JP5533515B2 - Polyester expanded foam container - Google Patents

Description

  The present invention relates to a stretched polyester container made of polyester, and more particularly to a stretched container made of polyester that is foamed using 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 bubbles are present in the container wall to form a foam container, and various such foam containers have been proposed. Patent Document 1 uses a foam extrusion blow technique using a chemical foaming agent, and Patent Documents 2 to 3 use a microcellular technique in which a polyester resin is impregnated with an inert gas and then heated by foaming. A foamed molded product is proposed.

  Foaming using the microcellular technique has the advantage that the bubble cell can be made finer and the degree of foaming can be easily controlled, and stretched foamed polyester containers using such a technique have attracted attention.

  The stretched and foamed polyester container as described above is, for example, formed a test tube-shaped preform by injection molding using a polyester impregnated with an inert resin, and then the preform is heated to form a foamed preform. It is manufactured by blow-drawing this foamed preform and shaping it into a container shape.

  By the way, also in the above-mentioned stretched and foamed polyester container, it is necessary to improve the heat resistance and strength of the mouth of the container by thermal crystallization. This is because a thread for attaching a cap is formed at the mouth of the container. In addition, since heat resistance is required for containers that are used for applications that are hot-filled with container contents or heated by a hot bender, etc., heat setting is required after blow molding. It is necessary to impart heat resistance.

  In the stretched and foamed polyester container using the above-described microcellular technology, there is a problem that crystallization of the container mouth becomes difficult. That is, since a thread that engages with the cap is formed at the container mouth, such foaming at the container mouth must be avoided. For this reason, heating at the time of foaming is selectively performed on portions other than the mouth of the container. However, since the foaming inert gas is dissolved in the container mouth, foaming occurs at this time if the container mouth is subjected to thermal crystallization (heating).

  Patent Document 4 proposes a stretched foamed polyester container in which such a problem of thermal crystallization of the container mouth is effectively solved. Such a container is formed by so-called overmolding, and includes a non-foamed polyester container main body and a foamed polyester layer provided on the outer surface of the body portion of the container main body. That is, in this container, since the container opening is formed from polyester that is not impregnated with an inert gas, even if thermal crystallization is performed on the container opening, foaming does not occur in this part.

JP 2003-26137 A JP-A-2005-246822 JP 2006-321887 A WO2009 / 1588397

  The stretched and foamed polyester container of Patent Document 4 can thermally crystallize the container mouth without causing foamed cells (formation of bubbles), but has insufficient heat resistance on the body and the like. The problem remains. That is, in general, heat resistance can be improved by a heat process after blow molding, but in a stretched and foamed polyester container having a structure composed of a non-foamed container body and a foamed layer by overmolding, The improvement in heat resistance due to fixation is insufficient, and for this reason, such a polyester container is unsuitable for applications in which the contents of the container are hot-filled or for use in warm sales, and improvements are required. In addition, there is a problem that bubbles are greatly grown at the time of heat setting, and the barrier property of the container is impaired, or the light shielding property due to foaming is lowered.

Accordingly, an object of the present invention is to have a structure in which a foamed layer formed by heating with impregnated inert gas is formed on the outer surface of the body portion of a non-foamed polyester container body and has excellent heat resistance. Another object of the present invention is to provide a stretched and foamed polyester container.
Another object of the present invention is to provide a stretched foamed polyester container in which thermal crystallization of the container mouth is performed without causing foaming.
Still another object of the present invention is to provide a stretched foamed polyester container in which the growth of foamed cells during stretch molding or heat setting is effectively suppressed.

  As a result of studying a stretched foamed polyester container formed by overmolding comprising a non-foamed polyester container body and a foamed polyester layer, the present inventors have found that when a preform is heated in such a container, A temperature difference occurs between the outer surface and the inner surface, and as a result, the molded container remains strained, and it is difficult to effectively improve heat resistance due to the remaining strain even after heat setting. Based on this knowledge, the present invention has been completed.

  According to the present invention, stretching comprising a non-foamed polyester container body provided with a mouth portion, a body portion, and a bottom portion, and a foamed polyester layer having foam cells provided therein on the outer surface of the body portion of the non-foamed polyester container body. A foamed polyester container, wherein the non-foamed polyester container body is formed using a polyester having an intrinsic viscosity of 0.78 or less, and the foamed polyester layer is formed using a polyester having an intrinsic viscosity of 0.80 or more. A stretched and foamed polyester container is provided.

In the stretched foamed polyester container of the present invention,
(1) The mouth is thermally crystallized,
(2) The crystallinity by the density method of the trunk part of the non-foamed polyester container body is 25% or more,
(3) An infrared absorber is dispersed in the polyester forming the non-foamed polyester container body,
(4) used for hot filling of contents;
Is preferred.

