JP2006063260A - Heat-shrinkable polyester-based film and heat-shrinkable label - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester-based film for a full label of a bottle, which hardly forms wrinkles, spots and warps by shrinkage and have a property of cutting off light without any further printing or processing. <P>SOLUTION: The heat-shrinkable polyester-based film is characterized by having total light transmittance of ≤40%, a haze value of ≥ 90%, 5-60% heat shrinkability after a treatment for 10 seconds at the temperature of 70°C, heat shrinkability of ≥75% after 10 seconds at 90°C in the main shrinkage direction and shrinkability of ≤10% after a treatment for 10 seconds at 90°C in the direction perpendicular to the main shrinkage direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film suitable for label applications. More specifically, for heat-shrinkable polyester for full labeling of bottles, particularly for full labeling of PET bottles, which is extremely free of wrinkles, shrinkage spots and distortions due to heat shrinkage, hardly suffers from shrinkage shortage, and has light-cutting properties. Relates to a film.

  As a heat-shrinkable film, particularly a heat-shrinkable film for labeling the body of a bottle, a film made of polyvinyl chloride, polystyrene or the like is mainly used. However, with regard to polyvinyl chloride, in recent years, there has been a problem of generation of chlorinated gas when incinerated at the time of disposal, and polyethylene has problems such as difficulty in printing. Furthermore, when recycling PET bottles, it is necessary to separate labels of resins other than polyethylene terephthalate such as polyvinyl chloride and polyethylene. For this reason, polyester-based heat-shrinkable films that do not have these problems are attracting attention.

  In recent years, colored bottles are unsuitable for recycling because of the recycling of PET bottles, and alternatives have been studied. Among them, there is a method of using a non-colored bottle and shrinking the printed label to the whole bottle. There is also a method of shrinking the label from the top to the bottom of the bottle to increase the returnable resistance of the glass bottle.

  Recently, an increasing number of cases have used shrink labels for the purpose of protecting the contents of containers from ultraviolet rays. Conventionally, a UV-cut type shrink film made of polyvinyl chloride has been used, but there is an increasing demand for UV-cut type of other materials. Although the specific cut property differs depending on the contents, in the case of food and beverage, the contents are altered or colored at a wavelength of 360 nm to 400 nm, which is ultraviolet light in the long wavelength area, so that the long wavelength area, particularly 380 nm and 400 nm Cutability is important

However, when used as a full label for a bottle, the bottle shape is complicated and there are many types, so the conventional heat shrinkable film may have a problem in shrink finish. In particular, in the case of a full bottle label, such as a beverage bottle, where the mouth portion is narrow and the diameter difference from the body is large, the conventional heat-shrinkable film is insufficiently contracted at the top (head and neck) of the bottle. The heat-shrinkable film used for the full label of such a bottle needs heat shrinkage characteristics such as a high shrinkage rate (for example, Patent Document 1).
JP 2000-135737 A

In addition, some conventional heat-shrinkable polyester films have concealment properties (for example, Patent Document 2), but none have both a shrinkage ratio that can be used as the above-mentioned full label and an ultraviolet cut in a long wavelength region. .
Japanese Patent Publication No. 7-33063

  In particular, by imparting light-cutting properties to the full label of the bottle, it is possible to block light from the contents in a more nearly complete form as compared with other labels, so that the effect of preventing deterioration of the contents is high. In the case of full label use for bottles, the performance of conventional polyester heat-shrinkable films has been insufficient.

  The present invention solves the above-mentioned problems, and its object is a heat-shrinkable polyester film and a heat-shrinkable label for bottle full labels, in particular, PET bottles and glass bottles, which are insufficiently shrunk. It is an object of the present invention to provide a heat-shrinkable polyester film and a heat-shrinkable label that are less likely to occur, in particular, have very few wrinkles, shrinkage spots, and distortion due to shrinkage, and are excellent in light-cutting properties.

  As a result of earnest research to solve the problems of the prior art, the present inventor can achieve the object by controlling the heat shrinkage rate, the total light transmittance, and the haze of the heat shrinkable polyester film to a specific range. As a result, the present invention has been completed.

  That is, the heat-shrinkable polyester film of the present invention has a total light transmittance of 40% or less, a haze of 90% or more, and a heat shrinkage of 70 ° C. and a treatment time of 10 in the main shrink direction. 5% to 60% in seconds, 75% or more at a treatment temperature of 90 ° C. and treatment time of 10 seconds, and a heat of 10% or less at a treatment temperature of 90 ° C. and treatment time of 10 seconds in a direction perpendicular to the main shrinkage direction. This is a shrinkable polyester film, which can solve the problem.

  In this case, it is preferable to have at least one layer containing titanium oxide. Furthermore, in this case, it is preferable that the content of the titanium oxide is in a range of 0.1 to 20.0% by mass in terms of a film.

  In this case, it is preferable to have at least one layer containing a polystyrene resin. Furthermore, in this case, it is preferable that the content of the polystyrene-based resin is in a range of 1.0 to 20.0% by mass in terms of a film.

  In this case, the thickness distribution is preferably 6% or less.

  In this case, a heat-shrinkable label produced using the film is a suitable application for a bottle.

