PROCESS FOR THE PRODUCTION OF HOLLOW PLASTIC ARTICLES BY ROTATIONAL MOLDING POLYMERIC COMPOUNDS IN A ROTOMOLD

Abstract

The present invention relates to a process for the production of hollow plastic articles in a rotational molding process as well as to hollow plastic articles made by such a process, in particular to a process for the production of hollow plastic articles which exhibit a colored surface exhibiting striking pearlescent or metallic effects.

Claims

1. Process for the production of hollow plastic articles by rotational molding polymeric compounds in a rotomold, characterized by the following steps: A) forming a colored outer shell of a hollow plastic article in a stationery open rotomold having an inner surface, by applying a colored polymer particulate composition comprising a first polymer and coloring pigments to the inner surface of the rotomold, B) charging a rotomolding polymer composition comprising a second polymer into the rotomold, C) closing the rotomold, and D) processing a rotomolding procedure by rotating the rotomold, thereby forming an inner layer of the hollow plastic article.

2. Process for the production of hollow plastic articles according to claim 1, wherein the inner surface of the rotomold in step A) exhibits a temperature which is at or above the glass transition temperature of the first polymer.

3. Process according to claim 1 or 2, wherein the colored polymer particulate composition in step A) comprises platelet-shaped effect pigments as coloring pigments.

4. Process according to one or more of claims 1 to 3, wherein the colored polymer particulate composition in step A) additionally comprises additives and/or further non platelet-shaped coloring pigments.

5. Process according to claim 3, wherein the platelet-shaped effect pigments are selected from the group consisting of metal effect pigments, pearlescent pigments and interference pigments.

6. Process according to one or more of claims 1 to 5, wherein the colored polymer particulate composition in step A) is applied to the inner surface of the rotomold by means of a spraying process.

7. Process according to claim 6, wherein the spraying process is executed by means of a powder coating gun.

8. Process according to one or more of claims 1 to 7, wherein the first polymer is composed of one or more selected from the group consisting of polyethylenes, polyvinylchlorides, polycarbonates, nylons, polypropylenes, polystyrenes, polyurethanes, epoxy resins and phenolic resins, or of mixtures or copolymers of two or more of these polymers.

9. Process according to one or more of claims 1 to 8, wherein the first polymer and the second polymer are of the same chemical composition.

10. Process according to one or more of claims 1 to 9, wherein the rotomolding procedure in step D) is carried out at a temperature of the rotomold at or above the glass transition temperature of the second polymer.

11. Hollow article being composed of a colored outer shell and an inner layer which are inseparably connected to each other, wherein the hollow article is produced by a process according to one or more of claims 1 to 10.

12. Hollow article according to claim 11, wherein the colored outer shell comprises platelet-shaped effect pigments.

13. Hollow article according to claim 12, wherein the colored outer shell has an outer surface exhibiting a metallic or pearlescent optical behavior.

14. Hollow article according to one or more of claims 11 to 13, wherein the inner layer does not contain platelet-shaped effect pigments.

15. Hollow article according to one or more of claims 10 to 14, wherein the hollow article is a tank, a means for transportation, a container, a toy or a leisure article, a product for materials handling, a product for the marine industry, a medical product or an industrial product.

Description

EXAMPLE 1

[0090] An open 2 part metal rotomold is pre-heated to a temperature of about 200 C. in a common oven.

[0091] A mixture of 5% by weight of a pearl pigment (Iriodin 305 Solar Gold, Product of Merck KGaA, Germany), 0.2% by weight of an inorganic coloring pigment (Phthalocyanine Blue, product of Clariant, Germany) and 94.8% by weight of a standard polyethylene powder is dry blended and filled into a standard powder coating gun.

[0092] Both halves of the hot rotomold are removed from the oven and hung in a powder coating spray booth. A mask or a tape is applied onto the flanges of the open halves of the rotomold.

[0093] Afterwards, the inside surface of the pre-heated rotomold halves is sprayed by means of the powder coating gun as long as the rotomold halves are still hot with the dry blend composition to build a skin on the entire inner surface that will melt on contact with the rotomold inner surface and a plastic outer shell that exhibits a pearly appearance of the golden interference pigment as well as the blue color of the inorganic coloring pigment is created.

[0094] The mold is then be filled with an uncolored rotomolding grade polyethylene (Novapol TR-0735-U Hexene MDPE, product of NOVA Chemicals, Canada).

[0095] Afterwards, the mask or tape is removed from the flange and the rotomold is closed and bolt together.

[0096] After the rotomold is closed, a usual rotomolding procedure is started, comprising heating the rotomold to about 200 C., rotating the rotomold in a usual manner and cooling the rotomold while further having it rotated, until the inner layer of the hollow plastic article is created. After appropriate cooling, the ready hollow plastic particle may be removed from the open rotomold. Since the inorganic coloring pigment contained in the outer shell applies an opaque appearance thereto, the colorless inner layer of the hollow plastic article may not be observed when the outer surface of the product is evaluated. Instead, the blue color of the inorganic coloring pigment as well as the golden pearlescent effect which is due to the content and the proper surface orientation of the platelet-shaped pearlescent pigment in the outer shell may be observed.

EXAMPLE 2

[0097] An open 2 part metal rotomold is pre-heated to a temperature of about 200 C. at targeted areas of the inner surface thereof by flame treatment of the corresponding areas.

[0098] A mixture of 2% by weight an interference pearl pigment (Pyrisma T 30-23 Color Space Blue, product of Merck KGaA, Germany) and 98% by weight of a polyethylene powder (Novapol TR-0735-U Hexene MDPE, product of NOVA Chemicals, Canada) is dry blended and filled into a standard powder coating gun.

[0099] Both halves of the hot rotomold are hung in a powder coating spray booth immediately after the heat treatment. A mask or a tape is applied onto the flanges of the open halves of the rotomold.

[0100] Afterwards, the inside surface of the pre-heated rotomold halves is sprayed by means of the powder coating gun with the dry blend composition, whereby a skin is built only at the pre-heated areas of the inner surface of the rotomold that will melt on contact with these parts of the rotomold inner surface and a transparent layer that exhibits a soft pearly appearance and the bluish interference color of the interference pearl pigment is created on the targeted areas of the inner surface of the rotomold when the rotomold is cooled.

[0101] The mold is then be filled with an colored rotomolding grade polyethylene (Novapol TR-0735-U Hexene MDPE, product of NOVA Chemicals, Canada) containing 0.2% by weight, based on the weight of the mixture of polyethylene and pigment, of a red colored absorption pigment. Afterwards, the mask or tape is removed from the flange and the rotomold is closed and bolt together.

[0102] Subsequently, a usual rotomolding procedure is started, comprising heating the rotomold to a temperature of about 200 C., rotating the rotomold in a usual manner and cooling the rotomold while further having it rotated, until the inner layer of the hollow plastic article is created. After appropriate cooling, the ready hollow plastic particle may be removed from the open rotomold.

[0103] The resulting hollow plastic article exhibits on the targeted areas of the exterior surface thereof a pearlescent appearance with a bluish interference color, whereas the red color of the coloring pigment contained in the inner layer of the resulting hollow article may be observed throughout the exterior surface of the resulting product, at the targeted areas mixed with the blue interference color and the pearly gloss of the interference pigment.