METHOD OF BLOW-MOULDING A BIAXIALLY ORIENTED POLYETHYLENE TEREPHTHALATE RESIN BOTTLE-SHAPED CONTAINER

Abstract: A method of blow-moulding a biaxially oriented polyethylene terephthalate resin bottle-shaped container is disclosed. The method comprises the steps of heating the body portion of preform at 100 to 120°C, biaxial-orientation blow-molding the preform in a primary blowing mold heated at 110 to 230°C to form a primary intermediate molded bottle-shaped piece, heating the primary intermediate molded bottle-shaped piece at 130 to 255°C or at a tempera­ ture which is 20°C or higher than the primary blowing mold temperature to form a secondary intermediate molded bottle-shaped piece, and blow-molding the secondary inter­ mediate molded bottle-shaped piece in a secondary blowing mold heated at 100 to 150°C to form a bottle-shaped container. The temperature of the secondary blowing mold is several degrees greater than the maximum temperature the molded bottle-shaped container will be subjected to during use. The bottle-shaped container has no stress remaining from biaxial orientation blow-molding and has a high heat resistance temperature value.

Description: METHOD OF BLOW-MOLDING A BIAXIALLY ORIENTED POLYETHYLENE TEREPHTHALATE RESIN BOTTLE-SHAPED CONTAINER BACKGROUND OF THE INVENTION The present invention relates to a method of blow-molding 'a biaxially-oriented polyethylene terephthalate resin bottleshaped container. Polyethylene terephthalate resin (hereinafter referred to as "PET") has stable physical properties, no public pollution, exellent transparency and high mechanical strength. Also, PET causes no pollution when incinerated. PET is widely used in the production of biaxially-oriented blow-molded bottle-shaped containers, and is particularly useful for bottling foodstuffs. PET bottle-shaped containers have a number of excellent properties as described above; however, blow-molded bottle-shaped containers of biaxially-oriented PET which are not heat treated suffer remarkable deformation at temperatures of 70 0C or more. Therefore, such PET bottleshaped containers cannot be used to bottle retort food, which is heat treated by allowing the food to stand for 30 min. 0 at 120 C, or other heat-treated food. Accordingly, there is great demand for PET bottle-shaped containers which have high heat resistance. There are several conventional methods of imparting heat resistance to PET bottle-shaped containers such as (1) heating a blowing mold during blow-molding of a PET bottle-shaped container to a temperature higher than the target heat resistance temperature value to increase the density of the PET bottle-shaped container; (2) heat setting a PET bottle-shaped container after blow-molding to remove residual strain produced by blow-molding; and (3) blowmolding a intermediate mold piece by first molding a primary blow-molded container, then reheating it at approximately 1100C, and finally blowing it again to produce a bottleshaped container. In method (1), the moldability of the PET decreases as the mold temperature rises. According to this method, the PET is heat resistant up to a maximum of approximately 1000C. This PET cannot be used for bottle-shaped containers containing food which is heat treated at temperatures much higher than 1000C. The methods (2) and (3) of imparting heat resistance to the PET bottle-shaped container cannot expect the heat resistance higher than the method (1). SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method of blow-molding a biaxially-oriented PET bottle-shaped container which can eliminate the aforementioned drawbacks and disadvantages of the conventional methods. It is another object of the present invention to provide a method of blow-molding a biaxially-oriented PET bottle-shaped container having very high heat resistance. This object is accomplished by a method in which a preform is biaxial-orientation blow-molded to form a primary intermediate molded piece, the primary intermediate molded piece is heat treated to thermally contract and deform the piece to form a secondary intermediate molded piece and then the secondary intermediate molded piece is blow-molded to form a final bottle-shaped container. Thr foregoing objects and other objects, as well as the characteristic features of the invention will become more fully apparent and more readily understandable from the following description and the appended claims when read in conunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal sectional view depicting the primary blow-molding state of a primary intermediate molded piece according to the present invention; Fig. 2 is a longitudinal sectional view showing the secondary blow-molding state of a secondary intermediate molded piece according to the present invention; and Fig. 3 is a graphic diagram showing the relationship between the density and the blow-molding temperature of the blow-molded bottle-shaped container of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. With reference to Fig. 1, a method of blow-molding a biaxially-oriented PET bottle-shaped container according to the present invention comprises the steps of: heating the body portion 2 of a preform 1, which is formed in a desired shape in advance, at 100 to 12 0C until the temperature approaches but does not reach the thermal crystallization temperature of the PET, biaxial-orientation blow-molding the preform in a primary blowing mold heated at 1100 to 230 0C to form a primary intermediate molded bottle-shaped piee 4, heating the primary intermediate molted bottle-shaped piece 4 at 1300 to 2550C which is in a range so as not to exceed the termperature 255 0C immediately before the melting point of polyethylene terephthalate from 130 0C) or at a temperature which is 200C or higher than the primary blowing mold temperature to form a secondary intermediate molded bottle-shaped piece 5, and blow-molding the secondary