JPH0476860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an ironed plastic can in which biaxial molecular orientation is imparted to the circumferential side wall and an improved longitudinal/width strength ratio, and a method for manufacturing the same.

(Prior art) An amorphous preform made of plastic such as polyethylene terephthalate is supported by a punch, and the side wall portion of the preform is ironed by engaging it with an annular die having a smaller diameter than its outer circumference. It is already known from Japanese Unexamined Patent Publication No. 57-34925 and US Pat. No. 4,405,546 to produce a container in which molecules are oriented on the side wall.

(Problem to be Solved by the Invention) In this prior art method, relative axial movement of the punch and die causes the circumferential sidewall of the preform to be stretched in the axial direction, resulting in molecular orientation only in the axial direction. . Therefore, in this ironed can, the strength in the axial direction is significantly improved, but the strength in the circumferential (horizontal) direction is extremely low, and the longitudinal and lateral strength ratios are significantly unbalanced.

In fact, when plastic containers are filled with contents that have a self-generating pressure, such as carbonated drinks, expansion in the circumferential direction of the container body occurs on an order of magnitude that cannot be ignored, which is a problem with biaxially stretched bolts, etc. It is easy to understand that in the above-mentioned uniaxially oriented ironed can, problems such as circumferential expansion of the container body or, in severe cases, longitudinal tearing, occur.

For this reason, in conventional plastic ironing containers, a method is actually adopted in which the material stretched in the axial direction by ironing is further expanded in the circumferential direction by blowing. Another method of blow-stretching is required.
This method is still not fully satisfactory in terms of the number of steps and manufacturing cost.

Therefore, the present invention aims to improve the above-mentioned drawbacks of conventional iron-molded plastic cans, provide a method for imparting biaxial molecular orientation to the circumferential side wall of a can in the ironing process, and provide a unique method for the circumferential side wall. It is an object of the present invention to provide a plastic ironed can which is provided with a biaxial molecular orientation, has an improved longitudinal and lateral strength ratio, and is free from the above-mentioned problems such as expansion in the circumferential direction and longitudinal tearing.

(Means for Solving the Problems) The present inventors have developed an amorphous preform made of polyester mainly composed of ethylene terephthalate units, by squeezing it between a punch and a die at a temperature higher than the glass transition point of the polyester. In a method for producing ironed plastic cans that involves processing, when ironing a preform while rotating the punch and die relative to each other, it is possible to impart biaxial molecular orientation to the circumferential side wall. I found that.

The inventors further found that in the ironed plastic can thus produced, the circumferential side wall has an oriented crystallinity of 25% or more as measured by the density method; Principal axis orientation coefficient (l), measured at
and the minor axis orientation coefficient (m) is l+m≧0.4 and 1.5≧
The molecules are oriented biaxially so that l/m≧1.1, and the main axis of orientation is 3 to
It has been found that it has a bias of 30 degrees, and that it is possible to significantly improve the longitudinal and lateral strength ratio.

(Function) In FIG. 1 for explaining the rotary ironing method used in the present invention, an amorphous bottomed preform 1 made of polyethylene terephthalate (PET) is shown with a punch 2 inserted therein. Supported by An annular die 3 is provided coaxially with the punch 2 and movable relative to it in the axial direction. Further, the annular die 3 is supported rotatably in the circumferential direction.

The bottomed preform 1 has a bottom portion 4 and a circumferential side wall portion 5, and the annular die 3 has an inner diameter larger than the outer diameter of the punch 2 but smaller than the outer diameter of the preform circumferential side wall portion 5. It has a processing tip part 6 having a shape.

In FIG. 1, the annular die 3 rotates in the direction of the arrow, and in this state the punch 2 moves downward.
As a result, the preform circumferential side wall 5 engages with the rotating annular die machining tip 6, and the circumferential side wall 5 is thinned to a thickness regulated by the outer surface of the punch 2 and the die 3 machining tip. The ironing process is then completed.