  The heat-shrinkable polyester film and label of the present invention are less likely to cause insufficient shrinkage, in particular, the occurrence of wrinkles, shrinkage spots, and distortion due to shrinkage is extremely low, and because of excellent light-cutting properties, In particular, it can be suitably used for applications such as plastic bottles and glass bottles.

  Embodiments of the present invention will be specifically described below.

  The heat-shrinkable polyester film can be obtained as follows.

  The heat-shrinkable polyester film can be obtained as follows. A polyester composed of a dicarboxylic acid component and a polyvalent glycol component is melt-extruded from an extruder and cooled with a conductive cooling roll (such as a casting roll) to form a film (unstretched film).

In the extrusion, the copolyester is extruded alone, or a plurality of polyesters (copolyester, homopolyester, etc.) are mixed and extruded. That is, the film contains a second alcohol component that is different from a base unit (such as a crystalline unit such as polyethylene terephthalate) and a polyvalent glycol component (such as an ethylene glycol component) that constitutes the base unit.
In addition, the content rate of the acid component of this invention and a diol component is a content rate with respect to the acid component of the whole polyester, and a diol component, when mixing and using 2 or more types of polyester. It does not matter whether transesterification has taken place after mixing.

  Any of the above polyesters can be produced by polymerization according to a conventional method. For example, the polyester can be obtained by using 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 polymerization may be performed by either a batch method or a continuous method.

  The polyester film containing the second alcohol component can be stretched to obtain a heat-shrinkable polyester film.

As the second alcohol component, a diol component and a trivalent or higher alcohol component can be used. The diol component includes ethylene glycol, propylene glycol, 1,4-butanediol, 2,2-diethyl-1,3-propanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, -Alkylene glycols such as methyl-1,5-pentanediol, 1,9-nonanediol, 1,10-decanediol; cyclic alcohols such as 1,4-cyclohexanedimethanol; diethylene glycol, collected ethylene glycol, polypropylene glycol, poly Ether glycols such as oxytetramethylene glycol, alkylene oxide adducts of bisphenol compounds or derivatives thereof; and dimer diols. Trivalent or higher alcohols include trimethylolpropane, glycerin, pentaerythritol and the like.

In the polyester resin composition, it is also possible to use a polyester and a polyester elastomer together. In that case, the blending ratio of the polyester and the polyester-based elastomer is usually about 50 to 98% by mass, particularly about 70 to 95% by mass, and about 2 to 50% by mass, especially about the latter with respect to the total amount of both. The amount is preferably about 5 to 30% by mass.

The polyester elastomer is, for example, a polyester block copolymer comprising a high melting crystalline polyester segment (Tm 200 ° C. or higher) and a low melting point soft polymer segment (Tm 80 ° C. or lower) having a molecular weight of 400 or more, preferably 400 to 800. Polyester elastomers using polylactones such as ε-caprolactone in the low melting point soft polymer segment are particularly preferred.

In order to achieve the total light transmittance and haze specific to the film of the present invention and to impart light-cutting properties to the film, for example, particles such as inorganic particles and organic particles are added to the film in an amount of 0. It is suitable to contain 1 to 20% by mass, preferably 0.5 to 10% by mass. When the content of the particles is less than 0.1% by mass, it is difficult to obtain, for example, sufficient light-cutting property, which is not preferable. On the other hand, if it exceeds 20% by mass, for example, the film strength is lowered, and film formation tends to be difficult.

The particles may be added before polyester polymerization, but are usually added after polyester polymerization. Examples of the inorganic particles to be added include known inert particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium tephrate, aluminum oxide, titanium oxide, calcium phosphate, and carbon black, and insoluble when melt-forming polyester resin. Such a high melting point organic compound, a crosslinked polymer, and a metal compound catalyst used during the synthesis of the polyester, such as an alkali metal compound, an alkaline earth metal compound, and the like, may be internal particles formed inside the polymer during the production of the polyester. Of these, titanium oxide particles are preferable from the viewpoint of providing the necessary light-cutting properties.

The average particle size of the particles contained in the film is usually in the range of 0.001 to 3.5 μm. Here, the average particle diameter of the particles is measured by a Coulter counter method. The average particle size of the particles is preferably 0.001 μm to 3.5 μm, more preferably 0.005 μm to 3.0 μm. If the average particle size of the particles is less than 0.001 μm, for example, it will be difficult to obtain the necessary light-cutting properties. When the average particle size of the particles exceeds 3.5 μm, for example, the film surface is inferior in smoothness and problems such as printing omission are likely to occur.

  In the present invention, in order to obtain an appropriate light transmittance, for example, it is preferable to contain fine cavities inside. For example, a foam material or the like may be mixed and extruded, but a preferred method is to obtain a cavity by mixing an incompatible thermoplastic resin in polyester and stretching it in at least one axial direction. The thermoplastic resin incompatible with the polyester used in the present invention is arbitrary, and is not particularly limited as long as it is incompatible with the polyester. Specific examples include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, and cellulose resins. In particular, a polystyrene resin or a polyolefin resin such as polymethylpentene or polypropylene is preferable because of the formation of cavities.

