JP2002127273A - Manufacturing method of paper container with excellent water resistance - Google Patents

Abstract

(57) [Problem] To provide a method for producing a paper container excellent in biodegradability and excellent in water resistance which does not require a long drying time and a large amount of energy and does not increase the cost of a mold. SOLUTION: A pulp fiber 22 and a thermoplastic resin powder 24 and / or a thermoplastic resin fiber made of a biodegradable plastic are mixed on an inner surface of a concave mold 10, or the respective powders are alternately electrostatic powder. Coating spray gun 30
This is a method for producing a paper container 2 having excellent water resistance, which is spray-coated and laminated by heating and pressurized and solidified by a press mold 40 having a convex shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a paper tray formed from pulp and the like, and more particularly to the production of a dry, environment-friendly, highly accurate, water-resistant paper container. About the method.

[0002]

2. Description of the Related Art In view of the frequent occurrence of environmental problems related to the increase of waste in recent years, plastic containers and metal containers have been used instead.
Paper containers, such as paper trays and paper cups, are widely used in the beverage, food, and toiletry product fields because they contribute to resource and energy savings and are easy to recycle and incinerate when disposed. It is becoming.

Conventionally, as a method of forming a pulp mold (formed body) such as a paper tray, paper (including waste paper) is dissolved in water to form a pulp slurry (liquid), which is adapted to the intended use. It is obtained by casting it on a mold with various shapes of wire mesh or a water-permeable ceramic mold, draining it by vacuum papermaking (molding), and evaporating the remaining water by heating. Products that require precision are obtained by after-pressing.

However, this wet vacuum papermaking (forming)
The method requires a large amount of energy and time for draining and heating and evaporating, and the wastewater treatment to avoid secondary pollution of the wastewater discharged by this draining (dehydration) requires a great deal of cost including its equipment. was there.

[0005] In order to solve the above problem,
For example, as disclosed in Japanese Unexamined Patent Publication No. Hei 7-124914, a small piece of paper, powdered starch and water are simultaneously sprayed on the inner surface of an open mold, and the mold is closed and then solidified by heating. There is a dry manufacturing method.

[0006] However, this dry production method requires an expensive mold having a large number of degassing holes, and requires a long drying time because a large amount of water is used together with fine paper chips and powdered starch for spraying. There is a fear that time and a large amount of energy are required, and there is a fear that powdered starch may generate mold and the like. Particularly, as a food container, there is a problem in terms of hygiene.

[0007] On the other hand, these paper containers are provided with water resistance so as to be used for beverage cups and lunch trays. For example, a polyethylene film is laminated on the inner and outer surfaces of a paper cup, or a paper tray is used. It is obtained by laminating a crystalline polyester film (C-PET), a polypropylene film, a polyethylene film, or the like on the inner surface of the container body by air pressure or vacuum forming. Alternatively, it may be obtained by coating an inner or outer surface of a paper cup with an emulsion or dispersion of polyethylene or polypropylene resin powder and drying by heating.

[0008]

However, in the prior art of paper cups and paper trays, since a film such as polyethylene or polyester is first laminated on the inner surface of the container, the biodegradability of the paper itself is high. Impair,
It cannot contribute to the reduction of environmental load during disposal, and in particular, it is not possible to precisely laminate a small part of the inner surface of the container by pressurized air forming or vacuum forming on a paper tray, etc., or it becomes thin at the corner of the inner surface of the container, The yield of the product is reduced, and the waste of the film used for air pressure molding and vacuum molding (the part not used due to chamfering) is increased.
There is a problem that the material cost increases.

The present invention solves the above-mentioned problems of the prior art, and it is an object of the present invention to provide a long drying time, a large amount of drying energy, and a more expensive wastewater treatment facility as in the prior art. It is applicable to beverage paper cups and paper trays that do not require mold, do not increase the mold cost and material cost, and do not impair the biodegradability of the paper itself, that is, consider the environmental conservation related to disposal It is an object of the present invention to provide a method for producing a paper container having excellent water resistance.

