WO2003061969A1

WO2003061969A1 - Laminate material for paper containers and paper containers for liquids

Info

Publication number: WO2003061969A1
Application number: PCT/JP2003/000540
Authority: WO
Inventors: Noriyuki Sasaki; Hidenobu Miyake; Hajime Ishikawa; Toshiyuki Suzuki
Original assignee: Toppan Printing Co., Ltd.
Priority date: 2002-01-22
Filing date: 2003-01-22
Publication date: 2003-07-31
Also published as: JP4239821B2; JPWO2003061969A1

Abstract

A laminate material for paper containers and paper containers for liquids which are mainly employed in storing retort-packed liquid foods. In the laminate material (10) for paper containers, a cushioning layer (12), a barrier layer (13) and a sealant layer (14) are successively laminated on one face of a hot waterproof paper (11). In the case of folding the laminate material (10) in the process of forming a paper container (20) for liquids by molding, the cushioning layer serves as a cushioning and thus pinholing can be prevented.

Description

Specification

Laminated materials for paper containers and liquid paper containers

Technical field

The present invention relates to a laminated material for a paper container and a liquid paper container, and more particularly to a laminated material for a paper container and a liquid paper container capable of retorting without generating pinholes.

Background art

As food containers that can be distributed at room temperature for a long period of time, metal cans, plastic molded containers, and retort bouches mainly composed of flexible packaging films are distributed. However, in recent years, environmental issues have become increasingly important, and containers and packaging materials have to be easily disposed of, and the need for easy incineration and recycling is increasing.

In the field of plastic containers such as bottles and trays, and composite containers consisting of paper and plastic, containers with significantly reduced plastic, and easy separation of paper and plastic at the time of disposal Various composite containers and the like have been proposed. In particular, there is a growing need for eco-friendly paper containers.

On the other hand, using a laminated material in which paperboard and a gas barrier layer such as aluminum foil are sandwiched with a moisture-proof thermoplastic resin layer such as polyethylene or polypropylene, a sandwich is used. A paper container formed in a cup shape or a box shape is known.

In this paper container, by directly laminating a thermoplastic resin layer on the surface, direct contact of the paperboard with water or moisture from the surface is avoided. However, in this paper container, when heat treatment such as retorting treatment using hot water is performed, paperboard is cut from the end face of the laminated material. It absorbs water inside.

Even if the container is cooled after the heat treatment, the water absorbed during the retort treatment cannot be evaporated and remains on the paperboard. As a result, there is a problem in that the interlayer strength, rigidity, etc. of the paperboard are reduced, and the strength of the packaging container is reduced. '

In order to solve the problem of the paper container as described above, the inventors of the present invention have replaced the paperboard with a resin selected from silane-based resins, melamin-based resins, isocyanate-based resins, and acryl-based resins. We tried a method using heat-resistant water-treated paper impregnated with paper. Specifically, a laminated material was formed by combining this heat-resistant processed paper with the barrier layer and the sealant layer via an adhesive or a low-density polyethylene resin. Next, we tried a method of forming this laminated material into a paper container and retorting.

However, this method allows retort processing, but it is not possible to fold paper that has multiple layers at a deep angle, such as when molding brick-shaped containers. There is a problem that pinholes are easily generated from the part.

An object of the present invention is to provide a laminated material for a paper container and a liquid paper container that can be retorted without generating pinholes.

Disclosure of the invention

In order to achieve the above object, the laminated material for paper containers of the present invention is configured as follows.

(1) The laminated material for a paper container of the present invention has a buffer layer, a non-layer, and a sealant layer sequentially laminated on one surface of heat-resistant water-treated paper. With such a laminated structure, when forming into a paper container, even if several layers of laminated material are folded and bent, the buffer layer acts as a buffer material and pinholes are generated in the barrier layer. There is nothing.

(2) In the laminated material for a paper container of the present invention, in the configuration according to (1), the buffer layer is selected from a medium-density polyethylene resin, a high-density polyethylene resin, a polypropylene resin, and a polyamide resin. Alternatively, it may be composed of one or a mixture of these resins.

(3) In the laminated material for a paper container of the present invention, in the configuration described in (1) or (2), the buffer layer may have a thickness of 10 to 70 m.