  The content of the incompatible resin is preferably in the range of 1.0 to 20.0% by mass in terms of film. If the incompatible resin is less than 1.0% by mass, for example, the amount of cavities in the film is reduced, and the light-cutting property tends to be insufficient, which is not preferable. If the incompatible resin exceeds 20% by mass, for example, kneading in the extrusion process tends to be uneven, and it is difficult to obtain a stable film, which is not preferable.

  Polystyrene resin refers to a thermoplastic resin containing a polystyrene structure as a basic component, and is grafted or block copolymerized with homopolymers such as atactic polystyrene, syndiotactic polystyrene, isotactic polystyrene, and other components. Modified resins, such as impact-resistant polystyrene resins and modified polyphenylene ether resins, and mixtures of thermoplastic resins having compatibility with these polystyrene resins, such as polyphenylene ether, are included.

  In preparing the polymer mixture obtained by mixing the polyester and the incompatible resin, for example, the chips of each resin may be mixed and melt-kneaded in an extruder and extruded, or both resins may be preliminarily mixed by a kneader. The kneaded product may be further melt extruded from an extruder. Moreover, a polystyrene resin may be added in the polyester polymerization step, and a chip obtained by stirring and dispersing may be melt-extruded.

  In the film of the present invention, it is preferable to provide the layer A having fewer cavities than the B layer on at least one side of the layer B containing a large number of cavities inside. At this time, the A layer may not contain cavities. In order to achieve this configuration, different raw materials are charged into different extruders A and B, melted, bonded together in the molten state before the T-die or inside the die, and cooled with a conductive cooling roll (such as a casting roll). To form a film (unstretched film).

  The stretching is preferably uniaxial stretching, but may be biaxial stretching that is stretched at a lower magnification in a direction different from the direction of the uniaxial stretching (main direction). The stretching direction (main direction) is not particularly limited, and may be a film flow direction or a direction perpendicular to the flow direction (hereinafter referred to as a width direction). Preferably, it extends | stretches in the width direction of a film from a viewpoint on production efficiency. At this time, it is preferable that the incompatible resin blended in the A layer as a raw material is less than the B layer. By doing so, there are few cavities in the A layer, the surface roughness is reduced, and the film does not impair the aesthetics of printing. Moreover, since there are not many cavities, the film does not become weak and the film has excellent wearability. In addition, since the shrinkage rate is reduced by forming cavities, a high thermal shrinkage rate can be provided by providing a layer having few cavities.

  Furthermore, it is particularly preferable that the film in the present invention has a layer B containing a large number of cavities inside as an intermediate layer, and A layers having few cavities are provided on both surface layers. When polystyrene resin is added, smoke is generated at the time of melt-extrusion. For example, the process may be deteriorated by fouling the process, but the problem of fuming is eliminated by using the B layer as an intermediate layer and stable for a long time. Production becomes possible.

  The layer to which the above-mentioned fine particles are added may be any of the A layer, the B layer, and both the A layer and the B layer. By using together with a resin component incompatible with polyester, there is an effect of further reducing the total light transmittance of the film. Therefore, when the A layer does not contain voids, it is preferable to add fine particles only to the B layer. .

Further, the total of one or more monomer components that are amorphous components in 100 mol% of the polyhydric alcohol component in the film is preferably 18 mol% or more, and particularly preferably 20 mol% or more. When the total of the monomer components is less than 18 mol%, for example, it is difficult to achieve a high shrinkage rate in a high temperature range, which is not preferable.
Examples of the monomer that can be an amorphous component include neopentyl glycol, 1,4-cyclohexanedimethanol, and isophthalic acid.

  Common to the A layer and the B layer is an aliphatic diol having 8 or more carbon atoms (for example, octanediol) or a trihydric or higher polyhydric alcohol (for example, trimethylolpropane, trimethylolethane, glycerin, diglycerin). Etc.) is preferably not contained. In a heat-shrinkable polyester film obtained by using polyesters containing these diols or polyhydric alcohols, for example, it becomes difficult to achieve a necessary high shrinkage rate.

  Moreover, it is preferable not to contain diethylene glycol, triethylene glycol, and polyethylene glycol as much as possible. In particular, diethylene glycol is likely to be present because it is a by-product component during polyester polymerization. However, in the polyester used in the present invention, the content of diethylene glycol is preferably less than 4 mol%.

In addition, the content rate of the acid component of this invention and a diol component is a content rate with respect to the acid component of the whole polyester, and a diol component, when mixing and using 2 or more types of polyester. It does not matter whether transesterification has taken place after mixing.
Furthermore, in order to improve the slipperiness of the heat-shrinkable film, for example, an inorganic lubricant such as titanium oxide, particulate silica, kaolin, calcium carbonate, or an organic lubricant such as a long-chain fatty acid ester may be included. preferable. Moreover, you may contain additives, such as a stabilizer, a coloring agent, antioxidant, an antifoamer, an antistatic agent, and an ultraviolet absorber, as needed.

  Any of the above polyesters can be produced by polymerization according to a conventional method. For example, the polyester can be obtained by using 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 polymerization may be performed by either a batch method or a continuous method.

   [Light Transmittance] The polyester film of the present invention needs to have a total light transmittance of 40% or less as measured according to JIS K 7136. When the transmittance is 40% or more, it is not preferable since the contents can be seen through or the contents cannot be cut and the contents deteriorate. The transmittance is particularly preferably 30% or less.

