JPH0414430A - Method and apparatus for manufacturing deep-drawn plastic container - Google Patents

Abstract

PURPOSE:To position a container stably and contrive prevention of collapse, deviated draw-out or the like of the container from occurring at the time of trimming, by sliding an annular body in a direction for reducing a step between the annular body and an opening part of a mold cavity while maintaining an airtight condition by a cooling plate, upon completion of a drawing operation. CONSTITUTION:At the time of drawing a molten plastic sheet, a plug 20 is in the condition of being inserted deepest into a metallic mold, and an upper mold 24 is also lowered, whereby sealing is made between an engaging projected part 28 of the upper mold 24 and an opening part 14 of a mold cavity through the plastic sheet. Immediately before or after completion of a drawing operation, an air cylinder 30 is operated to press an annular body 15 by a cooling plate 32, thereby sliding the annular body 15 in a direction for reducing a step between the opening part 14 and an upper surface of the annular body 15 until the step is eliminated. Concurrently, pressurized air is sucked in through an annular gap 29 between the upper mold 24 and the plug 20, and the cavity 11 is evacuated through vent holes 19. As a result, the molten plastic sheet 1 is expanded, and is cooled by making contact with the mold surface, thereby being formed to be a deep-drawn container 33.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for manufacturing deep-drawn plastic containers. The present invention relates to a method and apparatus for manufacturing deep-drawn plastic containers that allow for stable trimming of the container afterwards.

(Prior Art) Conventionally, methods for manufacturing deep-drawn plastic containers from plastic sheets, etc. include plug-assisted pressure forming or vacuum forming methods that use a combination of a female mold and a plug (for example, U.S. Pat. .893,882 specification)
Also known are vacuum forming methods using a combination of a clamp for holding a plastic sheet, a guide ring, and a cylindrical male mold (for example, Japanese Patent Application Laid-Open No. 60-92827).

Furthermore, the plug-assisted molding method involves preheating a plastic sheet to a temperature lower than its melting point but still allowing stretch molding, and then introducing the plastic sheet between a molding plug and an opening mold to bulge the sheet with the molding plug. A solid phase sheet molding method in which molding is performed on the mold surface by moving the plug into the mold and introducing pressure fluid between the plug and the sheet, or by creating a vacuum between the sheet and the mold. There is also a molten sheet molding method in which molding is carried out in the same manner as above except that the plastic sheet is heated above its melting point.

The former solid-phase molding method imparts molecular orientation to the side wall of the container and is expected to improve strength, transparency, gas barrier properties, etc. However, on the other hand, there is a problem of a decrease in heat resistance due to the heat shrinkage of the container wall. In particular, it cannot be applied to storage containers that require hot filling or retort sterilization.

On the other hand, the most problematic point when manufacturing deep-drawn containers using sheet melt molding is that, unlike solid-phase molding, the tension of the resin melt is quite low. For this reason, the formed container does not have uniform wall thickness in the height direction, and there is a strong tendency for the wall thickness to be particularly thin at the bottom corner portions and the upper portion in the height direction. Further, when the molten sheet is squeezed into the mold cavity, there is a problem in that a drag line (contact mark) is likely to be generated in the upper part of the container in the height direction due to the contact of the sheet material with the upper part of the mold.

The most important issue in solving the above problems that occur when deep drawing a molten sheet is how much of the molten sheet can be drawn into the mold cavity without lowering the temperature as much as possible. It is taking place.

Even if the prior art deep drawing method described above is applied to a molten sheet, the sheet cannot be sufficiently drawn into the mold, and the above-mentioned problem has not yet been solved.

Furthermore, the following method has been proposed as a method for solving the above-mentioned problem, minimizing the temperature drop of the molten sheet, and making it possible to draw a large amount of the molten sheet into the mold cavity.

In Japanese Patent Application No. 62-315377 (Japanese Unexamined Patent Publication No. 1-156039) proposed by the present inventors, a plastic sheet in a molten state is
Or, in a method of manufacturing a plastic container that involves pressure forming, the plug and the mold are moved relative to each other in the closing direction to generate positive pressure between the mold and the molten sheet, and the heat insulation property is improved. The molten sheet is squeezed into the mold while sliding the molten sheet on the upper surface of the mold, which has smoothness, and after the mold is clamped, the molten sheet is brought into contact with the mold and cooled. A method for manufacturing squeezed plastic containers has been proposed. The upper surface of the mold is annular and serves as a guide member when squeezing the plastic sheet.

(Problem to be Solved by the Invention) However, in the conventional method, it was possible to draw a large amount of the plastic sheet into the mold cavity by providing an annular guide member during molding. It is fixed to the mold above the opening and radially outward, and when the plastic sheet is being pulled in with the plug during molding, there is a predetermined step between the guide ring and the mold cavity to ensure smooth retraction. However, the stepped portion remains even after the container is molded after plug insertion is completed. That is, a large step is formed between the flange portion of the container and the unformed portion outside the flange portion.