intermediate molded bottle-shaped piece 5 in a secondary blowing mold heated at 1000 to 1500C,which is higher than the sterilizing temperature of the content filled in the molded bottle-shaped container, to form a final bottle-shaped container 6. More particularly, the method of blow-molding a biaxially-oriented PET bottle-shaped container according to the present invention includes the first step of injection molding in advance a preform 1 in a desired shape, the second step of thermally crystallizing, without orienting deformation, a neck portion of the bottle-shaped container 6 of the shape which remains in the shape at the injection molding time, and the third step of blow-molding the body of the bottle-shaped container 6. The preform 1 is injection molded by ordinary injection molding techniques. In the exemplifed embodiment, the injection molded preform 1 is formed in dish shape as shown by solid lines in Fig. 1. The preform 1 has a neck portion 3 and a body portion 2. The body portion 2 becomes the body, including a bottom, of the biaxially-oriented blow-molded bottle-shaped container 6. The body 2 is oriented in the orienting amount of 5 to 13 times that the orienting density may become 'p 1.36 or more so that the body 2 may not be thermally crystallized even at the mold temperature of 1100 to 230 0C of the primary blowing mold at the blow-molding time. Thus, the body 2 is formed in the primary intermediate molded piece 4 without thermal crystallization even at the mold temperature of 1100 to 2300C (which is higher than the crystallizing temperature) of the primary blowing mold. The peripheral end of a connecting portion between the body portion 2 and the neck portion 3 and the central portion of the body portion are hardly oriented as compared with other parts of the body portion 2 and are also readily crystallized. These portions are therefore preferably reduced in thickness relative to the other parts of the body portion 2 so as to be readily oriented. The neck portion 3 of the preform 1 is, preferably, thermally crystallized or whitened piror to biaxial-orientation blowomolding the preform to form the primary intermediate molded bott-shaped piece 4. The whitening of the neck portion 3 may be performed by sufficiently heating the neck portion 3 to crystallize the PET followed by gradual cooling. It should be noted, however, that all deformation of the neck portion 3 should be avoided when whitening the neck portion 3. Particularly, deterioration of the degree of the circularity of the neck portion 3 should be avoided since such deformation would largely reduce the function of the final blow-molded bottle-shaped container 6. After the neck portion 3 of the preform 1 is whitened in this manner, the preform 1 is blow-molded to form the bottle-shaped container 6. The blow-molding step involves biaxial-orientation blow-molding the preform 1 to form a primary intermediate molded bottle-shaped piece 4, heating the primary intermediate molded bottles-shaped piece 4 to thermally shrink it and form a secondary intermediate molded bottle-shaped piece 5, and blow molding the secondary intermediate molded bottle-shaped piece 5 to form a final bottle-shaped container 6. The step of biaxial-orientation blow-molding the preform 1 to form the primary intermediate molded bottleshaped piece 4 is performed by first heating the body portion 2 of the preform 1 at 100 to 1200C until the temperature approaches but does not reach the thermal crystallization temperature of the PET. Next, the preform 1 is blow-molded in a blow mold heated at 1100 to 230 0C to form the primary intermediate bottle-shaped piece 4. The primary intermediate molded bottle-shaped piece 4 is oriented in a range that the area magnification of the preform 1 to the primary intermediate molded bottle-shaped piece 4 is 5 to 13 times so that the orienting magnification of the resin becomes 1.36 or more so as to prevent the bottle-shaped piece 4 from thermally crystallizing by the heating temperature of the primary mold and the heating temperature of the secondary intermediate molded piece. The primary intermediate molded bottle-shaped piece 4 is then heated to thermally shrink it to form the secondary intermediate molded bottle-shaped piece 5. This thrinking step is performed to prevent thermal deformation by eliminating residual stress developed in the blow-molded piece 4 from biaxial-orientation blow-molding. The orientation blow-mloded portion of the primay intermediate molded bottle-shaped piece 4 is deformed by the internal residual stress by heating the primary intermediate molded bottle-shaped piece 4, preferably in the primary blowing mold, at 1300 to 2550C or a temperature which is 200C higher than the primary blowing mold temperature, thereby to eliminate the-residual stress. The deformation produced by the elimination of the internal residual stress acts to contract or shrink the orientation-molded portion of the primary intermediate molded bottle-shaped piece 4. Consequently, the orientation-molded portion of the secondary intermediate molded bottle-shaped piece 5 is molded by this contraction deformation. The body portion of the secondary intermediate molded bottle-shaped piece 5 formed by the shrinkage deformation is predetermined in the orienting magnification from the preform 1 to the primary intermediate molded piece 4 and the size of the primary intermediate molded piece 4 to be substantially equal to or slightly smaller than the orientation-molded body portion of the final bottleshaped container 6 as shown in Fig. 2. Finally, the secondary intermediate molded bottleshaped piece 5 is blow-molded to from the final bottle-shaped container 6. The secondary intermediate molded bottle-shaped piece 5 thermally shrunk by heating at 1300 to 255 0C or at a temperature which is 20 0C or higher than the primary blwong mold temperature as described above, is placed in the secondary