   [Haze] The polyester film of the present invention needs to have a haze of 90% or more measured according to JIS K 7136. If the haze is less than 90%, the contents can be seen through, or the contents can deteriorate without being able to cut light rays. The haze is particularly preferably 95% or more.

  In order to satisfy the above characteristics, the film of the present invention may be composed of a single layer, but the preferred layer structure is A / B / A. The thickness ratio of the A layer and the B layer is preferably A / B / A = 25/50/25 to 10/80/10. If the thickness ratio of the B layer is less than 50%, the light-cutting property is insufficient, and the contents can be seen through, or the contents cannot be cut and the contents are deteriorated.

   [Heat Shrinkage Rate] The heat-shrinkable polyester film of the present invention is treated with warm water in an unloaded state, and from the length before and after shrinkage, heat shrinkage rate = ((length before shrinkage−length after shrinkage). ) / Length before shrinkage) × 100 (%) The thermal shrinkage rate of the film is 5 to 60% at a treatment temperature of 70 ° C. and a treatment time of 10 seconds in the main shrinkage direction, preferably 10 -50%, 75% or more at a processing temperature of 90 ° C. and a processing time of 10 seconds, preferably from 76 to 95%. In the direction orthogonal to the main shrinkage direction, the treatment temperature is 90 ° C. and the treatment time is 10 seconds, and it is 10% or less, preferably 6% or less.

  When the heat shrinkage rate in the main shrinkage direction is less than 5% at a treatment temperature of 70 ° C. and a treatment time of 10 seconds, the low-temperature shrinkability is insufficient, and for example, it is necessary to increase the shrinkage temperature. On the other hand, if it exceeds 60%, for example, jumping of the label due to heat shrinkage tends to occur, which is not preferable.

  When the heat shrinkage rate in the main shrinkage direction is less than 75% at a treatment temperature of 90 ° C. and a treatment time of 10 seconds, for example, the shrinkage of the head of the bottle is not preferable. On the other hand, if it exceeds 95%, the force of further shrinkage remains even after heat shrinkage, which is not preferable because, for example, the label tends to jump up due to heat shrinkage.

  When the heat shrinkage rate in the direction orthogonal to the main shrinkage direction exceeds 10% at a treatment temperature of 90 ° C. and a treatment time of 10 seconds, for example, label distortion or jumping due to heat shrinkage is likely to occur, which is not preferable.

  Although the thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, the heat-shrinkable film for labels is preferably 10 to 200 μm, and more preferably 20 to 100 μm.

  Next, although a specific example is demonstrated about the manufacturing method of the heat-shrinkable polyester film of this invention, it is not limited to this manufacturing method.

  The polyester raw material used in the present invention is dried using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer, melted at a temperature of 200 to 300 ° C., and extruded into a film. In extruding, any existing method such as a T-die method or a tubular method may be employed. After extrusion, it is cooled rapidly to obtain an unstretched film.

  In addition to using the polyester having the above-mentioned composition, it is preferable to stretch the unstretched film under the following conditions as a means for achieving the necessary high shrinkage. The film is preferably stretched at a high magnification of, for example, 4.0 times or more, preferably 4.5 times or more, and more preferably 5 times or more. The upper limit of the draw ratio is not particularly limited, but if the draw ratio exceeds 7 times, there is a problem that the film forming property deteriorates.

  In addition to the above, the stretching temperature is preferably stretched at a low temperature of the glass transition temperature (Tg) −5 ° C. or more and Tg + 10 ° C. or less of the film. By stretching at a high magnification and a low temperature, the molecular orientation of the film can be enhanced and a high shrinkage can be expressed. Furthermore, it is a preferable embodiment that the heat setting after stretching is performed at a low temperature of Tg + 10 ° C. or lower or no heat setting is performed.

Furthermore, the heat-shrinkable polyester film used in the present invention has a melt specific resistance value of 0.70 × 10 ⁸ Ω · cm or less at a temperature of 275 ° C. When such a film is used, as will be described in detail below, the uniformity of the film thickness can be improved, and the printability on the film and the workability when processing the film into a form that can be mounted on a container. (Stable workability) can be improved.

   [Melting resistivity value] In order to control the melting resistivity value within the above range, it is preferable to contain an alkaline earth metal compound and a phosphorus-containing compound in the film. The melting specific resistance value can be lowered only with the alkaline earth compound, but the melting specific resistance value can be remarkably lowered when the phosphorus-containing compound coexists. Although it is not clear why the specific melt resistance value can be remarkably lowered by combining the alkaline earth metal compound and the phosphorus-containing compound, the amount of foreign matter can be reduced by containing the phosphorus-containing compound, and the charge carrier It is estimated that the amount can be increased.

  In order to increase the uniformity of the film thickness, (A) a method of homogenizing the polyester raw material during film production, (B) production together with the above-mentioned method of stabilizing electrostatic adhesion from the beginning to the end of film production It is desirable to employ a method for stabilizing the process and / or a method for stabilizing the (C) film stretching process.

