JP3816238B2 - Molding method of crystallized polyethylene terephthalate molding - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for molding a crystallized polyethylene terephthalate molded article.
[0002]
[Prior art]
Among the main saturated polyesters currently on the market, polyethylene terephthalate (hereinafter referred to as PET) and polybutylene terephthalate occupy an important position as thermoplastic molding materials. In particular, PET is a stretch blowing technology. Development of high-performance PET bottles is possible, and consumption is growing rapidly.
[0003]
By the way, although the crystallization characteristics of the resin greatly influence the moldability and physical properties, from the standpoint of using a molded product having excellent mechanical strength, a resin having a high degree of crystallinity is desirable. The crystallization temperature range of PET is 120 ° C. to 220 ° C., and the maximum crystallization rate is shown particularly in the vicinity of 170 ° C. to 180 ° C. Generally, however, crystallization is slower than that of polyamide or polyacetal.
[0004]
Therefore, a crystallized polyethylene terephthalate (Crystallized PET, hereinafter simply referred to as CPET), in which a nucleating agent is added to this PET and crystallized at high speed in the process of heating to cooling, has been developed. In addition to being excellent in heat resistance, it is not deformed even at an atmospheric temperature close to the melting point (250 ° C.) and is excellent in heat resistance, so it is also used as a heat resistant food container such as an oven / microwave tray.
[0005]
One compression molding method for molding this CPET is a transition mold as shown in FIG. This method is also called a two-mold method, in which a heating zone 41 and a cooling zone 46 are installed, and a heating die 42 and a cooling die 47 are arranged corresponding to each zone 41, 46, and each die 42, 47 has Correspondingly, plugs (pressing molds) 43 and 48 are arranged. The cooling mold 47 is for cooling and solidifying the molded product cured by the heating mold 42, and the inside of the mold 47 has the same shape as the inside of the heating mold 42. .
[0006]
In the cooling zone 46, cooling water is passed through the cooling mold 47 and the plug 48, and the molded product is cooled and solidified through the cooling mold 47 and the plug 48.
[0007]
At the time of molding, first, a sheet-like material S formed by heating to a molding temperature with a resin material of CPET and a crystallization accelerator is put into the heating mold 42, and pushed into the plug 43 for curing.
[0008]
Next, the molded product 30 is taken out from the heating mold 42, moved to the cooling zone 46, inserted into the cooling mold 47, and solidified.
[0009]
Further, as a transitional type deformation, there is a one mold method as shown in FIG. In this method, there is no cooling zone, only a pair of heating molds 52 and plugs 53 are disposed in the heating zone 51. After the heat molding and curing with the heating molds 52, the plugs 53 are inserted. In this state, the cooling water is passed through the plug 53. The plug 53 acts as a cooling plug, and cools and solidifies the molded product 30. Compared to the above-described two-mold method, the one-mold method requires only half the molding area (molding zone) for one molded product, and only one set of molds, so that both the equipment efficiency and the equipment cost are excellent.
[0010]
[Problems to be solved by the invention]
However, in the molding method as described above, a molded product of CPET having a complicated shape, for example, a container 10 having a reverse taper R inclined inward with respect to the direction of extraction from the mold as shown in FIG. 5, the container (lid) 20 having a recessed portion as indicated by the symbol Q cannot be molded. This is due to the following reasons.
[0011]
As described above, CPET can obtain a molded product that can withstand high heat close to its melting point (250 ° C.). For this purpose, the temperature of the heating mold 42 is set to 169 ° C. during molding. As described above, molding conditions such as up to 200 ° C. and a curing time of 3 seconds or more are required. This is to increase the crystallinity after cooling and solidification by exposing to such a high temperature. Incidentally, the heat resistance temperature of ordinary PET is 70 to 80 ° C., and the molding temperature for that is 65 ° C.
[0012]
Accordingly, when heated at such a high temperature (169 ° C. to 200 ° C.), the molded product 30 in the heating mold 42 is very soft, and therefore, the one having the reverse taper R or the depression Q as described above is used. When pulling out from the heating mold 42, the irregularities of the reverse taper R and the depression Q hit against the irregularities of the corresponding heating mold 42, resulting in a malfunction.
[0013]
Accordingly, an object of the present invention is to solve the above-described problems in the manufacture of CPET and to have a complex-shaped CPET molded product, for example, a reverse taper, protrusion, or protrusion on the peripheral surface. However, it is to be able to be molded so as not to lose its shape.
