JPH02106318A - Manufacture of plastic container - Google Patents

Abstract

PURPOSE:To mold a drawn plastic container by relatively moving a plug or a mold and a guide member in a direction for closing them to each other, and sweeping a plastic sheet or the like to the surface of its outer surface of the plug or the mold while feeding fluid such as the air between the sheet and the member. CONSTITUTION:A guide member 20 is moved down from a molding preparing state in a male mold forming method, a male mold 10 is moved up, and the bottom forming top 14 of the male mold and a guide ring 23 starts contacting with a plastic sheet 1. In this case, since pressurized fluid such as the air is supplied into a cylindrical space 24, the fluid is fed between the ring 23 and the sheet 1 outward, thereby maintaining the sheet 1 in a floating state by the ring 23. Accordingly the sheet is effectively swept to the surface of the male mold or its outer surface to manufacture a drawn plastic container having high strength and uniform thickness distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a plastic container, and more particularly to a method for manufacturing a drawn plastic container having a uniform wall thickness distribution with excellent molding workability. .

(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.

Japanese Patent Application No. 62-315377 proposed by the present inventors describes a method of manufacturing a plastic container that involves plug-assisted vacuum and/or pressure forming of a molten plastic sheet, in which a plug and a mold are used. The molten sheet is moved relatively in the closing direction to generate positive pressure between the mold and the molten sheet, and the molten sheet is slid over the upper surface of the mold, which has heat insulation and slip properties. A method for manufacturing a deep-drawn plastic container has been proposed, which comprises drawing the molten sheet inward, then clamping the mold, and then bringing the molten sheet into contact with a mold to cool it.

(Problems to be Solved by the Invention) However, in the conventional drawing method for plastic sheets, etc., there is little pulling of the plastic sheet into the mold, high reduction on the container wall, and local thinning of the side wall tends to occur. There is a problem. For this reason, the strength of the container decreases, and in order to prevent this, it is necessary to form a thick sheet, which tends to slow down the heating cycle of the sheet and reduce the workability of sheet forming. At the same time, materials tend to be wasted due to thicker bottoms and more skeletons.

In the conventional method, attempts have been made to increase the pulling of the plastic sheet into the mold by using a guide ring, but the material and shape of the guide ring, such as slipperiness, heat insulation, non-adhesiveness to heated resin, and surface There are severe restrictions on roughness, radius of curvature of the shoulder, etc., and it is necessary to use expensive materials such as polytetrafluoroethylene and lubricants. In addition, the plastic sheet used is also subject to restrictions, and resins that exhibit adhesiveness in a molten state or resins that have a large coefficient of friction with the guide ring are not suitable for drawing.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method that eliminates the above-mentioned drawbacks that occur when drawing a plastic sheet or the like, and can produce a drawn plastic container having a uniform wall thickness distribution with excellent molding workability.

Another object of the present invention is to provide a method for manufacturing a squeezed container that can increase the drawing of plastic sheets or the like into a mold.

(Means for Solving the Problems) According to the present invention, in a method for manufacturing a plastic container, a plug or a mold and a guide member are relatively moved in a direction in which they engage with each other (closing direction), and a plastic sheet or preform is A method for manufacturing a drawn plastic container is provided, which comprises drawing a plastic sheet or preform onto or around the surface of a plug or mold while flowing a fluid between the plug and the guide member to perform drawing forming.

(Function) In the method for forming a drawn plastic container of the present invention, a plug or mold and a guide member are moved relatively in the direction of engagement with each other, and a plastic sheet or preform is drawn and formed. A distinctive feature is that a fluid, such as air, is passed between the guide member and the guide member to levitate the sheet or preform from the guide member and draw the sheet or preform into and around the surface of the plug or mold.

By flowing fluid between the sheet or preform and the guide member, the sheet or preform is brought into a floating state continuously or intermittently, and continuous contact between the sheet or preform and the guide member is prevented. As a result, the friction in the guide member can be reduced to a negligible order, and as a result, the amount of retraction of the sheet or preform when the plug or mold and the guide member are deeply engaged can be significantly reduced. It becomes possible to increase the The drawing ratio (Rd) of a sheet, etc. is defined by the following formula, where D represents the diameter of the drawn object, and D represents the diameter of the sheet or preform actually used for the drawn object. be able to. In conventional drawn plastic containers, this drawing ratio (Rd) was 1.0 to 1.5, but in the present invention, this Rd can be improved to about 2.0 or more.

