JP2006305754A - Laminating film of paper container, paper container equipped with it and manufacturing method of laminating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the laminating film of a paper container excellent in processability, moldability, transparency, stability with the elapse of time, solvent resistance, dimensional stability, electronic oven heat resistance and glossiness. <P>SOLUTION: The laminating film of the paper container is achieved by a laminating polyester film which is composed of a polyester layer B having a substantially non-oriented structure the polyester layers A, which have an oriented structure provided on both sides of the polyester layer B in a contact state, and is characterized in that the ratio (a/b) of the sum total thickness (a) of each of the polyester layers A and the thickness (b) of the polyester layer B is 0.01-0.60 and the total thickness (a+b) is 20-100 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a paper container laminating film that is used by laminating it in a paper container into which food or the like is placed. More specifically, the present invention relates to a paper container laminating film used by being pasted on a paper container used in a mode in which food is frozen or refrigerated and eaten and eaten in a microwave oven, and a paper container using the same.

  In recent years, food packaging field (for example, trays, instant food containers, etc.), medicine packaging field (for example, PTP drug packaging such as capsules, tablets, etc.), laminate molding field (for example, furniture, interior / exterior decorations, electrical appliances, automobile parts) Etc.), IC, semiconductor field, magnetic recording card material field (for example, cash card, ID card, credit card, etc.), agriculture Plastic films (including sheets; the same shall apply hereinafter) are used in a wide range of fields such as green houses.

  The material used for these applications is not only a flat form, but also many products that have a non-planar surface form such as a curved surface or an uneven surface, so a film made of a rigid polyvinyl chloride resin with excellent workability and moldability Is mainly used. As a polyester material, a non-oriented polyethylene terephthalate film called A-PET (trade name) is often used, and is excellent in moldability. However, when A-PET is used for a long time, the embrittlement phenomenon occurs, and there are problems such as opacity and decrease in elongation. In order to eliminate this drawback, Japanese Patent Application Laid-Open No. 8-279150 proposes a method using a non-oriented heat-crystallized polyethylene terephthalate film.

  In addition, polyolefin, polystyrene, polycarbonate, polyester, etc. have been preferably used as containers for contents such as sugar beet and lunch boxes in terms of moldability, but toxic gas when burned by incineration etc. There is a problem of generation, and new materials have been demanded by recent environmental needs.

  In addition, a paper container excellent in microwave oven heat resistance that can directly heat edible side dishes in a microwave oven has side plates that stand up from each side of the rectangular bottom plate, and adhesive strips at the adjacent side edges It has been proposed in a shape to be bonded and fixed (Japanese Patent Laid-Open No. 7-277318). On the other hand, a film characterized by vacuum suction molding along a paper container under heating or preheating against a complicated partition shape on the inner surface side of the paper container has also been proposed (Japanese Patent Application Laid-Open No. 2004-268441). Publication).

JP-A-8-279150 Japanese Patent Laid-Open No. 7-277318 JP 2004-268441 A

  The above materials are excellent in processability and moldability and are often used in the above-mentioned applications. For example, polyvinyl chloride resin is inferior in heat resistance and chemical resistance, and therefore deforms under heating in a microwave oven. There is. In addition, when polyvinyl chloride resin is incinerated after use, it is easy to produce toxic substances due to chlorine, causing the problem of environmental pollution. Moreover, although the microwave oven heat resistance is improved as compared with the non-polyester film by a method using a non-oriented heat-crystallized polyethylene terephthalate film such as A-PET, it is inferior in terms of chemical resistance and gloss of the product surface. In addition, 1,4-cyclohexanedimethanol derivative copolymerized polyester has good moldability and change with time, but when printed using ink, the polymer on the film surface dissolves in the ink solvent. Dimensional stability is inadequate in terms of poor durability to organic solvents, such as being easy to set off, and curling and deformation of processed products.

  The present invention aims to remedy such problems. An object of the present invention is to provide a film for laminating paper containers excellent in processability, moldability, transparency, stability over time, solvent resistance, dimensional stability, microwave oven heat resistance, and glossiness. .

