JPH0767742B2 - Plastic can manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a plastic thin can having excellent strength and heat resistance by subjecting plastic to an ironing method and a heat treatment method.

(Prior Art) A composite container formed by winding a plastic container body and a metal lid at their engaging end portions is known, as has been known for a long time as seen in Japanese Utility Model Publication No. 37-25894. A composite container using a polyester such as polyethylene terephthalate (PET), which is excellent in transparency, flavor retention and mechanical properties, as a plastic container body is already known from JP-A-55-3915.

As a method of manufacturing this container body, U.S. Pat.No. 4,405,546 describes a plastic bottomed tubular preform for ironing between a punch and a die, and a tubular side wall portion in a height direction thereof. To produce a plastic stretch can.

(Problems to be solved by the invention) In ironing of plastic, the side wall part is stretched by uniaxial pulling at the punch tip, but when thinning the thickness of this side wall part, it is often the case that bottoming out and necking at the beginning of ironing occur. However, if it is attempted to prevent this, it will be difficult to impart molecular orientation while sufficiently reducing the thickness of the side wall portion.

Also, in this ironed plastic can, the strength in the can axis direction is increased by uniaxial stretching, but the hoop (circumference)
Inferior strength in the direction, as an internal pressure can of carbonated drinks, beer, etc., and a can for can with a pressure difference between the inside and outside of a vacuum can,
In terms of pressure resistance, it was still unsatisfactory.

Therefore, an object of the present invention is to impart sufficient molecular orientation to the side wall portion while preventing the occurrence of the above-mentioned bottom omission and constriction during the ironing of a plastic bottomed cylindrical preform, and further, in the hoop (circumferential) direction. Another object of the present invention is to provide a method for producing a plastic stretched can that can also increase the container strength.

(Means for Solving the Problems) According to the present invention, a plastic bottomed tubular preform is subjected to ironing between the punch and the die to stretch the tubular side wall portion in the height direction thereof. In the method for producing a plastic can, which comprises subjecting the open end of the molded body to flanging, a cylindrical preform with a bottom is provided with a sidewall whose temperature is equal to or higher than the glass transition temperature of the plastic and whose bottom is made of plastic. Provided is a method for producing a plastic can, which comprises preheating to a temperature lower than the glass transition point by at least 3 ° C. to perform ironing and heat setting the body of the can after flange processing. .

(Operation) In FIG. 1 showing a series of steps of a method of manufacturing a plastic can, first, in a preform molding step (A), a plastic having stretch formability is injection-molded to form a cylindrical side wall portion 2 and a lower end thereof. A bottomed cylindrical preform 1 (thickness t _O ) having a bottom 3 is manufactured.

Next, in the preheating step (B), the bottomed tubular preform 1 is preheated to the stretch molding temperature. At this time, in the present invention, the temperature T _W of the side wall portion 2 of the preform becomes the glass transition point of the plastic (T _g) above, and the temperature T _B is the glass transition point of the plastic of the bottom (T _g) of at least than The first feature is that the preform is preheated with a temperature distribution so that the temperature becomes 3 ° C. lower. That is, when the entire preform is heated to the gas transition point (T _g ) or more, bottoming out, necking at the beginning of ironing, etc. occur, but according to the present invention, the ironing step to be performed subsequently by providing the temperature difference described above ( In C), the side wall portion 2 can be effectively stretched while preventing the occurrence of bottom omission and constriction. In order to selectively heat substantially only the side wall portion 2, the side wall portion 2 of the preform is brought into contact with the core 10 and the outer core 11 having a heating mechanism therein, and the side wall portion 2 is heated by heat conduction. .

In the ironing (ironing) step (C), the preheated preform 1a is supported by the punch 12, and the side wall portion 2 thereof is engaged with the ironing die 13 to perform ironing. During this ironing, the preform side wall 2 is thinned by stretching and molecularly oriented in the ironing direction (the can axis direction). For ironing, the diameter of the can is D, the height of the can is H, the thickness of the control part is t _W , and the thickness of the original preform side wall is
When t _O is set, it is preferable that the formula H / D≈2 to 4 (1) t _W <t _O (2).

