JP2005162305A - Bottle made from polyethylene terephthalate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bottle made from polyethylene terephthalate, which is lightweight, is sufficiently heat-resistant and rigid, and can be filled with hot contents. <P>SOLUTION: In the bottle made from polyethylene terephthalate, the average wall thickness of a body is 0.27 mm or less, the average storage elastic modulus of the bottle body at 87°C is 2.7 GPa or greater, and a rate at which the capacity of the bottle containing 87°C hot water changes is 2% or less. It is preferable that the average wall thickness Tp of a preform body and the average wall thickness Tb of the bottle body formed by biaxially stretch-blowing it is Tp/Tb>10.0 or more. Further, it is preferable to have a stretch part and unstretch part and to be 14 to 19g in the weight of the stretched part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-resistant bottle formed by biaxially stretching blow-molding a polyethylene terephthalate preform.

  A method for producing a bottle by injection molding a bottomed preform using polyethylene terephthalate, heating the obtained preform to a stretchable temperature, and performing biaxial stretch blow molding has been conventionally used. Bottles obtained by this method are excellent in transparency, surface gloss, impact resistance, gas barrier properties, etc., and are widely used as containers for various beverages, foods, liquid detergents and the like.

Generally, when filling a bottle with a beverage, in order to improve the storage stability of the beverage, the beverage is hot-filled at 85 to 90 ° C., and the beverage and the inside of the bottle are sterilized by heating. However, since the glass transition temperature of polyethylene terephthalate is around 75 ° C., a polyethylene terephthalate bottle undergoes thermal deformation when exposed to a high temperature of 70 ° C. or higher. Therefore, in order to impart heat resistance to the bottle, heat setting (heat setting) is performed after biaxial stretch blow molding. In order to produce a bottle that does not cause any practical problems even when hot-filled, the capacity change rate before and after filling with hot water at 87 ° C. needs to be 2% or less. If the capacity change rate of the bottle is too large, it becomes difficult to control the filling amount when filling the beverage.
In order to suppress the deformation of the bottle, it is also important to improve the rigidity of the bottle, and the elastic modulus and thickness of the bottle body are important factors.

By increasing the elastic modulus of the bottle body, the rigidity of the bottle is increased and the bottle can be made difficult to deform. In order to increase the elastic modulus of the stretched bottle body, the ratio Tp / Tb of the average thickness Tp of the preform body and the average thickness Tb of the bottle body may be increased. To increase Tp / Tb, it is conceivable to increase the average thickness Tp of the preform body. However, when the average thickness Tp of the preform body is large, there is a problem that the preform cooling time in the mold becomes long in the injection molding, and the productivity of the preform is lowered. For this reason, Tp / Tb of the bottle used for hot filling remains at 8.0 to 9.5.
By increasing the thickness of the bottle body, it is possible to improve the rigidity of the bottle and to make the bottle difficult to deform. However, if the wall thickness of the bottle body is increased, there is a problem that the amount of resin used increases and the bottle unit price increases. In addition, with the enforcement of the Containers and Packaging Recycling Law, there is an increasing demand for reducing the amount of resin used in plastic containers. For this reason, weight reduction of the bottle made from a polyethylene terephthalate is calculated | required.

Bottles used for hot filling are designed from the viewpoints of heat resistance, rigidity, moldability, productivity, and the like. For example, a bottle filled with 500 ml of beverage has an average body thickness of 0.30 to 0.35 mm, and the weight of the stretched portion is 19.5 to 25.0 g, so the beverage is hot filled at 85 to 90 ° C. Even so, it is possible to suppress the thermal deformation of the bottle to the extent that there is no practical problem. However, if the body is thinned for weight reduction, there is a problem that the rigidity of the bottle decreases and thermal deformation increases.
As a method for reducing the weight of the bottle, it is conceivable to reduce the wall thickness. Japanese Patent Application Laid-Open No. 2003-191319 (Patent Document 1) describes a bottle-shaped container having an average wall thickness of 0.1 to 0.2 mm as a thin-walled bottle-shaped container and a manufacturing method thereof. Yes. In addition, it is described that the area stretch ratio of biaxial stretch blow molding is 15 times or more in order to make the average thickness 0.1 to 0.2 mm. Since this bottle-shaped container is thin, it is lightweight. However, it is clear that it cannot be used for hot filling because it does not have sufficient elastic modulus and heat resistance.
JP 2003-191319 A

  Accordingly, an object of the present invention is to provide a polyethylene terephthalate bottle that is lightweight and has heat resistance and rigidity that can be hot-filled.

