JP6277678B2 - Paper cup manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a paper cup having a barrier property.

Containers provided with a barrier property to paper cups are widely used for foods that dislike moisture or want to protect their flavors, such as snacks, rice confectionery, chocolate, and candy.
Or it is widely used also as a cup for liquids, and a cup for drinks.

Japanese Patent Laid-Open No. 10-53243

As one means for imparting barrier properties to a paper cup, a method of laminating a film obtained by depositing an inorganic compound on a paper base material is known. (Japanese Patent Laid-Open No. 10-53243)
However, the vapor-deposited layer of the inorganic compound is easy to crack on the one hand because it is transparent and has very few incineration residues, and has a problem of cracking and lowering the barrier property when molding a paper cup or container.
In addition, in-line coating with a coating agent with barrier properties is also conceivable, but in general gravure coating, since the surface shape of the coated surface is affected by the uneven shape of the substrate surface, This may cause processing defects and may make the barrier property unstable.
An object of the present invention is to provide a paper cup having a high barrier property and excellent moldability and post-processing suitability.

As a means for solving the above problems, the invention according to claim 1, the surface of the paper substrate, coating the aqueous polyurethane resin alone or an aqueous polyurethane resin, polyvinyl alcohol, isocyanate, a coating agent made of an inorganic mineral A method for manufacturing a paper cup molded using a base paper cup made of paper ,
A method for producing a paper cup , characterized in that the coating is filled with irregularities on the surface of a substrate to be coated with a coating agent using a Mayer bar method, and further smoothed to obtain a smooth surface .

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  According to the first aspect of the present invention, since a method of applying a coating agent containing a water-soluble polymer using a coating method is used as means for forming a barrier layer, compared to a barrier layer formed by vapor deposition of an inorganic compound. A cup base paper excellent in flexibility can be obtained, and a paper cup excellent in barrier properties can be obtained without causing cracks even when a paper cup is molded.

Further, according to the invention described in claim 1 , compared to the case where the coating is performed by a technique such as gravure coating, the coating surface in which the barrier layer is smooth without being affected by the unevenness of the base material by the coating of the Mayer bar system. Thus, it is a production method capable of realizing a paper cup excellent in stable barrier properties, moldability and post-processing suitability.

It is a cross-sectional schematic diagram of one embodiment of the layer constitution of the paper cup according to the present invention. It is a cross-sectional schematic diagram of one reference aspect of the laminated constitution of the paper cup which concerns on this invention. It is a cross-sectional schematic diagram of the coating layer by a transfer system. It is a cross-sectional schematic diagram of the coating layer by a Mayer bar system.

Details of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of one embodiment of a paper cup according to the present invention.
First, the paper substrate (3) is provided with a printing layer (2) by printing a pattern or the like using a printing machine.
Next, a barrier layer (5) is provided by coating the surface opposite to the printed surface.
If the coating is carried out on a printing press, the paper substrate can be reversed and the barrier layer (5) can be formed by coating inline on the surface opposite to the printing surface.
Alternatively, the coating can be performed as a separate process using a coating machine.
Or it can also carry out using a coating unit on the extruder of resin at the next process.
After coating, a polyethylene layer (1) is provided on the printed layer (2) and a polyethylene layer (6) is provided on the barrier layer (5) to complete a paper cup base paper (10).
The polyethylene layer (1) and the polyethylene layer (6) are provided using a resin extruder.

FIG. 2 is a schematic cross-sectional view of one reference embodiment of a paper cup according to the present invention.
In this case, a printed layer (2) is provided on the paper substrate (3), and a polyethylene layer (4) is provided on the surface opposite to the printed layer (2) by an extruder, and then the barrier is coated. Layer (5) is formed.
The coating can be performed using a coating machine after providing the polyethylene layer (4), or can be performed using a coating unit on a resin extruder in the next step.
After coating, as in the case of FIG. 1, a polyethylene layer (1) and a polyethylene layer (6) are provided to complete a paper cup base paper (10).

FIG. 3 is a schematic cross-sectional view of a coating layer formed by a transfer method.
The present invention is characterized in that a barrier layer is formed by applying a coating agent having a barrier property, rather than laminating a film on which an inorganic compound is deposited to provide a barrier property.
When laminating a film deposited with an inorganic compound, the deposited layer of the inorganic compound is easily broken, and at the same time, the film must be bonded in a separate process, which is disadvantageous in terms of cost. .

In the case of coating, if a printing unit or an extruder is equipped with a coating unit, an in-line barrier layer can be formed, which is preferable from the viewpoint of productivity.
However, in the case of gravure coating that is generally used, the surface shape of the coating surface is affected by the surface irregularity shape of the substrate to be coated (7) and lacks surface flatness. When a thin part is formed on the convex part of (7), the barrier property is destabilized, and there is a possibility that suitability may be impaired in post-processing.
Gravure coating is a system in which a certain amount of coating agent is supplied to the surface of a gravure plate and transferred to a substrate (7) to be coated.
In the case of a transfer-type coating layer (8) obtained by gravure coating, the coating layer is affected by the surface of the substrate to be coated, and the unevenness is reproduced along the surface shape of the substrate to be coated. It is inevitable that the smoothness and the uniformity of the film thickness are impaired.