According to the laminated material for paper containers described in (2) or (3) above, the material and Z or thickness of the buffer layer are specified, so that even if the laminated material is bent, the buffer layer has a sufficient buffer effect. Demonstrate.

(4) The laminated material for a paper container according to the present invention, in the configuration according to any one of the above (1) to (3), wherein the tensile elastic modulus of the buffer layer is lower than the tensile elastic modulus of the barrier layer. It has become.

Thereby, the role of the buffer material in the buffer layer can be easily and reliably realized.

(5) The liquid paper container of the present invention is manufactured using the laminated material for a paper container according to any one of (1) to (4). BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an explanatory sectional view showing an embodiment of the laminated material for a paper container of the present invention.

FIG. 2 shows a paper container formed using the laminated material for a paper container of the present invention. It is a perspective explanatory view showing one embodiment of a vessel.

FIG. 3 is an explanatory sectional view showing an example of a conventional laminated material for paper containers.

FIGS. 4 to 11 are cross-sectional views for explaining stress due to the insertion of a wire in a conventional laminated material for paper containers.

FIG. 12 and FIG. 13 are cross-sectional views for explaining relaxation of stress in the laminated material for a paper container of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The laminated material for a paper container of the present invention will be described in detail below based on one embodiment. FIG. 1 is an explanatory sectional view showing an embodiment of the laminated material for a paper container of the present invention. The laminated material 10 for a paper container has a structure in which a buffer layer 12, a barrier layer 13, and a sealant layer 14 are sequentially laminated on one surface of heat-resistant water-treated paper 11.

The heat-resistant water-treated paper 11 is obtained by impregnating or applying a resin to a paper base material.

As the paper base material, for example, various types of paper such as the following (11a) to (llf) can be used.

(11a) Paper made of 100% virgin pulp.

(lib) Paper made of 100% recycled waste paper.

(11c) Paper (lid) obtained by mixing the above (11a) and (lib) at an arbitrary ratio, and any one of the above (11a) to (11c), and NBKP (softwood bleached curve) obtained from conifers Paper mixed with wood pulp (wood pulp) wood and LBKP (hardwood bleached kraft pulp) wood obtained from hardwood at an arbitrary ratio.

(He) Other than wood pulp in (11a) to (lid) above Paper made of vegetable fiber materials such as naph and bamboo.

(llf) Paper obtained by subjecting the above papers (11a) to (lie) to crack coating.

In addition, paper having strong peeling strength of the laminating layer and hot water resistance, such as cup base paper, can be particularly preferably used. Here, the cup base paper is a paper obtained by mixing the NBKP material and the LBKP material of 100% virgin pulp, and adding a sizing agent, a paper strength enhancer, and the like.

The hot water-treated paper 11 is obtained by impregnating or applying a resin capable of imparting hot water resistance to these paper base materials. The heat-resistant paper 11 can be further impregnated with a paper strength enhancer when wet, a water-proofing agent, and a water-repellent agent, if necessary. In addition, these paper base materials may be impregnated with a resin that imparts rigidity and water resistance in a papermaking stage or in a secondary processing stage after papermaking. The fiber structure and the paper substrate referred to here include all fiber structures made of pulp or the like, and are not limited to what is called paper.

When hot water is to be imparted, the resin to be impregnated or applied may be a thermosetting resin such as a silane resin, a melamine resin, a urethane resin, an isocyanate resin, or an acrylic resin. Resins, polyester resins, thermoplastic resins such as polyethylene resins and polypropylene resins can be selected and used depending on the required heat-resistant water temperature. Further, even when high water repellency is required as an additional function, the above resin materials may be compounded or mixed according to the required level of water repellency as long as the required hot water resistance is not impaired. It can be used. Further, when imparting dry strength, water resistance, and wet strength, polyvinyl alcohol resin, polyacrylamide resin, starch and the like can be used as the resin to be impregnated.

Urea-formaldehyde resin, melamine-formaldehyde resin, starch, polyamide amide, modified epichlorohydrin, and various latexes are used as wet strength agents. It is possible. Examples of the various types of latex include natural rubber latex, synthetic rubber latex such as SBR, NBR, and polystyrene, polyvinyl acetate, acrylic resin, polyvinyl chloride, polyvinylidene chloride, or a mixture thereof. Examples include polymer resin latex.

