JP2012036272A - Heat-shrinkable polyester film, and insulated container using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester film extremely excellent in natural shrinkage resistance, and hardly generating shrinkage deficiency when being heated at ≥80°C, especially a heat-shrinkable polyester film capable of forming an insulated gripping part of the insulated container by being quickly shrunk by heating when being used for the insulated container, and dispensing with storage under temperature control even in such a period that the outside air temperature rises.SOLUTION: In this heat-shrinkable polyester film, the maximum shrinkage stress at 75°C in the main shrinkage direction of the film is ≥4.4 MPa and ≤12.0 MPa, and a shrinkage rate in the main shrinkage direction when the film is stored for 8 hours under the 60°C×40% RH atmosphere is ≤2.0%, and the shrinkage rate in the main shrinkage direction when the film is dipped for 10 seconds into warm water at 80°C is ≥10% and <80%.

Description

  The present invention relates to a heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film useful as a heat-shrinkable film for a heat insulating container.

  A cup-like container having a heat insulating structure has been proposed for uses such as tableware and beverage cups for vending machines. For example, in Patent Documents 1 and 2, an outer sleeve is slidably fitted on the outer peripheral surface of the body wall of the container body, and either the upper or lower side is fixed, and the outer sleeve is compressed in the vertical direction. The heat insulation container which forms the heat insulation holding part by making the some slit formation area part provided in FIG. However, the heat insulating containers disclosed in Patent Documents 1 and 2 have to form the heat insulating grips using human power or the like.

  Patent Document 3 discloses a method in which a heat-shrinkable film is attached to the inner wall surface of the outer sleeve, and the heat-shrinkable film shrinks to project the slit forming section and form a heat-insulating grip. Yes. The heat-shrinkable film used here is not limited in its characteristics and materials, but is required to be a film having a certain level of shrinkage stress and a low natural shrinkage rate.

  About the heat-shrinkable film used for this heat insulation container, when the shrinkage stress is too low, the said slit formation area part cannot be pushed up, and the heat insulation which is the characteristic of this heat insulation container cannot be provided. On the other hand, the insulated container is stored in a warehouse with the containers overlapped after formation. However, when a film having a high natural shrinkage rate is used, the film shrinks as the temperature of the warehouse increases. Since the heat insulating gripping portion protrudes, there arises a problem that the stacked containers are difficult to come off. Furthermore, although the domestic distribution of the heat insulating containers is mainly transported by truck, the same phenomenon occurs when the temperature of the truck bed rises, and as a result, the stacked containers are difficult to come off. For this reason, it is necessary to suppress natural shrinkage by using a cold storage warehouse, a cold storage vehicle, or the like, particularly during product transportation and storage in the season when the outside air temperature rises, which is a cause of increasing costs.

As a heat shrinkable film having a low natural shrinkage rate, a film made of a single material of a polyester resin or a polystyrene resin, a laminated film of a polystyrene resin and a polyester resin, and the like have been studied.
As a film made of a single material, for example, Patent Document 4 is made of at least two or more polyester copolymers, and shows a sharp rise between 60 ° C. and 95 ° C. in the heat shrinkage rate-temperature graph. A heat shrinkable film is disclosed. Patent Document 5 includes a polyester resin or a polystyrene resin, and the shrinkage in the main stretching direction is 10% or less at 70 ° C. × 10 seconds and 2.5% or less at 40 ° C. × 7 days. A heat shrinkable film is disclosed.
As a laminated film, for example, Patent Document 6 contains a front and back layer containing a polyester resin and a modified styrene elastomer having reactivity with the polyester resin, and a polystyrene resin and a polyester resin. A heat-shrinkable laminated film comprising an intermediate layer and having a natural shrinkage rate of 3.0% or less in the main shrinkage direction after being stored at 30 ° C. for 30 days is disclosed. Patent Document 7 includes at least three layers of a polyester resin layer, a tackifier resin layer, and a styrene resin layer, and is natural when stored in an atmosphere of 30 ° C. and 50% RH for 30 days. A heat-shrinkable laminated film having a shrinkage rate of less than 3% is disclosed.

