JP2002046766A - Container lid composite polyester film and cup container using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a container lid composite polyester film that is excellent in transparency, surface strength, and heat resistance and a cup container that is excellent in unsealability and distinctness between pictures and characters. SOLUTION: The composite polyester film that is formed from two or more kinds of layers including a layer A and a layer B has a polyester film layer (layer B) having tiny holes, and a thermoplastic resin layer (layer A) adjacent to the layer B and substantially having no holes in its outermost layer. The composite polyester film for the container lid has an opacity of greater then or equal to 0.3, an apparent density of less than or equal to 1.3 g/cm3, and a thickness of greater than or equal to 25 μm. The opening of the cup container made of a plastic is closed by a film in which a printing layer is formed on at least one side of the composite polyester film and a heat seal layer is formed on the surface of the outer most layer on the layer A side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to miso, cup noodles,
The present invention relates to a film for a lid material suitable for over-the-counter cup containers such as desserts such as confectionery, yogurt, pudding, jelly, and ice cream, and potion cups such as coffee fresh, and a cup container using the same.

[0002]

2. Description of the Related Art In general, desserts such as miso, cup noodles, confectionery, yogurt, pudding, jelly, ice cream, potion cups such as coffee fresh, etc., which are sold in stores at supermarkets and convenience stores. As a food case, a cup container mainly made of a plastic base material has been widely used. This cup container is composed of a container portion formed of polyolefin such as polystyrene and polypropylene, polyvinyl chloride, polyethylene terephthalate, and the like, and a lid material that is heat-sealed to the opening side of the container.

Conventionally, as a lid material of a cup container, a composite material of a paper base material and an aluminum foil or a plastic film on which aluminum is deposited has been generally used.

However, in recent years, from the viewpoint of environmental protection and resource saving, the promotion of separated collection and recycling has been called for, and the Packaging Container Recycling Law has been enforced. In view of this, the review of container materials has become active.

[0005] An important characteristic required from the viewpoint of functionality of the lid material of the cup container is a light-blocking property for protecting the contents from light deterioration, that is, opacity. Here are many of the reasons why a plastic film in which aluminum foil or aluminum is deposited on an opaque paper base material has been used in many cases in the form of a laminate in many lid materials.

[0006] Further, another reason why these are frequently used is a dead hold property at the time of opening the lid material. The dead hold property refers to a property indicating whether or not the form of the lid material can be maintained as it is when the lid material of the cup container is opened.
That is, the presence or absence of the dead hold property relates to the ease of taking out the contents when opened, the ease of pouring hot water into the cup, and the like.

[0007] For the above reasons, composite materials made of paper and aluminum have been frequently used. However, from the viewpoint of ease of collection for recycling of packaging containers as described above, they are composite materials. However, there is a major problem that paper, metal, and plastic cannot be separately discarded.

[0008] Further, the material in which the above-mentioned metal is composited,
In addition to environmental issues, it is difficult to perform a foreign substance check by a metal detector that is generally performed for product safety (confirm that the contents do not contain foreign substances such as nails and needles).

In addition, desserts such as miso, yogurt, ice cream, and ice desserts have a large content of water.
For applications that are refrigerated or stored frozen, the use of paper as a material cannot solve the essential problem that curling or deformation is likely to occur due to moisture absorption. Therefore, a method of laminating a plastic film on the surface of paper has been applied.However, even if this method is used, it does not completely solve the problem such as curling, and the process of laminating the film on both sides of the paper is not performed. It is a factor of cost increase due to increase.

Further, many attempts have been made to change the cover material to a film material only. However, when a normal transparent plastic film is used as the lid material, it is difficult to see the front and back printing of the contents and instruction manual, and since there is no concealment, the contents are deteriorated due to ultraviolet rays etc. Prone to the above important issues.

On the other hand, in the case of a white film containing a concealing material such as titanium oxide particles in the film, the specific gravity of the titanium oxide particles is high. It has not been used practically because it is up.

Therefore, application of a white polyolefin-based film, which is generally called synthetic paper, having an appearance close to paper quality and containing voids therein, to the lid material has been studied.
However, in this case, although the above-described problem caused by the moisture of paper is solved, since the base material contains cavities,
When the lid material is to be peeled off from the container, it is broken near the surface layer of the lid material to cause breakage, so that it cannot be put to practical use by itself as it is.