According to the present invention, when relative rotation is applied to the die 3 and the punch 2 while relative axial stroke movement is performed, biaxial molecular orientation is created on the circumferential side wall of the formed plastic can. This is based on the new discovery that . Preform 1
As already mentioned, the axial stroke movement of the punch 2 and the die 3 that support the axially extending and thinning of the circumferential side wall 5 is carried out, and molecular orientation is carried out in the axial direction. However, in the present invention, molecular orientation in the circumferential direction is also effectively imparted by the engagement of the rotating die processing tip and the side wall portion 5.

FIG. 2 is an orientation distribution curve obtained by measuring the side wall of an ironed can obtained by the rotary ironing method of the present invention using a polarized fluorescence method. In this drawing, Y is the axial direction of the can, and X is the The circumferential direction (axial direction and perpendicular direction) of the can is shown. It can be seen from this figure that the side wall of the ironed can according to the invention exhibits a typical biaxial orientation distribution.

In this specification, the degree of molecular orientation in biaxial directions can be defined by the degree of orientation crystallinity determined by the density method and the orientation coefficients (l, m) of the major and minor axes determined by the fluorescence polarization method.

The degree of crystallinity (D _c ) determined by the density method is determined by the method described in ASTM1505 using a density gradient tube using the following formula D _c = P _s − P _a /P _c − P _a ×100…(1) 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 density of the crystal calculated from the unit cell parameter (1.455 g/cc).

This is the value calculated from

This degree of crystallinity (D _c ) represents the degree of oriented crystallization as a whole, and the ironing can according to the present invention has a degree of crystallinity of 25% or more, particularly 30% or more, so that it can withstand internal pressure. It satisfies the rigidity, tensile strength, pressure resistance, etc. required for ironing cans.

The orientation coefficient by fluorescence polarization method is determined as follows.

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

Polarized fluorescence photometer FOM manufactured by Nippon Bunkoki Co., Ltd.
-1, a 365 nm light source is used, the sample is set, a polarizer and an analyzer are set in parallel, and while the sample is rotated, the angular distribution of transmitted light is determined as a chart.

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

It is expressed as

Now, the rotation angle of the main axis (the orientation axis whose rotation angle is closest to zero is the main axis, and the orientation axis far from this is the secondary axis) is α, the rotation angle of the secondary axis is β, and the relationship between the main axis and the secondary axis is Let γ be the rotation angle at which the fluorescence polarization intensity is minimum between the two, and the fluorescence polarization intensity I at each angle above
(α), I(β), and I(γ) are determined from the chart. Substituting the value of each angle and intensity value into equation (2),
Calculate the values of l, m, and n from the three equations.

In addition, if the polarized light intensity distribution of Chart's fluorescent light is not point symmetric, it is sufficient to find the average value of I(α) and I(α+π) and use this as the value of I(α), which is equal to I( The same applies to β) and I(γ).

In the plastic ironing can according to the present invention, the in-plane orientation coefficient (l+m) is 0.4 or more, particularly 0.42 or more, and the orientation coefficient ratio between the main axis and the minor axis (l+m)
is in the range of 1.1 to 1.5, especially 1.1 to 1.45.
The in-plane orientation coefficient (l+m) indicates the absolute magnitude of the in-plane orientation in the circumferential side wall of the can, and if it is smaller than the above range, the rigidity, strength, pressure resistance, etc. will be unsatisfactory. . The major axis-minor axis orientation coefficient ratio (l/m) indicates the degree of balance of biaxial orientation, and if this value is larger than the above range,
If the circumferential expansion due to internal pressure becomes large and the body is likely to crack vertically due to impact, on the other hand, if it is smaller than the above range, the buckling strength of the can tends to decrease.

The ironing can according to the present invention has an angle (α) of the main axis of orientation of 3 to 30 degrees from the container axis direction (height direction),
A particularly notable feature is that it has a deviation of 4 to 28 degrees, which is an orientation characteristic unique to rotary ironing.