  In the stretched and foamed polyester container of the present invention, the polyester container body provided with the mouth portion is a non-foamed body and is not impregnated with an inert gas that is a foamed material. Therefore, thermal crystallization of the container mouth can be performed without causing foamed cells.

Moreover, the non-foamed polyester container body is formed using a polyester having a low intrinsic viscosity, and the foamed polyester layer provided on the outer surface of the trunk is formed using a polyester having a high intrinsic viscosity. As a result, in the manufacturing process of the polyester container, it is possible to effectively avoid the occurrence of distortion due to heating of the preform and to impart excellent heat resistance.
That is, the preform to be stretch-molded is made of a polyester in which the inner part serving as a container body is not impregnated with an inert gas, and a polyester layer impregnated with an inert gas is formed on the outer surface of the body part. Is formed. The preform having such a structure is heated from the outer surface side by an infrared heater or the like, whereby the inert gas dissolved in the resin becomes supersaturated, and foam cells are generated in the polyester layer on the outer surface. Will be formed. In this case, the foam cell is generated only in the polyester layer on the outer surface side of the body portion, and is not generated in the portion that becomes the inner container body. For this reason, when the above heating for foaming is performed, the thermal conductivity on the outer surface side of the preform is greatly reduced due to the formation of the foam cells, and as a result, the temperature on the outer surface side of the preform is high, and foam cells are generated. The temperature on the inner surface which is not lower is lower than that on the outer surface. In particular, when heating with infrared rays is performed, infrared rays, which are electromagnetic waves, are scattered by the foam cell on the outer surface side, so that the heating on the inner surface side is not sufficiently performed, and the temperature difference between the outer surface side and the inner surface side is further increased. There is a tendency to grow.

  Thus, if a temperature difference arises between the inner surface side and the outer surface side, distortion occurs on the inner surface side, and such strain finally remains in the stretch-molded container. Therefore, even if crystallization is performed by heat setting, crystallization is hindered due to residual strain, and the heat resistance and other characteristics are low compared to a non-foamed container.

  However, in the present invention, since the inherent viscosity of the polyester forming the preform outer surface side (part forming the foam layer) is high, the polyester foaming temperature is high, and in order to maintain a transparent non-foamed state up to a higher temperature, It is possible to effectively suppress a decrease in thermal conductivity and infrared scattering during heating. Furthermore, since the intrinsic viscosity of the polyester that forms the inner surface side of the preform (portion of the container body) is low and the intrinsic viscosity of the polyester that forms the outer surface side is high, the temperature on the inner surface side of the preform is low as described above. In addition, it is possible to effectively suppress the occurrence of strain in the state where the temperature distribution that the temperature on the outer surface side is high occurs (that is, the thermal mobility of both polyesters in the state where the temperature distribution as described above occurs). Are almost equivalent). That is, the crystallinity is enhanced, and characteristics such as heat resistance can be effectively improved by heat setting.

  Further, in the present invention, since the intrinsic viscosity of the polyester forming the foamed layer is high, the growth of foamed cells (cell coarsening) during the stretching of the preform performed after foaming or the subsequent heat setting is effectively avoided. It is possible to effectively prevent deterioration of physical properties due to stretching or heat setting.

  Further, according to the present invention, an infrared absorbent such as graphite can be dispersed in the polyester forming the non-foamed polyester container body, whereby the inner surface side of the preform (portion serving as the container body). The heat absorbability of the resin can be improved, the inner and outer surface temperature distribution during the heating of the preform can be avoided, and the occurrence of distortion can be more effectively suppressed.

  The stretched and foamed polyester container of the present invention can improve properties such as heat resistance by heat setting in the same manner as a non-foamed polyester container. Therefore, the heat-resistant application is required, for example, a container for hot filling. Alternatively, it can be suitably used as a container for warming sales.

It is a partial sectional side view of the stretched foam polyester container of this invention. In the manufacturing process of the stretched and foamed polyester container of the present invention, FIG. It is a figure for demonstrating the manufacturing process of the extending | stretching foaming polyester container of this invention.

<Stretched foam polyester container>
With reference to FIG. 1, a stretched foamed polyester container of the present invention indicated by 10 as a whole is composed of a polyester container body 1 and a foamed polyester layer 3 formed on the outer surface of the container body 1.

  As can be understood from FIG. 1, a mouth portion 5 is formed on the upper portion of the container body 1, and a screw thread 5 a for attaching a cap is formed on the outer surface of the mouth portion 5. A support ring 5b is formed on the lower side. Further, a trunk portion 7 is formed below the mouth portion 5 via a curved shoulder portion 6, and a lower end of the trunk portion 7 is closed by a bottom portion 9.

