JPH07148460A - Coating of food container made of polypropylene such as lunch box - Google Patents

Abstract

PURPOSE:To apply perfect surface coating to a food container made of polypropylene such as a lunch box by a reduced number of processes by utilizing corona discharge technique. CONSTITUTION:The surface to be coated of a molded food container made of polypropylene such as a lunch box is uniformly irradiated with corona discharge utilizing high frequency high voltage to be electrically and chemically activated to be enhanced in adhesiveness or printability. Thereafter, mixed coating of polypropylene exclusive coating and general urethane coating is applied to the activated surface to be coated by spray coating to perform surface coating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating a polypropylene food container such as a lunch box.

[0002]

2. Description of the Related Art Polypropylene is widely used as a material for food containers such as lunch boxes because it has excellent elasticity, is hard to break, is lightweight, and has excellent moldability and processability. As a method of coating a pattern or the like on the polypropylene food container molded product, a polypropylene film having a pattern or the like printed on a female die of a molding die is subjected to an electrostatic action, and the polypropylene as a material is applied to the female die by about 180 to A method of molding by pouring at a temperature of 190 ° C,
A method of welding a film on which a design or the like is silk-printed is known.

[0003]

By the way, in the former among those described in the prior art, since the film is also polypropylene, the adhesion with the same quality material is poor, and in some cases air may enter, and for many years. In use,
There is a problem that the film is peeled off, and also in the latter case, there is a problem that the film is easily peeled off and it is difficult to weld the film when the welding surface is uneven.

In order to solve these problems, the present inventors have first carried out a pretreatment by corona discharge,
Patent application for painting method for painting (Japanese Patent Application No. 4-15268)
No. 3), the present invention is a further improvement of the above painting method, and its purpose is to make it possible to reliably coat a polypropylene food container such as a lunch box with a few steps. It was done.

[0005]

[Means for Solving the Problems] To achieve this object, the present invention activates a coated surface of a polypropylene food container molding such as a lunch box by irradiating a corona discharge utilizing a high frequency high voltage. After being activated, the activated surface to be coated is subjected to coating treatment with a mixed coating of a polypropylene-specific coating and a general urethane coating.

[0006]

EXAMPLES Examples will be described with reference to the drawings.
FIG. 1 is a process diagram of the present coating method, and FIGS. 2 and 3 are process explanatory diagrams. In these diagrams, a food container such as a lunch box is obtained as an integrally molded product of polypropylene, and the polypropylene food container molded product 1 ( Hereinafter, this is simply referred to as the molded product 1.)
First, the surface 2 to be coated is subjected to corona discharge treatment. To further explain, the corona discharge means 1 utilizing high frequency high voltage
When 0, the corona discharge is uniformly irradiated, and the irradiation surface as the surface to be coated is electrically and chemically activated to improve the adhesiveness and printability.

In the illustrated embodiment, only the upper surface of the molded article 1 is the surface to be coated, and only the upper surface is irradiated with corona discharge. However, the entire outer surface of the molded article 1 or the entire inner and outer surfaces thereof are treated. In the case of applying the coating to the above, it is necessary to irradiate the entire surface to be coated with corona discharge through the discharge electrode of each mode to activate the entire surface.

Next, means 20 such as spray coating is known in which a mixed paint prepared by mixing a paint for exclusive use of polypropylene and a general urethane paint at a predetermined ratio on the activated surface to be painted 20.
Coating is applied to form a coating layer 3, and if necessary, a pattern is added, clear coating is applied, and then a drying process is performed at a temperature of about 80 ° C., whereby a series of coating steps is performed. Has been completed and is considered a finished product.

As described above, in the coating method according to the present invention, the coating treatment with the mixed coating of the polypropylene-only coating and the general urethane coating is performed through the corona discharge irradiation step on the coated surface. The irradiation, the coating on the irradiation surface, and the like are performed by a series of automatic continuous steps under automatic control.

[0010]

According to the present invention, the surface coating of a polypropylene food container molding such as a lunch box is pre-treated by irradiating the surface to be coated with corona discharge using high frequency and high voltage. Then, the irradiated surface is electrically and chemically activated to improve the adhesiveness and printability, and then a surface coating treatment such as spray coating is performed with a mixed paint of a polypropylene-specific paint and a general urethane paint. Therefore, the adhesion is strong and the coating is complete, and there is no peeling of the coating,
In terms of process, it is painted with a mixed paint of polyurethane special paint and general urethane paint.
Since it is not necessary to paint with a polyurethane-dedicated paint and then with a general urethane paint, the number of painting processes is reduced, and a high-quality polypropylene food container can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a process drawing of an example of a coating method according to the present invention.

FIG. 2 is a schematic explanatory diagram of a corona discharge treatment step.

FIG. 3 is a schematic explanatory diagram of a surface coating treatment step.

[Explanation of symbols]

 1 Polypropylene food container moldings such as lunch boxes 2 Surface to be coated 3 Coating layer 10 Corona discharge means 20 Coating means

Claims (1)

[Claims] 1. A coating material for polypropylene, which is prepared by irradiating a coated surface of a polypropylene food container molding such as a lunch box with corona discharge using a high frequency high voltage to activate the coated surface. A coating method for a polypropylene food container such as a lunch box, which is characterized in that a coating treatment is carried out with a mixed coating of a urethane paint for general use.