JP2006089516A - White polyester film for heat-shrinkable packaging - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a white polyester film for heat-shrinkable packaging, which is a film useful for a white label of a PET bottle, has especially high opacifying properties and excellent protection of contents and handleability. <P>SOLUTION: The white polyester film for heat-shrinkable packaging comprises a polyester composition containing 20-40 wt.% of white pigment, has 1,400-1,800 kg/m<SP>3</SP>apparent density, ≥0.70 optical density and ≥20% shrinkage percentage in treatment in warm water at 80°C for 10 seconds in the main shrinkage direction and ≤10% in the direction perpendicular to the main shrinkage direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a white polyester film for heat shrink wrapping used for heat shrink wrap. More specifically, the present invention relates to a white polyester film for heat-shrinkable packaging, which is a stretched polyester film that is excellent in white hiding properties and useful as a label material having contents protection.

  Conventionally, a film made of polyvinyl chloride or polystyrene has been used as a heat-shrinkable film for the label of the PET bottle body. Among these, for polyvinyl chloride, in recent years, there is a problem of generation of chlorine gas when incinerated at the time of disposal, and for polyethylene, there are problems such as difficulty in printing. Furthermore, when collecting and recycling PET bottles, it is necessary to separate resin labels other than PET, such as polyvinyl chloride and polyethylene. For this reason, polyester-based heat-shrinkable films that do not have these problems are attracting attention.

  Under such circumstances, depending on the type of the contents of the PET bottle, there has also appeared a product using a white film substrate as a label in order to prevent deterioration from light from the outside. That is, there is a technique for imparting white hiding properties to a polyester-based shrink film. For example, a method has been proposed in which a film has a foamed structure or a slight amount of a white pigment is added (Japanese Patent Laid-Open No. 2002-36356).

  In recent years, the contents of PET bottles have been diversified more and more, and the quality and functionality of the label for PET bottle barrels have been remarkably increased, and the conventional white shrink film technology lacks the concealability. In particular, in the contents of medicinal ingredients and the PET bottle body label used for contents such as beer that require high flavor, it is necessary to conceal the light from outside as much as possible. Originally, the concentration of white pigment added is low, and the concealability due to the low density foam structure is also low compared to the pigment added type, making it difficult to meet market demands.

Furthermore, white films having a foamed structure are weak and often cause poor transport in the label insertion process and the like, and improvements are desired.
JP 2002-36356 A

  The present invention solves the above-mentioned problems, and the object thereof is a film used for a white label of a PET bottle, particularly a label having high concealability and excellent content protection and handling properties. It is to provide a white polyester film for heat shrink packaging.

That is, the present invention comprises a polyester composition containing 20 to 40% by weight of a white pigment, and is treated for 10 seconds in warm water at an apparent density of 1400 to 1800 kg / m ³ , an optical density of 0.70 or more, and 80 ° C. Is a white polyester film for heat-shrinkable packaging having a shrinkage ratio of 20% or more in the main shrinkage direction and 10% or less in the direction perpendicular to the main shrinkage direction.

  The white polyester film for heat-shrink packaging of the present invention is characterized by containing 20 to 40% by weight of white pigment, preferably 26 to 40% by weight of white pigment, per 100% by weight of the polyester composition constituting the film. .

  ADVANTAGE OF THE INVENTION According to this invention, it is a film used for the white label of a PET bottle, and can provide the white polyester film for heat-shrink packaging for labels which is high in concealment property and excellent in content protection and handling properties. .

Hereinafter, the present invention will be described in detail.
[polyester]
The white polyester film for heat shrink packaging of the present invention is composed of a polyester composition. This polyester composition contains a white pigment.