[0010]

In order to achieve the above-mentioned objects, the present invention first provides a method for producing a pulp fiber and a thermoplastic resin powder and / or a thermoplastic resin on an inner surface of a concave mold. The fibers are mixed with each other, or each of the above is alternately spray-coated and laminated by a spray gun of an electrostatic powder coating method, and then heated and heated by a convex press mold fitted onto the inner surface of the mold from above. This is a method for producing a paper container excellent in water resistance characterized by being solidified by pressurization.

According to the first aspect of the present invention, since the paper tray or the like is formed by the electrostatic powder coating method using no water, drying time and energy can be saved, and drainage treatment is required. Provide a method for manufacturing paper containers that are environmentally friendly, and furthermore, by using a simple mold that does not require degassing holes, the mold cost does not increase, and the container has water resistance. When applying, thermoplastic resin powder and / or
Or it can be obtained by mixing thermoplastic resin fibers with pulp fibers, or by laminating these two fibers and powders alternately and finely evenly to the corners of the container by spraying by electrostatic powder coating method. Compared to imparting water resistance by air pressure molding or vacuum molding, the product yield is improved, and the unused thermoplastic resin powder that is sprayed and not applied can be collected and reused, so material cost It is possible to provide a method for producing a paper container excellent in water resistance which is not bulky.

According to a second aspect of the present invention, there is provided the method for producing a paper container excellent in water resistance according to the first aspect, wherein the thermoplastic resin is a biodegradable plastic.

According to the second aspect of the present invention, when water resistance is given to the paper container, the thermoplastic resin is made of a biodegradable plastic, so that the biodegradability of the paper itself is not impaired. It is possible to provide a method for producing a paper container excellent in water resistance in consideration of environmental conservation.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. The method for producing a paper container excellent in water resistance of the present invention, as shown in the schematic side sectional view of FIG.
For example, a pulp fiber (22) and a thermoplastic resin powder (24) mixed on the inner surface of a concave mold (10) are coated with two spray guns by, for example, an electrostatic powder coating method called a tribocharge process. Spray coating along the flow of air (P) from (30) to form a laminate (21) of a paper container made of pulp fiber and thermoplastic resin as shown in FIG. 1 (b). As shown in FIG. 1 (c), a convex press die (40) fitted from above onto the inner surface of the concave die (10) heats and pressurizes and solidifies it to make it water resistant. This is a method for producing an excellent paper container (2).

Alternatively, for example, a pulp fiber and a thermoplastic resin powder (not shown) are alternately spray-coated and laminated to form a paper container laminate (20) made of pulp fiber as shown in FIG. 2 (a). Then, a film (27) made of a thermoplastic resin is laminated thereon, and as shown in FIG. 2 (b), a convex press die (see FIG. 2 (b)) fitted on the inner surface of the concave die (10). 40) A method for producing the paper container (2) having excellent water resistance by heating and pressurizing to solidify.
Further, as shown in the schematic side sectional view of FIG. 3, a laminate (20) of a paper container made of this pulp fiber and a film (27) made of a thermoplastic resin are alternately formed by two layers. The paper container (2) having excellent properties can also be obtained.

Instead of the above-mentioned thermoplastic resin powder, thermoplastic resin fibers can be used, or thermoplastic resin fibers can be mixed with the thermoplastic resin powder or sprayed alternately.

Further, the present invention relates to a method for producing a paper container (2) having excellent water resistance, wherein the thermoplastic resin is a biodegradable plastic, and the obtained paper container (2) comprises:
The present invention provides a method for producing a paper container (2) which does not impair the biodegradability of the paper itself, that is, which is excellent in water resistance in consideration of environmental protection related to disposal.

The electrostatic powder coating method suitable for the method for producing a paper container excellent in water resistance of the present invention includes, for example, the above-mentioned tribo (meaning of friction) charging process and a general corona charging system. In the former tribocharge process, powder particles (referred to as pulp fiber powder and thermoplastic resin powder in the present invention) are triboelectrically charged in a specially processed tube before being discharged from a spray gun. The powder particles travel along the flow of air after being discharged from the spray gun, and are applied to the substrate (in the present invention, the inner surface of the concave mold (10) or the pulp fiber laminate (20), the thermoplastic resin). (In some cases, a resin film (27)).