FIG. 4 is a schematic sectional view of a coating layer by the Mayer bar method.
The Mayer bar method is a coating method in which a certain amount of coating agent is applied to the substrate to be coated with a roll, and then the excess coating agent is scraped off while smoothing the surface with a bar called a Mayer bar. .
The effect of the Mayer bar is that the unevenness of the surface of the substrate to be coated is filled with a coating agent and further smoothed to obtain a smooth surface.
In the Mayer bar type coating layer (9), the surface of the coating layer (9) can be smooth without being affected by the irregularities of the surface of the substrate (7) to be coated. The coating amount can be increased as compared with.
Since the necessary coating amount is ensured and the surface of the coating layer (9) is smooth, the barrier performance is stabilized, and at the same time, processing defects and yields can be improved in a subsequent process.

As a coating agent for the purpose of imparting barrier properties, an aqueous polyurethane resin alone or a solution containing an aqueous polyurethane resin, polyvinyl alcohol, isocyanate, and an inorganic mineral is used.
As the inorganic mineral, for example, montmorillonite, layered mica and the like can be used.

Prior to coating, in order to improve the wettability of the substrate surface to be coated and to improve adhesion, an anchor coat layer is provided in advance on the coating surface of the paper substrate when coating directly on the paper substrate. In the case of coating via the polyethylene layer (4) as in the case of FIG. 2, the surface of the polyethylene layer (4) may be subjected to corona treatment and then coated.
In order to provide a sufficient barrier property, the coating amount of the coating agent is preferably 2.5 g / m ² or more in terms of the coating amount after the coating agent is dried.

<Example 1>
After printing on the outer surface of paper having a basis weight of 260 g, the other surface, that is, the surface that becomes the inner surface of the container, is coated with aqueous polyurethane resin using a # 6 Meyer bar, and then coated on the printed surface side by 40 μm. A paper cup base paper was prepared by extruding 60 μm of polyethylene onto the surface side.
WPB341 manufactured by Mitsui Chemicals was used as the aqueous polyurethane resin.
The coating amount after drying was 2.63 g / m ² .
Using this material, a fan-shaped side material and a circular bottom material were punched out, and a container was prepared using a cup molding machine.
The created container is a frustoconical paper cup having a diameter of 81.1 mm, an overall height of 89.4 mm, a bottom height of 9 mm, and a container taper of 4.8 °.
The produced paper cup was sealed with a material having a structure of (polyethylene terephthalate 12 μm / aluminum foil 20 μm / polyethylene film 40 μm), and the oxygen permeability per package was measured by the Mocon method, 0.24 cc / kg. / Day.

<Comparative Example 1>
After printing on the outer surface side of the paper having a basis weight of 260 g, the other surface, that is, the surface that becomes the inner surface of the container is subjected to gravure coating with a 200 L 20 μm gravure plate, and then 40 μm to the printed surface side, the coated surface 60 μm polyethylene was extruded and applied to the side to prepare a paper cup base paper.
WPB341 manufactured by Mitsui Chemicals was used as the aqueous polyurethane resin.
The coating amount after drying was 2.47 g / m ² .
Using this material, a fan-shaped side material and a circular bottom material were punched out, and a container was created using a cup molding machine in the same manner as in the example.
In the same manner as in the example, after sealing the produced paper cup using a material having a structure of (polyethylene terephthalate 12 μm / aluminum foil 20 μm / polyethylene film 40 μm), the oxygen permeability per package was measured by the Mocon method. It was 1.27 cc / pg. / Day.

(Evaluation results)
As a result of comparing the coating amount of the coating layer and the oxygen permeability per package in the example and the comparative example, the coating amount is small in the comparative example, and the oxygen permeability per package is greatly inferior.
From this result, it was verified that the coating by the Meyer bar method is clearly superior in the barrier performance of the finished paper cup compared with the coating by the gravure coating.

DESCRIPTION OF SYMBOLS 1 ... Polyethylene layer 2 ... Print layer 3 ... Paper base material 4 ... Polyethylene layer 5 ... Barrier layer 6 ... Polyethylene layer 7 ... Coated substrate 8 ... Coating layer 9 by transfer method ... Coating layer 10 by Mayer bar method ... Base paper for paper cups

Claims (1)

On the surface of the paper substrate, the aqueous polyurethane resin alone or an aqueous polyurethane resin, polyvinyl alcohol, isocyanate, a molded process for producing paper cups with coated paper cup base paper coating agent comprising an inorganic mineral,
A method for producing a paper cup , characterized in that the coating is filled with irregularities on the surface of a substrate to be coated with a coating agent using a Mayer bar method, and further smoothed to obtain a smooth surface .

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