JP4784149B2 - Container preform and plastic container - Google Patents

Description

The present invention relates to a plastic container obtained from the container preform and the preform made of resin foam obtained by utilizing the microcellular technology.

  Currently, polyester containers represented by polyethylene terephthalate (PET) are excellent in properties such as transparency, heat resistance and gas barrier properties, and are widely used in various applications.

  On the other hand, in recent years, the reuse of resources has been strongly demanded, and with respect to the polyester container as described above, a used container is collected and reused for various purposes as a recycled resin. By the way, as for the contents stored in the packaging container, those that are easily altered by light, for example, certain beverages, pharmaceuticals, cosmetics, etc., are molded using a resin composition in which a colorant such as a pigment is blended in a resin. Provided in a sealed opaque container. However, from the viewpoint of resource reuse, it is not desirable to add a colorant (it would be difficult to ensure transparency in the recycled resin). For this reason, the use of a transparent container is required. Therefore, it is necessary to improve recyclability of opaque containers suitable for accommodating photo-altered contents.

  In order to impart light-shielding properties (opacity) without blending a colorant, it is conceivable that the container wall is formed of a resin foam. However, in this case, characteristics such as gas barrier properties and strength are impaired. Such a container has not yet been put into practical use because there is a problem in terms of printing characteristics.

Recently, a resin foam using so-called microcellular technology has attracted attention. That is, as a technique for producing a resin foam, those using so-called chemical foaming agents, hydrocarbons, or fluorocarbon gas foaming agents are generally known, but these foaming agents are used to form the resin foam. The foam cell has a problem that the cell diameter is considerably large and the material strength is lowered, and the foam cell has a problem that it is difficult to form a foam state in which the foam cell is uniformly distributed over the whole. Since the active gas is impregnated into the resin as a foaming agent and this gas is grown into bubbles to form the foamed cells, the foamed cells have a small diameter and form a foamed state that is uniformly distributed throughout the entire area. There is an advantage that the physical properties such as strength are low.
The microcellular plastic referred to in the present application refers to a foam having a relatively small diameter cell (about 100 μm or less) formed by using an inert gas as a foaming agent, and is defined in some documents. It is not limited to a foam having a cell diameter of 10 μm or less.

Many resin foams using such microcellular technology have also been proposed. For example, Patent Document 1 discloses a core layer in which spherical foam cells are distributed, and foam cells are not distributed on both surfaces of the core layer. A foam in which a skin layer is formed has been proposed. In Patent Document 2, a core layer in which foam cells are not distributed is formed inside a foam layer in which cylindrical foam cells are distributed. Resin-molded parts having a skin layer formed on the outer surface have been proposed, and it may be possible to impart light shielding properties by applying these foams or resin-molded parts to containers.
JP-A-8-333470 JP 2005-6023 A

  However, in the resin foam of Patent Document 1, since the foam cell does not exist in the skin layer on the surface, although the printing property is good, the foam cell is distributed throughout the inside except the thin skin layer. Therefore, insufficiency of strength is unavoidable, and a decrease in gas barrier property is unavoidable, and it is difficult to apply to a container.

  In addition, the resin molded article of Patent Document 2 has a skin layer in which no foam cells are present, and further a core layer in which no foam cells are distributed. Both strength and gas barrier properties appear to be satisfactory. However, in Patent Document 2, since the foam cells have an elongated cylindrical shape, and such foam cells are distributed along the resin flow direction at the time of molding, it is difficult to apply this to the container. is there. That is, plastic containers such as bottles and cups are manufactured by molding a preform by injection molding, compression molding, or the like, and subjecting this preform to secondary molding such as blow molding or plug assist molding. . Therefore, when the technique of Patent Document 2 is applied to a container, a preform is molded according to Patent Document 2, and a preform in which foamed cells are distributed as described in Patent Document 2 is secondarily molded. Thus, the container is manufactured. When manufacturing containers in this way, the foamed cells in the preform are cylindrical and oriented in one direction, causing anisotropy in the vessel wall during secondary molding such as blow molding, resulting in cracks. Or the thickness of the container wall becomes non-uniform. Actually, the resin molded product of Patent Document 2 is used as a speaker diaphragm, and Patent Document 2 does not mention any means for applying this to a container.

