Heat-shrinkable polyester-based film

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a heat-shrinkable polyester-based film, and particularly to a heat-shrinkable polyester-based film suitable for label applications. More specifically, the present invention relates to a heat-shrinkable polyester-based film for labels, which has extremely few wrinkles, shrinkage spots, and strain due to heat shrinkage, and has both high compressive strength and adhesiveness due to a non-halogen solvent.

【0002】

[Conventional technology]

As a heat-shrinkable film, particularly a heat-shrinkable film for a label on the body of a PET bottle, a film made of polyvinyl chloride, polystyrene or the like is mainly used. However, in recent years, polyvinyl chloride has a problem of generating chlorine-based gas when incinerated at the time of disposal, and polystyrene has a problem that printing is difficult. Furthermore, when collecting and recycling PET bottles, it is necessary to separate labels for 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.

【0003】

However, many heat-shrinkable polyester-based films shrink rapidly, leaving wrinkles, shrinkage spots, and strain after shrinkage, and as a shrinkage film for labels that is prone to breakage due to external impact after shrinkage. I wasn't satisfied.

【0004】

In order to avoid some of these drawbacks, Japanese Patent Application Laid-Open No. 7-77757 discloses a method for improving the shrinkage finish by remarkably reducing the breaking strength in the direction orthogonal to the main shrinkage direction.

【0005】

Further, Japanese Patent Application Laid-Open No. 58-64958 discloses a method for improving shrinkage finish by reducing the orientation return stress.

【0006】

However, the film obtained by the above method cannot obtain a sufficient shrinkage finish for small PET bottle applications in which the shrinkage tunnel passage time is short, and is not satisfactory as a shrinkage film. That is, when a tubular label formed of a shrink film is attached to a PET bottle and the shrink film is shrunk by heat treatment, wrinkles, shrinkage spots, and distortion due to shrinkage may occur on the film.

【0007】

Further, the speed of the beverage filling line such as PET bottles has been increased, and as described above, the label has good shrinkage finish, and of course, high-speed mounting suitability is required. That is, as shown in FIGS. 1 and 2, when the label 2 is attached to the PET bottle 1 at high speed by the pressurizing member 3, if the label is not suitable for high-speed attachment, the label may be broken and cannot be attached. .. The suitability of labeling is largely due to the strength of the film, and although it can be dealt with by increasing the thickness of the film, it also causes harmful effects. For example, as the thickness of the film increases, the weight increases and the handleability decreases. In addition, the cost may increase due to the increase in film thickness.

【0008】

Further, although halogen-based solvents have been widely used as adhesive solvents when processing films into tubes, non-halogen-based solvents are increasingly used due to health and safety issues. Non-halogen solvents tend to have lower film adhesiveness than halogen-based solvents, and improving the solvent adhesiveness of the film may cause problems such as lower film stiffness. ..

【0009】

[Problems to be Solved by the Invention]

The present invention solves the above-mentioned problems, and an object of the present invention is to provide excellent high-speed mounting suitability and shrinkage finish in all applications including small PET bottles without increasing the thickness setting. An object of the present invention is to provide a heat-shrinkable polyester-based film that can be bonded with a halogen-based solvent.

【0010】

[Means for solving problems]

In the heat-shrinkable polyester film of the present invention, the hot water shrinkage rate of the film is 20% or more in the main shrinkage direction at a treatment temperature of 70 ° C and a treatment time of 5 seconds, and a treatment temperature of 75 ° C and a treatment time of 5 seconds. 35 to 55%, the processing temperature is 80 ° C, the processing time is 50 to 60% at 5 seconds, and the compressive strength of the label formed from the film satisfies the following formula (1). Excellent adhesion with non-halogen solvent. y> x^2.2... (1) In the formula, y represents the compression strength (mN) and x represents the film thickness (μm).

【0011】

In one embodiment, the thickness distribution is 6% or less.

