JP2004058565A - Method for manufacturing container made of polyester resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for biaxially oriented blow molding for a container made of a polyester resin with excellent mechanical strengths whose surface exhibits a glossy semitranslucent white. <P>SOLUTION: A preform is molded by using a resin composition prepared by mixing, dispersing and melting a polyethylene terephthalate and a polyolefin such as a high density polyethylene or a polypropylene, and the preform is inserted into a mold heated at a predetermined temperature under a softened condition at an appropriate temperature for drawing, and the preform is biaxially oriented blow-molded to a prescribed drawing ratio by using a stretch rod and a blowing gas. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a polyester resin container having a glossy translucent milky white appearance, and in particular, by mixing and dispersing a polyolefin in polyethylene terephthalate and performing biaxial stretching blow molding, a glossy translucent milky white color is obtained. The present invention relates to a method for producing a polyester resin container having the above-mentioned appearance and excellent mechanical strength.
[0002]
[Prior art]
Conventionally, an intermediate molded body such as a preform or parison is formed from a raw material resin such as polyethylene terephthalate, polyethylene, or polypropylene, and a blow-molded plastic container such as a bottle or cup is used for liquids such as drinking water, food and food. It is known that it is widely used for viscous materials such as cosmetics and fine powders such as seasonings.
[0003]
These plastic containers are made by extruding or injection molding a raw resin such as polyethylene terephthalate, polyolefin such as low-density polyethylene, high-density polyethylene, or polypropylene, and molding it into a preform for blow molding or an intermediate molded body such as parison. In a molding die at a temperature suitable for blow molding, it is molded by blowing a blown gas and stretching, or by a stretching method using a stretch rod and a blown gas.
[0004]
In particular, polyethylene terephthalate containers with excellent transparency, mechanical strength, appearance and moldability are widely used for liquids, viscous materials, fine powders, etc. due to these characteristics. The preform obtained by injection molding is heated to an appropriate temperature for stretching, inserted into a molding die, and stretched in the longitudinal (axial) direction with a stretch rod and in the transverse (circumferential) direction with a blowing gas. Axial stretch blow molding is employed.
[0005]
In addition, low-density polyethylene containers are milky white translucent and are used as relatively small and medium-sized containers due to their high flexibility, and high-density polyethylene containers are small in size due to their excellent rigidity. Widely used up to large containers, and polypropylene containers are also widely used from small to large containers due to their light weight and high strength, and these containers are generally obtained by extrusion. A blow molding method is employed in which a preform is inserted into a molding die and a pressurized gas is blown into the die.
[0006]
[Problems to be solved by the invention]
In these containers, coloring agents such as pigments and dyes are added to the raw material resin for the purpose of decoration, identification, protection of contents, etc., and the containers are colored while having transparency or translucency. It is being done.
[0007]
Generally, when a container is colored using a coloring agent, the raw material resin to which the coloring agent is added is used as a main component, and a master batch obtained by dispersing and processing the coloring agent in the raw material resin is used. Is added to a raw material resin to produce a desired coloring.
[0008]
However, this has good handleability of the colorant, but depending on the type of the colorant, it may cause difficulty in compatibility with the raw material resin used as the main component, or the price may be high, or the type of the colorant, Depending on the degree, the desired coloring may not be exhibited.
[0009]
The present invention relates to mixing and dispersing a polyolefin having different properties, preferably high-density polyethylene or polypropylene, into polyethylene terephthalate, molding a preform with a resin composition obtained by melting the same, and then vertically forming the preform. This is a method of obtaining a container such as a bottle or a cup made of a polyester resin having a glossy translucent milky white (hereinafter, referred to as pearl-like gloss) appearance by biaxial stretching blow molding in which the film is stretched in the transverse and transverse directions.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the invention according to claim 1 forms a preform with a resin composition in which polyethylene terephthalate and polyolefin are mixed, dispersed, and melted, and the preform is softened to an intermediate temperature. Inserting the preform into the molding die in a state, the preform is biaxially stretch blow-molded to a predetermined stretching ratio with a stretch rod and blowing gas in the molding die and swelled until it matches the cavity of the molding die. It is characterized by.
[0011]
The invention described in claim 2 is a container made of a polyester resin composed of two or more layers, wherein at least one layer is a layer composed of a resin composition of polyethylene terephthalate and polyolefin.