  The polyester in the present invention is a polyester in which the acid component is terephthalic acid and the glycol component is ethylene glycol. This polyester preferably contains a copolymer component. As copolymer components, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dimer acid, succinic acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, cyclohexanedicarboxylic acid Aliphatic dicarboxylic acid such as isophthalic acid, 2-6 naphthalene dicarboxylic acid, 2-7 naphthalene dicarboxylic acid, 1-5 naphthalene dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, 5-sodium sulfoisophthalic acid, 4- Examples thereof include aromatic dicarboxylic acids such as hydroxybenzoic acid, diphenyl ether dicarboxylic acid and anthracene dicarboxylic acid, and oxycarboxylic acids such as ε-caprolactone and lactic acid. Examples of the alcohol component include diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, cyclohexanedimethanol, neopentylglycol and other aliphatic diols, polyethylene glycol Examples thereof include polyalkylene glycols such as polypropylene glycol and polytetramethylene glycol, and glycols such as ethylene oxide adducts of bisphenol A and bisphenol S. Polyfunctional compounds such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, and pentaerythritol may be used as the copolymerization component. Of these, isophthalic acid and 2,6-naphthalenedicarboxylic acid are particularly preferred as the acid component. As the alcohol component, diethylene glycol, propylene glycol, neopentyl glycol, butanediol, and cyclohexanedimethanol are particularly preferable. One of these copolymer components may be used, or two or more thereof may be used.

  Polyester may be used independently and may mix and use 2 or more types. The polyester may be used by mixing other homopolyester resins. Examples of the homopolyester resin include polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyneopentylene terephthalate, and polyneopentylene isophthalate.

  When a component other than polyester terephthalic acid and ethylene glycol is used as the copolymer component, the copolymer component is a total of the acid component and the glycol component, preferably 5 to 40 mol%, more preferably 10 to 30 mol%. Is done. If it is less than 5 mol%, the crystallinity is too high and the shrinkage properties are deteriorated, which is not preferable. On the other hand, if it exceeds 40 mol%, the amorphous property is too high and the mechanical strength of the film is greatly reduced, making film formation difficult. Therefore, it is not preferable. In particular, an embodiment in which the polyester contains an isophthalic acid component and / or a 2,6-naphthalenedicarboxylic acid component as a copolymer component in an amount of 5 to 40 mol% is a preferable embodiment in order to obtain good shrinkage characteristics.

  The intrinsic viscosity of the polyester is preferably 0.50 to 1.0, more preferably 0.52 to 0.80, and particularly preferably 0.55 to 0.75.

[Polymerization catalyst]
In the present invention, it is preferable to use a titanium compound as a catalyst for the polymerization of the polyester. The titanium compound as the catalyst may be used alone or in combination with a germanium compound. By using a polyester obtained by polymerizing a titanium compound as a polymerization catalyst, it is possible to obtain a good film-forming property while keeping the crystallinity of the polymer low during film formation, even though the film contains a large amount of white pigment. . On the other hand, when an antimony compound is used as a polymerization catalyst, the crystallinity of the polymer tends to be high, and as a result, the film of the present invention containing a white pigment at a high concentration tends to be oriented and crystallized at the time of stretch film formation. In order to make it worse, it is not preferable to use an antimony compound in the present invention.

  As the titanium compound, for example, tetrabutoxy titanium, tetraisopropoxy titanium, titanium acetate, preferably tetrabutoxy titanium may be used. The addition amount of the titanium compound as a catalyst is preferably 1 to 30 ppm, more preferably 2 to 25 ppm as the titanium element concentration in the polyester. For example, germanium dioxide may be used as the germanium compound.

  The polyester in the present invention can be produced by a known method. Specifically, oligomers are obtained by transesterification from dimethyl terephthalate and ethylene glycol and the desired copolymerization component monomer, or by direct esterification of terephthalic acid and ethylene glycol and the desired copolymerization component monomer. And then obtained by melt polymerization. If necessary, these may be subjected to solid phase polymerization by a conventional method.

[White pigment]
Examples of the white pigment in the present invention include titanium oxide, silicon oxide, aluminum oxide, barium sulfate, zinc sulfide, calcium carbonate, kaolin, and clay, preferably titanium oxide, silicon oxide, barium sulfate, and zinc sulfide, particularly preferably. Titanium oxide, especially titanium dioxide.

  The ratio of the white pigment in the copolymerized polyester is 20 to 40% by weight, preferably 26 to 40% by weight. When the proportion of the white pigment is less than 20% by weight, the white hiding property is insufficient. If it exceeds 40% by weight, the film forming property is insufficient and stable production cannot be achieved. From the viewpoint of film formation stability, the average particle size of the white pigment is preferably 0.05 to 1.0 μm, more preferably 0.1 to 0.8 μm, and particularly preferably 0.2 to 0.5 μm. .