【0012】

The label for a bottle of the present invention is produced by using the heat-shrinkable polyester-based film, thereby achieving the above object.

【0013】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be specifically described.

【0014】

The heat-shrinkable polyester-based film of the present invention is made of a polyester containing a dicarboxylic acid component and a diol component as constituent components.

【0015】

Examples of the dicarboxylic acid component constituting the polyester include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and orthophthalic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decandicarboxylic acid, and An alicyclic dicarboxylic acid and the like can be mentioned.

【0016】

When an aliphatic dicarboxylic acid (for example, adipic acid, sebacic acid, decandicarboxylic acid, etc.) is contained, the content is preferably less than 3 mol% (the same applies hereinafter with respect to all the dicarboxylic acid components used). In the heat-shrinkable polyester-based film obtained by using a polyester containing 3 mol% or more of these aliphatic dicarboxylic acids, the breaking elongation in the direction orthogonal to the main shrinkage direction after the shrinkage treatment tends to decrease, and the speed is high. Insufficient film waist when worn.

【0017】

Further, it is preferable not to contain a polyvalent carboxylic acid having a valence of 3 or more (for example, trimellitic acid, pyromellitic acid and anhydrides thereof). It is preferably 3 mol% or less. In the heat-shrinkable polyester-based film obtained by using the polyester containing these polyvalent carboxylic acids, the determined elongation in the direction orthogonal to the main shrinkage direction after the shrinkage treatment tends to decrease, and the required high shrinkage rate is high. Is difficult to achieve.

【0018】

Examples of the diol component constituting the polyester used in the present invention include aliphatic diols such as ethylene glycol, propanediol, butanediol, neopentyl glycol and hexanediol; alicyclic diols such as 1,4-cyclohexanedimethanol, and aromatics. Examples include group diols.

【0019】

The polyester used in the heat-shrinkable polyester-based film of the present invention contains one or more of diols having 3 to 6 carbon atoms (for example, propanediol, butanediol, neopentyl glycol, hexanediol, etc.) and contains glass. A polyester having a transition point (Tg) adjusted to 60 to 75 ° C is preferable.

【0020】

Further, in order to obtain a heat-shrinkable polyester-based film having particularly excellent shrinkage finish, neopentyl glycol can be used as one of the diol components. It is preferably 15 to 25 mol% (the same applies hereinafter for all diol components used).

【0021】

It is preferable not to contain a diol having 8 or more carbon atoms (for example, octane diol) or a polyhydric alcohol having 3 or more valences (for example, trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.). It is preferably 3 mol% or less. A heat-shrinkable polyester-based film obtained by using a polyester containing these diols or a polyhydric alcohol makes it difficult to achieve the required high shrinkage rate.

【0022】

The polyester preferably contains as little diethylene glycol, triethylene glycol, and polyethylene glycol as possible. In particular, diethylene glycol is likely to be present because it is a by-produced component during polyester polymerization, but the polyester used in the present invention preferably has a diethylene glycol content of less than 4 mol%.

【0023】

Preferred acid and diol components used in the polyester of the present invention are as follows. The main acidic content of both outer layers is terephthalic acid, isophthalic acid is 13 mol% or more, and adipic acid is 2.6 mol% or more and less than 5 mol%. The main glycol component is ethylene glycol, and 10 to 15 mol% of butanediol is added. The main acid component of the intermediate layer is terephthalic acid, with 13 mol% or more of isophthalic acid and 1 mol% or more and less than 2.1 mol% of adipic acid. Further, the main glycol component is ethylene glycol, and butanediol is blended in an amount of 5 mol% or more and less than 9 mol%.

【0024】

The content of the acid component and the diol component is the content of the acid component and the diol component of the entire polyester when two or more kinds of polyesters are mixed and used. It does not matter if transesterification is done after mixing. Further, in order to improve the slipperiness of the heat-shrinkable film, an inorganic lubricant such as titanium dioxide, fine silica, kaolin and calcium carbonate, and an organic lubricant such as a long-chain fatty acid ester may be contained. preferable. Further, if necessary, additives such as stabilizers, colorants, antioxidants, antifoaming agents, antistatic agents, and ultraviolet absorbers may be contained.

