JPH04211919A - Mold for plastic bottle - Google Patents

Abstract

PURPOSE:To manufacture a molded product which has little unevenness to be caused by an air rich area and a high glossiness in the case where plastic bottle is molded by low molding. CONSTITUTION:Center line mean roughness of a cavity forming wall surface 5a forming a mouth part of a plastic bottle and a bottle main body part, whose bore is expanded, form the mouth part is established at 0.25mum or less by swelling-out of parison to be fed. Then an air suction hole communicating with an air sucking device decompressing a cavity space at the time of mold clamping is opened at any part of this cavity forming wall surface 5a.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a mold for molding plastic bottles.

0002

[Prior Art] Conventionally, when the mold for molding plastic bottles is opened, a parison is supplied between the opposing cavity forming walls, and when a parison of a predetermined length is supplied, the mold is closed. After the mold is clamped, compressed air is supplied to the parison in the mold to press the parison against the wall surface forming the cavity, and after the molded product is cured, the mold is opened.

The wall surface forming the cavity is set to be rough so that when compressed air is blown into the parison, air does not remain between the parison and the wall surface forming the cavity.

0004

[Problems to be Solved by the Invention] However, in the case of conventional molds for molding plastic bottles, the surface of the cavity forming wall is rough, so when compressed air is blown into the parison, the parison swells and the outer surface of the molded product is formed. becomes matte and the gloss level decreases.

Therefore, in order to increase the gloss of the outer surface of the molded product, if the average roughness of the wall surface forming the cavity is made smooth, when the parison expanded by compressed air comes into close contact with the wall surface forming the cavity, the parison and the cavity There has been a problem in that air pockets are formed between the molded product and the molded wall surface, causing unevenness on the outer surface of the molded product, resulting in a significant decrease in commercial value.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to improve the quality of the appearance of molded plastic bottles by minimizing the traces of air pockets as much as possible.

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, a plastic bottle molding die according to claim 1 of the present invention is provided, in which the mouth of the plastic bottle and the mouth of the plastic bottle are The center line average roughness of the cavity forming wall surface that forms the bottle body part whose diameter widens from the part to the bottle body part is set to 0.25 μm or less, and air is applied to any part of this cavity forming wall surface to depressurize the cavity space during mold clamping. It is characterized in that an air suction hole communicating with the suction means is opened.

[0007] Furthermore, in the plastic bottle molding die according to claim 2 of the present invention, in the plastic bottle molding mold according to claim 1, the cavity forming wall surface is a boundary between the mouth portion and the bottle body portion. A first air suction hole extending along the periphery of the mouth part is formed in a wall part forming the cavity, and a first air suction hole extending along the circumference of the mouth part is formed in a wall part from the bottle body part to the bottle bottom part of the cavity forming wall part, and the peripheral wall of the bottle body A second air suction hole is formed extending along the .

[0008]

[Operation] According to the plastic bottle molding mold according to claim 1 of the present invention, when or before supplying compressed air to the parison in the mold, the air suction means sucks the inside of the cavity through the suction hole. By reducing the pressure and then supplying compressed air to the parison, even if the parison comes into close contact with the cavity-forming wall surface, no air pockets are generated between the cavity-forming wall surface and the parison. Since the center line average roughness of the wall surface forming the cavity is set to 0.25 μm or less, the outer surface of the blow-molded molded product has a high degree of gloss, and the marketability of the molded product is improved.

According to the mold for forming a plastic bottle according to claim 2 of the present invention, on the cavity-forming wall surface of the mold, at the boundary between the mouth of the plastic bottle and the bottle body, there is a mold around the mouth. A first air suction hole is formed along the periphery of the bottle body, and a second air suction hole is formed along the periphery of the bottle body from the bottle body to the bottom of the bottle. When the air inside the cavity is sucked when air is blown to the parison inside the bottle, the air present on the wall surface forming the cavity is sucked along the circumferential surface of the bottle. Therefore, there are significantly fewer traces of air pockets on the surface of the bottle as a molded product, and the appearance quality of the molded product is significantly improved.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS A plastic bottle molding die according to an embodiment of claim 1 of the present invention will be described below with reference to the drawings.

FIG. 1 shows a plastic bottle molding die (simply referred to as a die in the following description of the embodiment) according to this embodiment. A cavity 3 is formed when the mold 2 is clamped with another mold 2. Since the configuration of mold 2 is similar to that of mold 1,
The description of mold 1 is cited.