Therefore, a transparent plastic film substantially free of voids, for example, a biaxially stretched polyethylene terephthalate (hereinafter abbreviated as PET) film is laminated on the surface of the void-containing film to strengthen the film surface layer of the cover material. Are also being considered. But,
In this case, costs for a film to be bonded and a laminating process are required, and the cost is greatly increased, which is not preferable.

When the above-mentioned white polyolefin-based film, for example, a polypropylene-based void-containing film is used as a cover material, the heat resistance of polypropylene is insufficient, so that a sealant material for printing or heat sealing is laminated on the film surface. The thermal dimensional change during the process is large. Therefore, not only does the cost increase due to a decrease in product yield and productivity deteriorate, but also there is a problem that the laminated product is easily curled.

[0015]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, the present invention does not require the use of materials such as paper and metal which need to be separated, and provides opacity (light blocking property), surface strength, and the like.
A composite polyester film suitable for use as a container lid material with excellent dead-hold properties and heat resistance during processing, and with excellent printing characteristics (pattern / character discrimination) and no breakage when the lid material is opened It is intended to provide a cup container.

[0016]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above situation, and has been made in view of the above circumstances. A composite polyester film for a container lid material and a cup using the same, which can solve the above problems. The container is as follows.

That is, a first invention of the present invention is a composite polyester film comprising at least two layers including an A layer and a B layer, wherein the composite polyester film is a polyester film containing fine voids. Layer (B
Layer) and a thermoplastic resin layer (layer A) that is substantially free of voids in the outermost layer adjacent to layer B, has an opacity of 0.3 or more, an apparent density of 1.3 g / cm ³ or less, A composite polyester film for a container lid material having a thickness of 25 μm or more.

A second invention is characterized in that a printing layer is provided on at least one side of the composite polyester film, and a heat seal layer made of a heat-adhesive resin layer is provided on the outermost layer A side surface. It is a composite polyester film for container lid materials according to the invention.

According to a third aspect of the present invention, there is provided a cup container wherein the opening of the cup container made of a plastic material is closed by the composite polyester film for a container lid material according to the second invention.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The composite polyester film used for the container cover film of the present invention is obtained by orienting at least uniaxially a polymer mixture comprising a polyester and a thermoplastic resin incompatible with the polyester. A layer (A) made of a thermoplastic resin substantially free of an incompatible resin is simultaneously provided on at least one surface of the polyester layer (B) containing fine voids produced by It is obtained by laminating a thermoplastic resin layer (A) containing no void. In particular, a void-containing polyester film laminate having a void content of not more than 8% by volume from the surface to 3 μm and an average void content of the entire film of not less than 10% by volume and not more than 50% by volume is preferably used.

Further, the layer (A) made of a thermoplastic resin containing substantially no voids is preferably a polyester resin, particularly preferably a PET resin. The thickness of layer A is 3 μm
The thickness is preferably at least 5 μm. A
If the thickness of the layer is less than 3 μm, it is not possible to sufficiently prevent the breakage that occurs when the lid material is peeled off. On the other hand, the upper limit of the thickness of the layer A is not particularly limited, but the point of the paper quality effect by the void-containing polyester film layer (layer B), the suitability for the secondary processing such as printing, the cushioning effect which affects the feeling, and the density of the whole film. Therefore, it is not practical to make the thickness 10 μm or more.

Further, if the content of voids contained within 3 μm from the film surface exceeds 8% by volume, it is not preferable because the surface of the film is easily broken when the lid material is peeled off.

The polyester mixture constituting the layer B of the present invention and a polymer mixture obtained by mixing an incompatible thermoplastic resin with the polyester resin include, for example, 1) mixing chips of each resin and melt-kneading in an extruder. 2) A method in which both resins are kneaded in advance by a kneader and then melt-extruded and solidified by an extruder. 3) A thermoplastic resin incompatible with the polyester resin in the polyester resin polymerization step. It can also be obtained by a method in which a resin is added, and chips obtained by stirring and dispersing are melt-extruded and solidified.

