JP2000335559A - Paper container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the low temperature sealability and the mechanical strength, and to eliminate the transfer of the resin odor to a content, and the defective filling of the resin by providing a paper layer and an inner layer consisting of the blend of a straight-chain low-density polyethylene polymerized using a single site catalyst and a low density polyethylene. SOLUTION: A paper container 1 is formed of hollow prismatic shape having a roof-shaped top part 3 and a flat bottom part 2. A container body is formed of a laminate body comprising an inner layer 11, a paper layer 12 and an outer layer 13. At least the inner layer is formed by blending a straight-chain low- density polyethylene polymerized using a single site catalyst at the ratio of, for example, 80/20. The low temperature sealability and the mechanical strength of the paper container 1 can be improved, the defective resin filling, and the resin odor transfer to the content can be eliminated in the heat seal process, and the productivity can be improved due to the excellent low temperature sealability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paper container capable of containing liquids such as milk and juice.

[0002]

2. Description of the Related Art Conventionally, a paper container for liquid has been constituted by a laminated material in which a heat seal layer made of polyolefin, for example, low density polyethylene, is used as an inner layer, and a paper, a printed layer, a protective layer and the like are stacked on the outer layer. Are often used. However, low-density polyethylene is not good in transparency and mechanical strength of the film,
There was a smell of resin odor, and there was still room for improvement in the low-temperature sealing property.

[0003] For these reasons, in recent years, conventional polyolefins have been polymerized using a single-site catalyst, for example, ethylene polymerized using a single-site catalyst as described in JP-A-7-148895. −
Attempts have been made to substitute α-olefin copolymers. When a polyolefin polymerized using a single-site catalyst is used, the mechanical strength is improved as compared with the case where a conventional polyolefin is used, and the smell of resin odor is not transferred. Further, since the low-temperature sealing property and the hot tack property are improved, the productivity is improved. However, in the heat sealing process of the paper container, especially in the top and bottom sealing processes of the paper container, there is often a time lag from the heating to the pressure bonding. There was a problem that defects occurred.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, has good low-temperature sealability and mechanical strength, has little transfer of resinous odor to contents, and has a high heat resistance. It is an object of the present invention to provide an improved paper container that exhibits good sealing properties in a sealing step and does not cause poor resin filling.

[0005]

SUMMARY OF THE INVENTION The present invention provides a paper container having a paper layer and an inner layer consisting essentially of a blend of linear low density polyethylene and low density polyethylene polymerized using a single site catalyst. .

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In order to improve the heat-sealing property of a paper container using linear low-density polyethylene polymerized using a single-site catalyst and to improve resin filling failure,
Diligent research was conducted.

[0007] Linear low-density polyethylene polymerized using a single-site catalyst has a narrow composition distribution and molecular weight distribution, a thin crystal lamella, and a large number of tie molecules. For this reason, it is possible to lower the melting point by reducing the density, and a film using this is excellent in low-temperature sealability. Also, the hot tack and mechanical properties of the film are better than other low density polyethylenes.

[0008] The linear low-density polyethylene polymerized using the single-site catalyst has almost no raw material odor peculiar to resin as compared with other low-density polyethylenes, and is used as the innermost layer of a package. However, there is little odor transfer in the contents.

However, when a paper container is formed by using only a linear low-density polyethylene polymerized using the single-site catalyst as a heat seal layer, a resin filling defect at a bottom portion occurs. Poor resin embedding, for example, when forming the bottom portion of a paper container, by folding the sealing pieces and bonding them together, a step occurs between the sealing pieces, and the molten resin does not sufficiently flow between the steps. To happen. In addition, poor adhesion often occurs when the top portion of the paper container is folded and sealed. This means that, even once bonded, by the time the molten resin solidifies,
Due to the repulsion of the paper, a peeling force is applied to the bonded portion, which is generated. It is considered that the resin embedding failure at the bottom portion and the adhesion failure at the top portion are caused by the melt flow rate, melt tension, and melt viscosity of the resin.

[0010] The melt flow rate is higher for linear low density polyethylene polymerized using a single site catalyst than for low density polyethylene, but the melt tension is higher for low density polyethylene. This is because, when the gap is filled with the molten low-density polyethylene by heating and pressing, when a strong peeling force is applied to the gap, the linear low-density polymerized by using a single-site catalyst is lower than the low-density polyethylene. This means that high density polyethylene is easier to escape.

At low shear rates, the apparent melt viscosity of linear low-density polyethylene polymerized using a single-site catalyst is smaller, and at high shear rates, the apparent melt viscosity is lower than that of a single-site catalyst. Chain low density polyethylene is larger. This indicates that when the shear rate applied to the molten resin is high, the linear low-density polyethylene polymerized using the single-site catalyst is difficult to flow, so that the resin filling is poor.

Therefore, increasing the melt tension of the linear low-density polyethylene polymerized using a single-site catalyst and improving the fluidity of the linear low-density polyethylene is effective in improving resin filling failure. .

[0013] From the above, the present inventors have found that a blend of linear low-density polyethylene and low-density polyethylene polymerized using a single-site catalyst is used as the inner layer of a paper container. Was.

