JP5011651B2 - Heat-shrinkable polyester film and heat-shrinkable label - Google Patents

Description

  The present invention relates to a heat-shrinkable polyester film useful for recycling PET bottles, corresponding to environmental problems and effective use of resources.

  Polystyrene and polyester films are mainly used as heat-shrinkable films for trunk labels such as PET bottle containers and cap seals such as glass containers. The heat-shrinkable polystyrene film is mainly used as a general-purpose type because it is less expensive than the heat-shrinkable polyester film and can be subjected to shrinkage treatment relatively easily. On the other hand, heat-shrinkable polyester film is used for applications that require high quality mainly because it has superior heat resistance, good film gloss, and high tightening stress after shrinkage compared to polystyrene film. Yes.

  On the other hand, from the viewpoint of environmental problems and effective utilization of resources, there is an active movement to recycle polyester recycled materials such as PET bottles, and one of the heat shrinkable polyester films that can be used. For example, Patent Document 1 describes an invention of a heat-shrinkable film material composed of a resin derived from a polyethylene terephthalate container and an amorphous polyester resin.

However, polyethylene terephthalate recycled raw materials such as PET bottles are a mixture of various containers, and are mixed with different polymers such as labels and caps, as well as sand adhered during distribution and recycling processes. The film using the recycled raw material has a problem in that a protrusion having the above-mentioned contaminants as a core is formed, and defective printing is generated.
JP 2004-196918 A

  The present invention provides a heat-shrinkable polyester film that is less likely to lose printing even when a recycled material such as a PET bottle is used.

The heat-shrinkable polyester film of the present invention that has solved the above problems is a heat-shrinkable polyester film in which a layer that does not contain a PET bottle reclaimed raw material is laminated on at least one surface of the base layer that contains a PET bottle reclaimed raw material. The content of the PET bottle recycled raw material in the base layer is 40% by mass or less , the ethylene terephthalate unit is 50 mol% or more in 100 mol% of the constituent unit of the heat-shrinkable polyester film, and the polyhydric alcohol component When the total amount is 100 mol%, neopentyl glycol and / or 1,4-cyclohexanedimethanol is contained in an amount of 10 to 30 mol%, and 1,4-butanediol and / or 1,3-propanediol is 5 Heat shrinkage in the main shrinkage direction when it is contained in ˜30 mol% and pulled up by being immersed in warm water at 80 ° C. for 10 seconds 30% or more, 10% or less the direction of the heat shrinkage rate orthogonal to the main shrinkage direction, and at least one side an outermost layer a layer containing no recycled PET bottles material, characterized in that uniaxially stretched even without least It is said.

  In the above-mentioned film, the thickness of the layer not containing the recycled material of the PET bottle on the surface to be the printing surface is 4 μm or more, and the content of the recycled PET bottle material in the base layer is preferably 40% by mass or less.

  The heat-shrinkable polyester film of the present invention has good printability and mechanical strength in spite of the use of recycled raw materials for PET bottles, from the viewpoint of environmental problems and effective utilization of resources. Useful.

  The heat-shrinkable polyester-based film of the present invention is a heat-shrinkable polyester-based film in which a layer not containing a plastic bottle recycling raw material is laminated on at least one side of a base layer containing the plastic bottle recycling raw material. In the recycling process of PET bottles, different materials are separated and washed in the recycling process, but caps and printing labels are mixed, and sand adhered to PET bottles is mixed. When a film is formed using the recycled raw material, these foreign substances become nuclei and form protrusions of 0.1 to several μm on the film. When ink is transferred and printed on the film by a gravure plate or the like, floating occurs around the protrusion, and the ink in this portion is not transferred, resulting in printing failure.