The heat-shrinkable films disclosed in Patent Documents 4 to 7 have good natural shrinkage resistance such that they hardly shrink at room temperature, and quickly shrink when heated to 60 ° C or higher. It also has shrink finish and shrink workability.
However, in the season when the outside air temperature rises, the ambient temperature of the warehouse or truck bed may exceed 50 ° C., and approaches the shrinkage start temperature of these heat-shrinkable films. Therefore, when the heat-shrinkable film disclosed in Patent Documents 4 to 7 is used for the heat insulating container, it is indispensable to store it in a cold storage warehouse and transport it in a cold vehicle.

JP 2006-044723 A JP 2006-160346 A International Publication No. 2009/054110 JP-A-6-122152 JP 2000-229357 A Japanese Patent No. 4364085 Japanese Patent No. 4426488

  An object of the present invention is a heat shrinkable polyester film that is extremely excellent in spontaneous shrink resistance and at the same time is less susceptible to insufficient shrinkage when heated to 80 ° C. or more, particularly when used as a heat insulating container. An object of the present invention is to provide a heat-shrinkable polyester film that shrinks to form a heat-insulating gripping portion of the heat-insulating container and that does not need to be stored under temperature control even in the season when the outside air temperature rises.

The present invention relates to the following [1] to [4].
[1] The maximum shrinkage stress at 75 ° C. in the main shrinkage direction of the film is 4.4 MPa or more and 12.0 MPa or less, and when the film is stored in an atmosphere of 60 ° C. × 40% RH for 8 hours, A heat shrinkable polyester system having a shrinkage ratio of 2.0% or less and a shrinkage ratio in the main shrinkage direction of 10% or more and less than 80% when the film is immersed in warm water at 80 ° C. for 10 seconds. the film.
[2] In all polyester resin components, the main component of the dicarboxylic acid component is terephthalic acid, the main component of the diol component is ethylene glycol, and (a) isophthalic acid, (b) 1,4-cyclohexanedimethanol, and ( c) The heat-shrinkable polyester film according to the above [1], which is a copolyester containing at least one selected from the group consisting of neopentyl glycol.
[3] The shrinkage rate in the main shrinkage direction when immersed in warm water at 60 ° C. for 5 minutes is 2.7% or less, and the shrinkage rate in the main shrinkage direction when immersed in warm water at 70 ° C. for 10 seconds is 3%. The heat-shrinkable polyester film according to [1] or [2] above.
[4] A heat insulating container using the heat-shrinkable polyester film according to any one of [1] to [3].

  The heat-shrinkable polyester film of the present invention is hardly shrunk under an atmosphere of 60 ° C. or less and has a very low natural shrinkage rate. When the film is used for a heat insulating container, it is possible to provide a heat insulating container that quickly shrinks by heating to form a heat insulating gripping part and that does not need to be stored under temperature control even in the season when the outside air temperature rises.

  Hereinafter, the heat-shrinkable polyester film of the present invention and the heat insulating container using the film will be described in detail.

[Heat-shrinkable polyester film]
The heat-shrinkable polyester film of the present invention has a maximum shrinkage stress at 75 ° C. in the main shrinkage direction of the film of 4.4 MPa to 12.0 MPa, preferably 4.4 MPa to 10.0 MPa, more preferably It is 5.0 MPa or more and 8.0 MPa or less. When the maximum shrinkage stress at 75 ° C. is less than 4.4 MPa, when the film is used for a heat insulating container, it takes too much time until the heat insulating grip portion is formed, or the heat insulating grip portion cannot be completely formed (so-called May be badly shaped). On the other hand, when it exceeds 12.0 MPa, the natural shrinkage rate of the film increases, which is not preferable.

The maximum shrinkage stress of the film can be controlled by the material and components of the film and the stretching conditions in the main shrinkage direction.
As a material for the shrinkable label of the PET bottle, a heat-shrinkable film formed by stretching polyvinyl chloride (PVC), polystyrene resin, polyester resin or the like is preferably used, and the effect of the present invention is achieved. It is important that the film is made of a polyester resin. This is because a heat-shrinkable film made of a polyester-based resin is superior in natural shrinkage resistance to other materials and can easily control shrinkage stress.
When the component which comprises a polyester-type film changes, crystallinity will change, for example, it exists in the tendency for shrinkage stress to become high, so that a film with high crystallinity. However, a film having high crystallinity tends to cause insufficient shrinkage. Therefore, in the present invention, it is preferable to use a film component that suppresses crystallinity.
Regarding the stretching conditions, the shrinkage stress can be controlled by adjusting the stretching temperature, the heat treatment temperature, the relaxation rate, and the like. Among them, the stretching temperature greatly affects the shrinkage stress, and the shrinkage stress can be controlled to a higher value as the stretching temperature is set lower.

