JPH01133777A - Printing method for rotationally molded product - Google Patents

Abstract

PURPOSE:To enable efficient and favorable printing on a rotationally molded product, by providing a main body of a metallic mold with through-hole parts, fitting a printing mold with a thermosetting printing ink applied thereto is fitted to the main body, thereby forming a metallic mold for rotational molding, and a polymeric material is rotationally molded by placing the material in the metallic mold. CONSTITUTION:A main body 1 if a metallic mold is provided with through-hole parts 2 in patterns for printing, whereas a printing plate 3 is provided with a coated film 4 of a thermosetting ink by applying the ink in patterns substantially coinciding with the through-hole parts 2. The printing mold 3 is coated thereon with a fluororesin for ensuring easy release of a printed part after molding. A polyethylene powder is placed in the mold 1, 3, and molding is conducted by operating a rotational molding machine in a heating furnace or the like. The polyethylene is melted to form a resin layer on the entire inner surface of the mold, and simultaneously, a straght-chain low-density polyethylene contained in the ink film 4 is also melted. Particularly, the low-density polyethylene is melted to form a quasi-interstitial high molecular weight network structure, so that a body comprising a polyethylene resin layer 7 and the ink film 4 adhered to each other is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method of printing a plastic rotomolded article.

(b) Prior Art Rotational molding is known as a method for molding thick, hollow plastic products (eg, polyethylene, polyvinyl chloride, polypropylene, etc.) and products with complex shapes. In this process, a powdered or liquid polymer material is placed in a mold, and the mold is rotated around two orthogonal axes in a heating furnace to press the material against all inner surfaces of the mold using centrifugal force. This is the way to do it.

Conventionally, printing on rotary molded products has been carried out by masking and printing after molding, or by screen printing.

(c) Problems to be Solved by the Invention However, rotomolded products are not easy to print because they have surface runout and sink marks. In particular, if the molded product has irregularities or a complicated shape, it is difficult to print without peeling off the printed surface. Furthermore, materials such as medium-density polyethylene and linear low-density polyethylene, which are often used in rotational molding, have a problem in that ink adhesion is poor, making it difficult to print on molded products.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a printing method that solves the above-mentioned problems and can perform good printing on rotary molded products with high work efficiency.

(d) Means for solving the problems The present invention forms a through hole in the mold body, and attaches a printing mold imprinted with thermosetting ink to be printed thereon to form a rotary molding mold, By placing a polymer material in this mold and rotationally molding it, printing can be performed simultaneously with molding.

(E) A printing mold on which a thermosetting ink is printed to form an ink coating is attached to the mold body in which a working hole is formed, and a polymer material is placed in this mold and rotationally molded while heating. The polymer material is melted and pressed against the inner surface of the mold by centrifugal force. At the same time, the linear low-density polyethylene in the thermosetting ink coating also melts and fuses with the resin, giving the molded article a non-peelable print.

(f) Example FIG. 1 shows a mold for a rotary molding machine, and the mold consists of a mold body 1 and a printing mold 3. Although not shown, the mold body 1 Printing mold 3 is attached with bolts. The mold body 1 has a through hole 2 formed in the shape to be printed, and the printing mold 3 is coated with thermosetting ink in a shape that roughly matches the through hole 2. A film 4 is formed on the surface of the printing mold 3 after molding.
The printed part is coated with fluororesin so that it can be easily peeled off.

In addition, thermosetting ink is a thermosetting clear material such as epoxy, melamine, urethane, polyester, etc. with a pigment concentration of 0.
1 to 5% by weight linear low density polyethylene powder, 10
When this thermosetting ink is applied to the printing mold 3, as shown in the cross-sectional view of FIG. Thermosetting ink coating 4 in which density polyethylene particles 6 are present
becomes.

After attaching the printing mold 3 to this mold body 1 so that the through hole 2 and the thermosetting ink coating 4 match, this mold (1
, 3), and when molded by operating a rotary molding machine in a heating furnace etc., as shown in Fig. 3,
The polyethylene melts to form a resin layer on the entire inner peripheral surface of the mold, and at the same time, the linear low-density polyethylene in the thermosetting ink coating 4 also becomes molten, and especially the linear low-density polyethylene melts. Since a quasi-interpenetrating polymer network structure is formed, the polyethylene resin N7 and the ink coating film 4 are in close contact with each other. After molding, the mold is cooled to room temperature and the mold is divided to obtain a rotationally molded product with printing applied to the convex portions of the molded product. The printed surface of this molded product is in close contact with the resin layer and will not peel off.

In the above embodiment, the through-hole part 2 and the thermosetting ink coating film 4 were of almost the same shape and were printed on the convex surface of the molded product. The size may be larger than the size of the printing part, and a convex part may be formed on the surface of the printing mold 3 corresponding to the through hole part 2, so that the printed part of the molded product is not a convex part but a flat surface. You may do so. Alternatively, the through holes 2 may be shaped to be printed, and a thermosetting ink coating may be formed all over the printing mold 3.

(G) Effects of the Invention As described above, according to the present invention, a through hole is formed in the mold body corresponding to the printed part of the molded product, and a thermosetting ink coating is to be printed on the through hole. A printing mold is attached to form a mold, a polymer material is placed in the mold and rotational molding is performed, and printing is performed at the same time as molding, making it possible to print rotationally molded products efficiently and easily, which is difficult to print conventionally. Moreover, good printing can be performed.

[Brief explanation of the drawings] Figure 1 is an exploded perspective view of a mold consisting of a mold body and a printing mold, Figure 2 is a sectional view of the printing mold, and Figure 3 is a partial cutaway of the printing part during molding. It is a cutaway enlarged sectional view. 1...Mold body, 2...Through hole part, 3...Printing mold,
4...Thermosetting ink coating film, 7...Resin layer. Figure 1! Figure 2 Figure 3

Claims (2)

[Claims] (1) A printing mold with a thermosetting ink film formed thereon is attached to the through-hole part of the mold body, which has a through-hole part corresponding to the part to be printed, to form a rotary molding mold. A printing method for rotationally molded products, which is characterized by printing at the same time as molding by placing a polymer material inside a mold and performing rotational molding. (2) In claim 1, the thermosetting ink coating film is a thermosetting clear film with a pigment concentration of 0.1 to 5.
1. A method for printing on rotary molded articles, comprising blending 10 to 50% by weight of linear low-density polyethylene powder.