In the trimming step (D), the edge portion 5 of the edge of the obtained ironing can 4 is cut off, and in the flange processing step (E), the flange 6 is formed at the open end of the can using a flange die. This flanging is performed by maintaining a tool such as a flange die at a temperature above the glass transition point of plastic.

In the present invention, the ironing can 1b thus obtained
In the heat setting step (F), the body part of is subjected to heat setting. This heat setting causes stress relaxation of the side wall of the can, promotes oriented crystallization, improves heat resistance of the side wall of the can, and significantly improves mechanical strength. Thus, according to the present invention, the pressure resistance can be remarkably improved without performing lateral stretching (hoop direction stretching) on the side wall of the can.

Finally, if necessary, in the necking step (G), the necking 7 is formed, and the plastic can body 1c for winding is tightened.
And

INDUSTRIAL APPLICABILITY The present invention can be widely applied to various plastics capable of molecular orientation such as thermoplastic polyester, polypropylene resin, polycarbonate, styrene resin, and nylon resin. Since the method of the present invention can be advantageously applied to ironing cans made of thermoplastic polyester, thermoplastic polyester will be described below as an example, but the present invention is not limited to this example.

As the thermoplastic polyester, polyester having ethylene terephthalate repeating units as a main component is advantageous. Here, the thermoplastic polyester having ethylene terephthalate as the main repeating unit is usually 80 mol% or more of the acid component, preferably 90 mol% or more is terephthalic acid, and 80 mol% of the glycol component, preferably 90 mol% or more. Means a polyester in which ethylene glycol is used, and isophthalic acid and diphenyl ether as the remaining other acid components 4,
4'-dicarboxylic acid, naphthalene 1,4- or 2,6-dicarboxylic acid, adipic acid, sebacic acid, decane 1,10-dicarboxylic acid, hexahydroterephthalic acid, and other glycol components, propylene glycol, 1,4 -Butanediol, neopentyl glycol, diethylene glycol, 1,6-hexylene glycol, cyclohexanedimethanol, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyethoxyphenyl)
Propane, or p-oxybenzoic acid as oxyacid,
It means a polyester containing p-hydroethoxybenzoic acid or the like. Further, a polyfunctional component having a functionality of 3 or more may be copolymerized within a range that does not impair the moldability. Further, it may be a mixed polyester of two or more kinds such that ethylene terephthalate becomes 80 mol% or more by mixing polyethylene terephthalate and another thermoplastic polyester.

The thermoplastic polyester used must have an intrinsic viscosity of 0.55 or more, preferably 0.6 or more, more preferably 0.7 to 1.4. The intrinsic viscosity is the intrinsic viscosity measured at 30 ° C. in a solution of polyester dissolved in a phenol / tetrachloroethane mixed solvent (6/4 weight ratio). Further, the present invention is a blend of polyester and another resin such as a metaxylylene group-containing polyamide, a poly (yen coin vinylidene), an acrylonitrile styrene copolymer, a resin having a more excellent gas barrier property such as an ethylene vinyl alcohol copolymer, or a blend thereof. It is also advantageously applied to a multilayer laminate (hereinafter, these are also referred to as polyester).

In order to manufacture the ironing can of the present invention, first, a bottomed cylindrical preform of amorphous polyester is manufactured. This bottomed tubular preform is advantageously manufactured by injection molding of polyester. Alternatively, polyester is melt extruded into a pipe shape, rapidly cooled to produce an amorphous pipe, cut into a predetermined size, and then the bottom is closed to produce a bottomed preform, or a pipe-shaped melt extrudate. Pinch off with a split mold,
A method of producing a bottomed preform by preblowing can also be adopted.

In the preheating process, the preform side wall is 70-100
℃, especially 70 to 80 ℃, while the bottom is 70
The temperature should be below ℃, especially below 67 ℃.

The ironing may be performed in a single step using a single die, or a plurality of dies having different inner diameters may be used so that the side walls of the preform are sequentially engaged with the dice having a smaller diameter. May be performed in.

