JP2007290321A - Multilayered heat-shrinkable polyester film and label - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester film which is suitable for label use, has light-shielding property and exhibits a white color which is excellent particularly in the appearance in a shrinked state. <P>SOLUTION: The multilayered heat shrinkable polyester film is composed of at least two layers, the film has a total light permeability of 40% or less, and exhibits a heat-shrinkability difference in the main axis direction between the value after the treatment for 10 seconds at 80°C [SHW10] and that after the treatment for 5 seconds at the same temperature [SHW 5] of 2% or more, and a maximum heat-shrinking modulus in the main axis direction in hot wind at 90°C of 10 MPa or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

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 milk bottle cap seals, especially for home delivery milk labels, wrinkles, shrinkage spots, distortions and jumps due to heat shrinkage are extremely small, shrinkage is unlikely to occur, and printing is not performed. In particular, the present invention relates to a heat-shrinkable polyester film that is white and has light-cutting properties.

  As a heat-shrinkable film, particularly a heat-shrinkable film for labeling a bottle body, 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 collecting and 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, beverage containers and food containers have been provided with cap seals on their stoppers or lids. Some containers are integrated with the label, and there are types in which the lid is peeled off by tearing along the perforation. The purpose of applying the cap seal is not only to give decorativeness, but also to prevent contamination with poisons and the like.

However, when used as a cap seal, since the bottle shape is complicated and there are many types, the conventional heat-shrinkable film may cause a problem in shrinkage finish. In particular, when a quarter of the entire milk bottle is covered as a cap seal, the lower part of the label often jumps up without stopping. (For example, refer to Patent Document 1).
JP 2000-301609 A

  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.

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 cap seal described above and an ultraviolet cut in a long wavelength region. It was.
JP 2004-114498 A

  Moreover, the conventional transparent film has printed on the side which hits the inner surface of a label. Since the inside of the label is in direct contact with the milk bottle, the safety of residual solvent is a problem. In particular, the cap seal has a danger that the ink may be transferred to a bottle called milk blocking because the printing surface touches the part where the mouth is to be attached.

  The heat-shrinkable film used for such a milk bottle cap seal needs heat shrinkage characteristics such as shrinkage and concealment. Conventional polyester heat-shrinkable films have insufficient performance.

  The present invention solves the above-mentioned problems, and its object is a heat-shrinkable polyester film for cap sealing of containers, particularly for cap sealing of milk glass bottles, and it is difficult for insufficient shrinkage to occur. In particular, it is to provide a heat-shrinkable polyester film having very little wrinkles, shrinkage spots, distortions and jumps due to shrinkage and having sufficient light-cutting properties without printing on the inner surface of the label.

  A multilayer heat-shrinkable polyester film comprising at least two layers, wherein the polyester film has a total light transmittance of 40% or less, a heat shrinkage rate of 80 ° C. in the main shrinkage direction, and a treatment time of 10 seconds. The difference [SHW10]-[SHW5] between the value [SHW10] and the processing time 5 seconds [SHW5] is 2% or more, and the maximum value of the heat shrinkage stress in hot air at 90 ° C. is 10 MPa or less in the main shrinkage direction. This is a multilayer heat-shrinkable polyester film characterized in that it can solve the problem.

  The present invention is a multilayer film composed of an A layer and a B layer, and achieves multiple functions by imparting different characteristics to the A layer and the B layer, respectively.

  In this case, it is preferable to use a polyester elastomer. The polyester elastomer is, for example, a polyester block copolymer composed of 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 this case, when the total of one or more monomer components that can be amorphous components in 100 mol% of the polyhydric alcohol component in all the polyester resins is 12 mol% or more, secondary processing such as solvent adhesion is performed. It becomes easy to satisfy the characteristics, and it is particularly preferably 14 mol% or more.

  In this case, it is preferable that the monomer that can be an amorphous component in the total polyester resin component of the film is neopentyl glycol or cyclohexanedimethanol.