Further, by performing drawing forming while increasing the amount of retraction, reduction in the side wall portion of the container can be reduced and the strength of the container can be increased. Here, reduction (R
1) is a value defined by the following formula dO, where do is the original thickness of the plastic sheet or preform, and dI is the thickness of the side wall of the drawn product, and is a value defined by the conventional drawing method. Then R1 is 7
In the present invention, it can be reduced from 0 to 90% to 50% or less.

Furthermore, since the guide element and the plastic sheet or preform are kept in contact with low and constant friction during the entire molding process, the wall thickness distribution of the squeezed container is also made more uniform.

Moreover, since direct contact between the guide member and the plastic sheet or preform is prevented, the various constraints mentioned above, such as the need for the guide member to be slippery, are alleviated, and the plastic sheet used also The above-mentioned restrictions, such as not being limited to non-adhesive ones, are also relaxed.

(Preferred embodiment of the invention) In the molding method of the bottom-shaped basic invention, the plug or mold means the male mold when a male mold is used, and the plug when a combination of a female mold and a plug is used. shall be taken as a thing.

In Figures 1-A to 1-D for explaining the male molding method, Figure 1-A shows the preparation state before molding, and shows a male mold generally designated by 10 and a guide generally designated by 20. The members are located at the farthest position, and a molten plastic sheet 1 supported by a fixture 2 such as a chuck is supplied between the male die 10 and the guide member 20.

The male mold 10 has a cylindrical body 11 for forming a container, a shallow groove-shaped part 12 for forming a flange at its root, and a shoulder part 13 on its outer periphery. The container forming cylindrical body 11 is
It has an upper part 14 for forming a bottom part and a circumferential part 15 for forming a side wall part, and an exhaust passage 16 is provided inside thereof. The male mold 10 is provided so as to be movable in the height direction of the cylindrical body 11, that is, in the vertical direction in the figure, and is at the lowest position in FIG. 1-A.

The guide member 20 consists of a base part 21, a cylindrical part 22 provided at the base part, and a guide ring 23 provided at the tip of the cylindrical part. A pressurized fluid supply port 25 is provided for supplying fluid. In this specific example, the guide member 20 is also provided movably in the axial direction of the cylindrical portion 22, that is, in the vertical direction in the figure, and is at the highest position in FIG. 1-A.

From the preparation state shown in FIG.
And the guide ring 23 of the guide member 20 begins to come into contact with the plastic sheet 1.

In this case, since the pressurized fluid is supplied into the cylindrical internal space 24 of the guide member 20, the pressurized fluid passes between the guide ring 23 and the plastic sheet 1 and flows outward, thereby causing the plastic sheet to While the plastic sheet 1 is maintained in a state floating above the guide ring 23, the narrowing of the plastic sheet 1 is started (Fig. 1-B).
The guide member 20 and the male mold 10 continue in eight shifts until the plastic sheet 1 comes into contact with the shoulder 13 of the male mold 10 (1st-
During the entire drawing process, direct contact between the plastic sheet 1 and the guide ring 23 is avoided, so that the plastic sheet 1 can be drawn into the male mold surface or around it very effectively. be exposed.

Next, the male die 10 and the guide member 20 are clamped together, and air pressure is applied to the inner space 24 of the cylindrical portion, thereby forming the male die 1.
Air pressure forming is performed according to the shape of 0 (Fig. 1-D), and the forming operation is completed.

In FIG. 2 for explaining the plug assist molding method, a female mold generally designated 30 and a plug generally designated 40 are arranged, and a fixture 2 such as a chuck is placed between the female mold 30 and the plug 40. A plastic sheet 1 in a molten state supported by a plastic sheet 1 is supplied.

The female mold 30 has a cavity 31 open therein, a bottom wall surface 32 that defines the bottom wall of the container to be molded, and a side wall surface 33 that defines the side walls of the container. Side wall surface 33
An opening 34 defining an opening flange of the container is provided at the upper end of the container.
is located. Above the female mold 30 and on the outer circumferential side,
A guide ring 23 is provided integrally with 0. The female mold 30 is provided with a pressurized fluid supply port 35 for supplying pressurized fluid to the cavity 31 and an exhaust port 36 for maintaining the inside of the cavity at a vacuum or reduced pressure. The female die 30 and the guide ring 23 are provided so as to be movable up and down.