In general, the expression Where t _B is the thickness of the preform sidewall (which is generally equal to the bottom thickness of the can), t _{W is} the thickness of the ironing can sidewall, and the ironing rate is 30-75% overall, In particular
It is recommended to be 35 to 70%.

In the present invention, a high degree of molecular orientation is imparted so that the principal axis orientation coefficient (l) measured by the polarized fluorescence method is 0.3 or more, particularly 0.5 or more by combining the above-mentioned preheating and ironing. Is possible.

The orientation coefficient by the fluorescence deflection method is obtained as follows.

The sample to be measured is immersed in a 0.5 wt / vol% benzene solution of a fluorescent agent (White Fluor PSN manufactured by Sumitomo Chemical Co., Ltd.) for 20 hours, and the sample taken out is washed with benzene to obtain a treated sample.

Using a polarization spectrophotometer FOM-1 manufactured by JASCO Corporation, using 365 nm as a light source, set the sample, set the polarizer and the analyzer in parallel, while rotating the sample , The angular distribution of transmitted light is obtained as a chart.

The fluorescence polarization intensity at the rotation angle (ω) is I (Ω) = Kφ (lcos^Fourω + msin^Fourω + 3n / 8) ……
(4) where l is the orientation coefficient in the direction of the principal axis of the sample plane,
m is an orientation coefficient in the minor axis direction of the sample surface, and n is a non-orientation coefficient.
Yes, l + m + n = 1.

It is represented by.

Now, the main axis (the orientation axis whose rotation angle is the closest to zero is the main axis
And the orientation axis away from this is the minor axis)
Is α, the rotation angle of the sub-axis is β, and the fluorescence polarization between the main axis and the sub-axis is
Let γ be the rotation angle that minimizes the light intensity, and
Fluorescence polarization intensity I (Α), I (Β), I (Γ)
From the chart. The value of each angle and the intensity value are given in equation (4).
Substitute and calculate the values of l, m, n from the three equations.

If the fluorescence polarization intensity distribution on the chart is not point-symmetric,
Is I (Α) and I Calculate the average value of (α + π) and
I The value of (α) may be used, which is I (Β) and
And I The same applies to (γ).

In the heat setting step, the side wall of the ironing can is heated to a temperature of generally 90 to 180 ° C, especially 120 to 150 ° C.
This heat setting is preferably carried out under restrained conditions so as not to cause thermal deformation, and it is generally good that the mandrel used in the previous step is fitted tightly in the ironing can. The time required for this heat setting is a small number of temperatures, and the higher the temperature, the shorter the time. In general, a time of 5 to 120 seconds, especially 5 to 60 seconds, is selected so that sufficient crystallization can be obtained.

In the present invention, the crystallinity (D _c ) by the density method is 25%
As described above, the pressure resistance and the like of the can can be remarkably increased by crystallizing so that the concentration becomes 30% or more.
The crystallinity (D _c ) according to the density method is a method described in ASTM 1505 using a density gradient tube, and the following formula Where P _s is the density of the sample to be tested (g / cc), P _a is the density of an amorphous film with _a crystallinity of 0% (1.333 g / cc), and P _c is the crystal calculated from the unit cell parameters. Density of (1.455g
/ cc) is the calculated value.

In the heat setting step, the bottom of the unoriented can may be prevented from being heated so as to maintain transparency, or the bottom of the unoriented may be simultaneously heated to be whitened.

During flanging and necking, it is recommended that the tool be maintained at a temperature of 100 to 130 ° C for processing.

(Effect of the Invention) According to the present invention, in the ironing forming of a plastic bottomed cylindrical preform, a high degree of molecular orientation is imparted to the side wall while preventing the occurrence of bottom omission and constriction, and a heat setting step is also used. By doing so, mechanical strength such as pressure resistance could be sufficiently increased even in the case of uniaxial molecular orientation.

Example 1 A bottomed tubular preform having an outer diameter of 57 mm, an inner diameter of 53 mm, a wall thickness of 2 mm and a cup height of 50 mm was produced by injection molding polyethylene terephthalate by a conventional method.

