufficient film orientation, resulting in a decrease in heat shrinkage and mechanical strength. Preheating is preferably performed before transverse stretching, preferably until the film surface temperature reaches 95°C to 150°C. Preheating at a high temperature improves crystallinity before stretching in the width direction, increasing crystallinity and orientation after stretching, thereby increasing mechanical strength and suppressing early breakage. Therefore, even when using low-strength polyester resins such as amorphous polyethylene terephthalate, sufficient strength can be achieved for coating applications. Thus, the ability to achieve sufficient strength even when using soft, amorphous raw materials is another feature of this patent. It is also recommended to pass the film through a heating zone at 30°C to 150°C for 1 to 30 seconds after stretching.Furthermore, if necessary, the film may be placed in this heating zone, and while both widthwise edges of the film are held by clips inside the tenter, the film may be relaxed by narrowing the tenter in the width direction at a temperature of 60°C to 100°C so that the relaxation rate calculated by the following formula (2) is in the range of 0% to 10% in the width direction (a relaxation rate of 0% means that no relaxation is performed): Relaxation rate = {(length before relaxation - length after relaxation) / length before relaxation} × 100 (%) (2) By performing such a treatment, the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction can be suppressed, improving the appearance after shrinkage.

[0036] 3.2-2. Biaxial Stretching (Transverse Stretching After Longitudinal Stretching) If necessary, it is also possible to stretch the film in the longitudinal direction before transverse stretching as described above in 3.2-1. The cooled and solidified unstretched film may be introduced into a longitudinal stretching machine having multiple roll groups arranged in series and stretched longitudinally. It is preferable to preheat the film using preheating rolls until the film temperature reaches 65°C to 90°C, and then stretch the film longitudinally at a stretching speed of 200% / sec or more and 300% / sec or less, to approximately 1.1 to 1.8 times. A stretching speed exceeding 300% / sec is undesirable because it promotes void formation, reduces density, and may deteriorate flame retardancy. On the other hand, a speed below 200% / sec is undesirable because it results in insufficient film orientation, worsening thickness unevenness in the longitudinal direction and reducing mechanical strength. A film temperature lower than 65°C is undesirable because it becomes difficult to stretch in the longitudinal direction and is prone to breakage. Furthermore, if the temperature is higher than 90°C, the film tends to stick to the roll, which is likely to cause the film to wrap around the roll or to stain the roll during continuous production, which is undesirable. Furthermore, if the stretching ratio exceeds 1.8 times, the heat shrinkage rate in the direction perpendicular to the main shrinkage direction increases, which is undesirable because it deteriorates the appearance after coating. In addition to increasing the preheating temperature during transverse stretching, introducing longitudinal stretching before transverse stretching in this way can achieve high orientation, which improves mechanical strength and makes it possible to suppress early breakage.

[0037] 3.3. When the Main Shrinkage Direction is the Longitudinal Direction 3.3-1. Longitudinal Uniaxial Stretching The cooled and solidified unstretched film is preferably introduced into a longitudinal stretching machine with multiple roll groups arranged in series and longitudinally stretched. It is preferable to preheat the film using preheating rolls until the film temperature reaches 65°C to 150°C, and then longitudinally stretch the film at a stretching speed of 200% / sec to 300% / sec, approximately 3.0 to 6.0 times. A stretching speed exceeding 300% / sec is undesirable because it promotes void formation, reduces density, and may deteriorate flame retardancy. On the other hand, a speed below 200% / sec is undesirable because it results in insufficient film orientation, worsening thickness unevenness in the longitudinal direction, and reducing the thermal shrinkage and mechanical strength. A film temperature below 65°C is undesirable because it becomes difficult to stretch in the longitudinal direction and is prone to breakage. Furthermore, if the temperature is higher than 150°C, the film tends to stick to the roll, and the film tends to wrap around the roll or become dirty during continuous production, which is undesirable. Furthermore, if the stretching ratio is less than 3.0 times, thickness unevenness in the longitudinal direction worsens, which is undesirable. Furthermore, if the stretching ratio is more than 6.0 times, stretching becomes difficult during longitudinal stretching, and breakage is likely to occur, which is undesirable.

[0038] 3.3-2. Biaxial Stretching (Transverse Stretching Followed by Longitudinal Stretching) Stretching in the first direction (transverse or width direction) is preferably performed in a tenter with both ends of the film in the width direction (the direction perpendicular to the longitudinal direction) held with clips at 65°C to 90°C and a stretching speed of 5% / sec to 13% / sec, approximately 1.2 to 5.0 times the original length. A stretching speed exceeding 13% / sec is undesirable because it promotes void formation, reducing density and potentially deteriorating flame retardancy. On the other hand, a speed below 5% / sec is undesirable because it results in insufficient film orientation, resulting in a decrease in heat shrinkage and mechanical strength. Preheating is preferably performed until the film surface temperature reaches 95°C to 150°C. It is also recommended that the film be passed through a heating zone at 30°C to 150°C for 1 to 30 seconds after stretching. Furthermore, if necessary, the film may be placed in this heating zone, and while both ends in the width direction within the tenter are held with clips, the film may be relaxed by narrowing the tenter in the width direction at a temperature of 60° C. to 100° C. so that the relaxation rate calculated by equation (2) is in the range of 0% to 10% in the width direction (a relaxation rate of 0% means that no relaxation is performed). By carrying out such a treatment, the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction can be suppressed, and the appearance after shrinkage can be improved.