The base material of the fibrous structure that becomes heat-resistant water paper is made by impregnating (internally or externally) in the papermaking process or in the secondary processing after papermaking. The aforementioned resin can be evenly distributed over the entire thickness direction.

In addition, since the resin is impregnated at the papermaking stage, the density, thickness, amount of resin to be internally added, etc. of the impregnated paper can be arbitrarily determined according to the desired functional level as the laminated material of the present invention.

Next, a method of impregnating a paper base material with a resin that imparts rigidity, water resistance, and hot water resistance as a secondary process after or after the papermaking process will be described. Examples of the impregnation method by external addition include a dipping method in which a fibrous structure is immersed in an impregnating agent and an excessive amount of the impregnating agent is temporarily applied, or preferably, a fixed amount of the impregnating agent is applied or impregnated. Gravure coating method and roll coating method. In addition, as an impregnation method by external addition, It is also possible to impregnate the impregnating agent from both sides of the fiber structure. In the gravure impregnation method having two or more units, first, an impregnating agent for impregnating the inside of the paper base material is applied from one side or both sides, and the impregnating agent penetrates into the inside of the base material. After that, a coating unit can be formed on the surface of the paper substrate in the last unit. The obtained impregnated paper has high wet strength, for example, by impregnating the entire inside of the impregnated paper with a wet paper strength enhancer or the like. In addition, a high water-repellent effect can be imparted by disposing a water-repellent agent or the like on the surface layer of the impregnated paper. That is, as long as the impregnating agent can be supplied to the paper substrate, a desired impregnation method can be used depending on the paper substrate and the impregnating agent. Furthermore, since these impregnation methods are secondary processes, they require a small amount of processing compared to the papermaking process and can be performed at low cost.

As the impregnating agent for impregnating the paper substrate, an isocyanate-based resin is preferable from the viewpoint of further improving water resistance and heat resistance. The isocyanate resin has the property of improving the wet strength of paper when impregnated into a paper base material. The urea compound formed by the isocyanate and the water in the paper has extremely high heat resistance, water resistance, and hot water resistance, so the isocyanate resin significantly reduces the water absorption of the paper base material. it can. Therefore, the paper container using the isocyanate resin-impregnated paper has extremely excellent shape retention and buckling strength not only in the dry state but also in the wet state. In addition, paper containers made of heat-resistant water-treated paper impregnated with isocyanate resin show extremely high shape retention and hot water resistance even under hot water conditions such as boil sterilization and retort sterilization processes. ing.

As the resin to be impregnated, a well-known polyiso resin is used. The cyanate compound can be used. Well-known polyisocyanate compounds include, for example, phenylene diisocyanate (PDI), tolylene diisocyanate (chond DI), naphthene diisocyanate (NDI), and 4,4 'diisocyanate Aromatic diisocyanates such as diphenyldimethanane (MDI), aromatic and aliphatic diisocyanates such as xylylene diisocyanate (XDI), hydrogenated TDI, hydrogenated XDI, hydrogenated MDI, hexamethylene Aliphatic or alicyclic diisocyanates such as range isocyanate (HMDI) and isophorone diisocyanate (IPDI), and their derivatives, such as polyol adducts and burettes, 3 In addition to trifunctional isocyanates, such as polyisocyanates with three or more functional groups, resin trisolysate (LTI), etc. Each kind of cage Goma, there is a poly-mer.

When filling a liquid food into a paper container using the heat-resistant water-treated paper 11, it is preferable to use XDI or IPDI.

The amount of impregnation may be set so that the impregnated paper has a tensile strength when wet of 10% or more when dry. According to such a setting, heat resistance and water resistance can be improved, and the shape retention and rigidity of the container when wet can be maintained.

The buffer layer 12 is a layer located between the heat-resistant water-treated paper 11 and a barrier layer 13 described later. The buffer layer 12 needs a buffering property and heat resistance. Films such as high-density polyethylene, high-density polyethylene, and polypropylene can be preferably used. The thickness of the buffer layer 12 is preferably about 10 to 70 _t m, and more preferably 30 to 50 m.

If the thickness of the buffer layer 12 is less than 10 m, it will not be possible to obtain sufficient cushioning for stress due to stress or heat applied during molding into a container or during retorting. There is a problem that holes are easily generated. If the thickness of the buffer layer 12 exceeds 70, problems occur that it is not economical and that formability is deteriorated.