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention is formed by crystallized polyethylene terephthalate, preheated to a predetermined molding temperature, put into a heating mold and molded, and after the mold is removed, the molded product is cooled. While blowing the air, it was pulled out from the mold while the whole was not solidified uniformly.
[0015]
In this way, only the vicinity of the surface to which air is blown is solidified first, and the inside is still in a soft state, so that the soft portion inside can flexibly cope with extraction from the mold, and the surface The solidified part in the vicinity protects the soft part inside and can resist the reaction from the mold at the time of extraction, so that it does not easily lose its shape. After extracting from the mold, it is allowed to solidify naturally.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, as shown in FIG. 1, only one heating mold 11 and a plug 12 paired therewith are provided. In CPET, as described above, if the molding conditions are adjusted, a product that can withstand heat up to 220 ° C. can be molded, and heat-resistant food containers such as oven / microwave trays have been developed, The molding condition is that the molding temperature (temperature of the heating mold) is 169 ° C. or higher and 200 ° C., and is cured for 3 seconds or longer in that state. In this embodiment, the molding temperature is set to 170 ° C., and the heating mold 11 is set to 170 ° C. The curing time was 4 seconds.
[0017]
First, the sheet S formed by adding a crystallization accelerator to the material of CPET is preheated to the molding temperature of 170 ° C., and the sheet S is put into the heating mold 11 and then plug 12 is used. Press to mold. The plug 12 only serves as a male mold at the time of molding, and is immediately extracted from the mold 11 after the sheet S is molded. The curing time of the molded product 10 in the mold 11 is 4 seconds as described above.
[0018]
When the curing is finished, the molded product 10 is extracted from the heating mold 11. At this time, the molded product 10 is extracted while blowing air 1.
[0019]
By doing so, the molded product 10 is solidified only in the vicinity of the surface to which the air 1 is blown, and the inside is still in a soft state that is not completely solidified. In addition, it is possible to flexibly cope with the reaction from the mold wall due to the softness inside thereof, and it is possible to prevent a defect due to a collision with the mold 11 at the time of extraction at a hard surface portion. After extracting from the mold, it is allowed to solidify naturally.
[0020]
Further, according to the method of this embodiment, only one zone consisting of only the heating mold 11 and its plug 12 is required, so that the two heating and cooling zones 41 and 46 are used as in the case of the two-mold method. Thus, a large molding area is not required, the mold cost can be halved, and the equipment efficiency can be improved and the equipment investment can be reduced.
[0021]
【The invention's effect】
In this invention, after a sheet formed by CPET material and preheated is thermoformed, it is cooled while blowing cooling air on the surface when it is extracted from the mold, With different softness forms, the molded product can be removed from the mold flexibly by the soft part inside, and the soft part inside can be protected by the hard part on the surface. Therefore, a complicated CPET molded product can be obtained by removing a complicatedly shaped portion such as a reverse taper, a protrusion, or a protrusion without being deformed.
[0022]
Compared with the transition type, only one zone consisting of a heating die and its pressing die is required, and the die cost is reduced by half, so that the equipment efficiency can be improved and the equipment investment can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an embodiment of the present invention. FIG. 2 is a schematic sectional view showing a two-mold method. FIG. 3 is a schematic sectional view showing a one-mold method. FIG. 5A is a plan view, FIG. 5B is a front view partially including a cross section, and FIG. 5C is a side view. FIG. 5A is a front view of an example of a container that can be manufactured according to the embodiment. (B) shows a cross-sectional view of the main part.
1 Cooling Air 11 Heating Mold 12 Plug (Pushing)
41 Heating zone 46 Cooling zone 42, 52 Heating die 47 Cooling die 43 Heating plug 48, 53 Cooling plug 10, 20, 30 Container (molded product)
S sheet R reverse taper Q dent

Claims (1)

A method for molding a crystallized polyethylene terephthalate molded article,
A sheet formed of crystallized polyethylene terephthalate and preheated to a predetermined molding temperature is put into a heating mold, pressed and molded with a pressing mold, and after removing the pressing mold, cooling air is blown onto the surface of the molded product. A method for molding a crystallized polyethylene terephthalate molded product, wherein the molded polyethylene terephthalate molded product is drawn out from a mold before the whole is solidified uniformly.

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