  In addition, the foamed cell distribution structure as in Patent Document 2 is such that a thermoplastic resin whose crystallization is accelerated in the resin flow direction is filled in a mold while continuously adding carbon dioxide gas at a predetermined pressure. It is said that it can be obtained by moving the mold later, but since the resin is not limited to crystalline ones, the foaming mechanism is not clear. For example, the thickness of the core layer in which the foam cells are not distributed Therefore, it is difficult to make practical use not only in containers but also in other fields.

Accordingly, an object of the present invention is to provide a container preform made of a resin foam that is excellent in printing characteristics, strength, gas barrier properties, scratch resistance, and the like, and that is effectively applied to a container, a method for producing the same, and the preform. The object is to provide a plastic container obtained from renovation .

According to the present invention, in the container preform made of the resin foam, the container wall of the preform has an outer skin layer formed on the inner surface and the outer surface, a base layer positioned at a central portion, and the outer skin. A layer structure having a foam layer positioned between the layer and the base layer, the foam layer is substantially absent in the skin layer and the base layer, and the foam layer has an average diameter of 5 to 50μm foamed cells are distributed isotropically, the density of the foam cells is provided a container preform, which is a 1 × 10 ⁶ to 1 × ¹⁰ 9 cells / cm ³ The
According to the present invention, there is also provided a light-shielding plastic container obtained by molding the preform .
In the present invention, that the foamed cells are distributed isotropic means that the distribution of the cells does not show anisotropy. That is, this foam cell has, for example, a spherical shape or an indeterminate shape close to a spherical shape, and these are distributed randomly. For example, cylindrical cells are distributed so as to be directed in the resin flow direction. It is not.

According to the invention,
Providing a container preform impregnated with an inert gas;
Releasing the inert gas from the skin layer of the container preform impregnated with the inert gas;
The container preform is heated from the surface side and foamed at a portion excluding the base layer at the center , and foam cells having an average diameter of 5 to 50 μm are distributed isotropically, and the density of the foam cells is 1 Forming a foamed layer of × 10 ^{6 to} 1 × 10 ⁹ cells / cm ³ between the skin layer and the substrate layer ;
A method for producing a container preform is provided.

In the production method of the present invention,
(1) impregnating the entire preform with an inert gas by holding the container preform formed in a predetermined shape in a high-pressure inert gas atmosphere;
(2) impregnating a portion of the central portion excluding the base layer with an inert gas by holding the container preform formed in a predetermined shape in a high-pressure inert gas atmosphere;
(3) By holding the container preform impregnated with an inert gas in a cooled and solidified state under normal pressure, the inert gas is released from the skin layer of the preform ;
(4) The heating of the container preform is stopped at a stage before starting the foaming of the base layer, thereby foaming at a portion excluding the base layer,
Such means can be preferably employed.

In the container preform of the present invention, since a skin layer in which no foamed cells are present is formed on the foamed layer, it is excellent in surface characteristics such as printing characteristics, label stickability, appearance, and scratch resistance. ing. In addition, since a base layer in which foam cells are not distributed is formed inside the foam layer, a decrease in strength and a decrease in gas barrier properties due to the formation of the foam layer are effectively suppressed.

In the container preform of the present invention, the foamed cells in the foamed layer are distributed isotropically, so anisotropy due to the foamed cells is effectively avoided. That is, it is possible to effectively avoid inconveniences due to the anisotropy of the foamed cells, such as cracking of the molded body and variation in thickness when the resin foam is subjected to secondary molding such as blow molding.

Therefore, the container preform having the above-described characteristics exhibits high light shielding properties due to light scattering by the foamed cell , and secondary molding of the preform does not cause inconveniences such as thickness variations and cracks. The container can be molded. Since such a container has a light shielding property, it is extremely useful for accommodating contents that are likely to be altered by light, and also has excellent recycling characteristics because it does not use a colorant.

