JP6947249B2 - Polyester films, laminates and packaging for sealants - Google Patents

Description

The present invention relates to a polyester-based film having excellent heat-sealing strength, and more particularly to a polyester-based film for a sealant having excellent heat-sealing strength with a polyester-based film, and a laminate and a packaging bag using the same.

Conventionally, in many of the distribution articles represented by foods, pharmaceuticals and industrial products, a biaxially stretched film is used as a base film, and a laminated film obtained by heat-sealing or laminating a sealant film is used as a packaging material. ing. A sealant layer made of a polyolefin resin such as polyethylene or polypropylene showing high sealing strength or a copolymer resin such as ionomer or EMMA is provided on the innermost layer of the packaging material constituting the packaging bag or lid material. It is known that these resins can achieve high adhesion strength by heat sealing.

However, the non-stretched sealant film made of a polyolefin-based resin as described in Patent Document 1 is excellent in heat-sealing strength between polyolefin-based films, but heat-sealing with a film made of another material such as polyester, for example. It has the disadvantage of low strength. In addition, since the unstretched sealant film made of polyolefin resin easily adsorbs components made of organic compounds such as fats and oils, the packaging material in which the sealant film is the innermost layer, that is, the layer in contact with the contents, has the scent of the contents. It has the disadvantage that it easily changes the taste and taste. Therefore, it is often unsuitable to use a sealant layer made of a polyolefin resin as the innermost layer for packaging chemical products, pharmaceuticals, foods, and the like.

On the other hand, a sealant film made of an acrylonitrile resin as described in Patent Document 2 is suitable for use as the innermost layer of a packaging material because it does not easily adsorb organic compounds contained in chemical products, pharmaceuticals, foods and the like. ing. However, like the film of Patent Document 1, the acrylonitrile-based film has a problem that the heat-sealing strength with the non-stretched or biaxially stretched polyester-based film is low.

In view of such a problem, Patent Document 3 discloses a polyester-based film for sealant use, which has non-adsorptive properties of organic compounds. However, the polyester film of Patent Document 3 has a disadvantage that it has a high heat shrinkage rate. For example, when the film of Example 1 of Patent Document 3 is used as a sealant and left in a high temperature environment such as in a car in midsummer (about 80 ° C.), there is a problem that the sealant shrinks and the original shape cannot be maintained. ..
Further, since the polyester film of Patent Document 3 has low thickness accuracy, there is a problem that missing dots and faint characters occur when printing is performed. Further, if heat treatment is performed to reduce the shrinkage of the film of Patent Document 3, the thickness accuracy is further lowered and devitrification (whitening) occurs due to an increase in haze. A reduced polyester film for sealant use could not be obtained.

JP-A-2002-256116 Japanese Unexamined Patent Publication No. 7-132946 International Publication No. 2014/175313

An object of the present invention is to solve the above-mentioned problems of the prior art. That is, not only has a high heat-sealing strength between the polyester-based films of the present invention, but also excellent heat-sealing strength with other non-stretched polyester-based films and other biaxially stretched polyester-based films, and various organic compounds can be used. It is intended to provide a polyester-based film for a sealant, which is not only difficult to adsorb but also has little shrinkage even in a high temperature environment and has excellent thickness accuracy, transparency and hygiene. Further, the present invention is intended to provide a laminate containing the polyester film for sealant use as at least one layer, and a packaging bag using the same.

The present invention has the following configuration.
1. 1. A polyester-based film for sealants, which is composed of a polyester resin containing ethylene terephthalate as a main component and satisfies the following requirements (1) to (5).
(1) It is composed of two or more layers having at least one heat-sealing layer, and has a heat-sealing layer on at least one surface layer of the film surface.
(2) In the heat-sealing layer, the total amount (amorphous component amount) of one or more monomer components that can be amorphous components is 12 mol% or more and 30 mol% or less, and the heat-sealed layer is non-heat-sealed. The difference in the amount of amorphous components obtained by subtracting the amount of amorphous components in the other layers from the amount of crystalline components is 4 mol% or more and 30 mol% or less.
(3) The peel strength when the heat-sealing layers of the polyester-based film are heat-sealed at 160 ° C., 2 kg / cm ² , 2 seconds is 2N / 15 mm or more and 25N / 15 mm or less.
(4) The peel strength when the biaxially stretched polyester film composed of the heat-sealing layer and the crystalline polyester is heat-sealed at 160 ° C., 2 kg / cm ² for 2 seconds is 2N / 15mm or more and 20N / 15mm or less.
(5) The heat shrinkage rate when treated in hot water at 80 ° C. for 10 seconds is 0% or more and 15% or less in both the longitudinal direction and the width direction.
2. The haze is 1% or more and 15% or less. Polyester film for sealant use described in.
3. 3. 1. The thickness unevenness in both the longitudinal direction and the width direction is 18% or less. 2. A polyester film for sealant use according to any one of.
4. 1. It is characterized by being a uniaxially stretched film or a biaxially stretched film. ~ 3. Polyester film for sealant use described in.
5. The above 1. ~ 4. A packaging bag characterized in that at least a part of the polyester-based film for sealant use described in the above is used.
6. The above 1. ~ 4. A laminate characterized by having at least one layer of the polyester-based film for sealant use according to the above.
7. 6. A packaging bag characterized in that at least a part of the laminate described in the above is used.

The polyester-based film of the present invention not only exhibits high heat-sealing strength between itself, but is also excellent in heat-sealing strength with other non-stretched polyester-based films and other biaxially stretched polyester-based films. In addition, since the polyester-based film of the present invention does not easily adsorb various organic compounds, it is possible to hygienically wrap articles containing oils and fragrances such as chemical products, pharmaceuticals, and foods. Further, since the film shrinks less when heated, its shape can be maintained even in a high temperature environment. In addition, the polyester-based film of the present invention has good thickness accuracy, so that it has good printability and high transparency.
Further, it is possible to provide a laminate containing the polyester-based film as at least one layer and a packaging bag using the same.