Before the molds 1 and 2 are clamped together, a parison 4 (see FIGS. 4 to 6) is supplied, and this parison 4 is of a single layer type or a laminated type. The outermost layer is, for example, polyethylene, polypropylene, polybutene, polyester, polyacrylonitrile,
It is considered to be a resin such as polycarbonate.

The molds 1 and 2 are made of, for example, aluminum and carbon steel, and a recess 5 is formed in the parting surface 1a of the mold 1, which is in close contact with the mold 2, to form a cavity 3 when the molds are clamped. In the present invention, the wall surfaces of the recesses 5 of the molds 1 and 2 forming the cavity 3 are formed into cavity forming wall surfaces 5.
It is set as a. The center line average roughness of the cavity forming wall surface 5a is set to 0.25 μm or less.

Suction recesses 6 and 7 are formed in the parting surface 1a so as to surround the recess 5. The suction recesses 6 and 7 form air suction holes 8 and 8 when the molds 1 and 2 are clamped. Communication holes 9 and 10 communicating with the outside of the molds 1 and 2 are opened at the bottoms of the suction recesses 6 and 7. Air suction means 11 disposed outside the molds 1 and 2 is connected to the communication holes 9 and 10. Suction recess 6,
7 and the cavity forming recess 5 has a shallow groove 6 at the bottom.
a, 7a are formed. These grooves 6a and 7a are formed in the mold 1.
, 2, when the mold is closed, it forms a part of the air suction holes 8, 8, and when the mold is closed, the cavity 3 and the air suction holes 8, 8
The air is sucked from the cavity 3 by communicating with the cavity 3. Groove 6
The depths a and 7a are such that the parison 4, which expands when compressed air is blown into the parison 4, does not enter.

An extruder (not shown) is provided at the upper end of the recess 5.
A compressed air supply nozzle 21 is inserted into the upper end of the parison 4 and holds the parison 4 cut away from the parison 4.
can be held through the parison 4. Further, a blade portion 13 is provided at the lower end of the recess 5 to cut off the lower end of the parison 4 supplied from the extruder. On the wall surface 5b on the lower end side of the recess 5, an air suction means 1, which will be described later, is provided.
Air suction holes 14a, 14a connected to 1 are opened. As shown in FIG. 2, thin plate-shaped plugs 15, 15 made of sintered metal are fitted into the openings of the air suction holes 14a, 14a on the cavity side. It is designed to suck out the air inside.

As shown in FIG. 3, the air suction means 11 includes a vacuum pump 16, a vacuum chamber 17, pipes 18a and 18b, and valves 19 and 20. The vacuum pump 16 is connected to the chamber 17 via a pipe 18a, and the chamber 17 is connected to the communication hole 9 via a pipe 18b.
10 and air suction holes 14a, 14a. Valve 19 is provided in pipe 18a, and valve 20 is provided in pipe 18a.
b. Vacuum pump 16 and valves 19, 2
0 is driven by a drive device (not shown). valve 19
, 20, the valve 19 is opened and the valve 20 is closed until the parison 4 of a predetermined length is supplied between the molds 1 and 2.
When the chamber 17 is closed, the vacuum pump 16 is activated to reduce the pressure inside the chamber 17. The chamber 17 is a vacuum pump 16
As a result of the operation, the atmospheric pressure becomes 300 mmHg lower than normal pressure. In this embodiment, before the compressed air supply nozzle 21 is inserted into the parison 4 held in the molds 1 and 2, the valve 19
is closed and valve 20 is opened to suck air in cavity 3 into chamber 17. As a result, the air inside the cavity 3 is removed from the air suction holes 8, 8, 14a, 14.
It is introduced into the chamber 17 through the plugs 12 and 15 of b, and the pressure inside the cavity 3 is reduced. Once the pressure in the cavity 3 is reduced, the valve 20 is closed, the valve 19 is opened and the vacuum pump 16 is operated, and the pressure in the chamber 17 is reduced again. On the other hand, when compressed air is supplied from the compressed air supply nozzle 21 in a state where the pressure of the cavity 3 is reduced, the parison 4 expands and comes into close contact with the cavity forming wall surface 5a of the recess 5, and the molded product 2
2 is molded.

FIGS. 7 to 10 show an embodiment of a plastic bottle molding die according to claim 2 of the present invention, and a molding die 30 according to this embodiment has a mold and a mold (not shown). A cavity for blow molding is formed by clamping the mold.