The plug 40 has a tip portion 41 that engages with the sheet and a tapered side wall portion 42 for squeezing the sheet.
Connected to 3. The plug 40 is also provided so as to be movable in the height direction of the side wall portion 42, that is, in the vertical direction in the figure. An upper mold 44 is provided coaxially with the plug 40. Upper mold 4
4 consists of a cylindrical side wall part 45 and a bottom wall part 46, and the bottom wall part 46 is provided with an opening part 47 through which the plug 40 can go in and out. An engaging protrusion is provided on the lower side of the bottom wall portion 46 to engage with the female mold opening 34 via a plastic sheet to compression mold the container flange portion and to seal the female mold 30 and the upper mold 44. 48 are provided. The upper mold 44 is also provided to be movable in the vertical direction, but its vertical movement can be performed independently of the plug 40. Even in this state, an annular gap is formed between the two. Further, the inside of the upper mold 44 is connected to a pressurized gas mechanism (not shown), and this pressurized gas is supplied to the lower side through a gap.

Plastic sheet 1 is narrowed down from 1-A to 1-D.
This is done in the same way as for the male type shown in the figure.

That is, the female die 30 is raised, the plug 4o is lowered, and the surface of the side wall portion 42 of the plug 40 or its surroundings is squeezed. In this case, also during the whole process of squeezing, the pressurized fluid in the cavity 31 flows out between the guide ring 23 and the plastic sheet 1, which causes the plastic sheet 1 to be released from the guide ring 23 intermittently or continuously. The plastic sheet is maintained in a floating state, and the plastic sheet is sufficiently retracted during squeezing.

After the squeezing operation is completed, the upper die 44 and the female die 30 are clamped, and pressurized fluid is blown into the squeezed sheet, or the outside of the sheet is evacuated.
A container having a shape corresponding to the female mold cavity surface is formed.

The present invention is not limited to drawing and forming plastic sheets.
It can also be applied to drawing (re-drawing) from preforms such as plastic cups.

In FIG. 3 showing this aspect, the guide member 20 is located at the first
It has a structure similar to that of Figures A to 1-D. bunch 1
1 is also 1st-A~! It has the same structure as the cylindrical body shown in FIG.

The cup-shaped preform 1a heated to a solid state molding temperature (stretching temperature) is held by the bunch 11 and the wrinkle presser ring 50, and the bunch 11 is raised and the guide member 20 is lowered. Thereby, the preform 1a is drawn into a small-diameter cylindrical body along the side wall portion 15 of the bunch 11 while being held by the guide ring 23 and the wrinkle holding ring 5o. Throughout the drawing process, fluid flows between the guide ring 23 and the preform 1a from the space 24 of the guide member 20, and the preform 1a is held floating above the guide ring 23.

Resin material In the present invention, any thermoplastic resin material that can be melt-molded can be used as the plastic sheet or preform, such as olefin resin, styrene resin, vinyl chloride resin, vinylidene chloride, etc. Resin, polyester resin, polyamide resin, etc. alone or in combination
Can be used in combination of more than one species. 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 copolymers, ethylene-acrylic acid ester copolymers, and ionically crosslinked olefin copolymers (ionomers) can also be used alone or with other olefin resins within the range that satisfies the condition of crystallinity. Can be used in combination. Polypropylene is particularly suitable for use as a retort sterilization or reheating container.

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/cta2・
5 ecta Hg or less (37° C., O% RH), for example, ethylene-vinyl alcohol copolymer, polyamide resin, vinylidene chloride resin, high nitrile resin, etc. 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-vinyl acetate copolymers, ethylene-acrylic acid ester copolymers, ionomers, etc. can be used. Additionally, a layer of a scrap resin composition from the sheet (i.e., a composition of a moisture-resistant resin, an oxygen barrier resin, and an adhesive resin) is interposed between the adhesive resin layer and the moisture-resistant thermoplastic resin layer. You can also do that.

The plastic sheet used in the present invention is a molded container, which can contain compounding agents for plastics known per se, such as antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents, fillers, colorants, etc. For the purpose of making it 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. Can be done.

The plastic sheet used in the present invention generally has a thickness of 0.5 to 5 m+n, although it varies depending on the size of the container etc.
In particular, it is preferable to have a thickness of 0.7 to 3 mm.

In the above-described plastic sheet having a laminated structure, the thickness (ta) of the moisture-resistant resin inner and outer layers and the thickness (t8) of the oxygen barrier resin intermediate layer are tA:tBB12O31 to 4:
1 It is particularly desirable that the ratio be within the range of 25:1 to 5:1.