The polymer mixture may be added with a colorant, a light stabilizer, a fluorescent agent, an antistatic agent and the like according to the application. The obtained polymer mixture is further stretched between rolls having different speeds (roll stretching), stretched by gripping and spreading with a clip (tenter stretching), or stretched by air pressure (inflation stretching). For example, orientation treatment is performed in at least one axial direction.
By the orientation treatment, peeling occurs at the interface between the polyester and the void developing agent that is incompatible with the polyester, and voids are developed.

Therefore, the content of the thermoplastic resin incompatible with the polyester resin to be mixed with the polyester resin varies depending on the amount of the target cavity, but is 3 to 40% by weight based on the whole polymer mixture. It is preferable that If the content is less than 3% by weight, there is a limit in increasing the amount of cavities formed, and it is difficult to obtain the intended flexibility, lightness and drawing properties. On the other hand, if it exceeds 40% by weight, the heat resistance and strength of the polyester film tend to be significantly impaired.

The conditions for orienting the polymer mixture are as follows:
Closely related to cavity formation. That is, as a condition for achieving the object of the present invention, a sequential biaxial stretching method most commonly performed as a method for producing a biaxially stretched film is exemplified. In the case of the sequential biaxial stretching method in which the unstretched sheet of the polymer mixture is roll-stretched in the longitudinal direction and then tenter-stretched in the width direction, the following conditions are employed. In roll stretching, the temperature is preferably Tg to Tg + 30 ° C. of the polyester and the stretching ratio is preferably 1.2 to 5 times in order to generate a large number of cavities. In the tenter stretching, it is preferable that the stretching temperature is 80 to 140 ° C. and the stretching ratio is 1.2 to 5 times in order to stably form the film without breaking. When the void-containing polyester film subjected to the stretch orientation treatment is subjected to heat setting at 130 ° C. or higher, preferably 180 ° C. or higher, dimensional stability at high temperatures can be improved. Further, the relaxation treatment may be used in both the vertical and horizontal directions.

In the present invention, a so-called composite film in which a surface layer (A layer) and a center layer (B layer) are laminated must be used. The method is not particularly limited. However, considering productivity, it is most preferable that the raw materials for the surface layer and the center layer are extruded from separate extruders, led to one die to obtain an unstretched sheet, and then oriented at least uniaxially, that is, lamination by a so-called coextrusion method. preferable.

The void-containing polyester film thus obtained has a void content of not more than 8% by volume in a layer from the surface to a depth of 3 μm and an average void content of not less than 10% by volume of the whole film. Preferably, there is.
The void content of the surface layer from the surface to the depth of 3 μm is 8% by volume
If the amount is larger, it is difficult to obtain a material having excellent surface strength, and the interlayer is easily broken as described above. 3 from the surface
It is particularly preferred that the void content of the surface layer up to μm be 4% by volume or less. Further, even if the void content is 8% by volume or less, even if the thickness of the surface layer portion is less than 3 μm, a material having excellent surface strength cannot be obtained. Accordingly, it is most preferable that the surface layer of the layer A having a lower void content than the central portion has a thickness of 3 μm or more and the void content of the surface A layer is 4% by volume or less.

Further, it is preferable that the entire composite polyester film has an average void content of 10% by volume or more. When the average void content is less than 10% by volume,
The flexibility inherent in the void-containing polyester film is insufficient, and the texture and cushioning properties are also insufficient.

The composite polyester film of the present invention has an opacity of 0.3 or more and an apparent density of 1.3 g / c.
m ³ or less, and a thickness of 25 μm or more.

When the opacity of the composite polyester film is less than 0.3, when used as a lid for a cup container, it is difficult to identify the printed content of the front and back sides, and the design effect as the lid is poor. It is not preferable because the content of the cup container for protection against ultraviolet deterioration, that is, the light blocking property is poor. The opacity of the film is preferably 0.6 or more.

If the apparent density of the composite polyester film exceeds 1.3 g / cm ³ , the cushioning properties and the texture of the paper become poor, and the processing characteristics such as punching properties are undesirably deteriorated. The apparent density is 0.8 to 1.2 g /
cm ³ is preferred.