However, in the present invention, the heat-shrinkable polyester film has a multi-layer structure, and separately from the layer containing the PET bottle recycling raw material, at least the layer that does not contain the PET bottle recycling raw material is laminated on the printing surface to improve the printing omission. Can be obtained. It is preferable that the thickness of the layer that does not contain the PET bottle recycled raw material to be the printing surface of the film is 4 μm or more. This is because if the thickness of the layer is less than 4 μm, the effect of covering the protrusions caused by the PET bottle reclaimed raw material of the base layer is reduced and printing omissions increase. More preferably, the thickness of the layer not containing the PET bottle recycling raw material is 6 μm or more, and more preferably 10 μm or more. When performing double-sided printing, it is necessary to provide a layer that does not contain 4 μm or more of PET bottle recycling raw material on both front and back sides.

  The heat shrinkable polyester film of the present invention has a heat shrinkage rate of 30% or more in the main shrink direction in warm water at 80 ° C. The reason why the heat shrinkage rate is less than 30% is that when the container is shrunk as a label, a portion that does not adhere to the container is generated and becomes defective. The heat shrinkage rate in the main shrinkage direction is more preferably 40% or more, and still more preferably 50% or more.

  Further, the thermal shrinkage rate in the direction orthogonal to the main shrinkage direction is 10% or less. When the shrinkage rate exceeds 10%, the container is greatly displaced in the vertical direction when the container is shrunk to cover the container, which results in poor appearance and unstable label position. The thermal shrinkage rate in the direction orthogonal to the more preferred main shrinkage direction is 8% or less, more preferably 6% or less.

  In the present invention, the addition rate of the PET bottle recycled raw material to the base layer is preferably 40% by mass or less. More preferably, it is 30 mass% or less. In addition to the problem of mixing foreign materials such as foreign materials and sand, PET bottle recycled materials have a variety of pets with different melt viscosity, molecular weight, molecular weight distribution, monomer composition, crystallinity, polymerization catalyst type and addition amount, etc. Since these are made of bottles, these physical properties vary widely among production lots of recycled raw materials. A film to which 40% by mass or more of such a regenerated raw material is added has a large variation in quality, and the heat shrinkage rate and mechanical strength required as a heat shrinkable label may not be obtained. Although there is no restriction | limiting in particular about the minimum of the addition rate of the PET bottle reproduction | regeneration raw material to a base layer, Preferably it is 10 mass% or more, More preferably, it is 15 mass% or more.

  However, in the present invention, the heat-shrinkable film has a multilayer structure, the amount of addition of the PET bottle recycling raw material is limited, and a layer that does not contain the PET bottle recycling raw material is provided to ensure the heat shrinkage rate and mechanical strength. Is. A more preferable addition amount of the PET bottle recycling raw material is 25% by mass or less in the whole film, and can be achieved by adjusting the ratio of the base layer and the layer to which no PET bottle recycling raw material is added. A preferred layer ratio is 40:60 to 95: 5. Furthermore, the preferable addition amount of a PET bottle reproduction raw material is 20 mass% or less with respect to the whole film.

  The lower limit of the addition amount is not particularly limited, but preferably 5% by mass or more, more preferably 10% by mass or more, the higher the ratio of recycled raw materials used, the higher the recycling efficiency of PET bottles. It is preferable from the viewpoint of effective utilization.

  The recycled plastic bottle material here refers to a recycled raw material for a polyethylene terephthalate container such as a plastic bottle, and there are a recycled material material and a recycled chemical material, both of which can be used. Only one of them may be used or a mixture of them may be used.

  In the present invention, the intrinsic viscosity of the film is preferably 0.61 dl / g or more. This is because by setting the intrinsic viscosity of the film to 0.61 dl / g or more, the mechanical strength and tear resistance of the film are improved, and defects such as breakage can be reduced during printing and solvent bonding. In order to make the intrinsic viscosity of the film 0.61 dl / g or more, for example, it can be achieved by using a high molecular weight raw material for the polyester used. In the present invention, the intrinsic viscosity may be different between the base layer and the printed layer, but the intrinsic viscosity of the whole film may be 0.61 dl / g or more. The more preferable intrinsic viscosity of the film is 0.63 dl / g or more.

