JPS6250117A - Method and apparatus for forming plastic container - Google Patents

Abstract

PURPOSE:To uniformize the formation of a hollow biaxially stretched blow- molded container having a large depression, by providing a part having temp. lower than the heating temp. of the inner wall of a blow mold to said inner wall. CONSTITUTION:A wall insert 33 forming a depression to a molded container is engaged with a blow mold and set to temp. 10-30 deg.C lower than the temp. of the wall surface 34 of other mold. This cooling is performed by flowing a cooling stream in the cooling channel 36 provided in the wall insert 33 to lower the heat of the inside surface 39 of the wall insert 33. By this temp. difference, the blow-molded container is not too stretched at the depression forming part thereof and the plastic container having the depression having no difference in a stretching degree is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for forming hollow blow-molded containers of biaxially oriented thermoplastic material, which in particular are compatible with partial evacuation without adversely affecting appearance or strength. The present invention relates to a method and apparatus for forming a thin-walled plastic container configured to have a shape.

Lightweight, thin-walled containers made of thermoplastic materials such as polyester resins and thermoplastic polymers containing at least 50% by weight of monomers containing polymerized nitrile groups (hereinafter referred to as nitriles) are popular in the container industry. For example, polyethylene terephthalate (hereinafter referred to as PET) has a wide range of applications in the field of containers for foods, fragrances, cosmetics, beverages, etc.

By stretch blowing, PET can be molded into transparent, thin-walled containers that are hard, have high impact strength, have high molding precision, and are highly hygienic.

If the parison is stretched in the horizontal and vertical directions using a biaxial stretch blow molding method at a temperature range suitable for biaxial stretching, a container that is highly impact resistant, transparent, and heat resistant can be molded.

Nitrile and heat-set PET containers are particularly heat resistant; biaxial stretch blow molded containers have improved hardness and strength, as well as improved gas barrier properties and transparency.

When a thermoplastic container is filled with a hot liquid (such as a liquid that has been sterilized at high temperature) and sealed, cooling causes the liquid to contract, resulting in a partial vacuum evacuation of the container.
Backflow in the filling mechanism and the use of vacuum filling equipment in the filling operation, which often result in deformation of the container walls, can also cause
A partial vacuum may be created inside the container, resulting in deformation. Such deformations are usually concentrated in areas of weak mechanical strength of the container, often resulting in containers having an irregular and commercially unacceptable appearance.

Furthermore, if the part where the label is attached to the container becomes deformed,
As a result of the deformation of the container, the appearance of the label will also suffer.

By increasing the wall thickness of the container, it is possible to strengthen the container wall to some extent and thereby reduce the vacuum deformation effect. However, increasing the wall thickness results in a significant increase in the amount of raw material required to produce the container and a significant reduction in production rate. The resulting increased costs are unacceptable to the container industry.

Although prior art approaches use recessed panels to overcome thermal distortion of containers, containers designed with large recessed panels suffer from various problems. Larger recessed panels can accommodate larger deformations, but as the width of the recessed panel increases, the strength of the container body decreases.

Furthermore, the wider the recessed panel, the more difficult it becomes to form the container.

When the container is removed from the heated mold that forms the recessed panel, the wide recessed panel often becomes distorted.

As previously understood, thermoplastic containers differ in their degree of axial molecular stretching. During the manufacture of a container, the parison is stretched to varying degrees to form different parts of the container. Also, the parts of the parison forming the body of the container other than the recessed panel parts are stretched to a slightly greater degree than the parts forming the recessed panel, i.e., the parts of the body of the container The part of the parison that forms the outermost part will be more stretched.

U.S. Pat. No. 4,233,022 to Brady et al. discloses an attempt to reduce molecular stretching in the axial direction of the container to varying degrees. The US patent discloses a method and apparatus for promoting strain crystallized structures in thermoplastic containers through post-blow molding heat treatment. This heat treatment involves heating the blow molded container to varying degrees along its length, thereby heat treating only the portion of the molecules that are of interest to be stretched.

Thermoplastic containers with varying degrees of molecular orientation along the axis must be manufactured in such a way that the differences in molecular orientation do not affect physical strength, appearance, or ease of container manufacture. The present invention relates to methods and apparatus that are effective in meeting the above requirements.

SUMMARY OF THE INVENTION The present invention relates to a method and apparatus for forming hollow biaxial stretch blow molded containers having large recessed panels. More particularly, the method of the invention comprises forming a blow molded container in a mold having a wall insert on the inner wall surface. In a preferred embodiment, the container is heat set in the mold and the temperature of the wall insert is maintained slightly lower than the temperature of the remainder of the inner surface of the wall. In this preferred embodiment, the portion of the container wall adjacent to the mold wall insert (the portion of the container that is stretched to a lesser extent during manufacturing) is heat set at a temperature lower than the temperature of the remaining portion of the container to be heat set. Ru.

The apparatus of the invention comprises a mold having an inner surface substantially corresponding to the size and shape of the final blow-molded container, the inner surface of the mold being formed by at least one wall insert.

