JP5169246B2 - Foamed paper cup manufacturing method and foamed paper cup - Google Patents

Description

  The present invention relates to a paper cup, and more particularly, to a foamed paper cup having excellent heat insulation, such as a hot beverage paper cup and an instant food paper cup, and a method for producing the same.

  As the heat insulating cups, many synthetic resins having foaming properties, particularly those made of expanded polystyrene resin as a raw material, are often used. In addition, a paper cup with a corrugated shape around the entire circumference of the paper cup, or a double structure with an inner and outer structure with a space between two layers, and both sides of the paper made of polyethylene There is a foamed polyethylene resin layer on the surface of a paper cup using a material laminated with a resin layer.

  However, in the above-mentioned heat insulating cup, the cup made of polystyrene foam resin is manufactured by molding a resin added with a foaming agent and is excellent in heat insulating properties, but it is difficult to treat as waste after use, and the environment There is a problem in terms of correspondence. In addition, there are disadvantages such as low surface smoothness and poor printability.

  In addition, paper cups with corrugated paper around the entire circumference are excellent in terms of heat insulation and environmental friendliness, but in manufacturing, the process of making the corrugated part corrugated and winding it around the body is required However, there are technical difficulties and the cost is high.

  In addition, a cup having a double structure of an inner cup and an outer cup uses a smooth material for the outer cup and has features such as good printability, but is expensive in material and manufacturing.

  These heat-insulating cups have heat-insulating properties, printability, easy disposal as waste after use, simple manufacturing processes, and low cost. It is a paper cup made by foaming.

  This foamed paper cup is disclosed in Patent Document 1, which is a method for producing an irregular uneven surface without an embossing roll, that is, a polyethylene resin processed paper is heated by heating a polyethylene resin processed paper and the vapor pressure of moisture contained in the paper. Is applied to the formation of a heat insulating layer of a paper cup.

  For example, Patent Document 2 discloses an application to a paper cup as a paper container composed of a barrel member and a bottom plate member in which a foamed layer of a thermoplastic synthetic resin film is coated or laminated on one side wall surface of the barrel member. . Further, in Patent Document 3 and Patent Document 4, a thick foam layer is provided at the printed portion as a heat-insulating paper container having a printed layer of colored ink between the polyolefin-based resin layer and the base material layer mainly composed of paper. A manufacturing method is disclosed.

  A thermoplastic resin foam layer, a printing layer, a base material layer mainly composed of paper, and a thermoplastic resin layer are provided at least from the outer surface side, and between the thermoplastic resin foam layer and the base material layer mainly composed of paper. Patent Document 5 proposes a foamed paper cup that forms a transparent varnish layer before foaming.

However, the resin foam, which is the trace of moisture escape from the paper, depends on several factors, such as the resin temperature during polyethylene extrusion, the surface properties of the paper, and the nip pressure during lamination. The degree and uniformity of foaming vary.
Japanese Patent Publication No. 48-32283 JP-A-57-110439 Japanese Patent Laid-Open No. 5-50536 Japanese Patent Laid-Open No. 7-232774 JP-A-9-142435

  As described above, paper cups with a foamed polyethylene resin layer have excellent heat insulation, workability, and ease of use, but the conventional methods have not been sufficiently foamed. It was difficult to obtain a foam layer that was uniform overall and had a sufficient heat insulating effect. On the other hand, in the present invention, it is an object to provide a method for producing a foamed paper cup having a foamed layer that is sufficiently foamed, uniform, entirely uniform, and has a sufficient heat insulating effect, and a foamed paper cup thereby obtained. It is.

The present invention provides a foamed paper cup comprising a body portion and a bottom portion provided with a foam layer of a thermoplastic resin, a base material layer mainly composed of paper, and a thermoplastic resin layer at least from the outer surface side. In the method, fine embossing is performed on one side of the base material layer mainly composed of paper before coating of the thermoplastic resin that becomes the outer surface side foam layer ,
The foaming is characterized in that the embossing is formed at a uniform pitch with a concave portion having a fixed shape having a depth in a range of 20 μm to 200 μm and a diameter in a range of 50 μm to 300 μm. It is a manufacturing method of a paper cup.

The invention according to claim 2 is characterized in that the thermoplastic resin used as the outer foam layer is a low density polyethylene resin having an MFR in the range of 1 to 15 and a melting point in the range of 90 ° C to 130 ° C. 1. A method for producing a foamed paper cup according to 1 .