The polyester-based film of the present invention is a polyester-based film for sealants, which is composed of a polyester resin containing ethylene terephthalate as a main component and satisfies the following requirements (1) to (5).
(1) It is composed of two or more layers having at least one heat-sealing layer, and has a heat-sealing layer on at least one surface layer of the film surface.
(2) In the heat-sealing layer, the total amount (amorphous component amount) of one or more monomer components that can be amorphous components is 12 mol% or more and 30 mol% or less, and the heat-sealed layer is non-heat-sealed. The difference in the amount of amorphous components obtained by subtracting the amount of amorphous components in the other layers from the amount of crystalline components is 4 mol% or more and 30 mol% or less.
(3) The peel strength when the heat-sealing layers of the polyester-based film are heat-sealed at 160 ° C., 2 kg / cm ² , 2 seconds is 2N / 15 mm or more and 25N / 15 mm or less.
(4) The peel strength when the biaxially stretched polyester film composed of the heat-sealing layer and the crystalline polyester is heat-sealed at 160 ° C., 2 kg / cm ² for 2 seconds is 2N / 15mm or more and 20N / 15mm or less.
(5) The heat shrinkage rate when treated in hot water at 80 ° C. for 10 seconds is 0% or more and 15% or less in both the longitudinal direction and the width direction.

The polyester-based film of the present invention that satisfies the above requirements is a polyester-based film having excellent heat-sealing properties. In particular, it is a film for a sealant having good heat sealability with a biaxially stretched polyester-based film made of crystalline polyester and a non-stretched polyester-based film made of crystalline polyester. Further, since it is difficult to adsorb various organic compounds, it is possible to provide a sealant material suitable as a packaging bag. Further, since the film shrinks less when heated, its shape can be maintained even in a high temperature environment. In addition, the polyester-based film of the present invention has good thickness accuracy, so that it has good printability and high transparency.
In particular, the heat-sealing property and low shrinkage property, and the heat-sealing property and good thickness accuracy are each two contradictory characteristics, and there has been no polyester-based film that can satisfy all of these characteristics. Hereinafter, the polyester-based film of the present invention will be described.

1. 1. Layer structure of polyester-based film In the polyester-based film of the present invention, the number of film layers must be two or more in order to achieve both low shrinkage and heat-sealing properties, and at least one of the surface layers must be a heat-sealing layer. Must be. The constituent requirements for the heat seal layer and other layers will be described later. A preferable layer structure is a two-kind three-layer structure in which both surface layers are heat-sealed layers and the central layer is the other layer.
The layer ratio of the heat seal layer is preferably 20% or more and 80% or less. If the layer ratio of the heat seal layer is less than 20%, the heat seal strength of the film is lowered, which is not preferable. When the layer ratio of the heat-sealing layer is higher than 80%, the heat-sealing property of the film is improved, but the shrinkage rate is higher than 15%, which is not preferable. The layer ratio of the heat seal layer is more preferably 30% or more and 70% or less.
Further, the heat seal layer and other layers may be provided with a layer subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesiveness of the film surface, which deviates from the requirements of the present invention. It can be provided arbitrarily as long as it does not.

2. Polyester raw materials that make up polyester films 2.1. Types of polyester raw materials The polyester used in the present invention contains an ethylene terephthalate unit as a main component.
Further, it is preferable that the polyester used in the present invention contains at least one monomer component that can be an amorphous component (hereinafter, simply referred to as an amorphous component) as a component other than the ethylene terephthalate unit. This is because the heat-sealing strength of the film is improved by the presence of the amorphous component. Since the content of each component differs between the heat seal layer and the other layers, it will be described later. Examples of the monomer of the carboxylic acid component that can be an amorphous component include isophthalic acid, 1,4-cyclohexanedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid.
Examples of the monomer of the diol component that can be an amorphous component include neopentyl glycol, 1,4-cyclohexanedimethanol, 2,2-diethyl1,3-propanediol, and 2-n-butyl-2-ethyl-1. , 3-Propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, and hexanediol.
Among these, by using any one or more of isophthalic acid, neopentyl glycol, and 1,4-cyclohexanedimethanol, the amorphousness of the film is enhanced and the heat seal strength can be easily increased to 4N / 15 mm or more. It is more preferable to use any one or more of neopentyl glycol and 1,4-cyclohexanedimethanol, and it is particularly preferable to use neopentyl glycol.

In the present invention, components other than ethylene terephthalate and amorphous components may be contained. Examples of the dicarboxylic acid component constituting the polyester include aromatic dicarboxylic acids such as orthophthalic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decandicarboxylic acid, and alicyclic dicarboxylic acids. .. However, it is preferable that the polyvalent carboxylic acid having a valence of 3 or more (for example, trimellitic acid, pyromellitic acid and anhydrides thereof) is not contained in the polyester.
Examples of the diol component other than ethylene glycol constituting the polyester include long-chain diols such as diethylene glycol and 1,4-butanediol, aliphatic diols such as hexanediol, and aromatic diols such as bisphenol A. can. However, the polyester may not contain a diol having 8 or more carbon atoms (for example, octanediol) or a polyhydric alcohol having 3 or more valences (for example, trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.). preferable.
Further, as a component constituting the polyester, a polyester elastomer containing ε-caprolactone, tetramethylene glycol or the like may be contained. Since the polyester elastomer has the effect of lowering the melting point of the film, it can be particularly preferably used for the heat seal layer.

In the polyester film of the present invention, various additives such as waxes, antioxidants, antistatic agents, crystal nucleating agents, thickeners, heat stabilizers, coloring pigments, and colorings are used as required. An inhibitor, an ultraviolet absorber, etc. can be added. Further, it is preferable to add fine particles as a lubricant that improves the slipperiness of the film, at least to the surface layer of the film. Any fine particles can be selected. For example, examples of the inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate, and examples of the organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, and crosslinked polystyrene. Particles and the like can be mentioned. The average particle size of the fine particles can be appropriately selected within the range of 0.05 to 3.0 μm when measured with a Coulter counter, if necessary.
As a method of blending particles into the polyester-based film of the present invention, for example, it can be added at any stage of producing a polyester-based resin, but a polycondensation reaction is carried out at the stage of esterification or after the transesterification reaction is completed. It is preferable to add it as a slurry dispersed in ethylene glycol or the like at a stage before the start to proceed with the polycondensation reaction. In addition, a method of blending a slurry of particles dispersed in ethylene glycol, water, or other solvent with a polyester resin raw material using a kneading extruder with a vent, or a method of kneading and extruding dried particles and a polyester resin raw material. There is also a method of blending using a machine.
The preferable amorphous component contained in the heat seal layer will be described below.

