JP2803213B2 - Sheet heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an apparatus for heating a sheet of thermoplastic material for plastic working.

[Prior art]

As means for heating and plasticizing a sheet of thermoplastic material typically for vacuum forming, there are various means such as an infrared lamp and an electric heater. May be preferred. For example, such a case is a case where a decorative sheet or a transfer sheet in which painting is performed at the same time as injection molding is preformed by vacuum forming prior to being put into an injection mold. The hot plate used for such a purpose usually has a heating source such as an electric heater placed on the back surface of a metal plate, so that the sheet is in close contact with the hot plate and the whole is uniformly heated. A number of fine holes are provided on the surface, and suction is performed under reduced pressure through the fine holes. In a hot plate of this type, when the sheet is brought into close contact with the surface by suction, if there is a portion where air remains, the heating cannot be performed uniformly, which hinders the heating. However, if the cycle cannot be performed quickly, the productivity is low. Further, it is not preferable that the presence of the pores leave traces of the pores on the molded article after vacuum forming. The conventional hot plate has not reached a level where these points are sufficiently satisfactory.

[Problems to be solved by the invention]

An object of the present invention is to solve the above-mentioned problems, and in a device for heating and plasticizing a sheet of a thermoplastic material, even if the pressure is rapidly reduced and absorbed, the sheet adheres to the surface without leaving air, and uniform heating is achieved. It is an object of the present invention to provide a device which can perform the above-mentioned process and furthermore, the trace of the suction pore does not substantially remain in the vacuum molded product.

[Means for Solving the Problems]

As shown in the drawing, the sheet heating apparatus of the present invention has a substantially planar surface (1), has a heating source (3) inside, and has a large number of pores (2) formed on the surface. ,
By suctioning through the pores under reduced pressure, a sheet of thermoplastic material is held in close contact with the surface, and in the meantime, heat is applied from the heating source to plasticize the sheet. / cm ² density, and the average surface roughness of the surface is 20 to 800 μm, preferably 20 to 200 μm
m is adjusted. In the figure, reference numeral (4) denotes an air runner for suction under reduced pressure. The pores are preferably formed to have a diameter of 0.3 to 0.6 mm.

[Operation]

As a result of studying the conditions under which air does not remain when a sheet of thermoplastic material is brought into close contact with the hot plate by vacuum suction, the inventors found that the distribution of the pores to be sucked and the roughness of the hot plate surface were reduced. I found something to choose properly. That is,
The presence of at least 0.1, and preferably one or more pores per cm ² of the surface reduces the risk of air remaining between the sheet and the sheet. When the hot platen surface is a mirror surface, air is easily trapped between the sheet and the sheet, which is not sufficiently heated, whereas a rough surface allows air to flow through a channel provided by unevenness. There is no worry that air will be trapped. To ensure this effect, the surface roughness should be 20μ.
It was found that it would be better if m or more. When the roughness is too large, the sheet and the hot platen surface do not completely adhere to each other, the thermal conductivity varies depending on the location, the sheet temperature does not increase uniformly, or the sheet is formed according to the unevenness of the hot platen surface, It may interfere with vacuum forming. Of course, there are many cases where it is difficult to transfer the unevenness of the hot plate to the sheet. In consideration of these points, the upper limit of Arasa is set to 800 μm. The thickness of the decorative sheet used for injection painting is usually 25 ~
To heat a sheet of this thickness, Arasa up to 200 μm is suitable. The unevenness in the range of 20 to 800 μm can be formed by subjecting a metal plate to processing such as hairline processing, sandblasting, or etching. On the other hand, in order to leave no trace of pores on the sheet that has been suctioned and heat plasticized, the number of pores is preferably small. The upper limit of 2.5 pieces / cm ² was set from this viewpoint. The smaller the pore size, the smaller the traces left on the molded product are inconspicuous, but it is better that the air can easily pass through in order to realize quick suction adhesion.
I chose mm.

【Example】

A SUS304 stainless steel plate was subjected to sandblasting to be processed into a rough surface having an average arasa of 100 μm and a maximum of 200 μm. A hot plate with a 0.4 mm diameter hole was provided in a zigzag pattern at a pitch of 10 mm on both the top and bottom and the left and right sides.
The size of the hot plate is 29 cm × 20 cm, and the hole starts from 10 mm from the edge both vertically and horizontally, so the area of the hole is 28 cm
× 19 cm = 532 cm ² , the number of holes is 28 in one row, 19 columns and 27 in one row
The total of 18 rows of 10 pieces is 1018 pieces, the density is 1.91 pieces / cm ²
It is. This hot plate was used for the production of a molded article which is painted simultaneously with injection molding, as represented by the method for producing a painted and synthetic resin molded article described in Japanese Patent Publication No. 50-19132. In other words, when the decorative sheet for painting is preformed by vacuum molding using the injection molding die cavity, the decorative sheet drawn out from the winding roll is sucked into this hot platen, heated and plasticized. While moving the hot platen on the cavity side of the opened injection mold while moving it, it is shifted by moving, the vacuum side is applied to the cavity side after vacuum suction,
In this cycle, the hot platen is pulled up by vacuum forming, the injection mold is closed, and injection molding is performed.

【The invention's effect】

The heating device of the present invention is used when heating a sheet of a thermoplastic material for plastic working such as vacuum forming, and air is left between the hot platen and the sheet when suction is performed under reduced pressure. It can adhere quickly and can perform uniform heating quickly. Moreover, the suction holes and the unevenness of the hot platen surface are not transferred to the plasticized sheet, so that a beautiful molded product is obtained.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show the structure of the sheet heating apparatus of the present invention, FIG. 1 is a plan view showing the inside of the sheet heating device with a part cut away, FIG. FIG. 3 is an enlarged view of a part of FIG. DESCRIPTION OF SYMBOLS 1 ... Surface 2 ... Pore 3 ... Heating source 4 ... Air runner

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B29C 51 / 42,51 / 18-51/26 B29C 33/42

Claims (2)

(57) [Claims] 1. A sheet of thermoplastic material having a substantially planar surface, a heating source inside, and a large number of pores formed on the surface. In the apparatus for plasticizing the sheet by applying heat from the above-mentioned heating source while holding it in close contact with
A sheet heating apparatus characterized in that the pores are provided at a density of 0.1 to 2.5 / cm ² and the surface roughness is adjusted to an average of 20 to 800 μm. 2. The sheet heating apparatus according to claim 1, wherein said fine holes have a diameter of 0.3 to 0.6 mm.