The name of the buffer layer 12 may be arbitrarily changed as long as it has flexibility and plasticity and alleviates the stress of the barrier layer 13. For example, the buffer layer 12 may be called an arbitrary name such as the cushion layer 12, the relaxation layer 12, the plastic layer 12 or the flexible layer 12 instead of the name of the buffer layer.

The barrier layer 13 is a layer provided inside the buffer layer 12 and imparting gas barrier properties and water vapor barrier properties. As the barrier layer 13, for example, aluminum oxide or silicon oxide is formed on a stretched film such as a uniaxially or biaxially stretched polyethylene terephthalate film, a polyamide film, or a polyolefin. Inorganic compound vapor-deposited plastic films, aluminum foil (A1), etc., in which a thin film of an inorganic compound such as is provided in a thickness of about 20 to 500 nm by a vapor deposition method such as physical vapor deposition or chemical vapor deposition. Can be used favorably. Further, the thickness of the Nori layer 13 is preferably about 7 to 30 m.

It should be noted that the type to be selected as the barrier layer 13 may be determined appropriately according to the purpose of use, purpose, and the like. Since the sealant layer 14 requires retort resistance as well as heat sealing properties, cast polypropylene (CPP) film or linear low-density polyethylene (L-L LDPE) film can be used preferably. The thickness of the sealant layer 14 is preferably about 30 to 100 m.

The laminated material 10 for a paper container is made of a two-component reaction type poly- lylate, which is a known laminating method of each of a heat-resistant water-treated paper 11, a buffer layer 12, a barrier layer 13, and a sealant layer 14. It is manufactured by laminating by a known laminating method such as a dry laminating method using an ester resin-based or polyester resin-based adhesive or an extruder-lamination method.

The laminated material 10 for a paper container manufactured in this manner is attached to a paper container molding machine, and molded into a brick-shaped paper container 20 as shown in FIG. 2, for example.

The types of the paper container forming machine include a sheet type, a sleeve type and a roll type. The sheet type is a method in which a laminated paper container material 10 punched into a blank is formed into a paper container 20. The sleeve type is a method of forming a paper container laminated material 10 semi-formed into a cylindrical shape into a paper container 20. The roll type is a method in which a roll-shaped laminated material 10 for a paper container is formed into a paper container 20. Needless to say, the laminated material 10 for a paper container of the present embodiment can be applied to any type of paper container forming machine.

Paper containers that can be formed using the laminated material 10 for paper containers include not only brick-shaped paper containers, but also roof-type containers and four-sided containers. It can also be used for body containers, cup-shaped containers, etc.

[Example]

Hereinafter, the present invention will be described in detail with reference to Examples. Example 1 describes the effect of checking the effect of the presence or absence of the buffer layer 12. Example 2 is to confirm the effect of the heat resistance of the buffer layer 12.

(Example 1)

First, a cup base paper having a basis weight of 180 g / m 2 was impregnated with an isocyanate resin by dipping to prepare a heat-resistant water-treated paper 11.

A 40 m thick CPP film, which is a buffer layer 12, is attached to one side of the heat-resistant water-treated paper 11 1 by a dry laminating method using an adhesive, and the heat-resistant water-treated paper 11 is buffered. A composite paper with layer 12 was prepared. The adhesive was Takerac A 515 (manufactured by Mitsui Takeda Chemical Co., Ltd.), which is a two-part reactive polyester resin adhesive.

On the other hand, dry lamination of the 50 m thick CPP film, which is the sealant layer 14, and the 9 m thick A 1, which is the nori layer 13, using the Takerack A 5 15 described above. The composite film of the sealant layer 14 and the barrier layer 13 was produced by bonding.

Next, the buffer layer 12 side of the composite paper and the barrier layer 13 side of the composite film were opposed to each other, and were bonded to each other by the dry laminating method using the above-mentioned bamboo rack A515.

Thus, the laminated material 10 for the paper container of Example 1 was produced. Was. The laminated material 10 for the paper container of Example 1 is made of heat-resistant water-treated paper (180 g Zm2, 11) Z adhesive (not shown) ZCPP film (40 / zm, 12) Z It has a layer structure of adhesive (not shown) / A1 (9 m, 13) / adhesive (not shown) / CPP film (50m, 14).