In addition, according to the above-described container preform manufacturing method, the amount of impregnation of the inert gas into the resin body (container preform) , the inert gas release time, the heating time for foaming, and the like are adjusted. Thus, the thickness of the skin layer and the base layer in which no foam cell is present, or the size of the foam cell and the thickness of the foam layer can be controlled . Furthermore, it is possible to form a multilayer structure of a non-foamed skin layer and a base layer and a foamed layer in a single resin layer without using a normal laminating technique, multilayer extrusion technique or multilayer injection molding technique. There are also production advantages.

<Raw resin>
In the present invention, the resin used for the production of the resin foam is not particularly limited as long as it can be impregnated with an inert gas, and a thermoplastic resin known per se can be used. Random or block copolymers of polyethylene, high density polyethylene, polypropylene, poly 1-butene, poly 4-methyl-1-pentene or α-olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene Olefin resins such as cyclic olefin copolymers; ethylene / vinyl acetate copolymers, ethylene / vinyl alcohol copolymers, ethylene / vinyl chloride copolymers and other ethylene / vinyl copolymers; polystyrene, acrylonitrile / styrene Copolymers, ABS, styrene-based trees such as α-methylstyrene / styrene copolymers Fat; Vinyl-based resins such as polyvinyl chloride, polyvinylidene chloride, vinyl chloride / vinylidene chloride copolymer, polymethyl acrylate, polymethyl methacrylate; nylon 6, nylon 6-6, nylon 6-10, nylon 11, Examples include polyamide resins such as nylon 12; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and copolyesters thereof; polycarbonate resins; polyphenylene oxide resins; biodegradable resins such as polylactic acid; In particular, olefin-based resins and polyester resins that are preferably used in the field of containers are suitable, and among these, polyester resins are most suitable for maximizing the advantages of the present invention.

<Manufacture of container preform >
FIG. 1 shows the basic concept of the manufacturing process of the container preform of the present invention. Referring to FIG. 1, in order to produce the resin foam for forming the container preform of the present invention, first, the above-mentioned various raw material resins (of course, blends of the raw material resins are used depending on the application). May be impregnated with an inert gas (for example, carbon dioxide gas or nitrogen gas) under high pressure to dissolve the inert gas in the resin body (step (a) in FIG. 1). The resin body is then cooled and solidified for a predetermined time under normal pressure (atmospheric pressure) to release inert gas from the surface of the resin body, and the surface layer or inert gas in which the inert gas is not dissolved. A surface layer having a low gas concentration is formed (step (b) in FIG. 1). Next, foam molding is performed by heating the resin body on which such a surface layer is formed (step (c) in FIG. 1). Needless to say, the surface layer has no inert gas or its concentration is low, so that it does not foam even if heated, and it is not substantially foamed to the extent that bubbles cannot be confirmed unless observed carefully. Become. That is, by this heating, foaming cells (indicated by 10 in FIG. 1) are formed in order from the surface layer side in the resin body where the inert gas remains. However, if this foam molding is performed for a long time, the foamed cells 10 are formed in the entire interior of the resin body excluding the surface layer. Therefore, heating is stopped at an appropriate point to cool the resin body (step (d in FIG. 1 (d )). As a result, as shown in FIG. 1, the obtained resin foam is formed with a skin layer 1, 1 having no foam cell 10 on the surface thereof, and below the foam cell 10. The foam layers 3 and 3 distributed isotropically are formed, and the base layer 5 in which the foam cell 10 does not exist is formed in the central portion.

  In the above manufacturing process, impregnation of the resin body with the inert gas in the step (a) is performed by cooling and solidifying the resin body in which a sufficient amount of gas is dissolved to obtain a desired characteristic (for example, light shielding property). As long as is obtained, it can be performed by various means. For example, the resin body can be heated and impregnated with an inert gas under high pressure, or can be performed under non-heating. In this case, the higher the temperature, the smaller the amount of gas dissolved, but the faster the impregnation rate. The lower the temperature, the larger the amount of dissolved gas, but the impregnation takes time.

  Further, as understood from the above description, impregnation with an inert gas may be performed in the form of a molded body in which a resin body is molded into a predetermined shape, for example, an extruder, an injection molding machine, a compression molding machine, etc. Impregnation can be performed by supplying an inert gas at a predetermined pressure to a resin body held in a heated and melted state in a resin kneading part or a plasticizing part in the molding machine.