[0012]
The invention according to claim 3 is characterized in that the resin composition is a mixture of 80 to 99.5% by weight of polyethylene terephthalate and 0.5 to 20% by weight of high density polyethylene or polypropylene.
[0013]
The invention described in claim 4 is characterized in that the stretching ratio is at least 1.5 times and not more than 3.5 times in the longitudinal stretching ratio.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for producing a polyester resin container according to the present invention comprises mixing, dispersing and mixing polyethylene terephthalate and polyolefin to form a preform with a molten resin composition, and forming a preform in a state where the preform is softened to a suitable temperature for stretching. The preform is biaxially stretch blow-molded to a predetermined stretching ratio with a stretch rod and blowing gas in a molding die and swelled until it matches the cavity of the molding die. And a polyester resin container having excellent mechanical strength.
[0015]
Hereinafter, an embodiment of the method for producing a polyester resin container of the present invention will be specifically described.
[0016]
That is, the resin composition used in the present invention is obtained by mixing, dispersing and melting polyethylene terephthalate as a raw material resin and polyolefin as a raw material resin, alone or a high-density polyethylene or polypropylene alone or a blend thereof. A high-density polyethylene or polypropylene alone or a blend of 0.5 to 20% by weight of polyethylene terephthalate in an amount of 80 to 99.5% by weight, or a blend of 0.5 to 20% by weight of polyethylene terephthalate in a proportion of 85 to 98% by weight of polyethylene terephthalate A single substance or a blend of 2 to 15% by weight thereof is mixed, dispersed, and melted. In addition, the raw material resin such as polyethylene terephthalate and polyolefin may be a recycled product.
[0017]
The polyethylene terephthalate used in the present invention is a polyethylene terephthalate produced using terephthalic acid and ethylene glycol as main raw materials, and has an intrinsic viscosity (IV) of 0.7 to 1.2 and a melting point (Tm) of 210 ° C to 265. ° C and a secondary transition temperature (Tg) of 50 ° C to 120 ° C are used. The polyethylene terephthalate may be copolymerized with 20 mol% or less of a dicarboxylic acid such as isophthalic acid.
[0018]
The high-density polyethylene is a high-density polyethylene such as an ethylene homopolymer or a copolymer of ethylene and some α-olefin monomer, and has a density of 0.941 to 0.965 and a melting point (Tm) of 125 ° C. ~ 135 ° C is used.
[0019]
The polypropylene is a polypropylene such as a homopolymer of propylene or a copolymer of propylene and ethylene or some α-olefin monomer, and has a density of 0.90 to 0.91 and a melting point (Tm) of 135 ° C to 165 ° C. ° C is used.
[0020]
In addition, additives such as a heat stabilizer, an ultraviolet absorber, a lubricant, and a coloring agent may be added to these resin compositions, as long as the objects and effects of the present invention are not impaired.
[0021]
The resin composition in the form of fine granules, granules, flakes, and flakes is mixed in advance with a usual mixer, and the mixture is dispersed and melted with an injection molding machine or an extruder to form a bottomed preform. This preform is mechanically stretch-blow-molded biaxially in a longitudinal direction and a transverse direction in a molding die at a predetermined temperature in a state where the preform is softened to an appropriate stretching temperature, and molecular orientation is formed along a stretching direction into a molded bottle. Cause.
[0022]
In the stretch blow molding, a bottomed preform is molded by injection molding, and after a certain cooling time is applied to the preform, the preform is moved into a molding die in a state where the preform is stretched at an appropriate temperature, and is stretched in a longitudinal direction. The so-called cold parison method, which is a method of stretch-blow molding in the biaxial direction in the horizontal direction, or after injection molding of a preform, is moved into a molding die in a softened state at an appropriate stretching temperature without cooling, and then vertically and horizontally. And a parison extruded into a pipe from an extruder by blow-molding to form a bottomed parison, and then moved into a molding die in a softened state at an appropriate temperature for stretching. A so-called hot parison method, which is a method of stretch blow molding in biaxial directions in the horizontal direction, may be used.