[Apparent density]
The apparent density of the film of this invention is 1400-1800 kg / m < ³ >, Preferably it is 1500-1750 kg / m < ³ >, Most preferably, it is 1600-1700 kg / m < ³ >. If it is less than 1400 kg / m ³ , the film does not have sufficient waist, making it difficult for the tube to open in the label mounting step, which is likely to cause a conveyance failure. If it exceeds 1800 kg / m ³ , the film becomes brittle and the film-forming property is deteriorated.

[Shrinkage factor]
The shrinkage of the film of the present invention needs to be 20% or more in the main shrinkage direction and 10% or less in the direction perpendicular to the main shrinkage direction when treated in warm water at 80 ° C. for 10 seconds. Further, it is preferably 35% or more in the main shrinkage direction and 5% or less in the direction perpendicular to the main shrinkage direction. If it has such a property, when it uses for the white label of a PET bottle, the concealing property is especially high, and the container for drinks excellent in the content protection property and handling property can be obtained.

[Crystal melting heat]
The crystal melting heat quantity ΔHm measured by the differential scanning calorimeter of the film of the present invention is preferably 20 to 60 J / g, more preferably 25 to 55 J / g, and particularly preferably 30 to 50 J / g. ΔHm is an index of the amount of crystals (orientated crystals at the time of film formation and cold crystallization during heating) existing in the film, and it is considered that the larger the ΔHm, the more crystals are present. If ΔHm is less than 20 J / g, the film is close to amorphous and the mechanical strength of the film may be insufficient. On the other hand, if it exceeds 60 J / g, the degree of crystallinity becomes too high and the shrinkage property tends to be lowered, which is not preferable.

[Optical density]
The optical density of the film of the present invention is 0.70 or more, preferably 0.75 or more, more preferably 0.80 or more. When the optical density is less than 0.70, the concealability is insufficient and the content is not sufficiently protected.

[Lubricant]
The film of the present invention preferably contains a slight amount of a lubricant composed of fine particles having an average particle size of 5.0 μm or less in order to maintain handling properties. When the lubricant is contained, if the average particle size of the lubricant exceeds 5.0 μm, the surface flatness of the film tends to be lowered, which is not preferable. The average particle size of the lubricant is preferably at least 1.0 μm from the viewpoint of film forming properties and slipperiness. Although the amount of the lubricant added depends on the particle size, it may be selected within a range that does not adversely affect the winding property and surface flatness of the film. The lubricant may be inorganic or organic, and is preferably an inorganic lubricant. Examples of the inorganic lubricant include bulk silica and true spherical silica, and examples of the organic lubricant include silicone particles.

[Thickness]
The film of the present invention preferably has a thickness of 20 to 70 μm, more preferably 30 to 60 μm, and particularly preferably 35 to 55 μm. If it is less than 20 μm, the rigidity (waist) of the film becomes weak, and it may be bent when the label is mounted, which may cause a defective product. If it exceeds 70 μm, the rigidity (waist) of the film is too strong, and handling during processing becomes difficult, which is not preferable.

[Production method]
Next, the production method of the film of the present invention will be described in detail by taking as an example the case of using titanium dioxide powder as a white pigment.

  When the polyester chip is charged into the extruder, the titanium oxide powder is added at a ratio that gives the desired amount of addition with a screw feeder immediately above the inlet of the extruder, fed into the extruder screw, and heated and melted. Thereafter, the sheet is extruded and discharged from the die orifice of the T die. The softened sheet discharged from the die orifice is tightly wound around the cooling drum and cooled. Subsequently, the obtained unstretched sheet is preheated at a temperature of 85 to 135 ° C. and then stretched uniaxially at a stretch ratio of 3.0 to 5.0 times at a temperature of 60 to 80 ° C. If the stretching temperature is less than 60 ° C, a homogeneous stretched film may not be obtained. If the stretching temperature exceeds 80 ° C, the crystallization of the polyester is promoted and the film becomes brittle and the film production may be poor. . Further, if the draw ratio is less than 3.0 times, the strength is small, and pinholes are easily generated when folded into a tube shape, and if it exceeds 5.0 times, the thermal shrinkage rate is undesirably lowered. Longitudinal stretching may be performed before the unstretched sheet is laterally stretched. In this case, the stretching temperature may be stretched at a stretching ratio of 1.1 to 5.0 times at a temperature of 70 to 145 ° C. and immediately after that, it may be cooled to a temperature of 25 ° C. or less. The stretched film is heat-treated at a temperature of 60 to 70 ° C. When the heat treatment temperature is lower than 60 ° C., the dimensional stability of the film is deteriorated, which may cause deformation of the film in the printing process, the transportation process, or over time. Too low. As the stretching method, any of a tubular method, a roll and / or a tenter stretching method may be used.