As a result of diligent research in view of the above object, the present inventor has increased the ratio of the thickness of the preform body to the thickness of the bottle body in biaxial stretch blow molding, and increased the average storage elastic modulus of the bottle body. Thus, it was discovered that a polyethylene terephthalate bottle having heat resistance and rigidity that can be hot-filled even if the weight is reduced is obtained, and the present invention has been conceived.
That is, the bottle made of the polyethylene terephthalate of the present invention has an average thickness of the bottle body portion of 0.27 mm or less, and an average storage elastic modulus at 87 ° C. of the bottle body portion of 2.7 GPa or more. The capacity change rate when filled with 87 ° C. hot water is 2% or less.

  A preform made of polyethylene terephthalate is formed by biaxial stretch blow molding, and the ratio Tp / Tb of the average thickness Tp of the preform body and the average thickness Tb of the bottle body is 10.0 or more. Is preferred. It has a stretched part and a non-stretched part, and the weight of the stretched part is preferably 14 to 19 g. The capacity of the bottle is preferably 450 to 600 ml.

  The polyethylene terephthalate bottle of the present invention has an average storage elastic modulus at 87 ° C. of the bottle body of 2.7 GPa or more, and a capacity change rate when the bottle is filled with 87 ° C. hot water is 2% or less. Therefore, even if the average thickness of the stretched portion is 0.27 mm or less, it has heat resistance and rigidity capable of hot filling. Therefore, it is a bottle having heat resistance and rigidity that is lightweight and can be hot-filled.

[1] Polyethylene terephthalate bottle (1) Bottle shape FIGS. 1 and 2 show an example of a polyethylene terephthalate bottle. The bottle has a substantially cylindrical body part 13, a shoulder part 12 extending to the upper end of the body part 13, an open end part 11 provided at the upper end of the shoulder part 12, and a lower end of the body part 13. And a bottom portion 14 provided so as to be closed. In the case of a bottle formed by biaxial stretch blow molding, the body portion 13, the shoulder portion 12 and the bottom portion 14 are stretched portions, and the open end portion 11 is a non-stretched portion.

The trunk | drum 13 should just be substantially cylindrical, and may have a dent and a constriction. As shown in FIG. 2, the body portion 13 has a cross section having a shape close to a hexagon (generally hexagonal), but the shape of the cross section of the body portion 13 is not limited thereto. For example, the cross section of the trunk portion 13 may be a shape close to an octagon (generally an octagon).
A screw portion is formed on the outer surface of the opening end portion 11, and a cap is fitted into the screw portion.

(2) Average thickness of bottle body portion Since the body portion 13 occupies most of the polyethylene terephthalate bottle, if the body portion 13 has a small average wall thickness, the entire polyethylene terephthalate bottle becomes light. The average thickness of the bottle body 13 is 0.27 mm or less, and preferably 0.23 mm or less. If the average thickness is more than 0.27 mm, the weight of the body portion 13 is too large to obtain a lightweight bottle. The average thickness of the bottle body is an average value of the thickness of the bottle body 13. Since the thickness of the bottle body 13 may vary depending on the part, it is preferable to measure 50 or more points and obtain the average value. The wall thickness can be measured with a commercially available wall thickness measuring instrument.