  After impregnation of the resin body with the inert gas, in step (b), the resin body surface that has been cooled and solidified to room temperature is released under normal pressure (atmospheric pressure), so that the surface of the resin body To release inert gas. That is, since the solubility of the inert gas at normal pressure and room temperature is almost zero, the inert gas is gradually released from the surface of the resin body by holding the cooled and solidified resin body at normal pressure. Will be. Therefore, the relationship between the opening time under atmospheric pressure and the amount of dissolved gas is measured in advance, and the holding time (opening time) under normal pressure is adjusted based on the measurement result, thereby A surface layer in which the inert gas is not dissolved or a surface layer having a low inert gas concentration can be formed on the surface with an appropriate thickness.

  Furthermore, in the step (c), the resin body on which the surface layer in which the inert gas is not dissolved is formed as described above is heated to a temperature equal to or higher than the glass transition point of the resin body. Inert gas dissolved in the body is foamed. That is, this heating causes a sudden change in the internal energy (free energy) of the gas dissolved in the resin body, causing phase separation, and foaming occurs due to separation from the resin body as bubbles. .

  In the above case, since the temperature of the resin body is gradually increased from the surface, foaming is sequentially generated from the surface layer side where the gas is not dissolved in the resin body. Therefore, when foaming occurs moderately, in step (d), heating is stopped and cooling is performed so that foaming cells 10 are distributed below the skin layers 1 and 1 where the foaming cells 10 are not present. Layers 3 and 3 are formed, and a base layer 5 without the foamed cells 10 is formed between the foamed layers 3 and 3. In addition, the foamed cells 10 formed in this way are, for example, spherical or indeterminately close to a spherical shape, have no anisotropy, and are randomly distributed as a whole as a whole.

  When the resin foam is formed as described above, the larger the dissolved amount of the inert gas such as carbon dioxide, the smaller the diameter of the foamed cell and the larger the cell density. On the other hand, as the dissolved amount of gas increases, the glass transition point of the resin decreases linearly or exponentially. Further, the viscoelasticity of the resin also changes due to the dissolution of the gas. For example, the viscosity of the resin decreases due to an increase in the amount of dissolved gas. Therefore, depending on the intended function, foaming conditions such as gas dissolution amount, gas pressure, temperature, etc. can be obtained so that an appropriate cell diameter and cell density can be obtained and the foamed cells 10 can be uniformly distributed in the foamed layer. It is preferable to set the skin layer 1, the foam layer 3 and the base layer 5 with appropriate thicknesses for each resin using various treatment times.

  In the above-described method, the base layer 5 is formed by adjusting the foaming time (heating time) in the step (c), but the gas impregnation time is controlled in the step (a) regardless of the foaming time. Accordingly, the base body layer 5 in which the foam cell 10 does not exist in the central portion can be formed by not impregnating the gas throughout the resin body and stopping the impregnation at a stage before the gas reaches the central portion. .

Further, by performing heating for foaming from both sides of the resin body, by adjusting the foaming time (heating time), as shown in FIG. A resin foam having a five-layer structure in which the skin layer 1 is formed on each of both surface sides via the foam layer 3 is obtained.

<Container formed from resin foam>
The resin foam produced by the above-described method is effective in the field of containers. For example, a preform made of a resin foam is formed according to the above-described method, and this is subjected to predetermined secondary processing, whereby a bottle is obtained. Various cup-shaped containers can be manufactured. In such a container, since the foam layer is formed on the vessel wall, light shielding properties are imparted without using a colorant. In addition, since it has a core layer in which no foam cell exists, a decrease in strength or gas barrier property due to the formation of the foam layer is effectively suppressed, and further, weight reduction and heat insulation due to the formation of the foam layer. Can also be achieved. Moreover, since the skin layer in which the foam cell does not exist is formed on the surface, the printing characteristics, label sticking property, and scratch resistance of the container are good.

  That is, in order to manufacture a preform and a container using the resin foam having the layer structure described above, the following may be performed.

  First, according to a conventional method, a preform is formed by injection molding or compression molding using a resin for a container represented by a polyester resin such as polyethylene terephthalate. For example, this preform has a test tube shape when a bottle is manufactured, and has a plate shape when a cup-shaped container is manufactured.