Therefore, when the molded container is trimmed from the plastic sheet with a cup trimmer after the container is molded, the molded stepped portion is thin and long, making the positioning with the blade unstable, resulting in the container being crushed or pulled out. Furthermore, the blade of the cup trimmer becomes thinner and has a higher blade height due to the stepped portion, resulting in a problem in that the strength and life of the blade are reduced.

Therefore, an object of the present invention is to stabilize the positioning of the container during trimming after drawing of a plastic sheet, etc. in the production of deep-drawn plastic containers by the sheet melt-molding method, and to prevent the container from being crushed or pulled out during trimming. To provide a method for producing a deep-drawn plastic container that does not cause the occurrence of water damage and has excellent trimming workability, and a production apparatus used for the production.

Furthermore, another object of the present invention is to improve the strength and life of a cup trimmer blade when trimming a plastic sheet, etc. after drawing, and to improve the appearance of the trimmed part in the production of deep drawn plastic containers by the sheet melt forming method. An object of the present invention is to provide an excellent method and apparatus for manufacturing deep-drawn plastic containers.

(Means for Solving the Problems) According to the present invention, a plastic sheet in a molten state is sandwiched between the plug and the mold, and the plug is located above and radially outward from the opening of the mold and the mold cavity. A heat-insulating and slippery annular body that maintains airtightness is placed between the mold cavity, the plastic sheet is supported by the annular body, and in this state, the plug and the mold are moved relative to each other in the closing direction. The plastic sheet is then slid over the annular body and squeezed into the mold while creating a positive pressure between the mold and the plastic sheet, and immediately before or after the completion of this squeezing operation, the plastic sheet is squeezed into the mold. A method for manufacturing a deep-drawn plastic container is provided, which comprises moving an annular body in a direction to reduce the height difference between the annular body and the opening of a mold cavity, then clamping the mold, and then performing vacuum and/or pressure forming.

The invention also provides a combination of a supporting and feeding mechanism for a plastic sheet in a molten state, a plug placed on one side of the plastic sheet, and a mold having a cavity placed on the other side of the sheet. A plug assist vacuum and/or pressure forming mechanism consisting of a plug assist vacuum and/or pressure forming mechanism, a drive mechanism for relatively stroking the plug and the mold in the closing direction, and a heat insulator disposed above and radially outward from the opening of the mold cavity. an annular member for supporting a sheet having elasticity and slipperiness, an elastic member that supports the annular member so as to be able to move backward from the above-mentioned position in a direction that reduces the level difference between the annular member and the opening of the mold cavity, and an annular member and the mold. The drive mechanism and the annular body are provided with an air-tight mechanism for maintaining an air-tight state, and the driving mechanism and the annular body are arranged so that the plastic sheet is supported by the annular body and the mold is molded by a plug while the plastic sheet is supported by the annular body and positive pressure is generated between the sheet and the mold. Deep drawing, characterized in that drawing is carried out into the mold, and the annular body is associated with the annular body so as to move in a direction that reduces the step with respect to the opening of the mold cavity immediately before or immediately after the completion of the drawing operation. An apparatus for manufacturing a plastic container is provided.

As a mechanism for moving the annular body from the above-mentioned position in a direction to reduce the level difference with the opening of the mold cavity, a cooling plate drive mechanism is provided on the bottom wall of the upper mold having an opening through which the plug enters and exits. It is preferable to provide a cooling plate for pressing the annular body at the tip of the plate drive mechanism.

(Function) In the manufacturing method of the present invention, a plastic sheet in a molten state is positioned between a plug and a mold, and the plug and mold are relatively moved in a closing direction to perform molding.
This relative movement is carried out while supporting the molten sheet with an annular body having heat insulating properties and sliding properties, and generating positive pressure between the mold and the molten sheet, and moving the molten sheet over the annular body. The sheet is squeezed into the mold while sliding and molded, but the annular body is kept airtight by means of supporting pressure in the direction of reducing the level difference with the opening of the mold cavity immediately before or after the completion of the squeezing operation. A distinctive feature is that the mold is moved and slid while the mold is closed, and then vacuum and/or pressure molding is performed after the mold is clamped.

The manufacturing apparatus of the present invention also includes a supporting and feeding mechanism for a plastic sheet in a molten state, a plug assist vacuum and/or pressure forming mechanism consisting of a combination of a plug and a mold having a cavity, and a direction in which the plug and the mold are closed. a drive mechanism for driving the stroke relative to the mold cavity; This device is supported by an annular body and can be molded by drawing the molten sheet into the mold while sliding the molten sheet over the annular body while generating positive pressure between the mold and the molten sheet. A mold for molten sheets using a plug, which is equipped with an elastic member that supports the annular body so as to be retracted in a direction that reduces the level difference from the opening of the mold cavity, and an airtight mechanism that supports pressure and holds the annular body and the mold in an airtight state. A distinctive feature is that the annular body is associated with movement in a direction that reduces the step with the opening of the mold cavity just before or immediately after the completion of the inward squeezing operation.

First, placing an annular body having heat insulation and sliding properties above and radially outward of the opening of the mold cavity to support the molten sheet reduces the gap between the mold and the molten sheet. It has the dual function of allowing positive pressure to be generated and maximizing the amount of molten sheet drawn in without substantial temperature drop.