Examples of plastic preforms include those having arbitrary shapes such as a cup shape, a tray shape, and a hemispherical shape, and these preforms can be obtained by molding methods known per se such as injection molding and compression molding. It will be done.

In the present invention, it has been pointed out that the guide ring can be made of any material without any restrictions, but generally plastics having heat insulating properties and heat resistance, such as Bakelite (phenolic resin) are used as the guide ring. ), polycarbonate,
Polytetrafluoroethylene, polyphenylene oxide, polyacetal, etc. are preferably used, and metal materials such as aluminum, various steels, and various alloys, and ceramics such as alumina, zirconia, and silicon nitride can also be used. When using metal as the guide ring, it is desirable to heat the metal to prevent cooling of the plastic due to heat conduction.

The cross-sectional shape of the guide surface in the guide ring may be a plane with rounded corners, a semicircle, a semiellipse, a semiellipse, a trapezoidal surface with rounded corners, etc., and its inner diameter (D g) is: Maximum diameter of plug or male mold (D g) 1.05 to 2.30
In terms of molding workability, it is preferable that the height be within the range of 1.10 to 2.00 times, and the floating support of plastic sheets etc. by guide rings is generally 1.0 to 5 m.
It is preferred that the width be 0.5 to 3 mm.

Air is the most suitable fluid for floating and supporting plastic sheets, but inert gas such as nitrogen can also be used to prevent oxidative deterioration of the plastic, and heated air or Steam can also be used. Fluid pressure is 0.02 to 7 Kg/cm2
The gauge is preferably in the range of 0.1 to 5 kg/cm' gauge, and the flow rate of the fluid flowing between the seat and the guide ring is 10 when converted to a standard condition of 25°C latm.
Preferably, the rate is in the range from 1000 to 1000,5 p/min, particularly from 50 to 400 p/min.

In the molding method of the present invention, it was an unexpected finding that the plastic sheet floats intermittently or continuously at approximately uniform intervals along the entire guide surface of the guide ring. This is probably because the pushing pressure and fluid pressure during molding are balanced, and a fluid passage with a similar spacing is formed between the guide surface and the sheet.

In the present invention, although generally not necessary, in order to further ensure the floating guide of the plastic sheet by the fluid, a groove is provided in the center of the ring as a guide ring 23, as shown in FIG. 28 and a fluid supply port 29 communicating with the groove 28, pressurized fluid is supplied from the groove 28 between the plastic sheet 1 and the guide surface 27, and the sheet 1 is floated. good.

The mold may be made of any metal material, but aluminum or aluminum alloy is used because it is lightweight and has good thermal conductivity. As for the male type, the radius of curvature (R) of the bottom corner is preferably 0.5 mm or more, especially 1 mm or more, and the draft angle of the side wall is 0.1 mm.
The surface roughness is preferably 0.3° or more, particularly 0.3° or more, and the center line average roughness is preferably in the range of 0.1 to 10 μm. This also applies to the female type.

In the case of plug assist molding, the plug is made of a plastic that has excellent heat resistance and insulation properties and is non-adhesive to molten resin, such as polytetrafluoroethylene or polyacetal, and the curvature of the tip corner is A radius of 111ff1 or more, particularly 3ma+ or more is suitable.

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.

In addition, it is desirable that the temperature of the mold is such that the plastic does not solidify too quickly and that the shape is sufficiently determined after molding. ~100℃, 5 for female type
It is desirable to set it as the range of -40 degreeC.

It is desirable that the molding timing be such that the plug or male mold and the guide ring contact the plastic sheet at approximately the same time.

The present invention is suitable for those having a height-to-aperture ratio of about 0.8 or more, particularly 1
．． It is useful for producing 0 to 2.5.

(Effects of the Invention) According to the present invention, fluid such as air is caused to flow between the plastic sheet or preform and the guide member, the sheet or preform is floated from the guide member, and the sheet or preform is inserted into the plug or mold. It is now possible to draw it into the surface or its surroundings, and in conventional squeezed plastic containers, the drawing ratio (Rd) was 1.0 to 1.5.
In the present invention, this Rd can be improved to about 2.0 or more.

Furthermore, by performing drawing forming while increasing the amount of retraction, the reduction at the side wall of the container can be reduced, and the strength of the container can be increased even when formed from a thin sheet.