  Furthermore, in this case, it is preferable to have at least one layer containing titanium oxide.

  Furthermore, in this case, it is preferable to have at least one layer containing a thermoplastic resin incompatible with polyester.

  Furthermore, in this case, a label made using the film is suitable for a bottle.

  Furthermore, in this case, a label produced using the film so as to print on the outer surface of the label without printing on the inner surface (container side) of the label is a suitable application for the bottle.

  When the heat-shrinkable polyester film of the present invention is used as a cap seal of a container, it is possible to achieve a good finish with very little occurrence of wrinkles, shrinkage spots, distortion, jumping up and insufficient shrinkage due to heat shrinkage, and light-cutting. It is extremely useful as a cap seal for milk bottles because of its excellent properties.

Embodiments of the present invention will be specifically described below.
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.
In the present invention, terephthalic acid is preferable as the main acid component, and ethylene glycol is preferable as the main diol component.

  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.

  When a polyester film containing the second alcohol component is stretched, a heat-shrinkable polyester film can be obtained.

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

Further, the total of at least one monomer component that can be an amorphous component in 100 mol% of the polyhydric alcohol component in all the polyester resins is preferably 14 mol% or more, and more preferably 16 mol% or more. Particularly preferred is 18 mol% or more.
Here, examples of the monomer that can be an amorphous component include neopentyl glycol and 1,4-cyclohexanediol.

  Further, in addition to a heat-shrinkable polyester film having particularly excellent shrinkage finish, in order to improve the shrink finish while having a high heat shrinkage rate, in 100 mol% of the polyhydric alcohol component in the total polyester resin, The amount of neopentyl glycol or cyclohexane dimethanol component is preferably 14 mol% or more, more preferably 16 mol% or more, and particularly preferably 18 mol% or more. The upper limit of the component is not particularly limited, but if the amount of the component is too large, the thermal shrinkage rate may become excessively high or the rupture resistance of the film may be deteriorated. It is preferable that it is 35 mol% or less, and it is especially preferable that it is 30 mol% or less.

In order to improve the shrink finish, the polyester elastomer content is preferably 3% by mass or more. Here, the polyester elastomer is a polyester block copolymer comprising, for example, 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. And polyester elastomers using polylactones such as poly-ε-caprolactone in the low melting point soft polymer segment.
Moreover, it is possible to make the shrinkage rate of the direction orthogonal to the main shrinkage | contraction direction appropriate by making a polyester elastomer into the said range and combining with the preferable manufacturing method and conditions mentioned later.

  In common, an aliphatic linear diol having 8 or more carbon atoms (eg, octanediol) or a trihydric or higher polyhydric alcohol (eg, trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.) It is preferable not to contain. In the heat-shrinkable polyester film obtained by using polyester containing these diols or polyhydric alcohols, it becomes difficult to achieve a necessary 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 order to achieve the specific total light transmittance of the film of the present invention and impart light-cutting properties to the film, for example, in the film, particles such as inorganic particles and organic particles are 0.1% relative to the film mass. It is suitable to contain -20 mass%, preferably 1-15 mass%. When the content of the particles is less than 0.1% by mass, for example, it is difficult to obtain 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, which is not preferable.

  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; High melting point organic compounds that are insoluble in the membrane, cross-linked polymers, and metal compounds used during polyester synthesis Catalysts such as alkali metal compounds and alkaline earth metal compounds can be internal particles formed inside the polymer during polyester production. . 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 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 necessary light-cutting properties. If the average particle size of the particles exceeds 3.5 μm, for example, the film surface is inferior in smoothness and defects such as printing omission are likely to occur. The average particle diameter of the anatase form is generally 2.0 μm or less, and the average particle diameter of the rutile form is 2.0 μm or more. In order to conceal visible light, a particle size of 2.0 to 3.0 μm is most efficient, and rutile titanium oxide generally has higher concealability than anatase form.