A heating device may be provided to heat-treat the blow-molded container.
Preferably, the heating of adjacent portions of the container by the wall insert is small compared to the heating of the remaining portions of the container body by the remaining portions of the mold wall.

The method and apparatus of the present invention for forming monomolecularly stretched thermoplastic containers that are dent resistant facilitates the production of containers with increased strength without the need for additional reinforcing elements in the container. , you can also replace the mold wall inserts without replacing the entire mold.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a thin-walled blow molded plastic container l formed by the method and apparatus of the present invention. The container is made of a hot-fillable material (a material that allows the container to be safely filled at temperatures between 65 and 100°C, more commonly between 75 and 95°C), such as polyethylene terephthalate (PET) or Made from nitrile.

The container l comprises a body part 2 with a shoulder part 3. The body part 2 can have any cross section, for example rectangular, square, hexagonal or polygonal, such as hexagonal, or The lower end of the body part 2, which may be circular, is closed by a bottom part 4. The body part 2 extends upwardly from the bottom part 4 and the top of the body part 2 and tapers diametrically inwardly to form a shoulder. 3 , the shoulder terminating in a neck 5 . The neck portion 5 may have external threads for attachment of a cap (not shown), and the neck portion 5
can also be crystallized to impart thermal, chemical and mechanical strength to the unstretched neck as disclosed in, for example, US Pat. No. 4,379,099.

The body 2 of the container is specially shaped to accommodate a controlled change in the volume of the container when the container is partially evacuated. As can be seen from FIG. 1, a concave recessed panel 6 is formed around the main body portion 2. Recessed panels 6 are formed on each side of the preferably polygonal body 2, and adjacent recessed panels 6 are formed on lands 7.
are separated from each other by. The recessed panel may preferably include reinforcing ribs 8.

One method of forming a container l with recessed panels will be described below.

Conventional methods and equipment for forming thin-walled plastic containers are known to those skilled in the art. In conventional methods, the parison is stretch blown into a mold into the final container shape. Referring to FIG. 2, a parison (not shown) is placed within a mold 30 having an inner portion 31 and an outer portion 32. The inner part 31 has at least a wall insert 33 and at least one wall part 34
It is formed by The wall 34 may also be an insert member. The outer part 32 of the mold 30 includes a heating device therein, for example, an internal fluid duct 35 into which heated liquid or It is connected to the device that supplies the gas. The outer part 32 may also include air holes to allow air to escape from between the parison and the mold during blowing, and a wall insert 33 when the parison is stretched into the final container shape against the inner surface of the mold. The wall insert 33 is positioned so that it forms a recessed panel in the container body 2. Preferably, the wall insert 33 is formed such that when the mold is heated, the temperature of the innermost surface 39 is slightly lower than the temperature of the surface of the adjacent wall 34. Also preferably.

The wall insert 33 is formed so that air can escape through the air holes through gaps around all or part of its edges.

Various apparatuses are known to those skilled in the art for placing the parison in a mold, blowing the parison, and heat treating the blown container.According to embodiments of the invention, the parison is blown into the final container shape and Heat set inside. The heating is performed at a temperature of about 10 to 30° C., preferably 15 to 25° C., lower than the temperature of the rest of the container, and the heating is carried out for 1 to 20 seconds, preferably 2 seconds. Since the final blown container is not stretched much in the area corresponding to the recessed panel, the present invention prevents different degrees of stretching in the container body by controlling the heat sink temperature. Become.

The wall inserts may be replaced to form recessed panels of different sizes and shapes in the final blown container. For example, the wall inserts may be fitted with protrusions corresponding to the shape of the reinforcing ribs 8 in the recessed panels. Alternatively, by slanting the wall insert outwardly into the mold cavity toward the longitudinal center transverse line 53, the third
A recessed panel may be formed that slopes longitudinally inward toward the transverse reinforcement line as shown. To form a new surface pattern on the container, mold different wall inserts 30
It is only necessary to replace it with .

The apparatus of the present invention will now be described more fully. Type 3
0 includes an outer part 32 having an inner duct 35 therein. The mold 30 also includes at least one wall 34.
(also consisting of an insert) and at least one wall insert 33 as described above. Wall portion 34 may be made of stainless steel or any other thermally conductive material; wall insert 33 may be made of aluminum or an insulating material that reduces heat transfer from outer portion 32 and wall portion 34 to wall insert 33; Alternatively or additionally, the wall insert 33 may include internal cooling ducts or channels 36 that blow a cooling flow through the wall insert and remove heat from the inner surface 39 of the wall insert 33. decrease. These cooling channels 36 are formed by ducts 3 in the mold wall.
The wall insert 33 may also include one or more cutouts 37, which may be in communication with a cooling flow source through the mold 30 and the wall insert. 33 and/or wall 3
4 and the wall insert 33 to reduce heat transfer.

FIG. 3 is a perspective view of a preferred wall insert 33 showing cooling channels 36 and cutouts 37 more clearly.

FIG. 4 is a plan view of the wall insert 33 of FIG.

In a preferred embodiment, wall insert 33 may have an anodized surface and may be formed from aluminum.