On the other hand, the foamed polyester layer (hereinafter simply referred to as the foamed layer) 3 is provided so as to cover the outer surface of the lower part of the mouth part 5 of the container body 1. 3 is covered. Inside the foamed layer 3, a large number of foamed cells formed by microcellular using an inert gas as a foaming agent are distributed, and thereby the light shielding property is imparted to the container 10.
In the example of FIG. 1, the foam layer 3 is provided so as to cover the entire shoulder portion 6, the trunk portion 7, and the bottom portion 9 located below the mouth portion 5. As long as it does not cover 5, it should just be provided so that the trunk | drum 7 may be covered, for example, the foaming layer 3 does not necessarily need to be provided in the outer surface of the bottom part 9.

  The stretched and foamed polyester container 10 having the structure as described above is formed by so-called overmolding. For example, the preform 20 having an overmold structure shown in FIG. The expanded foamed polyester container shown in FIG.

  That is, the preform 20 of FIG. 2 is formed from a non-foamed polyester and has a test tube shape as a whole, and a foam precursor layer 23 formed from a polyester impregnated with an inert gas. It is made up of. The core tube 21 is shaped to the main body 1 of the container 10 shown in FIG. 1, and the same opening 5 as the main body 1 is formed at the upper end of the core tube 21. The foam precursor layer 23 is the foam layer 3 of the container 10, and is provided so as to cover the lower part of the mouth portion 5 of the core tube 21 corresponding to the foam layer 3. More preferably, the foam precursor layer 23 is substantially in a non-foamed state. In this case, since the preform is transparent, the infrared rays from the heater can be effectively transmitted to the inner surface immediately after the preform heating is started. That is, compared with the case where the precursor 23 is foamed from the beginning at the time of preform molding, the heating to the inner surface side is more effectively performed when the precursor 23 is in the non-foamed state, and the outer surface side The temperature difference between the inner surface and the inner surface becomes smaller, and distortion is less likely to occur.

  In the expanded foamed preester container 10 of the present invention obtained from the preform 20 described above, examples of the polyester that forms the container body 1 (core tube 21) and the foamed layer 3 (foamed precursor layer 23) include, for example, poly (ethylene Representative examples thereof include terephthalate), poly (butylene terephthalate), poly (ethylene terephthalate / ethylene isophthalate), and poly (ethylene terephthalate / cyclohexanedimethylene terephthalate). Furthermore, diols such as ethylene glycol, butylene glycol, cyclohexanedimethanol, neopentyl glycol and pentanediol as copolymerization components; or isophthalic acid, benzophenone dicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenylmethane dicarboxylic Dicarboxylic acids such as acid, propylene bis (phenylcarboxylic acid), diphenyl oxide dicarboxylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, diethyl succinic acid Copolyesters can also be used.

  In the present invention, among the polyesters described above, the polyester forming the container body 1 (core tube 21) has an intrinsic viscosity (IV) of 0.78 dl / g or less, preferably 0.65 to 0.76 dl / g. As the polyester for forming the foam layer 3 (foam precursor layer 23), an intrinsic viscosity (IV) of 0.80 dl / g or more, preferably 0.82 to 1.0 dl / g is used. . That is, the container body 1 is formed using polyester having a low intrinsic viscosity (IV), and the foam layer 3 is formed using polyester having a high intrinsic viscosity. It is possible to effectively prevent the occurrence of distortion in the container body 1 positioned, and to improve the crystallinity and to improve the heat resistance and the like by heat fixation. In addition, it is possible to effectively avoid the growth and growth of the foamed cell during container molding (blow-stretching or heat-setting) and prevent deterioration of physical properties. Furthermore, polyester having a high intrinsic viscosity (IV) is generally a copolyester, and the formation of the foamed layer 3 using such a polyester is advantageous also in terms of miniaturization of foamed cells.

  When the intrinsic viscosity (IV) of the polyester used is smaller than necessary, it is difficult to mold the container body 1 (core tube 21), and when the intrinsic viscosity (IV) is higher than necessary, foaming is difficult. There is a fear. For this reason, it is desirable that the intrinsic viscosity (IV) of the polyester forming the container body 1 and the polyester forming the foamed layer 3 is in the above-described preferable range.

  The polyester forming the container body 1 has an intrinsic viscosity (IV) in the above range and is preferably a homopolymer, and a polyethylene terephthalate homopolymer is most suitable. By forming the main body 1 using such a homopolyester, its crystallinity can be improved, and characteristics such as heat resistance can be greatly improved by heat setting.

  Furthermore, it is preferable that an infrared absorber is blended in the polyester forming the container body 1. By blending the infrared absorber, the heat absorption of the container body 1 is enhanced, the temperature distribution generated when the preform 20 is heated and stretch-molded is effectively avoided, and the generation of strain due to the temperature distribution is prevented. This is because it can be effectively prevented.