  The heat-shrinkable polyester film of the present invention has a shrinkage ratio in the main shrinkage direction of 2.0% or less, preferably 1.8% or less when stored at 60 ° C. × 40% RH atmosphere for 8 hours. More preferably, it is 1.6% or less. When the shrinkage rate when stored for 8 hours in an atmosphere of 60 ° C. × 40% RH exceeds 2.0%, when the film is used in a heat-insulating container, the film shrinks due to an increase in temperature during storage. It will occur and the heat insulating gripping part will protrude slightly. As a result, as described above, it is not preferable because the stacked heat insulating containers are difficult to come off.

  In order to suppress the shrinkage rate to 2.0% or less when stored in an atmosphere of 60 ° C. × 40% RH for 8 hours, it is useful to control the stretching conditions in the main shrinkage direction of the film. For example, when stretching in the main shrinkage direction by the tenter method, it is necessary to control the stretching temperature, the heat treatment temperature, and the relaxation rate, and the stretching temperature is stretched at a temperature that is as low as possible without breaking, and subsequently causes insufficient shrinkage. It is preferable to perform the heat treatment at a temperature as high as possible. If the heat treatment is then performed while relaxing, the shrinkage rate can be further suppressed. More specifically, the stretching temperature should be stretched in the range of the glass transition temperature Tg to (Tg + 25 ° C.) of the film, preferably in the range of Tg to (Tg + 20 ° C.). It is better to process at temperature. The relaxation rate in the reheat treatment is preferably in the range of 0.1 to 10%. As described above, after stretching at a low temperature as much as possible, the shrinkage rate when stored for 8 hours in a 60 ° C. × 40% RH atmosphere is relaxed by 2.0% or less by relaxing the orientation in the low temperature region by heat treatment or relaxation. Can be suppressed.

  The heat shrinkable polyester film of the present invention has a shrinkage ratio in the main shrinkage direction of 10% or more and less than 80%, preferably 15% or more and less than 75%, more preferably when immersed in warm water at 80 ° C. for 10 seconds. 20% or more and less than 70%. When the shrinkage rate when immersed in warm water at 80 ° C. for 10 seconds is less than 10%, there is a case where the heat insulation gripping part of the heat insulation container cannot be completely formed due to insufficient shrinkage when heated to 80 ° C. or higher. Absent. Moreover, since the natural shrinkage rate of a film will become high that it is 80% or more, it is unpreferable.

  The heat-shrinkable polyester film of the present invention comprises terephthalic acid as the main component of the dicarboxylic acid component, ethylene glycol as the main component of the diol component, and (a) isophthalic acid, (b) 1, A copolymerized polyester containing at least one selected from the group consisting of 4-cyclohexanedimethanol and (c) neopentyl glycol is preferred.

  The main dicarboxylic acid component constituting the polyester-based resin is terephthalic acid as described above, and terephthalic acid is preferably 50 mol% or more, more preferably 55 mol% or more, still more preferably based on 100 mol% of the dicarboxylic acid component. Contains 60 mol% or more. Dicarboxylic acid components other than terephthalic acid include, for example, isophthalic acid, adipic acid, sebacic acid, orthophthalic acid, naphthalenedicarboxylic acid, succinic acid, azelaic acid, decanoic acid, dimer acid, cyclohexanedicarboxylic acid, trimellitic acid, etc. Among them, isophthalic acid can be preferably contained.