  The preform formed, cooled and solidified as described above is maintained in a high-pressure inert gas atmosphere for a predetermined time in a pressure vessel, and an appropriate amount of inert gas is impregnated and dissolved in the preform. . In this case, in order to adjust the dissolved amount of gas and the processing time, the preform can be heated to a temperature at which the shape is not impaired.

  After the appropriate amount of inert gas is dissolved, the preform is taken out of the pressure vessel and, if necessary, cooled to room temperature and simultaneously released to atmospheric pressure. As a result, a surface layer in which inert gas does not exist is formed on the preform surface, and the inert gas exists only in the interior excluding the surface layer.

  After being released under atmospheric pressure for a reasonable time and forming a surface layer with a predetermined thickness, the preform is heated to a temperature above the glass transition point (below the melting point), and the dissolved inert gas is foamed. Form a foam cell. Thereby, a foam cell is formed sequentially from the site | part close | similar to a surface layer.

  When the foamed cells in which the foamed cells are distributed as described above have an appropriate thickness, the heating is stopped and cooled to room temperature. As a result, a base layer in which foam cells are not distributed in the center is formed, and a multilayer structure as shown in step (d) in FIG. 1 is formed in the preform.

  Further, impregnation with an inert gas can be performed when the preform is molded. For example, a high-pressure inert gas is supplied to a plastic part or a kneading part of a resin in an injection molding machine, and a preform is molded by being extruded into a predetermined mold while impregnating the molten resin with an inert gas. By cooling the preform to room temperature, a preform impregnated with an inert gas can be obtained. At this time, it is more preferable to manufacture a preform without foaming in the mold by adjusting injection conditions or using a technique that utilizes counter pressure by an inert gas in the mold. Next, by holding the taken preform under atmospheric pressure for a predetermined time, the inert gas is released from the surface layer, and the skin layer can be formed. The preform thus formed can form a base layer by forming foamed cells by heating and stopping heating in the same manner as described above.

In the container preform having such a distribution structure of foamed cells, although it varies depending on the size of the container to be finally formed, the secondary molding conditions, or the characteristics of the resin to be used, It is preferable to set conditions so that a skin layer having a thickness of about 20 to 200 μm is formed in order to ensure the scratch resistance of the final container. The average diameter of 5 to 50μm of foam cells, the density of the foamed cells in the foamed layer, 1 × 10 ⁶ to must be from ^{1 × 10 9 cells / cm 3} , and the foam layer thickness is 100 to 1000μm It is preferable to set various conditions so as to obtain a degree, and it is preferable to secure an appropriate light-shielding property, and it is appropriate to set the base layer to be 100 μm or more. In order to ensure gas barrier properties and secondary formability, it is preferable.

  The preform having the structure as described above is attached to secondary molding such as vacuum molding represented by known blow molding or plug assist molding, and molded into a bottle or cup-shaped container. Since the foamed cells are distributed isotropically and have no anisotropy, cracks and thickness unevenness can be effectively prevented even in the secondary molding for thinning.

  Since such a container has a light shielding property, it is effectively applied to contain contents that cause alteration due to light, and is suitable for recycling because it does not contain a colorant.

[Molding of resin foam]
Example 1
Using a copolymerized polyethylene terephthalate resin (PET) containing 5 mol% of isophthalic acid and having an intrinsic viscosity of 0.90, a sheet (resin body) having a thickness of 0.70 mm was obtained by extrusion molding. The sheet was cut into 30 × 90 mm, placed in a pressure resistant container at 40 ° C., and kept at a pressure of 15 MPa for 4 hours to impregnate carbon dioxide gas. Thereafter, the pressure was reduced to atmospheric pressure over about 5 minutes, the sample was taken out from the container, and kept at atmospheric pressure for 15 minutes. Further, the sample was immersed in hot water at 90 ° C. for 10 seconds to foam.