【0025】

All of the above polyesters can be produced by polymerizing by a conventional method. For example, a polyester can be obtained by using a direct esterification method in which a dicarboxylic acid and a diol are directly reacted, a transesterification method in which a dicarboxylic acid dimethyl ester and a diol are reacted, and the like. The polymerization may be carried out by either a batch method or a continuous method.

【0026】

The heat-shrinkable polyester-based film of the present invention is composed of at least three layers, both outer layers and an intermediate layer, and the thickness of both outer layers is 0.1 μm or more, preferably 1 μm to 30 μm. When the thickness of the outer layer is 0.1 μm or less, sufficient solvent adhesive strength cannot be obtained. Further, if the thickness of the outer layer exceeds 30 μm, it affects the properties other than the solvent adhesiveness of the film, which is not preferable.

【0027】

The heat-shrinkable polyester film of the present invention is treated in warm water under no load and has a heat shrinkage rate = ((length before shrinkage-length after shrinkage) / before shrinkage from the length before and after shrinkage. The hot water shrinkage rate of the film calculated by the formula of length) × 100 (%) is 20% or more, preferably 22 to 35% at a treatment temperature of 70 ° C. and a treatment time of 5 seconds in the main shrinkage direction. , 75 ° C. for 5 seconds is 35 to 55%, preferably 40 to 50%, and 80 ° C. for 5 seconds is 50 to 60%.

【0028】

If the shrinkage rate of hot water in the main shrinkage direction is less than 20% at 70 ° C for 5 seconds, the low temperature shrinkage is insufficient and the shrinkage temperature needs to be raised, which is not preferable. On the other hand, if it exceeds 50%, the label jumps due to heat shrinkage, which is not preferable.

【0029】

The shrinkage rate at 75 ° C for 5 seconds is 35 to 55%, and if it is less than 35%, the shrinkage of the mouth of the bottle is insufficient, which is not preferable (that is, the packaged object such as a bottle is wrapped. When passed through a contraction tunnel, the edges are wide like petals and contraction spots and wrinkles are likely to occur). On the other hand, if it exceeds 55%, the label has a force of further shrinking even after heat shrinkage, so that the label easily jumps up.

【0030】

The shrinkage rate at 80 ° C for 5 seconds is 50 to 60%, and if it is less than 50%, the shrinkage of the mouth of the bottle becomes insufficient, which is not preferable. On the other hand, if it exceeds 60%, the label has a force to further shrink even after heat shrinkage, so that the label easily jumps up.

【0031】

Further, the heat-shrinkable polyester-based film of the present invention satisfies the formula (1) shown below in the compressive strength of the label produced from the film. y> x^2.2... (1) In the formula, y represents the compression strength (mN) and x represents the film thickness (μm).

【0032】

The compression strength y of the preferred label is as follows. y> 1.1x^2.2 ... (1) The compression strength is affected by the thickness of the film, but if the above formula is not satisfied due to the suitability of a high-speed mounting machine, there is a possibility that a problem of label mounting failure may occur.

【0033】

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

【0034】

Next, a specific example of the method for producing the heat-shrinkable polyester film of the present invention will be described, but the method is not limited to this production method.

【0035】

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

【0036】

Next, the obtained unstretched film is placed in the longitudinal direction (extrusion direction) at a temperature of Tg-5 ° C or higher for polyester and lower than Tg + 15 ° C for polyester (for example, 70 ° C to 90 ° C). Stretch 1.05 times or more, preferably 1.05 to 1.20 times. Next, after preheating the film, it is stretched 4.5 times or more in the lateral direction (main contraction direction) (primary stretching). It is preferably 4.7 to 5.2 times. Here, by preheating the film, shrinkage can be suppressed and the film can be made stiff. Then, the film is further stretched 1.05 times or more in the lateral direction at 65 to 85 ° C (secondary stretching) to obtain the heat-shrinkable polyester-based film of the present invention.