2.2. Acrylic component of polyester raw material contained in heat seal layer The polyester used in the heat seal layer of the present invention preferably has an amorphous component content of 12 mol% or more, more preferably 13 mol% or more, and 14 mol% or more. Is particularly preferable. The upper limit of the amount of amorphous components is 30 mol%. The amount of the amorphous component here refers to the total amount of the carboxylic acid or diol monomer component that can be the amorphous component. This means that for one unit of an ester component (one unit in which a carboxylic acid monomer and a diol monomer are connected by an ester bond), if either the acid component or the diol component can be an amorphous component, the ester unit is not. This is because it can be regarded as crystalline.
If the amount of amorphous components in the heat seal layer is lower than 12 mol%, even if the molten resin is extruded from the die and then rapidly cooled and solidified, it will crystallize in the subsequent stretching and heat fixing steps, so the heat seal strength will be 4N. It is not preferable because it becomes difficult to make it / 15 mm or more.
Further, when the total amount of amorphous components in the heat seal layer is 30 mol% or more, the heat seal strength of the film can be increased, but the thickness accuracy of the film is extremely deteriorated, resulting in poor printability. It ends up. Further, if the amount of the amorphous component of the heat seal layer is 30 mol% or more, the heat resistance of the film is lowered, so that the periphery of the seal portion is blocked during heat sealing (intentionally due to heat conduction from the heating member). This is a phenomenon in which the seal is sealed in a wider range than the specified range), which makes it difficult to perform proper heat sealing.

The ethylene terephthalate unit contained in the heat seal layer is preferably 50 mol% or more and 85 mol% or less in 100 mol% of the polyester constituent units. If the amount of the ethylene terephthalate unit is less than 50 mol%, the mechanical strength and heat resistance of the film may be insufficient. On the other hand, if the amount of the ethylene terephthalate unit is more than 85 mol, the amount of the amorphous component is relatively small, so that it is difficult to set the heat seal strength to 4 N / 15 mm or more.
Further, the amount of the amorphous component contained in the heat-sealed layer of the present invention is 4 mol% or more and 30 mol% or less (the amount of the amorphous component contained in the heat-sealed layer) than the amount of the amorphous component contained in the layer other than the heat-sealed layer. The difference when the amount of the amorphous component contained in the layer other than the heat seal layer is subtracted from the amount is preferably in the range of 4 mol% to 30 mol%). When the difference in the amount of amorphous components is less than 4 mol%, the raw material composition of each layer approaches a single layer, so that the heat seal strength and shrinkage rate of the film cannot be compatible with each other. The difference in the amount of amorphous components is more preferably 4.5 mol% or more. Further, since the upper limit of the amount of the amorphous component contained in the heat seal layer is 30 mol%, the upper limit of the difference in the amount of the amorphous component is 30 mol%.

3. 3. Characteristics of the Polyester Film of the Present Invention Next, the characteristics suitable for using the polyester film of the present invention as a sealant will be described.
3.1. Heat-seal strength First, it is preferable that the heat-seal strength when the polyester films of the present invention are heat-sealed at a temperature of 160 ° C., a seal bar pressure of 2 MPa, and a sealing time of 2 seconds is 2N / 15 mm or more and 25N / 15 mm or less.
If the heat seal strength is less than 2N / 15 mm, the seal portion is easily peeled off, so that it cannot be used as a packaging bag. The heat seal strength is preferably 2.5 N / 15 mm or more, more preferably 3 N / 15 mm or more. It is preferable that the heat seal strength is high, but the upper limit that can be obtained at present is about 25 N / 15 mm.
Further, the polyester-based film of the present invention has a heat-sealing strength of 2N / 15 mm or more and 20N / 15 mm or less when the film and a biaxially stretched polyester-based film made of crystalline polyester are heat-sealed at 160 ° C. preferable. If the heat seal strength is less than 2N / 15 mm, the seal portion is easily peeled off, which is not preferable. The heat seal strength is preferably 2.5 N / 15 mm or more, and more preferably 3 N / 15 mm or more. It is preferable that the heat seal strength is high, but the upper limit that can be obtained at present is about 20 N / 15 mm.
Further, the polyester-based film of the present invention preferably has a heat-sealing strength of 2N / 15 mm or more and 25N / 15 mm or less when heat-sealed with a non-stretched polyester-based film made of crystalline polyester at 160 ° C. If the heat seal strength is less than 2N / 15 mm, it is easily peeled off, which is not preferable. 3.5N / 15mm or more is preferable, and 3N / 15mm or more is more preferable. It is preferable that the heat seal strength is high, but the upper limit that can be obtained at present is about 25 N / 15 mm.
The heat-sealing strength of the polyester-based film of the present invention varies depending on the mating material, but correlates with the heat-sealing strength of the polyester-based films of the present invention. Therefore, when the term "heat seal strength" is used in the following description, it refers to the heat seal strength between the polyester films of the present invention unless otherwise specified.

3.2. Shrinkage rate The polyester-based film of the present invention must have a hot water heat shrinkage rate of 0% or more and 15% or less in both the width direction and the longitudinal direction when treated in hot water at 80 ° C. for 10 seconds.
When the shrinkage rate exceeds 15%, the shrinkage becomes large when the film is in a high temperature environment, and the original shape cannot be maintained. The hot water heat shrinkage rate is more preferably 14% or less, and further preferably 13% or less. On the other hand, when the heat shrinkage rate of hot water is less than 0%, it means that the film is stretched, which is not preferable because it becomes difficult for the film to maintain its original shape as in the case of a high shrinkage rate.