[0023]
In the stretch blow molding, a stretch rod and a blowing gas are used to stretch a predetermined stretching ratio in a vertical direction by a stretch rod inserted into a preform having an appropriate stretching temperature in a molding die, and at the same time, in a transverse direction by a blowing gas. Or a preform at an appropriate temperature is stretch blow-molded in a molding die, and then heat-treated in a molding die at a predetermined die temperature of, for example, 80 to 140 ° C. for several seconds, for example, one second or more. (Heat setting) to improve the heat resistance of the container.
[0024]
By these stretch blow moldings, it is possible to obtain a polyester resin container which exhibits a desired pearly glossy appearance and has a suitable mechanical strength.
[0025]
In the present invention, the raw material resin polyethylene terephthalate is mixed and dispersed with the raw resin polyolefin, in particular, a high-density polyethylene or polypropylene alone or a blend thereof, and the polyethylene terephthalate is 80 to 99.5% by weight and the high-density polyethylene or From a resin composition of polypropylene alone or a blend of 0.5 to 20% by weight, preferably 85 to 98% by weight of polyethylene terephthalate, and a high density polyethylene or polypropylene alone or a blend of 2 to 15% by weight of these blends The bottomed preform is stretch-blow-molded in two directions, a longitudinal direction and a lateral direction.
[0026]
Here, when the content of polyethylene terephthalate is less than 80% by weight, the suitable mechanical strength of polyethylene terephthalate cannot be sufficiently exhibited, and the addition amount of polyolefin is less than 0.5% by weight. When the amount is small, a satisfactory pearly glossy appearance cannot be exhibited, which is not preferable.
[0027]
Stretch blow molding is a process in which a preform is heated to a temperature equal to or higher than the secondary transition point of polyethylene terephthalate, which is a suitable temperature for stretching, and usually to a temperature of 90 ° C to 120 ° C and softened before biaxial stretch blow molding. It is moved into a mold, and the longitudinal stretching ratio is 1.5 to 3.5 times, preferably 2 to 3.2 times, and the horizontal stretching ratio is 1.5 to 4 times, excluding the opening of the preform. Preferably, a stretch of 2 to 3.5 times stretch blow molding gives a pearly appearance and obtains a polyester resin container having suitable mechanical strength and the like.
[0028]
The reason for the appearance of pearly luster according to the present invention is that polyethylene terephthalate is a matrix resin by adding polyolefin, which is a raw material resin having different properties, to polyethylene terephthalate as a raw material resin. Are dispersed in an incompatible state, and when this is mechanically stretched, the preform is stretched, thereby causing separation at the interface between polyethylene terephthalate and polyolefin, and when light strikes this interface, light is emitted at this interface. It is presumed that pearl-like appearance is exhibited due to the diffusion of.
[0029]
Therefore, the polyolefin to be added to polyethylene terephthalate is selected from the group consisting of polypropylene, high-density polyethylene, low-density polyethylene having a density of 0.915 to 0.929, and medium-density polyethylene having a density of 0.929 to 0.941. When the resin is dispersed in a state incompatible with polyethylene terephthalate and is mechanically stretched, peeling occurs at the interface between the polyethylene terephthalate and the raw material resin added, causing a phenomenon in which light is diffused and a pearly luster is exhibited. Can be used as appropriate, and the molding conditions such as the addition weight%, the molding temperature and the stretching ratio can be selected in accordance with this.
[0030]
In the polyester resin container of the present invention, it is important that the constituent layer of the container is formed of a resin composition of polyethylene terephthalate and polyolefin, but the container is formed as a single layer, and this layer is formed of the resin. Depending on the purpose of use of the container, the container may be formed into a plurality of layers, and one or more of the outer layer, the inner layer, and the intermediate layer may be formed of the resin composition. May be.
[0031]
In general, the container is composed of a single layer, and this layer is made of the resin composition and has a bright pearly luster, or the container is composed of two layers, the outer layer is made of the resin composition, and the inner layer is made of the inner layer. One having a pearl-like luster formed by using a single material resin on the side and a resin having a pearl-like luster formed by using the resin composition on the inner layer side and a single-material resin on the outer layer side.
[0032]
Further, various shapes of protruding ribs, protrusions or concave grooves may be formed on the body of the container or the like as necessary for decoration or strength improvement.
[0033]
【Example】
Examples are described below to explain the present invention in further detail, but the present invention is not limited to these.