【0037】

By stretching the film in two steps in this way, it is possible to strengthen the waist of the film so that it does not support high-speed shrinkage and high-speed mounting.

【0038】

The stretching method is to stretch in the transverse direction with a tenter in addition to the stretching in the longitudinal direction to perform biaxial stretching, and such biaxial stretching can be performed by either a sequential biaxial stretching method or a simultaneous biaxial stretching method. However, if necessary, re-stretching may be performed in the longitudinal direction or the lateral direction.

【0039】

In order to achieve the object of the present invention, the lateral direction is practical as the main contraction direction. Therefore, in the above, an example of the film forming method when the main contraction direction is the lateral direction has been shown. Even when the contraction direction is the longitudinal direction, the 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.

【0040】

In the present invention, it is preferable to stretch the unstretched film obtained from polyester at a temperature of Tg-5 ° C or higher and lower than Tg + 15 ° C.

【0041】

When stretched at a temperature lower than Tg-5 ° C, not only is it difficult to obtain the heat shrinkage rate, which is a constituent requirement of the present invention, but also the transparency of the obtained film is deteriorated, which is not preferable.

【0042】

Further, when the film is stretched at a temperature of Tg + 15 ° C or higher, the obtained film has insufficient film stiffness when mounted at high speed, and the thickness unevenness of the film is significantly impaired, which is not preferable.

【0043】

The heat-shrinkable polyester film of the present invention has a film thickness distribution of 6% or less calculated from the film thickness by the formula: ((maximum thickness-minimum thickness) / average thickness) × 100 (%). Is preferable. More preferably, it is 5% or less.

【0044】

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

【0045】

In order to make the thickness distribution of the heat-shrinkable polyester film uniform, when stretching in the lateral direction using a tenter, the heat transfer coefficient is 0.0013 calories / cm in the preheating step performed prior to the stretching step.²-It is preferable to heat the film at a low wind speed to a predetermined film temperature so as to be sec · ° C or less.

【0046】

In addition, in order to suppress the internal heat generation of the film due to stretching and reduce the film temperature unevenness in the width direction, the heat transfer coefficient in the stretching step is 0.0009 calories / cm.² Sec ° C or higher, preferably 0.0011 to 0.0017 calories / cm² The conditions of sec and ° C are good.

【0047】

The heat transfer coefficient of the preheating process is 0.0013 calories / cm² If it exceeds sec, and the heat transfer coefficient in the stretching process is 0.0009 calories / cm.²-If it is less than sec, the thickness distribution is difficult to be uniform, and when the obtained film is printed in multiple colors, the pattern shifts due to the superposition of multiple colors, which is not preferable.

【0048】

The label of the present invention is prepared by rolling a rectangular heat-shrinkable film having a predetermined size into a tubular shape and adhering the ends to each other to form a tubular body, which is further cut. The bonding method is not limited, but for example, a solvent or a swelling agent is applied to at least one surface of the bonding surface of the polyester film, and the film is bonded before drying.

【0049】

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples as long as the gist of the present invention is not exceeded.

【0050】

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

【0051】

(1) Heat shrinkage rate The film is cut into 10 cm x 10 cm squares, treated in warm water at a predetermined temperature of ± 0.5 ° C for a predetermined time under no load, and heat-shrinked, and then the vertical and horizontal dimensions of the film are measured. The heat shrinkage rate was calculated according to Eq. (2). The direction in which the heat shrinkage rate was large was defined as the main shrinkage direction. Thermal shrinkage = ((length before shrinkage-length after shrinkage) / length before shrinkage) x 100 (%) (2) [0052]

(2) Shrinkage finish The heat-shrinkable film was pre-printed in three colors with grass, gold, and white ink manufactured by Toyo Ink Mfg. Co., Ltd.