  In the present invention, the mechanical strength is preferably 70% or less, more preferably 25% or less, as the initial breaking rate in the evaluation methods of Examples described later. A preferable mechanical strength can be obtained by controlling the above-described layer structure, the amount of the PET bottle recycled raw material mixed, and the intrinsic viscosity of the film.

  The heat-shrinkable polyester film of the present invention has an ester unit formed from a polyvalent carboxylic acid component and a polyhydric alcohol component as a main constituent unit. Considering the tear resistance, strength, heat resistance, etc. of the film, it is preferable to select the ethylene terephthalate unit to be 50 mol% or more in 100 mol% of the constituent unit of the heat-shrinkable polyester film. Therefore, in 100 mol% of the polyvalent carboxylic acid component, the terephthalic acid component (component comprising terephthalic acid or its ester) is 50 mol% or more, and in 100% mol of the polyhydric alcohol component, the ethylene glycol component is 50 mol% or more. It is preferable to do. As for an ethylene terephthalate unit, 55 mol% or more is more preferable, and 60 mol% or more is further more preferable.

  Polyhydric alcohols for forming the polyhydric alcohol component in the ester unit include propylene glycol, triethylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyl in addition to the above-mentioned ethylene glycol. -1,5-pentanediol, neopentyl glycol, 2-methyl-1,5-petanediol, 2,2-diethyl-1,3-propanediol, 1,9-nonanediol, 1,10-decandiol Aliphatic diols such as 1,4-cyclohexanedimethanol and the like, trimethylolpropane, glycerin, pentaerythritol, diethylene glycol, dimer diol, polyoxytetramethylene glycol, bisphenol compounds or alkylene oxide adducts thereof Etc. can also be used in combination.

  In addition to terephthalic acid and its esters, aromatic dicarboxylic acids, their ester-forming derivatives, aliphatic dicarboxylic acids, etc. can be used as the polyvalent carboxylic acids for forming the polyvalent carboxylic acid component. is there. Examples of the aromatic dicarboxylic acid include isophthalic acid, naphthalene-1,4- or -2,6-dicarboxylic acid, and 5-sodium sulfoisophthalic acid. Moreover, derivatives of these aromatic dicarboxylic acids and terephthalic acids include derivatives such as dialkyl esters and diaryl esters. Examples of the aliphatic dicarboxylic acid include glutaric acid, adipic acid, sebacic acid, azelaic acid, oxalic acid, succinic acid and the like, and an aliphatic dicarboxylic acid usually called dimer acid. Furthermore, an oxycarboxylic acid such as p-oxybenzoic acid, and a polyvalent carboxylic acid such as trimellitic anhydride and pyromellitic anhydride may be used in combination as necessary.

  In addition, although not polyhydric alcohols or polycarboxylic acids, lactones represented by ε-caprolactone may be used in part. Lactones are those that ring-open to become units having ester bonds at both ends, and a unit derived from one lactone can be considered to be a carboxylic acid component and an alcohol component. Therefore, when lactones are used, the amount of 1,4-cyclohexanedimethanol component and the amount of other polyhydric alcohol components is 100 mol% of the amount obtained by adding the unit amount derived from lactones to the amount of polyhydric alcohol components. Calculate as Also, when calculating the amount of each polycarboxylic acid component, the amount obtained by adding the unit amount derived from the lactone to the amount of the polyvalent carboxylic acid component is 100 mol%.

  As a preferable component constituting the unit other than the ethylene terephthalate unit, a component capable of reducing the high crystallinity by the ethylene terephthalate unit and ensuring low-temperature heat shrinkability and solvent adhesion is preferable. Examples of such a crystallinity-reducing component include isophthalic acid, naphthalene-1,4- or -2,6-dicarboxylic acid for polyvalent carboxylic acid components, and neopentyl glycol, 1,4-dicarboxylic acid for polyhydric alcohol components. Preferred examples include cyclohexanedimethanol, 1,4-butanediol and 1,3-propanediol. The combined use of these crystallinity-reducing components can improve the heat shrink characteristics, tear resistance and solvent adhesion of the film in a well-balanced manner. In particular, from the viewpoint of solvent adhesiveness, it is desirable to use, as a part of the raw material, a polyester containing a unit composed of at least one of these preferable components in at least the surface layer. In 100 mol% of the constituent unit of the raw material polyester, the unit containing these crystallinity-reducing components is preferably 10 mol% or more, more preferably 12 mol% or more, and further preferably 15 mol% or more. When the total amount of the polyvalent carboxylic acid component is 100 mol% and the total amount of the polyhydric alcohol component is 100 mol%, neopentyl glycol and / or 1,4-cyclohexanedimethanol is contained at 10 to 30 mol%, And it is a particularly preferable embodiment that it contains 5 to 30 mol% of 1,4-butanediol and / or 1,3-propanediol.