  That is, the present invention comprises a polyester layer B having a substantially non-oriented structure and a polyester layer A having an oriented structure provided on both sides in contact with this layer. The total thickness (a) of the polyester layer A and the polyester layer B The thickness (b) ratio (a / b) is 0.01 to 0.60, and the total thickness (a + b) is 20 to 100 μm.

  According to the present invention, it is possible to provide a paper container laminating film excellent in processability, moldability, transparency, stability over time, solvent resistance, dimensional stability, microwave oven heat resistance, and glossiness. .

Hereinafter, the present invention will be described in detail.
[Polyester layer A]
The polyester layer A is a layer having a polyester orientation structure, and this orientation structure is formed by stretching. The stretching may be either uniaxial stretching or biaxial stretching. As the polyester constituting the polyester A layer, a polyester in which a main dicarboxylic acid unit is a terephthalic acid unit or a terephthalic acid unit and an isophthalic acid unit and a main glycol unit is an ethylene glycol unit is preferable.

  This polyester may be, for example, 2,6-naphthalenedicarboxylic acid, orthophthalic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, 2,2- It may contain other carboxylic acid units such as biphenyldicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, and for example, propylene glycol, 1,4-butanediol, 1,5-pentanediol, It may contain other glycol units such as 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol, polytetramethylene glycol.

  The melting point of the polyester of the polyester layer A is, for example, 200 to 270 ° C., preferably at least 15 ° C. higher than the melting point of the polyester constituting the polyester layer B, more preferably at least 20 ° C., particularly preferably at least 30 ° C.

  In view of the dimensional stability, deformation resistance, and curl resistance of the film and processed product, the glass transition temperature of the polyester of the polyester layer A is preferably 60 ° C. or higher, more preferably 70 ° C. or higher. The glass transition temperature refers to a structural change (specific heat change) temperature when a sample obtained by once melting polyester and then rapidly cooling and solidifying is heated at a rate of 20 ° C./min with a differential calorimeter.

  The melting point of the polyester of the polyester layer A is preferably at least 15 ° C., more preferably at least 20 ° C., particularly preferably at least 30 ° C. higher than the melting point of the polyester of the polyester layer B. When the difference in melting point between the polyester layer A and the polyester layer B is less than 15 ° C., the polyester layer B is not sufficiently melted during the heat treatment, so that the change to a substantially non-oriented structure becomes insufficient. In this case, the heat treatment temperature is too close to the melting point of the polyester layer A, and the melting of the polyester layer A begins to occur partially. Therefore, when the film is manufactured, the film is cut and the roll-up material is melted. Troubles such as wearing are more likely to occur.

  The polyester layer A preferably contains inert particles from the viewpoint of obtaining easy slipping. The average particle diameter of the inert particles is preferably 0.05 to 5 μm, more preferably 0.1 to 2 μm. If the average particle size is less than 0.05 μm, sufficient slipperiness is not imparted to the film, which is not preferable, and if it exceeds 5 μm, the transparency of the film is lost.

  The shape of the inert particles is preferably spherical particles. By selecting spherical inert particles, light scattering can be reduced and high light transmittance can be obtained. As the inert particles, those containing one or more elements of Al, Si, Ca, and Mg are preferable.

[Polyester layer B]
The polyester layer B is a substantially non-oriented polyester layer. This non-oriented structure is formed by heat-treating the oriented structure once formed by stretching the film at a temperature equal to or higher than the melting point of the crystal. The polyester constituting the polyester layer B is, for example, 180 to 250 ° C., preferably 190 to 250 ° C., and preferably has a melting point that is at least 15 ° C. lower than the melting point of the polyester constituting the polyester layer A. The melting point is a melting endothermic peak temperature when a polyester, once melted, rapidly cooled and solidified, is heated at a rate of 20 ° C./min with a differential calorimeter. Therefore, when the film of the present invention is analyzed, the polyester peak of layer A and layer B is detected, and two or more peaks are detected.