  Titanium oxide particles are classified into anatase and rutile crystal forms. Both are used for kneading plastics. The anatase type is likely to cause yellowing and resin degradation due to direct sunlight, etc. When used outdoors, the surface of titanium oxide may be subjected to special treatment (alumina, silica, organic, etc.) or the rutile type may be selected. Many.

  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, in addition to the layer B containing a large number of cavities, it is preferable to provide a layer A that does not substantially 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 not to contain incompatible resin in the A layer as a raw material. By doing so, there is no cavity in the A layer, and the film can maintain the strength after printing. In addition, since there are no cavities, the film does not become weak and has excellent wearability.
In addition, since the shrinkage rate is reduced by the formation of the cavity, a high thermal shrinkage rate can be provided by providing a layer without the cavity.

  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 the A layer having no cavities on both surface layers. By adding polystyrene resin, smoke is generated at the time of melt extrusion, fouling the process and causing deterioration in operability. By using the B layer as an intermediate layer, the problem of smoke generation is eliminated, and stable production over a long period of time becomes possible.

  Furthermore, you may contain additives, such as a stabilizer, a coloring agent, antioxidant, an antifoamer, an antistatic agent, and an ultraviolet absorber, as needed. Moreover, you may add a fluorescent whitening agent in order to improve the whiteness of a film.

[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) antioxidant to polyester (for example, 0.01 to 1 quality) Such as% of content) is a method to the like.

  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.

[Heat shrinkage stress]
The maximum value of the heat shrinkage stress in the 90 ° C. hot air in the main shrinkage direction is preferably 10 MPa or less, and more preferably 4 MPa or more and 10 MPa or less.
When the maximum value of the heat shrinkage stress is less than 4 MPa, for example, depending on the shape of the container, after the label is shrunk, the label is not sufficiently adhered, and the problem that the label also rotates is not preferable. Further, if the maximum value of the heat shrinkage stress exceeds 10 MPa, it rapidly jumps and jumps to cause problems such as wrinkles.
[Heat shrinkage]
From the length before and after shrinkage after treatment in warm water with no load, the rate of heat shrinkage = ((length before shrinkage−length after shrinkage) / length before shrinkage) × 100 (%) The calculated heat shrinkage ratio of the film in the main shrinkage direction is that the difference [SHW10]-[SHW5] between the value [SHW10] for the processing temperature 80 ° C. and 10 seconds and the value [SHW5] for the processing time 5 seconds is 2% or more. Preferably there is. If the difference in shrinkage is less than 2%, wrinkles and shrinkage spots during shrinkage are likely to occur due to rapid shrinkage. Preferably, the difference in shrinkage is 3% or more. The upper limit of the difference in shrinkage is not particularly specified, but is preferably 9% or less, more preferably 7% or less, and particularly preferably 5% or less. If the shrinkage rate difference becomes too large, shrinkage may be insufficient in high-speed (short time) processing. The difference in shrinkage can be set to 2% or more by adopting the above-mentioned preferable raw material composition and the preferable film forming conditions described later.

  The heat shrinkage rate at 80 ° C. for 10 seconds is preferably 45 to 60%, and if it is less than 45%, for example, the shrinkage of the head of the milk bottle becomes insufficient, which is not preferable. On the other hand, if it exceeds 60%, the force for further shrinkage remains even after heat shrinkage.

  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.

  The extrusion temperature is preferably in the range of 250 ° C to 290 ° C. When the extrusion temperature is lower than 250 ° C., for example, a load is excessively applied and normal extrusion becomes difficult. When the extrusion temperature exceeds 290 ° C, for example, the polyester resin is likely to be thermally deteriorated in the extruder, resulting in problems such as a decrease in mechanical strength of the resulting film and excessive shrinkage in the longitudinal shrinkage resulting in a decrease in shrink finish. Arise.

  When the unstretched film is stretched, first, preheating is performed. The temperature of preheating shall be in the range of Tg + 10 ° C. to Tg + 20 ° C. of the unstretched film. Next, stretching is performed. The stretch ratio is 3.4 times or more and 5.0 times or less, preferably 3.6 times or more and 4.5 times or less with respect to the unstretched film. The stretching temperature is a predetermined temperature in the range of Tg-5 ° C to Tg + 15 ° C.

