METHOD OF STRENGTHENING NECK PORTION OF BOTTLE-SHAPED CONTAINER OF POLYETHYLENE TEREPHTHALATE RESIN

Abstract: A method of strengthening the neck portion (2) of a bottle-shaped container (1) of polyethylene terephthalate resin which has the steps of heating the neck portion (2) at approx. 140 to 170°C, then inserting a cylindrical die pin (6) having an outer diameter slightly smaller than the bore of the neck portion and cooling function, and blowing chilled air (C) to the neck portion (2), thereby gradually cooling the neck portion (2) to whiten the neck portion. Thus, the neck portion of the bottle-shaped container (1) is strengthened. However, it can effectively prevent the production of incorrect contrac­ tion deformation of the neck portion (2) due to the thermal influence of the heat applied from the exterior.

Description: "I < lethod of Strengthening Neck Portion of 3ott1e#s#aapVe##V# Container of Pol ,rethylene #re#htha1ate Resign" This invention relates to a method of strengthening the neck portion of a hollow blow-molded bottle-shaped container of a biaxially oriented polyethylene terephthalate resin. A blow-molded bottle-shaped container of a biaxially oriented polyethylene terephthalate resin, hereinafter referred to as "a PET", has a-wide range of applications in a great deal of quantities due to its excellent physical properties and durability. However, some of the excellent physical properties and durability of a--bottle-shaped container of PET can be formed effectively after the resin material of the bottle-shaped container has been biaxially oriented. Therefore, the neck portion of the bottle-shaped container which has been molded without being almost oriented at the time of molding the container has been deteriorated in certain physical properties and durability as compared with the body which has been molded with being sufficiently oriented. In a representative event, when alcohol of high density is contacted with the neck portion the bottle-shaped container, the alcohol thus contacted is impregnated into the wall of the neck portion, and a crazing occurs at the impreg nated neck portion, causing whitening of the impregnated neck portion. There has heretofore been a method of increasing the density of the resin material by heat treating the neck portion to allow the neck portion to be crystallized and whitened as means for eliminating the atorementioned drawback of the blow-molded bottle-shaped container of the PET. This conventional method of increasing the density of the neck portion of the bottle-shaped container of the PET has performed the excellent effect to improve the impact resistance, the wear resistance and the external pressure resistance of the container due to the large increase of the crazing resistance of the neck portion and by improving the mechanical rigidity of the neck portion. However, the neck portion has always been subjected to thermal contraction phenomenon due to the thermal influence of the heat treatment conducted to whiten the resin material of the neck portion, and the neck portion has sometimes been incorrectly deformed due to the thermal contraction. In other words, the neck portion pf.the bottle-shaped container of the PET of this type has been provided with a spiral thread or a collar formed onon'the outer per#ipheral surface, causing irregular thickness to be produced, the neck portion has not always been uniformly heated in the entirety and has not been as well cooled uniformly simultaneously as a whole. Accordingly, the contraction deformation of the neck portion due to the thermal influence affected to the neck portion has not uniformly occurred, and the circularity of the neck portion has sometimes been lost or the flatness of the top surface of the neck portion has been lost as its drawbacks. Accordingly, an object of the presentlinvention is to provide a method of strengthening the neck portion of a bottle-shaped container of polyethylene terephthalate resin which can eliminate the aforementioned drawbacks and disadvantages of the conventional method of increasing the density of the neck portion of the bottle-shaped container of the PET and which can prevent the occurrence of the incorrect contaction deformation of the neck portion due to the thermal influence applied externally when the neck portion is heat treated to be whitened and strengthened. Another object of the present invention is to provide a method of strengthening the neck portion'of a bottle-shaped container of polyethylene terephthalate resin which can perform the heat treatment and blow-molding of the neck portion with the same number of steps and molding time as those of the conventional method merely by applying an inserting work of a die pin into the neck portion. Still