3.3. Thickness unevenness in the longitudinal direction The polyester film of the present invention preferably has a thickness unevenness of 18% or less when the measurement length is 10 m in the longitudinal direction. If the thickness unevenness in the longitudinal direction exceeds 18%, printing defects are likely to occur when printing the film, which is not preferable. The thickness unevenness in the longitudinal direction is more preferably 16% or less, and particularly preferably 14% or less. Further, it is preferable that the thickness unevenness in the longitudinal direction is small, but it is considered that the lower limit is about 1% from the performance of the film forming apparatus.

3.4. Thickness unevenness in the width direction In the width direction, the thickness unevenness when the measurement length is 1 m is preferably 18% or less. If the thickness unevenness in the width direction exceeds 18%, printing defects are likely to occur when printing the film, which is not preferable. The thickness unevenness in the width direction is more preferably 16% or less, and particularly preferably 14% or less. The thickness unevenness in the width direction is preferably closer to 0%, but the lower limit is considered to be 1% from the viewpoint of the performance of the film forming apparatus and the ease of production.

3.5. Haze The polyester film of the present invention preferably has a haze of 1% or more and 15% or less. If the haze exceeds 15%, the transparency of the film deteriorates, so that the visibility of the contents becomes poor when used as a packaging material such as a bag. The upper limit of haze is more preferably 13% or less, and particularly preferably 11% or less. The lower the haze, the higher the transparency, which is preferable. However, at the current state of the art, 1% is the lower limit, and 2% or more is sufficient for practical use.

3.6. Thickness The thickness of the polyester film of the present invention is not particularly limited, but is preferably 3 μm or more and 200 μm or less. If the thickness of the film is thinner than 3 μm, the heat seal strength may be insufficient and processing such as printing may become difficult, which is not very preferable. Further, the film thickness may be thicker than 200 μm, but this is not preferable because the weight of the film used increases and the chemical cost increases. The thickness of the film is more preferably 5 μm or more and 160 μm or less, and further preferably 7 μm or more and 120 μm or less.

4. Film formation conditions for polyester film 4.1. Melt extrusion The polyester film of the present invention is described in 2. above. The polyester raw material described in "Polyester raw material constituting a polyester-based film" is melt-extruded into a heat-sealed layer and other layers by separate extruders to form an unstretched laminated film, which is shown below. It can be obtained by uniaxial stretching or biaxial stretching according to the above method. The film obtained by biaxial stretching is more preferable. As described above, polyester can be obtained by polycondensing by selecting the type and amount of the dicarboxylic acid component and the diol component so as to contain an appropriate amount of a monomer that can be an amorphous component. Further, two or more kinds of chip-shaped polyester can be mixed and used as a raw material for a film.
When the raw material resin is melt-extruded, it is preferable to dry the polyester raw material of each layer using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After the polyester raw material of each layer is dried in this way, it is melted at a temperature of 200 to 300 ° C. using an extruder and extruded as a laminated film. For extrusion, any existing method such as a T-die method or a tubular method can be adopted.
Then, the unstretched laminated film can be obtained by quenching the laminated film melted by extrusion. As a method for rapidly cooling the molten resin, a method of casting the molten resin from a base onto a rotary drum and quenching and solidifying the molten resin to obtain a substantially unoriented resin sheet can be preferably adopted. The film may be stretched in at least one of the longitudinal (longitudinal) direction and the horizontal (width) direction. In the following, the sequential biaxial stretching method by longitudinal stretching-transverse stretching in which longitudinal stretching is first performed and then transverse stretching will be described. However, even in the case of transverse stretching-longitudinal stretching in which the order is reversed, the main orientation direction is It doesn't matter because it only changes. Further, the simultaneous biaxial stretching method may be used.

4.2. Longitudinal stretching For stretching in the longitudinal direction, it is preferable to introduce the non-stretched film into a longitudinal stretching machine in which a plurality of roll groups are continuously arranged. In the longitudinal stretching, it is preferable to preheat the film with a preheating roll until the film temperature reaches 65 ° C. to 90 ° C. If the film temperature is lower than 65 ° C., it becomes difficult to stretch the film when it is stretched in the vertical direction, and breakage is likely to occur, which is not preferable. Further, if the temperature is higher than 90 ° C., the film tends to adhere to the roll, and the film is easily wrapped around the roll or the roll is easily soiled due to continuous production, which is not preferable.
When the film temperature reaches 65 ° C. to 90 ° C., longitudinal stretching is performed. The longitudinal stretching ratio is preferably 1 to 5 times or less. Since 1x is not longitudinally stretched, the longitudinal stretching ratio is 1x to obtain a horizontally uniaxially stretched film, and 1.1 times or more is required to obtain a biaxially stretched film. The upper limit of the longitudinal stretching ratio may be any number, but if the longitudinal stretching ratio is too high, it becomes difficult to laterally stretch and fracture is likely to occur, so it is preferably 5 times or less.
Further, by relaxing the film in the longitudinal direction after longitudinal stretching (relaxation in the longitudinal direction), the shrinkage rate in the longitudinal direction of the film caused by the longitudinal stretching can be reduced. Furthermore, by relaxing in the longitudinal direction, the Boeing phenomenon (distortion) that occurs in the tenter can be reduced. Since the polyester-based film of the present invention uses an amorphous raw material, it is considered that the shrinkage in the longitudinal direction caused by longitudinal stretching is dominant for Boeing strain. This is because in the lateral stretching and final heat treatment in the subsequent process, both ends in the film width direction are gripped and heated, so that only the central portion of the film shrinks in the longitudinal direction. The relaxation rate in the longitudinal direction is preferably 0% or more and 70% or less (a relaxation rate of 0% means that relaxation is not performed). Since the upper limit of the relaxation rate in the longitudinal direction is determined by the raw materials used and the longitudinal stretching conditions, relaxation cannot be performed beyond this. In the polyester film of the present invention, the relaxation rate in the longitudinal direction is up to 70%. Relaxation in the longitudinal direction can be carried out by heating the film after longitudinal stretching at a temperature of 65 ° C. to 100 ° C. or lower and adjusting the speed difference of the rolls. As the heating means, any of roll, near infrared ray, far infrared ray, hot air heater and the like can be used. Further, relaxation in the longitudinal direction can be performed not immediately after longitudinal stretching, but also in lateral stretching (including preheating zone) and final heat treatment by narrowing the clip interval in the longitudinal direction (in this case, both ends in the film width direction). (Because it is relaxed in the longitudinal direction, Boeing distortion is reduced), it can be performed at any time.
After relaxing in the longitudinal direction (longitudinal stretching if not relaxing), it is preferable to cool the film once, and it is preferable to cool it with a cooling roll having a surface temperature of 20 to 40 ° C.

