JPS6212023B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a polyethylene terephthalate molded container and a method for manufacturing the same, and more specifically, at least one outer layer contains an additive such as a pigment,
The present invention relates to a hygienic transparent polyethylene terephthalate homogeneous multilayer molded container whose innermost layer is made of substantially pure polyethylene terephthalate, and a method for producing the same.

(Prior art) Polyethylene terephthalate molded containers, especially 2
Axial-stretched blow containers have excellent creep resistance, rigidity, transparency, etc., and have low permeability to gases such as oxygen and carbon dioxide, and have a high content retention capacity, so they are currently used as bottles for beer and carbonated drinks in the United States. It is widely used and is being used in some parts of Japan as bottles for soy sauce, and is expected to be applied to bottles for food such as salad oil and sauces, cosmetic bottles, medicine bottles, etc. in the future.

(Problems to be Solved by the Invention) However, conventionally known polyethylene terephthalate molded containers contain only trace amounts of polymerization catalyst residues, unreacted monomers, and components other than low molecular weight components generated during polymerization and chip molding. That is, it usually does not contain external additives (herein referred to as additives) such as colorants, antistatic agents, ultraviolet absorbers, antioxidants, lubricants, nucleating agents, crosslinking agents, etc., that is, it is substantially pure. Manufactured from polyethylene terephthalate. These additives may migrate into the contents of the container and cause unfavorable hygienic effects by coloring or changing the flavor of the contents. One of the reasons why conventional polyethylene terephthalate molded containers that do not contain these additives is attracting attention as storage containers for foods, drugs, cosmetics, etc. is thought to be that there is no risk of the above-mentioned negative effects. . However, when used as a beer bottle, for example, it is desirable that the beer be colored blue-green or brown to block sunlight and prevent the beer from deteriorating.Also, when used as a cosmetic bottle or medicine bottle, it is preferable that the product be colored blue-green or brown. Beautiful transparent coloring is often preferred to increase value. In addition, conventional polyethylene terephthalate containers are highly electrostatically charged, and foreign matter such as dust and dirt often adheres to the container surface during the distribution stage, reducing the product value. In order to prevent such drawbacks, it is desirable to add an antistatic agent during the molding process. However, this requirement is in conflict with the requirement that the contents do not become colored, do not change the flavor of the contents, and do not have an undesirable effect on hygiene. No polyethylene terephthalate molded container was known. The present invention aims to provide a new molded container that solves the problems of these conventional polyethylene terephthalate molded containers.

(Means and effects for solving the problem) The present invention provides a polyethylene terephthalate molded container having a homologous multilayer structure consisting of at least two layers, at least one outer layer containing an additive, and the innermost layer containing an additive. The above-mentioned problem was solved by using substantially pure polyethylene terephthalate to serve as the additive barrier layer. A molded container obtained by stretch-molding a polyethylene terephthalate preform with a total thickness of 4 mm or less molded by a coextrusion method or a co-injection method, the molded container being a polyethylene terephthalate homologous multilayer. , wherein at least one outer layer contains an additive, the innermost layer does not contain an additive, and the innermost layer has a thickness of at least 50μ, and The manufacturing method of the container is described as follows: ``At least one of the outer layers of the molded container contains an additive, the innermost layer is an additive-free layer, and the thickness of the outer layer is is 3 mm or less, and the total thickness of the entire layer is 4 mm or less.The inner layer of the polyethylene terephthalate preformed product is made of a plurality of homologous fused inner and outer layers and is heated so that it reaches the stretch forming temperature faster than the outer layer. This allows the inner layer to serve as a barrier layer for additives such as pigments contained in the outer layer. It is possible to provide a polyethylene terephthalate molded container with excellent hygienic properties that does not cause coloring due to migration of additives, change in the flavor of the contents, or contamination due to migration of additives, and also has excellent gas barrier properties. It is possible to provide a polyethylene terephthalate molded container that is beautiful, rigid, and has great commercial value.