【0053】

Using a steam tunnel made by Fuji Astec Inc (model: SH-1500-L), the passage time is 2.5 seconds, the zone temperature is 80 ° C, and a 500 ml round bottle (height 20.6 cm, central diameter 6.5 cm: Yoshino Co., Ltd.) It was tested using a bottle manufactured by Kirin Beverage Co., Ltd. for afternoon tea (measured number = 20).

【0054】

The evaluation was performed visually, and the criteria were as follows.

【0055】

No wrinkles, jumps, or insufficient shrinkage: Wrinkles, jumps, or insufficient shrinkage: × [0056]

(3) Compression strength A label having a folded diameter of 175 mm and a length of 120 mm was prepared, and the bottom surface of the folded label became a quadrangular cylinder, and the compression strength in the vertical direction of the cylinder was measured. Using a strograph (model: V10-C) manufactured by Toyo Seiki Co., Ltd., the maximum value of compression strength (mN) at a crosshead speed of 200 mm / min was measured in compression mode (n = 5).

【0057】

(4) Tg (glass transition point) Using DSC (model: DSC220) manufactured by Seiko Electronics Co., Ltd., 10 mg of unstretched film was heated from -40 ° C to 120 ° C at a heating rate of 20 ° C / min. Obtained from the endothermic curve. Tangent lines were drawn before and after the inflection point of the endothermic curve, and the intersection was defined as Tg (glass transition point).

【0058】

(5) Thickness distribution Using a contact thickness gauge (model: KG60 / A) manufactured by Anritsu Co., Ltd., measure the thickness of samples 5 cm in the vertical direction and 50 cm in the horizontal direction (measurement number = 20), and for each sample, the following (3) The thickness distribution (thickness variation) was calculated by the formula. In addition, the average value (n = 50) of the thickness distribution was evaluated according to the following criteria.

【0059】

Thickness distribution = ((maximum thickness-minimum thickness) / average thickness) x 100 (%) (3) 6% or less Greater than 6% and less than 10% 10% or more × [0060]

(6) Solvent adhesiveness Using a tubular molding device, 1.3 dioxolane was applied to one side of the film at a coating amount of 3 g / sq.m, and the films were immediately (while not drying) laminated to form a tube. The joint portion of the obtained tubular film was sampled to a width of 15 mm and a length of 50 mm, and the adhesive strength peeled off in the circumferential direction was evaluated according to the following criteria (n = 5).

【0061】

<img file="JP2002103545A_D0001.tif" />【0062】

(7) Extreme viscosity 200 mg of a sample was added to 20 ml of a mixed solvent of phenol / tetrachloroethane = 50/50, heated at 110 ° C for 1 hour, and then measured at 30 ° C.

【0063】

The polyester used in the examples is as follows.

【0064】

Polyester A: Polyethylene terephthalate (extreme viscosity (IV) 0.75 dl / g) Polyester B: Polyester consisting of 78 mol% terephthalic acid, 22 mol% isophthalic acid and ethylene glycol (IV 0.72 dl / g) Polyester C: Polyester consisting of 65 mol% terephthalic acid, 10 mol% isophthalic acid, 25 mol% adipic acid and butanediol (IV 0.77 dl / g) Polyester D: Polyester consisting of terephthalic acid, 70 mol% ethylene glycol and 30 mol% neopentyl glycol (IV 0.72 dl / g) Polyester E: Polybutylene terephthalate (IV 1.20 dl / g) [0065]

(Example 1) Polyester A19% by weight, polyester B66% by weight, polyester C15% by weight is mixed in both outer layers, and polyester A21% by weight, polyester B74% by weight, polyester C5% by weight is mixed in the intermediate layer at 280 ° C. The film was co-extruded from a T-die and rapidly cooled with a chill roll to obtain an unstretched film. The Tg of this unstretched film was 69 ° C.