[0039] After the first (transverse) stretching and heat treatment, the film is preferably introduced into a longitudinal stretching machine having a plurality of rolls arranged in series for second (longitudinal) stretching. For longitudinal stretching, it is preferable to preheat the film using a preheating roll until the film temperature reaches 65°C to 150°C, and then longitudinally stretch the film at a stretching speed of 200% / sec to 300% / sec at a ratio of 2.0 to 5.0. A stretching speed exceeding 300% / sec is undesirable because it promotes void formation, reduces density, and may deteriorate flame retardancy. On the other hand, a stretching speed below 200% / sec is undesirable because it results in insufficient film orientation, worsening thickness unevenness in the longitudinal direction, and reducing heat shrinkage and mechanical strength. A film temperature lower than 65°C is undesirable because it is difficult to stretch in the longitudinal direction and breaks easily. On the other hand, a temperature higher than 150°C is undesirable because the film is prone to sticking to the rolls, causing the film to wrap around the rolls and contaminating the rolls during continuous production. Furthermore, if the stretching ratio is less than 2.0, the heat shrinkage rate in the main shrinkage direction (longitudinal) decreases, resulting in poor appearance and poor bundling when the film is applied to an object, which is undesirable. Furthermore, if the stretching ratio is more than 5.0, the film becomes difficult to stretch in the longitudinal direction, which makes it more likely to break, which is undesirable. Similar to biaxial stretching in which the main shrinkage direction is transverse, high orientation by biaxial stretching makes it possible to suppress initial breakage.

[0040] 3.3-3. Biaxial Stretching (Transverse Stretching After Longitudinal Stretching) Stretching in the first direction (longitudinal or machine direction) is preferably performed by introducing a cooled and solidified unstretched film into a longitudinal stretching machine with multiple roll groups arranged in series and longitudinally stretching it. It is preferable to preheat the film using preheating rolls until the film temperature reaches 65°C to 150°C, and then longitudinally stretch the film at a stretching speed of 200% / sec or more and 300% / sec or less, approximately 3.0 to 6.0 times. A stretching speed exceeding 300% / sec is undesirable because it promotes void formation, reduces density, and may deteriorate flame retardancy. On the other hand, a speed below 200% / sec is undesirable because it results in insufficient film orientation, worsening thickness unevenness in the longitudinal direction, and reducing heat shrinkage and mechanical strength. A film temperature below 65°C is undesirable because it becomes difficult to stretch in the longitudinal direction and is prone to breakage. Furthermore, if the temperature is higher than 150°C, the film tends to stick to the roll, which is likely to cause the film to wrap around the roll or to become soiled during continuous production, which is undesirable. Furthermore, if the stretching ratio is less than 3.0 times, the longitudinal heat shrinkage rate decreases, which is undesirable, resulting in poor appearance and poor bundling when the film is applied to an object. Furthermore, if the stretching ratio is more than 6.0 times, it becomes difficult to stretch the film in the longitudinal direction, which is undesirable, and breakage is likely to occur.

[0041] The film after the first (transverse) stretching is introduced into a tenter, and while both edges of the film in the width direction (the direction perpendicular to the longitudinal direction) are held with clips in the tenter, it is preferably stretched transversely at a stretching rate of 5% / sec or more and 13% / sec or less, approximately 1.2 to 1.8 times, at 65 to 90°C. A stretching rate exceeding 13% / sec is undesirable because it promotes void formation, reducing density and potentially deteriorating flame retardancy. On the other hand, a stretching rate below 5% / sec is undesirable because it results in insufficient film orientation and reduced mechanical strength. A stretching rate exceeding 1.8 times is undesirable because it reduces the shrinkage rate in the main shrinkage direction (longitudinal) and increases the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction (transverse), thereby deteriorating the appearance after coating when used as a coating material. Preheating is preferably performed until the film surface temperature reaches 95 to 150°C. It is also recommended that the film be passed through a heating zone at 30 to 150°C for 1 to 30 seconds after stretching. Furthermore, if necessary, the film may be placed in this heating zone, and while both ends in the width direction within the tenter are held with clips, the film may be relaxed by narrowing the tenter in the width direction at a temperature of 60° C. to 100° C. so that the relaxation rate calculated by equation (2) is in the range of 0% to 10% in the width direction (a relaxation rate of 0% means that no relaxation is performed). By carrying out such a treatment, the thermal shrinkage rate in the direction perpendicular to the main shrinkage direction can be suppressed, and the appearance after shrinkage can be improved.

[0042] 3.4. Final Heat Treatment and Width Direction Relaxation Treatment (Relaxation Treatment) After the second (longitudinal) stretching, heat treatment is preferably performed in the final heat treatment zone at 60°C or higher and 120°C or lower. Temperatures below 60°C are undesirable because the maximum shrinkage stress exceeds 15.0 MPa, which may cause deformation of the object when the film is applied to the object as a covering material. On the other hand, temperatures above 120°C are undesirable because the maximum shrinkage rate falls below 30%, which may cause insufficient shrinkage and wrinkles when the film is applied to the object as a covering material.