``Conventionally, plastic containers with a two-layer structure consisting of layers containing additives such as pigments have been known. For example, in Utility Model Publication No. 16959/1986, the inner wall is made of plastic containing a light-shielding coloring pigment, and the outer wall is made of plastic containing a light-shielding coloring pigment. A light-shielding double-walled packaging container is disclosed in which the container is made of a beautiful colored plastic that has the effect of preventing the color of the inner wall from being seen through. There is no idea that the inner layer can serve as a barrier layer for additives. A similar fact is that Tokko Akira
The same can be said of the synthetic resin hollow article with triple-layer walls of three colors disclosed in No. 39-26290.

(Example) Examples of the present invention will be described in detail below.

The molded container of the present invention is constituted by a homologous multilayer of polyethylene terephthalate, in which at least one outer layer contains an additive, and the innermost layer does not contain an additive, i.e., is additive-free and substantially pure. It is important that the material be made of polyethylene terephthalate.

The molded container of this invention can take any desired shape depending on the purpose of use, such as a bottle or cup, but the inner layer that comes into contact with the contents must be made of substantially pure polyethylene terephthalate with no additives. is important. As mentioned above, the innermost layer functions as an additive barrier layer, but other synthetic resins, such as polyolefins such as polyethylene and polypropylene, have the advantage of being low cost, but do not contain inorganic or organic pigments or antistatic agents. ,
Depending on these resins, additives such as ultraviolet absorbers, antioxidants, stabilizers, lubricants, plasticizers, nucleating agents, and crosslinking agents can easily pass through, and they also have poor oxygen and carbon dioxide gas barrier properties. The purpose of the invention cannot be achieved. On the other hand, synthetic resins with polar groups such as polyamide resins and ethylene-vinyl alcohol copolymers have additive barrier properties and oxygen barrier properties, but they are water absorbent, so they are used in water-based products such as beer, carbonated drinks, and soy sauce. Direct contact with the contents is undesirable and inappropriate for this invention. Therefore, the resin constituting the inner layer is limited to this polyethylene terephthalate, but as copolymerization components, isophthalic acid, p-β-oxyethoxybenzoic acid, naphthalene 2,6 -Dicarboxylic acid components such as dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, adibic acid, sebacic acid, or alkyl ester derivatives thereof, and propylene glycol, 1,4 Polyethylene terephthalates containing glycol components such as -butanediol, neopentyl glycol, 1,6-hexylene glycol, cyclohexanedimethanol, and ethylene oxide adducts of bisphenol A are also referred to as polyethylene terephthalates of the present invention.

At least one outer layer is constituted by polyethylene terephthalate containing additives. That is, this outer layer is composed of a resin of the same type as the inner layer. For almost the same reason as the inner layer, that is, from the viewpoint of gas barrier properties, the resin constituting the outer layer is limited to polyethylene terephthalate. In this case as well, it is possible to contain an appropriate copolymer component as in the inner layer.

Examples of additives include colorants such as pigments, antistatic agents, ultraviolet absorbers, antioxidants, lubricants, nucleating agents, crosslinking agents, and the like. These may be added alone or in a mixed state. Since polyethylene terephthalate is heated to a high temperature of approximately 280 to 300° C. during extrusion molding or injection molding, all additives must have heat resistance so that they do not easily change in quality at the above temperatures.

Pigments and dyes can be used as coloring agents, but dyes generally have high diffusivity, so in this invention,
Pigments are suitable as the coloring agent. Among pigments, pigments that can impart transparency to the resin are desirable. As pigments of this type, bat orange, aniline black, titanium white, zinc sulfide, iron oxide, yellow lead, chrome vermilion, cobalt blue, ultramarine blue, carbon black, and azo pigments are used singly or in combination. can be used.

The pigment content varies depending on the type, but is generally about 1.0% by weight or less, more preferably about 0.1% by weight or less, which impairs the transparency of the container and the fusion properties of the inner and outer layers. To color without approx.
It needs to be 0.05% by weight or less. Pigments are generally not used alone, but are often used as a mixture of various pigments and a dispersant.

As the antistatic agent, those with excellent heat resistance are used, such as nonionic internal antistatic agents, anionic internal antistatic agents, cationic internal antistatic agents, and amphoteric internal antistatic agents. .