Examples of such infrared absorbers include graphite, metal antimony, iron oxide, and organic pigments. These infrared absorbers can be used alone or in combination of two or more. it can.
In addition, since the characteristic of the foam container that is suitable for recyclability is impaired when a large amount of such an infrared absorber is used, it is desirable that the amount be as small as possible. It is preferable to blend in an amount of 0.005 to 3.0 parts by weight, particularly 0.01 to 1.0 parts by weight per 100 parts by weight of the polyester to be formed.

In the above-mentioned stretched and foamed polyester container 10 of the present invention, it is preferable that the mouth portion 5 is thermally crystallized, and this heat crystallization enhances the heat resistance and strength of the mouth portion 5 and improves the screwability with the cap. It is possible to improve and form a stable sealing structure.
That is, the thermal crystallization is performed by heating the mouth portion 5 to the thermal crystallization temperature region (generally 140 to 200 ° C.) of the polyester forming the container body 1 described above. Is non-foamed and is not impregnated with an inert gas to form foamed cells. Therefore, foaming does not occur during heat treatment for thermal crystallization, and inconvenience due to foaming of the mouth portion 5 is completely prevented.
This thermal crystallization may be performed on the mouth portion 5 of the container 10 formed by blow stretching, or may be performed on the mouth portion 5 of the preform 20 used for blow stretching.

In addition, as described above, in the present invention, since the foam layer 3 is formed using polyester having a high intrinsic viscosity (IV), the growth and growth of the foam cells in the foam layer 3 due to heating is effectively prevented. Has been. Therefore, the heat resistance can be improved by heat-fixing the body portion 7 of the container body 1 without growing and coarsening the foamed cells. For example, by such heat fixation, heat fixation can be performed so that at least the crystallinity of the body portion 7 (and the bottom portion 9) is 25% or more, particularly 30 to 40%.
In addition, this heat setting is made by heating and holding the trunk | drum 7 etc. of the container main body 1 in the thermal crystallization temperature range of the said polyester.

  Furthermore, in the stretched and foamed polyester container 10 of the present invention, although not shown in FIG. 1, a thin skin layer (usually having a thickness of about 5 to 100 μm) having no foamed cells on the outer surface of the foamed layer 3 is provided. It is preferable to form it. Although this skin layer will be described later, by forming the skin layer, the outer surface can be made a smooth surface, and its printability and label sticking property can be enhanced.

  In the above-mentioned stretched and foamed polyester container 10, the thickness of the container body 1 and the foamed layer 3 is not particularly limited and can be appropriately set depending on the usage form, size, etc. of the container 10. The thickness of the body portion 7 is in the range of about 20 to 1000 μm, and the thickness of the foam layer 3 on the body portion 7 is in the range of about 20 to 500 μm.

<Manufacture of stretched foam polyester container>
As described above, the stretched and foamed polyester container 10 of the present invention described above is manufactured by molding the preform 20 having the structure shown in FIG. 2 and then blow-stretching. It is manufactured as follows.

  First, the polyester for forming the container body 1 described above is used, an infrared absorber is appropriately blended with the polyester, and the core tube 21 having the shape shown in FIG. 2 is formed by injection molding according to a conventional method.

  Next, the above-described polyester for forming the foam layer 3 is used, and this polyester is supplied to the melt kneading part of the injection molding machine, and an inert gas (carbon dioxide gas or nitrogen gas) is supplied at a high pressure while melt kneading. The polyester is impregnated with an inert gas.

  The impregnation with the inert gas is performed so as to dissolve a sufficient amount of gas according to the number of the foam cells present in the foam layer 3 of the container 10 to be finally formed. For example, when the number of foamed cells is increased to improve the light shielding property, the amount of gas impregnation is increased, and otherwise, the amount of gas impregnation is set small.

  On the other hand, a previously molded non-foamed core tube 21 is disposed in the injection mold, and the polyester impregnated with the inert gas as described above is injected as it is, and the outer surface of the core tube 21 is injected. The foam precursor layer 23 to be the foam layer 3 is formed.

The subsequent processes are performed according to the procedure shown in FIG.
Referring to FIG. 3, the preform 20 obtained in the above step is placed under normal pressure (atmospheric pressure) for a predetermined time in a state of being cooled and solidified (FIG. 3A). That is, by releasing to atmospheric pressure, the inert gas is released from the surface of the foam precursor layer 23, and thereby the skin layer 25 in which the inert gas is not dissolved or the inert gas concentration is lowered. Will be formed. Since the solubility of the inert gas at normal pressure and normal temperature is almost zero, by holding the foamed precursor layer 23 that has been cooled and solidified under normal pressure, the inert gas is gradually released from the surface, The skin layer 25 as described above is formed.
When heating is performed in the subsequent steps and the entire foam precursor layer 23 is foamed, irregularities due to foaming are formed on the surface, and the smoothness is impaired. Alternatively, problems such as a decrease in printing suitability and label sticking property occur. However, by forming the skin layer 25 as described above, the outer surface of the container to be finally formed (particularly the trunk portion). A surface layer in which foam cells are not distributed can be formed on the surface), and a decrease in surface smoothness due to foaming can be avoided.