Preferred Embodiments of the Invention The present invention is advantageously applicable to containers made of thermoplastic polyesters, particularly polyesters based on ethylene terephthalate repeating units. Here, the thermoplastic polyester whose main repeating unit is ethylene terephthalate is usually 80 mol% or more of the acid component, preferably 90 mol% or more of terephthalic acid, and 80 mol% or more of the glycol component, preferably 90 mol% or more. is ethylene glycol, and the remaining acid components are isophthalic acid, diphenyl ether 4,4'-dicarboxylic acid,
Naphthalene 1,4- or 2,6-dicarboxylic acid, adipic acid, sebacic acid, decane 1,10-dicarboxylic acid, hexahydroterephthalic acid, as well as propylene glycol as other glycol components,
1,4-butanediol, neopentyl glycol, diethylene glycol, 1,6-hexylene glycol, cyclohexanedimethanol, 2,
2-bis(4-hydroxyphenyl)propane,
It means 2,2-bis(4-hydroxyethoxyphenyl)propane, or a polyester containing p-oxybenzoic acid, p-hydroethoxybenzoic acid, etc. as an oxyacid. Further, a polyfunctional component having trifunctionality or more may be copolymerized within a range that does not impair moldability. Further, it may be a mixed polyester of two or more types such that polyethylene terephthalate is mixed with another thermoplastic polyester so that the content of ethylene terephthalate is 80 mol% or more.

The thermoplastic polyester used must have an intrinsic viscosity of 0.55 or more, preferably 0.6
Above, it more preferably has an intrinsic viscosity of 0.7 to 1.4. Intrinsic viscosity is the intrinsic viscosity measured at 30°C of a solution in which polyester is dissolved in a mixed solution of phenol/tetrachloroethane (6/4 weight ratio). The present invention also applies to polyesters and other resins such as metaxylylene group-containing polyamides, polyvinylidene chloride, acrylonitrile styrene copolymers,
Blends with resins with better gas barrier properties such as ethylene vinyl alcohol copolymers,
It is also advantageously applied to multilayer laminates thereof (hereinafter, these will also be referred to as polyester).

To manufacture the ironed can of the present invention, first, a bottomed cylindrical preform of amorphous polyester is manufactured. This bottomed cylindrical preform is advantageously manufactured by injection molding of polyester. Alternatively,
After melt-extruding polyester into a pipe shape, rapidly cooling it to produce an amorphous pipe, and cutting it to the specified size,
A method of manufacturing a preform with a closed bottom,
Pinch off the pipe-shaped melt extrudate with a split mold,
It is also possible to adopt a method of manufacturing a bottomed preform by pre-blowing.

This bottomed preform is heated at a temperature above the glass transition point of polyester and below the crystallization temperature of polyester, specifically at a temperature of 50 to 100°C.
The temperature is maintained at 60 to 100°C and subjected to rotary ironing between the punch and die described above. The rotation is preferably performed while rotating the die, but it is of course possible to rotate the punch, and it is also possible to rotate both the die and the punch. Moreover, although it is desirable that the stroke for ironing is performed by reciprocating the punch, it is also possible to reciprocate the die, and it is also possible to reciprocate both.

The relative rotational speed of the die and punch is 300 to 2000 mm/sec at the tip of the die, especially
It was found that a range of 300 to 1800 mm/sec is appropriate. On the other hand, the stroke speed for ironing is generally between 50 and 1500, although there is no particular limit.
mm/sec, particularly preferably in the range of 100 to 1000 mm/sec.

Ironing forming may be performed in one stage using a single die, or may be performed in multiple stages using multiple dies with different inner diameters so that the preform side wall portion successively engages the dies with gradually smaller diameters. You may also do so.

In general, the formula D _R = t _B − t _W / t _B × 100 ... (3) where t _B is the thickness of the preform side wall (this is equal to the thickness of the bottom of the can), t _W is the thickness of the side wall of the can The overall ironing rate defined by the thickness is 30 to 75
%, especially 35 to 70%.

The plastic can after ironing is extracted from the punch and, if necessary, is subjected to neck-in processing, flange processing, etc., and is provided with a seaming flange to form a plastic ironed can. Further, if desired, the orientation of the can can be thermally fixed after ironing while it is supported by a punch or after stripping.

The produced plastic ironed cans are filled with the contents either cold or hot, and then double-sealed with a metal lid to produce a canned product.

(Operations and Effects of the Invention) According to the present invention, it is possible for the first time to impart biaxial molecular orientation to the side wall of an ironed plastic can, making it possible to manufacture a plastic can with a significantly improved longitudinal and transverse strength ratio. It became. In addition, biaxial molecular orientation can be imparted in a single process, and the relative rotation between the punch and die reduces the load required for ironing, improves ironing formability and productivity, and reduces the number of defects. It has also become possible to reduce the rate.