[0043] Furthermore, if necessary, during the final heat treatment, it is preferable to carry out the relaxation treatment described in [3.2-1. First Axial Stretching] at a temperature range of 60°C to 100°C so that the relaxation ratio in the width direction is in the range of 0% to 30%. Temperatures below 60°C for the relaxation treatment are undesirable because the film does not shrink sufficiently upon relaxation, resulting in the formation of wrinkles. Temperatures above 100°C are also undesirable because the shrinkage ratio decreases significantly, resulting in insufficient shrinkage when used as a heat-shrinkable film. The temperature at which the relaxation treatment is carried out is more preferably 65°C to 95°C, particularly preferably 70°C to 90°C. The final heat treatment step and the relaxation step serve to reduce the maximum shrinkage ratio and maximum shrinkage stress generated by stretching.

[0044] The time for passing through the final heat treatment zone is preferably 2 to 20 seconds. If the time is 2 seconds or less, the film passes through the heat treatment zone before the surface temperature of the film reaches the set temperature, making the heat treatment meaningless. If the time is 20 seconds or more, the maximum shrinkage rate may fall below 10%, which is not preferable. A time of 3 to 18 seconds is more preferable, and a time of 5 to 16 seconds is even more preferable.

[0045] 3.5. Surface Treatment The heat-shrinkable polyester film of the present invention may be surface-treated on either or both of its surface layers. Examples of surface treatments include corona treatment, plasma treatment, flame treatment, sandblasting, and coating. These surface treatments are intended to improve adhesion and charging properties, and can be applied within the scope of the present invention. Furthermore, a flame-retardant coating can be applied during the coating process. This can help achieve the flame retardancy desired in this patent. The timing of the surface treatment can be selected as desired, either during or after film formation.

[0046] 4. Packaging 4.1. Manufacturing Method of Annular Label The label of the present invention uses at least a portion of the flame-retardant heat-shrinkable polyester film of the present invention, and the flame-retardant heat-shrinkable polyester film of the present invention may be made of itself or may be bonded to another film. The length (circumferential length) of the label and the number of bonded portions may be arbitrary. As the other film constituting the label of the present invention, any conventionally known film may be used in any length. The material of the film may also be arbitrary, and examples thereof include polyester, polyolefin, polyamide, etc.

[0047] Adhesion methods required to produce the label of the present invention include solvent-based center sealing, heat sealing, ultrasonic sealing, and methods using hot glue (hot melt) or cold glue. Of these, solvent-based center sealing, heat sealing, or ultrasonic sealing is preferred. When using solvent-based center sealing, solvents such as 1,3-dioxolane and tetrahydrofuran can be used, but are not limited to these. Heat seal strength varies depending on the temperature, pressure, and sealing time of the heat seal bar (the surface that contacts the film), and is determined by the combination of these conditions. For example, even if the heat seal temperature is increased, the actual temperature applied to the film will be lower if the sealing time is shortened. As an example, the heat seal temperature is preferably 100°C or higher and 180°C or lower, more preferably 110°C or higher and 170°C or lower, and even more preferably 120°C or higher and 160°C or higher. If the heat seal temperature is lower than 100°C, the heat seal strength is likely to fall below 20 N / 15 mm. A heat-sealing temperature above 180°C improves the heat-sealing strength and is therefore preferable, but the film is more susceptible to thermal shrinkage, which may result in changes in the label dimensions at the heat-sealed portion and a deterioration in appearance. The heat-sealing pressure is preferably 0.05 MPa or more and 0.6 MPa or less, more preferably 0.1 MPa or more and 0.55 MPa or less, and even more preferably 0.15 MPa or more and 0.5 MPa or less. If the pressure is below 0.05 MPa, the seal bar will not transfer sufficient heat to the film, and the heat-sealing strength is likely to fall below 20 N / 15 mm. As far as the inventors have investigated, if the pressure is higher than 0.05 MPa, there is no significant change in the heat-sealing strength, but if it is higher than 0.6 MPa, there is a risk of the film tearing.

[0048] The heat sealing time is preferably 0.1 seconds or more and 3 seconds or less, more preferably 0.2 seconds or more and 2.9 seconds or less, and even more preferably 0.3 seconds or more and 2.8 seconds or less. If the sealing time is less than 0.1 seconds, the heat seal strength is likely to fall below 20 N / 15 mm. If the sealing time exceeds 3 seconds, the heat seal strength is improved, which is preferable, but this is not preferable because it goes against the purpose of the present invention of improving productivity. There are no limitations on the objects to be packaged with the label of the present invention, and examples include plastic containers, PET bottles, electronic components, etc., which have a square or round shape.