  In view of the dimensional stability, deformation resistance, and curl resistance of the film and processed product, the glass transition temperature of the polyester of the polyester layer B is preferably 50 ° C. or higher, more preferably 70 ° C. or higher. In particular, it is preferable to have a glass transition temperature of 80 ° C. or higher in applications where products are exposed to high temperatures such as storage in vehicles in summer. The glass transition temperature refers to a structural change (specific heat change) temperature when a sample obtained by once melting polyester and then rapidly cooling and solidifying is heated at a rate of 20 ° C./min with a differential calorimeter.

  As the polyester constituting the layer B, a copolyester in which the main dicarboxylic acid units are terephthalic acid and / or 2,6-naphthalenedicarboxylic acid and / or isophthalic acid units is preferable.

  Specific examples of this copolyester include 1) a copolyester composed of a dicarboxylic acid unit mainly composed of terephthalic acid units and naphthalenedicarboxylic acid units and a glycol unit mainly composed of ethylene glycol units, and 2) a terephthalic acid unit and an isophthalic acid unit. A copolyester composed of a dicarboxylic acid unit mainly composed of an ethylene glycol unit and a glycol unit composed mainly of an ethylene glycol unit, 3) a dicarboxylic acid unit mainly composed of a terephthalic acid unit, a naphthalene dicarboxylic acid unit and an isophthalic acid unit, and an ethylene glycol unit And a copolyester composed of glycol units.

  Among them, preferred as the copolyester is a copolyester comprising 90 to 60 mol% of terephthalic acid, 5 to 20 mol% of naphthalenedicarboxylic acid, 5 to 20 mol% of isophthalic acid as a dicarboxylic acid component, and ethylene glycol as a diol component. It is.

  The glass transition temperature of the polyester layer B is preferably 50 ° C. or higher, more preferably 70 ° C. or higher. In particular, it is preferable to have a glass transition temperature of 80 ° C. or higher in applications where products are exposed to high temperatures such as storage in vehicles in summer.

[Layer structure]
The layer structure of the film of the present invention usually comprises a polyester layer A and a polyester layer B. For example, the polyester layer A is a surface layer, and the polyester layer B is an inner layer. A / B / A (where “/” indicates a layer structure) type three-layer structure, A / B / A / B / A There are multi-layer configurations such as a 5-layer configuration of the type, and a 7-layer, 9-layer, and 2n + 1 (n is a natural number) configuration in this order. Further, if necessary, when the polyester layer A is two or more layers, one or more layers can be composed of different polymers. The same applies when the polyester layer B has two or more layers. For example, when the polyester layer A is composed of two types of polymers (A1, A2) and the polyester layer B is composed of two types of polymers (B1, B2), a three-layer configuration of A1 / B1 / A2 type, A1 / B1 / A2 / A B2 / A1 type five-layer structure can be exemplified. Of these layer configurations, 3 layers and 5 layers are preferable, and 3 layers are particularly preferable.

  The film of the present invention comprises a substantially non-oriented polyester layer B and an oriented polyester layer A provided on both sides in contact with this layer. In other words, it has a laminated structure of a polyester layer A having a uniaxial stretched orientation structure and a polyester layer B in which the uniaxial stretched oriented structure is made into a non-oriented structure by heat treatment, and the surface layer is the polyester layer A. Is a multilayer film of at least 3 layers. The heat treatment for making the polyester layer B non-oriented is performed at a temperature lower than the melting point of the polyester of the polyester layer A and higher than the melting point of the polyester of the polyester layer B, with the polyester layer A laminated on both sides of the polyester layer B. Do. Thereby, since the polyester in the polyester layer B is temporarily melted, the polymer orientation structure of the layer B becomes a substantially non-oriented structure from a uniaxial or more stretched orientation structure.

  This heat treatment is preferably performed by setting the temperature during the heat setting treatment after the stretching treatment in the coextrusion film forming method to a temperature lower than the melting point of the polyester of the polyester layer A and higher than the melting point of the polyester of the polyester layer B. It can be done effectively.

