JP2009262550A - Molded product impregnated with non-foaming gas and foamed plastic container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a resin molded product impregnated with non-foaming gas which is obtained by injection-molding resin melted material impregnated with gas, is free from the occurrence of swirl mark, has a smooth surface and is used as a preform for manufacturing a formed molded product. <P>SOLUTION: The resin melted material impregnated with non-foaming gas is injected and charged into a mold cavity retained in a high pressure while applying a hold pressure so as not to cause foaming and is cooled and solidified. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-foamed gas-impregnated resin molded body obtained by injection molding a resin melt impregnated with an inert gas, and a foamed plastic container obtained from the molded body.

  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. For example, Patent Document 1 discloses a plastic container having bubbles. In the case where the size of the bubble viewed from the front of the container is defined by the average bubble diameter of the bubble (foamed cell), the average bubble diameter of 80% or more bubbles is 200 micrometers or less, In addition, a plastic container has been proposed in which the area ratio occupied by bubbles as viewed from the front of the container is 70% or more.

  Patent Document 2 discloses that a mold cavity previously held in a pressurized state by a gas body is injection-filled with a synthetic resin containing a foaming agent, and contains a foaming agent, but has a smooth surface with little foaming. Forming a tubular parison (preform), with at least a portion of the surface of the preform cooled and the inner core uncooled, the preform is transferred to a large mold cavity and molded with compressed gas and / or vacuum and There has been proposed a method for producing a container-like foamed product characterized by foaming.

Furthermore, Patent Document 3 discloses a method for producing a partially foamed resin integrated molded body using microcellular technology proposed by the present applicant. In this manufacturing method, an integrally molded body of a thermoplastic resin (for example, a container) Foaming due to generation of bubbles by the impregnated gas by molding a preform for molding), then impregnating the integral molded body with gas, and partially heating the obtained gas-impregnated molded body. By selectively performing the above, a partially foamed resin integrated molded body having a foamed region and a non-foamed region is manufactured.
JP 2003-26137 A Japanese Patent Publication No.62-18335 JP 2007-320082 A

  The technique proposed in Patent Document 1 is to provide a light shielding property to a plastic container by adjusting the size of the foam cell viewed from the front of the container and the area ratio occupied by the foam cell to a certain range. In such a means, the light transmittance of the container wall is only given about 40 to 50%, and the present situation is that it is required to provide a higher light shielding property. For example, since beverages such as milk are altered by light in a short period of time, visible light transmittance (total light transmittance) is suppressed to about 5 to 10% in milk paper packs and the like. Yes.

  Patent Document 2 discloses that a resin containing a foaming agent is injected into a mold so that foaming does not occur and a preform is molded, and foamed when the preform is molded into a container. Since this method is applied to so-called chemical foaming, the diameter of the foamed cells is large and non-uniform, and a container with high light shielding properties cannot be obtained. In addition, when physical foaming using an inert gas as a foaming agent is applied to the method of Patent Document 2, foaming at the time of injection molding cannot be effectively suppressed. Although it has a small cell diameter as compared with foaming, the number of foamed cells in the wall is also small, and the cell diameter is not uniform, so that sufficient light shielding properties cannot be obtained. Further, in a container such as a bottle, a mouth portion having a screw portion for attaching a cap is formed. However, in the method of Patent Document 2, foaming of the mouth portion cannot be completely suppressed, and the appearance It will cause problems such as deterioration and strength reduction.

  In Patent Document 3, by selectively heating a preform impregnated with an inert gas, the foam is partially foamed. When molding such a foamed preform into a container, the mouth portion is formed. It is non-foamed and the body can be selectively foamed. However, in this method, since the molded preform is impregnated with gas, a step of impregnating the preform in a pressure vessel is necessary prior to foaming the preform, which is problematic in terms of productivity. is there.

  Therefore, the present applicant first impregnates the resin melt with gas and performs injection molding so as not to cause foaming by holding pressure, and after forming the preform and heating the preform to foam. And a method for producing a container by secondary molding (Japanese Patent Application No. 2007-227852). In this method, since the resin melt can be impregnated in the cylinder of the injection molding machine, the obtained preform can be immediately heated and foamed, so that the production efficiency is extremely high and the foaming is performed. The cell diameter and number can be easily adjusted, and there is an advantage that a container with extremely high light shielding properties can be obtained. However, this method still has problems to be improved. Specifically, in spite of the suppression of foaming inside the preform by holding pressure during injection molding, foaming occurs in the mold during injection, so foam marks remain on the surface of the preform, so-called swirl marks. There is a problem that the surface smoothness is reduced. When such a preform is foamed by selective heating, and a part other than the mouth is foamed, and a container is formed by secondary molding, a swirl mark is present in the mouth, which is originally a non-foaming region, so that it is translucent In addition to being in a state, the surface roughness causes inconveniences such as a decrease in appearance characteristics, a decrease in strength, and a decrease in sealing performance.