Ultraviolet absorbers, antioxidants, lubricants, nucleating agents, cross-linking agents, etc. are required depending on the application, for example, when the contents are sensitive to ultraviolet rays, heat-resistant ultraviolet absorbers, etc. and added within a range that does not impair the properties of the container.

As described below, these additives become crystal nuclei and promote the crystallization of polyethylene terephthalate during melt molding or preheating for stretch molding, causing a whitening phenomenon and making stretch molding impossible. , which affects heating/forming conditions and container thickness. In this case, the size of the additive is extremely small (micron (10 ^-3 mm) or less than a micron), so the number of additive particles contained in polyethylene terephthalate (the additive that becomes the crystal nucleus) is more important than the size. In other words, it is thought that the volume ratio of the additive directly affects crystallization.

From the viewpoint of the strength of the container, it is important that the outer layer and the inner layer are completely joined together. This is especially possible with multilayer extrusion (coextrusion) without the use of adhesives.
Alternatively, it can be easily realized by employing a multi-layer injection molding (co-injection) method. That is, by these molding methods, a container in which the inner and outer layers are completely fused together can be obtained.

From the standpoint of additive barrier properties, it is important that the inner layer of the molded container has a thickness of at least 50 microns.
If the thickness of the inner layer is less than 50μ, as shown in the chart in Figure 4 below, if the contents are stored for a long time, the additives in the outer layer will diffuse through the inner layer and migrate into the contents, causing the contents to deteriorate. This is because they can color or contaminate the product or change the flavor.

Next, it is important from the viewpoint of stretch formability and transparency that the thickness of all the layers of the preform does not exceed 4 mm, and that the thickness of at least one outer layer containing additives does not exceed 3 mm. The container of this invention is a preformed product (bottomed parison) made by a multilayer extrusion blow method or a multilayer injection molding method, or a preformed product (bottomed parison) made from a pipe with open ends formed by a multilayer extrusion method. It is formed into a cup shape by stretch-blow molding a bottom parison) into a bottle shape, or by vacuum or plug-assisted air pressure forming of a sheet made by multilayer extrusion.
That is, it is once formed into a preform (a parison or sheet with a bottom), but since polyethylene terephthalate is a crystalline resin, it tends to crystallize during the cooling process. As crystallization progresses, microcrystals grow and become white, reducing stretch formability, and even if stretch forming is possible, transparency and strength are impaired.
To prevent this crystallization, when forming a preform from the molten state, the extruded resin is directly quenched with cold water, or the resin is cooled with cold water or a refrigerant such as liquefied carbon dioxide. Measures are taken to increase the cooling rate as much as possible by extruding or injecting into a mold. Even if such measures are taken, if the thickness of all layers of the preform exceeds 4 mm, or if the thickness of the outer layer containing additives exceeds 3 mm, a substantially amorphous product with crystallization prevented as much as possible will result. It is not possible to obtain a polyethylene terephthalate preform, making stretch molding impossible.

The molded container of this invention has a mouth part like a bottle etc.
When the body and bottom have different thicknesses, the thickness of the inner layer or the outer layer does not necessarily have to be uniform over the entire surface. Particularly in parts such as the bottom which are normally not visible from the outside, there may be no problem even if there is no outer layer containing pigment or the like. Generally, the thickness of the outer layer is preferably as thin as possible within a range that does not impair the practical purpose.

The polyethylene terephthalate molded containers of this invention are produced by the melt molding method and the stretch molding method as described above. Rigidity due to stretch molding
It has improved properties such as creep resistance, impact resistance, and gas barrier properties, can be made thinner and lighter, is less likely to break, and is not dangerous, so it can be used in the field of conventional glass containers, especially bottles.

However, according to research by the inventor of this invention,
Although it is not impossible to obtain the above-mentioned excellent properties by performing injection molding (bottomed parison) → biaxial stretching blowing to form the multilayer bottle of the present invention using a conventional method, Temperature control proved extremely difficult. That is, in the conventional method, the preform before stretch blow molding is heated by externally heating the preform with infrared rays or heating wires, or by heating it in a hot air oven, preferably at about 70 to 130°C. This is done by raising the temperature to about 80-110°C. In either case, the outside of the preform heats up faster than the inside. Therefore, even if the outer layer, which contains additives and is easily crystallized, begins to crystallize, the temperature of the inner layer remains
The temperature suitable for stretch blow molding, that is, the stretch molding temperature is often not reached. The inventors of the present invention have found that this problem of the prior art can be overcome by heating the preform using suitable means such that the inner layer of the preform heats up faster than the outer layer.