By generating positive pressure between the mold and the molten sheet, the molten sheet is pressed toward the plug and is prevented from coming into contact with the mold surface. In particular, when observing the insertion state of the plug into the mold, it was found that the wrapping height of the molten sheet around the side wall of the plug increased significantly. Therefore, even when the plug was inserted deeply into the mold cavity, the molten sheet is effectively prevented from coming into contact with the mold opening end. In this way, the generation of drag lines in the upper part of the side wall of the molded container and the deterioration of the appearance characteristics due to this are prevented, and the increase in the height of wrapping around the side wall of the plug reduces the amount of the molten sheet drawn into the mold. This will also contribute to an increase in

Further, since the molten sheet is squeezed while sliding on the annular body, there is an advantage that the amount of the molten sheet drawn in can be maximized. In other words, by making the annular body heat insulating and slippery, and by combining it with the above-mentioned positive pressure generation operation, the molten sheet slides on the annular body and is uniformly stretched as a whole, thereby allowing it to flow into the mold. This makes it possible to maximize the amount of molten resin drawn in. As a result, according to the present invention, the basis weight of the container is increased compared to plastic sheets of the same thickness, and excessive thinning of the side wall of the container and non-uniformity of the wall thickness can be effectively prevented. It becomes.

An elastic member that supports the annular body so as to be able to retreat in a direction that reduces the level difference with the opening of the mold cavity supports the pressure by pressing the annular body, enables the annular body to move and slide, and also resists the pressure. When released, it serves to return the annular body to its original position. In addition, the airtight mechanism installed on the upper part of the outside wall of the mold allows the annular body to slide freely, seals the sliding gap between the mold and the annular body, maintains airtightness, and reduces the pressure in the mold cavity. I'm trying to keep it. Further, the cooling plate provided on the outer side of the plug diameter facing the annular body is supported at the end of the cooling plate drive mechanism provided on the upper die, so that the cooling plate drive mechanism is actuated to cause the cooling plate to actuate. By pressing the annular body, the annular body can be moved in a direction that reduces the level difference between the annular body and the opening of the mold cavity. Thus, just before or immediately after the completion of the squeezing operation of the plastic sheet, the annular body is moved by the above means in a direction to reduce the level difference with the opening of the mold cavity, and after the mold is clamped, vacuum and/or pressure forming can be performed. . Further, the cooling plate can cool the plastic sheet by coming into close contact with the plastic sheet.

According to the present invention, unlike conventional methods, no step is created between the flange of the molded container and the unformed part outside of it after molding, so the rigidity around the cutting part is increased and the positioning with the blade is stable. Eliminates the occurrence of container soaking and slippage. Furthermore, when trimming with a cup trimmer, a deep-drawn plastic container is provided that improves the strength and life of the cup trimmer blade and provides an excellent appearance of the trimmed portion.

(Preferred Embodiment of the Invention) In Figures 1 to 3 for explaining the manufacturing method and manufacturing apparatus of the present invention, Figure 1 is a side view showing the preparation state before molding, and this preparation stage And overall! The mold indicated by 0 and the plug indicated by 20 are in the most distant positional relationship, and a plastic sheet 1 in a molten state supported by a fixture 2 such as a chuck is placed between the mold 10 and the plug 20. Supplied.

In the present invention, a plastic sheet in a molten state refers to a temperature higher than the melting point of a crystalline thermoplastic resin, and a temperature higher than the glass transition point 6 or the softening point of an amorphous thermoplastic resin. A plastic sheet that is at a temperature of

The mold 10 has an open cavity 11 inside.
It has a bottom wall surface 12 that defines the bottom wall of the container to be molded, and a side wall surface 13 that defines the side walls of the container. At the upper end of the side wall surface 13 is located the opening 14 of the mold cavity, which defines the opening flange of the container. An annular body 15 having heat insulating properties and sliding properties is provided above and radially outward of the opening 14 of the mold cavity, and is supported by an elastic member 16 . The elastic member 16 is, for example, a metal spring,
According type spring made of rubber elastomer,
It can be constituted by an air spring, other fluid cylinders such as air cylinders, oil cylinders, etc. An airtight mechanism part 17 is provided at the upper part of the outer wall surface of the mold.
The annular body 15 is able to move and slide downward while maintaining airtightness between it and the outer wall surface of the mold by the airtight mechanism part 17. 18 is a mold base.

The mold 10 is provided so as to be movable in the height direction of the side wall portion 13, that is, in the vertical direction in the figure, and is in the lowest position in FIG. A vent hole 19 is provided in the bottom wall of the mold to exhaust air between the wall of the container being molded and the inner surface of the mold, or to reduce the pressure in the space.

The plug 20 has a tip 21 that engages with the plastic sheet 1 and a tapered side wall 22 that squeezes the plastic sheet 1, and is connected to a drive shaft 23.