A third aspect of the present invention is a foamed paper cup manufactured by the method for manufacturing a foamed paper cup according to the first or second aspect.

  According to the present invention, by performing embossing on the side coated with the thermoplastic resin layer that becomes the foam layer of the base material layer mainly composed of paper, insufficient foaming due to variations in the surface of the base material, uneven foaming, Overall non-uniform foaming can be eliminated. As a result, it is possible to obtain a foamed paper cup having a foam layer that has a sufficient heat insulating effect and an anti-slip effect.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an example of a foamed paper cup. The foamed paper cup A is composed of a body part C and a bottom part D. FIG. 2 is an enlarged cross-sectional view of a part B of the body portion C of the foamed paper cup A of FIG. The material composition of the body C is that the base paper 1 is used as a base material, the moisture in the paper is evaporated from the uniformly embossed recesses on the surface side, and the surface thermoplastic resin layer is foamed by the force of the vapor pressure. There is a low-density polyethylene (LDPE) foam layer 4 containing uniform bubbles 3, and the inside is covered with a high-density polyethylene (HDPE) layer 2. An aluminum foil layer or the like may be provided between the cup base paper 1 and the HDPE layer 2 in order to improve barrier properties.

  The manufacturing method of the foamed paper cup of this invention is demonstrated below using a schematic diagram.

  FIG. 5 is a schematic cross-sectional view schematically showing variations in the shape of the surface of the cup base paper 1 as a base material used for the foamed paper cup. FIG. 6 is a schematic cross-sectional view schematically showing the surface shape after embossing to form a uniform recess in the cup base paper 1. FIG. 7 is a schematic cross-sectional view schematically showing the cross-sectional shape of the body B before foaming in which the LDPE layer 4 and the HDPE layer 2 are provided on the surface of the cup base paper 1 of FIG. FIG. 2 shows a state of the body part B after being heated and foamed from the state of FIG.

  The feature of the foamed paper cup manufacturing method of the present invention is that in the heat insulating foamed cup coated on both sides with a thermoplastic resin, the surface of the base paper of the cup base paper used as the base material is coated with fine embossing in advance. By forming a fine uniform space between the front side resin layer and the surface of the cup base paper, bubbles having a stable size are formed in the front side resin layer during heating and foaming.

  3 and 4 are schematic cross-sectional views schematically showing the characteristics after foaming due to the surface shape of the cup base paper. FIG. 3 is a schematic cross-sectional view after foaming when a cup base paper having a high surface smoothness is used. Since the gap between the surface of the cup base paper and the resin layer is small, the bubbles after foaming are small, and the thickness of the foam layer This is an example in which the heat insulation is reduced because of a small amount. FIG. 4 is a schematic cross-sectional view after foaming when using a cup base paper with varying surface smoothness. Since the gap between the surface of the cup base paper and the resin layer varies, the size of the bubbles after foaming This is an example in which the thickness of the foamed layer varies and the thickness of the foamed layer becomes non-uniform so that the heat insulating property varies and the surface shape is uneven, making it difficult to handle.

  Based on the above matters, one embodiment of the manufacturing method of the present invention will be described.

(1) A fine depression is made on the entire surface with an embossing roll with fine embossing on the front side of the cup base paper (outside of the cup).

The cup base paper preferably has a basis weight in the range of 100 to 400 g / m ² in the production of a paper cup. Moreover, there may be a barrier layer for protecting the contents on the back side of the cup base paper (inside the cup), and there may be a decorative layer such as printing on the front side (outside of the cup). Although the embossing method is arbitrary, the press embossing with the embossing roll which can perform continuous pressurization is desirable.

  In order to obtain a uniform foamed layer, the shape of the embossing roll must have regular fine protrusions. The embossing depth is desirably in the range of 20 μm to 200 μm. When the emboss depth is less than 20 μm, the original surface shape is partially left, and the effect of obtaining a uniform foamed layer is reduced. If the embossing depth is more than 200 μm, individual bubbles become large at the time of foaming, and not only a uniform foamed layer is formed but also the cup base paper surface and the LDPE layer are often peeled off.