The molding die 30 is a split mold, and is composed of split parts 31, 32, and 33 that are separably connected. The dividing portion 31 has a mouth forming wall surface 31a that forms the mouth of the plastic bottle.
A blade portion 31b for cutting the softened parison is formed at the upper part of a. A first air suction hole 31 is provided in the mouth forming wall surface 31a of the boundary portion of the dividing portion 31 separated from the dividing portion 32.
c is open. The first air suction hole 31c is formed around the mouth-forming wall surface 31a, so that air can be sucked almost uniformly from around the parison. A semicircular plug 31d made of sintered metal is attached to the air suction hole 31c. Alternatively, the clearance is set to such an extent that the expanded parison does not enter. The thickness of the air suction hole 31c and the plug body 31d is set to a width of 0.3 to 1 mm when the plug body 31d is included, and 0.3 mm to 1 mm when the plug body 31d is not included.
The thickness is 0.01 to 0.10 mm, and the thickness is such that the mark of the stopper 31d cannot be seen unless one looks closely enough at the boundary between the mouth of the bottle and the main body of the bottle. This part is when the cap is attached to the mouth of the bottle.
Since the position is covered by the end of the cap,
When displaying with a cap attached, the viewer should use the stopper 31d.
No trace of it can be found. The lower part of the air suction hole 31c communicates with an air hole 32f formed in the divided portion 32.

The dividing part 32 is a part that forms the bottle body of the plastic bottle, and since the bottom of the plastic bottle is raised, it is separably joined to the dividing part 33 to facilitate the removal of the molded product. , is separably joined to the dividing portion 31 in order to facilitate removal of the mouth portion. A cavity forming wall surface 32b forming the bottle main body is bored in the parting surface 32a of the dividing portion 32,
A shallow groove 32c is formed in the peripheral edge of the cavity forming wall surface 32b to form a slit for sucking air from the cavity when the molding die 30 is clamped. An air hole 32d is formed in this shallow groove portion 32c, one end of this air hole 32d is open to the shallow groove portion 32c, and one end of this air hole 32d is made of a sintered metal that is permeable to air. A plug body 32e is fitted. The other end of the air hole 32d opens to the joint surface of the divided portion 33 of the divided portion 32, and communicates with the air hole 33e of the divided portion 33. The divided part 32 has a divided part 3 by joining with the divided part 31.
An air hole 32f communicating with the first air suction hole 31c passes through the air hole 32f.

The dividing part 33 is for forming a raised part on the bottom of the plastic bottle to improve the strength by being raised inside the bottle, and has a curved bottom forming wall surface 33a to round the corners of the bottom. are doing. This bottom forming wall surface 33a corresponds to the boundary between the bottle body and the bottom, and a semicircular groove 33b as a second air suction hole is formed in this bottom forming wall surface 33a. This groove portion 33b forms a second air suction hole 33g by joining the divided portion 32 and the divided portion 33. A semicircular plug 33c made of air-permeable sintered metal is fixed to the groove 33b, but the width of the groove 33b may be set to a clearance that prevents the expanded parison from entering. The outer periphery of the plug body 33c is a space, and this space is a second space.
It forms a part of the air suction hole, and communicates with the air hole 33d passing through the divided portion 33. In addition to the air hole 33d, air holes 33e and 33f are formed in the divided portion 33. The air hole 33e communicates with the air hole 32d of the divided portion 32, and the air hole 33f communicates with the air hole 32f of the divided portion 32. Pipes (not shown) are connected to the air holes 33d, 33e, and 33f, respectively, and the air inside the cavity is sucked when the cavity is formed by controlling the amount of air of an air suction pump that communicates with each pipe.

[0021] In order to mold a symmetrical plastic bottle by blow molding, it is necessary to prepare a mold with a shape symmetrical to the mold 30, but this mold is used for forming the cavity and for forming the first and second molds. For the air suction hole in No. 2, mold 30 is used.
Since the configuration is the same as that of , the above explanation will be cited. or,
34 is a mounting plate for fixing the mold 30.

Next, the opening/closing operation of the mold and the air suction control when blow molding is performed using this mold 30 will be explained.