[0049] 4.2. Manufacturing Method of Packages When the film of the present invention is used as a covering material, it is preferable to adhere it to an object by the manufacturing method described above and then heat-shrink the covering material, which creates a taut feel and a beautiful appearance. The method for heat-shrinking the covering material is not particularly limited, and known methods such as blowing hot air and / or steam using a heating tunnel, immersion in warm water, contact with a hot plate, atmospheric heating, and microwaves can be used. Among these methods, blowing hot air and / or steam is preferred in consideration of the effects on the contents. Furthermore, using a conveying device such as a belt conveyor in combination with the covering material for heat-shrinkage is also preferred because it improves productivity. Taking these factors into consideration, it is most preferable to use a steam tunnel equipped with a belt conveyor and a mechanism for blowing hot air and / or steam. The steam-blowing conditions are not particularly limited and can be freely changed as long as they do not cause deformation of the object. The temperature inside the steam tunnel or the temperature of the hot air needs to be set taking into account the heat-shrinkability characteristics of the film. In one example of the present invention, the temperature of the steam tunnel is preferably 70°C or higher and 100°C or lower. If the temperature inside the steam tunnel is below 70°C, the temperature may not reach a sufficient level for the covering material to shrink. Furthermore, the hot air temperature is preferably 80°C or higher and 150°C or lower. If the hot air temperature is below 80°C, the temperature may not reach a sufficient level for the covering material to shrink. If the hot air temperature exceeds 150°C, the covering material will not only be thermally contracted excessively, making the object more likely to deform, but the object itself will also be more likely to thermally deform, which is undesirable. The hot air temperature is more preferably 90°C or higher and 140°C or lower, and even more preferably 100°C or higher and 130°C or lower. Furthermore, the hot air speed is preferably 1 m / s or higher and 20 m / s or lower. If the hot air speed is less than 1 m / s, the covering material may not reach a sufficient level for shrinking. If the hot air speed exceeds 20 m / s, not only will the covering material be more likely to deform, but the object will also be more likely to be blown away by the hot air, which could reduce productivity. The velocity of the hot air is more preferably 2 m / sec or more and 19 m / sec or less, and even more preferably 3 m / sec or more and 18 m / sec or less.The residence time in the heating tunnel is preferably 2 seconds or more and 50 seconds or less. If the residence time is less than 2 seconds, the temperature may not reach a level sufficient for the covering material to shrink. If the residence time exceeds 50 seconds, not only is excessive thermal shrinkage of the covering material likely to cause deformation of the object, but productivity also decreases, which is undesirable. A residence time of 3 seconds or more and 49 seconds or less is more preferable, and 4 seconds or more and 48 seconds or less is even more preferable. In addition to these hot air blowing conditions, it is preferable to adjust the blowing position (air flow) so that the hot air hits only the lid material, as this suppresses thermal deformation of the object itself.

[0050] This application claims the benefit of priority based on Japanese Application No. 2023-193905, filed on November 14, 2023. The entire contents of the specification of Japanese Application No. 2023-193905, filed on November 14, 2023, are incorporated herein by reference.

[0051] Next, the present invention will be specifically explained using examples and comparative examples, but the present invention is not limited to the embodiments of these examples and can be appropriately modified within the scope of the present invention.

[0052] <Preparation of Polyester Raw Materials> [Synthesis Example 1] A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 100 mol% dimethyl terephthalate (DMT) as a dicarboxylic acid component and 100 mol% ethylene glycol (EG) as a polyhydric alcohol component, with the ethylene glycol being 2.2 times the molar ratio of dimethyl terephthalate. Using 0.05 mol% (relative to the acid component) of zinc acetate as a transesterification catalyst, a transesterification reaction was carried out while distilling off the resulting methanol. Subsequently, 0.225 mol% (relative to the acid component) of antimony trioxide was added as a polycondensation catalyst, and a polycondensation reaction was carried out at 280°C under reduced pressure of 26.7 Pa to obtain a polyester A with an intrinsic viscosity of 0.75 dL / g. This polyester (A) was polyethylene terephthalate. The composition of polyester A is shown in Table 1.

[0053] Synthesis Example 2 Polyesters B to H were obtained by changing the monomers using the same procedure as in Synthesis Example 1. The composition of each polyester is shown in Table 1. In Table 1, TPA is terephthalic acid, IPA is isophthalic acid, BD is 1,4-butanediol, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, and DEG is diethylene glycol. In addition, when polyester F was produced, SiO ２ A flame retardant (Sylysia 266 manufactured by Fuji Silysia Ltd.) was added at a ratio of 7,000 ppm to the polyester. Furthermore, during the production of polyester G, a flame retardant aluminum phosphinate (Clariant Exolit OP series powder OP1240: phosphorus atom content 23 wt%) was added at a ratio of 20 wt% to the polyester. Polyester H has the same composition as polyester A, but is designed to have a higher intrinsic viscosity. Each polyester was appropriately cut into chips. The intrinsic viscosity (IV) of each polyester was: (B) 0.87 dL / g, (C) 0.73 dL / g, (D) 0.77 dL / g, (E) 0.80 dL / g, (F) 0.75 dL / g, (G) 0.53 dL / g, and (H) 1.32 dL / g. The compositions of polyesters B to H are shown in Table 1.