  In addition, the thickness of said skin layer 25 can be adjusted with the time to open | release under normal pressure in the state solidified by cooling. That is, the longer the opening time, the greater the thickness of the skin layer 25, and the shorter the opening time, the thinner the skin layer 25. However, if this open time is too long, the inert gas is almost released, and it becomes difficult to form a sufficient number of foamed cells to obtain the desired characteristics such as light shielding properties. .

  Next, the preform 20 on which the skin layer 25 as described above is formed is heated (step (b)) and stretch-molded following the heating (step (c)), whereby the expanded foamed polyester of FIG. The container 10 can be obtained.

  The heating in the above step (b) is performed at a temperature equal to or higher than the glass transition point (Tg) of the polyester forming the core tube 21 and the foam precursor layer 23 and lower than the crystallization temperature (that is, lower than the melting point). 20 is held. That is, when it is heated to a temperature higher than the crystallization temperature, stretch molding becomes difficult.

The heating described above is performed to stretch-mold the preform 20, and the foaming cell 40 is generated in the foam precursor layer 23 by the heating at this time, and the pre-foamed layer 3 ′ is formed. It becomes. That is, an abrupt change in the internal energy (free energy) of the inert gas dissolved in the polyester forming the foam precursor layer 23 is brought about, resulting in phase separation and bubbles (foaming). The cell 40) is separated from the polyester to cause foaming.
Since the inert gas is released in the skin layer 25 formed on the surface of the foam precursor layer 23, the foam cell 40 is not formed in the skin layer 25, and this heating step ( Even in b), the skin layer 25 remains as it is.

  Further, the foamed cells 40 generated as described above are substantially spherical and are distributed isotropically. Although the light shielding property is exhibited at this stage, since the foamed cell 40 has a spherical shape, the light shielding property is low, and the foamed cell 40 is stretched and flattened by stretching in the next stretch molding step (c). Thus, the light shielding property is improved.

  The cell density of the foamed cells 40 in the pre-foamed layer 3 ′ formed in the heating step (b) (density in the region excluding the skin layer 25) depends on the dissolved amount of the inert gas described above. The larger the amount, the higher the cell density and the smaller the diameter of the spherical foamed cell 40. The smaller the dissolved amount, the smaller the cell density and the larger the diameter of the foamed cell 40. The diameter of the foam cell 40 can be adjusted by the above heating time. For example, the longer the heating time for foaming, the larger the diameter of the foam cell 40, and the shorter the heating time, Small diameter.

The diameter and cell density of the foam cell 40 can be adjusted by setting the heating conditions in the heating step (b) using the phenomenon as described above. Since the foam precursor layer 23 to be the layer 3 ′ is formed of polyester having a high intrinsic viscosity (IV), the foam cell 40 is prevented from being coarsened (the foam cell 40 is unlikely to have a large diameter). The diameter of 40 is fine and the cell density can be increased. For example, by performing heating so that the temperature of the foam precursor layer 23 (pre-foamed layer 3 ′) is 95 to 115 ° C. and adjusting the heating time, the cell density of the foamed cells 4A in the pre-foamed layer 3 ′ can be increased. It can be set to about 10 ^{5 to} 10 ¹⁰ cells / cm ³ and the average diameter can be set to about 3 to 50 μm, and thereby stably imparting a high light-shielding property to the foam layer 3 finally obtained. Can do.

  In addition, the said heating can be performed using publicly known means, such as infrared heating, high frequency induction heating, hot air heating, and an oil bath.

  By the way, when heating as described above is performed, the foam cell 40 is generated only in the pre-foamed layer 3 ′ on the outer surface of the core tube 21, and is not generated in the inner core tube 21 (portion that becomes the container body 1). In addition, the thermal conductivity of the pre-foamed layer 3 ′ is greatly reduced by the formation of the foamed cells 40. Therefore, in this heating step (b), when the preform 20 is heated, the temperature of the pre-foamed layer 3 ′ located on the outer surface side is high, and the temperature of the core tube 21 on the inner surface side is higher than that of the pre-foamed layer 3 ′. And it becomes low temperature. As described above, in the case of infrared heating, since infrared rays are scattered by the foam cell 40, the temperature difference between the pre-foamed layer 3 'and the core tube 21 is further increased. Therefore, if stretch molding (and heat setting) is performed while such a temperature difference is generated, strain will remain in the main body 1 of the finally obtained container 10, which is sufficient by crystallization by heat setting. It becomes difficult to impart heat resistance and the like.