When the film thickness of the composite polyester film is less than 25 μm, the rigidity and strength of the lid material are insufficient, so that it is not practical. The film thickness is preferably at least 50 μm, particularly preferably at least 75 μm. The upper limit of the film thickness is not particularly limited, but is practically up to about 250 μm from the viewpoint of handleability and cost.

In the film lid material of the present invention, it is necessary to laminate a thermoplastic resin A layer containing substantially no voids on at least one surface of the polyester B layer containing the fine voids. Any of a two-layer structure of / B and a three-layer structure of A / B / A may be used. In the case of a three-layer structure, the outer layer A may be of the same type of resin composition or of a different type, if necessary, as long as the object of the present invention is satisfied. Further, the A layer is not necessarily required to be a single layer, and in some cases, a layer configuration of three or more layers may be formed by laminating another A layer resin having substantially no void on the A layer.
To the surface resin to be composited, if necessary, various additives, for example, a surfactant, an inorganic or inorganic material, in order to impart slipperiness, adhesiveness, printability, hiding properties, antistatic properties and other functions.
Of course, various organic particles, wax, a thermoplastic resin as the third component and the like may be added. Further, if necessary, the printability of the surface of the layer A, the improvement of the adhesiveness with the heat-adhesive resin, the provision of antistatic properties, and the addition of various additional functionalities such as antifouling properties and glazing. For this purpose, various kinds of resins and treatment agents can be coated.

The composite polyester film obtained as described above is particularly suitable as a lid material for a cup container.
When the composite polyester film is used as a lid material for a cup container, it is necessary to close the dome opening and the lid material by bonding them to enclose the contents of the cup container.

As a method of bonding the two, a heat bonding method usually called heat sealing is used in an automatic container packaging machine or the like. Specifically, a heat-meltable resin is laminated on the lid member side, and the resin is bonded by heating the contact surface with the molding container. Examples of such heat-adhesive resins include olefin-based resins such as polyethylene and polypropylene alone or copolymers and mixtures, polyvinyl acetate, ethylene-vinyl acetate copolymer, vinyl chloride / vinyl acetate copolymer, Various vinyl-based polymers such as vinyl / vinylidene chloride copolymer, acrylate / vinyl chloride copolymer, and others, as well as urethane-based copolymers and polyester-based copolymers are appropriately selected according to the use conditions. .

The method of laminating such a heat-adhesive resin on the composite polyester film for a lid material is as follows: 1) An extrusion coating method in which the heat-adhesive resin is extruded onto the composite polyester film for a lid material by a melt extruder. Alternatively, a known method such as an extrusion lamination method or 2) a method of applying a thermoadhesive resin melted at a high temperature by a die coating method, a gravure roll coating method, or the like can be arbitrarily applied.

[0038] The thickness of the heat-adhesive resin layer depends on the type, shape, size, weight and the like of the contents to be packaged in the cup container, and the required properties such as the required adhesive force are different. The thickness of the heat-adhesive resin layer is usually about 5 to 80 μm.

For example, when the contents of the container are relatively heavy, such as miso, it is often required to have a high sealing strength between the lid member and the container. Therefore, unstretched polyolefin such as polyethylene or polypropylene is required. The film is laminated with a thickness of about 20 to 60 μm.

When the contents are relatively light, such as snacks, a hot melt resin of an ethylene-vinyl acetate copolymer is applied by about 30 μm by a gravure coating method.

Normally, the lid material for the cup container is printed on the surface of the lid material for the purpose of describing the contents or for the purpose of a design effect.
Depending on the thickness, size, continuous or sheet-fed printing, any printing method can be used, such as offset printing, gravure printing, screen printing, or the like. Most commonly, continuous gravure printing is used. Generally, after printing is performed on the composite polyester film for the lid material, the thermoadhesive resin is laminated on the opposite surface. Therefore, the method of continuously laminating the heat-adhesive resin layer after the gravure printing is the most efficient, and is advantageous in cost.

When properties such as oxygen barrier properties are required from the viewpoint of protecting the contents, for example, a metal foil such as aluminum or a plastic film on which a metal or inorganic oxide is deposited is dry-laminated. It is preferable to stick them together. However, as described above, from the viewpoint of container recycling and foreign substance inspection with a metal detector for safety, etc., inorganic oxides such as silicon oxide, alumina, or a composite oxide thereof are more preferable than metal foils and metal deposited films. A vapor deposited composite polyester film is most preferably used.