[0054] [Example 1] Polyester resins A, E, F, and G were dried under vacuum at 140°C for 10 hours, and polyester resin C was dried at 75°C for 100 hours to a moisture content of 85 ppm. Polyester A, polyester C, polyester E, polyester F, and polyester G were mixed (dry blended) in a mass ratio of 10:60:10:5:15, then fed into a screw extruder and heated to 265°C to melt and mix the mixture so that the melt line residence time was 5 minutes. The molten resin was continuously extruded from a T-die and cooled on a chill roll set at a surface temperature of 30°C to obtain an unstretched laminated film with a thickness of 135 μm. The take-up speed of the unstretched film (rotational speed of the metal roll) was approximately 10.0 m / min. The unstretched film obtained after cooling and solidification was introduced into a tenter and preheated for 8 seconds until the film temperature reached 100°C, after which it was stretched 4.5 times in the width direction (transverse direction) at a stretching speed of 11% / sec. After transverse stretching, the film was directly introduced into a heat treatment zone and heat-treated at 80°C for 4.8 seconds to obtain a uniaxially stretched film with a thickness of 30 μm. The properties of the obtained film were evaluated using the methods described above. The production conditions and evaluation results are shown in Table 3.

[0055] [Example 2] Polyester resins B, E, F, and G were dried in a vacuum at 120°C for 20 hours, and polyester resin C was dried by heating at 70°C for 144 hours to a moisture content of 75 ppm. Film formation was performed in the same manner as in Example 1, except that polyester B, polyester C, polyester E, polyester F, and polyester G were mixed in a mass ratio of 17:60:10:5:8, yielding a biaxially stretched film with a thickness of 30 μm. The evaluation results are shown in Table 3.

[0056] [Example 3] Polyester resins E, F, and G were dried in a vacuum at 160°C for 5 hours, and polyester resin C was dried by heating at 78°C for 80 hours to a moisture content of 70 ppm. Film formation was performed in the same manner as in Example 1, except that polyester C, polyester E, polyester F, and polyester G were mixed in a mass ratio of 55:5:5:35, to obtain a biaxially stretched film with a thickness of 30 μm. The evaluation results are shown in Table 3.

[0057] Example 4: The unstretched film was stretched 4.5 times in the transverse direction at 11% / sec in a tenter in the same manner as in Example 1, except that the take-up speed (rotational speed of the metal roll) of the unstretched film was adjusted to approximately 4.4 m / min and the thickness was adjusted to 304 μm. The transversely stretched film was then introduced directly into a heat treatment zone and heat-treated at 100°C for 4.8 seconds. Simultaneously with the heat treatment, the clip spacing in the film width direction was narrowed to perform a 3% relaxation treatment in the width direction, resulting in a transversely uniaxially stretched film with a thickness of 70 μm. The heat-treated film was introduced into a longitudinal stretching machine equipped with multiple roll groups arranged in series, preheated on a preheating roll until the film temperature reached 75°C, and then stretched 2.7 times at a stretching speed of 300% / sec between a low-speed stretching roll set at a surface temperature of 60°C and a high-speed stretching roll whose internal circulating water temperature was set at 30°C. The speed of the low-speed roll (the speed of the film moving together with the low-speed roll) was adjusted to 4.4 m / min., and the speed of the high-speed roll (the speed of the film moving together with the high-speed roll) was adjusted to 11.9 m / min., thereby obtaining a biaxially stretched film with a thickness of 30 μm. The evaluation results are shown in Table 3.

[0058] [Example 5] Polyester resins B, F, and G were dried by heating under vacuum at 140°C for 10 hours, and polyester resin D was dried by heating at 65°C for 100 hours to a moisture content of 86 ppm. An unstretched film was obtained in the same manner as in Example 1, except that polyester B, polyester D, polyester F, and polyester G were mixed (dry blended) in a mass ratio of 10:70:5:15 and charged, the take-up speed (rotation speed of the metal roll) of the unstretched film was approximately 8.8 m / min, and the thickness was adjusted to 154 μm. The cooled and solidified unstretched film was introduced into a longitudinal stretching machine equipped with multiple roll groups arranged in series, preheated on a preheating roll until the film temperature reached 80°C, and then stretched 1.2 times at a stretching speed of 500% / sec between a low-speed stretching roll set at a surface temperature of 60°C and a high-speed stretching roll whose internal circulating water temperature was set at 30°C. The speed of the low-speed roll (the speed of the film moving with the low-speed roll) was adjusted to 8.8 m / min, and the speed of the high-speed roll (the speed of the film moving with the high-speed roll) was adjusted to 9.6 m / min, thereby obtaining a longitudinally uniaxially stretched film with a thickness of 128 μm. The longitudinally stretched film was introduced into a tenter and preheated for 7.7 seconds until the film temperature reached 80°C, after which it was stretched 4.5 times in the width direction (transverse direction) at 11% / sec. The transversely stretched film was then introduced directly into a heat treatment zone and heat-treated at 95°C for 4.6 seconds to obtain a biaxially stretched film with a thickness of 30 μm. The properties of the obtained film were evaluated using the methods described above. The production conditions and evaluation results are shown in Table 3.