[0034]
Embodiment 1
To 97% by weight of polyethylene terephthalate having an intrinsic viscosity (IV) of 0.75, 3% by weight of high-density polyethylene having a density of 0.951 and a melt flow rate (MFR) of 0.3 were added and mixed with a high-speed mixer. An injection molding machine was used to obtain a preform with a bottom having a total length of 100 mm, a diameter of 24 mm, a thickness of 3 mm, and a height of 80 mm excluding a plug portion.
[0035]
This bottomed preform is once cooled to room temperature, and then heated by an infrared heater so that the surface temperature of the center of the preform body becomes 100 ° C., and immediately placed in a molding die having a surface temperature of 60 ° C. After inserting and clamping, the forming condition of the bottomed preform with a longitudinal stretching ratio of 2.3 times and a transverse stretching ratio of 2.5 times using a stretch rod of 500 mm length and a blowing gas at an air pressure of 30 atm. Thus, a round bottle with a plug having a height of 210 mm, a body diameter of 62 mm, an average thickness of 0.4 mm, and an internal volume of 500 ml was obtained.
[0036]
Observation of this bottle with the naked eye revealed that the outer surface of the trunk had a smooth surface similar to that of polyethylene terephthalate alone, and was a translucent milky white bottle having excellent gloss.
[0037]
In addition, a bottle of a sample is randomly collected from the molded bottle, filled with a predetermined amount of water, sealed with a stopper, left at room temperature at 5 ° C for 24 hours, and then repeatedly dropped from a height of 1 m five times. However, no abnormalities such as breakage were observed.
[0038]
Embodiment 2
In Example 1, 1% by weight of high-density polyethylene having a density of 0.951 and a melt flow rate (MFR) of 0.3 was added to 99% by weight of polyethylene terephthalate having an intrinsic viscosity (IV) of 0.75. A bottomed preform similar to 1 was obtained.
Under the same molding conditions as in Example 1, a round bottle with an inner volume of 500 ml with a plug was obtained from this preform.
[0039]
Observation of this bottle with the naked eye revealed that the outer surface of the body had a smooth surface similar to that of Example 1, and was slightly higher in transparency and better gloss than the bottle of Example 1. It was a translucent milky white bottle.
A drop test was performed in the same manner as in Example 1, but no abnormality such as breakage was observed.
[0040]
Embodiment 3
In Example 1, 15% by weight of a density polyethylene having a density of 0.951 and a melt flow rate (MFR) of 0.3 were added to 85% by weight of polyethylene terephthalate having an intrinsic viscosity (IV) of 0.75. A preform with a bottom similar to that described above was obtained.
Under the same molding conditions as in Example 1, a round bottle with an inner volume of 500 ml with a plug was obtained from this preform.
[0041]
Observation of this bottle at the wall limit showed that the outer surface of the body had the same smooth surface as in Example 1, and was slightly less transparent and deeper in gloss than the bottle of Example 1. Was a translucent milky white bottle with
A drop test was performed in the same manner as in Example 1, but no abnormality such as breakage was observed.
[0042]
Embodiment 4
Using the same resin composition as in Example 1 and mixing with a high-speed mixer, a 100-ton injection molding machine was used to form a bottomed preform having a total length of 80 mm, a diameter of 20 mm, a thickness of 3 mm, and a height of 60 mm excluding the plug portion. Obtained.
[0043]
This bottomed preform is once cooled to room temperature, and then heated by an infrared heater so that the surface temperature of the center of the preform body becomes 100 ° C., and immediately placed in a molding die having a surface temperature of 60 ° C. After inserting and clamping, a 500 mm long stretch rod and a blowing gas at an air pressure of 30 atm are used in combination to form a bottomed preform in a longitudinal stretch ratio of 3.2 times and a transverse stretch ratio of 3.1 times. The same round bottle as in Example 1 having an inner volume of 500 ml with a plug was obtained.
[0044]
Observation of this bottle with the naked eye revealed that it was a translucent milky white bottle having a good smooth surface and excellent gloss as in Example 1.
A drop test was performed in the same manner as in Example 1, but no abnormality such as breakage was observed.
[0045]
Embodiment 5
Using the same resin composition as in Example 1 and mixing with a high-speed mixer, a 100-ton injection molding machine was used to form a bottomed preform having a total length of 120 mm, a diameter of 31 mm, a thickness of 3 mm, and a height of 100 mm excluding the plug portion. Obtained.