The plug 20 is also provided so as to be movable in the height direction of the side wall portion 22, that is, in the vertical direction in the figure, and is in the highest position in FIG. An upper mold 24 is provided coaxially with the plug 20. The upper mold 24 consists of a cylindrical side wall 25 extending below the bottom wall and a bottom wall 26, and the bottom wall 26 is provided with an opening 27 through which the plug 20 can go in and out. The lower side of the cylindrical side wall portion 25 is engaged with the opening 14 of the mold cavity through the plastic sheet 1 to compression mold the container flange portion and to seal the mold 10 and the upper mold 24. An engagement protrusion 28 is provided. The upper mold 24 is also provided to be movable in the vertical direction, but its vertical movement can be performed independently of the plug 20. Even when the plug 20 is moved to the lowest position relative to the upper mold 24, an annular void [29] is formed between the two. Further, the inside of the upper mold 24 is connected to a pressurized gas mechanism, and this pressurized gas can be supplied to the lower side through the gap 29. Further, the bottom wall portion 26 of the upper die 24 is provided with a cooling plate driving air cylinder 30 installed on the bottom wall portion 26 and a cooling plate 32 fixed to the tip of the piston rod 31 and moving up and down together. plug 2
0 and the mold 10 are relatively driven in the closing direction, the lower surface of the cooling plate 32 and the upper surface of the annular body 15 engage with each other, and the annular body 15
When moving the cooling plate 3 backward from the above-mentioned position in a direction to reduce the level difference between the mold cavity opening 14 and the mold cavity opening 14, the cooling plate driving air cylinder 30 is activated to push out the piston rod 31 and move the cooling plate 3
2 can press the annular body 15 to eliminate the difference in level. Further, by retracting the piston rod 31, the pressure can be released and the original position can be restored by the anti-light force of the elastic member 16.

Figure @2 shows the molten plastic sheet under drawing. That is, from the preparatory stage shown in FIG. 1, the mold 10 begins to rise and the plug 20 begins to descend. The annular body 15 and the elastic member 16 supporting it are interlocked with the mold 10. This causes the annular body 15 to engage the underside of the molten plastic sheet 1 .

Even if the annular body 15 engages with the molten plastic sheet 1,
Since this has heat insulating properties, the temperature of the molten plastic sheet 1 does not drop during actual purchase. Tip 2 of plug 20
1 engages the upper surface of the molten plastic sheet 1 and squeezes the molten plastic sheet 1 toward the cavity 11 of the mold. During this squeezing, the upper surface of the mold is sealed with the molten plastic sheet 1, and the molten plastic sheet 1 is squeezed into the cavity, so a positive pressure is generated within the cavity 11. Due to the downward movement of the plug 20 and the generation of positive pressure inside the mold cavity 11, the molten plastic sheet 1 is wrapped around the plug side wall 22 to a large length,
In addition, this increased winding length also prevents the molten plastic 1 from coming into contact with the opening 14 of the mold cavity. Due to the relative movement of the plug 20 and the mold 10 in the closing direction, the molten plastic sheet 1 is inserted into the cavity 11 of the mold.
be effectively drawn into. That is, since the annular body 15 has slipperiness, the molten plastic sheet 1
As already mentioned above, it is effectively drawn into the cavity 11 of the mold while sliding on the top.

Furthermore, when squeezing the molten sheet, it is also effective to introduce pressurized gas into the mold through the ventilation holes 19) to control the pressure inside the mold cavity 11.

In FIG. 3, which shows the vacuum and/or pressure molding state, the plug 20 is in the deepest inserted state in the mold, and the upper mold 24 is also lowered, and its engagement protrusion 28 and the mold cavity opening are inserted. 14 through a plastic sheet. Immediately before or immediately after the completion of the narrowing operation, the cooling plate air cylinder 30 is operated to press the annular body 15 with the cooling plate 32 to close the opening 14 of the mold cavity and the annular body 1.
5 to eliminate the difference in level. At the same time, the upper die 24 and the plug 20
Pressurized gas is blown between the molten plastic sheet 1 and the molten plastic sheet 1 squeezed through the annular gap 29 between the mold cavity 11 and the mold cavity 11 is evacuated (depressurized) through the vent hole 19. Molten plastic sheet 1 narrowed down by this
is expanded, cooled by contacting the mold surface, and is formed into a deep-drawn container 33.

In the present invention, any thermoplastic resin material that can be melt-molded can be used as the plastic sheet, such as olefin resin, styrene resin, vinyl chloride resin, vinylidene chloride resin, Polyester resins, polyamide resins, etc. can be used alone or in combination of two or more. Among these, olefin resins are advantageous for the molding method of the present invention, and as olefin resins, the main constituent monomer is composed of olefin, and they are also crystalline, and have low, medium, and high densities. Polyethylene, isotactic polypropylene, crystalline propylene-ethylene copolymer, crystalline ethylene-butene copolymer, crystalline ethylene-propylene-butene copolymer, or blends thereof are used. Ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, within the range that satisfies the condition of crystallinity,
Ionically crosslinked olefin copolymers (ionomers) may also be used alone or in combination with other olefinic resins. Polypropylene is particularly well suited for use as retort sterilization or reheating containers.