The main diol component constituting the polyester-based resin is ethylene glycol as described above, and ethylene glycol is preferably 50 mol% or more, more preferably 55 mol% or more, and still more preferably 60 with respect to 100 mol% of the diol component. Containing at least mol%. Examples of the diol component other than ethylene glycol include neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, 1,5- Pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, hexanediol, nonanediol, dimer diol, ethylene oxide adduct or propylene oxide adduct of bisphenol A, polyethylene glycol, Polypropylene glycol, polytetramethylene glycol, 2-butyl-2-ethyl-1,3-propanediol, tricyclodecane dimethanol, 2,2,4-trimethyl-1,5-pentanediol and the like can be contained. , But it is possible to suitably containing neopentyl glycol and 1,4-cyclohexanedimethanol. Further, 1,4-cyclohexanedimethanol has two types of isomers, cis type and trans type, which may be any.
However, when a component such as 1,4-butanediol that has a glass transition temperature (Tg) lower than that of ethylene glycol is contained, the content of diol is reduced from the viewpoint of suppressing an increase in the natural shrinkage rate. Preferably it is 5 mol% or less with respect to 100 mol% of components, More preferably, it restrains to 3% or less.

In the present invention, heat shrinkage in which the dicarboxylic acid component is 100% by mole of terephthalic acid, the diol component is mainly composed of ethylene glycol and 1,4-cyclohexanedimethanol as the second component is particularly preferably used. Is a conductive polyester film. The main component and the second component referred to here are those having the highest molar ratio in each component when the dicarboxylic acid component and the diol component in the total polyester resin component are each 100 mol% (total 200 mol%). The second highest component is called the second component. Similarly, the third highest component is referred to as the third component, and even if it contains the third component and thereafter, it does not matter as long as it satisfies the requirements of the present invention.
A heat-shrinkable film containing isophthalic acid or neopentyl glycol as the second component can also be suitably used, but the glass transition temperature is set to a more appropriate range to control the natural shrinkage resistance, shrinkage stress, and shrinkage rate. From the viewpoint of performing efficiently, a film containing 1,4-cyclohexanedimethanol as the second component is more preferable. From the above viewpoint, the content of 1,4-cyclohexanedimethanol is preferably 10 mol% or more and 45 mol% or less, more preferably 20 mol% or more and 40 mol% or less, in 100 mol% of all diol components. .

The polyester resin according to the present invention can be produced by a batch method or a continuous method by a conventional method for producing a polyester resin, that is, a direct polymerization method or a transesterification method. Here, the optional copolymerization component can be added at any stage of the polycondensation reaction process. Alternatively, a polyester resin can be produced by producing an oligomer having a low polymerization degree from a dicarboxylic acid compound and a diol compound, and polycondensing this with an arbitrary copolymer component.
The resin obtained by the polycondensation reaction is usually extracted in the form of a strand from an extraction port provided at the bottom of the polycondensation reaction tank, and is cooled with water or after water cooling, and then cut into a pellet by cutting with a cutter. Furthermore, by subjecting the pellets after polycondensation to heat treatment and solid phase polycondensation, the degree of polymerization can be further increased, and reaction by-products such as acetaldehyde and low-molecular oligomers can be reduced.
In the above production method, the esterification reaction is performed in the presence of an esterification reaction catalyst such as antimony trioxide, an organic acid salt such as antimony, titanium, magnesium, calcium, or an organic metal compound, if necessary. The transesterification reaction can be carried out in the presence of a transesterification reaction catalyst such as an organic acid salt or an organic metal compound such as lithium, sodium, potassium, magnesium, calcium, manganese, titanium, or zinc, if necessary. It can be carried out.
The polycondensation reaction can be carried out in the presence of phosphorus compounds such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid, and esters and organic acid salts thereof. It can also be carried out in the presence of a polycondensation catalyst such as metal oxides such as diantimony, germanium dioxide and germanium tetroxide, or organic acid salts and organometallic compounds such as antimony, germanium, zinc, titanium and cobalt. Of these polycondensation catalysts, at least one selected from tetrabutoxy titanate, antimony trioxide, and germanium dioxide is preferably used.
Further, an antifoaming agent such as silicone oil can be added to promote defoaming in the polycondensation process.

The heat-shrinkable polyester film of the present invention has a shrinkage ratio in the main shrinkage direction when immersed in warm water at 60 ° C. for 5 minutes from the viewpoint of high natural shrinkage resistance, which is difficult to heat shrink even at an atmospheric temperature exceeding 50 ° C. Is preferably 2.7% or less, more preferably 2.6% or less, and even more preferably 2.5% or less.
From the same viewpoint, the heat-shrinkable polyester film of the present invention preferably has a shrinkage in the main shrinkage direction of not more than 3%, more preferably not more than 2.5% when immersed in warm water at 70 ° C. for 10 seconds. It is.