In the case where such a vapor-deposited film is laminated and used, it is generally the most preferred embodiment that the laminated film is laminated between the composite polyester film for lid material and the heat-adhesive resin layer. is there.

[0044]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the embodiments described in the examples. Various evaluation items in Examples and Comparative Examples were performed by the following methods.

(1) Intrinsic viscosity of polyester 60% by weight of phenol and 40% by weight of tetrachloroethane
The polyester raw material (or polyester film) was dissolved in the mixed solvent of (1), and the solid content was substantially filtered with a glass filter, and then measured at 30 ° C.

(2) Apparent density The film is accurately cut into a 10 cm × 10 cm square, and its thickness is measured at 50 points to determine the average thickness t (μm). Next, the weight of the sample was measured to 0.1 mg and W
(G), and the value calculated by the following equation was defined as the apparent density. Apparent density (g / cm ³ ) = (W / t) × 100

(3) Opacity Using a Macbeth densitometer Model TR-972, the optical density of the film by transmission under a G filter was measured.

(4) Thermal dimensional change rate under tension Assuming the temperature and tension during printing and hot melt processing, a film is applied with a tension of 20 kgf / m width and heat-treated at 80 ° C. and 120 ° C. for 30 minutes. The dimensional change rate in the longitudinal direction of the film before and after was measured. The indication was obtained by the following formula, where elongation (the length after the heat treatment was longer than before the heat treatment) was + and shrinkage (the length after the heat treatment was shorter) was-. Dimensional change rate during heating (%) = (length after treatment / length before treatment) × 100

(5) Openability As a model for evaluating the thermal adhesion between the container and the film for the lid material,
The heat-adhesive resin layer surfaces of various films for lid materials prepared in Examples and Comparative Examples are superimposed on an unstretched PET sheet having a thickness of 200 μm, and heated with a heat sealer at 120 ° C. (hot plate surface temperature).
For 2 seconds to obtain a sample for evaluating the openability. Next, when the lid material film thermally bonded to the container was peeled off by hand at a high speed, the following three grades were evaluated according to the state of occurrence of breakage and tearing of the lid material. ：: The lid material is cleanly peeled without tearing or tearing △: Partial tearing occurs on the lid material surface ×: The lid material is not completely peeled and is torn

(6) Printing Effect Character printing using gravure ink was performed on one side of the film for the lid material, and picture printing was performed on the other side, and the character discrimination ability when exposed to a fluorescent lamp was visually determined. ○: Characters and patterns can be clearly distinguished from front and back △: Can be distinguished, but characters and patterns appear to partially overlap ×: Characters and patterns overlap, making it difficult to distinguish front and back printing

Example 1 As a raw material of the layer B, 80% by weight of a PET resin having an intrinsic viscosity of 0.62 dl / g was added to a melt flow index of 2.0 g / 1.
15 minutes polystyrene resin with 0 minutes, average particle size 0.3μ
m of anatase type titanium dioxide, 95% by weight of PET resin as raw material of the A layer, and 5% by weight of rutile type titanium dioxide having an average particle diameter of 0.3 μm. Melt extrusion at 290 ° C from a die,
The layer is electrostatically adhered to the cooling rotating roll and solidified, and the thickness of each layer is A / B / A = 50/730/50 (unit:
μm) and an unstretched sheet having a thickness of 830 μm. Next, the unstretched sheet was heated at 83 ° C. with a roll stretching machine.
Stretched 3.5 times in the machine direction, and
After stretching 3.4 times in the transverse direction at 30 ° C, 4% at 235 ° C
Heat treatment was carried out while relaxing, to obtain a biaxially stretched composite polyester film containing a large number of cavities inside.

The thickness of the obtained biaxially stretched composite polyester film is 75 μm, and the thickness of each layer is B / A / B = 4.5.
/66/4.5 (unit: μm). The overall average void content of the obtained composite film was 21% by volume. In addition, a portion having few cavities was present from the surface layer to a depth of about 5 μm. The opacity of the obtained void-containing composite polyester film was 0.72, and the apparent density was 1.10 g.
/ Cm ³ .