The cross-sectional observation result of the obtained foam is shown in FIG. This foam had a 150 μm base layer (core layer) made of unfoamed material, a 430 μm foamed layer on both surfaces, and a skin layer made of 110 μm unfoamed material on the outer surface. (In FIG. 2, the white portions are the skin layer and the base layer (core layer) without foamed cells. The same applies to the following figures.)
The average diameter of foam cells from microscopic photograph of FIG. 2 is in the range of 5 to 50 [mu] m, the density of the foam cells is calculated to 10 ⁶ to ¹⁰ 9 cells / cm ³ range of the number of cells per unit area It can be seen that

(Example 2)
A foam was obtained in the same manner as in Example 1 except that the gas impregnation time was 0.5 hour and the gas release time after impregnation was 5 minutes. The cross-sectional observation result of the obtained foam is shown in FIG. The foam had a 440 μm base layer (core layer) made of unfoamed material, a 300 μm foamed layer on both surfaces, and a skin layer made of 30 μm unfoamed material on the outer surface.
The average diameter of foam cells from microscopic photograph of FIG. 3 is in the range of 5 to 50 [mu] m, the density of the foam cells is calculated to 10 ⁶ to ¹⁰ 9 cells / cm ³ range of the number of cells per unit area It can be seen that

(Example 3)
A foam was obtained in the same manner as in Example 1 except that the gas impregnation time was 6 hours and the immersion time in hot water was 0.5 seconds. The cross-sectional observation result of the obtained foam is shown in FIG. The foam had a 300 μm base layer (core layer) made of unfoamed material, a 300 μm foamed layer on both sides thereof, and a skin layer made of 100 μm unfoamed material on each outer surface.
The average diameter of foam cells from microscopic photograph of FIG. 4 is in the range of 5 to 50 [mu] m, the density of the foam cells is calculated to 10 ⁶ to ¹⁰ 9 cells / cm ³ range of the number of cells per unit area It can be seen that

(Comparative Example 1)
A foam was obtained in the same manner as in Example 1 except that the gas impregnation time was 6 hours. The cross-sectional observation result of the obtained foam is shown in FIG. The foam had no base layer (core layer) made of unfoamed material, and a 1060 μm foamed layer and a skin layer made of unfoamed material of 170 μm were formed on both sides thereof.

(Comparative Example 2)
A foam was obtained in the same manner as in Comparative Example 1 except that the foam was immediately foamed without being kept open to the atmosphere after being taken out from the pressure vessel. The cross-sectional observation result of the obtained foam is shown in FIG. The foam consisted of a 1500 μm foam layer, and the base layer (core layer) and skin layer were not formed.

  Table 1 summarizes the foam molding conditions and the thicknesses of the skin layer and the core layer of Examples 1 to 3 and Comparative Examples 1 and 2. As can be seen from this result, the thickness of the skin layer and the core layer can be controlled by adjusting the gas impregnation time (gas dissolution amount), the gas release time, and the heating time.

[Impact performance evaluation]
The impact performance of the foams of Examples 1 and 2 and Comparative Example 1 was evaluated. The apparatus was evaluated by a tensile impact test method using a universal impact tester manufactured by Toyo Seiki Seisakusho. The hammer used was a T10 type, a weight of 1.19 kg, a distance R from the center of the rotation axis to the center of gravity of the hammer of 4.91 cm, and a crosshead weighing 94.0 g. The test piece was a ASTM D1822-Type S dumbbell shape.
As a result, the breaking energy E required for breaking each test piece was E = 0.5 J in Comparative Example 1 without a core layer, whereas E = 0.6 J in Example 1 having a 150 μm core layer. In Example 2 having a core layer of 440 μm, E = 0.8 J, and the impact performance of the foam could be prevented from being lowered by providing the core layer.

[Molding of container]
Example 4
Foamed preform was molded and blow molded.
First, a so-called PET bottle preform was produced using homo-PET having an intrinsic viscosity of 0.84. The preform was molded by regular injection molding, and the shape was a test tube type that was already commercialized for 500 ml PET bottles. The thickness of the preform is approximately 3 mm depending on the part.