4.3. Lateral Stretching After the longitudinal stretching, it is preferable to perform the transverse stretching at a stretching ratio of about 3.5 to 5 times at 65 ° C. to 110 ° C. in a state where both ends of the film in the width direction are gripped by clips in the tenter. Preheating is preferably performed before stretching in the lateral direction, and preheating is preferably performed until the film surface temperature reaches 75 ° C. to 120 ° C.
After transverse stretching, it is preferable to pass the film through an intermediate zone where no aggressive heating operation is performed. Since the temperature is higher in the next final heat treatment zone than in the transverse stretching zone of the tenter, the heat of the final heat treatment zone (hot air itself or radiant heat) will flow into the transverse stretching process unless the intermediate zone is provided. In this case, since the temperature of the laterally stretched zone is not stable, not only the thickness accuracy of the film deteriorates, but also the physical properties such as heat seal strength and shrinkage rate vary. Therefore, it is preferable that the film after the transverse stretching is passed through the intermediate zone to allow a predetermined time to elapse, and then the final heat treatment is performed. In this intermediate zone, the accompanying flow accompanying the running of the film, the lateral stretching zone, and the final so that when the strip-shaped piece of paper hangs down without passing through the film, the piece of paper hangs down almost completely in the vertical direction. It is important to block hot air from the heat treatment zone. It is sufficient that the transit time of the intermediate zone is about 1 second to 5 seconds. If it is shorter than 1 second, the length of the intermediate zone becomes insufficient and the heat blocking effect is insufficient. On the other hand, it is preferable that the intermediate zone is long, but if it is too long, the equipment will become large, so about 5 seconds is sufficient.

4.4. Final heat treatment After passing through the intermediate zone, it is preferable to perform heat treatment in the final heat treatment zone at a transverse stretching temperature of 180 ° C. or lower. If the heat treatment temperature is not equal to or higher than the transverse stretching temperature, the effect of the heat treatment will not be exhibited. In this case, the shrinkage rate of the film at 80 ° C. is higher than 15%, which is not preferable. The higher the heat treatment temperature, the lower the shrinkage rate of the film, but if it is higher than 180 ° C., the haze of the film becomes higher than 15% and the transparency cannot be maintained, which is not preferable.
At the time of the final heat treatment, the shrinkage ratio in the width direction can be reduced by reducing the distance between the clips of the tenter at an arbitrary magnification (relaxation in the width direction). Therefore, in the final heat treatment, it is preferable to relax in the width direction in the range of 0% or more and 10% or less (a relaxation rate of 0% means that relaxation is not performed). The higher the relaxation rate in the width direction, the lower the shrinkage rate in the width direction, but the upper limit of the relaxation rate (shrinkage rate in the width direction of the film immediately after lateral stretching) is the raw material used, the stretching conditions in the width direction, and the heat treatment temperature. It is not possible to carry out relaxation beyond this, as it is determined by. In the polyester film of the present invention, the relaxation rate in the width direction is limited to 10%.
The passage time of the final heat treatment zone is preferably 2 seconds or more and 20 seconds or less. If the passing time is 2 seconds or less, the surface temperature of the film passes through the heat treatment zone without reaching the set temperature, which makes the heat treatment meaningless. The longer the transit time, the higher the effect of the heat treatment. Therefore, it is preferably 2 seconds or longer, and more preferably 5 seconds or longer. However, if the transit time is to be lengthened, the equipment will become huge, so 20 seconds or less is sufficient for practical use.
After that, a polyester-based film roll can be obtained by winding while cutting and removing both ends of the film.

Next, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the aspects of such Examples, and may be appropriately modified without departing from the spirit of the present invention. Is possible.
The film evaluation method is as follows. If the longitudinal direction and the width direction cannot be specified immediately due to the small area of the film, etc., the longitudinal direction and the width direction may be tentatively determined for measurement, and the tentatively determined longitudinal direction and the width direction become the true direction. On the other hand, the difference of 90 degrees does not cause any particular problem.

<Film evaluation method>
[Heat seal strength]
The heat seal strength was measured according to JIS Z1707. The specific procedure is briefly shown. With a heat sealer, the heat-sealed surfaces that had not been coated or corona-treated were bonded to each other. The sealing conditions were an upper bar temperature of 160 ° C., a lower bar temperature of 100 ° C., a pressure of 2 kg / cm ² , and a time of 2 seconds. The adhesive sample was cut out so that the seal width was 15 mm. The peel strength was measured at a tensile speed of 200 mm / min using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corporation). The peel strength is indicated by the strength per 15 mm (N / 15 mm).
The biaxially stretched polyester film used in the heat seal strength measurement with other biaxially stretched polyester films was E5100-12 μm (manufactured by Toyobo Co., Ltd.), and the heat seal strength was measured with other non-stretched polyester films. The non-stretched polyester film used was A-PET-30 μm (manufactured by Toyobo Co., Ltd.).

[Hot water heat shrinkage rate]
The film was cut into 10 cm × 10 cm squares, immersed in warm water at 80 ± 0.5 ° C. for 10 seconds under no load to shrink, and then immersed in water at 25 ° C. ± 0.5 ° C. for 10 seconds. I took it out of the water. Then, the vertical and horizontal dimensions of the film were measured, and the shrinkage ratio in each direction was determined according to the following equation 1. The measurement was performed twice, and the average value was calculated.

Shrinkage rate = {(length before contraction-length after contraction) / length before contraction} x 100 (%) Equation 1

[Haze]
The measurement was performed using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., 300A) in accordance with JIS-K-7136. The measurement was performed twice, and the average value was calculated.