(Examples) Example 1 A cup-shaped 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 of polyethylene terephthalate using a conventional method.

This preform was preheated to 70° C. and ironed using a rotary ironing device shown in FIG. The processing conditions at this time are as follows.

Dice rotation speed: 300 r.pm Punch speed: 500 mm/s Ironing rate (D _R ): 65% The properties of the plastic can body thus obtained are as follows.

Can body thickness 0.35mm Can bottom thickness 1.5mm Crystallinity (density method) 30% In-plane orientation coefficient (l + m) 0.65 Orientation coefficient ratio (l + m) 1.4 Main axis orientation deviation 10 degrees This can body is flanged. , further 130℃
A container was prepared by heat fixing the orientation for 5 seconds.

Fill this container with 4.0 gas volume carbonated water,
Approximately 2,000 cans of carbonated water were made by sealing aluminum metal lids.

Of these 2,000 cans, each was placed in a constant temperature room at 50℃ and 37℃.
After conducting a storage test on 100 cans for one week,
It was found that resistance to high temperatures, ie creep resistance, was significantly improved. In particular, the outer diameter expansion coefficients were all suppressed to 2% or less.

In addition, when we conducted a drop test using the remaining filled cans (cartons containing 30 cans per case), we found that even one can cracked vertically despite being dropped from a height of 1 m. It wasn't done.

Example 2 A plastic can body was produced in the same manner as in Example 1, except that the number of rotations of the die was changed among the rotational ironing conditions. The rotation speed of the dice at this time was 450 rpm.

The properties of the plastic can body produced in this way are as follows.

Crystallinity (density method) 32% In-plane orientation coefficient (l + m) 0.72 Orientation coefficient ratio (l + m) 1.25 Deviation of main axis orientation 15 degrees This container was also filled in the same manner as in Example 1, and the aging properties and impact resistance of the container were We evaluated gender, etc., but no problems were found.

Comparative Example 1 A plastic can body was made in the same manner as in Example 1 above, except that the ironing conditions were that the rotation of the die was stopped and ironing was performed with both the die and punch fixed. Created.

The properties of the plastic can body produced in this way are as follows.

Crystallization (density method) 28% In-plane orientation coefficient (l + m) 0.883 Orientation coefficient ratio (l + m) 1.6 Deviation of principal axis orientation 0 degrees This container was also filled in the same manner as in Example 1, and the aging and impact resistance of the container were examined. As a result of the evaluation, regarding the aging change of the can body, the outer diameter expansion coefficient was at most 10.
%, and the variation was extremely large. On the other hand, as for impact resistance, drop tests revealed that there were many cases where vertical cracks occurred in the can body, and the crack occurrence rate was about 20%.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the rotary ironing method according to the present invention, and FIG. 2 is a drawing showing an example of an orientation distribution curve obtained by the rotary ironing method according to the present invention. 1... preform, 2 is punch, 3... annular die, 4... bottom, 5... circumferential side wall, 6... annular die processing tip, X... circumferential direction of the can, Y... axial direction of the can.

Claims (1)

[Scope of Claims] 1. An ironed plastic can formed by ironing a polyester mainly containing ethylene terephthalate units and having a substantially unoriented bottom portion and an oriented circumferential side wall portion, comprising: has an orientational crystallinity of 25% or more as measured by the density method, and the circumferential sidewall has a major axis orientation coefficient (l) and a minor axis orientation coefficient (m) as determined by the fluorescence polarization method.
is biaxially oriented such that l+m≧0.4 and 1.5≧l/m≧1.1, and the main axis of orientation is deviated by 3 to 30 degrees with respect to the can axis direction. Axially ironed plastic can. 2. A method for manufacturing an ironed plastic can comprising ironing an amorphous preform made of polyester mainly containing ethylene terephthalate units between a punch and a die at a temperature higher than the glass transition point of the polyester,
A method for manufacturing a biaxially oriented ironed plastic can, characterized in that the preform is ironed while relatively rotating a punch and a die, thereby imparting molecular orientation in biaxial directions to the circumferential side wall.