Although the olefin resin can be used alone, it is preferable to use it in combination with an oxygen gas barrier resin from the viewpoint of preserving the contents. The oxygen barrier resin has an oxygen permeability coefficient of 5.5×10-”cc-cm/cm2・s
Resins having a temperature of ec-cm Hg or less (37°C, O%RH), such as ethylene-vinyl alcohol copolymers, polyamide resins, vinylidene chloride resins, and high nitrile resins, are used.

In FIG. 4 showing the cross-sectional structure of a plastic sheet suitably used for the purpose of the present invention, this sheet 1 includes an inner layer 3a and an outer layer 3b made of a moisture-resistant thermoplastic resin such as an olefin resin or a styrene resin; It has a laminated structure including an intermediate layer 4 made of gas barrier resin, and adhesive layers 5a and 5b provided for firmly adhering the inner and outer layers and the intermediate layer if necessary. This laminate structure is preferably produced by coextruding the moisture resistant thermoplastic resin, gas barrier resin and optionally adhesive resin into the multilayer structure through a multilayer die, but of course by sandwich lamination. It can also be manufactured by other lamination techniques such as extrusion coating.

As the adhesive resin, a resin exhibiting adhesiveness to both the moisture-resistant thermoplastic resin and the oxygen barrier resin, for example, an acid-modified olefin resin such as maleic anhydride graft-modified polyethylene or maleic anhydride graft-modified polypropylene; Ethylene-ff [vinyl copolymer, ethylene-ff]
Acrylic ester copolymers, ionomers, etc. can be used. Also, between the adhesive resin layer and the moisture-resistant thermoplastic resin layer, a scrap resin composition from the sheet (
That is, a layer of a moisture-resistant resin, an oxygen barrier resin, and an adhesive resin composition may be interposed.

The plastic sheet used in the present invention may contain compounding agents for plastics known per se, such as antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents, fillers, colorants, and the like. For the purpose of making molded containers opaque,
Fillers such as calcium carbonate, calcium silicate, alumina, silica, various clays, calcined gypsum, talc, magnesha, etc., and inorganic and organic pigments such as titanium white, yellow iron oxide, red iron oxide, ultramarine blue, and chromium oxide may be blended. I can do it.

The plastic sheet used in the present invention generally has a thickness of 0.5 to 5 mad, although it varies depending on the size of the container etc.
In particular, it is preferable to have a thickness of 1 to 3 mm. In the above-mentioned plastic sheet having a laminated structure, the thickness (tA) of the moisture-resistant resin inner and outer layers and the thickness (ta) of the oxygen barrier resin intermediate layer are tA:ts=100:1 to 4:1.
In particular, it is desirable that the ratio be within the range of 25:1 to 5.1.

Molding Conditions According to the present invention, the plastic sheet is first heated to a temperature above its melting point or softening point. The plastic sheet can be heated by infrared rays to far infrared rays, heating with a hot air oven, heating by heat transfer, or the like.

The annular body with heat insulation and sliding properties is made of heat-resistant plastic with a low coefficient of friction, such as Bakelite (novolac type phenolic resin), polycarbonate, and Teflon (
It is preferably made of polytetrafluoroethylene) or the like.

On the other hand, the mold is desirably made of a metal material with excellent thermal conductivity, ceramic, etc., especially aluminum or aluminum alloy, so that the wall of the resin container being molded can be rapidly cooled. The cooling plate is desirably made of a material with excellent thermal conductivity so that rapid cooling is possible like the mold. In addition, the structure that allows cooling fluid to pass through the inside is also a structure that can be cooled.

The annular body 15 should be provided above and radially outward from the opening of the mold cavity, so that the tangent between the inner periphery of the annular body and the opening of the mold cavity is relative to the plane that includes this part. The angle (θ) formed by the
In particular, it is desirable that the angle be in the range of 35 to 45 degrees from the viewpoint of preventing drag lines and improving the utilization rate of plastic sheets for containers. That is, if this angle (θ) is smaller than the above range, drag lines are likely to occur,
On the other hand, if it is larger than the above range, the amount of retraction of the plastic sheet decreases, and the upper part of the container tends to become thinner.

On the other hand, if a special heating means is not provided for the plug, a material with high heat insulation properties, such as heat-resistant plastics such as polyoxymethylene resin or polytetrafluoroethylene, is used; in the case of a plug with a built-in heating means, An aluminum plug can be used. From the viewpoint of molding workability, it is preferable that the outer diameter (DP) of the plug tip is in the range of 35 to 80%, particularly 60 to 70%, of the inner diameter (DM) of the opening of the mold cavity. On the other hand, it is desirable that the taper angle (α) of the plug taper side surface be in the range of 0.5 to 10 degrees, particularly 2 to 6 degrees, in order to increase the height by wrapping the plastic sheet around the side surface. The radius of curvature (R) of the curvature section provided between the plug tip and the tapered side surface is generally in the range of 1 to 25 mm, particularly preferably in the range of 3 to 10 mm. That is, if this R is larger than the above range, the bottom and corners of the container tend to become thinner.
If it is smaller than the above range, the bottom tends to become thicker.