[0059] [Example 6] Polyester resins B, F, and G were dried by heating under vacuum at 140°C for 10 hours, and polyester resin D was dried by heating at 65°C for 100 hours to a moisture content of 82 ppm. An unstretched film was obtained in the same manner as in Example 1, except that polyester B, polyester D, polyester F, and polyester G were mixed (dry blended) in a mass ratio of 10:70:5:15 and charged, the take-up speed (rotation speed of the metal roll) of the unstretched film was approximately 7.8 m / min, and the thickness was adjusted to 173 μm. The cooled and solidified unstretched film was introduced into a longitudinal stretching machine equipped with multiple roll groups arranged in series, preheated on a preheating roll until the film temperature reached 80°C, and then stretched 4.8 times at a stretching speed of 500% / sec between a low-speed stretching roll set at a surface temperature of 60°C and a high-speed stretching roll whose internal circulating water temperature was set at 30°C. The speed of the low-speed roll (the speed of the film moving with the low-speed roll) was adjusted to 7.8 m / min, and the speed of the high-speed roll (the speed of the film moving with the high-speed roll) was adjusted to 37.4 m / min, thereby obtaining a longitudinally uniaxially stretched film with a thickness of 144 μm. The longitudinally stretched film was introduced into a tenter and preheated for 3.0 seconds until the film temperature reached 75°C, after which it was stretched 1.2 times in the width direction (transverse direction). The transversely stretched film was introduced directly into a heat treatment zone and heat-treated at 95°C for 2.0 seconds to obtain a biaxially stretched film with a thickness of 30 μm. The properties of the obtained film were evaluated using the methods described above. The production conditions and evaluation results are shown in Table 3.

[0060] Example 7: Polyester B, polyester F, and polyester G were mixed in a mass ratio of 77:8:15 and dried under vacuum in a hopper dryer at 140°C for 10 hours, resulting in a moisture content of 84 ppm. The dried mixed material was fed into a screw extruder, heated to 270°C, and melted and mixed so that the melt line residence time was 5 minutes. An unstretched film was obtained in the same manner as in Example 1, except that the take-up speed (metal roll rotation speed) of the unstretched film was approximately 11.3 m / min and the thickness was adjusted to 120 μm. The unstretched film obtained after cooling and solidification was then introduced into a tenter and preheated for 7.1 seconds until the film temperature reached 140°C, after which it was stretched 4.0 times in the width direction (transverse direction). After transverse stretching, the film was directly introduced into a heat treatment zone and heat-treated at 85°C for 4.3 seconds to obtain a uniaxially stretched film with a thickness of 30 μm. The evaluation results are shown in Table 3.

[0061] [Example 8] Polyester B, polyester F, and polyester G were mixed in a mass ratio of 77:8:15 and dried under vacuum in a hopper dryer at 160°C for 10 hours to adjust the moisture content of the mixed material to 62 ppm. The dried mixed material was fed into a screw extruder, heated to 270°C, and melted and mixed so that the melt line residence time was 5 minutes. A transversely uniaxially stretched film having a thickness of 81 μm was obtained in the same manner as in Example 2, except that the take-up speed (rotational speed of the metal roll) of the unstretched film was approximately 4.1 m / min and the thickness was adjusted to 324 μm. The heat-treated film was introduced into a longitudinal stretching machine equipped with multiple roll groups arranged in series, preheated on a preheating roll until the film temperature reached 130°C, and then stretched 2.7 times at a stretching speed of 500% / sec between a low-speed stretching roll set at a surface temperature of 60°C and a high-speed stretching roll with an internal circulating water temperature set at 30°C. The speed of the low-speed roll (the speed of the film moving together with the low-speed roll) was adjusted to 4.1 m / min., and the speed of the high-speed roll (the speed of the film moving together with the high-speed roll) was adjusted to 11.1 m / min., thereby obtaining a biaxially stretched film with a thickness of 30 μm. The evaluation results are shown in Table 3.

[0062] Comparative Example 1 Film production was carried out in the same manner as in Example 1, except that Polyester C, Polyester E, and Polyester G were mixed (dry blended) in a mass ratio of 50:5:10:45 and then added, to obtain a uniaxially stretched film with a thickness of 30 μm. The evaluation results are shown in Table 3. Although the appearance of the finished shrink film was relatively good, the intrinsic viscosity was below 0.6 dl / g because the flame retardant was added so that the phosphorus atom concentration in the polyester film was 2.1 wt% based on the weight of the polyester film. As a result, the initial break was poor and the film had poor mechanical strength. The density was also 1.20 g / cm ３ Since the flame retardancy was below this, the film did not exhibit flame retardancy, and the flame retardancy was insufficient for use as a covering material.

[0063] Comparative Example 2 A film was produced in the same manner as in Example 1, except that Polyester B, Polyester C, Polyester E, and Polyester F were mixed (dry blended) in a mass ratio of 25:60:10:5 and then added, to obtain a uniaxially stretched film with a thickness of 30 μm. The evaluation results are shown in Table 3. Although the appearance and initial breakage of the shrunk finished film were relatively good, flame retardancy was not exhibited because no flame retardant was added. Therefore, the film had insufficient flame retardancy for use as a coating material.

