JP2006077253A - Heat-shrinkable polyester-based film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester-based film for a label, generating very little wrinkle, shrinkage unevenness and warpage caused by the shrinkage. <P>SOLUTION: The heat-shrinkable polyester-based film is obtained by charging different two-kind polyester resins A and B as raw materials to separated extruders A1 and B1 respectively to melt them, charging the resins A and B in molten states to a mixture to mix them, extruding the mixed product from a T-die, cooling an extruded sheet and at least monoaxially orienting the cooled unoriented sheet. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film suitable for label applications. More specifically, the present invention relates to a heat-shrinkable polyester-based film that has very few wrinkles, shrinkage spots, and distortion due to heat shrinkage, has good perforation cutability, and has a sufficient label strength upon impact.

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

  In recent years, cases in which heat-shrinkable polyester films are used for glass bottles for the purpose of preventing broken bottles and decorating the bottles are increasing. Among them, in particular, from the viewpoint of hygiene and safety, it may be used as a full bottle label that is used by attaching a label to the entire glass bottle, which may cause a problem in shrink finish. In particular, the type of the heat-shrinkable polyester-based heat-shrinkable film, which has a gentle shoulder inclination, may cause wrinkles, jumping, and uneven color after shrinkage at the shoulder of the bottle. Further, in the case of beverage bottles, in order to improve productivity, label mounting and shrinkage are increasingly performed in a beverage filling line. Since the filling line is high-speed, label mounting and shrinking are fast, and the shrinking time is short. Therefore, the heat-shrinkable film requires a film that can withstand high-speed mounting and a shrinkage performance that provides a high shrinkage rate in a short time.

  Thus, in the case of full-bottle label use and further high-speed mounting, the performance of conventional polyester heat-shrinkable films has been insufficient.

  In addition, there are cases where the perforation for opening is provided on the label, but when the product is a glass bottle for beverages, it is usually refrigerated, and since the temperature is low when the label is opened, there is a problem that poor opening is likely to occur. is there. In order to improve it, there is one in which the temperature condition at the time of stretching is devised (for example, see Patent Document 1).

JP 2003-268131 A

However, as a result, the improvement degree of perforation opening is not sufficient, and since the shrinkage speed that can be said to be a feature of the conventional polyester-based shrink film is too fast and the maximum shrinkage rate is sometimes too high, it is about 500 ml. When a label is applied to the inclined portion of the PET bottle, particularly at an inclined part, shrinkage unevenness, wrinkles or color unevenness may occur when the label is attached at a high speed.

In addition, there is one that attempts to improve unevenness at the time of wearing by relatively reducing the contraction speed (see, for example, Patent Documents 2, 3, and 4).
JP-A-6-320621 JP-A-8-27285 JP-A-8-25477

However, these have been problematic in that the perforation openability has not been improved.

  The present invention solves the above-mentioned problems, and the object of the present invention is that the occurrence of wrinkles, shrinkage unevenness and distortion due to shrinkage is extremely small, the perforation opening property is good, and the label adheres to the bottle. Relates to a sufficiently heat-shrinkable polyester film.

  In the film of the present invention, at least two different polyester resins A and B as raw materials are charged into separate extruders A1 and B1, respectively, melted, and the resins A and B are charged into a static mixer in a molten state. After mixing, it is a heat-shrinkable polyester film obtained by extruding from a slit die and stretching a cooled unstretched sheet at least uniaxially.

  The heat-shrinkable polyester film of the present invention exhibits a beautiful shrink finish with very little wrinkling, shrinkage unevenness and distortion due to shrinkage, good perforation openability, and sufficient adhesion to the bottle of the label It has excellent practical characteristics.

The present invention is described in detail below.
The heat-shrinkable polyester film of the present invention is produced from a polyester having a dicarboxylic acid component and a diol component as constituent components.

  The heat-shrinkable polyester film of the present invention is treated with no load in warm water and the length before and after shrinkage is calculated as follows: thermal shrinkage rate = ((length before shrinkage−length after shrinkage) / before shrinkage The hot water shrinkage rate of the film calculated by the formula of (length) × 100 (%) is 20% or more and 95% or less as the heat shrinkage rate after being immersed in 85 ° C. warm water in any one direction (main direction) for 5 seconds. It is preferably 30% to 90%, more preferably 10% to 50% at a treatment temperature of 70 ° C. and a treatment time of 5 seconds, and 35% to 75% at 85 ° C. for 5 seconds. is there.