  Furthermore, in a conventionally known stretched foamed polyester container in which a foamed region formed by impregnation with an inert gas is formed on the container wall, heating is performed when excessive foaming gas is dissolved in the preform surface. There is a problem in that molding defects such as cracks are likely to occur on the surface of the container wall (particularly the body surface) in the blowing process.

Accordingly, an object of the present invention is obtained by injection molding a resin melt impregnated with gas, has no generation of swirl marks, has a smooth surface, and is used for producing a foam molded article. The object is to provide a non-foamed gas-impregnated resin molded article used as a preform and a method for producing the same.
Another object of the present invention is to provide a method for producing a stretched foam using the above-mentioned non-foamed gas-impregnated resin molded body and a partially foamed plastic container produced from the above-mentioned non-foamed gas-impregnated resin molded body. is there.
Still another object of the present invention is to provide a stretched foam container made of polyester in which molding defects such as cracks on the body surface are effectively prevented, and a method for producing the same.

According to the present invention, the resin melt impregnated with an inert gas is injected and filled so as not to cause foaming while being held in a mold cavity held at a high pressure, and then cooled and solidified. A method for producing a non-foamed gas-impregnated resin molded body is provided.
In such a production method, it is particularly preferable to produce a non-foamed gas-impregnated polyester resin molded product (injection molded product) using a polyester resin as the resin melt.

According to the present invention, there is also provided a non-foamed gas-impregnated resin molded article obtained by injection molding a resin melt impregnated with an inert gas, at least part of which has a smooth surface. A non-foamed gas-impregnated resin molded product is provided.
Here, at least a part indicates, for example, a mouth part that requires smoothness of the surface in the case of a container molding preform.

The non-foamed gas-impregnated resin molded body is
(1) The maximum height Pt (JIS B 0601) has a smooth surface of less than 10 μm,
(2) having a light transmittance of 75% or more,
(3) Use as a preform for container molding,
Is preferred.

  According to the present invention, furthermore, at least a part of the non-foamed gas-impregnated resin molded body is heated to obtain a foamed molded body, and the foamed molded body is stretch-molded. A method is provided.

According to the present invention, furthermore, in the stretched and foamed plastic container, which is a resin-integrated molded article comprising a mouth part, a body part, and a bottom part, at least a part of the body part is a foaming region having foam cells. ,
There is provided a stretched foamed plastic container characterized by having a smooth surface with a maximum height Pt (JIS B 0601) of less than 10 μm at least in a non-foamed region having no foamed cells.

In the above stretched foam plastic container,
(1) The mouth is a transparent region having a total light transmittance of 75% or more, and no swirl mark is present in the mouth,
(2) In the foamed region, the thickness of the non-foamed skin layer where the foamed cells present on the surface of the wall portion are not present is suppressed to 100 μm or less,
(3) The total light transmittance in the foaming region is 40% or less,
(4) The outer surface of the foamed region of the body portion is made of polyester resin, and infrared light is incident at an incident angle of 45 degrees with respect to the outer surface by a total reflection absorption method using infrared light and a germanium prism. When the light is irradiated, the reflected light is expressed by the following formula:
R = I ₁₃₄₀ / I _1409
Where I ₁₃₄₀ represents the absorbance of the peak corresponding to the longitudinal vibration mode of CH ₂ in the region where the wave number is 1340 ± 2 cm ⁻¹ .
I ₁₄₀₉ indicates the absorbance of the reference peak in the region where the wave number is 1409 ± 2 cm ⁻¹ .
Showing an infrared absorption characteristic in which the absorbance ratio R defined by is 1.30 or less,
Is preferred.