  The polyester constituting the heat-shrinkable polyester film can be produced by melt polymerization according to a conventional method, but a so-called direct polymerization method in which an oligomer obtained by directly reacting a dicarboxylic acid and a glycol is polycondensed is used. A so-called transesterification method in which a dimethyl ester and a glycol are subjected to a transesterification reaction and then polycondensed, and any production method can be applied. Moreover, the polyester obtained by another polymerization method may be sufficient. Various conventional catalysts can be used as the polymerization catalyst. For example, titanium-based catalysts (titanium tetrabutoxide, etc.), antimony-based catalysts (antimony trioxide, etc.), germanium-based catalysts (germanium dioxide, etc.), cobalt-based catalysts (cobalt acetate) Etc.).

  Moreover, in order to improve the slipperiness of the heat-shrinkable film, for example, an inorganic lubricant such as titanium dioxide, particulate silica, kaolin, calcium carbonate, or an organic lubricant such as a long-chain fatty acid ester may be added. Good. Moreover, you may add additives, such as a stabilizer, a coloring agent, antioxidant, an antistatic agent, and an ultraviolet absorber, as needed.

  The following method is desirable for producing the heat-shrinkable polyester film of the present invention. First, a chip-like PET bottle recycling raw material and other polyester raw materials are prepared, and these are dried using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. Then, it mixes suitably and it extrudes into a film form at the temperature of 200-300 degreeC from an extruder. Alternatively, the undried chips are similarly extruded into a film while removing moisture in a vented extruder. What is necessary is just to co-extrusion for the method of using the laminated film of a multilayer structure. As the PET bottle recycling raw material, it is preferable to use a chip-like material that has been cleaned and pulverized by a known method.

 When extruding, any existing method such as T-die method or tubular method may be adopted. After extrusion, it is quenched with a casting roll to obtain an unstretched film. The “unstretched film” includes a film on which a tension necessary for feeding the film in the manufacturing process is applied. By placing an electrode between the extruder and the casting roll and applying a voltage between the electrode and the casting roll, it is possible to electrostatically adhere the film to the roll in terms of suppressing film thickness unevenness. To preferred.

  The unstretched film is stretched. The stretching treatment may be performed continuously after cooling with the above-described casting roll or the like, or may be wound once in the form of a roll after cooling and then performed. Since it is practical in terms of production efficiency that the maximum shrinkage direction is the film transverse (width) direction, an example of a stretching method in the case where the maximum shrinkage direction is the transverse direction will be shown below. Even when the maximum shrinkage direction is the longitudinal (longitudinal) direction of the film, the film can be stretched according to a normal operation such as changing the stretching direction by 90 ° in the following method.

  When the heat-shrinkable polyester film is stretched in the transverse direction using a tenter or the like, prior to the stretching step, the film surface temperature is heated to a certain temperature within the range of Tg + 0 ° C. to Tg + 60 ° C., and Tg-20 The film is stretched 2.3 to 7.3 times, preferably 2.5 to 6.0 times at a predetermined temperature in the range of from C to Tg + 40C. Thereafter, heat treatment is performed at a predetermined temperature in the range of 50 ° C. to 110 ° C. while stretching 0 to 15% or relaxing 0 to 15%, and if necessary, at a predetermined temperature in the range of 40 ° C. to 100 ° C. Further heat treatment is performed to obtain a heat-shrinkable polyester film.