  The heat-shrinkable film of the present invention may be a single layer film or may be used for at least one layer of a laminated film. In the case of a laminated film, as long as the requirements of the present invention are satisfied, there is no particular limitation on the material and the number of layers of the laminated film, and it may be the same or different material as the film of the present invention. I do not care. Examples of the heterogeneous material include polystyrene resins and polyolefin resins. However, in order to maintain the excellent natural shrinkage resistance, which is a feature of this film, the other layers are preferably composed of a polyester resin. In addition, the thickness of the film in the case of a laminated film is not particularly limited, but if it is 50% or more with respect to the thickness of all layers, it is preferable because the natural shrinkage resistance is hardly inhibited.

  In the present invention, in addition to the above-described components, recycled resins and other resins generated from trimming loss of film ears and the like within a range that does not significantly impair the effects of the present invention; inorganics such as silica, talc, kaolin, calcium carbonate, etc. Particles: Pigments such as titanium oxide and carbon black; Add additives such as flame retardants, ultraviolet absorbers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers, etc. as appropriate You can also.

[Method for producing heat-shrinkable polyester film]
The heat-shrinkable film of the present invention is a sheet or film produced by melt-extruding a mixture composed of the above-described polyester-based resin, additives, and the like with a single screw extruder or a biaxial (same direction, different direction) extruder, Furthermore, it is preferable to produce at least one axis. The mixture may be prepared by a known method such as a Henschel mixer, or may be melted and pelletized by an extruder. As the extrusion method, a known method such as a T-die method or a tubular method may be employed. Moreover, when manufacturing a laminated | multilayer film, the method of superimposing after extruding or extruding for every single layer can be employ | adopted.

  The melt-extruded sheet or film is cooled with a cooling roll, air, water, etc., and then reheated by a suitable method such as hot air, hot water, infrared rays, etc., and at least 1 by a roll method, a tenter method, a tubular method, etc. It is preferred to be stretched on the axis. The stretching temperature needs to be changed depending on the glass transition temperature (Tg) of each resin constituting the heat-shrinkable film and required characteristics, but is generally Tg to (Tg + 25 ° C.) from the viewpoint of productivity and shrinkage characteristics. It is good.

  Although the draw ratio in the main shrinkage direction is not particularly limited, a range of 2 to 8 times is preferable from the viewpoint of productivity and shrinkage characteristics.

  The stretched film is preferably heat-treated in a heat treatment step for the purpose of preventing rapid shrinkage during heat shrinkage and improving spontaneous shrinkage resistance. Any known method such as a roll or a tenter may be used for the heat treatment. The heat treatment conditions are not particularly limited, but from the viewpoint of productivity and shrinkage characteristics, it is preferable to perform the treatment at a stretching temperature to (stretching temperature + 40 ° C.) for 2 to 120 seconds.

  The heat treatment step is preferably a combination of a step of heat treatment without relaxation and a step of heat treatment while relaxing in the main shrinkage direction. The higher the relaxation rate in the main shrinkage direction, the better the natural shrinkage resistance. However, the relaxation rate is preferably in the range of 0.5 to 10% from the viewpoint of productivity and shrinkage characteristics.

  The thickness of the polyester-based heat-shrinkable film obtained in the present invention is not particularly limited. However, when used in a heat-insulating container, the thickness is 10 μm from the viewpoint of forming a heat-insulating gripping part and workability in the processing step of bonding the film to the container. It is preferable that the thickness is not less than 200 μm, preferably not less than 20 μm and not more than 150 μm.