[Thickness unevenness in the longitudinal direction]
The film was sampled in a roll shape of 11 m in the longitudinal direction and 40 mm in the width direction, and the measurement speed was 5 m / min using a continuous contact thickness gauge manufactured by Micron Measuring Instruments Co., Ltd. The thickness was continuously measured along the longitudinal direction of the film (measurement length was 10 m). The maximum thickness at the time of measurement was Tmax., The minimum thickness was Tmin., And the average thickness was Tave., And the thickness unevenness in the longitudinal direction of the film was calculated from the following equation 2.

Thickness unevenness = {(Tmax.-Tmin.) /Tave.} × 100 (%) ・ ・ Equation 2

[Thickness unevenness in the width direction]
The film was sampled into a wide strip of 40 mm in length and 1.2 m in width, and the measurement speed was 5 m / min using a continuous contact thickness gauge manufactured by Micron Measuring Instruments Co., Ltd. The thickness was continuously measured along the width direction of the film sample (measurement length was 1 m). The maximum thickness at the time of measurement was Tmax., The minimum thickness was Tmin., And the average thickness was Tave., And the thickness unevenness in the longitudinal direction of the film was calculated from the above equation 2.

[Incense retention]
Two films were cut into a square of 10 cm × 10 cm and then superposed, and three sides were heat-sealed at 160 ° C. to prepare a bag in which only one side was open. After adding 20 g each of limonene (manufactured by Nacalai Tesque Co., Ltd.) and menthol (manufactured by Nacalai Tesque Co., Ltd.), the open side was also heat-sealed to create a sealed bag. The bag was covered with a glass container having a capacity of 1000 ml. One week later, a person (4 people in their 20s, 4 people in their 30s, 4 people in their 40s, 4 people in their 50s, a total of 16 people. The ratio of men and women was 50% in each age group) covered the glass container. Was opened so as to smell the air inside, and the air in the glass container was smelled, and the judgment was made as follows.

Judgment ○ Number of people who felt the smell 0 to 1 Judgment △ Number of people who felt the smell 2-3 people Judgment × Number of people who felt the smell 4 to 16

[Adsorption]
The film was cut into 10 cm × 10 cm squares and the weight of the film was measured. Next, the film was permeated into a container containing 500 ml of a solution prepared by adding ethanol to a concentration of 30% each of limonene (manufactured by Nacalai Tesque Co., Ltd.) and menthol (manufactured by Nacalai Tesque Co., Ltd.) for one week. I took it out later.
The removed film was pressed with a Bencot to remove the solution, and dried in a room at a temperature of 23 ° C. and a humidity of 60% RH for 1 day. After drying, the weight of the film was measured, and the difference in film weight obtained from the following formula 3 was taken as the adsorption amount.

Adsorption amount = Film weight after permeation-Film weight before permeation ... Equation 3

This adsorption amount was determined as follows.

Judgment ○ 0 mg or more and 5 mg or less Judgment △ Higher than 5 mg and 10 mg or less Judgment × Higher than 10 mg

[Appearance after being left in a high temperature environment]
After cutting the film into a square of 10 cm x 10 cm, another biaxially stretched polyester film E5100-12 μm (manufactured by Toyobo Co., Ltd.) and an adhesive for dry lamination (Takelac manufactured by Mitsui Chemicals, Inc.), which was also cut into a square of 10 cm × 10 cm. It was laminated using (registered trademark) A-950). This laminate was placed in a constant temperature and humidity chamber (IG400 manufactured by Yamato Scientific Co., Ltd.) in which the temperature and humidity were set to 80 ° C./65% RH, and the mixture was left to stand for 24 hours. After 24 hours, the laminate was taken out and the shrinkage rate obtained from the above formula 1 was calculated. When the shrinkage rate differs depending on the direction of the film, the shrinkage rate in the more shrinkage direction was adopted. This shrinkage rate was evaluated as follows as the appearance after being left in a high temperature environment.

Judgment ○ The rate of contraction from the original shape is less than 2% Judgment △ The rate of contraction from the original shape is 2% or more and 5% or less Judgment × The rate of contraction from the original shape is more than 5%

<Preparation of polyester raw material>
[Synthesis Example 1]
A stainless steel autoclave equipped with a stirrer, thermometer and partial recirculation cooler contains 100 mol% of dimethyl terephthalate (DMT) as a dicarboxylic acid component and 100 mol% of ethylene glycol (EG) as a polyhydric alcohol component. Ethylene glycol was charged so as to be 2.2 times the molar ratio of dimethyl terephthalate, and 0.05 mol% (relative to the acid component) of zinc acetate was used as a transesterification catalyst to distill off the produced methanol. While doing so, the transesterification reaction was carried out. Then, 0.225 mol% of antimony trioxide (relative to the acid component) was added as a polycondensation catalyst, and a polycondensation reaction was carried out at 280 ° C. under a reduced pressure of 26.7 Pa to obtain an intrinsic viscosity of 0.75 dl / g. Polyester (A) was obtained. This polyester (A) is polyethylene terephthalate. The composition of the polyester (A) is shown in Table 1.
[Synthesis example 2]
Polyesters (B) to (E) having different monomers were obtained in the same procedure as in Synthesis Example 1. The composition of each polyester is shown in Table 1. In Table 1, TPA is terephthalic acid, BD is 1,4-butanediol, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, and DEG is diethylene glycol. In the production of the polyester (E), SiO2 (Silicia 266 manufactured by Fuji Silysia Chemical Ltd.) was added as a lubricant at a ratio of 7,000 ppm to the polyester. Each polyester was appropriately formed into chips. The compositions of the polyesters (B) to (E) are shown in Table 1.

[Evaluation film]
The films used other than the films shown in the examples of this patent are a commercially available 30 μm non-stretched polyproprene film for sealants and a commercially available 30 μm polyacrylonitrile-based film for sealants.