An alternative embodiment is shown in FIG. 5, where like reference numbers refer to like parts. In another embodiment,
The mold 30 includes a first portion 40 defining an internal cavity and a container! The first part 4 at the position corresponding to the inner recessed panel
at least one wall insert 41 attached to 0
and is included. The wall insert 41 preferably has a depth d that corresponds to the depth of a recessed panel or other recess formed in the container. Various embodiments other than those described above for wider walls include smaller wall inserts 4.
For example, as shown in FIG. 6, a smaller wall insert 41 can have a cutout 50 that increases insulation. It is also possible for the small insert to have an anodized surface 51. The wall insert may be connected to the outer portion 32 of the mold 30, for example at ports 52.

[Brief explanation of the drawing]

1 is a side view of a container with a recessed panel; FIG. 2 is a partial sectional view of a mold of the invention; FIG. 3 is a perspective view of a wall insert of one mold of the invention; FIG. FIG. 5 is an enlarged partial sectional view of another embodiment of the invention; FIG. 6 is a partial sectional view of another embodiment of the invention. 1: Container, 2: Main body, 3: Shoulder, 4: Bottom, 5: Neck, 6: Recessed panel, 7: Land, 8: Reinforcement rib,
30: mold, 31: inner part, 32: outer part, 33: wall insert, 34: wall, 35: duct, 36: cooling channel, 37: cutout, 38: duct, 39: inner surface, 40: 1st part, 41: wall insert, 50:
Cutout part, 51 two surfaces, 52: Porto.

Claims (1)

Claims: 1. A method of manufacturing a blow molded container, comprising blow molding a thermoplastic material comprising a mold cavity having an inner wall and corresponding to a large recessed panel formed in the container. forming the container in a mold having an inner protruding wall insert, heating the mold to heat set the container, the inner surface of the wall insert being heated to a temperature at which the inner wall of the mold is heated; A method for producing a blow-molded container characterized by heating at a temperature lower than . 2. The method of claim 1, wherein the material is polyethylene terephthalate. 3. The method of claim 2, wherein the temperature of the inner surface of the wall insert is about 10-30<0>C lower than the temperature of the inner wall. 4. The method of claim 3, wherein the temperature of the inner surface of the wall insert is about 15 to 25 degrees Celsius lower than the temperature of the inner wall. 5. The method of claim 3, wherein said heating is performed on said mold for about 1 to 20 seconds. 6. The method of claim 5, wherein said heating is applied to said mold for about 2 to 15 seconds. 7. The method of claim 1, wherein said inner wall has a plurality of said inner protruding wall inserts corresponding to a plurality of said large recessed panels. 8. A method of manufacturing a blow-molded container, wherein a polyethylene terephthalate parison is blow-molded in a mold, the mold having an inner surface consisting of a container body and a large inwardly projecting recessed panel; heating the inner surface of the mold for about 2 to 15 seconds with a temperature difference such that the large recessed panel portion of the mold is at a temperature of about 10 to 30° C. lower than the container body of the mold; A method of manufacturing a blow-molded container characterized by: 8. A method of manufacturing a blow-molded container, the method comprising: blow-molding a parison made of thermoplastic material into a mold comprising a mold cavity having an inner wall and having at least one inwardly projecting wall insert; A method of manufacturing a blow-molded container, characterized in that forming the wall and allowing air in the mold cavity to escape through air holes behind the wall insert. 10. a mold having an inner wall defining an inner cavity substantially corresponding to the size and shape of the final blow-molded container; at least one wall insert attached to the inner wall of the mold; and a protrusion of the cavity; A device for manufacturing blow-molded containers. 11. The apparatus of claim 10, further comprising a device for heating the inner wall of the mold. 12. The apparatus of claim 11, wherein the wall insert is heated less than the inner wall. 13. The apparatus of claim 12, wherein the wall insert comprises a cooling duct extending therethrough. 14. The apparatus of claim 12, wherein said at least one wall insert is replaceable. 15. The apparatus of claim 12, wherein the wall insert is made of a thermally insulating material. 16. The apparatus of claim 12, wherein the wall insert has an anodized surface. 17. Claim 12, wherein said wall insert has a partially cut-out periphery to provide greater insulation, thereby reducing heat transfer from said inner wall.
Equipment described in Section. 18. further comprising at least one air hole in the inner wall behind at least one of the wall inserts;
11. The device of claim 10, wherein the wall insert is adapted to pass air around its edges and into the air holes. 19. An apparatus for producing a blow-molded container, the apparatus comprising a mold having an inner wall and at least one wall insert connectable to the inner wall, the inner wall and the wall insert forming a final blow-molded container. An apparatus for producing a blow-molded container, the apparatus defining a cavity that substantially conforms to the shape of the container, the wall insert conforming to the shape of a recessed panel on the final blow-molded container. 20. The apparatus of claim 19, wherein the wall insert includes projections that match the shape of ribs on the recessed panel. 21. The apparatus of claim 19, wherein the wall insert slopes outwardly into the cavity toward a longitudinal mid-transverse line.