First, the mold 30 is opposed to a symmetrical mold in an open state so that a cavity can be formed, and a parison is extruded from an extruder into the space facing the mold. When the parison has been extruded to a sufficient length, extrusion is stopped and the molds forming the cavity are closed. With the mold closed, an air suction pump (not shown) is driven to suck air in the cavity from the air holes 33d, 33e, and 33f, and also to suck air from the blow device into the parison in the mold. The air in the cavity passes through air-permeable sintered metal plugs 31c, 32e, and 33c to the first air suction hole 31d and the air hole 32d in the shallow groove 32c.
Since air is sucked from the second air suction hole 33g, when the parison extends along the cavity forming wall surfaces 31a, 32b, 33a, the gap between the parison and the cavity forming wall surfaces 31a, 32b, 33a increases. The occurrence of air pockets can be significantly suppressed. During air blowing of the parison, air suction from the air holes 33d, 33e, and 33f continues, and air suction is stopped at the same time as the air blowing is completed. As a result, the outer surface of the parison in the mold has very few traces of air pockets, that is, it has a very high degree of smoothness. After air blowing to the parison is stopped and the parison is cooled and hardened, the mold is opened and the molded product is dropped into a storage box below the mold.

[0024]

[Effect] As explained above, the plastic bottle molding die according to claim 1 of the present invention prevents air pockets between the cavity forming wall surface and the parison even when a molded product is molded by blow molding. There is no unevenness caused by air pockets on the surface of the molded product, and
Since the centerline average roughness of the wall surface forming the cavity is set to 0.25 μm or less, the outer surface of the molded product has a high degree of gloss, which has the effect of improving the marketability of the molded product.

[0025] Furthermore, according to the plastic bottle molding die according to claim 2 of the present invention, when air is blown into the parison in the clamped mold, when the air in the cavity is sucked, the cavity forming wall surface The air present in the bottle is sucked along the circumference of the bottle. Therefore, there are significantly fewer traces of air pockets on the surface of the bottle as a molded product, and the appearance quality of the molded product is significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a mold for forming a plastic bottle according to an embodiment of claim 1 of the present invention.

2 is an explanatory diagram of air suction means connected to the mold for forming the plastic bottle of FIG. 1; FIG.

FIG. 3 is an explanatory diagram showing the configuration of air suction means.

FIG. 4 is an explanatory diagram of a process of supplying a parison between opened molds.

FIG. 5 is an explanatory diagram showing a process of sucking air while blowing air to the parison in the mold.

FIG. 6 is an explanatory diagram of a state in which the parison in the mold is completely filled with air. It is an explanatory view showing a vacuum suction process.

FIG. 7 is a perspective view of a mold for forming a plastic bottle according to an embodiment of claim 2 of the present invention.

8 is a partial cross-sectional view showing the configuration of a first air suction hole provided at the boundary between the mouth of the molding die and the bottle main body in FIG. 7. FIG.

9 is a partial cross-sectional view showing the configuration of a second air suction hole provided between the bottle main body and the bottom of the molding die shown in FIG. 7. FIG.

10 is a perspective view showing a schematic configuration of the molding die shown in FIG. 7. FIG.

[Explanation of symbols]

1, 2... Mold (plastic bottle mold) 1a...
Parting surface 3... Cavity 4... Parison 5... Recess 5a... Wall surfaces of the recess (cavity forming wall surface) 6, 7... Suction recesses 6a, 7a... Groove 8... Air suction hole 10... Communication hole 11... Air suction means 12... Plug 30... Mold 31c... First air suction hole 31d... Plug body 32c... Shallow groove portion 32d... Air hole 32e... Plug body 32f... Air hole 33g... Second air suction hole 33c... Plug body 33d, 33e, 33f ...Air hole

Claims (2)

[Claims] Claim 1: The average roughness of the center line of the cavity forming wall surface, which forms the mouth of the plastic bottle and the bottle body whose diameter widens from the mouth due to the expansion of the supplied parison, is set to 0.25 μm or less. A mold for forming a plastic bottle, characterized in that an air suction hole communicating with an air suction means for reducing the pressure in the cavity space during mold clamping is opened in any part of the cavity forming wall surface. 2. The plastic bottle molding die according to claim 1, wherein the cavity forming wall surface forming a boundary between the mouth portion and the bottle body portion includes:
A first air suction hole extending along the circumference of the mouth part is formed, and a second air suction hole extending along the peripheral wall of the bottle body is formed in a wall surface portion of the cavity forming wall surface from the bottle body part to the bottle bottom. A mold for forming a plastic bottle characterized by having a suction hole formed therein.