(2) Average storage elastic modulus of the bottle body portion The average storage elastic modulus at 87 ° C of the bottle body portion 13 is 2.7 GPa or more. The average storage elastic modulus of the bottle body 13 is preferably 3.0 Pa or more. In this specification, an average storage elastic modulus shows the value which averaged the storage elastic modulus of each extending | stretching direction (direction of each axis | shaft) of the bottle trunk | drum which carried out biaxial stretching blow molding. In general biaxial stretch blow molding, since the bottle is stretched in the longitudinal direction and the circumferential direction, the average storage elastic modulus is a value obtained by averaging the storage elastic modulus in the vertical direction and the circumferential direction of the bottle body. It is preferable to measure three or more storage elastic moduli in the longitudinal direction and the circumferential direction, and obtain an average value. The storage elastic modulus can be measured by a general dynamic tensile viscoelasticity measuring method.
When the average storage elastic modulus is less than 2.7 GPa, a problem occurs when a beverage or the like is hot-filled into a bottle having an average thickness of the trunk portion 13 of 0.27 mm or less. Specifically, since the bottle has insufficient rigidity, the bottle expands due to thermal deformation, making it difficult to control the filling amount.

By increasing the average storage elastic modulus of the body 13 and increasing the rigidity of the bottle, the bottle can be reduced in weight, and deformation that occurs during hot filling can be suppressed even if the average thickness of the bottle body is reduced. Can get a good bottle.

(3) Heat resistance of the bottle When the bottle is filled with hot water at 87 ° C., the capacity change rate is 2% or less. For this reason, it can be used for hot filling. The smaller the capacity change rate, the better. However, 2% or less is sufficient. The capacity change rate can be obtained from the bottle capacity before and after filling with hot water of 87 ° C.

(4) Weight of stretched part of bottle In the case of a bottle having a capacity of 500 to 550 ml, the weight of the stretched part of the bottle is 19 g or less when the average thickness of the bottle body 13 is 0.27 mm or less. As the bottle becomes lighter as the bottle becomes lighter, it is preferable that the bottle that can be used for hot filling has an average body thickness of 0.20 to 0.26 mm and a weight of the stretched portion of 14 to 18 g. The average thickness is 0.21 to 0.24 mm, and the weight of the stretched portion is particularly preferably 15 to 17 g. A conventional bottle having a capacity of 500 to 550 ml has a weight of 19.5 to 25.0 g of the stretched portion, and thus it can be said that the bottle of the present invention has been reduced in weight.
(6) Capacity of the bottle The capacity of the bottle is preferably 450 to 600 ml, more preferably 500 to 550 ml. A bottle having a bottle capacity of 520 to 550 ml is suitable for a bottle filled with 500 ml of a beverage, and is therefore widely used.

(5) Composition of polyethylene terephthalate The polyethylene terephthalate is preferably a homopolymer. When the total of monomer units of terephthalic acid and ethylene glycol, which are the main components, is 100 mol%, other monomers may be contained in a range of 20 mol% or less.
As monomers that may be contained, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 4,4′-sulfonebisbenzoic acid, 4, Aromatic dicarboxylic acids such as 4′-biphenyldicarboxylic acid, 4,4′-sulfide bisbenzoic acid, 4,4′-oxybisbenzoic acid, diphenoxyethanedicarboxylic acid, malonic acid, succinic acid, glutaric acid, fumaric acid, Aliphatic dicarboxylic acids such as maleic acid, adipic acid, sebacic acid, azelaic acid, and decanedicarboxylic acid; dicarboxylic acids such as alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid, diethylene glycol, 1,2-propanediol, 1,3- Propanediol, 1,4-butanediol, 1,6-hexanediol, neo N-glycol, dodecamethylene glycol, triethylene glycol, tetraethylene glycol and other aliphatic diols, cyclohexanedimethanol and other alicyclic diols, 1,3-bis (2-hydroxyethoxy) benzene, 1,2-bis ( 2-hydroxyethoxy) benzene, 1,4-bis (2-hydroxyethoxy) benzene, bis [4- (2-hydroxyethoxy) phenyl] sulfone, 2,2-bis (4-β-hydroxyethoxyphenyl) propane, Diols containing aromatic groups such as bisphenols, hydroquinone, resorcin, glycolic acid, diglycolic acid, lactic acid, 3-hydroxybutyric acid, p-hydroxybenzoic acid, m-hydroxybenzoic acid, p-hydroxymethylbenzoic acid, m-hydroxy Methylbenzoic acid, p- 2-hydroxyethyl) benzoic acid, m-(2-hydroxyethyl) hydroxycarboxylic acid unit such as benzoic acid.