Also, the latter corona charge system
A high voltage of -30 to 100 kV is applied to the corona pin at the tip of the spray gun from the high pressure generator, and a corona discharge occurs from the corona pin, and the object to be coated (in the present invention, the inner surface of the concave mold (10) or the pulp). An electric field is created between the fiber laminate (20) and a paper container main body which is a film (27) made of a thermoplastic resin, and powder particles passing through the electric field (the pulp in the present invention) Fiber powder and thermoplastic resin powder) are charged and adhered to an object to be coated.

The heating temperature by the convex press mold (40) is set to a laminate (21) composed of a mixture of pulp fibers and a thermoplastic resin powder as a biodegradable plastic as shown in FIG. 1 (b). As shown in FIG. 2 (a), in the case of the laminate (20) composed of only pulp fibers and the laminate (27) composed of a thermoplastic resin alternately laminated, there is a difference depending on the thermoplastic resin. About 200 ° C. is preferable.

The materials used in the method for producing the paper container (2) having excellent water resistance of the present invention will be described below. First, as the pulp fiber used in the method for producing a water-resistant paper container of the present invention, for example, a fiber obtained by pulverizing various kinds of paper (including waste paper but cannot be used for food-related containers from a sanitary point of view) with a pulverizer. Pulp fibers with a length of 500 μm or less, or pulp in the papermaking or pulp sheet process, mechanical pulp obtained by mechanically crushing wood, chemical pulp obtained by adding chemicals to wood chips to elute lignin, and disintegrating into fibrous form, or Using semi-chemical pulp, which is a combination of removal of lignin by a chemical and mechanical defibration, and further pulverized into pulp fibers having a fiber length of 500 μm or less.

A paper container in which an additive (powder) is mixed with the above pulp fiber may be used. As the additive, for example, a sizing agent for preventing bleeding of ink or the like (a rosin-based resin acid maleic acid resin). , To add opacity
(Eg, calcium carbonate, white carbon, etc.), and powders such as polyacrylamide as a dry paper strength enhancer and melamine formaldehyde resin for improving wet strength, which can be appropriately selected according to the use of the paper container.

The biodegradable plastic, which is a thermoplastic resin used in the method for producing the paper container (2) having excellent water resistance according to the present invention, includes polyester-based biodegradable plastics. Polyester is used. Examples of the aliphatic polyester include a resin containing lactic acid as a main component, an aliphatic polyester produced from a microorganism having a hydroxyalkanoate unit, and an aliphatic polyester produced by chemical synthesis.

The lactic acid-based resin is preferably lactic acid having a number average molecular weight of 10,000 to 100,000, and may be a copolymer of lactic acid and oxycarboxylic acid. The lactic acid may be D-lactic acid, L-lactic acid or a mixture thereof. Further, as the oxycarboxylic acid, glycolic acid or 6-hydroxycaproic acid can be used.

The aliphatic polyester produced from the microorganism having the above hydroxyalkanoate unit includes 3-hydroxyvalerate, 3-hydroxybutyrate, 3-hydroxycaproate, 3-hydroxyheptanoate and the like. One or a mixture of two or more P (3HA) copolymers having various functional groups in the side chain can be used. As the aliphatic polyester obtained by chemical synthesis, the number average molecular weight is 10,10.
000 to 100,000 of the following resin represented by the following (Chemical formula 1), or 25,000 to 70,
000 or a mixture of these resins.

[0026]

Embedded image (Wherein m is the degree of polymerization, M is a number of 0 or 1 or more, R ₁ and R ₂
Is an alkylene group having 2 to 10 carbon atoms, a cyclotube group, or a cycloalkylene group, and R ₃ represents a di- or polyisocyanate residue.

[0027]

Embedded image (In the formula, m is the degree of polymerization. R ₁ and R ₂ represent an alkylene group having 2 to 10 carbon atoms, a cyclotube group, or a cycloalkylene group, but may be branched.)

In addition to the above aliphatic polyesters, aliphatic aromatic polyesters are used, and examples thereof include polybutylene adipate / terephthalate copolymer and modified polyethylene terephthalate.