[Insulated container]
A heat insulation container can be manufactured using the heat-shrinkable polyester film of the present invention. Although it does not specifically limit as the said heat insulation container, For example, the heat insulation container described in said patent document 1-3 etc. may be sufficient. The manufacturing method is not particularly limited, and for example, the methods described in the above Patent Documents 1 to 3 can be referred to. Specifically, a slit group is formed in the height direction of the outer sleeve that forms the heat insulating protruding portion, and a mountain fold ruled line and a valley fold ruled line are formed on the strip portion so that the strip formed by the slit is compressed in the vertical direction and protrudes. A heat-shrinkable film of the present invention is formed on the outer sleeve formed so that the film contacts the outer surface of the cup between the sleeve and the cup, and covers the strip group formed by the slit of the sleeve. A heat insulating container can be manufactured by attaching to the above.
When the sleeve is wound around the cup, an adhesive part of the sleeve is necessary. However, since the adhesive part becomes double, only the adhesive part is difficult to transmit heat conduction. May be weak or may not protrude. Therefore, it is preferable to cut out the protruding portion of the bonding portion so as not to overlap.
In the heat insulating container using the heat-shrinkable polyester film of the present invention, when hot water is poured into the heat-insulating container (cup), heat is transferred to the heat-shrinkable film disposed on the outer surface of the cup so that the film is in the height direction. The heat insulating gripping part is formed by shrinking and projecting the strip formed by the slit.
The said heat insulation container is suitable as a container for instant noodles, soup, etc. which can be eaten / drinked by pouring hot water in a container, and the heat insulation of the part (heat insulation holding part) which a user hold | grips by hand is excellent.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited at all by these. In addition, the measured value shown in the Example and evaluation were implemented as follows.

[Shrinkage stress]
(Maximum shrinkage stress at 75 ° C in the main shrinkage direction of the film)
A film was cut to a size of 10 mm in width and 120 mm in length so that the main shrinkage direction was the longitudinal direction, and used as a sample. Both ends of the sample were gripped so that the distance between chucks was 50 mm, the load when immersed in an oil bath adjusted to 75 ° C. was detected, and the value calculated from the maximum load was taken as the maximum contraction stress.

[Heat shrinkage]
(1) 60 ° C. × 40% RH atmosphere × heat shrinkage rate in the main shrinkage direction after storage for 8 hours The film is cut into a size of 30 mm in width and 600 mm in length so that the main shrinkage direction becomes the longitudinal direction, and intervals of 500 mm A sample line was inserted and used as a sample. The sample was placed in a thermostatic chamber adjusted to an atmosphere of 60 ° C. × 40% RH. After storage for 8 hours, it was taken out from the thermostatic chamber, and the dimension between the marked lines A (mm) was measured. From the dimensions, the thermal contraction rate was calculated by the following equation.
Shrinkage rate (%) = [(500−A) / 500] × 100
(2) Heat shrinkage rate in the main shrinkage direction after immersion at 80 ° C. in warm water for 10 seconds The mark is cut into a size of 10 mm in width and 140 mm in length so that the main shrinkage direction becomes the longitudinal direction, and a marked line having an interval of 100 mm Was used as a sample. The sample was immersed in warm water at 80 ° C. for 10 seconds, and then quickly cooled with cold water, and then the dimension between the marked lines B (mm) was measured. From the dimensions, the thermal contraction rate was calculated by the following equation.
Shrinkage rate (%) = [(100−B) / 100] × 100
(3) Heat shrinkage rate in the main shrinkage direction after 70 ° C. warm water × 10 seconds immersion The film is cut into a size of 10 mm in width and 140 mm in length so that the main shrinkage direction is the longitudinal direction, and a marked line having an interval of 100 mm Was used as a sample. The sample was immersed in warm water at 70 ° C. for 10 seconds, and then quickly cooled with cold water, and then the dimension between the marked lines C (mm) was measured. From the dimensions, the thermal contraction rate was calculated by the following equation.
Shrinkage rate (%) = [(100−C) / 100] × 100
(4) Heat shrinkage rate in the main shrinkage direction after immersion at 60 ° C. in warm water × 5 minutes Marked lines with a width of 30 mm and a length of 600 mm so that the main shrinkage direction is the longitudinal direction and 500 mm intervals Was used as a sample. The sample was immersed in warm water at 60 ° C. for 5 minutes, and then quickly cooled with cold water, and then the dimension between marked lines D (mm) was measured. From the dimensions, the thermal contraction rate was calculated by the following equation.
Shrinkage rate (%) = [(500−D) / 500] × 100

[Evaluation of insulated containers]
(1) Evaluation of heat resistance A heat insulating container is put in a constant temperature and humidity chamber adjusted to 55 ° C x 50% RH, and after storage for 8 hours, the heat insulating container is taken out from the constant temperature and humidity chamber and visually observed for deformation of the strip gripping portion. did.
The evaluation criteria for heat resistance were as follows: ◯ = no deformation, Δ = round deformation, x = deformation with protrusion corners formed.
(2) Functionality evaluation The hot water of 85 degreeC was poured in the heat insulation container, and the state of the strip holding part after 3 minutes was observed visually.
The evaluation criteria for functionality were as follows: ◯ = completely deformed, Δ = incomplete deformation, x = slight or no deformation.