  Next, it is preferable to heat-fix the film. The heat setting temperature is in the range of Tg + 10 ° C. to Tg + 20 ° C. Moreover, you may heat-set in the state strained in the extending direction of the film. In that case, the tension rate is desirably 6% or less.

  From the viewpoint of controlling the heat shrinkage stress of the film, it is preferable that the number of stretching steps is large. However, if the number of steps is too large, it is difficult to design a stretching facility in industrial production. It is desirable to have 4 or less steps.

  In order to set the total light transmittance to 40% or less, it is possible to increase the thickness ratio of the B layer. The thickness ratio of A layer / B layer / A layer is preferably 15 to 35/70 to 30/15 to 35.

[Melting resistivity]
The heat-shrinkable polyester film used in the present invention has a melting specific resistance value at a temperature of 275 ° C. of 0.70 × 10 ⁸ Ω · cm or less. 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.

  In order to control the melting specific resistance 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.

  There is no particular limitation on the timing of addition of the above-mentioned compounds for reducing the specific resistance value (alkali metal compounds, alkaline earth metal compounds, phosphorus-containing compounds, etc.), and polymerization is performed before esterification, during esterification, and after completion of esterification. It may be at any stage during polymerization, during polymerization, or after polymerization. It is preferably at any stage after the esterification step, more preferably from the end of esterification to the start of the polymerization step. When an alkaline earth metal compound and a phosphorus-containing compound (and an alkali metal compound if necessary) are added after the esterification step, the amount of foreign matter generated can be reduced as compared with the case where it is added before that.

[Thickness distribution value in the maximum shrinkage direction]
Even if the melt specific resistance value is lowered and the film thickness uniformity is increased as described above, it is not sufficient. That is, when forming a film roll, since the said film is elongate (for example, about 300-6000m), there exists a prisoner whose thickness uniformity falls depending on a measurement location.

  The uniformity of the thickness can be determined based on the thickness distribution value represented by the following formula.

Thickness distribution value = (maximum thickness−minimum thickness) / average thickness × 100
The maximum thickness, the minimum thickness, and the average thickness are obtained by cutting a test piece from a roll so that the length in the main shrinkage direction is 20 cm and the width is 5 cm, and the thickness is displaced with respect to the main shrinkage direction using a contact-type thickness meter. Can be determined by measuring.

  The heat-shrinkable polyester film of the present invention preferably has a film thickness distribution value calculated by the above formula of 6% or less. More preferably, it is 5% or less.

A film having a thickness distribution of 6% or less is easy to superimpose colors by, for example, three-color printing performed at the time of shrinkage finish evaluation, whereas a film exceeding 6% is preferable in terms of color superposition. Absent.

  In order for the sample at each location to have the predetermined thickness distribution value, it is not sufficient that the film forming process and the stretching process reach a steady state, and when the molten polyester is extruded and cooled with a cooling roll, It is necessary to stabilize the electrostatic adhesion of the film from the beginning to the end of film production. As the electrode used for the cooling, it is preferable to use an electrode provided with an electrode contaminated surface retracting means and an electrode contaminated surface supplying means. That is, when electricity is applied from an electrode during film formation of molten polyester and the film is electrostatically adhered, the polyester contains a plurality of types of polymers (homopolymers, copolymerized polymers, etc.) and monomers. Since it often contains molecular components, the low molecular components volatilize during melt extrusion and gradually contaminate the electrode. Therefore, if production of the film is continued, the contamination of the electrode gradually becomes severe, and it becomes impossible to apply sufficient electricity to the film, and there is a captive that the electrostatic adhesion of the film is lowered. Therefore, by using the specific electrode, electrode contamination can be saved, and a non-contaminated surface can be supplied instead, and the electrode surface can be maintained in a state with little contamination. Therefore, even if production of the film is continued, there is no prisoner that the electrostatic adhesion decreases, and the samples at each location have the predetermined thickness distribution.