By blending a low-density polyethylene with a linear low-density polyethylene polymerized using a single-site catalyst, the melt viscosity is reduced, but the linear low-density polyethylene polymerized using a single-site catalyst is used. Melt tension can be increased while maintaining low-temperature sealing properties, hot tack properties and mechanical properties to some extent. This makes it easy for low-density polyethylene to flow even if a force is applied in the direction of peeling off the sealed part due to the repulsion of the paper after heating and pressure-bonding, and even if a step occurs in the sealed part. Since it is difficult to escape from the resin, the resin filling becomes good.

The blend ratio of the linear low-density polyethylene and the low-density polyethylene polymerized using a single-site catalyst is preferably 90/10 to 70/30, and more preferably 80/20.

In the paper container of the present invention, the resin thus obtained is used as a heat seal layer. In addition, a blend of linear low-density polyethylene and low-density polyethylene polymerized using a single-site catalyst includes, for example, an antioxidant, an ultraviolet absorber, an antistatic agent, an antiblocking agent, a lubricant, a flame retardant, Additives such as inorganic and organic fillers, dyes, and pigments can be added.

Here, the single site catalyst refers to a catalyst comprising a metallocene transition metal compound and an organoaluminum compound.

Examples of the metallocene-based transition metal compound include a transition metal element selected from Group IVB, such as titanium, zirconium, and hafnium, as well as a cyclopentadienyl group, a substituted cyclopentadienyl group, an indenyl group, a tetrahydroindenyl group, A substituted tetrahydroindenyl group, a fluoronyl group, or a substituted fluorenyl group has 1 to 2 bonds, or a bond obtained by linking two of these groups by a covalent bond, and further includes a hydrogen atom,
Has ligands such as oxygen atom, halogen atom, alkyl atom, alkoxy atom, aryl group, acetylacetonate group, carbonyl group, nitrogen molecule, oxygen molecule, Lewis base, substituent containing silicon atom, unsaturated hydrocarbon, etc. There are things.

Further, as the organoaluminum compound,
Examples thereof include alkyl aluminum, and chain or cyclic aluminoxane.

Here, as the alkyl aluminum,
Examples include triethylaluminum, triisobutylaluminum, dimethylaluminum chloride, diethylaluminum chloride, methylaluminum dichloride, ethylaluminum dichloride, dimethylaluminum fluoride, diisobutylaluminum hydride, diethylaluminum hydride, and ethylaluminum sesquichloride.

The chain or cyclic aluminoxane is produced by bringing alkyl aluminum into contact with water.

Further, the single-site catalyst can be supported on an inorganic substance carrier such as silica gel, zeolite, and diatomaceous earth.

Examples of the polymerization method include bulk polymerization, solution polymerization, suspension polymerization, gas phase polymerization and the like.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a view showing an embodiment of the paper container of the present invention. FIG. 2 is a view showing a state in which a part of the paper container shown in FIG. 1 is cut out, and FIG. 3 is a partially enlarged view of a cross section 10 in FIG.

As shown in FIG. 1, the paper container 1 is a hollow rectangular cylindrical container having a roof-shaped top 3 and a flat bottom 2 and is called a Gabel-top type. This paper container 1
As shown in FIG. 3, for example, is constituted by a laminate composed of an inner layer 11, a paper layer 12, and an outer layer 13. Among the inner layer 11 and the outer layer 13, at least the inner layer of the paper container 1 is made of a linear low-density polyethylene and a low-density polyethylene polymerized using a single-site catalyst, for example, 80/2.
It consists of blended at a ratio of 0.

FIG. 4 shows another embodiment of the laminate constituting the paper container of the present invention.

The laminate 20 is used for a paper container having a printed layer 18 formed on the outer surface, and includes an inner layer 17, a paper layer 12, and an outer layer 19. The inner layer 17 is made of a blend (80/20) of linear low-density polyethylene and low-density polyethylene polymerized using a single-site catalyst.

FIG. 5 shows still another embodiment of the laminate constituting the paper container of the present invention. This laminate 30
Is used for a paper container having a barrier property, and includes an inner layer 17, a silicon oxide deposited layer 33, a polyester layer 32,
Low density polyethylene layer 34, low density polyethylene layer 3
5, a paper layer 12, and an outer layer 19 are sequentially laminated. The silicon oxide deposited layer 33 is deposited on the polyester layer 32 in advance. Inner layer 17 and silicon oxide deposited layer 33
Preferably, an anchor layer is provided between the polyester layer 32 and the low-density polyethylene layer 34 in order to improve adhesion.

The inner layer 17 is made of a blend (80/20) of linear low-density polyethylene and low-density polyethylene polymerized using a single-site catalyst, and is used as an inner layer of a paper container. The anchor layer is made of, for example, a urethane resin or a resin composed of a saturated polyester / isocyanate compound, and is used to improve the adhesion between the silicon oxide-deposited polyester layer 32 and the inner layer 17 or the low-density polyethylene layer 34. Low density polyethylene layer 3
4 and the low-density polyethylene layer 35 are provided for bonding between the layers and for securing the overall rigidity.