  In the multilayer polyester film of the present invention, it is necessary that the polyester layer A having a uniaxial stretched orientation structure constitutes the outermost layer. When the polyester layer B having a substantially non-oriented structure constitutes the outermost layer, when printing characters, images, etc. on the film surface with ink, an organic solvent such that the film is partly dissolved with a solvent etc. In particular, the surface glossiness after commercialization is lowered, and the film is likely to stick to various rolls in the process during film production.

  In the film of the present invention, the ratio (a / b) of the total thickness (a) of the polyester layer A having a uniaxial stretched orientation structure and the total thickness (b) of the polyester layer B having a substantially non-oriented structure. Is 0.01 to 0.60, preferably 0.02 to 0.43, and more preferably 0.05 to 0.17. For example, when the layer structure is composed of three layers of A1 (thickness: a1) / B (thickness: b) / A2 (thickness: a2), the total thickness ratio of layer A and layer B (a / b) That is, (a1 + a2) / (b) means 0.01 to 0.60, and the layer structure is A1 (thickness: a1) / B1 (thickness: b1) / A2 (thickness: a2) / B2. In the case of five layers (thickness: b2) / A3 (thickness: a3), the total thickness ratio (a / b) of layer A and layer B, that is, (a1 + a2 + a3) / (b1 + b2) is 0.01 to 0.60. It means that. If the total thickness ratio (A / B) is less than 0.01, the outermost layer thickness of the polyester layer A is small, so that it is difficult to control the thickness during film production, and the polyester layer B is partially exposed to the surface layer. This causes problems, and the dimensional stability of the film is insufficient, and at the same time, the heat resistance of the microwave oven is inferior. On the other hand, when the total thickness ratio exceeds 0.60, the polyester film B having a substantially amorphous structure is present in a small proportion, and therefore, when the polyester film is vacuum-suctioned along a paper container under heating or preheating. The formability becomes insufficient with respect to the stress.

  The total thickness of the film is 20 to 100 μm, preferably 25 to 80 μm, and more preferably 30 to 60 μm. When the total thickness exceeds 100 μm, the formability becomes insufficient with respect to the stress when the film is subjected to vacuum suction molding along a paper container under heating or preheating. When the total thickness is less than 20 μm, problems of film breakage and thickness unevenness occur during film formation.

[Polyolefin]
The film of the present invention may contain 0.1 to 30% by weight of a polyolefin resin. The polyolefin resin may be contained in either one of the polyester layer A and the polyester layer B, or may be contained in both. Examples of the polyolefin resin include polyethylene, polypropylene, and poly-4-methylpentene.

  The film of the present invention may further contain various additives as long as the object of the present invention is not impaired. Examples of the additive include elastomer resins such as polybutylene terephthalate-polytetramethylene glycol block copolymer, pigments, dyes, heat stabilizers, flame retardants, foaming agents, and ultraviolet absorbers. For example, in a card or packaging field that requires concealability and matte surface, particles having excellent concealability, such as titanium oxide and barium sulfate may be included.

[Production method]
The polyester constituting the polyester layer A and the polyester layer B can be produced by a known method. Specific examples include 1) a method of reacting one or more dicarboxylic acid ester-forming derivatives with one or more glycols in the reaction step of polyester production, and 2) two or more polyesters. Examples thereof include a method of melt-mixing and performing a transesterification reaction (redistribution reaction) using a single-screw or twin-screw extruder. In these steps, if necessary, particles, polyolefin, and other various additives may be contained in the polyester.