  This preform was placed in a pressure-resistant container at 40 ° C. as in the above-described example, and maintained at a pressure of 15 MPa for 2 hours for impregnation with carbon dioxide gas. Thereafter, the pressure was reduced to atmospheric pressure over about 5 minutes, the preform was taken out from the pressure vessel, and kept under atmospheric pressure for 5 minutes. Furthermore, 90 ° C. hot water was bathed on the inner and outer surfaces of the preform for 10 seconds to cause foaming. When the cross-section of the preform was observed, a 60 μm skin layer was formed on each of the innermost and outermost surfaces of the preform, and a 200 μm foam layer was formed on the inner side of each skin layer. The foam layer was composed of a number of substantially spherical bubbles having a cell diameter of 10 to 20 μm. Furthermore, a base layer (core layer) was formed between the two foam layers.

  The foamed preform thus obtained was stretch blow molded and formed into a PET bottle having an internal volume of 500 ml. Stretch blow molding was possible under the same conditions as ordinary preforms, and was good with no shape anisotropy and uneven thickness. The obtained PET bottle became white due to the presence of bubbles and had a light-shielding performance. Further, mechanical strength such as container rigidity and drop strength was not much different from that of unfoamed PET bottles.

(Example 5)
In the foaming step, a foamed preform was obtained in the same manner as in Example 4, except that 90 ° C. hot water was bathed for 10 seconds only on the outer surface of the preform. When the cross-section of the preform was observed, a 60 μm skin layer was formed on the outermost surface of the preform, a 200 μm foam layer was formed on the inside, and a base layer without foam cells was formed on the inside. As a three-layer structure. The foam layer was composed of a number of substantially spherical bubbles having a cell diameter of 10 to 20 μm. The foamed preform thus obtained was stretch blow molded and formed into a PET bottle having an internal volume of 500 ml. Stretch blow molding was possible under the same conditions as ordinary preforms, and was good with no shape anisotropy and uneven thickness. The obtained PET bottle became white due to the presence of bubbles and had a light-shielding performance. Further, mechanical strength such as container rigidity and drop strength was not much different from that of unfoamed PET bottles.

The figure which shows the basic concept of the manufacturing process of the resin foam of this invention. The figure which shows an example of the cross section of the foam of Example 1. FIG. The figure which shows an example of the cross section of the foam of Example 2. FIG. The figure which shows an example of the cross section of the foam of Example 3. FIG. The figure which shows an example of the cross section of the foam of the comparative example 1. FIG. The figure which shows an example of the cross section of the foam of the comparative example 2. FIG.

Explanation of symbols

1: Skin layer 3: Foamed layer 5: Base layer 10: Foamed cell

Claims (7)

In a container preform made of a resin foam, the container wall of the preform is composed of an outer skin layer formed on an inner surface and an outer surface, a base layer located in a central portion, and the outer skin layer and the base layer. The foam layer has a foam structure located between them, and the skin layer and the base layer are substantially free of foam cells, and the foam layer has an average diameter of 5 to 50 μm. foamed cells are distributed isotropically, the container preform density of the foam cells is characterized in that a 1 × 10 ⁶ to ^{1 × 10 9 cells / cm 3} . A plastic container having light-shielding properties obtained by forming the container preform according to claim 1 . Providing a container preform impregnated with an inert gas;
Releasing the inert gas from the skin layer of the container preform impregnated with the inert gas;
The container preform is heated from the surface side and foamed at a portion excluding the base layer at the center , and foam cells having an average diameter of 5 to 50 μm are distributed isotropically, and the density of the foam cells is 1 Forming a foamed layer of × 10 ^{6 to} 1 × 10 ⁹ cells / cm ³ between the skin layer and the substrate layer ;
The manufacturing method of the preform for containers characterized by comprising. The production method according to claim 3 , wherein the container preform formed in a predetermined shape is maintained in a high-pressure inert gas atmosphere so that the inert gas is impregnated throughout the preform. The manufacturing method according to claim 3 , wherein the container preform formed in a predetermined shape is held in a high-pressure inert gas atmosphere to impregnate the portion excluding the base layer in the central portion with the inert gas. Wherein the inert gas in the cooled and solidified state is impregnated the container preform by holding under normal pressure, in any one of claims 3 to 5 to release the inert gas from the epidermis layer of the preform Manufacturing method. The manufacturing method according to claim 3 , wherein the heating of the container preform is stopped in a portion excluding the base layer by stopping at a stage before the base layer starts to foam.

Images