  In order for the sample at each location to have the predetermined thickness distribution, (A) a method of homogenizing a polyester raw material during film production, together with the method of stabilizing electrostatic adhesion from the beginning to the end of film production It is desirable to employ (B) a method for stabilizing the production process and / or (C) a method for stabilizing the film stretching process.

(A) Method of homogenizing polyester raw material during film production Fine powder (fine powder polyester chip) generated by scraping raw material chips used promotes the occurrence of raw material segregation. Reduction in raw material segregation can also be achieved.

  The ratio of the fine powder in the polyester 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.

  Moreover, a method of using a funnel-shaped hopper as the final hopper and bringing its hypotenuse (side wall) closer to the vertical can be mentioned. 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 rotation speed fluctuation of the cooling roll (casting roll), for example, the rotation speed is preferably stabilized within a range of ± 2% of the average rotation 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.

  When controlling the stretching temperature, 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, and further, the strength of the film will be insufficient when the obtained heat-shrinkable film is mounted on a container (such as a bottle) at high speed. In some cases.

  The stretching temperature is preferably controlled to, for example, glass transition temperature (Tg) + 40 ° C. or lower (preferably + 15 ° C. or lower).

  Although the relationship with the thickness distribution value is small, the stretching temperature is preferably a glass transition temperature (Tg) of −20 ° C. or higher (preferably −5 ° C. or higher). If the stretching temperature is too low, the transparency of the film may decrease.

  When the internal heat generation of the film accompanying stretching is suppressed, the temperature unevenness of the film in the stretching direction (such as the width direction) can be reduced, and the uniformity of the thickness of the stretched film (heat-shrinkable film) can be enhanced.

  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 condition is represented by a heat transfer condition, for example, the heat transfer coefficient is 0.0038 J / cm ² · sec · ° C. (0.0009 calories / cm ² · sec · ° C.) or more, preferably 0.0046 to 0.00. It is about 0071 J / 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 equipped 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].

  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 It measured according to JISK7136 using Nippon Denshoku Industries Co., Ltd. NDH-2000T.

(2) Heat shrinkage stress Using a Tensilon (with heating furnace) strong elongation measuring machine manufactured by Toyo Seiki Co., Ltd., a sample having a length of 200 mm in the main shrinkage direction and a width of 20 mm was cut out from the heat shrinkable film, and the chuck was 100 mm in length. , Stop the air blowing in an atmosphere heated to 90 ° C. in advance, attach the sample to the chuck, then quickly close the heating furnace door and measure the stress detected when the air blowing (blowing air speed 5 m / sec) is started, The maximum value obtained from the chart was defined as heat shrinkage stress (MPa).

(3) Heat shrinkage rate The film was cut into a 10 cm × 10 cm square, and heat-shrinked in hot water at a hot water temperature of 80 ° C. ± 0.5 ° C. under no load for 5 or 10 seconds. The dimensions in the vertical and horizontal directions were measured, and 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)

(4) Shrinkage Finishing Properties Two-color printing was performed in advance on a heat-shrinkable film using grass / gold ink from Toyo Ink Manufacturing Co., Ltd. The printed surface was an uncoated surface. A label having a folding diameter of 98 mm and a height of 65 mm was produced from the printed film. The label was printed on the outside.

A 200 ml glass bottle (height 123 cm, central diameter 5.8 cm) at a passage time of 10 seconds and a zone temperature of 80 ° C. using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc (Meiji Dairies) (Bottle used for delicious milk) (number of measurements = 20).
Evaluation was made visually and the criteria were as follows.
○: No wrinkles, jumping up, or insufficient contraction occurred ×: Wrinkles, jumping up, or insufficient contraction occurred

(5) 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).