Moreover, it is desirable that the size of the opening of the embossed recess is in the range of 50 μm to 300 μm. If the size of the opening of the recess is less than 50 μm, not only the bubbles at the time of foaming are small, but also affected by the surface shape of the original paper and the conditions of extrusion coating of LDPE. If the size of the opening of the recess is more than 300 μm, the bubbles at the time of foaming become large and the cosmetic properties are lowered. As described above, a cup base paper having a surface with concave portions regularly arranged on the surface as schematically shown in FIG. 6 is obtained.
(2) Extrusion coating of LDPE with a certain thickness is performed on the embossed surface of the cup base paper with fine embossing on the front side (outside of the cup). HDPE is extrusion coated on the back side.

  The polyethylene resin used for the foamed layer in the present invention is laminated on the front side (the embossed side) of the base paper 1 of the base material. The lamination method includes an extrusion coating method in which the resin is melted and applied, or a laminating method in which the film is bonded, but in order to stably exhibit the effects of the present invention, it is melted with heat. An extrusion coating method in which the resin thus formed is coated from the die onto the surface of the extruded paper is preferable.

  The thickness of the polyethylene resin layer 4 on the surface to be the foam layer is usually in the range of 15 to 100 μm, but is not particularly limited. However, in order to form the foam layer, it is necessary to select an appropriate range according to the characteristics of the resin. Even if it is too thick or too thin, it becomes difficult to foam.

  The LDPE resin used for the polyethylene resin layer 4 on the surface to be the foam layer needs to have thermal characteristics in the following range. That is, the melt flow rate (MFR) of the resin is in the range of 1 to 15 as measured by the method of JIS K7210, and the melting point is in the range of 90 to 130 ° C. as measured by the method of JIS K7121. is there.

  When the MFR of the LDPE resin is low, it is difficult to hold the bubbles and it is difficult to form a foamed layer. When the MFR is higher than 15, not only the extrusion is difficult but also the taste of the contents is deteriorated. Preferably it is the range of 4-8.

  The melting point of LDPE resin is determined by foam layer formation and content protection, but it is necessary to soften at 100 ° C or lower, which is the temperature at the time of foaming, that is, the temperature at which water contained in the base paper changes into water vapor at once. Therefore, the lower limit of the melting point is suitably 90 ° C. The upper limit of the melting point is mainly determined by the relationship with the melting point of the HDPE resin used for the HDPE layer on the back surface (inside the cup). If the melting point is 130 ° C. or higher, the melting point of the HDPE resin on the back surface must be higher. It becomes difficult to mold the cup.

  There are no particular restrictions on the extrusion conditions for the LDPE resin, and the extrusion temperature, which is a normal extrusion condition, is approximately 280 ° C to 360 ° C directly under the die, and the nip pressure needs to be changed in particular to approximately 70% to 120% of the normal setting conditions. There is no.

  On the other hand, the thickness of the HDPE layer 2 on the back surface is not particularly limited. However, in order to foam only the surface without foaming the back surface, it is necessary to use a thermoplastic resin having a higher softening point than the LDPE resin on the surface in order to prevent evaporation of water vapor from the back surface.

  In this way, as shown schematically in cross section in FIG. 7, a cup in which an LDPE layer is laminated leaving substantially constant voids in concave portions regularly arranged on the surface of the cup base paper, and an HDPE layer is laminated on the back surface. A base paper is obtained.

(3) Next, after pattern printing is performed on the laminated cup base paper obtained as described above, it is processed into a blank plate in the shape of the body portion of the paper cup by punching, and is formed into a paper cup together with the bottom portion. Laminated cup base paper can also be used at the bottom.

  This paper cup can be manufactured by a general paper cup molding machine. By heating the molded paper cup, the water in the paper evaporates, and the vapor pressure and the thermal expansion of the air act on it, and the surface is ordered as schematically shown in FIG. The LDPE layer foams based on the voids of the concave portions arranged in a regular manner to generate a uniform foamed structure.

As a heating method, hot air, infrared rays, far infrared rays, microwaves, high frequencies, or the like can be used. There are a method of heating by standing or a method of heating while feeding by a conveyor. In the case of hot air drying in an oven, the heating conditions are based on a hot air temperature of 120 ° C. and a heating time of 6 minutes, but the range is not particularly limited.

Next, the present invention will be described more specifically with reference to examples.
<Example 1>
A fine embossing roll with a surface of 300 g / m ^{2 with} a smoothness of 60 seconds (Oken type) and a highly smooth cup base paper with a convex pitch of 300 μm in both vertical and horizontal directions and a convex height of 100 μm. And pressure embossing.
The embossed surface of this cup base paper is extrusion coated with an LDPE resin of MFR7 at a melting point of 108 ° C. and a thickness of 70 μm. A laminated cup base paper having a thickness of 450 μm was prepared. The laminated cup base paper was blanked for printing by punching after printing, and a paper cup having a height of 110 mm, a diameter of 95 mm, and a bottom diameter of 65 mm was prepared by a paper cup molding machine. Furthermore, this paper cup was heated for 6 minutes in a 120 degreeC hot air dryer, and the foamed paper cup which has a foam layer on the surface was obtained.