That is, in the conventional drawing method, Rr was 70 to 90%, but in the present invention, it can be reduced to 50% or less.

Furthermore, since the guide element and the plastic sheet or preform are kept in contact with low, constant friction during the entire molding process, the wall thickness distribution of the squeezed container is also made more uniform.

Moreover, since direct contact between the guide member and the plastic sheet or preform is prevented, the various constraints mentioned above, such as the need for the guide member to be slippery, are alleviated, and the plastic sheet used also The above-mentioned restrictions, such as not being limited to non-adhesive ones, are also relaxed.

(Example) Example 1 Polypropylene (MI=0.5) made by normal coextrusion sheet molding/adhesive (vinyl acetate alcohol copolymer)/gas barrier resin (Saran "PVDCJ")/
Total thickness 1 consisting of adhesive (vinyl acetate alcohol copolymer)/polypropylene (MI=0.5)
．． Container outer diameter φ66mm using 4mm multilayer sheet.
A flanged round container (inner volume: approximately 315 m, 5) having a height of 102 mm and a flange diameter of 75 mm was molded by the method of the present invention.

Aluminum family male type (with root part outer diameter φ66fflf
fi, height 102 mm, draft angle 0.5', center line average roughness 2.0 μm) is placed below the sheet with a bakelite guide ring (opening diameter φ100 mm, shoulder curvature radius 1
A guide member consisting of a cylindrical portion supporting the guide member was placed above the sheet. The temperature of the male mold was controlled at about 70° C. by an oil circulation heating device.

The ends of the sheet (200 ml 1 x 200 mm) were fixed with clamps, and in the heating step, the sheets were heated from above and below to a temperature above the melting point (18° C. to 190° C.) using far-infrared heaters, and then subjected to the molding step. First, the male die rises from below the sheet and comes into contact with the sheet to push it up, and at the same time, or a little later, the guide member descends from above and comes into contact with the sheet. At this time, pressurized air (pressure 1.0, g7 cm+', flow rate 100 p/min) was supplied from the pressurized air supply port provided at the base of the guide member at the same time as the guide member started to descend. The male mold and the guide member in contact with the sheet each move in a relative closing direction, squeezing the sheet onto or around the surface of the male mold. At this time, pressurized air flows between the sheet and the guide ring and flows out to the outside, lifting the sheet from the guide ring, so that the molten sheet is sufficiently compressed to have a uniform thickness. The members were clamped and the sheet was pressed against the male mold using pressurized air, and at the same time, the gap between the sheet and the male mold was evacuated, the sheet was brought into close contact with the male mold, and the sheet was cooled to complete the molding.

At this time, the drawing ratio Rd of the sheet was 2.0, and the flying distance of the sheet was 1.3 mm.

The side wall thickness distribution of the container formed by the above method is
When measured at 36 points, 4 points every 90 degrees in the circumferential direction and 9 points every 10 degrees in the height direction, the average wall thickness was 0.73 mm.
The range of variation was 0.10 mm, and the appearance was good with no scratches. Furthermore, add 8 pieces of meat sauce to the container above.
Filling at 0-85℃ (headspace 511110) L/
After that, a lid made of PET/aluminum/polypropylene was heat-sealed.

The container filled with the contents was subjected to isobaric retort sterilization at 115° C. for 40 minutes (come-up 25 minutes), but no deformation of the container occurred.

From the above results, it is clear that the container deep-drawn by the method of the present invention has a large sheet draw-in, a uniform wall thickness distribution in both the height direction and the circumferential direction, and has excellent container performance. It became.

Comparative Example 1 In Example 1, when the pressurized air was changed to be supplied after the shaping, the sheet broke during the shaping and could not be shaped.

Example 2 After heating and melting a multilayer sheet in the same manner as in Example 1, a Bakelite guide ring (
Aluminum female mold (opening diameter φ67 mm, depth 102 mm, draft angle O, S° , centerline average roughness of 2.0 μm) and a Teflon resin plug (tip outer diameter φ50 mm) placed above the sheet to form a container having the same shape as in Example 1. At this time, the female mold was water-cooled, and the plug was not provided with any heating means.