(A) Method of homogenizing polyester raw material and polystyrene raw material during production of film (1) Method of reducing the amount of fine powder polyester chip and polystyrene chip Fine powder (fine powder chip) generated due to scraping of raw material chip used, etc. Since the occurrence of the raw material segregation is promoted, the raw material segregation can also be reduced by reducing the ratio of the fine powder.

  The ratio of the fine powder in each raw material chip is preferably controlled within 1% by mass and more preferably within 0.5% by mass throughout the entire process until the raw material chip enters the extruder.

  As a method for reducing the fine powder, for example, a method of removing fine powder generated in the process (classification removal, etc.) can be adopted. For example, a method of passing a sieve at the time of chip formation by a strand cutter, a method of passing a cyclonic air filter when the raw material chips are fed by air, and the like can be adopted.

(2) Method for optimizing the shape of the final hopper For example, there is a method in which a funnel-shaped hopper is used as the final hopper and its hypotenuse (side wall) is brought close to the vertical. If the hypotenuse (side wall) is brought closer to the vertical, a large chip can be easily dropped like a small chip, and the upper end of the content descends while maintaining a horizontal plane, which is effective in reducing raw material segregation. is there.

  The inclination angle of the hypotenuse (side wall) is, for example, 65 ° or more, preferably 70 ° or more. The inclination angle of the hypotenuse (side wall) is an angle between the funnel-like hypotenuse (side wall) and a horizontal line segment.

(B) Method for Stabilizing Film Formation Methods for stabilizing the film formation process include a method for suppressing fluctuations in the discharge amount from the extruder, a method for suppressing fluctuations in the rotation speed of the cooling roll (casting roll), and the like. It is done.

  In order to suppress the discharge amount fluctuation from the extruder, for example, it is preferable to stabilize the discharge amount within a range of ± 2% of the average discharge amount. In order to suppress the discharge amount fluctuation, for example, it is preferable to use a gear pump as the discharge means.

  In order to suppress the rotational speed fluctuation of the cooling roll (casting roll), for example, it is preferable to stabilize the rotational speed within a range of ± 2% of the average rotational speed. In order to suppress the rotational speed fluctuation, it is preferable to use, for example, a means for controlling the rotational accuracy of the roll drive system, for example, an inverter for controlling the rotational speed.

(C) Method of Stabilizing Film Stretching Process In order to impart heat shrinkability to the film, it is necessary to stretch the unstretched film. When stabilizing the stretching process of the film, various devices for stabilization are applied to a general stretching method.

(1) Control of stretching temperature When the stretching temperature is controlled, the stretching temperature is controlled so as not to become too high. If the stretching temperature is too high, the film thickness distribution value may become too large. If the stretching temperature is too high, the heat shrinkage rate of the film may be insufficient as described above. Further, when the obtained heat shrinkable film is mounted on a container (such as a bottle) at a high speed, There may be a shortage of time.

  The stretching temperature is preferably controlled within the aforementioned range. If the stretching temperature is too low, a stretching residue may be generated locally and the film thickness distribution may become too large.

(2) Method of controlling internal heat generation due to stretching If internal heat generation of the film accompanying stretching is suppressed, temperature spots of the film in the stretching direction (such as the width direction) can be reduced, and the film after stretching (heat-shrinkable film) Thickness uniformity can be improved.

  In order to control the internal heat generation, it is preferable to appropriately control the heating conditions (for example, to increase the supply speed of hot air) so that the film is easily heated. When there is an insufficiently heated portion, internal heat generation due to stretching orientation occurs. On the other hand, when the film is sufficiently heated, the molecular chain easily slips during stretching, so that internal heat generation hardly occurs.

  When the heating conditions are expressed by heat transfer conditions, for example, the heat transfer coefficient is 0.0038 J / cm 2 · sec · ° C. (0.0009 cal / cm 2 · sec · ° C.) or more, preferably 0.0046 to 0.0071 J / ° C. It is about cm 2 · sec · ° C. (0.0011 to 0.0017 calories / cm 2 · sec · ° C.).

(3) Control of preliminary preheating conditions When controlling the preliminary preheating conditions, it is preferable to control so that the film is gradually heated. When the film is gradually heated in the preliminary preheating step, the temperature distribution of the film can be made substantially uniform, so that the uniformity of the thickness of the stretched film (heat-shrinkable film) can be enhanced.

  When the preheating condition is represented by a heat transfer condition, for example, the heat transfer coefficient is about 0.00054 J / cm 2 · sec · ° C. (0.0013 calories / cm 2 · sec · ° C.) or less. In the preheating, the film surface temperature is preferably heated until it reaches a temperature within the range of Tg + 0 ° C. to Tg + 60 ° C., and the temperature of the hot air is preferably about Tg + 10 ° C. to Tg 90 ° C.

  Examples of the method for achieving the heat transfer coefficient include a method of slowing the hot air supply rate.

(4) Soaking the surface temperature of the film during stretching When stretching the film, if the fluctuation of the surface temperature of the film is reduced (soaking), stretching or heat treatment is performed at the same temperature over the entire length of the film. The thickness distribution value and heat shrinkage behavior can be made uniform.