  In the present invention, as described repeatedly, since the intrinsic viscosity (IV) of the polyester forming the pre-foamed layer 3 ′ and the foamed precursor layer 23 to be the foamed layer 3 is high, the temperature at which bubbles are generated is high and high. Since the preform remains in a transparent non-foamed state up to the temperature and heating unevenness due to infrared scattering during heating is suppressed, the temperature of the core tube 21 (the portion that becomes the container body 1) of the preform 20 and the pre-foamed layer 3 ′ The difference becomes smaller. Furthermore, the intrinsic viscosity (IV) of the polyester that forms the core tube 21 of the preform 20 is low, and the intrinsic viscosity (IV) of the polyester that forms the foamed precursor layer 23 that becomes the prefoamed layer 3 ′ and the foamed layer 3. Since the temperature is high, the occurrence of strain in a state where a temperature distribution in which the temperature of the core tube 21 on the inner surface side is low and the temperature of the pre-foamed layer 3 ′ on the outer surface side is high is effectively suppressed. That is, the polyester of the pre-foamed layer 3 ′ having a high temperature has a low thermal mobility, the polyester of the core tube 21 having a low temperature has a high thermal mobility, the thermal mobility of both the polyesters is substantially equal, and distortion due to the temperature distribution is reduced. It is possible to suppress the occurrence.

  Further, in the present invention, when the above-described infrared absorber is blended in the polyester of the core tube 21, the heat absorption of the core tube 21 is enhanced, and accordingly, the pre-foamed layer 3 ′ to the core tube 21. As a result, the temperature of the core tube 21 rises rapidly, the temperature difference between the pre-foamed layer 3 'and the core tube 21 is relaxed, and the generation of strain is more effectively suppressed. It becomes possible.

  The preform 20 heated as described above is introduced into a stretch molding die, and stretch molding is performed (step (c)). That is, biaxial stretch blow molding is performed by blowing a pressurized fluid into the preform 20 in the stretch mold and performing axial tensile stretching and circumferential expansion stretching with a stretching rod, and the shape shown in FIG. The expanded foamed polyester container 10 is obtained.

  In such stretch molding, the axial stretch ratio and the circumferential stretch ratio are not particularly limited, but in general, the axial stretch ratio is 1.3 to 3.5 times, particularly 1.5 to 3 times. The stretching ratio in the circumferential direction is preferably 2 to 5.5 times, particularly 3 to 5 times. Furthermore, as the pressurized fluid to be blown at the time of blow molding, it is preferable to use a high-temperature fluid that is maintained at a temperature that is at least 10 ° C. higher than the temperature of the preform 20.

As shown in FIG. 3, the pre-foamed layer 3 ′, the skin layer 25, and the core tube 21 are stretched and thinned by such stretch molding, and the foamed layer 3 having the thin skin layer 25 on the surface is used. The container body 1 is formed in which the shoulder portion 6, the trunk portion 7 and the bottom portion 9 are covered.
In the foam layer 3, the foam cell 40 is also stretched to have a flat shape. Therefore, the light shielding property to light is enhanced by such a shape change of the foam cell 40. For example, the transmittance of light having a wavelength of 500 nm in the pre-foamed layer 3 ′ in which the shape of the foam cell 40 is spherical is about 50%, but the shape of the foam cell 40 is flat by stretch molding. In the foamed layer 3, the light transmittance under the same conditions is 15% or less, particularly 10% or less, and further 5% or less, and exhibits extremely high light shielding properties.

  In the above stretch molding, it is preferable to use a so-called one-mold method, and the temperature of the stretch molding die is set to the thermal crystallization temperature region of the polyester forming the foam layer 3 and the container body 1 (core tube 21) ( In general, it is preferable to hold at 140 to 200 ° C. and perform heat setting simultaneously with stretch molding. That is, in the present invention, since the intrinsic viscosity (IV) of the polyester forming the foam layer 3 is high, the growth and coarsening of the foam cell 40 during the heating for heat setting is effectively suppressed, and accordingly This is because it is possible to effectively prevent a decrease in light-shielding properties or a decrease in physical properties such as gas barrier properties due to heat fixation.

  The above-described heat setting is performed by using the mold temperature and the mold so that the crystallinity degree by the density method in the body portion 7 of the container body 1 is in the above-described range (25% or more, particularly 30% or more). The contact time may be set.