blowing mold which is heated at a temperature 0 of 1000 to 150 C. The temperature of the secondary blowing mold is several degrees greater than the maximum temperature the molded bottle-shaped container 6 will be subjected to during use. The body shape of the blow-molded portion of the secondary intermediate molded bottle-shaped piece 5 is substantially equal to or slightly smaller than the corresponding body shape of the bottle-shaped container 6 as described above. Accordingly, the orientation magnification from the secondary intermediate molded bottle-shaped piece 5 to the final bottle-shaped container 6 is quite small, and consequently a stress to be created when the bottle-shaped container 6 molded from the secondary intermediate molded bottle-shaped piece 5 is orientation-molded, is not almost generated. Further, since the bottle-shaped container 6 is blow-molded by a secondary blowing mold heated at a temperature greater than the temperature the bottle-shaped con.tainer will be subjected to during use, the bottle-shaped container 6 is heatset by the secondary blowing mold, and therefore the bottle-shaped container 6 has no residual stress as well as high heat resistance. Fig. 3 shows the relationship between the density of the molding material at the respective molding steps and the mold temperatures. A specific example of the method of blow-molding a biaxially-oriented PET bottle-shaped container according to the present invention will now be described. A preform 1 was biaxial-orientation blow-molded to form a primary intermediate molded bottle-shaped piece 4. 0 The preform was heated to a temperature of 115 C and was blow-molded at a primary blowing mold temperature of 180 0C under a blowing pressure of 25 kg/cm2 for a blowing time of 1.4 sec. The primary intermediate molded bottle-shaped piece 4 was then heated and thermally shrunk to form a secondary intermediate molded bottle-shaped piece 5 at a heating temperature of 225 0C. The secondary intermediate molded bottle-shaped piece 5 was blow-molded at a secondary blowing mold temperature of 1400 C under a blowing pressure of 30kg/cm2 for a blowing time of 4.4 sec. to form the final blow-molded bottle-shaped container 6. The heat resistance of the blow-molded bottle-shaped container 6 was then tested by immersing in the state without a cap for 30 minutes in a tank of glycerin heated at 1200C. The bottle-shaped container' 6 was then removed from the glycerin and water-cooled. The volumetric variation of the container before heating and after heating was measured. The volumetric rate of change of the bottle-shaped container 6 was found to be 0.33%. From this result, it is apparent that a PET bottle-shaped container having sufficiently high heat resistance can be provided by the present invention. According to the present invention as described above, the method of blow-molding a PET bottle-shaped container provides a blow-molded bottle-shaped container having to residual stress and having extremely high heat resistance. The heat resistance temperature value is remarkably increased when compared with that of a conventional container. While the present invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made without departing from the spirit and scope thereof.

Claims: Claims 1. A method of blow-molding a biaxially-oriented polyethylene terephthalate resin bottle-shaped container comprising the steps of: (a) heating a preform at 1000 to l200C; (b) biaxial-orientation blow molding-said preform o o in a primary blowing mold heated at 110 to 230 C to form a primary intermediate molded bottle-shaped piece; (c) heating said primary intermediate molded bottle-shaped piece at 1300 to 255 0C to from a secondary intermediate molded bottle-shaped piece ; and (d) biaxial-orientation blow-molding said secondary intermediate molded bottle-shaped piece in a secondary blowing mold heated at 1000 to 150 0C to form a bottle-shaped container. 2. A method of blow-molding a biaxially-oriented polyethylene terephthalate resin bottle-shaped container comprising the steps of: (a) heating a preform at 1000 to 1200C; (b) biaxial-orientation blow molding said preform o o in a primary blowing mold heated at 110 to 230 C to form a primary intermediate molded bottle-shaped piece; (c) heating said primary intermediate molded bottle-shaped piece at a temperature which is 200 or higher than the primay blowing mold temperature to form a secondary intermediate molded bottle-shaped piece; and (d) biaxial-orientation blow-molding said secondary intermediate molded bottle-shaped piece in a secondary blowing mold heated at 1000 to 1500C to form a bottle-shaped container. 3, The method of claim 1, wherein the orientationmolded portion of said secondary intermediate molded bottleshaped piece is substantially the same size as or slightly smaller than the orientation-molded portion of said bottleshaped container. 4. The method of claim 1, wherein said preform is orientation area magnified 5 to 13 times to form said primary intermediate molded bottle-shaped piece and wherein said secondary blowing mold has a mold size equal to or slightly smaller than said secondary intermediate molded bottle-shaped piece and smaller than said primary blowing mold size. 5. The method of claim 1, wherein said preform has a neck portion and a body portion, said body portion having a dish shape. 6. The method of claim 5, wherein said neck portion of said preform is theremally crystallized before said preform is blow-molded in said primary blowing mold. 7. The method of claim 1, wherein said primary intermediate molded bottle shaped piece is heated in said primary blowing mold to from said secondary intermediate moded bottle-shaped piece.

Inventors: SUGIURA, HIROAKI, TANAKA, FUMINORI, UESUGI, DAISUKE
Applicants: YOSHINO KOGYOSHO CO., LTD.
Application year: 1985
Main classification: B29C49
IPC codes: B29C49, B29C61, B29L22, B29K67, B65D1