  As for the fluctuation range of the surface temperature, the temperature at each point when the surface temperature of the film is measured at an arbitrary point is preferably, for example, within the average temperature of the film ± 1 ° C., and the average temperature ± 0.5 ° C. More preferably, it is within.

  When stretching the film, some of these steps are used to stretch the film through various steps such as a preheating step before stretching, a stretching step, a heat treatment step after stretching, a relaxation treatment step, and a re-stretching step. In all, it is preferable to use equipment that can reduce the fluctuation range of the surface temperature of the film (equalize). In particular, in order to make the thickness distribution value uniform over the entire length of the film, in the preheating step and the stretching step (and in the heat treatment step after stretching if necessary), the equipment that can reduce the surface temperature fluctuation range of the film Is preferably used. In order to make the heat shrinkage behavior uniform, it is preferable to use equipment that can reduce the fluctuation range of the surface temperature of the film in the stretching step.

  Examples of equipment that can reduce the fluctuation range of the film temperature include, for example, equipment equipped with a wind speed control means (such as an inverter) for controlling the supply speed of hot air for heating the film, and stably heating the air. Examples include equipment provided with heating means for adjusting the hot air [heating means using low pressure steam of 500 kPa or less (5 kgf / cm 2 or less) as a heat source].

   [Intrinsic viscosity] The heat-shrinkable polyester film of the present invention preferably has an intrinsic viscosity of 0.60 dl / g or more. If the intrinsic viscosity of the heat-shrinkable film is too small, the molecular weight of the polyester that composes the film will be low, which will reduce the durability of the shrinkage stress during heat shrinkage, resulting in defects such as shrinkage whitening and shrinkage spots. It becomes easy and it becomes inferior to shrink finish and appearance. Moreover, if the molecular weight of polyester falls, the mechanical strength and tear resistance of a film will be reduced.

  The intrinsic viscosity is preferably 0.60 dl / g or more, more preferably 0.63 dl / g or more.

  As a method for increasing the intrinsic viscosity of the film, for example, (1) a method in which a high molecular weight polyester is used as the polyester that is the raw material of the film (for example, the intrinsic viscosity is 0.63 dl / g or more, preferably 0.68 dl / g More preferably, a method of using a polyester of 0.70 dl / g or more), (2) a method of suppressing thermal decomposition and hydrolysis when forming a film by extruding the polyester (for example, preliminarily using a polyester raw material) (3) A method of using a hydrolysis-resistant polyester as the polyester (for example, having an acid value of 25 eq / ton or less) (Method of using polyester), (4) Acid value inhibitor for polyester (for example, 0.01-1 quality) Such as% of content) is a method to the like.

  The polyester used in the present invention can be obtained by a melt polymerization method or other polymerization methods. Examples of the melt polymerization method include a method in which an oligomer obtained from a direct reaction between a dicarboxylic acid and a glycol is polycondensed (direct polymerization method), a polycondensation after a transesterification reaction between a dimethyl ester of a dicarboxylic acid and a glycol. (Transesterification method) and any other production method can be applied. The degree of polymerization of the polyester is preferably about 0.5 to 1.3 dl / g in terms of intrinsic viscosity.

  As the polymerization catalyst, various conventional catalysts can be used. For example, titanium-based catalyst, antimony-based catalyst, germanium-based catalyst, tin-based catalyst, cobalt-based catalyst, manganese-based catalyst, etc., preferably titanium-based catalyst (titanium tetrabutoxide) Etc.), antimony catalysts (such as antimony trioxide), germanium catalysts (such as germanium dioxide), cobalt catalysts (such as cobalt acetate), and the like.

  If necessary, fine particles such as silica, titanium dioxide, kaolin and calcium carbonate may be added to the film raw material, and antioxidants, UV absorbers, antistatic agents, coloring agents, antibacterial agents, etc. are added. You can also

  The heat-shrinkable polyester film can be produced according to a conventional method. Particularly in the heat-shrinkable polyester film, when the second alcohol component is prepared in a specific range, the preparation method includes a method of using a copolymerized polyester (copolyester) alone, a method of mixing a plurality of polyesters [ For example, a method of mixing a plurality of different homopolyesters; a method of mixing a homopolyester (polyethylene terephthalate, etc.) and a copolymerized polyester; a method of mixing a plurality of different copolyesters, and the like.

  Specifically, the raw polyester chip is dried using a dryer (such as a hopper dryer, paddle dryer, or vacuum dryer), and the film is produced at a temperature of 200 to 300 ° C. using an extruder. And the extrusion method. Or the method of extruding an undried polyester raw material chip | tip similarly to a film form may be sufficient, removing a water | moisture content in a vent type extruder. For extrusion, various existing methods such as a T-die method and a tuber method can be adopted. After extrusion, it is desirable to obtain an unstretched film by quenching with a cooling roll such as a casting roll.

  The thickness of the heat-shrinkable polyester film is not particularly limited. For example, when used for labeling, it is about 10 to 200 μm, preferably about 20 to 100 μm.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples, unless the summary is exceeded.

  The evaluation method of the film of the present invention is as follows.

(1) Total light transmittance and film haze Measured according to JIS K 7136 using NDH-2000T manufactured by Nippon Denka Kogyo Co., Ltd.