  The film of the present invention can be subjected to surface treatment by corona discharge treatment, surface hardening treatment, or various coating treatments.

[Usage]
The film of the present invention is printed by a conventional method, processed into a tube shape, cut into a desired length, and can be used as a shrink label for, for example, a PET bottle, an aluminum bottle can, a lunch box tray or a vegetable tray. Even with such a label, a label having excellent appearance protection as well as excellent content protection can be obtained due to the high white hiding property of the film of the present invention. Even for contents that are easily deteriorated by light entering from the outside, such as pharmaceuticals and beer, it is possible to obtain a label that is more excellent in content protection against external light due to its excellent light shielding properties. it can.

Hereinafter, the present invention will be further described with reference to examples. Each characteristic was measured and evaluated according to the following method.
(1) Film thickness Using a dot-type film thickness gauge (Anritsu, K402B), the thickness was measured at 50 arbitrary locations in the film width direction and 50 arbitrary locations in the longitudinal direction near the center of the film width. The number average value of the locations is the film thickness.
(2) Optical density Using an optical densitometer (TR-310 type manufactured by X-Rite), V (Visual) optical density of the three primary colors of the film sample is measured.
(3) Apparent density 10 cm × 10 cm taking the size of the sample, and measuring the thickness of the試科a micrometer, determine the volume of the sample, then measuring the weight of試科, calculate the weight per 1 m ³ To do. The number of samples is five, and the average value is the apparent density.
(4) Thermal contraction rate In accordance with JIS-Z1709, the main contraction direction and the thermal contraction rate in the direction perpendicular to the main contraction direction when measured in warm water at 80 ° C. for 10 seconds are measured. The average value of each N = 3 is taken as the measured value. In addition, the film plane direction is measured, and the direction with the largest shrinkage is defined as the main shrinkage direction.
(5) Heat of crystal melting (ΔHm)
Using a DuPont Instruments 910 type DSC, the crystal melting peak area when the sample amount is 20 mg and the temperature is raised to 290 ° C. at a temperature rising rate of 20 ° C./min is determined. The measurement is performed 5 times in total, and the average value is defined as the heat of crystal fusion.

[Examples 1-6 and Comparative Examples 1-6]
Polyester having an intrinsic viscosity (o-chlorophenol, 35 ° C.) of 0.65 by a conventional method using dimethyl terephthalate, ethylene glycol, a copolymerization component shown in Table 1, and a polymerization catalyst, and using normal phosphoric acid as a stabilizer. A composition was prepared. The polyester contained titanium oxide as shown in Table 1, and 0.05% by weight of true spherical silica having an average particle diameter of 1.7 μm. As titanium oxide, titanium dioxide particles of JR603 manufactured by Teika Co., Ltd. having an average particle diameter of 0.28 μm were used.

  After drying the above polyester at 160 ° C. for 4 hours, it is supplied to an extruder hopper, melted at a melting temperature of 275 ° C., extruded onto a cooling drum having a surface temperature of 20 ° C. using a die, and rapidly cooled to obtain an unstretched film. It was. This unstretched film is supplied to a stenter, stretched in the direction (TD direction) perpendicular to the film forming direction at the stretching temperature and stretch ratio shown in Table 1, and then heat-set at 77 ° C. to obtain a uniaxially stretched polyester film. Obtained. In Example 2, longitudinal stretching (MD direction) was performed in the film forming direction under the conditions shown in Table 1, followed by immediate cooling with a metal roll at 20 ° C. and then lateral stretching with a stenter. A draw ratio of 1.0 means that the film is not substantially stretched. The properties of the obtained stretched polyester film are shown in Table 1.

