JPH04298346A - Paper container and laminate used in manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a laminated paper container having good aroma retentivity, heat-sealability and falling strength and the raw laminate thereof. CONSTITUTION:An ethylene/unsaturated carboxylic acid/unsaturated ester copolymer layer is provided to one surface of the paper layer becoming the base of a container and a modified polyethylene terephthalate layer containing 3-20mol% of the copolymer component is provided to the other surface of the paper layer as the outermost layer to form a laminate. A paper container excellent in aroma retentivity and having high falling strength is obtained from this laminate and can be used as a large paper container for juice.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated paper container suitable for beverages containing aroma components and its original fabric. More specifically, the present invention relates to a laminated paper container with good aroma retention, drop strength, heat sealability, etc., and its raw material.

0002

2. Description of the Related Art Multilayer paper containers are widely used as containers for various fruit drinks, lactic acid bacteria drinks, etc. These paper containers require heat sealing during packaging.
It is used by laminating a heat-sealable resin layer on the inner layer of paper. At this time, in order to improve gas barrier properties and light blocking properties,
In some cases, an aluminum foil layer is formed on the inner layer of the paper, and a heat-sealable resin layer is further formed on the inner layer. In any case, as such heat-sealable resin,
Conventionally, olefin polymers have been mainly used. Olefin polymers not only have excellent heat sealability but also excellent flexibility, and have excellent features such as no pinholes even when subjected to bending processing. However, such a heat-sealing layer is also a layer that comes into direct contact with the contents such as food and drinks, but in this case, olefin polymers tend to adsorb aroma components, and depending on the type of packaged product, the taste and aroma may change. It had the disadvantage of being variable.

[0003] In order to improve this drawback, a method of using glycol-modified polyethylene terephthalate in the inner layer is disclosed in JP-A-62-128752 and JP-A-62-29053.
This is proposed in No. 4, etc. As in the latter proposal, if a paper roll coated with a low-density polyethylene protective film is used as the outer layer of the container, and the container is formed by overlap sealing, a seal is formed between the low-density polyethylene and the modified polyethylene terephthalate, but the seal is Power is small. For this reason, as the shape of the container becomes larger, its drawbacks become more apparent, and when a drop test is performed after filling the container with juice or the like, the seal portion easily breaks, which poses a major problem in practice. According to the studies conducted by the present inventors, even if the low-density polyethylene layer was corona-treated, no significant improvement was observed, and even if the polyester layer was corona-treated in addition to the low-density polyethylene layer, there was no noticeable improvement No improvement was observed. A specific example of the glycol-modified polyester disclosed in these publications is amorphous PET-G, but if the inner layer is copolymerized polyethylene terephthalate, which has crystallinity and is easy to dry and laminated onto paper, , the above drawbacks were more noticeable.

0004

[Problems to be Solved by the Invention] The present inventors have developed a material that has good lamination properties on paper and has sufficient protection against moisture etc. for the paper outer layer, and a copolymer material for the paper inner layer. We investigated the structure of paper containers made of polyethylene terephthalate. Even if a copolymerized polyethylene terephthalate having crystallinity was used, studies were conducted to find a configuration that would provide sufficient sealing strength even when paper containers were manufactured by overlap sealing. As a result, I learned that the purpose could be achieved by adopting the configuration described below. Therefore, an object of the present invention is to provide a paper container with excellent aroma retention and drop strength, and its original fabric.

[0005]

[Means for Solving the Problems] The present invention provides ethylene, unsaturated carboxylic acid,
A layer of an unsaturated ester copolymer (hereinafter sometimes simply referred to as a terpolymer) is provided, and the outermost layer is a modified polyethylene terephthalate containing 3 to 20 mol% of the copolymer component on the other side of the paper layer. The present invention relates to a paper container laminate characterized in that it is provided with a layer (hereinafter referred to as a modified PET) layer, and a paper container formed from the same.

The layer structure in the present invention basically consists of terpolymer/paper/modified PET, but paper and modified PET
Adhesive layer (hereinafter sometimes referred to as T layer) between the layers
or a gas barrier layer (hereinafter sometimes referred to as B layer) may be provided. That is, layer configurations such as terpolymer/paper/modified PFT, tertiary copolymer/paper/T/B/T modified PET, etc. can also be adopted.