[0064] Comparative Example 3 A uniaxially stretched film with a thickness of 30 μm was produced in the same manner as in Example 4, except that the tenter preheating temperature was changed to 88° C. and the subsequent widthwise stretching temperature was changed to 78° C. The evaluation results are shown in Table 3. Although the flame retardancy and initial breakage of the film were good, the low widthwise stretching temperature caused crystallization of the polyester film to proceed due to stretching, resulting in a density of 1.34 g / cm. ３ The heat shrinkage in the width direction was less than 30%. Therefore, the film had poor appearance after shrinkage and was poorly bound, making it of low practical use.

[0065] Comparative Example 4: Polyester resins A, E, F, and G were dried by heating under vacuum at 140°C for 3 hours, and polyester resin C was dried by heating at 70°C for 70 hours, to a moisture content of 100 ppm. Film production was carried out in the same manner as in Example 1, yielding a 30 μm-thick uniaxially stretched film. Although the film had good flame retardancy and a good appearance after shrinkage, the drying temperature and time for the polyester raw material were insufficient, resulting in a moisture content exceeding 90 ppm. As a result, the intrinsic viscosity was below 0.6 dl / g, the initial break was poor, and the film had poor mechanical strength.

[0066] Comparative Example 5 Polyester F, Polyester G, and Polyester H were melted and mixed in the same manner as in Example 1, except that they were mixed in a mass ratio of 8:15:77. Because polyester resin H, which has a high intrinsic viscosity, was used, the intrinsic viscosity of the entire resin exceeded 1.0 dL / g. Therefore, an attempt was made to continuously extrude this molten resin from a T-die, but the melt viscosity of the polyester became too high, increasing the resin pressure and deforming the filter in the melt line, making it impossible to successfully melt extrude it.

[0067] The film was evaluated as follows.

[0068] [Heat Shrinkage (Hot Water Heat Shrinkage)] The film was cut into a 10 cm x 10 cm square parallel to the unwinding direction of the roll (hereinafter, for the cut film, the unwinding direction of the roll before cutting is referred to as the longitudinal direction, and the direction perpendicular to the unwinding direction on the film surface is referred to as the width direction), and the film was immersed in hot water at 80°C ± 0.5°C for 10 seconds under no load to allow heat shrinkage, and then immersed in water at 23°C ± 0.5°C for 10 seconds. The film was then pulled out of the water and the dimensions in the longitudinal and width directions of the film were measured, and the heat shrinkage ratio was calculated according to the following formula (1): Heat shrinkage ratio (%) = (dimension before heating - dimension after heating) / dimension before heating × 100 (1)

[0069] [Heat Shrinkage Stress] A strip-shaped film sample measuring 150 mm in length and 20 mm in width was cut from the heat-shrinkable film, and the shrinkage stress was measured using a Tensilon universal testing machine RTC-1210A (manufactured by Orientec Co., Ltd.) equipped with a heating furnace. When the lengthwise direction was the machine direction of the heat-shrinkable film, the longitudinal shrinkage stress was measured, and when the lengthwise direction was the machine direction, the transverse shrinkage stress was measured. The heating furnace of the strength and elongation tester was preheated to 90°C, and the distance between the chucks for holding the film sample was 100 mm. When attaching the sample to the chucks of the strength and elongation tester, the air flow to the heating furnace was stopped, the furnace door was opened, and 25 mm each on both ends of the 150 mm long sample was clamped between the chucks, with the distance between the chucks set to 100 mm, so that the distance between the chucks and the length direction of the sample were aligned and the sample was horizontal, without any looseness. After the sample was attached to the chuck, the door of the heating furnace was quickly closed and air flow was resumed. The point in time when the door of the heating furnace was closed and air flow was resumed was defined as the start point of shrinkage stress measurement, and the maximum value of the shrinkage stress measured from the start point of shrinkage stress measurement until 30 seconds after the start of measurement was defined as the maximum value of shrinkage stress (maximum shrinkage stress (MPa)).

[0070] [Initial Break] A rectangular film sample measuring 60 mm in the longitudinal direction and 15 mm in the transverse direction was cut out from the flame-retardant heat-shrinkable film and aged for 672 hours in an atmosphere of 30°C and 85% RH. The rectangular film sample was then clamped using a Tensilon universal testing machine RTC-1210A (manufactured by Orientec Co., Ltd.) and pulled to an elongation of 10% at a pulling rate of 200 mm / min. This operation was performed on 10 samples, and the number of samples that broke was recorded as the number of samples that broke initially.

[0071] [Intrinsic Viscosity] 1.2 g of a sample (polyester or film) was dissolved in 100 ml of orthochlorophenol, and the solution viscosity was measured at 25°C. From this, the intrinsic viscosity was calculated according to the following formula 2: ηsp / C=[η]+K[η]2×C (Formula 2) In the formula, ηsp=(solution viscosity / solvent viscosity)-1, C is the dissolved polymer weight per 100 ml of solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (0.343). The solution viscosity and solvent viscosity were measured using an Ostwald viscometer.