(2) Heat shrinkage rate The film is cut into a 10 cm × 10 cm square, heat-shrinked in warm water at a predetermined temperature ± 0.5 ° C. for a predetermined time in a no-load state, and then the vertical and horizontal directions of the film. Then, the thermal shrinkage rate was determined according to the following formula (1). The direction in which the heat shrinkage rate is large was taken as the main shrinkage direction.

  Thermal shrinkage rate = ((length before shrinkage−length after shrinkage) / length before shrinkage) × 100 (%) (1)

(3) Shrinkage finishing label A label having a folding diameter of 108.5 mm and a height of 110 mm was prepared from a heat-shrinkable film.

Using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc, with a transit time of 10 seconds and a zone temperature of 90 ° C., a 280 ml PET bottle (height 135 cm, central diameter 6.9 cm) (Coca-Cola ( (Bottle used in Marocha, Inc.)) (number of measurements = 20).
Evaluation was made visually and the criteria were as follows.
○: No wrinkles, jumping up, or insufficient shrinkage occurred ×: Wrinkles, jumping up, or insufficient shrinkage occurred

(4) Tg (glass transition point)
Using DSC (model: DSC220) manufactured by Seiko Denshi Kogyo Co., Ltd., 10 mg of an unstretched film was heated from −40 ° C. to 120 ° C. at a heating rate of 20 ° C./min. From the obtained endothermic curve Asked. A tangent line was drawn before and after the inflection point of the endothermic curve, and the intersection was defined as Tg (glass transition point).

(5) Intrinsic Viscosity 0.1 g of a sample (film or chip) is precisely weighed and dissolved in 25 ml of a mixed solvent of phenol / tetrachloroethane = 3/2 (mass ratio), and then 30 ± 0.1 with an Ostwald viscometer. Measured at ° C. The intrinsic viscosity [η] is obtained by the following formula (Huggins formula).

Here, η _SP : specific viscosity, t ₀ : solvent dropping time using Ostwald viscometer, t: chip solution dropping time using Ostwald viscometer, and C: solution viscosity of chip. In the actual measurement, the intrinsic viscosity was calculated by the following approximate equation where k = 0.375 in the Huggins equation.

  Here, ηr: relative viscosity.

(6) Thickness distribution Using a contact thickness meter (model: KG60 / A) manufactured by Anritsu Co., Ltd., the thickness of the sample of 5 cm in the vertical direction and 50 cm in the horizontal direction was measured (measurement number = 20). The thickness distribution (thickness variation) was determined by the following equation (2).
Thickness distribution = ((maximum thickness−minimum thickness) / average thickness) × 100 (%) (2)

(7) Film composition Composition ratio of copolymerized polyester Approximately 5 mg of polymer piece sample of the measurement target layer cut out from each side of the laminated film was dissolved in 0.7 ml of a mixed solution of deuterated chloroform and trifluoroacetic acid (volume ratio 9/1). 1H-NMR (manufactured by varian, UNITY 50) was used.

  The polyester used in the examples is as follows.

Polyester A: Polyethylene terephthalate (Intrinsic viscosity (IV): 0.75 dl / g)
Polyester B: Polyester composed of 30 mol% neopentyl glycol and terephthalic acid (IV: 0.72 dl / g)
Polyester C: Polybutylene terephthalate (IV: 1.24 dl / g)
Polyester D: Polyester consisting of 30 mol% 1,4-cyclohexanedimethanol and terephthalic acid (IV: 0.75 dl / g)
Polyester E: Polyester elastomer comprising 70% by mass of polyester C and 30% by mass of ε-caprolactone (reduced viscosity (ηsp / c) 1.30)

Example 1
A polyester composition in which 10% by mass of polyester A, 85% by mass of polyester B, and 5% by mass of a polyester elastomer are mixed as the raw material for layer A, and 10% by mass of polyester A and 65% of polyester B is used as the raw material for layer B. A polyester composition in which 5% by mass, 5% by mass of a polyester elastomer, 10% by mass of a crystalline polystyrene resin (G797N manufactured by Nippon Polystyrene Co., Ltd.) and 10% by mass of titanium oxide (TA-300 manufactured by Fuji Titanium Industry Co., Ltd.) , Put into separate extruders, mixed and melted, joined with a feed block, melt extruded through 280 ° C while laminating so that the A / B / A thickness ratio is 25/50/25 Then, it was rapidly cooled with a chill roll to obtain an unstretched multilayer film having a thickness of 250 μm. The unstretched multilayer film had a Tg of 67 ° C.

  The unstretched film was preheated until the film temperature reached 85 ° C., and then stretched 5 times at 75 ° C. in the transverse direction with a tenter to obtain a film having a thickness of 50 μm.

(Example 2)
As a raw material for the A layer, a polyester composition in which the polyester A is mixed by 6% by mass, the polyester B by 44.5% by mass, the polyester D by 44.5% by mass, and the polyester elastomer by 5% by mass is used as the raw material for the B layer. 10% by weight of polyester A, 32.5% by weight of polyester B, 32.5% by weight of polyester D, 5% by weight of polyester elastomer, 10% by weight of crystalline polystyrene resin (G797N made by Nippon Polystyrene Co., Ltd.) and titanium oxide (TA-300 manufactured by Fuji Titanium Industry Co., Ltd.) Each polyester composition mixed with 10% by mass is put into a separate extruder, mixed, and melted and joined with a feed block. / B / A melt extrusion while laminating so that the thickness ratio is 25/50/25, Quenching was performed to obtain an unstretched multilayer film having a thickness of 250 μm. The unstretched multilayer film had a Tg of 65 ° C.