  If the maximum shrinkage is less than 20%, the label is not sufficiently attached. It is technically difficult to make it 95% or more. More preferably, when the hot water shrinkage rate in the main shrinkage direction is less than 10% at 70 ° C. for 5 seconds, the low-temperature shrinkage property is insufficient and the shrinkage temperature needs to be increased, which is not preferred. On the other hand, when it exceeds 50%, the label jumps easily due to heat shrinkage.

  More preferably, the shrinkage rate at 85 ° C. for 5 seconds is preferably 35% or more and 75% or less, and when it is less than 35%, the shrinkage of the shoulder portion of the bottle becomes insufficient. On the other hand, when it exceeds 75%, there is a force to further shrink even after heat shrinkage, so that the label is likely to jump up.

  In the heat-shrinkable polyester film of the present invention, the perforation defect rate after shrinkage is preferably less than 20%, more preferably less than 7%. More preferably, it is less than 2%.

  Here, the perforation unsatisfactory defective rate means that a label made of a heat-shrinkable polyester film that has been printed is shrunk into a glass bottle, refrigerated at 5 ° C., and then the bottle label just after being taken out of the refrigerator This means the rate at which the perforation was cut with a fingertip and pulled, and the cut occurred in the middle of the perforation. A case where the film is cut along the perforation is regarded as good.

  When the perforation open defect rate is 20% or more, the label does not break along the perforation, and therefore, it is difficult to peel the label from the bottle surface.

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

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

  The polyester raw material used in the present invention is dried using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer.

  In the present invention, the method for melting and mixing the raw materials must be as follows. There are two types of raw materials, A and B. Each type may be a single resin or a blended resin, but A and B must have clearly different compositions and thermal characteristics. The blend may be a chip blend or a master batch. Raw materials A and B are charged into different extruders A1 and B1 and melted. The melting temperature is not particularly limited as long as it does not cause deterioration or deterioration for each resin. As one index, in the case of a resin exhibiting crystallinity, the melting point + (5 ° C. to 30 ° C.), and in the case of an amorphous resin, the softening temperature + (20 ° C. to 150 ° C.).

After the A and B resins are melted, they are led to the feed block in the molten state and then to the static mixer. A static mixer, for example, manufactured by Noritake Company, is an element in which rectangular plates are twisted 180 degrees alternately in the resin flow path, and the number of layers doubles each time this element is passed. Become. Therefore, logically, when passing through n elements, it becomes 2 ⁿ layers, but in reality it may change depending on the relationship between the flow path diameter, the discharge amount, the viscosity and surface tension of each resin, and the like.

  When a static mixer is used, a laminated unstretched sheet is obtained by extruding this laminated resin from a T-die and bringing it into close contact with a cooling roll.

  Next, the obtained unstretched sheet is stretched 3.0 times or more, preferably 3.5 times or more and 15 times or less in the lateral direction (direction orthogonal to the extrusion direction). The stretching temperature is 60 ° C. or higher and 120 ° C. or lower, preferably 70 ° C. or higher and 100 ° C. or lower. Furthermore, although it is not always necessary to perform longitudinal stretching before and after transverse stretching, longitudinal stretching may be performed as necessary.

  Next, if necessary, heat treatment is performed at a temperature of 70 to 100 ° C. to obtain a heat-shrinkable polyester film.

  The stretching method is not limited to lateral uniaxial stretching with a tenter, but may be additionally biaxially stretched in the longitudinal direction. Such biaxial stretching may be performed by any of a sequential biaxial stretching method and a simultaneous biaxial stretching method, and may be re-stretched in the longitudinal direction or the transverse direction as necessary.

  In order to achieve the object of the present invention, the lateral direction is practical as the main shrinking direction. Thus, the example of the film forming method in the case where the main shrinking direction is the lateral direction has been described above. Even when the shrinking direction is the longitudinal direction, a film can be formed according to the operation of the above method except that the stretching direction in the above method is changed by 90 degrees.

  A layer structure may be confirmed in the film of the present invention. In that case, it is preferable that the number of layers in at least the central portion in the thickness direction of the film and the region of 2 μm thickness is 5 layers or more, preferably 30 layers or more, and more preferably 100 layers or more. Moreover, although an upper limit does not exist theoretically, it is actually 100,000 layers or less. Even if polyesters A and B are used as separate raw materials, if they are copolymerized or highly uniformly mixed in an extruder or a subsequent melting tube, they appear as one layer, which is inappropriate in the present invention. It is.