Positive pressure (P) generated in the space between the mold and the molten sheet
is generally in the range of 0.02 to 0.5 kg/cm' gauge, particularly 0.06 to 0.2 kg/c+n2 gauge. If this pressure (P) is smaller than the above range, drag lines will easily occur, while if it is larger than the above range, the container wall will become thinner. This is done by controlling the escape of air from the bottom or by adjusting the relative speed of movement of the plug into the mold, or by introducing pressurized gas into the mold cavity through the bottom vent.

In the present invention, the plug depression rate defined by the following formula is:
In general, it is desirable that the range is 70 to 98%, especially 90 to 98%, and the plug volume ratio is 25 to 80%.
, particularly preferably in the range of 40 to 60%. According to the present invention, by using the above-described means, the sheet retraction rate defined by the formula described later can be adjusted to 2.4 to 3.
It is worth noting that values as high as 6, especially 2.7 and 3.3, can be achieved.

Immediately before or immediately after the completion of the narrowing operation, the air cylinder 3o for driving the cooling plate is operated as described above, and the cooling plate 32 is pushed by the stroke of the piston rod 31, and the annular body 15 is
is pressed to move and slide the annular body 15 in a direction that reduces the level difference with the opening 14 of the mold cavity, and the stroke stops at a position where the upper surface of the annular body 15 and the opening 14 of the mold cavity eliminate the level difference. adjusted so that The airtight mechanism part 17 is in close contact with the outer wall surface of the mold and the inner surface of the annular body 15, and allows the annular body 15 to move up and down while maintaining airtightness.

Expansion of the squeezed molten sheet within the mold can be easily performed by creating a vacuum between the sheet and the mold surface, introducing pressurized gas between the plug and the sheet, or a combination of the two. be exposed. It is generally advantageous to use 1 to 5 kg/cm2 of compressed air.

Advantageously, the temperature of the mold surface is generally in the range 5 to 40 t.

The present invention is particularly suitable for devices with a height-to-aperture ratio of about 0.8 or more.
1.0 to 1.7.

In the manufacturing method and manufacturing apparatus of the present invention, plastic containers can be molded one at a time, but usually a large number of molds are arranged and a large number of molds are molded at the same time.

FIG. 5 shows an example of a mold layout (plan view). Thirty molds 10 are arranged on the mold base 18, and 30 molds are placed at one time.
Can be individually molded. The arrow indicates plastic sheet 1
When the deep drawing process is completed, the plastic sheet 1 is fed by the length of the mold arrangement for the next forming process.

The deep-drawn plastic container manufactured by the present invention is characterized by excellent container trimming properties after molding.

FIG. 6 is a cross-sectional view of a deep-drawn plastic container that has been molded and has not yet been trimmed;
Figure 6-A is a sectional view of a molded container molded according to the present invention, and Figure 6-B is a sectional view of a molded container molded by a conventional method. The molded container 33 has a bottom part 34 and a wall part 35.
and a flange portion 36.

In the molded container according to the present invention, as shown in Fig. 6-A, the flange portion 36 continues to the unformed part 37 of the sheet 1 without any step, but in the molded container according to the conventional method, as shown in Fig. 6-B. , the flange portion 36 continues to the unformed portion 37 of the sheet 1 via a stepped portion 38 .

According to the present invention, since the flange portion 36 of the molded container continues to the unformed portion 37 of the sheet 1 without any difference in level, excellent container trimming performance can be achieved as described later.

Trimming the shaped container The shaped container is trimmed by a cup trimmer in a trimming process.

FIG. 7 is a cross-sectional view for explaining the trimming situation of a deep-drawn plastic container formed by a cup trimmer, and FIG. 7-A shows the trimming situation of a molded container according to the present invention. Figure 7-B shows the trimming situation for a molded container by the conventional method. As shown in the figure, the cup trimmer 40 has a lower blade 41 and an upper blade 4.
2, and a knockout plate 43. The outer portion of the flange portion 36 of the shaped container is trimmed by the lower blade 41 and the upper blade 42 to produce a deep drawn container, which is knocked out from the cup trimmer with a knockout plate.

In the case of the present invention, since there is no step between the flange portion 36 of the molded container and the unformed portion 3f, the upper blade 42 is lower than the conventional method.
Since the width of the blade is wide and the blade pattern is low, positioning of the blade is easy and stable, and the trimming dimensions are stable and trimming defects do not occur.
Since there is a stepped portion 38 between the upper blade 4 and the unformed portion 37, the upper blade 4
Since the width of the container 2 is narrow and the blade pattern is high, the positioning of the blade becomes unstable, and the trimming dimension becomes unstable, resulting in trimming defects such as container crushing and misalignment. In addition, in the conventional method, the upper blade is narrow and has a high blade pattern, so it deforms in a short time during trimming, resulting in poor cutting quality, and there are problems with the life of the blade. The strength and lifespan are significantly improved due to the low resistance.