  The film of the present invention is preferably produced by a coextrusion film forming method. A specific example of the case of a three-layer film (A / B / A) will be described. First, a polyester chip prepared for the polyester layer A is dried and melted. In parallel with this, the polyester chip prepared for the polyester layer B is dried and melted. Subsequently, these molten polymers are laminated in three layers inside the die. For example, the molten polymer is laminated in three layers inside the die provided with a feed block, and then cast on a cooling drum to form an unstretched multilayer film. The film is stretched in the direction of one axis or more on the vertical axis and / or the horizontal axis to obtain a multilayer stretched film having a stretch orientation structure of one axis or more. The same applies to the case of five or more layers. The stretching treatment is performed under the condition that the polyester layer A forms a desired orientation structure, for example, at a temperature (Tc) of Tg (glass transition temperature) -10 ° C. to Tg + 50 ° C. of the polyester constituting the layer A in the longitudinal direction. It is preferably stretched 5 times or more, preferably 3 to 6 times, and then stretched 2.5 times or more, preferably 3 to 6 times in the transverse direction at a temperature of Tg + 10 to Tg + 50 ° C. This stretching is preferably 8 times or more, more preferably 9 times or more in terms of area magnification.

  The multilayer stretched film obtained as described above is further subjected to heat treatment. It is important that the heat treatment temperature is higher than the melting point of the polyester layer B. By this heat treatment, the polyester layer B is melted and the stretched orientation structure formed by the uniaxial or more stretch treatment is substantially Changes to a non-oriented structure. The heat treatment temperature is preferably 5 ° C. or more higher than the melting point of the polyester layer B and 10 ° C. or more lower than the melting point of the polyester layer A. By this heat treatment, the polyester layer A has, for example, an effect of heat setting treatment. The heat treatment method is not particularly limited, and examples thereof include a method in which heat treatment is performed in the process immediately after stretching in film production, and a method in which heat treatment is performed after winding the film into a roll after completion of film production.

  The film for laminating a paper container according to the present invention can be arranged along a paper container and vacuum suction molded along the paper container under heating or preheating to obtain a paper container having a film layer as a surface layer. . In the resulting paper container, the thickness of the paper container laminating film is preferably 1 to 100 μm. When it is less than 1 μm, it is not preferable because it may cause cracks and pinholes when the contents are heated in a microwave oven by being attached to a paper container. If it exceeds 100 μm, vacuum suction molding may be difficult, which is not preferable.

Hereinafter, the present invention will be described more specifically with reference to examples.
In addition, the measuring method and evaluation method of the characteristic used in the Example and the comparative example are as follows.

(1) Evaluation of vacuum suction molding 1200W industrial use with a commercially available product from As One Co., Ltd., Bifnel funnel AF3 (φ105mm), a film for evaluation stuck to the upper mouth of this funnel with a double-sided tape without gaps, and set at 100mm above the film The film was heated with a dryer for about 60 seconds until the temperature near the film surface reached 100 ° C. Then, using a Tokyo Rika Kikai Co., Ltd. aspirator A-3S, the film was suction-molded for 10 seconds under a vacuum degree of 50 mmHg from the lower part of the funnel using a vacuum adjustment valve, and an evaluation sample was prepared. Formability was evaluated, for example, by measuring the followability and film thickness of the bottom end portion of the funnel that is most stretch-molded.
(Circle): The film is shape | molded so that it may fully follow a funnel end bottom part, and the film thickness of this end bottom part is kept at 10% or more of the original film thickness.
(Triangle | delta): Although the film is shape | molded so that it may fully follow a funnel end bottom part, the film thickness of this end bottom part is thin, and is less than 10% of the original film thickness.
X: Even if the film is not sufficiently follow-molded to the funnel end bottom part, or the film is follow-formed, breakage of the film at the end bottom part is confirmed.

(2) Microwave heat resistance evaluation The film container obtained by the vacuum suction molding evaluation of (1) above was charged with 50 cc of olive oil and observed for 3 minutes in a 1500 W microwave oven. The heat resistance of the microwave oven was evaluated according to the evaluation criteria.
○: No significant change.
Δ: Change such as deformation.
X: It is torn or melts.

(3) Evaluation of glossiness Using GM-268 manufactured by Minolta Co., Ltd., the glossiness was measured at an incident angle of 60 degrees.

(4) Film thickness 100 points were measured with an external micrometer, and the average value was obtained as the film thickness.