[0007] The unsaturated carboxylic acids in the terpolymer which is formed on one side of the paper layer of the present invention and which forms the outer layer when used as a paper container include acrylic acid, methacrylic acid,
Examples include monoethyl maleate and maleic anhydride, with acrylic acid and methacrylic acid being particularly preferred. Further, the unsaturated ester in the terpolymer is an ester of the above unsaturated carboxylic acid or a vinyl ester such as vinyl acetate. Specific examples of the former include methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and methyl methacrylate. As unsaturated esters, esters of acrylic acid or methacrylic acid are particularly suitable.

The polymerization ratio of each component in the terpolymer is 30 to 93% by weight of ethylene, preferably 50 to 88% by weight.
% by weight, 4-40% by weight of unsaturated esters, preferably 7-30% by weight, 3-30% by weight of unsaturated carboxylic acids,
Preferably it is 5 to 20% by weight. When the contents of the unsaturated ester and the unsaturated carboxylic acid are within such ranges, heat sealing with the modified PET can be firmly performed. Furthermore, if the ethylene content is less than the above range, the tackiness increases and blocking tends to occur, so it is preferable to set the polymerization ratio as above. The terpolymer preferably has a melt flow rate of 0.05 to 100 g/10 min, particularly 0.5 to 50 g/10 min at 190°C and 2160 g load.

The modified PET layer that forms the other outermost layer of the paper and becomes the innermost layer when it is made into a container is mainly composed of modified PET, and in order to improve it, other polymers,
For example, a small amount of an ethylene polymer or copolymer may be blended to improve impact resistance and pinhole resistance. It may also contain a small amount of other polyester such as polyethylene terephthalate.

[0010] In addition to ethylene glycol units and terephthalic acid units, modified PET is copolymerized with a copolymer component in a proportion of 3 to 20 mol%, preferably 5 to 15 mol%. Copolymerization components include isophthalic acid,
Aromatic carboxylic acids such as phthalic acid, 2,6-naphthalene dicarboxylic acid, p-oxybenzoic acid, aliphatic or alicyclic carboxylic acids such as adipic acid, sebacic acid, cyclohexane dicarboxylic acid, propylene glycol, 1, 4
Diols such as -butanediol, 1,4-cyclohexanedimethanol, diethylene glycol, and triethylene glycol can be mentioned. Among these copolymerizable components, isophthalic acid, 1,4-cyclohexanedimethanol, diethylene glycol, and the like are particularly preferred. These modified PETs have an intrinsic viscosity of 0.60 to 1.4 dl/g, particularly 0.65 to 1.0 dl/g.
g is preferred. If the copolymerization component is less than 3 mol %, the heat sealability will be poor, and a product with sufficient heat seal strength for use as an inner layer material of high-temperature filling paper containers cannot be obtained. Moreover, if the copolymerization component exceeds 20 mol %, the composition will not have sufficient flexibility, elongation, etc., and will be prone to pinholes and breakage due to bending.

Ethylene polymers or copolymers that can be blended into modified PET include low density polyethylene, medium/high density polyethylene, linear low density polyethylene, ethylene/vinyl acetate copolymer, ethylene and acrylic acid, or Copolymers of methacrylic acid with esters, ethylene/unsaturated acid copolymers, ethylene/unsaturated carboxylic acids/unsaturated ester copolymers, or their metal ions such as sodium, potassium, magnesium, and zinc, at least in part. is a neutralized salt, or two or more of these. These ethylene polymers or copolymers are
It can be incorporated into the modified PET layer in an amount of up to 40% by weight, preferably up to 30% by weight.

[0012] One or more adhesive layers or gas barrier layers can be provided between the paper layer and the modified PET layer. Examples of gas barrier layers that are preferably provided when used in containers for long-term storage include aluminum, biaxially oriented polyethylene terephthalate, and ethylene vinyl alcohol copolymer. In addition, as an adhesive layer,
The above-mentioned ethylene polymers or copolymers may also be used. Generally, in order to improve the pinhole resistance of the modified PET layer, it is preferable to provide a layer of such an ethylene polymer or copolymer, which also serves as an adhesive layer, adjacent to the modified PET layer.

[0013] The laminate as described above is appropriately bent and formed into a container shape using various operations such as heat sealing. The container shape may be of any shape, for example, it may be of the same shape as paper containers on the market. When sealing is performed between the modified PET and the terpolymer, the terpolymer layer is preferably sealed, and more preferably both the terpolymer layer and the modified PET layer are sealed by corona treatment. Good. This makes it possible to form a strong seal, so that even if a drop test is performed on the filled container, the sealing surface will not be easily damaged. Especially the terpolymer layer and modified PE
When both layers of the T layer are heat-sealed after corona treatment, a dramatic improvement in sealing strength is observed.