[Example 1]
Polyester A, polyester B, polyester D, and polyester E are mixed as raw materials for the heat seal layer (A layer) at a mass ratio of 10:75: 10: 5, and polyester A and polyester are used as raw materials for the other layers (B layer). B, polyester D and polyester E were mixed at a mass ratio of 55:30: 10: 5.
The mixed raw materials of the A layer and the B layer were put into separate twin-screw extruders, and both were melted at 270 ° C. Each molten resin was joined by a feed block in the middle of the flow path, discharged from a T die, and cooled on a chill roll set to a surface temperature of 30 ° C. to obtain an unstretched laminated film. The flow path of the molten resin is set so that both surface layers of the laminated film are A layer and the central layer is B layer (2 types of 3 layers of A layer / A layer / A layer), and the thickness of A layer and B layer is set. The discharge amount was adjusted so that the ratio was 50:50.
The unstretched laminated film obtained by cooling and solidifying is guided to a longitudinal stretching machine in which a plurality of roll groups are continuously arranged, preheated on preheating rolls until the film temperature reaches 90 ° C., and then stretched 4.1 times. bottom. The film immediately after longitudinal stretching was passed through a heating furnace set at 95 ° C. with a hot air heater, and a 20% relaxation treatment was performed in the longitudinal direction by utilizing the speed difference between the rolls at the inlet and the outlet of the heating furnace. Then, the vertically stretched film was forcibly cooled by a cooling roll set to a surface temperature of 25 ° C.
The film after the relaxation treatment was guided to a transverse stretching machine (tenter), preheated for 5 seconds until the surface temperature reached 95 ° C., and then stretched 4.0 times in the width direction (lateral direction). The film after the transverse stretching was directly led to the intermediate zone and passed in 1.0 second. In the intermediate zone of the tenter, the hot air from the final heat treatment zone and the lateral stretching zone so that when the strip-shaped piece of paper hangs down without passing through the film, the piece of paper hangs down almost completely in the vertical direction. The hot air from was cut off.
Then, the film that passed through the intermediate zone was led to the final heat treatment zone and heat-treated at 115 ° C. for 5 seconds. At this time, the heat treatment was performed and at the same time, the clip interval in the film width direction was narrowed to perform a 3% relaxation treatment in the width direction. After passing through the final heat treatment zone, the film was cooled, both edges were cut and removed, and the film was wound into a roll with a width of 500 mm to continuously produce a biaxially stretched film having a thickness of 30 μm over a predetermined length. .. The properties of the obtained film were evaluated by the above method. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 2]
Polyester A, polyester C, polyester D, and polyester E were mixed as raw materials for the A layer at a mass ratio of 10:75: 10: 5, and the same polyester raw materials as in Example 1 were mixed as the raw materials for the B layer. In each subsequent step, a film was formed under the same conditions as in Example 1, and a biaxially stretched film having a width of 500 mm and a thickness of 30 μm was obtained. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.
[Example 3]
Polyester A, polyester B, polyester D, and polyester E were mixed as raw materials for the A layer at a mass ratio of 35:50: 10: 5, and the same polyester raw materials as in Example 1 were mixed as the raw materials for the B layer. After that, a film was formed under the same conditions as in Example 1 except that the longitudinal stretching temperature was 95 ° C. and the relaxation rate in the longitudinal direction was 10%, to obtain a biaxially stretched film having a width of 500 mm and a thickness of 30 μm. Was done. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 4]
Polyester B, polyester D, and polyester E were mixed as raw materials for the A layer at a mass ratio of 5:90: 5, and the same polyester raw materials as in Example 1 were mixed as the raw materials for the B layer. After that, the film was formed under the same conditions as in Example 1 except that the longitudinal stretching temperature was 85 ° C., the relaxation rate in the longitudinal direction was 25%, the transverse stretching temperature was 93 ° C., and the final heat treatment temperature was 120 ° C. A biaxially stretched film having a width of 500 mm and a thickness of 30 μm was obtained. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.
[Example 5]
Polyester A, polyester B, polyester D, and polyester E were mixed as raw materials for the A layer at a mass ratio of 5:66: 24: 5, and the same polyester raw materials as in Example 1 were mixed as the raw materials for the B layer. After that, a film was formed under the same conditions as in Example 1 except that the longitudinal stretching temperature was 80 ° C., the relaxation rate in the longitudinal direction was 30%, and the transverse stretching temperature was 90 ° C., and the width was 500 mm and the thickness was 30 μm. The biaxially stretched film of was obtained. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 6]
As the raw material of the A layer, the same polyester raw material as in Example 1 was mixed, and as the raw material of the B layer, polyester A and polyester E were mixed at a mass ratio of 5:95. Then, a film was formed under the same conditions as in Example 1 except that the transverse stretching temperature was set to 100 ° C. to obtain a biaxially stretched film having a width of 500 mm and a thickness of 30 μm. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.
[Example 7]
As the raw material of the A layer, the same polyester raw material as in Example 1 was mixed, and as the raw material of the B layer, polyester A, polyester B, polyester D and polyester E were mixed at a mass ratio of 25:60: 10: 5. After that, a film was formed under the same conditions as in Example 1 except that the relaxation rate in the longitudinal direction was 30% and the final heat treatment temperature was 120 ° C. to obtain a biaxially stretched film having a width of 500 mm and a thickness of 30 μm. Was done. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 8]
The same polyester raw materials as in Example 1 were used as the raw materials for the A layer and the B layer, and the discharge amount was adjusted so that the thickness ratio of the A layer and the B layer was 70:30 under the same conditions as in Example 1. An unstretched laminated film was obtained. Then, a film was formed under the same conditions as in Example 1 to obtain a biaxially stretched film having a width of 500 mm and a thickness of 30 μm. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.
[Example 9]
The same polyester raw materials as in Example 1 were used as the raw materials for the A layer and the B layer, and the discharge amount was adjusted so that the thickness ratio of the A layer and the B layer was 30:70 under the same conditions as in Example 1. An unstretched laminated film was obtained. Then, a film was formed under the same conditions as in Example 1 to obtain a biaxially stretched film having a width of 500 mm and a thickness of 30 μm. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Example 10]
The raw materials for the A layer and the B layer were the same polyester raw materials as in Example 1, and the film was unstretched under the same conditions as in Example 1 except that the discharge amount was adjusted so that the film thickness after biaxial stretching was 12 μm. A laminated film was obtained. Then, a film was formed under the same conditions as in Example 1 to obtain a biaxially stretched film having a width of 500 mm and a thickness of 12 μm. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.
[Example 11]
The raw materials for the A layer and the B layer were the same polyester raw materials as in Example 1, and the film was unstretched under the same conditions as in Example 1 except that the discharge amount was adjusted so that the film thickness after biaxial stretching was 60 μm. A laminated film was obtained. Then, a film was formed under the same conditions as in Example 1 to obtain a biaxially stretched film having a width of 500 mm and a thickness of 60 μm. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Comparative Example 1]
Polyester A, polyester B, polyester D, and polyester E were mixed as raw materials for both the A layer and the B layer at a mass ratio of 5:66: 24: 5, and an unstretched laminated film was obtained under the same conditions as in Example 1. After that, the film was vertically stretched under the same conditions as in Example 1 except that the longitudinal stretching temperature was 80 ° C. and the longitudinal stretching ratio was 3.5, and the film after the longitudinal stretching was cooled without passing through a heating furnace (that is,). , The relaxation rate in the longitudinal direction is 0%). The film after longitudinal stretching was guided to a tenter, and transverse stretching and final heat treatment were performed under the same conditions as in Example 1 except that the transverse stretching temperature was 85 ° C. and the final heat treatment temperature was 95 ° C., and the width was 500 mm and the thickness was 30 μm. A biaxially stretched film was obtained. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.
[Comparative Example 2]
Polyester A, polyester B, and polyester E were mixed as raw materials for the A layer at a mass ratio of 65:30: 5, and the same polyester raw materials as in Example 1 were mixed as the raw materials for the B layer. Then, a film was formed under the same conditions as in Example 1 to obtain a biaxially stretched film having a width of 500 mm and a thickness of 30 μm. The manufacturing conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[Comparative Example 3]
It was evaluated by the above method using a commercially available unstretched polypropylene film for a sealant having a thickness of 30 μm. The evaluation results are shown in Table 3.
[Comparative Example 4]
It was evaluated by the above method using a commercially available polyacrylonitrile-based film for sealants having a thickness of 30 μm. The evaluation results are shown in Table 3.