another object of the present invention is to provide a method of strengthening the neck portion'of a bottle-shaped container of polyethylene. terephthalate resin which can form the neck portion to be contraction deformed with a cross section of regular circularity in accordance with the shape of a die pin to be inserted into the bore of the neck portion and with a flatness on the top surface of the neck portion. The above and other related objects and features of the invention will be apparent from a reading of the following description of. the disclosure found in the accompanying drawing and the novelty thereof pointed out in the appended claims. Figure is a view showing the steps of the method according to an embodiment of the present invention. The present invention will now be described ln¯more detail with reference to the accompanying drawing. In Figure, a method of strengthening the neck portion of a bottle-shaped contalner of PET according to the present invention comprises the steps of heating, as designated by H, the neck portion 2 of the bottle-shaped container 1 biaxially orientation blow-molded to approx. 140 to 1700C, then inserting a die pin 6 of a cylindrical shape having an outer diameter substantially smaller than the bore of the neck portion 2' and cooling function into the neck portion 2 thus heated, and blowing chilled air from outside to the neck portion 2 to cool, as designated by C, the neck portion 2 and to increase the strengthen the density of the resin material of the neck portion 2. Heating means for the neck portion¯2 2 may employ a variety of methods, and has, as in the embodiment exemplified in Figure, a heating furnace. 3 which contains therein a heater 4 in a frame wall 5 so that only the neck portion 2 of the bottle-shaped container 1 is'inserted into the furnace 3, and moves the bottle-shaped container 1 at a predetermined constant speed while rotating around its own axis in the state that the neck portion 2 is disposed in the furnace 3, thereby heating the entire neck portion 2 uniformly at approx. 140 to 1700C. The heating temperature of the neck portion 2 is determined as a reference to a temperature at which the material of PET is crystallized to be whitened, and is predetermined with respect to the reference temperature in accordance with the thickness of the wall of the neck portion 2 so as to perform the heating of the neck portion 2 to the accurate temperature by regulating the electric power supplied to the heater 4 and the moving speed of the bottle-shaped container 1. The neck portion 2 thus heated to the preset temperature and removed from the furnace 3 is gradually cooled by the die pin 6 and by blowing chilled air from a blower 7 in the state that the die pin 6 is inserted into the neck portion 2. In this manner, the resin material of the neck portion 2 is crystallized to be whitened and is thus #strengthened. The neck portion 2 is thus cooled by the die pin 6 and by the chilled air preferably -for approx. 20 to 25 seconds. The cooling step of the neck portion 2 by the die pin 6 and the chilled air may be gradually cooled with respect to the PET at its cooling speed, but the cooling degree and the cooling speed may not be regarded in this cooling step. The die pin 6 is formed in a cylindrical shape having an outer diameter substantially smaller than' the bore of the neck portion 2 before being heat treated, and has cooling function by means such as means for circulating and supplying cooling fluid therein. The outer diameter of the die pin 6 is set in accordance with the bore of and the thickness of the wall of the neck portion 2 to be thus formed. More particularly, the neck portion 2 of the bottleshaped container l of the PET is heated, c'ausing substantially thermal contraction, and the outer diameter of the die pin 6 is accordingly set to the value of the degree that the die pin 6 may be tightly inserted into the bore of the neck portion'2 merely heat treated in this manner. Therefore, the outer,dlameter of the die pin 6 becomes a value larger than the bore of the neck portion 2 cooled and solidified after being heated without the die pin 6 in the neck portion 2. As described above, the outer diameter of the die pin 6 is set to a value larger than the bore of the neck portion 2 thus cooled, solidified and contracted in the state without the die pin 6. Accordingly, the neck portion 2 is urged to the die pin 6 by means of the contraction of itself and is thus formed in the final 'shape. In this case, the die.pin 6 is formed in a-cylindrical shape having a section of a regular circle. Accordingly, the. neck portion 2 thus contracted and deformed is formed in a cylindrical shape having a section of a regular circle in accordance with the shape