  In the following examples and comparative examples, polyesters (A) to (C) having the compositions shown in Table 1 were used. The composition of the polyester resin shown in Table 1 was obtained by qualitative and quantitative analysis by NMR (nuclear magnetic resonance apparatus).

Example 1
After melting the polyester (A) shown in Table 1 with an extruder, the polyester (A) was extruded with a T-die, and the melt was cooled with a cast roll to obtain an unstretched film having a thickness of 260 μm. This unstretched film was stretched 1.05 times in the flow direction (MD) and then led to a tenter, and stretched 5.8 times in the perpendicular direction (TD) at 88 ° C. Subsequently, after heat treatment at 90 ° C. for 5 seconds, reheat treatment was performed at 85 ° C. for 5 seconds while relaxing in the 4.6% TD direction, and a 45 μm thick single layer film was produced. At this time, the main contraction direction is the TD direction.
A slit group is formed in the height direction of the outer sleeve that forms the heat insulating protruding portion of the produced film, and a mountain fold ruled line and a valley fold ruled line are formed in the strip part so that the strip formed by the slit is compressed in the vertical direction and protrudes. A heat insulating container is manufactured by attaching to the outer sleeve formed so that the film is in contact with the outer surface of the cup between the sleeve and the cup and covers the strips formed by the slits of the sleeve. did.
Table 2 shows the evaluation results of the obtained film and the heat insulating container.

Example 2
The heat treatment conditions after stretching in the TD direction of Example 1 were changed, and after heat treatment at 88 ° C. for 5 seconds, reheat treatment was performed for 5 seconds while relaxing in the 4.6% TD direction at 85 ° C. In the same manner as in Example 1, a 45 μm-thick single layer film and a heat insulating container were produced. Table 2 shows the evaluation results of the obtained film and the heat insulating container.

Example 3
In the same manner as in Example 1, an unstretched film having a thickness of 235 μm was obtained. This unstretched film was stretched 1.05 times in the flow direction (MD) and then led to a tenter, and stretched 5.2 times at 88 ° C. in the perpendicular direction (TD), followed by heat treatment at 90 ° C. for 5 seconds, A 45 μm-thick single layer film and a heat insulating container were produced in the same manner as in Example 1 except that reheating was performed for 5 seconds while relaxing in the 5.2% TD direction at 90 ° C. Table 2 shows the evaluation results of the obtained film and the heat insulating container.

Example 4
In the same manner as in Example 1, an unstretched film having a thickness of 275 μm was obtained. This unstretched film was stretched 1.05 times in the flow direction (MD) and then led to a tenter, and stretched 5.8 times in the perpendicular direction (TD) at 88 ° C. Subsequently, after heat treatment at 90 ° C. for 5 seconds, re-heat treatment was performed at 80 ° C. for 5 seconds without relaxation, and a 45 μm-thick single layer film was produced. At this time, the main contraction direction is the TD direction. Using this film, a heat-insulating container was produced in the same manner as in Example 1. Table 2 shows the evaluation results of the obtained film and the heat insulating container.

Comparative Example 1
An unstretched film having a thickness of 365 μm was obtained in the same manner as in Example 1. The unstretched film was stretched 1.05 times in the flow direction (MD) and then guided to a tenter, and stretched 5.8 times at 87 ° C. in the perpendicular direction (TD). Subsequently, after heat treatment at 84 ° C. for 5 seconds, re-heat treatment was performed at 80 ° C. for 5 seconds without relaxation, and a single layer film having a thickness of 60 μm was produced. Using this film, a heat-insulating container was produced in the same manner as in Example 1. Table 2 shows the evaluation results of the obtained film and the heat insulating container.