  As a stretching method, not only horizontal uniaxial stretching with a tenter, but also stretching in the longitudinal direction by 1.0 to 4.0 times, preferably 1.1 to 2.0 times may be performed. When biaxial stretching is performed in this manner, either continuous biaxial stretching or simultaneous biaxial stretching may be performed, and restretching may be performed as necessary. Further, in the sequential biaxial stretching, any of stretching methods such as vertical and horizontal, horizontal and vertical, vertical and horizontal and horizontal and vertical and horizontal directions may be used.

  Although the thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, for example, as a heat-shrinkable polyester film for labels, the total thickness is 20 μm or more, preferably 25 μm or more, and 300 μm or less, preferably 200 μm or less. It is recommended that

  In order to use the heat-shrinkable polyester film as a heat-shrinkable label, a known tube-shaped forming apparatus is used to apply an adhesive solvent with a predetermined width slightly inside from the edge of one side of the film, and immediately the film Are rolled and bonded with overlapping ends, and processed into a tube. This tube can be cut into a predetermined length to obtain the heat-shrinkable label of the present invention.

  The film can be bonded by a melt bonding method in which a part of the film is melted, but it is preferable to use a solvent from the viewpoint of suppressing fluctuations in the thermal shrinkage characteristics of the label. Examples of solvents that can be used include aromatic hydrocarbons such as benzene, toluene, xylene, and totimethylbenzene; halogenated hydrocarbons such as methylene chloride and chloroform; phenols such as phenol; furans such as tetrahydrofuran; Examples of the organic solvent include oxolanes such as 3-dioxolane; among them, 1,3-dioxolane and tetrahydrofuran are preferable in view of high safety. The heat-shrinkable label can be coated after being attached to a container such as a PET bottle and then heat-shrinkable by a known heat-shrinking means (hot air tunnel, steam tunnel, etc.).

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not intended to limit the present invention, and modifications and implementations within the scope of the present invention are included in the present invention. Moreover, the measuring method of the physical property of the film obtained by the Example and the comparative example is as follows.

(1) Thermal shrinkage rate The film was cut into a 10 cm × 10 cm square, immersed in warm water at 95 ° C. ± 0.5 ° C. for 10 seconds in a no-load state, and then thermally shrunk. It is a value obtained by immersing in 5 ° C. water for 10 seconds and then measuring the lengths of the sample in the vertical and horizontal directions according to the following formula. The direction with the largest shrinkage rate is defined as the maximum shrinkage direction.
Thermal shrinkage rate (%) = (length before shrinkage−length after shrinkage) ÷ (length before shrinkage) × 100

(2) Printability Using a PAS type printing machine manufactured by Toya Iron Works Co., Ltd., using ink (shrink EX grass color) manufactured by Toyo Ink Manufacturing Co., Ltd., using a 150-line × 30 μ × 20% gravure roll at a speed of 100 m / min The film was printed, the printing surface was magnified with a magnifying glass (15 times), the number of ink pinholes per square centimeter was counted, and the following criteria were used for evaluation.
○: 0 to 10 △: 11 to 50 ×: 51 or more

(3) Mechanical strength Tensile test (test specimen width: 15 mm, specimen length: 120 mm, distance between chucks: 20 mm) in the direction orthogonal to the maximum shrinkage direction after storage for 28 days in an atmosphere of 30 ° C. × 85% relative humidity The number of test pieces fractured at a tensile rate of 200 m / min, temperature of 23 ° C., number of samples: 20) and elongation of 5% or less was counted and evaluated according to the following criteria. In addition, the ratio (%) with respect to the total number of test pieces of the number of test pieces fractured at an elongation of 5% or less was defined as the initial fracture rate.
○: 0 to 5 (initial breakage rate 0 to 25%)
Δ: 6 to 14 (initial breakage rate 30 to 70%)
×: 15-20 (initial breaking rate: 75-100%)

(4) Intrinsic Viscosity 0.1 g of a sample (chip or film) is precisely weighed and dissolved in 25 ml of a mixed solvent of phenol / tetrachloroethane = 3/2 (mass ratio) and then 30 ± 0 using an Ostwald viscometer. Measure at 1 ° C. The intrinsic viscosity [η] is obtained by the following formula (Huggins formula).