Using the laminate having the structure shown in FIG. 5, a paper container as shown in FIG. 1 was formed, and the obtained paper container was subjected to an impact resistance test.

The structure of the used laminate is specifically as follows.

Laminate 1: low density polyethylene 20 μm /
320 g / m ^{2 of} paper / 40 μm of low-density polyethylene / 15 μm of low-density polyethylene / anchor layer / 12 μm of silicon oxide-deposited polyester layer / blend of linear low-density polyethylene and low-density polyethylene polymerized using a single-site catalyst (80/20 Here, the polyester layer on which the silicon oxide was deposited was arranged so that the silicon oxide deposited layer faced the low-density polyethylene blend layer side as the inner layer.

The linear low-density polyethylene polymerized using a single-site catalyst was SP-2040 manufactured by Mitsui Petrochemical Co., and the low-density polyethylene used was M-401PC manufactured by Mitsui Petrochemical Co., Ltd.

As a comparison, a low-density polyethylene (Mitsui Petrochemical Co., Ltd., M) was used instead of a layer composed of a blend (80/20) of a linear low-density polyethylene and a low-density polyethylene polymerized using a single-site catalyst. -4
[01PC] A similar paper container was formed using the laminate 2 formed by laminating 60 µm layers, and an impact resistance test was similarly performed.

Drop test: Dropping was performed at a maximum of 20 times from a height of 100 cm, and the number of bursts was examined. Table 1 shows the results.

[0037]

[Table 1]

As shown in Table 1, the drop test shows that the paper container according to the present invention has excellent impact resistance.

Compression test As another impact resistance test, a paper container made of the laminate 1 and a paper container made of the laminate 2 for comparison were each placed in the longitudinal direction.
It was compressed in the transverse direction and in another transverse direction and its strength was examined.
FIGS. 6 to 8 show the compression directions. In the figure, reference numeral 50 denotes a compression means. The test results are shown in Tables 2 to 4.

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

As is clear from Tables 2 to 4,
The paper container of the present invention has much better impact resistance than a conventional paper container using low-density polyethylene.

The shape of the paper container of the present invention is not limited to a goebel top type paper container as shown in FIG.
FIG. 9 is a view showing another embodiment of the present invention, and FIG. 10 is a view schematically showing a cross section of FIG. As shown in FIG.
The paper container of the present invention may have a cylindrical shape. This paper container can be formed using, for example, a laminate as shown in FIG. As shown in FIG. 10, as shown in FIG. 10, a cylindrical container body 120 formed by curving a sheet made of a laminated body into a cylindrical shape, and sealing the matched both sides to each other, A shallow cup-shaped bottom member 130 provided in one of the two openings, and a take-out port 111 provided in the other opening and having a shallow cup-shaped shape and having a bottom portion removably sealed with a seal member 140. And a lid member 110 having the same. The open ends of the container body 120 each have folded pieces 121 and 122 folded inward from the ends by a predetermined length, and a gap between the folded piece 122 and the main body 120 includes a side wall of the bottom member 130. 132 is inserted and the folded piece 121 is inserted.
In the gap between the main body 120 and the side wall 112 of the lid member 110,
Are inserted and sealed by heating.

In this container, the sealing member 140 is composed of the knob 1
The contents can be taken out from the take-out opening 111 by peeling off with the trigger 41. Also, this container has good low-temperature sealability and mechanical strength,
The filling of the resin was sufficient as in the case of the Gebel-top type paper container, and the transfer of the resin odor to the contents was small.

As described above, the paper container of the present invention has good resin filling and excellent impact resistance.

[0047]

According to the present invention, the low-temperature sealing property and the mechanical strength are good, the resin filling defect does not occur in the heat sealing step, and the odor of resin odor is less transferred to the contents. A quality paper container is obtained.

Further, the paper container of the present invention has good productivity because of its excellent low-temperature sealing property.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a paper container of the present invention.

FIG. 2 is a view showing a state in which a part of the paper container shown in FIG. 2 is cut out.

FIG. 3 is a partially enlarged view of section 10 of FIG. 3;

FIG. 4 is a view showing another embodiment of the laminate constituting the paper container of the present invention.

FIG. 5 is a view showing still another embodiment of the laminate constituting the paper container of the present invention.

FIG. 6 is a diagram showing a compression direction in a compression test.

FIG. 7 is a diagram showing a compression direction in a compression test.

FIG. 8 is a view showing a compression direction in a compression test.

FIG. 9 is a perspective view showing another embodiment of the paper container of the present invention.

FIG. 10 is a view schematically showing a longitudinal section of FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Paper container 2 ... Bottom part 3 ... Top part 10 ... Cross section 11, 17 ... Inner layer 13, 19 ... Outer layer 12 ... Paper layer 18 ... Printing layer 20, 30 ... Laminate 32 ... Silicon oxide vapor-deposited polyester layer 34, 35 ... Low density Polyethylene layer

Claims (2)

[Claims] 1. A paper container having a paper layer and an inner layer consisting essentially of a blend of linear low density polyethylene and low density polyethylene polymerized using a single site catalyst. 2. The paper container according to claim 1, wherein the low-density polyethylene is obtained by a high-pressure polymerization method.