[Film evaluation results]
From Table 3, all of the films of Examples 1 to 10 are excellent in heat seal strength, shrinkage rate, haze, thickness unevenness, aroma retention, adsorptivity, and appearance after being left in a high temperature environment, and are good. Evaluation results were obtained.
On the other hand, although the film of Comparative Example 1 was excellent in heat seal strength, haze, aroma retention, and adsorptivity, it was not a film that could withstand use in that it had a high shrinkage rate and poor thickness unevenness.
Further, the film of Comparative Example 2 is excellent in shrinkage rate, haze, uneven thickness, aroma retention, and adsorptivity, but even if it is heat-sealed with another biaxially stretched polyester film, it peels off immediately and cannot be measured. rice field.
In Comparative Examples 3 and 4, the strength could not be measured by heat-sealing not only with other biaxially stretched polyester films but also with other non-stretched polyester films. Further, Comparative Example 3 was inferior in the aroma-retaining property of menthol and limonene, and Comparative Example 4 had a high haze, so that the effect of the present invention was not exhibited.

The present invention relates to a polyester-based film having excellent heat-sealing strength, and not only has excellent heat-sealing strength with a polyester-based film, but also has less shrinkage during heating, and has excellent thickness accuracy and transparency, and is a sealant. It can be suitably used as an application. Further, the polyester-based film of the present invention may be used as at least one layer to form a laminate with another film, and a packaging bag can be provided from the laminate.

Claims (7)

A coextruded laminated polyester film for sealants, which is composed of a polyester resin containing ethylene terephthalate as a main component, has a thickness of 3 μm or more and 200 μm or less, and satisfies the following requirements (1) to ( 6).
(1) It is composed of two or more layers having at least one heat-sealing layer, and has a heat-sealing layer on at least one surface layer of the film surface (however, the layers other than the heat-sealing layer are sea islands. Except for films with structure).
(2) The heat seal layer contains 50 mol% or more of ethylene terephthalate unit in all the monomer components, and the total (amorphous component amount) of one or more kinds of monomer components that can be amorphous components is 12 mol% or more 30. The difference in the amount of amorphous components obtained by subtracting the amount of amorphous components in the other layers from the amount of amorphous components in the heat-sealed layer is 4 mol% or more and 30 mol% or less.
(3) The peel strength when the heat-sealing layers of the polyester-based film are heat-sealed at 160 ° C., 2 kg / cm ² , 2 seconds is 2N / 15 mm or more and 25N / 15 mm or less.
(4) The peel strength when a biaxially stretched polyester film composed of a heat-sealing layer and crystalline polyester is heat-sealed at 160 ° C., 2 kg / cm ² , for 2 seconds is 2N / 15 mm or more and 20N / 15 mm or less.
(5) The heat shrinkage rate when treated in hot water at 80 ° C. for 10 seconds is 0% or more and 15% or less in both the longitudinal direction and the width direction.
(6) The peel strength when a non-stretched polyester film composed of a heat-sealing layer and crystalline polyester is heat-sealed at 160 ° C., 2 kg / cm ² , for 2 seconds is 2N / 15 mm or more and 25N / 15 mm or less. The polyester-based film for a sealant according to claim 1, wherein the haze is 1% or more and 15% or less. The polyester film for sealants according to any one of claims 1 and 2, wherein the thickness unevenness in both the longitudinal direction and the width direction is 18% or less. The polyester-based film for sealants according to claims 1 to 3, which is a uniaxially stretched film or a biaxially stretched film. A packaging bag characterized in that the polyester-based film for sealant use according to claims 1 to 4 is used at least in part. A laminate characterized by having at least one layer of the polyester-based film for sealant use according to claims 1 to 4. A packaging bag characterized in that the laminate according to claim 6 is used at least in a part.