Pressurized air (pressure, Q Kg/cm2, flow rate too
f/min), the plug was lowered and the female die raised so that the plug and guide ring contacted the sheet at about the same time. The plug and female die in contact with the sheet each move in a relative closing direction, squeezing the sheet onto the surface of the plug or around it. At this time, pressurized air flows between the sheet and the guide ring to lift the sheet from the guide ring, so that the molten sheet has a uniform thickness and is sufficiently compressed.Then, the supply of pressurized air is stopped. After that, the flange ring and the female mold flange are shaded, the gap between the sheet and the female mold is evacuated, pressurized air is introduced between the plug and the sheet, and the sheet is transferred from the plug to the female mold and cooled. , completed the molding. At this time, the sheet retraction ratio Rd is 2.0
Met.

When the container obtained by the above method was evaluated in the same manner as in Example 1, the average wall thickness of the container side wall was 0.581010, the range of variation was 0.11 mm, and the appearance was good with no scratches. Even if the container was subjected to isobaric retort sterilization treatment in the same manner as above, no deformation of the container occurred.

Comparative Example 2 In Example 2, the material of the guide ring was replaced with Teflon resin, and the sheet was squeezed onto the surface of the plug or around it without supplying pressurized air. Despite being closed by a sheet, molding was performed while maintaining atmospheric pressure through a pressurized air supply port. At this time, the mouth of the female mold came into contact with the sheet, creating a drag line (contact trace), and despite the use of a Teflon resin guide ring with good sliding properties, the upper part of the side wall of the container Extremely thin areas occurred circumferentially.

Example 3 A polypropylene cup-shaped preform (inner diameter φ85 mm, height 50 mm) molded by normal injection molding.
, 1.5 mm thick) to form a cup with an inner diameter of 68 mm.

The molding tool used in this molding is a punch (outer diameter φ66 mm).
, draft angle 0.5°, center line average roughness 1.9 μm), wrinkle presser ring installed around the punch that can be moved up and down via pressure means such as a spring (outer diameter φ85 mm, center of the surface The guide ring (inner diameter φ70 mm, radius of shoulder curvature 10 mm, surface center line roughness 1.9 μm) is arranged to face these.

The temperature of each tool is controlled by a heater to 70°C for the punch and 100°C for the wrinkle press ring and guide ring.

The preform heated to a solid state molded state was attached to a wrinkle suppressing ring. Pressurized air (pressure 2.5 Kg/cm2, flow rate 30CM!) is supplied from the pressurized air supply port provided on the guide member.
/min), the punch is raised and the guide member is lowered. As a result, the preform was squeezed along the punch while being held by the guide ring and the wrinkle holding ring. At this time, pressurized air flows between the guide ring and the preform to keep the preform floating above the guide ring. In this way, the preform is completely squeezed and a cylindrical deep-drawn cup is formed. It was done.

When the side wall thickness of this cup was measured in the same manner as in Example 1, the average wall thickness was 0.70 [Om, and the range of variation was 0.11 mm.

The results revealed that the container molded from the preform by the method of the present invention exhibits a uniform wall thickness distribution both in the height direction and in the circumferential direction.

Example 4 Molding was carried out in the same manner as in Example 1 except that a guide member in which the pressurized air supply port and the supply groove were provided at the center of the guide ring as shown in FIG. 5 was used.

The side wall thickness distribution of the container formed by the above method is
When measured in the same manner as in Example 1, the average wall thickness was 0.
72 mm, the range of variation was 0.11 mm, and the appearance was good with no scratches.

[Brief explanation of the drawing]

Fig. 1-A is a side view showing a molding preparation state in the male molding method used in the present invention; Fig. 1-B is a side view showing a narrowing start state in the male molding method of Fig. 1-A; Figures 1-C are side views showing the completion state of narrowing in the male molding method shown in Figure 1-A, and Figures 1-D are side views showing the air pressure forming stage in the male molding method shown in Figure 1-A. Figure 2 is a side view showing the plug assist molding method used in the present invention, Figure 3 is a side view showing drawing forming from a preform, and Figure 4 is an example of the cross-sectional structure of the plastic sheet used. FIG. 5 is a cross-sectional view showing an example of the guide ring. 1 is a plastic sheet, 1o is a male mold, 2o is a guide member, 23 is a guide ring, and 4o is a plug.

Claims (1)

[Claims] (1) In a method for manufacturing a plastic container, the plug or mold and the guide member are moved relative to each other in the direction of engagement, and the plastic sheet or preform is moved while fluid is flowing between the plastic sheet or preform and the guide member. 1. A method for manufacturing a drawn plastic container, characterized by drawing the material into the surface of a plug or a mold or its surroundings, and performing drawing forming.