  Each of the stretched polyester films of Examples 1 to 6 had high concealability, excellent contents protection and handling properties, and also had good shrinkage characteristics necessary for heat shrink labels.

  The stretched polyester film of Example 1 was printed by a conventional method, processed into a tube shape, and a 500 ml round plastic bottle (Coca-Cola National Beverage refreshment) at a rate of 200 BPM using a labeler (SAJ3100 model made by Fuji Seal). When 100 pieces of each were inserted into those used in Kenmi-cha, 100 labels could be delivered with no conveyance failure, and excellent handling properties could be obtained.

  In Comparative Example 1, the content of titanium oxide was too low, the concealability was low, and the contents were inferior in protection.

  In Comparative Example 2, the content of titanium oxide was too high and the film was cut in the stretching process, and a stretched film could not be collected.

  In Comparative Example 3, the film was stretched and formed with homopolyethylene terephthalate without a copolymer component, but the required shrinkage characteristics as a shrink film could not be obtained because the crystallinity was too high.

  In Comparative Example 4, since the copolymerization ratio of the copolymer was too high, the mechanical properties of the film were too low and the film was cut in the stretching process, and the stretched film could not be collected.

  In Comparative Example 5, since the ratio of the copolymerization component was too low and the crystallinity was too high, the necessary shrinkage characteristics as a shrink film could not be obtained.

  In Comparative Example 6, the crystallinity of the copolyester was too high and was cut in the stretching process, and a stretched film could not be collected. Comparative Example 7 had a low concealability and was inferior in content protection.

  The stretched polyester film of Comparative Example 7 was printed by a conventional method, processed into a tube shape, and a 500 ml round PET bottle (Coca-Cola National Beverage Refresher) at a rate of 200 BPM using a labeler (SAJ3100 model manufactured by Fuji Seal). When 100 pieces of each were inserted into the one used in Kenmi-cha, the handling properties were poor and 4 pieces were caught during the conveyance.

[Comparative Example 7]
The same operation as in Example 1 was conducted except that 10% by weight of titanium dioxide and 10% by weight of crystalline polypropylene (FO-50F manufactured by Grand Polymer) were added in Example 1. The properties of the obtained stretched polyester film are shown in Table 1.

  The white polyester film for heat-shrinkable packaging of the present invention has an excellent high hiding property without impairing the shrinkage and handling properties of the polyester film used in conventional heat-shrink labels. Therefore, since it is excellent in the protection of the content easily changed by external rays such as pharmaceuticals and beer, it is extremely useful as these shrink labels.

Claims (7)

It consists of a polyester composition containing 20 to 40% by weight of a white pigment, has an apparent density of 1400 to 1800 kg / m ³ , an optical density of 0.70 or more, and a shrinkage ratio when treated in warm water at 80 ° C. for 10 seconds. A white polyester film for heat-shrink packaging, which is 20% or more in the shrinking direction and 10% or less in the direction perpendicular to the main shrinking direction.   The white polyester film for heat shrink packaging according to claim 1, wherein the polyester is a polyester polymerized using a titanium compound as a catalyst.   The white polyester film for heat-shrinkable packaging according to claim 1, wherein the polyester contains an isophthalic acid component and / or a 2,6-naphthalenedicarboxylic acid component as a total of 5 to 40 mol% copolymerization component per total dicarboxylic acid component.   The white polyester film for heat-shrink packaging according to claim 1, wherein the shrinkage rate when treated in warm water at 80 ° C for 10 seconds is 35% or more in the main shrinkage direction.   The white polyester film for heat shrink packaging according to claim 1, wherein the polyester composition contains 26 to 40% by weight of a white pigment.   The white polyester film for heat-shrink packaging according to claim 1, wherein the white pigment is titanium dioxide.   The white polyester film for heat-shrinkable packaging according to claim 1, wherein the heat of crystal fusion ΔHm measured by a differential scanning calorimeter of the film is 20 to 60 J / g.