JPH0698677B2 - Blow molding simultaneous coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of coating another resin on the inner surface of a plastic blow molding.

Conventionally, in the case of coating another resin on the inner surface of a plastic blow molded product, a method has been employed in which the liquid paint is spray-applied from the inside of the molded product which is once blow molded and solidified.

However, in the above-mentioned method, after the completion of the coating operation of the liquid paint, a drying step is required as the next step, which requires a large-sized drying device, the heat energy consumed by the drying apparatus, the working time, the worker's wages, etc. It required a considerable amount of expense. The motive of the present invention was to save the above-mentioned various expenses and save heat energy.

An object of the present invention is to perform a resin coating operation on a plastic blow molding product, at the same time as the blow molding, to coat the powder resin on the inner surface thereof, thereby omitting the conventional liquid paint coating step and its drying step, thereby improving the production efficiency. It is to improve.

The gist of the present invention is to spray the powder resin onto the inner surface of the pre-formed parison during the blow molding process of the plastic until the parison expands due to the blowing of the compressed gas. In this method, the powder resin is melted and applied by the heat of the parison itself or the heat of the molded product itself after the blow molding.

The method according to the present invention has the following four timings. Hereinafter, each example will be described.

First timing. See Figures 1A and 1B.
With respect to the parison PA which is extruded from the cross head die CD of the extruder of the blow molding device and gradually descends downward, the powder resin Pd is sprayed (SP) from the nozzle 8 together with the spray gas As inside the parison PA. It is a thing. In this manner, the entire inner surface of the parison PA is lowered while being coated with an appropriate amount of the powder resin and reaches a certain position. After that, as in the past, the mold M has been waiting in a double-open state.
Blow molding is performed by closing A and AB and blowing the blowing gas Ab. However, in this process, the powder resin Pd evenly applied inside the parison as described above.
Part ₁ melts partly or entirely (depending on the melting point of the powdered resin and the heat temperature of the parison PA itself) due to the heat of the parison itself, and melts into a film on the inner surface of the parison PA. Alternatively, apply (Pd ₁ ) in a semi-molten state.
This molten or semi-molten film does not follow the expansion of the parison expansion step to be performed next, and the coating film does not break. Furthermore, even after completion of the blow molding, the molded product itself Due to the retained heat, the part of the semi-molten material further progresses to become a complete molten material, which is applied to the inside of the blow molded product B ₁ as a coating film having a uniform thickness.

Further, as described above, the powder resin absorbs the heat of the parison itself, the heat of the parison itself during the expansion process, and the heat of the molded product itself after completion of expansion, so that the blow molded product is cooled. . Rather, it accelerates the solidification of the molded product in blow molding and can be cited as a secondary effect. Because, originally, after blow molding, it is necessary to cool the blow molded product, and therefore the blowing gas Ab and the mold MA, MB are forcibly cooled. The cooling action of the blow-molded product due to melting promotes the forced cooling and contributes to the saving of heat energy.

Second timing. See FIG. It is the same as before until the parison descends and the mold closes. The different point is that the powder resin Pd is sprayed (SP ₂ ) at the same time as the blowing gas Ab. In this case, powder resin Pd
It is necessary to make the pressure of the spraying gas As higher than that of the blowing gas Ab. Depending on the situation, it is possible to perform blow molding with the spray gas As of the powder resin Pd, and in this case, the blowing gas Ab can be omitted. In any case, it is necessary to adjust the pressure balance of both gases. It is also possible to further add the spray of the powder resin within the same time as the spray of the powder resin, and before and after that, that is, before and / or after the ejection of the blowing gas Ab. In any case, it is necessary to take into consideration the size of blow molding, the thickness of the coating film, the thermal characteristics of the resin, and the like.

Third timing. See FIG. Compressed gas Ab
It is the same as before until the blowing of. The difference is that the powder resin Pd is spray-coated (SP ₃ ) after blow molding. At this timing, the powder resin can be applied more uniformly on the inner surface. However, since the temperature of the blow molded product is slightly lower than that of the second timing, the heat energy of the blow molded product itself is small. Therefore, for powder resin with high melting temperature,
It can be said that it is not suitable.

Fourth timing. This is a combination of the second and third timings. That is, the powder resin Pd is sprayed at the same time as the blowing gas Ab, and the spray application of the powder resin Pd is still continued even after the expansion of the parison PA is completed. It can be said that it is suitable when you want to make the coating film thicker.

There are advantages and disadvantages of each of the above four timings. When selecting them, the thermal characteristics of the resin and powder resin of the blow molded product, the thickness of the coating film, the size of the molded product, the equipment cycle, the blow molding It should be decided in consideration of various conditions such as device characteristics.

As described above, according to the method of the present invention, the resin coating work on the inside of the blow molded product of the plastic can be performed simultaneously with the blow molding, that is, in one step. It is not necessary to use two steps like the drying step, and not only these equipment and labor cost but also contribute to the saving of heat resources.

[Brief description of drawings]

FIG. 1A is a sectional explanatory view of coating the resin powder on the inner surface of the parison at the first timing according to the present invention. FIG. 1B is a sectional explanatory view of a blow molding state according to the same method. FIG. 2 is at a second timing according to the present invention. , Cross-sectional explanatory view of coating powder resin on the inner surface of the parison simultaneously with the blowing gas. FIG. 3 is a cross-sectional explanatory view of coating the powder resin on the inner surface of the molded product after the parison expands at the third timing according to the present invention. Explanation of main symbols 5 ... Compressed gas blowing pipe, 7 ... Powder resin and spray gas transport pipe, 8 ... Nozzle, Ab ... Blowing gas, As ... Spraying gas, Pd ... Powder Body resin

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B29L 22:00 4F

Claims (1)

[Claims] 1. In a plastic blow molding process,
Compressed gas (Ab) against the inner surface of the preformed parison
By spray coating the powder resin (Pd) until the parison expands due to blowing, the heat of the parison itself, the heat of the parison itself during expansion, or the heat of the molded product itself after the blow molding, A blow molding simultaneous coating method, characterized in that the powder resin is melt-coated.