  With less than 5 layers, the adhesion between the label and the bottle is good, and there is no shrinkage unevenness or color unevenness even when the label is mounted at high speed. Can not do it. In particular, it is difficult to improve perforation opening.

  In the present invention, the adhesion between the label and the bottle is good, and there is no shrinkage unevenness or color unevenness even when the label is mounted at high speed. It is important that polyesters A and B exist independently within the film. It is assumed that this is due to the following resin characteristics.

  As long as the polyesters A and B used as raw materials have different thermal characteristics, the polyesters can be selected in any combination so as to meet the object of the present invention. Preferably, the difference in glass transition temperature between polyester A and B is 3 ° C. or more and 100 ° C. or less, and the difference in heat of crystal fusion is 5 (J / g) or more and 100 (J / g) or less, more preferably polyester A is made of glass. A crystalline polyester having a transition temperature of −50 ° C. or more and less than 60 ° C. and a heat of crystal fusion of 5 (J / g) or more and 100 (J / g) or less, polyester B has a glass transition temperature measured by DSC of 60 ° C. or more and 150 A substantially amorphous polyester having a heat of crystal melting of 0 (J / g) or more and 3 (J / g) or less at a temperature of 0 ° C. or less. Polyesters A and B used as raw materials are homopolymers and copolymer polyesters, and can be used as raw material polyesters that have the glass transition temperature and the heat of crystal melting as a result of blending two or more arbitrary polyesters. It is also possible to do.

Examples of polyester A include polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polypentamethylene terephthalate, and crystalline polyester resin of polyhexamethylene terephthalate. Moreover, what made less than 4 mol% copolymerization of the acid component and / or glycol component mentioned above by making these into frame | skeleton is also mentioned. Furthermore, polyethylene terephthalate (PET) as a base material and dimer acid copolymerized with 15 mol% or less (PET-D), polyethylene-2,6-naphthalate (P
EN) and 15% by mole or less of isophthalic acid copolymerized. More preferred are PBT, PTT, and PET-D.

  Examples of polyester B include a resin component mainly composed of terephthalic acid as an acid component and ethylene glycol as a glycol component, and more than 5 mol%, preferably 6 mol% to less than 40 mol% of different dicarboxylic acid components and And / or a copolymerized glycol component. Specific monomer components include dicarboxylic acid components such as isophthalic acid, naphthalenedicarboxylic acid, orthophthalic acid and other aromatic dicarboxylic acids, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid and other aliphatic dicarboxylic acids, and An alicyclic dicarboxylic acid etc. are mentioned. Examples of the glycol component include aliphatic diols such as propanediol, butanediol, neopentylglycol, and hexanediol; alicyclic diols such as 1,4-cyclohexanedimethanol, and aromatic diols.

  More preferably, a resin component mainly composed of terephthalic acid as an acid component and ethylene glycol as a glycol component is copolymerized with 7 to 35 mol% of neopentyl glycol and / or 1,4-cyclohexanedimethanol. Polyester resin.

  The mixing ratio of polyesters A and B is preferably 10/90 to 90/10 (weight ratio), more preferably 20/80 to 70/30, still more preferably 25/75 to 60/40. Outside this range, it becomes difficult to satisfy label mounting properties and shrinkage unevenness.

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

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

(2) Number of layers inside the film In the region of 2 μm × 2 μm in the center with respect to the cross-sectional direction of the film, the number of layers confirmed from the difference in dyeing degree of polyester A and B when observed with an electron microscope by the following method I counted the number.

  The cross-sectional layer structure of the film was observed using a transmission electron microscope. First, the film was embedded in an epoxy resin. As the epoxy resin used, a mixture of Luabeck 812, Luavec NMA (manufactured by Nacalai Tesque) and DMP30 (manufactured by TAAB) in a ratio of 100: 89: 3 was used. Next, after embedding the sample film in the above-described mixed resin, the sample film was left in an oven adjusted to a temperature of 60 ° C. for 16 hours to cure the resin and obtain an embedded block.