  Polymerization catalysts used for resin synthesis include alkali metals such as sodium, alkaline earth metals such as magnesium, aluminum, zinc, tin, titanium, copper, nickel, cobalt, zirconium, germanium, iron, antimony, vanadium, etc. A metal organic complex, oxide, or simple substance can be used, but an organic complex or oxide of a transition metal such as zinc, tin, titanium, cobalt, germanium, or antimony is particularly preferable, and germanium dioxide is particularly preferable.

Resin synthesis may be performed in the presence of various stabilizers or anti-coloring agents. Examples of stabilizers and anti-coloring agents include phosphorus compounds and hindered phenol compounds. Among these, it is particularly preferable to contain a phosphorus compound. Examples of phosphorus compounds include inorganic phosphorus compounds such as phosphoric acid, phosphorous acid, and polyphosphoric acid, phosphoric acid ester compounds such as trimethyl phosphoric acid and diphenyl phosphoric acid, triphenyl phosphite, and tris (2,4 di-t-butylphenyl). ) Phosphite compounds such as phosphites.
In general, the intrinsic viscosity (IV) of polyethylene terephthalate is preferably from 0.6 to 1.4 dl / g, particularly preferably from 0.65 to 0.9 dl / g.

[2] Method for Producing Bottles A method for producing the polyethylene terephthalate bottle of the present invention will be described below, but the bottle of the present invention is not limited to this method.
(1) Molding of preform Polyethylene terephthalate deteriorates due to rapid progress of hydrolysis reaction when water is present in a molten state. In order to prevent this, it is important to dry in advance. Although a drying method is not specifically limited, It is preferable to dry at 150-160 degreeC for about 4 hours under dehumidification air stream. The amount of water in the resin after drying is preferably 100 ppm or less, and particularly preferably 50 ppm or less.

The injection molding of the preform is performed using a general injection molding machine. The injection cylinder temperature is preferably set at 270 to 300 ° C. The mold temperature is preferably set to 5 to 15 ° C. in order to obtain a preform with good transparency. The molding conditions largely depend on the injection molding machine to be used, the shape of the preform, etc., and therefore will not be mentioned here.
The shape of the preform is shown in FIG. It consists of an open end 11, a cylindrical body 15, and a hollow hemispherical bottom 16. A screw portion is formed on the outer surface of the opening end portion 11, and a cap is fitted into the screw portion.

The average thickness Tp of the preform body is preferably 3.0 mm or less, more preferably 2.0 to 2.5 mm. If the average thickness Tp of the preform body is more than 3.0 mm, it is necessary to lengthen the cooling time in the mold of the preform, and the injection molding cycle becomes long, so that the productivity of the preform is lowered. If the average thickness Tp of the preform body is too small, it becomes difficult to completely fill the resin into the mold cavity, and the preform cannot be molded.
In order to impart heat resistance to the opening end of the obtained preform, the opening end is crystallized. The method of crystallization is not particularly limited, and there is a method of adjusting the size of the opening end after heating the opening end to 180 ° C. with an infrared heater and maintaining the state for a predetermined time for crystallization.

(2) Bottle formation Next, the bottle is formed using a biaxial stretch blow molding machine. Blow molding is also performed using a conventionally used blow molding machine. The body of the preform crystallized at the opening end is heated to 90 to 140 ° C. by an infrared heater, placed in a blow mold set at a mold temperature of 120 to 180 ° C., and stretched in the longitudinal direction from the opening end. For this purpose, a stretching rod is inserted, and at the same time or sequentially, compressed air is blown into a bottle.