(5) Thickness of each layer A sample was cut into a triangle, fixed in an embedded capsule, and then embedded in an epoxy resin. The embedded sample was microtomed (ULTRACUT-S), and the cross-section parallel to the longitudinal direction was made into a thin film section having a thickness of 50 nm, and then observed and photographed with a transmission electron microscope at an acceleration voltage of 100 kV. From these, the thickness of each layer was measured, and the average thickness and relative standard deviation were determined.

(6) Melting point About 10 mg of sample was sealed in an aluminum pan for measurement and attached to a differential calorimeter (DuPont V4.OB2000 DSC), and the temperature was increased from 25 ° C. to 300 ° C. at a rate of 20 ° C./min. It was warmed and held at 300 ° C. for 5 minutes, then taken out, immediately transferred onto ice and rapidly cooled. This pan was again attached to the differential calorimeter, and the melting point (Tm) (unit: ° C) was measured by raising the temperature from 25 ° C at a rate of 20 ° C / min.

[Example 1]
Using dimethyl terephthalate, ethylene glycol, and the copolymer components listed in Table 1 as raw materials, tetrabutoxytitanium as a transesterification catalyst, germanium dioxide as a polymerization catalyst, and orthophosphoric acid as a stabilizer. o-Chlorophenol, 35 ° C.) 0.69 copolymer polyesters A and B were produced.

  After the polyester A and the polyester B blended in the chip state at the ratio (wt%) shown in Table 1 are dried at 120 ° C. for 6 hours, they are supplied to an extruder hopper and melted at a melting temperature of 275 ° C., The molten polymer was laminated in three layers of A / B / A inside the die, extruded onto a cooling drum having a surface temperature of 20 ° C., and rapidly cooled to obtain an unstretched film.

  Subsequently, the unstretched film was successively biaxially stretched 3.0 times at 110 ° C. in the longitudinal direction and 3.2 times at 120 ° C. in the transverse direction, and then heat-set at 235 ° C. to obtain a three-layer film. . The three-layer film has a total thickness of 50 μm, 2 μm for the surface polyester layer A on both sides made of PET and 46 μm for the inner polyester layer B, vacuum suction moldability under heating, heat resistance in microwave oven and film gloss. All obtained good results.

[Examples 2-7, Comparative Examples 1-8]
Using polyester of the composition shown in Table 1, it carried out similarly to Example 1, and obtained the 3 layer film. The characteristics of the obtained three-layer film are as shown in Table 1, and Examples 2 to 7 satisfying the conditions of the present invention all obtained good results. On the other hand, in Comparative Examples 1 to 7 that do not satisfy the conditions of the present invention, all are poor in terms of formability under a predetermined degree of vacuum, and in Comparative Example 8 where the formability is good, the configuration of the oriented film is not included. Therefore, the heat resistance of the microwave oven was poor and the glossiness of the film was insufficient.

  The film for laminating a paper container of the present invention is a container for containing contents such as food by vacuum suction molding and laminating it on a paper container, sometimes frozen or refrigerated, and heated in a microwave oven when eating Can be used as a container.

Claims (4)

  A polyester layer B having a substantially non-oriented structure and a polyester layer A having an oriented structure provided on both sides in contact with this layer. The total thickness (a) of the polyester layer A and the thickness (b) of the polyester layer B The film for laminating paper containers, wherein the ratio (a / b) is 0.01 to 0.60 and the total thickness (a + b) is 20 to 100 μm.   The film for laminating paper containers according to claim 1, wherein the melting point of the polyester constituting the polyester layer A is 15 ° C or higher than the melting point of the polyester constituting the polyester layer B.   The paper container which equips the surface layer with the film for paper container bonding of Claim 1 or 2 by the thickness of 1-100 micrometers.   A paper container provided with a film layer as a surface layer by arranging the film for laminating a paper container according to claim 1 or 2 along the paper container, and vacuum suction molding along the paper container under heating or preheating. A method for producing a paper container.