(Comparative Example 1)

The laminated material 50 for a paper container of Comparative Example 1 (see FIG. 3) was produced using the same material and method as in Example 1 except that the buffer layer 12 was not used.

The laminated material 50 for the paper container of Comparative Example 1 is heat-resistant water-treated paper (180 g Zm2, 11) Z. adhesive (not shown) / A1 (9 m, 13) Z adhesive (Not shown) / CPP film (50 m, 14).

(Comparative Example 2)

The laminated material for a paper container of Comparative Example 2 used a low-density polyethylene film having a thickness of 20 m and a melting point of 110 ° C instead of the CPP film having a thickness of 40 m as the buffer layer. Except for the above, it was manufactured using the same materials and method as in Example 1.

The laminated material for the paper container of Comparative Example 2 is heat-resistant water-treated paper (180 g / m 2) / adhesive (not shown) / low-density polyethylene film (20 m) Z adhesive (shown ) / A1 (9 m) / Adhesive (not shown) ZCPP film (50 Aim).

One kind of such an example and two kinds of comparative examples, a total of three kinds of laminated materials for paper containers, are used to form brick-shaped paper containers. The paper container was set in a box-type paper container molding machine to form a brick-shaped paper container of the desired volume. The filling of the paper container is water.

The occurrence of pinholes at the bottom of the paper container after molding and retorting was checked and observed by the following method. The results are shown in Table 1.

The retort processing conditions were 121 and 30 minutes, and a constant pressure retort apparatus was used.

The pinhole check is performed by cutting each of the five paper containers in the horizontal direction, and then applying a dye penetration penetrant R — 1 ANT (produced by Eishin Chemical Co., Ltd.), which is a pinhole check solution, to the bottom of the paper container. After leaving it for 7 minutes and leaving it for 10 minutes, it was carried out by visually observing the penetration state of the flaw detector from the back surface of the bottom and measuring the number of pinholes generated. In Table 1, for example, 0Z5 indicates that the number of pinhole-generated paper containers among the five paper containers is zero.

[table 1 ]

〇… resistant

X ... no resistance

As shown in Table 1, according to Example 1 in which a 40 m-thick CPP film was used as the stress buffer layer 2, It was confirmed that a paper container without pinholes could be formed even after the treatment.

(Example 2)

Example 2a to 2c

In the same manner as in Example 1, a laminated material 10 for a paper container composed of the heat-resistant water-treated paper 11, the buffer layer 12, the barrier layer 13, and the sealant layer 14 was produced. However, the buffer layer 12 and the barrier layer 13 have the configurations shown in Table 2 described later. That is, the buffer layer 12 of Examples 2a to 2c is a nylon film having a thickness of 15 m or a CPP film having a thickness of 50. The barrier layer 13 in each of Examples 2a to 2c is a 12 m-thick PET film or a 9 m-thick aluminum foil which is formed by ceramic vapor deposition. Here, the PET film on which the ceramic is deposited is a GL film (manufactured by Toppan Printing Co., Ltd.). The heat-resistant water-treated paper 11 and the sealant layer 14 are the same as in the first embodiment.

Comparative Example 2 d, 2 e

Comparative Example 2d has a configuration in which the buffer layer 12 is omitted from Example 2a. Comparative Example 2e has a configuration in which LDPE (low-density polyethylene) having a melting point of 11 O is used for the buffer layer instead of the buffer layer 12 of Examples 2b and 2c. The melting point of the LDPE of Comparative Example 2e is lower than the temperature of the retort treatment described later.

Next, using the paper container laminate materials 10 and 50 of Examples 2a to 2c and Comparative Examples 2d and 2e, the paper container 2 was prepared according to the following procedures (i) to (vii). 0 was produced. (i) The sheet of the laminated material 10 for the paper container is punched out to a size required for the paper container 20, and a line is drawn in the bent portion.

(ii) The obtained laminated material 10 for a paper container is molded into a bag shape with one end opened, and the bonded portion is sealed.

(iii) The bag-shaped laminated material for paper containers 10 is filled with water as an example of a liquid food.

(iv) The open end of the paper container laminated material 10 after filling is sealed, and the bonded portion is sealed to produce a paper container 20 ′.