  The obtained embedding block was attached to an ultra cut N manufactured by Nissan Sangyo Co., Ltd., and an ultrathin section was prepared. First, trimming was performed using a glass knife until a cross section of a portion desired to be observed for the film appeared on the resin surface. Next, an ultrathin section was cut out using a diamond knife (Sumitomo Electric Sumiknife SK2045). The cut sections were collected on a mesh and then stained by standing in a ruthenium tetroxide vapor for 30 minutes at room temperature, followed by thin carbon deposition.

  The electron microscope observation was performed using JEM-2010 manufactured by JEOL under the condition of an acceleration voltage of 200 kV. The obtained image was recorded on an imaging plate (FDL UR-V manufactured by Fuji Photo Film). The signal recorded on the imaging plate was read out using digital luminography (Pixsys TEM manufactured by JEOL) and recorded as digital image information on a Windows personal computer.

(3) Shrinkage finish Three-color printing was performed on a heat-shrinkable film in advance with grass, gold, and white ink from Toyo Ink Manufacturing Co., Ltd. The printed film was bonded to both ends with dioxolane to form a cylindrical label. Using a steam tunnel manufactured by Fuji Astec Inc (model: SH-1500-L), heat shrinks into a 500 ml PET bottle (bottle diameter 62 mm, minimum neck diameter 25 mm) at a transit time of 2.5 seconds and a zone temperature of 80 ° C. It was attached by letting. In addition, the neck portion was set so that a portion having a diameter of about 40 mm became one end of the label when being mounted. Evaluation was made visually and the criteria were as follows.

Neither wrinkles, jumping up nor under-shrinkage occurs and no color unevenness is seen: ◎
Although wrinkles, jumping up, or insufficient shrinkage cannot be confirmed, color unevenness is slightly observed: ○
Neither jumping up nor insufficient shrinkage has occurred, but unevenness in the neck is seen:
Wrinkles, jumping up, insufficient shrinkage occurred: ×

(4) Label adhesion When the label and PET bottle mounted under the condition of (3) were lightly twisted, it was rated as “O” if the label did not move, and “X” if it slipped through and the label and the bottle shifted.

(5) Perforation unsatisfactory defective rate A label having perforations in a direction perpendicular to the shrinkage direction was attached to a PET bottle under the conditions of (3). However, perforations were provided with 1 mm long holes at 1 mm intervals, and two perforations in the longitudinal direction of the label with a width of 22 mm and a length of 120 mm.

  After that, this bottle was filled with about 500 ml of water, refrigerated to 5 ° C., and the perforation of the label on the bottle immediately after taking out from the refrigerator was torn with the fingertips, and the label was removed from the bottle. The number was counted and the ratio (%) to 50 samples was shown.

(6) Glass transition temperature (Tg) and heat of crystal melting (Hm) of raw material
Using DSC3100S manufactured by Mac Science, put about 7mg of crushed resin material into a sample pan, cover the pan, and raise the temperature from room temperature to 300 ° C at a rate of 20 ° C / min in a nitrogen gas atmosphere. It was measured. Tg (° C.) is based on JIS-K7121-1987, 9.3, and Hm (J / g) is the melting peak temperature (Tpm) and extrapolated melting start temperature defined in 9.1. The DSC curve surrounding (Tim) and the extrapolated melting end temperature (Tem) was determined by integration.

  The polyester used in the examples is as follows.

Polyester I: Polybutylene terephthalate (Intrinsic viscosity (IV) 1.20 dl / g)
Polyester II: Polytrimethylene terephthalate (IV 1.00 dl / g)
Polyester III: Polyester composed of 70 mol% ethylene glycol, 30 mol% neopentyl glycol and terephthalic acid (IV 0.72 dl / g)
Polyester IV: Polyester composed of 70 mol% ethylene glycol, 30 mol% 1,4 cyclohexanedimethanol and terephthalic acid (IV 0.72 dl / g)
Polyester V: Polyester composed of 91 mol% ethylene glycol, 9 mol% dimer acid and terephthalic acid (IV 0.72 dl / g)
Polyester VI: Polyethylene terephthalate (IV 0.75 dl / g)
Polyester VII: 85 mol% butanediol, polytetramethylene terephthalate 1
Polyester consisting of 5 mol% and terephthalic acid (IV 1.50 dl / g)
The properties of each resin are shown in Table 1.