After performing corona discharge treatment on both surfaces of the surface layer of the composite polyester film, using a gravure ink (PANN color, manufactured by Toyo Ink Mfg. Co., Ltd.), a pattern, a character, and a bar code were coated on one side at 40 m / min. Gravure printing at the speed of Next, a heat-melted polyethylene-based thermo-adhesive resin is laminated on the surface opposite to the printing surface by extrusion to a thickness of 40 μm (35 g / m ² ). A sample was obtained. Table 1 shows the obtained results.

Example 2 The total thickness of the unstretched sheet was 1100 μm, the total thickness of the film after biaxial stretching and heat treatment in the longitudinal and transverse directions was 100 μm, and the thickness of each layer was A / B / A = 5.
A heat-adhesive lid material film sample was obtained in the same manner as in Example 1, except that the conditions were adjusted so as to be / 90/5 (unit: μm). The opacity of the void-containing composite polyester film before printing and application of the heat-adhesive resin was 0.97, and the apparent density was 1.11 g / cm ³ . Table 1 shows the obtained results.

Comparative Example 1 Only the raw material of layer B was extruded from a single extruder into a T-die to obtain a single-layer sheet, which was adjusted to a single-layer void-containing polyester film having a thickness of 75 μm after stretching. Except that, a heat adhesive lid material film sample was obtained in the same manner as in Example 1. The average void content of the void-containing polyester film before printing and application of the heat-adhesive resin was 23% by volume, opacity was 0.73, and apparent density was 1.08 g /.
cm ³ . Table 1 shows the obtained results.

Comparative Example 2 As a lid material film, a void-containing polyolefin film having a thickness of 80 μm (Oji Yuka Synthetic Paper Co., Ltd.)
A heat-adhesive lid material film sample was obtained in the same manner as in Example 1 except that YUPO manufactured by KK was used. The opacity of the void-containing film before printing and application of the heat-adhesive resin was 0.71, and the apparent density was 0.70 g / cm ³ . Table 1 shows the obtained results.

Comparative Example 3 The same procedure as in Example 1 was carried out except that a transparent biaxially stretched PET film (E5100, manufactured by Toyobo Co., Ltd.) having a thickness of 75 μm and containing no voids was used as the film for the cover material. Thus, a heat-adhesive lid material film sample was obtained. The opacity of the film before printing and applying the thermal adhesive resin is 0.0
4. The apparent density was 1.40 g / cm ³ . Table 1 shows the obtained results.

[0058]

[Table 1]

[0059]

The composite polyester film of the present invention has
The center layer contains a void-containing layer.The outermost layer contains a layer that contains virtually no voids, and is a multilayer composite film with a specified opacity, apparent density, and thickness. Compared to polyester films and polyester films that do not contain voids, they have excellent opacity and thermal dimensional stability under tension during processing, so they have good printing effects (pattern / character discrimination). . Further, since it has excellent surface strength and does not break or break even when opened, there is no need to attach another film, and it is suitable as a container lid material in terms of characteristics and cost. Further, since there is no need to use paper or metal, there is an advantage that collection for recycling of packaging containers is easy, and a foreign substance inspection by a metal detector can be performed.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) BA10A BA10C BA13 DA03 DE01B DE01H DJ01B EJ38A EJ38B GB18 GB23 HB31 JA13 JA20 JL12C JN02 YY00

Claims (3)

[Claims] 1. A composite polyester film comprising two or more layers including at least an A layer and a B layer, wherein the composite polyester film has a polyester film layer (B layer) and a B layer containing fine voids. An adjacent thermoplastic resin layer (A
A composite polyester film for a container lid material, characterized in that the composite polyester film has an opacity of 0.3 or more, an apparent density of 1.3 g / cm ³ or less, and a thickness of 25 μm or more. 2. The container lid according to claim 1, wherein a printed layer is provided on at least one surface of the composite polyester film, and a heat sealing layer made of a heat-adhesive resin layer is provided on the outermost layer A side surface. Composite polyester film for materials. 3. A cup container, wherein an opening of a cup container made of a plastic material is closed by the composite polyester film for a container lid material according to claim 2.