(V) Four corners of the sealed paper container 20 are bent to form four ears, and each ear is adhered to the container body to form a brick-shaped paper container 20.

(vi) Retort the prick-shaped paper container 20 under the conditions of 121 ° (:, 30 minutes).

(vii) After the retort treatment, the paper container 20 is dried.

Table 2 shows the results.

[Table 2]

〇— N Y: Stretched nylon

CPPP: Undrawn polypropylene

X (* 1): Pinhole occurred.

X (* 2): Float occurred between layers 11 and 13.

(Result)

According to Examples 2a to 2c, as shown in Table 2, it is possible to provide a paper container laminated material 10 and a liquid paper container 20 that do not generate pinholes and can be retorted. And confirmed.

On the other hand, Comparative Examples 2d and 2e had the following problems.

In Comparative Example 2d, when the S-line was inserted in step (i) and when steps (ii) and (v) were formed, the paper was torn at the corners of the bending at each stage of the retorting process in the step. There has occurred. The reason for this is that the structure of Comparative Example 2d, in which the buckling heat-resistant paper 11 and the inflexible PET film (the barrier layer 13) were directly bonded with an adhesive, was used. Where the physical and z or thermal stresses form the corners of the bend

(Ear and proximal ends of the ears). Here, such a stress will be described with reference to FIGS. First, as partially shown in FIG. 4, the laminated material 50 of Comparative Example 2d was formed on the lower base 60 on which the groove 61 of the pattern corresponding to the bending line was formed, The pattern is arranged between an upper base (not shown) on which a pattern of go-line blades 71 facing the groove 61 is formed.

Next, as shown in FIG. 5, the laminated material 50 is sandwiched between the groove 61 and the wire drawing blade 71 to draw a wire drawing. At this time, heat-resistant paper

11, the Nori layer 13 and the Sealant layer 14 extend as indicated by arrows in the figure.

After the wire drawing in FIG. 5, the laminated material 50 is released from the groove 61 and the S-line blade 71 as shown in FIG.

At this time, as shown in FIG. 7, the heat-resistant paper 11 maintains the shape of the stretched X-ray by plastic deformation. On the other hand, the barrier layer 13 contracts as indicated by the arrow 13 s due to the slight residual elasticity. For this reason, a large shift occurs at the interface between the two, 11 and 13.

X in 7) occurs. This shift X is considered to cause pinholes and cracks in the Noria layer 13 and the like, and eventually to cause floating f and tear lib as shown in FIGS. 8 to 11.

Here, as shown in FIG. 8, the lift f occurs when the heat-resistant paper 11 and the barrier layer 13 are separated due to the displacement X. Tear 1

As shown in Fig. 9, 1b is generated on the heat-resistant paper 11 when the heat-resistant paper 11 and the barrier layer 13 do not peel off due to the displacement X. You. When the tear lib shown in FIG. 9 increases, as shown in FIG. 10, a step occurs in the heat-resistant paper 11. In addition, floating ί and tearing lib may occur at the same time, as shown in Fig. 11. On the other hand, in the case of Example 2a, the barrier layer 13 contracts as shown by the arrow 13s as shown in FIG. 12 after the grid lines shown in FIGS.

However, in the case of Example 2a, as shown in FIG. 13, the intermediate buffer layer 12 is deformed in accordance with the contraction of the barrier layer 13, and the elastic force of the barrier layer 13 is reduced. For this reason, in Examples 2a to 2c, it is considered that a large displacement does not occur at the interface between the layers 11 to 13.

The above is the description of the stress that occurred in Comparative Example 2d. When the barrier layer 13 of Comparative Example 2d is an aluminum box, the aluminum foil has good shape retention, and therefore, unlike the stress due to shrinkage described above, it is pulled by the go-line blade 71. Due to the stresses that occur, tearing cracks enter the barrier layer 13. However, according to Examples 2b and 2c, the buffer layer 12 is deformed in accordance with the tension of the wire blade 71, and the tensile force to the barrier layer 13 is relaxed. In addition, it is considered that no large displacement occurs at the interface between the layers 11 to 13.

Next, the results of Comparative Example 2e are described.