Specific means for this include, for example, the following method, but the present invention is not limited thereto.

In FIG. 1, a preform 1 consisting of an outer layer 2 and an inner layer 3 is supported at its neck by a grip 4. In FIG. The preform 1 is heated from the outside by an infrared ray or electric wire heater 5, and at the same time,
It is also heated from inside by the internal heater 6. As the internal heater 6, an appropriate one such as an infrared heater or a heating wire heater is selected. Instead of the internal heater 6, a hot air discharge pipe having holes for discharging hot air from inside may be used. Immediately after the preform 1 reaches a predetermined temperature, the internal heater 6 is removed, a stretching pin is inserted, and biaxial stretching blow molding is performed by known means. When a hot air discharge pipe is used instead of the internal heater 6, it is also possible to use this pipe also as a stretching pin.

In addition, when manufacturing a cup-shaped container by stretch-molding a sheet (preform) made by two-layer extrusion method by plug-assisted pressure forming or vacuum forming method, the additive-free side of the sheet (inner layer side) Crystallization, that is, whitening of the outer layer side can be prevented by heating with infrared rays or the like.

Examples of the present invention will be described below.

Experimental example 1 The weight ratio of phenol/tetrachloroethane is
The intrinsic viscosity at 30℃ in a 50/50 mixed solvent is
Using a screw in-line injection molding machine with a built-in screw of L/D (screw effective length/screw diameter) = 18, polyethylene terephthalate pellets of 0.1/g were molded to a length of 100 mm at a resin temperature of 290°C. Width 100mm and thickness 0.5mm, 1
mm, 2mm, 2.9mm, 3.2mm, 3.8mm, 4.2mm and 5
The molds were injected into 8 types of molds for sheet pieces of mm in thickness to obtain sheet pieces having the above-mentioned 8 types of thickness. At this time, the temperature of the mold was set at 2 to 3° C. using cold water.

Next, the polyethylene terephthalate pellets were mixed with 0.05% by weight each of titanium white (TiO ₂ ), red iron (Fe ₂ O ₃ ), and carbon black in a mixer, and then mixed under the same conditions using the injection molding process. , sheet pieces having the above-mentioned eight types of thickness were obtained. These sheet pieces with no pigment added are A, those with titanium white added are T, those with red iron are added as F, and those with carbon black added are C, and some of the 32 types of sheet pieces are Cut out the differential calorimeter to include all directions (heating rate 10℃/
min) thermogram was obtained. The results are shown in the diagram of FIG.

As is clear from FIG. 2, the glass transition temperature is not affected by the thickness of the sheet or the pigment. However, although not shown in FIG. 2, the characteristic on the thermogram (endothermic/exothermic curve) based on the glass transition temperature becomes unclear as the sheet thickness increases and as the amount of pigment added increases. It is found that the cold crystallization temperature decreases with the addition of pigment, and it is also found that the rate of decrease decreases in the order of carbon black, titanium white, and red iron even though the same weight ratio was added. That is, since the specific gravity of the pigment increases in the above order, it can be seen that the volume ratio of the added pigment to polyethylene terephthalate has a direct effect. In FIG. 2, the degree of crystallization of the polyethylene terephthalate itself in the sheet piece can be determined by comparing the cold crystallization exothermic peak area and the melting endothermic peak area. For example, in the case of A sheet with no pigment added, if you compare the thickness of 3.8 mm and 4.2 mm, the thickness is 4.2 mm.
It can be seen that the melting peak area is abnormally large compared to the cold crystallization exothermic peak area. That is, in order to obtain a substantially amorphous sheet in which crystallization of pigment-free polyethylene terephthalate is prevented as much as possible, the thickness must be 4 mm or less. On the other hand, in the case of T, F, and C sheets to which pigments have been added, it is clear from similar study results that a thickness of 3 mm or less is required.