Nezumi'ko1λi! FIG. 8 is a side view showing an example of a series of manufacturing steps from a plastic sheet to manufacturing a deep-drawn plastic container product. The plastic sheet 1 is unwound from a coiled plastic sheet 51 installed in an unwinding device 50, passes through a guide roll 52, enters a sheet heating device 53, is heated by a heater 54, becomes a molten sheet, and enters a multi-piece molding device 55. A trimming device 56 trims the molded container to form a deep-drawn plastic container 57.
is manufactured. The scraps are discharged into a scrap bin 58.

Deep-drawn plastic containers according to the present invention are manufactured through such a manufacturing process, and since the present invention provides excellent container trimming properties, deep-drawn plastic containers can be automatically processed without producing defective products. It can be manufactured efficiently.

(Effect of the invention) According to the present invention, by employing the above-mentioned means,
By increasing the amount of bowing of the molten plastic sheet into the mold, the thickness distribution in the height direction of the container is uniform, and there are no drag lines on the side walls of the container.

In addition, in the conventional method, after forming, a step remains between the container flange and the unformed part on the outside, and because this is thin and long, the positioning with the cup trimmer blade becomes unstable during trimming, resulting in the container being crushed. However, according to the present invention, the blade of the cup trimmer is thinner and has a higher blade pattern due to the stepped part, which reduces the strength and life of the blade.However, according to the present invention, the container flange part Since there is no stepped portion between the container and the unformed portion outside thereof, the rigidity around the cutting portion is increased, so the positioning with the blade of the cup trimmer is stable, and the occurrence of crushing and slipping of the container is eliminated. Furthermore, since there are no steps, the blade can be made thicker and the blade pattern lower.
When trimming, a deep-drawn plastic container is provided that improves the strength and life of the blade and provides an excellent appearance of the trimmed part.

According to the present invention, the utilization rate of plastic sheets for deep-drawn containers is significantly improved, and molding workability is also improved.

In addition, since this container is melt-sheet molded, it has excellent hot water resistance (heat deformation resistance), can be sterilized by retort sterilization, and the contents can be heated in a microwave oven. Further, by providing an oxygen barrier layer, it has many advantages such as excellent storage stability.

(Example) In the following Examples and Comparative Examples, containers were evaluated by the following method.

(1) Defective trimming After trimming, the trimming dimensions of the container flange were measured, and those that deviated by ±0.5111 m or more from the P4 standard specifications were judged as defective.

(2) Flange scratches A part of the flange is damaged due to misalignment between the container and the upper blade during trimming.

(3) When trimming the flange, the positional relationship between the container and the upper blade is misaligned, resulting in part of the flange being trimmed.

(4) Life of the upper blade The number of shots until the upper blade deforms and the trimming surface curls or leaves uncut parts.

[Example] Width 650 mm produced by normal coextrusion sheet molding
A coiled multilayer sheet consisting of polypropylene/layering agent (vinyl acetate alcohol copolymer)/gas barrier resin (Saran)/adhesive (same as above)/polypropylene (same as above) with a total thickness of 1.3 mm was prepared. The sheet was sent to a heating process while being clamped at both ends with a movable chain, heated to a temperature above the melting point (175 to 180°C) using a far infrared heater, and then transferred to a molding process.

The molding process uses an aluminum mold cavity (opening diameter: φ67) as the lower mold, depth: 95 mm, 5 x 6 rows, 3
On the top surface of the Teflon annular body (opening diameter: 90 m)
+n, opening height 15++un) were provided so that they were in close contact with each other and could be moved relative to the mold cavity while maintaining airtightness. In addition, a Teflon plug (
A cooling plate was provided at a position corresponding to the outer diameter of the tip (φ45 mm) and the annular body.

First, a mold having the annular body on its upper surface rises from below the heated and melted sheet, and the annular body comes into contact with the sheet I. At almost the same time, the plug is inserted into the opening of the annular body from above. The sheet is squeezed into the mold while generating positive pressure between the mold and the sheet. Immediately after the squeezing operation is completed, the upper mold cooling plate is pressed between the annular body and the sheet to open the mold cavity. The mold was clamped after moving in the direction to reduce the difference in level from the mold. After the mold is closed, the inside of the mold cavity is evacuated, and after a short delay, compressed air (2 kg/cm2: gauge pressure) is introduced between the plug and the sheet, the sheet is transferred from the plug to the mold cavity, and after cooling, molding begins. Completed. The unmolded part of the molded product was almost flat with respect to the flange part.

Next, the molded product is transported to a trimming process, and one row (5
A deep-drawn container was produced by trimming the outer part of the flange using the upper and lower blades for each container.

The above operation was performed continuously at 24 shots/min, and the resulting containers were evaluated for poor trimming, flange damage, and flange breakage. The results are shown in Table 1.

From the results shown in Table 1, it is clear that the method of the present invention produces containers with good appearance, with fewer trimming defects and with constant trimming dimensions.

[Comparative Example] After the multilayer sheet was heated and melted, deep drawing was performed in the same manner as in the example except that the annular body did not move relative to the mold cavity.

In the molded product, a step was created between the flange portion and the unmolded portion or the height of the opening of the annular body.