The above-mentioned polyester-based biodegradable plastic is pulverized to form a laminate (21) or a film (27) of a paper container by an electrostatic powder coating method. The particle size is preferably about 2 to 3 μm from the viewpoint of suitability for charging and film formation.

[0030]

As described above, the present invention has the following effects. That is, pulp fiber powder and thermoplastic resin powder and / or thermoplastic resin fiber are mixed on the inner surface of the concave mold, or each is alternately spray-coated and laminated by a spray gun of an electrostatic powder coating method, A method for producing a paper container excellent in water resistance, characterized by heating and pressurizing with a convex press mold fitted onto the inner surface of the mold from above, thereby solidifying the paper container. Since the powder coating method is used, drying time and energy can be saved, and a method for manufacturing a water-resistant paper container that is environmentally friendly and does not require wastewater treatment is provided. By using a simple mold that does not require the above, a method for manufacturing a paper container excellent in water resistance that does not increase cost can be provided.

When imparting the water resistance, the thermoplastic resin powder and / or the thermoplastic resin fibers are mixed with the pulp fibers or alternately sprayed by the electrostatic powder coating method to precisely and uniformly reach the corners of the container. Since it is obtained by laminating, compared with the conventional method of imparting water resistance by compressed air or vacuum forming, the yield is improved, and the unused thermoplastic resin powder that is not coated can be collected and reused. Therefore, it is possible to provide a method for producing a paper container excellent in water resistance without increasing the material cost.

Further, when the paper container is provided with water resistance, the biodegradability of the paper itself is not impaired by using a thermoplastic resin as a biodegradable plastic, that is, consideration is given to environmental protection related to disposal. A method for producing a paper container excellent in water resistance can be provided.

Accordingly, the present invention relates to a method for producing a paper container such as a paper tray or a paper cup in consideration of environmental preservation relating to waste, particularly a paper cup for instant noodles or a drink or a box made of bento paper. As a method for producing a paper container having excellent water resistance, such as a method for producing a paper container, it has an excellent practical effect.

[Brief description of the drawings]

FIG. 1 is a schematic side sectional view illustrating an embodiment of a method for producing a paper container excellent in water resistance according to the present invention, and FIG. 1 (a) shows a state of application by an electrostatic powder coating method. FIG.
FIG. 4 is a view showing a coated laminate, and FIG. 4 (c) is a view showing a paper container obtained by heating and pressing.

FIG. 2 is a schematic side sectional view for explaining another embodiment of the method for producing a paper container excellent in water resistance according to the present invention, and (a).
FIG. 2 is a view showing a coated laminate, and FIG. 2B is a view showing a paper container obtained by heating and pressing.

FIG. 3 is a schematic cross-sectional side view illustrating another embodiment of the method for producing a paper container excellent in water resistance of the present invention, which is obtained by heating and applying pressure to a coated laminate. It is a figure which shows a paper container.

[Explanation of symbols]

2. Paper container excellent in water resistance 10) Concave mold 20> Laminated paper container made of pulp fiber 21> Laminated paper container made of pulp fiber and thermoplastic resin 22 {Pulp fiber 24} Thermoplastic resin powder 27> Coating made of thermoplastic resin 30> Spray gun 40> Convex press P> Air flow

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) B65D 25/14 ZBP B65D 1/00 BRQC F term (reference) 3E033 AA10 BA10 BA17 BB01 BB08 CA09 FA01 GA03 3E062 AB01 JA01 JA07 JB23 JC02 JD02 3E075 BA30 CA01 DC18 DC28 DC45 DC46 DE22 4D075 AA01 AA09 BB05Z BB26Z BB56Z CA38 DA19 DA29 DB02 DC41 EA17 EB07 EC22

Claims (2)

[Claims] A pulp fiber and a thermoplastic resin powder and / or a thermoplastic resin fiber are mixed or sprayed on the inner surface of a concave mold by a spray gun of an electrostatic powder coating method. A method for producing a paper container excellent in water resistance, comprising: laminating and laminating, and then heating and pressing with a convex press mold fitted onto the inner surface of the mold to solidify the laminate. 2. The method for producing a paper container excellent in water resistance according to claim 1, wherein said thermoplastic resin is a biodegradable plastic.