(Example 1)
As raw material A, polyester I was charged into an extruder A1 and melted at 250 ° C. Further, as raw material B, polyester III was charged into extruder B1 and melted at 250 ° C. Resin ratio is A
/ B = 25/75 (weight ratio), led to the feed block in the molten state, then mixed and laminated with a static mixer (N20 element number 12 made by Noritake Company Limited), and then at 250 ° C. from a T-die Extruded and quenched with a chill roll to obtain an unstretched film. The unstretched film had a Tg of 69 ° C. This unstretched film was stretched 4.8 times in the transverse direction at 80 ° C. with a tenter to obtain a heat-shrinkable polyester film having a thickness of 50 μm.

(Comparative Example 1)
Polyester I and III are fed into a single extruder at 50/50 (weight ratio), extruded from a T-die without using a static mixer, and unstretched film is stretched 1.2 times in the machine direction at 80 ° C. A heat-shrinkable polyester film having a thickness of 50 μm was obtained in the same manner as in Example 1, except that the film was stretched in a roll and subsequently stretched 4.8 times in the transverse direction at 80 ° C. with a tenter.

(Comparative Example 2)
Exactly the same as Example 1 except that polyesters II, VI and VII were charged into a single extruder at 75 / 10.5 / 4.5 (weight ratio) and extruded from a T-die without using a static mixer. Thus, a heat-shrinkable polyester film having a thickness of 50 μm was obtained.

(Comparative Example 3)
23% by weight of polyester resin (A) consisting of 100 parts by mole of terephthalic acid and 100 parts by weight of ethylene glycol, 67% by weight of polyester resin (B) consisting of 100 parts by weight of terephthalic acid, 70 parts by mole of ethylene glycol and 30 parts by weight of cyclohexanedimethanol , 100 parts by weight of terephthalic acid and 10% by weight of polyester resin (C) consisting of 100 parts by weight of butanediol were mixed using a twin screw extruder, and 20% by mole of cyclohexanedimethanol in all alcohol components in the mixed resin. A polyester resin mixture having a butanediol content of 10 mol% was obtained. After drying the obtained polyester resin mixture, it was melt-extruded from a T-die using an extruder A1 at a resin temperature of 270 ° C. to prepare a raw film. This original film
Uniaxial stretching was performed 4.5 times in the transverse direction at 80 ° C. to obtain a heat-shrinkable polyester film having a thickness of 40 μm.

  Table 2 shows the evaluation results of the films obtained in Examples and Comparative Examples 1 to 3.

  The heat-shrinkable polyester film of the present invention exhibits a beautiful shrink finish with very little wrinkling, shrinkage unevenness and distortion due to shrinkage, good perforation openability, and sufficient adhesion to the bottle of the label It has a very high industrial utility value.

Claims (5)

  At least two different types of polyester resins A and B as raw materials are charged into separate extruders A1 and B1, respectively, melted, and A and B resins are charged and mixed in a static mixer in a molten state. A heat-shrinkable polyester film obtained by extruding from a die and stretching the cooled unstretched sheet at least uniaxially.   The heat shrinkage rate in the main shrinkage direction after being immersed in 85 ° C. warm water for 5 seconds is 35% or more and 75% or less, and the heat shrinkage rate in the main shrinkage direction after being immersed in 70 ° C. warm water for 5 seconds is 10% or more. The heat-shrinkable polyester film according to claim 1, which is 50% or less.   Polyester resin A is a crystalline polyester having a glass transition temperature measured by DSC of −50 ° C. or higher and lower than 60 ° C. and a crystal heat of fusion of 5 (J / g) to 100 (J / g), and polyester resin B 3. The heat according to claim 1, which is a substantially amorphous polyester having a glass transition temperature of 60 ° C. or more and 150 ° C. or less and a crystal heat of fusion of 0 (J / g) to 3 (J / g). Shrinkable polyester film.   Polyester resin A is a polyester in which polybutylene terephthalate, polytrimethylene terephthalate, or polyethylene terephthalate is used as a base material, and a dimer acid is copolymerized in an amount of 15 mol% or less. The heat-shrinkable polyester film according to claim 3, which is a polyester obtained by copolymerizing 7 to 35 mol% of neopentyl glycol and / or 1,4-cyclohexanedimethanol with a resin component mainly composed of ethylene glycol. .   Polyester resin A is polybutylene terephthalate, polyester resin B is copolymerized with 7 to 35 mol% neopentyl glycol in a resin component mainly composed of terephthalic acid as an acid component and ethylene glycol as a glycol component. The heat-shrinkable polyester film according to claim 4, which is a polyester obtained.