In Comparative Example 2e, floating occurred between the heat-resistant paper 11 and the barrier layer 13 after the retort treatment in step (vi). This is probably because the LDPE (melting point 110) used as the buffer layer 12 had insufficient sealing strength when the retort temperature was 121 ° C. According to the study of the present inventors based on the above results, in the case of the paper container 20 subjected to the retort treatment, as the buffer layer 12, as shown in the following conditions (cl) and (c2), It was found that it is preferable to have both heat resistance and flexibility. However, it is needless to say that the conditions are not limited to the conditions (cl) and (c2) in the case of the paper container 20 which is not subjected to the retort treatment.

(cl) The heat resistance of the buffer layer 12 is satisfied if the sealing strength between the buffer layer 12 and the barrier layer 13 at the temperature of heat sterilization is 1.5 N or more. Supplementally, even if the buffer layer 12 is melted at the temperature of heat sterilization, it is sufficient that the sealing strength is 1.5 N or more due to the melt tension. The seal strength of 1.5 N or more is a value measured by the T-peel method specified in JIS K 6854. If the seal strength is a value equivalent to the value of the T-peeling method described above, the value by another measurement method (eg, <adhesion> 180 degree peeling method specified in JISK 6854) is used as an index. May be used. (c2) The buffer layer 12 satisfies flexibility if its tensile elastic modulus is lower than that of the barrier layer 13. Specifically, tensile modulus of the cushioning layer 1 2 (tensile elastic modulus) 0. 1 ~ 2. 1 ( X 9. 8 X 1 0 4 [N / cm 2]) there Bayoi in the range of.

Representative resins satisfying these conditions (cl) and (c2) include, for example, as shown in Table 3, medium-density polyethylene, high-density polyethylene, polypropylene, and nylon. [Table 3]

The tensile modulus of elasticity in Table 3 can be found in the well-known document "Plastic Reader", revised 14th edition, Edited by: Osaka Municipal Industrial Research Association, Plastics Readers Editorial Board, Plastics Council, Published by: Plastics Age Co., Ltd. Based on

According to the study of the present inventor, in addition to the method satisfying the conditions (cl) and (c2) described above, the thickness of the barrier layer 13 having poor flexibility is increased to prevent the generation of pinholes. A method was also conceived. However, the method of increasing the thickness of the barrier layer 13 was not included in the present invention for the following two reasons. The first reason is that a barrier layer made of a metal foil such as A1 has dead holdability (shape retention after molding), and the moldability is not greatly reduced, but the price is high and the economy is high. This is because it is disadvantageous. The second reason is that, in the case of a PET-based evaporated barrier film, if the PET substrate with poor flexibility is made thicker, the laminated material becomes harder, making it difficult to bend even if wire drawing is performed. However, the moldability is very poor. Industrial applicability

As described above, the laminated material for a paper container and the liquid paper container according to the present invention are useful for forming a paper container that can be retorted without generating pinholes. It is suitable for use in a plied paper container having a bent portion that overlaps the other.

Claims

The scope of the claims

1. A laminated material for paper containers, characterized in that a buffer layer (12), a barrier layer (13), and a sealant layer (14) are sequentially laminated on one side of heat-resistant water-treated paper (11).

2. The buffer layer (12) is made of one selected from nylon resin, medium-density polyethylene resin, high-density polyethylene resin, and polypropylene resin, or a mixture of these resins. The laminated material for a paper container according to claim 1, wherein

3. The laminated material for a paper container according to claim 2, wherein the buffer layer (12) has a thickness of 10 to 70 x m.

4. The laminated material for a paper container according to claim 3, wherein the tensile elastic modulus of the buffer layer (12) is lower than the tensile elastic modulus of the barrier layer (13).

5. The laminated material for paper containers according to claim 1, wherein the buffer layer (12) has a thickness of 10 to 70 m.

6. The laminated material for a paper container according to claim 5, wherein the tensile elastic modulus of the buffer layer (12) is lower than the tensile elastic modulus of the barrier layer (13).

7. The laminated material for paper containers according to claim 1, wherein the tensile elastic modulus of the buffer layer (12) is lower than the tensile elastic modulus of the barrier layer (13).

8. The laminated material for paper containers according to claim 2, wherein the tensile elastic modulus of the buffer layer (12) is lower than the tensile elastic modulus of the barrier layer (13).

9. The paper container according to any one of claims 1 to 8 Paper container made using the laminated material (10).