Comparative Example 2
Among the raw material pellets listed in Table 1, blended at a ratio of polyester (A) / polyester (B) / polyester (C) = 58/27/15 (weight ratio), and put into an hopper of an extruder to melt. After that, it was extruded with a T die, and the melt was cooled with a cast roll to obtain an unstretched film having a thickness of 245 μm. This unstretched film was stretched 1.05 times in the flow direction (MD), guided to a tenter, and stretched 5.2 times at 81 ° C. in the perpendicular direction (TD). Subsequently, after heat treatment at 95 ° C. for 5 seconds, re-heat treatment was performed at 80 ° C. for 5 seconds without relaxation, and a 45 μm-thick single layer film was produced. Using this film, a heat-insulating container was produced in the same manner as in Example 1. Table 2 shows the evaluation results of the obtained film and the heat insulating container.

Comparative Example 3
The film formed by the same method as in Comparative Example 2 was further annealed for 24 hours in a thermostatic chamber adjusted to 60 ° C. to obtain a single-layer film having a thickness of 45 μm. Using this film, a heat-insulating container was produced in the same manner as in Example 1. Table 2 shows the evaluation results of the obtained film and the heat insulating container.

Comparative Example 4
A gravure proofing machine (manufactured by Nissho Gravure Co., Ltd., model: CM type) and a solid pattern plate (plate depth 36 μm, manufactured by Nabe Process Co., Ltd.) on both surfaces of a film formed in the same manner as in Comparative Example 2 After the white ink was applied using, it was naturally dried to obtain a printing film having a total thickness of 55 μm. At this time, the ink thickness per side was 5 μm. The white ink was mixed with 80% by volume of “Fine Wrap NTV PET-HC White 2” manufactured by DIC Corporation, and 20% by volume of “Univia NT No. 20 Reducer” manufactured by DIC Corporation. I used something. Using this printed film, the heat insulation container was produced like Example 1. FIG. Table 2 shows the evaluation results of the obtained film and the heat insulating container.

From the results in Table 2, the heat-shrinkable polyester films of Examples 1 to 4 are less likely to shrink in an atmosphere of 60 ° C. and 40% RH, and also shrink when immersed in hot water at 60 ° C. and 70 ° C. It is difficult to see and the natural shrinkage resistance is extremely excellent. On the other hand, it can be seen that the maximum shrinkage stress at 75 ° C. is in a suitable range, and when it is immersed in warm water at 80 ° C., it rapidly heat shrinks. And when this heat-shrinkable film is used for a heat insulation container, it turns out that it is excellent in the balance of heat resistance and functionality.
On the other hand, in the films of Comparative Examples 1 to 4, heat shrinkage occurs in an atmosphere of 60 ° C. and 40% RH, and product deformation occurs during product transportation and storage in the season when the outside air temperature rises. It turns out that the possibility is high. In the container produced using such a film, it turns out that a strip holding part (insulation holding part) protrudes and the diameter deformation amount of an insulation container becomes large. Moreover, in the container produced using the film of the comparative example 3 with low shrinkage stress, it turns out that a heat insulation grip part is not formed and the functionality as a heat insulation container is not expressed.

Claims (4)

  The maximum shrinkage stress at 75 ° C. in the main shrinkage direction of the film is 4.4 MPa or more and 12.0 MPa or less, and the shrinkage rate in the main shrinkage direction is 2 when the film is stored in an atmosphere of 60 ° C. × 40% RH for 8 hours. A heat-shrinkable polyester film having a shrinkage ratio in the main shrinkage direction of 10% or more and less than 80% when the film is immersed in warm water at 80 ° C. for 10 seconds.   In all polyester resin components, the main component of the dicarboxylic acid component is terephthalic acid, the main component of the diol component is ethylene glycol, and (a) isophthalic acid, (b) 1,4-cyclohexanedimethanol, and (c) neo The heat-shrinkable polyester film according to claim 1, which is a copolyester containing one or more selected from the group consisting of pentyl glycol.   The shrinkage rate in the main shrinkage direction when immersed in warm water at 60 ° C. for 5 minutes is 2.7% or less, and the shrinkage rate in the main shrinkage direction when immersed in warm water at 70 ° C. for 10 seconds is 3% or less. The heat-shrinkable polyester film according to claim 1 or 2.   The heat insulation container using the heat-shrinkable polyester-type film in any one of Claims 1-3.