Experimental Example 2 For 100kg of polyethylene terephthalate pellets used in Experimental Example 1, titanium white 0.014kg, polyazole 0.0029kg, polyazo yellow 0.0076kg, carbon black 0.001kg,
Barium sulfate 0.0067Kg and zinc stearate
A well-known forced feeder is a two-layer tube (pipe) with an outer diameter of 30 mm, with an outer layer made of 0.008 kg (that is, a total pigment content of 0.0402 weight %) mixed in advance with a mixer, and an inner layer made of additive-free polyethylene terephthalate. It was molded using an extrusion tube molding method with a built-in. At this time, the tube extruded in a molten state from the extruder was sufficiently cooled with cold water (approximately 2 to 3 DEG C.) in a so-called sizing unit and subsequent steps.

The pipe has a colored outer layer thickness of 1 mm, a total thickness of 4.5 mm (hereinafter referred to as A), and an outer layer thickness of 2.8 mm.
mm, total thickness is 3.8mm (hereinafter referred to as B), outer layer thickness is 3.2mm, total thickness is 3.8mm (hereinafter referred to as C), and outer layer thickness is 1mm, total thickness is 3mm (hereinafter referred to as D). Four types of pipes were obtained.

A part of each pipe was cut so that the entire thickness direction of the pipe was included, and the cold crystallization exothermic peak area and melting endothermic peak area were determined using the same method as in Experimental Example 1, and further based on the measurement method of JIS K 6714. The degree of haze (HAZE) was calculated. The results are shown in the diagram in Figure 3.

As is clear from FIG. 3, pipes B and D that satisfy the present invention have excellent transparency, and it can be seen that crystallization of polyethylene terephthalate is prevented as much as possible, resulting in substantially amorphous pipes. .

Experimental Example 3 The four types of pipes obtained in Experimental Example 2 were cut to appropriate lengths, and the mouth and bottom portions were locally heated to an appropriate temperature to obtain bottomed preforms by compression molding. The outside of these preforms is 90
After keeping the temperature inside at 100°C for 30 seconds using the method shown in Fig. 1, a brown bottle with an internal volume of 1100 c.c., a height of 255 mm, and a body diameter of 75 mm was formed by known biaxial stretching blowing. . Biaxial stretch blowing was not possible for pipe A, but it was possible for pipe C, but the bottle suffered from a significant whitening phenomenon, and as a result, when filled with tap water and dropped from a height of about 1 m onto a concrete surface, it broke. Ta. Both pipes B and D could be stretch-blown. Next, for Pipe D, both the outside and inside of the preform were held at 100° C. for 30 seconds and then stretched and blown, but the outer layer containing the additive showed a significant whitening phenomenon.

Experimental Example 4 By the method described in Experimental Examples 2 and 3, a brown transparent bottle with an outer layer of polyethylene terephthalate containing 0.04% by weight of the mixed pigment of Experimental Example 2 and an inner layer containing no pigment was molded according to the specifications shown in Figure 4. I went.
The inner volume, height, and maximum diameter of the bottle are the same as the bottle in Experimental Example 3, and the bottle weight is approximately 54 g and the overall average thickness.
It was 590μ.

These four types of bottles (one of which has only the outer layer and zero thickness of the inner layer) have an alcohol concentration of 5%.
After filling with water and sealing, the temperature is 50℃ and the relative humidity is about 60℃.
% in a constant temperature and humidity chamber for 6 months, and the weight of the pigment transferred into water and alcohol was determined by the evaporation method (water and alcohol are evaporated by heating). The results are shown in FIG.

According to the diagram of FIG. 4, it can be seen that the thickness of the additive-free inner layer of the homologous two-layer polyethylene terephthalate container of the present invention is required to be at least 50 microns.

Experimental Example 5 To 100 kg of polyethylene terephthalate pellets used in Experimental Example 1, 50 g of Sumiplast Green G (manufactured by Sumitomo Chemical Industries) was added and mixed in a mixer for 3 minutes at room temperature. Add this mixture to 180
Dry with a hopper dryer set at ℃ for about 5 hours, and form a homologous two-layer sheet with one layer of the mixture and the other layer of polyethylene terephthalate with no colorant added using a known two-layer T-die molding method. did.