This preform was preheated so that the side wall portion was 72 ° C. and the bottom portion was 67 ° C., and was ironed to form a plastic can barrel. The processing conditions at this time are as follows.

・ Ironing rate 65% ・ Approaching angle 15 ° ・ Ironing speed 500mm / sec 132m in height by adding trimming and flanging to this can
A can body having a length of m and a flange length of 3 mm was prepared, and then heat set. The heat setting process conditions at this time are as follows.

Heat set temperature 135 ℃ Heat set time 10 seconds Furthermore, neck-in processing was applied to this can body to make the inner diameter of the open end 50 mm.

The performance of the plastic can body thus obtained is as follows.

Compressive strength: 12.4 kgf / cm ² Crystallinity: 38% Orientation: l: 0.516 m: 0.337 n: 0.147 This plastic can body was filled with 4.0 gas volume carbonated water in a filling machine and made of aluminum (sheet thickness 0.39 mm,
(5052 material) A metal lid was double-wound, and a storage test was carried out at 50 ° C for 24 hours in a thermostat, but no expansion of the outer diameter, breakage, or leakage occurred.

Example 2 In Example 1 above, the preheating temperature was set to the sidewall portion of 76 ° C. and the bottom portion.
A plastic can barrel was produced in the same manner as in Example 1 except that the heat setting treatment condition was set to 65 ° C., the heat setting temperature was 150 ° C., and the heat setting time was 5 seconds. The performance of this can body is as follows.

Compressive strength: 12.1 kgf / cm ² Crystallinity: 42% Orientation: l: 0.578 m: 0.340 n: 0.082 The can body was subjected to the same filling and winding as in Example 1 above, and at 50 ° C. in an incubator. After conducting a storage test for 24 hours, expansion of the outer diameter, crushing and leakage did not occur.

Comparative Example 1 When the same preform as in Example 1 above was preheated to 72 ° C. for both the side wall and the bottom and subjected to ironing, the bottom was overhanging or the bottom was missing, and a plastic can barrel was produced. could not.

Comparative Example 2 A plastic can body was manufactured in the same manner as in Example 1 except that the heat setting treatment was not added. The performance of this can body is as follows.

Compressive strength: 7.1 kgf / cm ² Crystallinity: 22.8% Orientation: l: 0.469 m: 0.369 n: 0.162 The can body was subjected to the same filling and tightening as in Example 1 described above, and the temperature was set to 37 ° C. in an incubator. After a 24-hour storage test, all 200 filled cans had an outside diameter expansion of 10 to 15%, and 68 cans leaked from the wound part.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a plastic can according to the present invention. FIG. 1 (A) is a preform molding process diagram, FIG. 1 (B) is a preheating process diagram, and FIG. 1 (C) is an ironing process. Process drawing, FIG. 1 (D) is a trimming process drawing, FIG. 1 (E)
Is a flanging process diagram, FIG. 1 (F) is a heat setting process diagram, and FIG. 1 (G) is a necking process diagram. 1 ... preform, 1a ... heated preform,
1b: Ironing can body, 1c ... Plastic can body for winding,
2 ... Preform sidewall, 3 ... Preform bottom,
4 …… Ironing can, 5 …… Ear, 6 …… Flange, 7 ……
Necking, 10 …… Preheating core, 11 …… Preheating core, 12 …… Punch, 13 …… Ironing die, 14 …… Trimming cutter, 15 …… Flange die, 16, 17 …… Flange retainer , 18 …… Heat set mandrel, 19,20 ……
Necking tool.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area B29K 67:00 B29L 22:00

Claims (1)

[Claims] 1. A plastic bottomed cylindrical preform is subjected to ironing between a punch and a die to stretch a cylindrical side wall portion in its height direction, and then an open end of the molded body is flanged. In the method for producing a plastic can, the tubular preform with a bottom has a temperature at a side wall of which is equal to or higher than a glass transition point of plastic and a bottom of which is at least 3 ° C. lower than a glass transition point of plastic. A method for producing a plastic can, comprising preheating so as to perform ironing and forming, and heat setting the body of the can after flange processing.