[0072] [Flame Retardancy Evaluation] [UL94-VTM Test] The flame retardancy of heat-shrinkable films was evaluated in accordance with the UL-94 VTM method. Heat-shrinkable films were cut into 20 cm x 5 cm samples, which were left at 23±2°C and 50±5% RH for 48 hours. The lower end of the sample was then held vertically, 10 mm above the burner. A Bunsen burner with an inner diameter of 9.5 mm and a flame length of 19 mm was used as the heat source, and the lower end of the sample was exposed to the flame for 3 seconds. Flame retardancy was evaluated according to the VTM-0, VTM-1, VTM-2, and fail evaluation criteria, and the rank with the most common ranks among the five measurements (n=5) was selected.

[0073] [Flame Retardancy Evaluation] Flame retardancy was evaluated as follows based on the above flame retardancy evaluation: ◯: Flame retardancy evaluation was VTM-0, VTM-1, VTM-2; ×: Flame retardancy evaluation was unsatisfactory.

[0074] [Shrinkage finish] [Distortion of lid material film] A heat-shrinkable film previously patterned with a grid at 10 mm intervals was cut into a size of 200 mm length x 50 mm width, with the longitudinal direction being the vertical direction. A tubular film was prepared with the main shrinkage direction being the circumferential direction. The tubular film was then placed over a condenser case and heat-treated with hot air at 120°C for 1 minute to heat-shrink the film, which was then attached to the object. Thereafter, the finish after shrinkage was visually evaluated using the following two-point scale: ○: Insufficient shrinkage, almost no shrinkage spots ×: Either insufficient shrinkage or shrinkage spots occurred

[0075] [Sagging of Covering Film] After the covering film was heat-shrunk and attached to the container in the same manner as above, an iron ball with a radius of 10 mm and a mass of 30 g was placed on the covering film, and the sagging after shrinkage was evaluated based on the distance the film sagged in a direction perpendicular to the film. Evaluation was made according to the following criteria. ◯: The distance sagged in a direction perpendicular to the film was 5.0 mm or less. ×: The distance sagged in a direction perpendicular to the film was more than 5.0 mm.

[0076] [Film production conditions and evaluation results] As is clear from Table 3, the films obtained in Examples 1 to 8 all had high shrinkability in the machine direction and / or width direction, and therefore had good shrink finish when used as a covering material. They also had excellent flame retardancy and mechanical strength, making them practically usable as flame-retardant heat-shrinkable films. In contrast, the films obtained in Comparative Examples 1 to 3 did not have sufficient properties for practical use as flame-retardant heat-shrinkable films, as shown in Table 3 and the sections for each comparative example above.

[0077]

[0078]

[0079]

[0080]

[0081]

[0082] The flame-retardant polyester heat-shrinkable film of the present invention has excellent shrinkage properties, flame retardancy, and mechanical strength as described above, and can therefore be suitably used for packaging various articles, including films for covering materials.

Claims

1. A flame-retardant heat-shrinkable polyester film that is molded from a polyester resin containing at least one type of flame retardant and that satisfies the following requirements (1) to (3): (1) The heat shrinkage rate in the main shrinkage direction after immersion in 80°C hot water for 10 seconds is 30% to 80% (2) The shrinkage stress in the main shrinkage direction measured in 90°C hot air is 2.0 MPa to 15 MPa (3) After aging the film for 672 hours in an atmosphere of 30°C and 85% RH, the initial breakage rate is 2 or less out of 10 samples 2. The flame-retardant heat-shrinkable polyester film according to claim 1, which has a heat shrinkage rate of -15% or more and 15% or less in the direction perpendicular to the main shrinkage direction after immersion in 80° C. hot water for 10 seconds.

3. Density is 1.20 g / cm ３ 1.35g / cm or more ３ 2. The flame-retardant heat-shrinkable polyester film according to claim 1, wherein:

4. The flame-retardant heat-shrinkable polyester film according to claim 1, having an intrinsic viscosity of 0.6 dl / g or more and 1.0 dl / g or less.

5. A flame-retardant heat-shrinkable polyester film according to claim 1, which contains a phosphorus-based compound as a flame retardant, and the phosphorus atom concentration in said polyester film is 0.3% by weight or more and 2.0% by weight or less, based on the weight of the polyester film.

6. A flame-retardant heat-shrinkable polyester film according to claim 1, wherein the polyester is composed mainly of terephthalic acid or a derivative thereof as a polyvalent carboxylic acid component and mainly of ethylene glycol as a polyhydric alcohol component.

7. A flame-retardant heat-shrinkable polyester film according to claim 6, wherein the polyester constituting said flame-retardant heat-shrinkable polyester film contains 50 mol % or more of ethylene terephthalate units out of 100 mol % of the total resin components.

8. A flame-retardant heat-shrinkable polyester film according to claim 6, wherein the terephthalic component is 70 mol % or more out of 100 mol % of the dicarboxylic acid component constituting the polyester.

9. The flame-retardant heat-shrinkable polyester film according to claim 6, wherein the ethylene glycol component is 50 mol % or more out of 100 mol % of the diol component constituting the polyester.

10. The flame-retardant heat-shrinkable polyester film according to claim 6, wherein the polyhydric alcohol component comprises at least one member selected from the group consisting of 1,4-butanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol.

11. A covering material in which the flame-retardant heat-shrinkable polyester film according to claim 1 is adhered to at least a part of an object by heat shrinking it.

12. A package, at least a part of which is covered with the covering material according to claim 11.

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