JPH07209219A - Method for detecting softened or fused state of thermoplastic resin sheet - Google Patents

Abstract

PURPOSE:To improve the external view and the moldability of proiduct by detecting the amount of sagging of a sheet continuously through a noncontact displacement measuring means. CONSTITUTION:A sheet (c) fed into a vacuum molding machine is thermally softened or fused at heater sections (a), (b) and fed to a mold. It is brought into tight contact with the mold by means of a plug and the vacuum and then it is cooled to be molded. Subsequently, it is by a trimming machine thus obtaining a product. Softened or fused state of the sheet (c) is estimated by measuring the behavior of sagging sheet (c) at the time of heating through a displacement measuring means. A hole (q) is made in the center of the lower heater (b) and a laser displacement sensor (e) is inserted into the hole (g) in order to measure the behavior of sagging sheet (c) using laser light. Since the softened or fused state of sheet (c) can be controlled optimally, the external view and the moldability of product can be improved significantly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects the amount of sagging of a sheet in so-called thermoforming, in which a sheet made of a thermoplastic resin is heated and softened or melted, and is shaped by a method such as vacuum forming or pressure forming. The present invention relates to a method for detecting a softened state or a melted state of the.

[0002]

2. Description of the Related Art Generally, a method of detecting a predetermined amount of sag of a sheet by a photoelectric tube or the like is widely used to control the process after heating the sheet, but it is gradually changing. The amount of sagging could not be obtained continuously. On the other hand, as a method of continuously detecting the amount of sag, a method described in Japanese Patent Publication No. 62-34057 is known, but this method is a mechanical detection method in which a softened or melted sheet is pressed into contact with a sensor. It is not an accurate measurement method.

Further, since the temperature of the sheet surface is lowered by the contact of the sensor, the sagging amount was evaluated to be small, and a molded product having a uniform wall thickness could not be obtained in the subsequent molding step.

[0004]

The present inventor has improved the shortcomings of the conventional methods as described above, and as a result of studying a detection method that can be used in a narrow installation space and is easy to measure a high temperature object, as a result, non-contact The inventors have found that the above object can be achieved by using a sensor, and have reached the present invention.

[0005]

Means for Solving the Problems That is, the present invention holds a sheet made of a thermoplastic resin, and heats the upper and lower surfaces of the sheet or one of them to bring them into a softened state or a molten state, and to increase the temperature. A method of detecting a softened state or a molten state of a thermoplastic resin sheet is characterized in that the amount of sagging of the sheet is continuously detected by a non-contact type displacement measuring means.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the flow of thermoforming, and is an example of forming a rolled sheet into a cup-shaped product.
The sheet supplied into the vacuum forming machine is sent to the mold when it is in a softened (or melted) state due to the heating of the heater section. Then, it is molded by bringing the plug and the vacuum into close contact with the mold and cooling. After that, the product is transferred to a trimming machine to remove excess burrs and becomes a product.

Examples of the thermoplastic resin in the present invention include polyolefin such as polypropylene. In the main molding, control of the softened (or melted) state by heating with a heater greatly affects the appearance and moldability of the product. Generally, in an insufficiently softened (or melted) state, it does not adhere to the mold, resulting in poor molding.

In an excessively softened (or melted) state, defects such as bridging, uneven thickness of products, and perforation occur. In the present invention, the softened (or melted) state of the sheet is estimated by measuring the sagging behavior of the sheet when heated by a displacement measuring means. For example, as shown in FIGS. There is a method of making a hole in the sheet and measuring the sagging behavior of the sheet by laser using a laser type displacement sensor through the hole.

FIG. 4 shows an example in which a conventional infrared radiation temperature sensor is installed above the upper heater and a laser displacement sensor is installed below the lower heater to improve the estimation accuracy of the softened (or melted) state of the sheet. Is. Examples of the displacement measuring means include a laser irradiation light type sensor, an ultrasonic type sensor and a video camera. It is preferable to use a visible light laser as the laser sensor because the irradiation point, that is, the measurement point can be easily confirmed.

Further, it is preferable from the viewpoint of installation space in which a laser projecting portion and a light receiving portion are integrated. As an example of the method of installing the sensor, as shown in FIGS. 2-3, the installation interval of the individual heaters in the lower heater of the thermoforming machine is adjusted, and a hole for projecting and receiving laser light is provided. It is desirable to install the sensor below. The displacement signal from the sensor passes through the converter and is output to the conventional indicator and recorder. It may also be used as a control signal for the shaping process.

[0011]

【Example】

(Example 1) Polypropylene (Mitsubishi Polypro 4100
M) sheet is used, the heater temperature is 400 ° C., and the measurement results are shown in FIG.
The optimum softened (or melted) state for forming the sheet is the maximum point at which the sagging returns (tensioning back), and this forming optimum point is shown in the figure.

[0012] As an industrial manufacturing method, it is desirable that the heating time, which is the optimum molding point, is used as the cycle.

[0013]

According to the present invention, in a so-called thermoforming in which a sheet made of a thermoplastic resin is heated to soften or melt it and is shaped by a method such as vacuum forming or pressure forming, the amount of sagging of the sheet after heating. Can be accurately and continuously detected, so that the softened (or melted) state of the sheet can be optimally controlled, and the appearance and moldability of the product can be remarkably improved.

[Brief description of drawings]

FIG. 1 shows an example of a thermoforming flow to which the method of the present invention is applied.

FIG. 2 is an example of a heater which is an example of a sheet heating method in the method of the present invention.

FIG. 3 is a plan view of the heater shown in FIG.

FIG. 4 is a diagram when an infrared radiation temperature sensor is also used in FIG.

FIG. 5 is a diagram relating to an example using the method of the present invention.

[Explanation of symbols] a heater (upper) b heater (lower) c seat d gripping tool e displacement sensor (laser displacement sensor) f individual heater g laser light passage hole h infrared radiation temperature sensor i signal converter j vacuum pump k special Feed chain clamp l type m plug n burr o product p trimming machine q vacuum forming machine r punching

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area B29L 7:00

Claims (3)

[Claims] 1. Holding a sheet made of a thermoplastic resin,
It is characterized in that the sheet is made into a softened state or a molten state by heating the upper and lower surfaces or one of the both sides, and the amount of sagging of the sheet accompanying a rise in temperature is continuously detected by a non-contact displacement measuring means. A method for detecting a softened state or a molten state of a thermoplastic resin sheet. 2. The displacement measuring means according to claim 1 is provided on at least one side of the upper and lower surfaces of the seat according to claim 1 in a direction perpendicular to the seat.
A method for detecting a softened state or a molten state of the thermoplastic resin sheet as described above. 3. A method for detecting a softened state or a molten state of a thermoplastic resin sheet, wherein a sensor by laser irradiation light or ultrasonic waves is used as the non-contact type measuring means according to claim 1.