【0066】

The unstretched film was stretched 1.1 times in the longitudinal direction at 80 ° C, then preheated under the condition of a thermal conductivity coefficient of 0.033 W / (m · ° C) until the film temperature reached 89 ° C, and then with a tenter. It was stretched 4.7 times in the transverse direction at 70 ° C (primary stretching). Then, it was heat-treated at 70 ° C. for 10 seconds and further stretched 1.1 times at 68 ° C. in the lateral direction (secondary) to obtain a heat-shrinkable polyester film having a thickness of 50 μm.

【0067】

(Example 2) Polyester A6% by weight, polyester B79% by weight and polyester C15% by weight were used for both outer layers, and polyester A21% by weight, polyester B74% by weight and polyester C5% by weight were mixed for the intermediate layer. A heat-shrinkable polyester-based film having a thickness of 50 μm was obtained in the same manner as in Example 1 except for the above. The Tg of this unstretched film was 69 ° C.

【0068】

A heat-shrinkable polyester-based film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the film was stretched (primary) at 72 ° C in the lateral direction.

【0069】

(Example 3) 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 1.5 times in the longitudinal direction.

【0070】

(Comparative Example 1) A heat-shrinkable polyester film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the primary stretching temperature was 87 ° C.

【0071】

(Comparative Example 2) 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 1 times in the longitudinal direction and 4 times in the width direction.

【0072】

(Comparative Example 3) 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 in which 20% by weight of polyester A, 70% by weight of polyester B, and 10% by weight of polyester C was used. .. The Tg of this unstretched film was 69 ° C.

【0073】

(Comparative Example 4) A thickness of 50 μm was used in the same manner as in Comparative Example 3 except that polyester mixed with 25% by weight of polyester A, 50% by weight of polyester, and 25% by weight of polyester E was used and stretched at 74 ° C in the lateral direction. A heat-shrinkable polyester-based film was obtained. The Tg of this unstretched film was 66 ° C.

【0074】

Table 1 shows the evaluation results of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 4.

【0075】

[table 1]

<img file="JP2002103545A_D0002.tif" />【0076】

As is clear from Table 1, all the films obtained in Examples 1 to 3 had good shrinkage finish. In addition, the compressive strength was sufficient and the thickness distribution was also good. In addition, the non-halogen solvent adhesiveness was also good. The heat-shrinkable polyester-based film of the present invention is of high quality and highly practical, and is particularly suitable for shrinkable labels.

【0077】

On the other hand, the heat-shrinkable film obtained in Comparative Example 1 was inferior in shrinkage finish and thickness distribution. Further, the heat-shrinkable film obtained in Comparative Example 2 was inferior in shrinkage finish. The heat-shrinkable film obtained in Comparative Example 3 was inferior in non-halogen solvent adhesiveness. In addition, the heat-shrinkable film obtained in Comparative Example 4 was inferior in compressive strength. As described above, all of the heat-shrinkable polyester films obtained in the comparative examples were inferior in quality and had low practicality.

【0078】

[Effect of the invention]

According to the present invention, it is possible to achieve a good finish with extremely few wrinkles, shrinkage spots, distortion and insufficient shrinkage due to heat shrinkage, it is possible to perform adhesive processing with a non-halogen solvent, and it can withstand high-speed mounting. A heat-shrinkable film having a film waist and a shrinkage performance that gives a high shrinkage rate in a short time can be obtained.

【0079】

Therefore, it is suitable as a heat-shrinkable polyester-based film for PET bottle labels, which requires high-speed label attachment and shrinkage.

[Simple explanation of drawings]

[Figure 1]

It is explanatory drawing which shows the state which attaches the shrink film to the PET bottle.

[Figure 2]

It is a front view of the main part which shows the state after the shrink film is attached to the PET bottle and shrinks.

[Explanation of symbols]

1 PET bottle 2 label 3 Pressurizing member