The sheet extruded in a molten state from a die was formed so that the layer containing the colorant was in contact with the surface of the first chill roll of two chill rolls that were internally cooled with liquefied carbon dioxide gas. The total thickness of the sheet is 3
The rotational speed of the two extruders was adjusted so that the effective width in mm was 20 mm and the thickness of the layer containing the colorant was approximately 1 mm.

On the other hand, a 3 mm sheet of polyethylene terephthalate without the addition of Sumiplast Green G was molded by a known T-die molding method. At this time, the two chill rolls were internally cooled with liquefied carbon dioxide gas.

These two types of sheets were cut to a certain size, heated for 20 seconds so that both sides were heated to 100°C, and then immediately formed into cups by known plug-assisted pressure forming. A transparent cup was obtained from the sheet containing no colorant. In the case of the homologous two-layer sheet, a cup was obtained in which the layer to which the colorant was added had a significant whitening phenomenon. On the other hand, the layer side containing the colorant
90℃, so that the layer side that does not include the colored layer is 100℃
After being left for 20 seconds, a similar plug-assisted air forming process yielded a transparent cup colored light blue.

(Effect of the invention) The polyethylene terephthalate homologous multilayer molded container of the present invention has a coloring agent in at least one outer layer.
Antistatic agents, ultraviolet absorbers, antioxidants, lubricants,
By blending additives such as nucleating agents and crosslinking agents singly or in combination, color tone and other properties can be improved.Moreover, since it has an additive barrier layer (inner layer), these additives can improve the content. There is no risk of deterioration of the product or hygiene problems. The method of the invention also prevents crystallization of the outer layer during heating of the preform, especially in the case of biaxially stretched containers, since the inner layer of the preform is heated to reach the stretch forming temperature faster than the outer layer. Since it does not progress, it has the characteristic that a container with excellent rigidity, creep resistance, impact resistance, and gas barrier properties can be obtained.

In particular, since the thickness of the inner layer is at least 50μ, even if the contents are stored for a long period of time, the additives in the outer layer will not diffuse through the inner layer and transfer to the contents, coloring or contaminating them. It is extremely hygienic, and since the sum of the thicknesses of the inner layer and outer layer of the polyethylene terephthalate preform, that is, the total thickness, does not exceed 4 mm, and the thickness of the outer layer does not exceed 3 mm, crystallization is prevented. It is possible to obtain a container with excellent stretch formability and transparency.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing one embodiment of the method for producing a container of the present invention, FIG. 2 is a diagram of the results of Experimental Example 1, FIG. 3 is a diagram of the results of Experimental Example 2, and FIG.
The figure shows a diagram of the results of Experimental Example 4. 1... Preform, 2... Outer layer, 3... Inner layer, 5...
External heater (infrared), 6...Internal heater, 7
…a reflector.

Claims (1)

[Scope of Claims] 1. A molded product obtained by stretch-molding a polyethylene terephthalate preformed product having an outer layer thickness of 3 mm or less and a total thickness of 4 mm or less formed by coextrusion or co-injection. A container, the molded container being constructed of homologous multi-layer polyethylene terephthalate, at least one outer layer containing an additive, the innermost layer containing no additive and the outermost layer containing an additive. A molded container characterized in that the inner layer has a thickness of at least 50μ. 2 At least one of the layers to be the outer layer of the molded container
The two outer layers contain additives, the innermost layer is made up of additive-free layers, and the thickness of the outer layer is 3 mm or less, and the total thickness of the inner and outer layers is 4 mm or less. Production of a molded container, the innermost layer of which has a thickness of at least 50μ, characterized in that the inner layer of a polyethylene terephthalate preform consisting of a polyethylene terephthalate multi-layer fused together reaches the stretch forming temperature faster than the outer layer. Method. 3. The method for manufacturing a molded container according to claim 2, wherein the stretch molding is blow molding. 4. The method for manufacturing a molded container according to claim 2, wherein the stretch forming is plug-assisted pressure forming. 5. The method for manufacturing a molded container according to claim 2, wherein the stretch forming is vacuum forming.