[0014]

[Examples] Next, the present invention will be explained with reference to Examples. Example 1 A paperboard (layer B) having a density of 200 g/m2 was coated with ethylene/isobutyl acrylate/methacrylic acid (E/IBA
/MAA) terpolymer (E/IBA/MAA)
=80/10/10% by weight, MFR=10) at resin temperature 3
Extrusion coating was carried out at 00° C. and a line take-up speed of 80 m/min to form a coating film with a thickness of 25 μm as layer A. Next, a copolymer of ethylene/methacrylic acid (E/MAA) (E/MAA=90/10% by weight, MFR=8) was placed between the laminate and the 7 μm thick Al foil (D layer). Extrusion was carried out at a temperature of 300°C and a line take-up speed of 80/min, sandwich lamination was performed to form a copolymer film of 20 μm, and the resultant terpolymer/paper/copolymer/A
A laminate having a structure of 1 (A/B/C/D layers) was obtained. The above ternary copolymer was applied to the Al surface of this laminate at a resin temperature of 300.
℃ and extrusion coating at a line take-up speed of 80 m/min to form a coating film with a thickness of 20 μm as the E layer. Next, after corona treatment of this terpolymer (hereinafter sometimes referred to as terpolymer) coating film layer (E layer), modified polyethylene terephthalate (hereinafter referred to as modified PET) is applied as F layer on this terpolymer layer. The copolymerization composition is isophthalic acid/terephthalic acid/ethylene glycol = 10/
It is 40/50 mol%. Same below) Resin temperature under die 30
Extrusion coating was carried out at 0° C. and a line take-up speed of 80 m/min to form a coating film with a thickness of 20 μm to obtain a multilayer packaging material. After corona treatment was performed on the terpolymer layer (layer A) of this multilayer packaging material at a line speed of 100 m/min, the heat sealability between the terpolymer layer (layer A) surface and the modified PET layer (layer F) surface was evaluated. The results are shown in Table 1. The seal strength shows a value sufficient for practical use.

Example 2 A line speed of 100 was applied to the terpolymer layer (layer A) or modified PET layer (layer F) of the multilayer packaging material in Example 1
Table 1 shows the results of evaluating the heat sealability between the terpolymer layer (A layer) surface and the modified PET layer (F layer) surface after corona treatment at m/min. The seal strength is dramatically improved compared to the case where the modified PET layer is not subjected to corona treatment.

Comparative Example 1 Low density polyethylene (LDPE,
Same configuration as Example 1 except that MFR=10) was used (LD
A multilayer packaging material of PE/paper/copolymer/Al/terpolymer/modified polyethylene terephthalate was obtained. The LDPE surface of this multilayer packaging material was lined at a line speed of 100 m/min.
Table 1 shows the results of evaluating the heat sealability between the LDPE surface and the modified PET surface after the corona treatment. The sealing strength is weak, and when used as a container, the sealing surface is easily damaged by impact such as dropping, making it unsatisfactory for practical use.

Comparative Example 2 LDPE surface or modified P of multilayer packaging material in Comparative Example 1
Table 1 shows the results of evaluating the heat sealability between the LDPE surface and the modified PET surface after corona treatment was performed on the ET layer surface at a line speed of 100 m/min. Although the sealing strength is improved compared to the case where the modified PET layer is not subjected to corona treatment, it is not strong enough for practical use.

[0018]

[Table 1]

[0019]

Effects of the Invention According to the present invention, it is possible to provide a paper container with high fragrance retention and high drop resistance. In particular, it can be widely applied to containers ranging from relatively small capacity containers to large capacity containers of 1 liter or more.

Claims (5)

[Claims] Claim 1: A layer of ethylene/unsaturated carboxylic acid/unsaturated ester copolymer is provided on one side of a paper layer serving as the base of the container, and an outermost layer is provided on the other side of the paper layer with copolymer components 3 to 3. A laminate for a paper container, characterized in that a layer is provided that is a modified polyethylene terephthalate layer containing 20 mol%. 2. The laminate according to claim 1, wherein a layer including a gas barrier layer is provided between the paper layer and the modified polyethylene terephthalate layer. 3. The laminate according to claim 1, wherein at least a portion of the surface of the ethylene/unsaturated carboxylic acid/unsaturated ester copolymer layer is corona treated. 4. The laminate according to claim 3, wherein at least a portion of the surface of the modified polyethylene terephthalate layer is corona treated. 5. A paper container formed from the laminate according to claim 1, which has a sealing surface of an ethylene/unsaturated carboxylic acid/unsaturated ester copolymer layer and a modified polyethylene terephthalate layer.