As described above, the stretched and foamed container 10 of the present invention can be manufactured from the preform 20, and the container mouth portion 5 is thermally crystallized in this manufacturing process. In general, prior to heating the preform 20, the mouth 5 is heated to a temperature not lower than the melting point and lower than the melting temperature of the polyester forming the core tube 21. However, as described above, the mouth portion 5 can be thermally crystallized after the above stretch molding and heat setting.
Moreover, it is also possible to use a two-mold method regardless of the one-mold method. For example, a cooled stretch mold is used, and the molded container 10 is taken out from the stretch mold and is kept at a predetermined temperature. It is also possible to perform heat setting using a heated heat setting mold.

The stretched and foamed polyester container 10 of the present invention described above exhibits excellent light-shielding properties due to the formation of the foamed layer 3 and is not only excellent in recycling, but is also effective in thermal crystallization of the mouth portion 5 and heat fixing of the trunk portion 7. Therefore, it is extremely useful for applications requiring heat resistance (for hot filling and heated sales containers).
1 to 3, the present invention has been described by taking a bottle-shaped container as an example, but the present invention is not limited to a bottle-shaped container. For example, the present invention is applied to a cup-shaped container. It is also possible to do. In this case, the shape of the preform is a sheet, and this sheet covers a polyester base sheet having a high intrinsic viscosity (IV) and dissolved in an inert gas, and a portion corresponding to the trunk portion of the base sheet. And a non-foamed sheet made of polyester having a low intrinsic viscosity (IV), which is heated to a predetermined temperature for foaming, and then subjected to stretch molding such as vacuum molding and plug assist molding A cup-shaped container is also possible.

The invention is illustrated by the following experimental example. The measurement method implemented in the present invention is as follows.
[Measurement of crystallinity]
A test piece is cut out from the body of the container, the non-foamed container body layer is peeled off, and the density ρ (g / cm ³ ) of the test piece is obtained by a density gradient tube method. The crystallinity is calculated by the following formula.
Crystallinity (%) = {ρc (ρ−ρa) / ρ (ρc−ρa)} × 100
ρc: Crystal density (1.455 g / cm ³ )
ρa: amorphous density (1.335 g / cm ³ )
[Measurement of total light transmittance]
Using a spectrophotometer UV-3100PC (manufactured by Shimadzu Corporation), the total light transmittance of the bottle body at a wavelength of 500 nm was measured by an integrating sphere measurement method.

Example 1
Using a commercially available homopolymer PET resin for bottles (intrinsic viscosity: 0.75 g / dl), a thin-walled test tube-shaped container body preform having a mouth portion and a body portion was prepared by injection molding. Furthermore, 0.15% by weight of nitrogen gas was supplied to the body of this preform from the middle of the heating cylinder of the injection molding machine to a commercially available homopolymer PET resin for bottles (inherent viscosity: 0.84 g / dl). Kneading and dissolving, adjusting the degree of holding pressure so as not to foam (holding pressure 60 MPa, injection holding time 21 seconds) to inject and form the barrel outer layer, and gas is added to the mouth and barrel inner layer. In other words, the container outer layer was impregnated with gas, but a two-layer preform for a container that was substantially non-foamed was obtained. The weight of the preform was 31 g.
The mouth portion of this preform was heated with an infrared heater for thermal crystallization.

  The two-layer preform thus obtained is heated by an infrared heater in a stretch blow molding machine until the surface of the preform reaches about 105 ° C., blow-molded, and a bottle having a capacity of 500 ml (length: 208 mm, body part) The diameter was 65 mm and the body thickness was 0.3 mm. The temperature of the blow mold was adjusted to 150 ° C., the bottle was thermally fixed, and cooling blow was performed to blow air at room temperature (25 ° C.) into the container for 1 second at the time of mold release. Stretch blow molding was possible under almost the same conditions as ordinary preforms, and there was no shape anisotropy or thickness unevenness and the moldability was good. The obtained PET bottle had a pearly luster due to the presence of the flat bubbles in the outer body layer, and the surface was smooth and the appearance was good.

  When the crystallinity of the inner layer of the bottle body at a height of 60 mm from the bottom was measured by the density method, it was 32%. After measuring the internal volume of the bottle, the bottle was filled with hot water at 85 ° C. and sealed with a plastic closure. After standing for 5 minutes, it was cooled to room temperature with running water. After that, when the volume of the bottle was measured and the volume shrinkage rate before filling with hot water was calculated, it was 1.88%, and it had good heat resistance.

(Example 2)
Bottle molding was performed in the same manner as in Example 1 except that the container outer layer resin of Example 1 was changed to a commercially available copolymer PET resin for bottles (inherent viscosity: 0.84 g / dl, IPA: 2%). The bottle was white pearl tone, the surface was smooth and the appearance was good. The degree of crystallinity of the bottle body portion main body layer was 33%, and the volumetric shrinkage due to filling with hot water at 85 ° C. was 1.62%, which had good heat resistance.