The ratio Tp / Tb of the average wall thickness Tp of the preform body used in the biaxial stretch blow molding and the average wall thickness Tb of the obtained bottle body is preferably 10 or more, and preferably 12-16. 13 to 15 is particularly preferable. By setting Tp / Tb to 10.0 or more, the average storage elastic modulus at 87 ° C. of the bottle body can be set to 2.7 GPa or more. From the data of a known stretched polyethylene terephthalate film, the upper limit of the storage elastic modulus at 87 ° C. is estimated to be about 3.3 GPa, and when Tp / Tb is 16, the storage elastic modulus is about 3.3 GPa. Therefore, even if Tp / Tb exceeds 16, no further improvement effect of the storage elastic modulus can be obtained, resulting in a decrease in blow moldability and a decrease in bottle productivity.
For example, when using a preform having an average thickness Tp of the preform body of 3.0 mm, (a) when Tp / Tb is set to 15, a bottle having an average thickness Tb of the body 13 of 0.2 mm is obtained. (B) When Tp / Tb is set to 13, a bottle having an average thickness Tb of the body portion 13 of 0.23 mm is obtained.

Subsequently, the entire body of the bottle is brought into close contact with the mold and heat-fixed, and then cooled to 70 ° C. or lower and taken out to prevent deformation of the bottle. A heat-resistant bottle can be produced by heat-setting the stretched and oriented bottle. The blow mold temperature is preferably set to 120 to 150 ° C, particularly preferably set to 130 to 140 ° C. If the blow mold temperature is set to over 150 ° C., the effect of heat setting increases, but the amount of oligomer in polyethylene terephthalate adhering to the mold increases and the mold becomes dirty, so the mold cleaning frequency must be increased. . Also, a longer time is required to cool the bottle to 70 ° C., and the blow molding cycle becomes longer. As a result, bottle productivity is reduced and economic loss occurs. Conversely, if the blow mold temperature is set to less than 120 ° C., the effect of heat setting is reduced, the thermal deformation of the bottle when hot filled at 87 ° C. is increased, and the capacity change rate exceeds 2%.
When the bottle body average thickness is reduced, the temperature of the bottle body rapidly increases when the bottle body is heat-fixed, so that the effect of heat setting can be increased. Increasing Tp / Tb tends to increase the stress generated in the stretching orientation and increase the capacity change rate at 87 ° C. However, it has been found that the problem can be solved by reducing the average wall thickness of the bottle body in the present invention. Yes.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The measuring methods and evaluation methods for various physical properties and characteristics are as follows.
(Average thickness of bottle body)
The thickness of the bottle body was measured with a wall thickness measuring instrument. The average wall thickness was measured in 10 mm increments in the longitudinal direction of the bottle and in 60 ° increments in the circumferential direction, and the average value was used.
(Average thickness of preform body)
A section was cut out from the preform body, and the thickness was measured with calipers. The average thickness was measured by measuring the thickness of a total of three points, a point 10 mm from the open end 11, a point 10 mm from the association between the body and the bottom, and an intermediate point between the two points, and the average value was used.
(Average storage modulus of bottle body)
A 20 mm × 2 mm section was cut out from an arbitrary stretched portion of the bottle body, and the storage elastic modulus at 87 ° C. in the tensile mode was measured using a rheometric RSAII. The frequency was 1 Hz. The storage elastic modulus measurement was carried out at three points for each of the bottle in the longitudinal direction and the circumferential direction, and the numerical value obtained by averaging the measured values was taken as the average storage elastic modulus in the present invention.
(Bottle heat resistance)
Fill the bottle after molding with water, measure the weight, and measure the bottle capacity from the density of the water. Next, the bottle volume after the bottle is filled with 87 ° C. hot water and cooled is measured in the same manner. The capacity change rate is calculated from the bottle capacity before and after filling with hot water. A bottle having a capacity change rate of 2% or less was judged to have good heat resistance.
(Hot filling evaluation)
The obtained bottle was filled with hot water at 87 ° C., and thermal deformation was evaluated. The appearance was visually observed, and a bottle with no significant deformation was judged good.