(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). Moreover, the average value (n = 50) of the thickness distribution was evaluated according to the following criteria.
Thickness distribution = ((maximum thickness−minimum thickness) / average thickness) × 100 (%) (2)
○: 6% or less △: greater than 6% and less than 10% ×: 10% or more

(7) Intrinsic Viscosity 0.1 g of a sample (film or chip) was 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 determined by the following formula (Huggins formula).

η _sp / c = [η] + k [η] ² c
k is a so-called Huggins constant and is a measure of hydrodynamic interaction between solute molecules.
[Η] is obtained by plotting η _{sp /} c against _c from viscosity measurements of several solutions having different concentrations and extrapolating the obtained straight line from c → 0.
η _sp is the specific viscosity when the concentration is c.

(8) Composition ratio of film-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, 70 mol% ethylene glycol and terephthalic acid (IV: 0.75 dl / g)
Polyester c: Polyester composed of 30 mol% cyclohexanedimethanol, 70 mol% ethylene glycol and terephthalic acid (IV: 0.75 dl / g)
Polyester d: Polyester raw material comprising 50% by weight of polyester b and 50% by weight of titanium oxide (IV: 0.51 dl / g)
Polyester e: Polyester raw material comprising 50% by weight of polyester a and 50% by weight of titanium oxide (IV: 0.51 dl / g)
Polyester f: Polyester elastomer comprising 70% by mass of polybutylene terephthalate and 30% by mass of ε-caprolactone (reduced viscosity (ηsp / c) 1.30)
Polyester g: Polybutylene terephthalate (IV: 1.24 dl / g)

Example 1
As layer A, 6% by weight of polyester a, 18% by weight of polyester b, 61% by weight of polyester c, and 15% by weight of polyester f are mixed, and as layer B, 55% by weight of polyester c and 20% by weight of polyester d. %, Polyester f mixed with 15% by mass of polyester f and 10% by mass of crystalline polystyrene resin (G797N made by Nippon Polystyrene Co., Ltd.) were melted at 280 ° C., respectively, and the layer thickness ratio was A layer / B layer / A layer = 25 Co-extruded from a T-die so as to be / 50/25 and quenched with a chill roll to obtain an unstretched multilayer film having a thickness of 160 μm. The unstretched multilayer film had a Tg of 65 ° C.

  The unstretched film was preheated until the film temperature reached 80 ° C., and then stretched in the transverse direction with a tenter. Stretching was performed 4.0 times at 73 ° C. Next, the film was heat-set at 82 ° C. while maintaining the film width at the end of stretching to obtain a film having a thickness of 40 μm.

(Example 2)
Polyester a 30% by mass, polyester b 65% by mass and polyester f 5% by mass mixed as layer A, polyester b 65% by mass, polyester e 20% by mass, and polyester f 5% by mass as layer B % And a crystalline polystyrene resin (G797N manufactured by Nippon Polystyrene Co., Ltd.) 10 mass% are respectively melted at 280 ° C. so that the layer thickness ratio is A layer / B layer / A layer = 25/50/25 The film was coextruded from a T-die and quenched with a chill roll to obtain an unstretched multilayer film having a thickness of 160 μm. In addition, Tg of this multilayer film was 68 degreeC.

  The unstretched film was preheated until the film temperature reached 85 ° C., and then stretched in the transverse direction with a tenter. The stretching was performed at 70 ° C. and 4.0 times. Next, the film was heat-set at 81 ° C. while maintaining the film width at the end of stretching to obtain a film having a thickness of 40 μm.

(Example 3)
As the A layer, a polyester obtained by mixing 36% by mass of polyester a, 49% by mass of polyester b, and 15% by mass of polyester f, and as the B layer, 6% by mass of polyester a, 49% by mass of polyester b, and 20% by mass of polyester e. %, Polyester f mixed with 15% by mass of polyester f and 10% by mass of crystalline polystyrene resin (G797N made by Nippon Polystyrene Co., Ltd.) were melted at 280 ° C., respectively, and the layer thickness ratio was A layer / B layer / A layer = 25 A film having a thickness of 40 μm was obtained in the same manner as in Example 1 except that the thickness was 50/25. The multilayer film had a Tg of 65 ° C.