(Example 3)
Bottle molding was performed in the same manner as in Example 1 except that 0.05 part by weight of graphite was dispersed as an infrared absorber in the container body layer resin of Example 2. The resulting bottle had an ashish mouth, a white pearl tone, a smooth surface and good appearance. The degree of crystallinity of the bottle body portion main body layer was 38%, and the volumetric shrinkage due to filling with hot water at 85 ° C. was 0.27%, which had extremely good heat resistance.

(Comparative Example 1)
Bottle molding was performed in the same manner as in Example 1 except that the bottle outer layer resin of Example 1 was changed to the same homopolymer PET resin (intrinsic viscosity: 0.75 g / dl) as that of the main body layer resin. The bottle had irregularities due to coarsely grown bubbles on the surface, and the appearance was poor. The crystallinity of the bottle body part layer was 31%, and the volumetric shrinkage due to filling with 85 ° C. hot water was 2.40%.

(Comparative Example 2)
Bottle molding was performed in the same manner as in Example 1 except that the container body layer resin of Example 1 was changed to the same homopolymer PET resin (inherent viscosity: 0.84) as that of the outer container layer. The bottle was white pearl tone, the surface was smooth and the appearance was good. The degree of crystallinity of the bottle body part main layer was 28%, and the volumetric shrinkage due to filling with 85 ° C. hot water was 3.35%, and the heat resistance was poor.

(Comparative Example 3)
The container body layer resin of Example 1 was changed to homopolymer PET resin (intrinsic viscosity: 0.84), and the container outer layer resin was changed to homopolymer PET resin (intrinsic viscosity: 0.75). Bottle molding was performed. The bottle had irregularities due to coarsely grown bubbles on the surface, and the appearance was poor. The degree of crystallinity of the bottle body portion main body layer was 27%, and the volumetric shrinkage due to filling with 85 ° C. hot water was 3.61%, and the heat resistance was poor.

Example 4
Bottle molding was performed in the same manner as in Example 1 except that the container outer layer resin of Example 1 was changed to a commercially available PET resin for bottles (inherent viscosity: 1.12). The bottle was white pearl tone, the surface was smooth and the appearance was good. The crystallinity of the bottle body part layer was 32%, and the volumetric shrinkage due to filling with 85 ° C. hot water was 2.12%.

(Comparative Example 4)
Using a commercially available homopolymer PET resin for bottles (intrinsic viscosity: 0.75 g / dl), 0.15% by weight of nitrogen gas is supplied from the middle of the heating cylinder of the injection molding machine, and is kneaded and dissolved with the PET resin. The degree of holding pressure was adjusted so as not to foam (holding pressure 60 MPa, injection holding time 21 seconds), and a test tube-shaped preform consisting of a mouth part and a body part was prepared by injection molding. The shape of this preform is designed to be the same as the over-crystal preform with the mouth crystallized in Example 1, and a single-layer preform in which nitrogen gas is uniformly dissolved throughout the preform. Obtained.
This preform was blow-molded in the same manner as in Example 1 without subjecting the mouth to crystallization to obtain a single-layer foamed bottle having an amorphous mouth.
When this bottle was filled with hot water at 85 ° C., the mouth portion foamed, and further softened and deformed to impair the sealing performance, and could not be used as a container.

  Table 1 shows the body barrel crystallinity, volume shrinkage, and bottle barrel total light transmittance of (Example 1) to (Example 4) and (Comparative Example 1) to (Comparative Example 3).

1: Non-foamed polyester container body 3: Foamed polyester layer 3 ': Pre-foamed layer 5: Mouth part 7: Body part 9: Bottom part 10: Stretched foamed polyester container 20: Preform 21: Core tube 23: Foamed precursor layer 25 : Skin layer 40: Foamed cell

Claims (5)

  A stretched foamed polyester container comprising a non-foamed polyester container body having a mouth part, a body part, and a bottom part, and a foamed polyester layer having foam cells provided therein on the outer surface of the body part of the non-foamed polyester container body. The non-foamed polyester container body is formed using a polyester having an intrinsic viscosity of 0.78 or less, and the foamed polyester layer is formed using a polyester having an intrinsic viscosity of 0.80 or more. A stretched foamed polyester container.   The stretched and foamed polyester container according to claim 1, wherein the mouth is thermally crystallized.   The stretched and foamed polyester container according to claim 1 or 2, wherein the body portion of the non-foamed polyester container body has a crystallinity of 25% or more by a density method.   The stretched and foamed polyester container according to any one of claims 1 to 3, wherein an infrared absorbent is dispersed in the polyester forming the non-foamed polyester container body.   The stretched foamed polyester container according to any one of claims 1 to 4, which is used for hot filling of contents.

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