Polyester resin container and molding process thereof

#This invention relates to a polyester resin container to be used in the applications requiring retort processing, and to a process for molding such a container.

#In recent years, biaxially drawn, blow molded containers made of polyester resins, such as polyethylene terephthalate resins (hereinafter referred to as PET resins) have been much in use in the applications for those foods requiring retort processing.

#However, in the case of conventional polyester containers that have been biaxially drawn and blow molded, there occurred unavoidable shrinkage in the containers due to residual distortion caused by the deformation in the process of drawing when the containers were retort-processed at a temperature as high as about 120° C. Such shrinkage gave damage to appearance, and the containers could not be used as finished products. Later, various sorts of development were under way for the purpose of increasing heat resisting property of the PET resin containers. As one of the effective molding processes, what is called the “double blow molding process” was developed by the same applicant as that of this invention (See Patent Document 1). This process is now in use as a process for molding those containers to be retort-processed at a temperature of 120° C. for about 30 minutes.

#FIG. 1 is a front elevational view of the entire bottle in the first embodiment of this invention.

#FIG. 2 is an explanatory diagram showing front views of a preform and the molded products obtained respectively from the steps of the double blow molding process of this invention.

#FIG. 3 is a front elevational view of the synthetic resin bottle in the second embodiment of this invention.

#1. Bottle (Container) 2. Neck 3. Shoulder 4. Body 5. Bottom 5a. Central concave portion 6. Vacuum-absorbing panel 7. Pillar 8. Circular section 11. Preform 21. Primary intermediate product 31. Secondary intermediate product 106. Panel 106a. Dented panel portion 106b. Raised panel portion 107. Pillar 109. Peripheral-stepped portion 110. Stepped portion 111. Boundary 115. Swollen state 115a. Swollen and reversed state 115b. Swollen and deformed state 116. Dented state 116a. Dented and deformed state 116b. Dented and reversed state 121. Bottom plane 122. Heel portion 123. Grounding bottom rim portion 124. Central concave portion 125. Top area R1, R2. Radius of curvature H1. Height of the central concave portion D1. Maximum outer diameter of the heel portion D2. Outer diameter of the grounding bottom rim portion Tre. Retort autoclave temperature Pre. Retort autoclave pressure Pb. Pressure inside the bottle

#This invention is further described with respect to preferred embodiments, now referring to the drawings. It is to be noted here that this invention should not be construed as limitative to the description of these embodiments. FIG. 1 is a front elevational view of a bottle 1 in one embodiment of the polyester container of this invention. The bottle 1 is made of a PET resin, and was molded by the double blow molding process which will be described later. It is a round bottle having a height of 130 mm and a body diameter of 66 mm and comprising a neck 2, a shoulder 3, a cylindrical body 4, and a bottom 5. The neck has been thermally crystallized to a whitened state, and a central concave portion 5a is formed inside the bottom 5.

#Six vacuum-absorbing panels 6 are formed in the wall of the body 4 and are disposed in parallel at longitudinal positions by gently denting the body wall except for upper and lower areas of the body 4. Vertical rib-like pillars 7 are formed between two adjacent vacuum-absorbing panels 6 while leaving the pillars 7 in the undented state. And circular sections 8 in a short cylindrical shape are formed in the upper and lower areas of the body 4, likewise in the undented state. Rigidity of the entire bottle 1 is secured mainly by these pillars 7 and circular sections 8. If the vacuum-absorbing panels 6 of the body 4 are reversed and deformed into a swollen state at a high temperature during retort processing, the circular sections in the upper and lower areas of the body fulfill a function for confining the swelling deformation of the bottle 1 to a certain limit.