of the die pin 6. When the sectional shape of the neck portion 2 is thus formed in a-cylindrical shape having a section of a regular circle, the upper end face of the neck portion 2 should be retained in a flat surface. In this manner, the neck portion 2 is thermally contracted in the state accurately retaining the shape at the injection molding time as it is, and no incorrect distortion is produced due to the thermal contraction at the neck portion 2. As described above, the neck portion 2 is contracted and formed in the state that the die pin 6 is tightened. Therefore, the tightening of the die pin 6 by the neck portion 2 becomes very strong. Therefore, it is preferred that the outer surface of the die pin 6 is substantially reduced in the outer diameter in. a tapered peripheral surface toward the sharpened tip of the die pin 6 so as to smoothly perform the removal of the die pin 6 or the pulling of the die pin 6 from the bore of the neck portion 2 after the neck portion 2 is thermally contracted and formed. It should be appreciated from the foregoing description that since the method of strengthening the neck portion of the blow-molded'bottle-shaped container of the PET of the present invention has the steps of heat treating the neck portion.2 so as to increase the physical property resistance and the mechanical strength resistance upon enhancement of the density of the resin of the neck portion 2 and forming at that time of heat treati#ng the neck portion 2 the neck portion 2 thus thermally contacted and deformed in accordance with the die pin 6, the neck portion 2 is heat treated without being incorrectly strained and is thus thermally contacted, and thereby effectively preventing the production of the incorrect deformation of the neck portion 2 upon thermal contraction of the neck portion 2, and since the method can additionally have only the'step of inserting the die pin 6 into the neck portion 2, the method can perform'the heat treating formation of the neck portion 2 with the same number of steps and the same forming time as those of the conventional method.

Claims: CLAIMS 1. A method of strengthening the neck portion of a bottleshaped container of polyethylene terephthalate resin comprising the steps of: (a) heating the neck portion of said bottle-shaped container biaxially orientation blow-molded to substantially 140. to 17O0C, (b) inserting a die pin of a cylindrical shape' having an outer diameter substantially smaller than the bore of the neck portion into the neck portion thus heated, and (c) blowing chilled air from outside to ,the neck portion to cool the neck portion and to whiten the neck portion. 2. The method of strengthening the neck portion of a bottle-shaped container of polyethylene terephthalate resin according to claim 1, wherein said die pin has a cooling function. 3. The method according to claim 2, wherein said die pin is formed in a cylindrical shape having an outer diameter substantially smaller than the bore of the neck portion before being heat treated. 4. The method according to claim 2, wherein said die pin has means for circulating and supplying cooling fluid therein. 5. The method according to claim 2, wherein said die pin is set at the outer diameter in accordance with the bore of and the thickness of the wall of the neck portion to be thus formed, and is set to a value larger than the bore of the neck portion cooled, solidified and contracted in the state without said die pin. 6. The method according to claim 1, wherein the heating temperature of the neck portion is as a reference a temperature at which the material of poly'ethylene terephthalate resin is crystallized to be whitened and is predetermined with respect to the reference temperature in accordance with the thickness of the wall of the neck portion so as to perform the heating of the neck portion to the accurate temperature by regulating the electric power supplied to a heater and the moving speed of the bottle-shaped container. 7. The method according to claim 1, wherein the neck portion is cooled by said die pin and by the chilled air for substantially 20 to 25 seconds. 8. The method according to claim 1, wherein said die pin is formed in a cylindrical shape having a section of a regular circle. 9. The method according to claim 1, wherein said die pin is substantially reduced in the outer diameter in a tapered peripheral# surface toward the sharpened tip'thereof so as to smoothly perform the removal of said die pin or the pulling of said die pin from the bore of the neck portion after the neck portion is thermally contracted and formed.

Inventors: IIZUKA, TAKAO, TAKADA, TAKUZO
Applicants: YOSHINO KOGYOSHO CO., LTD.
Application year: 1982
Main classification: B29C71
IPC codes: B29C71, B29C49