[Formula 1] 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 a plot of η _SP / c against c from viscosity measurements of several solutions with different concentrations,
The obtained straight line is determined in general from c → 0.
It is the specific viscosity when the η _SP concentration is c.

Experiment 1
For the base layer, a polyester-based resin in which polyester A: 10% by mass, polyester B: 55% by mass, polyester C: 10% by mass, and polyester D: 25% by mass is used. For the front and back outer layers, polyester A: 35% by mass is used. %, Polyester B: 55% by mass, polyester C: 10% by mass of polyester resin, each melted at 270 ° C. by a separate single screw extruder, co-extruded from a T die, cooled with a chill roll, An unstretched film having a three-layer structure was obtained (thickness: 200 μm). This unstretched film was preheated at 88 ° C. for 10 seconds, stretched 3.9 times in the transverse direction at 80 ° C. with a tenter, and subsequently 10% at 78 ° C. Heat treatment was performed for 2 seconds to obtain a heat-shrinkable polyester film having a thickness of 50 μm (base layer: 25 μm / front and back layers: 12 μm each). Table 1 shows the composition and content of the polyester resin used. In Table 1, TPA means terephthalic acid, EG means ethylene glycol, BD means 1,4-butanediol, and NPG means neopentyl glycol. Table 2 shows the characteristics of the film.

Experiments 2-4
A heat-shrinkable polyester film having a thickness of 50 μm was obtained in the same manner as in Experiment 1 except that the thicknesses of the front and back layers were changed. The properties of the film are shown in Table 2.

Experiment 5
For the base layer, a polyester resin in which polyester B: 40% by mass, polyester C: 10% by mass, and polyester D: 50% are used, and for the front and back layers, polyester A: 35%, polyester B: 55% by mass, polyester C : A heat-shrinkable polyester film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that a polyester resin mixed with 10% by mass was used and the front and back layers were each 4 μm. The properties of the film are shown in Table 2.

  The heat-shrinkable polyester film of the present invention is useful as an environmentally friendly heat-shrinkable label film because it has a quality equivalent to that of a conventional film despite the use of recycled PET bottle materials.

Claims (5)

A heat-shrinkable polyester film in which a layer not containing a PET bottle recycling raw material is laminated on at least one side of the base layer containing the PET bottle recycling raw material, and the content of the PET bottle recycling raw material in the base layer is 40% by mass or less In addition, in 100 mol% of the constituent units of the heat-shrinkable polyester film, when the ethylene terephthalate unit is 50 mol% or more and the total amount of the polyhydric alcohol components is 100 mol%, neopentyl glycol and / or 1, It contains 10 to 30 mol% of 4-cyclohexanedimethanol and 5 to 30 mol% of 1,4-butanediol and / or 1,3-propanediol, and is immersed in warm water at 80 ° C. for 10 seconds. The heat shrinkage rate in the main shrinkage direction when pulled up is 30% or more, and the heat shrinkage rate in the direction orthogonal to the main shrinkage direction is 10% or less. There was at least one side an outermost layer a layer containing no recycled PET bottles material, heat-shrinkable polyester film you characterized by being stretched at least uniaxially. 2. The heat-shrinkable polyester film according to claim 1, wherein the layer not containing the PET bottle reclaimed material is at least one surface outermost layer, and the thickness of the layer is 4 μm or more. The heat-shrinkable polyester film according to claim 1 or 2 , wherein the intrinsic viscosity of the film is 0.61 dl / g or more. The heat-shrinkable polyester film according to any one of claims 1 to 3, wherein a layer that does not contain a PET bottle recycled raw material is used as a printing surface. A heat-shrinkable label produced from the heat-shrinkable polyester film according to any one of claims 1 to 4 .