(Preform molding)
Polyethylene terephthalate (manufactured by Mitsui Chemicals: J125, IV = 0.77 dl / g) was dried at 160 ° C. for 4 hours by a dehumidifying air dryer. The dried pellets were put into a hopper of an injection molding machine (manufactured by Nissei Plastic Industry: ES600-9E, screw diameter: 28 mm). Dehumidified air was also circulated in the hopper to prevent the resin from absorbing moisture. The molding temperature was set to 300 ° C for the nozzle and 285 ° C for the cylinder. The resin was weighed at a screw speed of 150 rpm, and then the molten resin was injected into a mold. The mold was provided with cooling piping, and 15 ° C. cooling water was circulated. The molten resin was cooled in the mold for 15 seconds, and removed from the mold when the resin solidified. The molding cycle at this time was 30 seconds. Further, as shown in FIG. 1, the obtained preform is a bottomed preform having a screw part for closing the lid at the opening end and a support ring for protecting the container. The dimensions of the preform were as follows: barrel outer diameter 24.8 mm, central inner diameter 18.9 mm, overall length 90.3 mm, distance from the opening end to the support ring 22.0 mm.
The opening end portion of the preform obtained by the above injection molding was heated and crystallized with an infrared heater.

(Bottle molding)
A biaxial stretch blow molding machine (manufactured by Corpopst:
BLOMAX 6E) was formed into a bottle. In this biaxial stretch blow molding machine, the preform body is heated uniformly by passing through the infrared heater zone while the preform rotates. Thereafter, the preform is fed into a blow mold, a stretching rod is inserted from the end of the opening and stretched in the longitudinal direction, and then compressed air is blown into the shape of a bottle. The temperature of the preform body immediately before stretching was 110 ° C. Further, the blow mold temperature was set to 135 ° C. in order to heat-fix the bottle body after stretching. The bottle molding cycle was 800 / mold / hour.
FIG. 2 shows the shape of the molded bottle. The bottle had an overall height of 205 mm and a bottle capacity of 546 ml after forming the barrel center outer diameter of 68 mm. The physical properties of the obtained bottle are shown in Table 1.

The bottle is formed in the same manner as in Example 1 except that the preform has a body outer diameter of 21.8 mm, a central inner diameter of 16.4 mm, a total length of 92.2 mm, and a distance from the opening end to the support ring of 22.0 mm. Got. The physical properties of the obtained bottle are shown in Table 1.

(Comparative Example 1)
The bottle was formed in the same manner as in Example 1, except that the preform had a body central outer diameter of 25.0 mm, a central inner diameter of 20.4 mm, a total length of 95.0 mm, and a distance from the opening end to the support ring of 22.0 mm. Got. The physical properties of the obtained bottle are shown in Table 1.

(Comparative Example 2)
The bottle was formed in the same manner as in Example 1 except that the preform had a body central outer diameter of 25.0 mm, a central inner diameter of 19.7 mm, a total length of 95.0 mm, and a distance from the opening end to the support ring of 22.0 mm. Got. The physical properties of the obtained bottle are shown in Table 1.

It is the shape of a PET bottle. FIG. 2 is a cross-sectional view of a body part of the bottle shown in FIG. 1. The shape of the preform.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Open end part 12 Shoulder part of a bottle 13 Body part of a bottle 14 Bottom part of a bottle 15 Body part of a preform 16 Bottom part of a preform

Claims (4)

A bottle made of polyethylene terephthalate, wherein the bottle body has an average thickness Tb of 0.27 mm or less, and the bottle body has an average storage elastic modulus at 87 ° C. of 2.7 GPa or more, and A bottle having a capacity change rate of 2% or less when hot water at 87 ° C. is filled. The bottle according to claim 1, wherein the preform is formed by biaxial stretch blow molding, and a ratio Tp / Tb of the average wall thickness Tp of the preform body and the average wall thickness Tb of the bottle body is 10.0 or more. Bottle characterized by being. The bottle according to claim 1 or 2, wherein the bottle has a stretched portion and a non-stretched portion, and the weight of the stretched portion is 14 to 19 g. The bottle according to any one of claims 1 to 3, wherein the bottle has a capacity of 450 to 600 ml.

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