  The unstretched film was preheated until the film temperature reached 85 ° C., and then stretched 5 times at 75 ° C. in the transverse direction with a tenter to obtain a film having a thickness of 50 μm.

(Comparative Example 1)
As a raw material for the A layer, a polyester composition in which 30% by mass of the polyester A, 65% by mass of the polyester B, and 5% by mass of the polyester C are mixed, and the raw material of the B layer is used. 65% by mass, 5% by mass of polyester elastomer, 10% by mass of crystalline polystyrene resin (G797N manufactured by Nippon Polystyrene Co., Ltd.) and 10% by weight of titanium oxide (TA-300 manufactured by Fuji Titanium Industry Co., Ltd.) Were put into separate extruders, mixed and melted, joined with a feed block, and melted at 280 ° C while laminating from the T die so that the A / B / A thickness ratio was 25/50/25. It was extruded and quenched with a chill roll to obtain an unstretched multilayer film having a thickness of 200 μm. The unstretched multilayer film had a Tg of 67 ° C.

  The unstretched film was preheated until the film temperature reached 82 ° C., and then stretched 4 times at 70 ° C. in the transverse direction by a tenter to obtain a film having a thickness of 50 μm.

(Comparative Example 2)
As raw materials for the A layer, 10% by mass of polyester A, 65% by mass of polyester B, 5% by mass of polyester elastomer, 10% by mass of crystalline polystyrene resin (G797N made by Nippon Polystyrene Co., Ltd.) and titanium oxide (TA-300) A polyester composition mixed with 10% by mass (made by Fuji Titanium Industry Co., Ltd.) was melt extruded and quenched with a chill roll to obtain an unstretched film having a thickness of 200 μm. The unstretched film had a Tg of 66 ° C.

  The unstretched film was preheated until the film temperature reached 82 ° C., and then stretched 4 times at 70 ° C. in the transverse direction by a tenter to obtain a film having a thickness of 50 μm.

(Comparative Example 3)
As a raw material for the A layer, a polyester composition in which 40% by mass of polyester A, 50% by mass of polyester B and 10% by mass of polyester C are mixed is melt-extruded and rapidly cooled with a chill roll to obtain an unstretched film having a thickness of 200 μm. It was. The unstretched film had a Tg of 66 ° C.

  The unstretched film was preheated until the film temperature reached 85 ° C., and then stretched 4 times at 72 ° C. in the transverse direction by a tenter to obtain a film having a thickness of 50 μm.

 The evaluation results of the films obtained in Examples 1-2 and Comparative Examples 1-3 are shown in Tables 1-3.

  The films obtained in Examples 1 and 2 were all excellent in shrink finish. The thickness distribution was also good. Moreover, all had favorable light-cut property. The heat-shrinkable polyester film of the present invention has high quality and high practicality, and is particularly suitable for shrinkage labels.

  On the other hand, the heat-shrinkable films obtained in Comparative Examples 1 and 2 have light-cutting properties but are inferior in shrink finish, and the heat-shrinkable polyester film obtained in Comparative Example 3 has shrink finish and The light cutting property was inferior. Further, the film of Comparative Example 2 has a problem that the process contamination due to smoke generation is remarkable at the time of melt extrusion from a T-die. Thus, the heat-shrinkable polyester film of the comparative example was inferior in quality and low in practicality.

  When the heat-shrinkable polyester film of the present invention is used as a full label for a bottle, it can have a good finish with very little wrinkles, shrinkage spots, distortion and insufficient shrinkage due to heat shrinkage, and further subjected to printing and processing. It has at least light-cutting properties and is extremely useful as a full bottle label.

Claims (6)

  A heat-shrinkable polyester film, wherein the heat-shrinkable polyester film has a total light transmittance of 40% or less, a haze of 90% or more, and a heat shrinkage rate of 70% in the main shrinkage direction. 5% to 60% at 10 ° C. and a processing time of 10 seconds, 75% or more at a processing temperature of 90 ° C. and a processing time of 10 seconds, 10 in a direction orthogonal to the main shrinkage direction % Heat shrinkable polyester film   The heat-shrinkable polyester film according to claim 1, wherein the heat-shrinkable polyester film has at least one layer containing titanium oxide.   The heat-shrinkable polyester film according to claim 1, wherein the heat-shrinkable polyester film has at least one layer containing a thermoplastic resin incompatible with the polyester. Film.   The heat-shrinkable polyester film according to any one of claims 1 to 3, comprising polyethylene terephthalate as a main component and 18 mol% or more of an auxiliary component monomer that is an amorphous component.   5. The heat according to claim 1, comprising at least one layer composed of two or more layers and containing no thermoplastic resin incompatible with titanium oxide or polyester. Shrinkable polyester film.   The heat-shrinkable label produced using the heat-shrinkable polyester-type film in any one of Claims 1-5.