The following items were measured for the foamed paper cups thus prepared. The results are shown in Table 1.
・ Total thickness of base cup paper including foam layer: by thickness meter ・ Insulation of cup body: surface temperature after boiling for 3 minutes in the cup ・ Smoothness after foaming: King after foaming Polishing smoothness / Beauty after foaming: Visual confirmation of surface irregularity <Example 2>
A foamed paper cup was prepared in the same manner as in Example 1 except that a low-smooth cup base paper having a smoothness of 30 seconds was used. The same items as in Example 1 were measured for the foamed paper cup thus prepared. The results are shown in Table 1.
<Comparative Example 1>
A foamed paper cup was prepared in the same manner as in Example 1 except that the surface of the cup base paper was not embossed. The same items as in Example 1 were measured for the foamed paper cup thus prepared. The results are shown in Table 1.
<Comparative example 2>
A foamed paper cup was prepared in the same manner as in Example 2 except that the surface of the cup base paper was not embossed. The same items as in Example 1 were measured for the foamed paper cup thus prepared. The results are shown in Table 1.

From the results shown in Table 1, in the case of Example 1 and Example 2 prepared by the production method of the present invention, a fine emboss is coated on the surface with a polyethylene resin, regardless of whether the surface smoothness of the cup base paper is high or low. By carrying out before, a foamed paper cup having the same foaming thickness and heat insulation, smoothness of the surface after foaming, heat insulation performance having a degree of unevenness of the surface after foaming and cosmetics was obtained.
On the other hand, in the case of the comparative example in which fine embossing was not performed on the surface of the cup base paper, the smoothness of the surface of the cup base paper is too high in Comparative Example 1, so that the surface smoothness and cosmetics after foaming are high. As a result, the thickness after foaming was insufficient and the heat insulation performance was clearly inferior. In Comparative Example 2, since the smoothness of the cup base paper surface was too low, the thickness after foaming was ensured, but the surface smoothness and cosmetic properties after foaming were low and the heat insulation performance was clearly inferior.

According to the production method of the present invention, it is possible to produce a foamed paper cup that has excellent heat insulation and is excellent in appearance and handling without being affected by variations in the surface properties of the cup base paper, using conventional processes. .

Cross-sectional schematic diagram of an example of foamed paper cup Sectional enlarged view of an example of a paper cup of the present invention (foaming after uniform embossing on the paper surface) Cross-sectional enlarged view of an example of a paper cup (when the paper surface is smooth) An enlarged section of an example of a paper cup (when the paper surface is uneven) An enlarged cross-sectional view of an example of a paper cup base paper (before embossing the base paper) An enlarged cross-sectional view of an example of a paper cup base paper (after embossing a base paper cup) Cross-sectional enlarged view of an example of a paper cup base paper (after double-sided PE coating)

Explanation of symbols

A ... Paper cup B ... Side wall C ... Body D ... Bottom 1 ... Cup base paper 2 ... HDPE layer 3 ... Bubble 4 ... LDPE (foam) layer 5 ... Base paper outer surface

Claims (3)

At least from the outer surface side, a foam layer of thermoplastic resin, a base material layer mainly composed of paper, and a base material layer mainly composed of paper in a method for producing a foamed paper cup comprising a body portion and a bottom portion provided with a thermoplastic resin layer. On one side of this, fine embossing is performed before the coating of the thermoplastic resin that becomes the outer foam layer ,
The foaming is characterized in that the embossing is formed at a uniform pitch with a concave portion having a fixed shape having a depth in a range of 20 μm to 200 μm and a diameter in a range of 50 μm to 300 μm. Paper cup manufacturing method. 2. The foamed paper cup according to claim 1, wherein the thermoplastic resin serving as the outer foam layer is a low-density polyethylene resin having an MFR in the range of 1 to 15 and a melting point in the range of 90 ° C. to 130 ° C. 3. Production method. Foamed paper cups, characterized in that it is manufactured by the manufacturing method of the foamed paper cup according to claim 1 or 2.