Next, the molded product was transported to a trimming process, and the outside portion of the flange was trimmed in the same manner as in Examples to produce a deep-drawn container. During work, a break in the flange caused a blockage in the trimming process, causing the front two lines to stop. Note that the width of the upper trimming blade was narrower and the height was higher than that of the example.

The containers were evaluated for trimming failure rate, damage, flange breakage, etc. The results are shown in Table 1.

From the results in Table 1, it is clear that methods other than the present invention do not stabilize the trimming dimensions and cause many trimming defects. It was also found that there was a problem with the lifespan of the blade, as the upper blade deformed in a short period of time and became less sharp.

Table 1 Remarks The results of trimming defects, flange scratches, and flange breaks show the number of trimming defects, number of flange defects, and number of flange breaks, respectively, per 1000 pieces.

[Brief explanation of drawings]

Figures 1 to 3 are explanatory diagrams of the manufacturing method and manufacturing apparatus of the present invention: Figure 1 is a mold in the preparation stage before molding;
It is an explanatory view showing the state of the plug and the molten sheet, and
The figure is an explanatory diagram showing the state of the mold, the plug, and the molten sheet in the drawing stage, and FIG. 3 is an explanatory diagram showing the state of the mold, the plug, and the container in the vacuum and/or pressure forming stage. FIG. 4 is an enlarged sectional view showing one example of the sectional structure of a plastic sheet. FIG. 5 is a plan view showing an example of a mold arrangement diagram used in the present invention. FIGS. 6-A and 6-B are cross-sectional views of plastic containers formed according to the present invention and the conventional method, respectively, and before trimming. FIG. M7-A and FIG. '$7-B are cross-sectional views illustrating a situation in which containers molded according to the present invention and a conventional method are trimmed using a cup trimmer, respectively. FIG. 8 is a side view showing an example of the manufacturing process of manufacturing a deep-drawn plastic container product from a plastic sheet according to the present invention. In the figure, ! ...Plastic sheet, 2...Fixing tool, 10...Mold, 1...
- Mold cavity, 4... Opening of the mold cavity, 5... Annular body having heat insulating properties and sliding properties, 6... Elastic member, 17... Airtight mechanism part, 8...・Mold base, 19...Vent hole, 0...Plug,
24...Upper mold, 0...Air cylinder for driving the cooling plate, 1...Piston rod, 32...Cooling plate, 3...
Molded container, 6... Molded container flange portion, 8... Step portion, 40... Cup trimmer 1... Lower blade, 42... Upper blade, 0... Unwinding device, 1... - Coiled plastic sheet, 3... Sheet heating device, 54... Heater, 5... Molding device,
56...Trimming device, 7...Deep drawing plastic container. Figure 3 Figure 2 Figure 5 Figure 6-A Figure j4 Figure 6-8 Figure 7-A Figure 7-B

Claims (3)

[Claims] (1) A plastic sheet in a molten state is sandwiched between the plug and the mold, which is located above and radially outward from the opening of the mold and the mold cavity, and airtightness is maintained between the plug and the mold cavity. A heat insulating and slippery annular body is arranged,
The plastic sheet is supported by an annular body, and in this state, the plug and the mold are moved relative to each other in the closing direction, thereby generating positive pressure between the mold and the plastic sheet, and the plastic sheet is moved into an annular shape. The annular body is squeezed into the mold by sliding it over the body, and just before or immediately after the completion of this squeezing operation, the annular body is moved in a direction to reduce the level difference with the opening of the mold cavity, and then after the mold is clamped, it is vacuumed and/or Alternatively, a method for producing a deep-drawn plastic container characterized by air pressure forming. (2) A plug assist consisting of a supporting and feeding mechanism for a plastic sheet in a molten state, a combination of a plug placed on one side of the plastic sheet and a mold having a cavity placed on the other side of the sheet. Vacuum and/or
or a pressure molding mechanism, a drive mechanism for relatively driving the stroke in the closing direction of the plug and the mold, and a heat insulating and sliding mechanism disposed above and radially outward from the opening of the mold cavity. An annular body for supporting a seat, an elastic member that supports the annular body so as to be able to retreat from the above-mentioned position in a direction that reduces the level difference between the annular body and the opening of the mold cavity, and an airtight mechanism that maintains the annular body and the mold in an airtight state. and the driving mechanism and the annular body are arranged such that the plastic sheet is squeezed into the mold by the plug while the plastic sheet is supported by the annular body and positive pressure is generated between the sheet and the mold. An apparatus for manufacturing a deep-drawn plastic container, characterized in that the annular body is moved in a direction to reduce the height difference between the annular body and the opening of the mold cavity immediately before or immediately after the completion of the squeezing operation. (3) As a mechanism for moving the annular body from the above position in a direction that reduces the level difference between the mold cavity opening and the mold cavity opening, a cooling plate drive mechanism is provided on the bottom wall of the upper mold having an opening through which the plug enters and exits. 3. The deep-drawn plastic container manufacturing apparatus according to claim 2, wherein a cooling plate for pressing the annular body is provided at the tip of the cooling plate drive mechanism.