[0046]
This bottomed preform is once cooled to room temperature, and then heated by an infrared heater so that the surface temperature of the center of the preform body becomes 100 ° C., and immediately placed in a molding die having a surface temperature of 60 ° C. After inserting and clamping, a 500 mm long stretch rod and a blowing gas with an air pressure of 30 atm are used in combination to form a bottomed preform under the molding conditions of a vertical stretching ratio of 1.9 times and a horizontal stretching ratio of 2 times. A round bottle with a stopper having a cap volume of 500 ml similar to that of Example 1 was obtained.
[0047]
Observation of this bottle with the naked eye revealed that it was a translucent milky white bottle having a good smooth surface and excellent gloss as in Example 1.
A drop test was performed in the same manner as in Example 1, but no abnormality such as breakage was observed.
[0048]
Embodiment 6
To 97% by weight of polyethylene terephthalate having an intrinsic viscosity (IV) of 0.75, 3% by weight of polypropylene having a density of 0.90 and a melt flow rate (MFR) of 2.5 were added under the same molding conditions as in Example 1. Then, a bottomed preform having a height of 80 mm except for a plug portion similar to that of Example 1 was obtained.
Under the same molding conditions as in Example 1, a round bottle with an inner volume of 500 ml with a plug was obtained from this preform.
[0049]
Observation of this bottle with the naked eye revealed that it was a translucent milky white bottle having a good smooth surface and excellent gloss as in Example 1.
A drop test was performed in the same manner as in Example 1, but no abnormality such as breakage was observed.
[0050]
Embodiment 7
Using the same resin composition as in Example 6, and under the same molding conditions as in Example 4, a bottomed preform having a height of 60 mm excluding the plug portion similar to that in Example 4 was obtained.
Under the same molding conditions as in Example 4, a round bottle with an inner volume of 500 ml with a plug was obtained from this preform under the same molding conditions as in Example 4.
[0051]
Observation of this bottle with the naked eye revealed that it was a translucent milky white bottle having a good smooth surface and excellent gloss as in Example 1.
A drop test was performed in the same manner as in Example 1, but no abnormality such as breakage was observed.
[0052]
Embodiment 8
Using the same resin composition as in Example 6, and under the same molding conditions as in Example 5, a bottomed preform having a height of 100 mm excluding the plug portion similar to that in Example 5 was obtained.
From this preform, under the same molding conditions as in Example 5, a round bottle with a cap section having an inner volume of 500 ml similar to that of Example 5 was obtained.
[0053]
Observation of this bottle with the naked eye revealed that it was a translucent milky white bottle having a good smooth surface and excellent gloss as in Example 1.
A drop test was performed in the same manner as in Example 1, but no abnormality such as breakage was observed.
[0054]
【The invention's effect】
The present invention relates to a biaxial method of mixing and dispersing a polyolefin having different properties into polyethylene terephthalate, forming a preform with a resin composition obtained by melting the same, and stretching the preform in the machine direction and the transverse direction. By stretching blow molding, a polyester resin container having a smooth and glossy translucent milky white (pearly gloss) appearance and exhibiting excellent mechanical strength can be easily molded. Moreover, since a relatively inexpensive general-purpose resin is added without using any special equipment, manufacturing costs can be reduced.

Claims (4)

A preform is molded from a resin composition in which polyethylene terephthalate and polyolefin are mixed, dispersed, and melted, and the preform is inserted into a molding die while being softened to an appropriate temperature for stretching, and the preform is stretched in the molding die. A method for producing a polyester resin container, comprising: biaxially stretch-blow-molding a rod and a blowing gas at a predetermined stretching ratio to swell until it matches a cavity of a molding die. 2. The polyester resin container according to claim 1, wherein the container is a polyester resin container comprising two or more layers, wherein at least one layer is a layer comprising a resin composition of polyethylene terephthalate and polyolefin. Method. The polyester resin container according to claim 1 or 2, wherein the resin composition comprises 0.5 to 20% by weight of high density polyethylene or polypropylene based on 80 to 99.5% by weight of polyethylene terephthalate. Manufacturing method. The method for producing a polyester resin container according to any one of claims 1 to 3, wherein the stretching ratio is at least 1.5 times or more and 3.5 times or less as a longitudinal stretching ratio.