  The unstretched film was preheated until the film temperature reached 82 ° C., and then stretched in the transverse direction with a tenter. Stretching was 4.0 times at 67 ° C. Next, the film was heat-set at 76 ° C. while maintaining the film width at the end of stretching to obtain a film having a thickness of 40 μm.

(Comparative Example 1)
A film having a thickness of 40 μm was obtained in the same manner as in Example 2 except that the film width at the end of stretching was maintained and heat fixed at 74 ° C. In addition, Tg of this multilayer film was 68 degreeC.

(Comparative Example 2)
As layer A, 15% by weight of polyester a, 80% by weight of polyester b and 5% by weight of polyester g are mixed, and as layer B, 65% by weight of polyester b, 20% by weight of polyester d, and 5% of polyester c. A polyester mixed with 10% by mass of a mass% and a crystalline polystyrene resin (G797N made by Nippon Polystyrene Co., Ltd.) was melted at 280 ° C., and the layer thickness ratio was A layer / B layer / C layer = 25/50 / It was extruded from a T die so as to be 25, and quenched with a chill roll to obtain an unstretched film having a thickness of 160 μm. The unstretched film had a Tg of 69 ° C.

  The unstretched film was preheated until the film temperature reached 86 ° C., and then stretched in the transverse direction with a tenter. Stretching was 4.0 times at 71 ° C. Next, the film was heat-set at 82 ° C. while maintaining the film width at the end of stretching to obtain a film having a thickness of 40 μm.

  Table 1 shows the evaluation results of the films obtained in Examples 1 to 3 and Comparative Examples 1 and 2. As is clear from Table 1, the films obtained in Examples 1 to 3 all had good shrinkage finish. The thickness distribution was also good. 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 are all inferior in shrink finish. Thus, all the heat-shrinkable polyester films obtained in the comparative examples were inferior in quality and low in practicality.

  The heat-shrinkable polyester film of the present invention has very few wrinkles, shrinkage spots, distortions, and jumps due to heat shrinkage, hardly causes shrinkage shortage, and exhibits a white color even without printing processing. It is extremely useful as a cap seal for milk bottles having a large amount, particularly as a label for home delivery milk.

Claims (7)

  A multilayer heat-shrinkable polyester film comprising at least two layers, wherein the polyester film has a total light transmittance of 40% or less, a heat shrinkage rate of 80 ° C. in the main shrinkage direction, and a treatment time of 10 seconds. The difference [SHW10]-[SHW5] between the value [SHW10] and the processing time 5 seconds [SHW5] is 2% or more, and the maximum value of the heat shrinkage stress in hot air at 90 ° C. is 10 MPa or less in the main shrinkage direction. A multilayer heat-shrinkable polyester film characterized by being   As a resin component constituting the film, a polyester elastomer is contained at 3% by mass or more, and the polyester elastomer has a high melting point crystalline polyester segment having a melting point of 200 ° C. or more, and a low melting point having a molecular weight of 400 or more and a melting point of 80 ° C. or less. The multilayer heat-shrinkable polyester film according to claim 1, which is a polyester block copolymer comprising a soft polymer segment.   The multilayer heat-shrinkable polyester film according to claim 1 or 2, wherein the monomer that can be an amorphous component in all the polyester resin components constituting the film is neopentyl glycol or cyclohexanedimethanol. .   The multilayer heat-shrinkable polyester film according to any one of claims 1, 2, and 3, wherein the multilayer film contains at least one layer containing titanium oxide.   5. The multilayer heat-shrinkable polyester film according to claim 1, comprising at least one layer containing a thermoplastic resin incompatible with polyester.   The label produced using the heat-shrinkable polyester-type film in any one of Claims 1, 2, 3, 4, or 5.   A label printed only on the outer surface using the heat-shrinkable polyester film according to any one of claims 1, 2, 3, 4, 5, and 6.