  In the present invention, foaming is prevented by applying pressure during injection molding of a resin melt filled with an inert gas. In such injection molding, a mold held at a high pressure is used. By injecting and filling the gas-impregnated resin melt into the inside, generation of swirl marks is effectively prevented, and a non-foamed gas-impregnated resin molded body having a smooth surface can be obtained. That is, when the gas-impregnated resin melt is filled into the mold maintained at atmospheric pressure, the gas impregnated in the resin melt at the tip of the resin melt flowing in the mold Expands due to a pressure difference from the mold inner space, and bubbles are broken. That is, since the resin melt flows in the mold with the tip portion broken, this state is transferred to the mold surface, and a swirl mark is formed on the surface of the molded body by cooling and solidifying on the mold surface. Appears and causes surface roughness. By applying pressure to the resin melt filled in the mold, foaming after filling can be prevented, but swirl marks and surface roughness due to bubble breakage during the flow of the resin melt cannot be prevented. However, according to the present invention, in order to inject the gas-impregnated resin melt into the mold held in a pressurized state, bubble breakage during the flow of the resin melt in the mold is effectively suppressed, It is possible to obtain a non-foamed gas-impregnated resin molded body having no surface of a swirl mark and having a high smoothness surface. For example, the non-foamed gas-impregnated resin molded article of the present invention obtained by such a method has no swirl mark, and the surface thereof is an extremely smooth surface having a maximum height Pt (JIS B 0601) of less than 10 μm. Yes. Furthermore, since the foaming after filling is effectively suppressed by the holding pressure, this molded body has high transparency while being impregnated with a gas having a function as a foaming agent, and transmits all light. The rate is 75% or more.

  Such a non-foamed gas-impregnated resin molded body can be made into a foamed molded body by heating at least a part thereof, but after foaming, stretched at least partly by further stretching A foam can be produced. This method does not require a step of impregnating with an inert gas, which is a foaming agent, after molding, and the impregnation of the inert gas can be easily performed in the melt-kneading part in the cylinder of the injection molding machine. Therefore, it is possible to produce a foam stretch-molded product with high productivity, and the industrial value is extremely large.

  In particular, the non-foamed gas-impregnated resin molded body can obtain a partially foamed molded body having a foamed region and a non-foamed region by selective heating, so that the mouth portion is non-foamed and the body portion is foamed. It is extremely useful for manufacturing foamed plastic containers.

  Further, in the foamed plastic container manufactured using the above-mentioned non-foamed gas-impregnated resin molded body, the surface with high smoothness possessed by the non-foamed gas-impregnated resin molded body is expressed as it is, and the mouth portion is high. It has transparency, no swirl mark, and good appearance characteristics, strength, sealing properties and the like.

  Furthermore, by adjusting the time until the foaming by heating after molding the non-foamed gas-impregnated resin molded body, the foamed cells present on the surface of the foamed molded body (for example, foamed preform) are distributed. It is possible to adjust the thickness of the non-foamed skin layer. That is, by heating the non-foamed gas-impregnated resin molded body, foam cells having a predetermined size are formed according to the degree of heating, and a foam region in which such foam cells are distributed is formed. When the time from molding to heating is long, the impregnated gas is released from the surface. Therefore, when foaming is performed immediately after molding, the amount of gas released can be brought to a level close to zero. For example, the foam cells are distributed to the very vicinity of the surface, and the foam cells are distributed. The thickness of the non-foamed skin layer can be made extremely thin. On the other hand, by performing foaming by heating after molding at an appropriate time, the amount of gas released can be increased and the thickness of the non-foamed skin layer can be increased.

  Therefore, in the foamed plastic container manufactured using the above-described non-foamed gas-impregnated resin molded body, for example, in the foamed region, the thickness of the non-foamed skin layer is made extremely thin with a thickness of 100 μm or less, so The foamed cells can be distributed, and thereby high light-shielding properties can be imparted. That is, by increasing the number of foam cells distributed in the thickness direction, multiple scattering and reflection of light occur, and the total light transmittance in the foam region (for example, the body) is made 40% or less, so that the decorative property is improved. And remarkably high light-shielding property can be provided.

Furthermore, in the present invention, a polyester resin melt is used as the resin melt, and the resin melt impregnated with an inert gas (polyester resin melt) is injected and filled into a mold held at a high pressure. In this case, it is preferable to perform stretch molding such as blow molding after molding the preform under appropriate conditions of pressure and injection speed.
By adopting such means, the above-mentioned absorbance R of the infrared absorption characteristics of the outer surface of the body wall (particularly, the portion where the foamed region is formed) of the resulting container is 1.30 or less. Can be adjusted. That is, in a stretched foamed polyester container having such infrared absorption characteristics, polyester crystallization during stretch molding such as blow molding can be reliably suppressed, and the body surface where the foamed region is formed can be suppressed. The occurrence of cracks is effectively suppressed.

  That is, when injection-filling a polyester resin melt impregnated with an inert gas in a mold held at a high pressure, the gas pressure in the mold and the injection speed are inadequate, especially the gas pressure If the injection speed is high and the resin melt is filled in the mold, the gas filled in the mold in advance will not be sufficiently discharged. Molding is performed while gas is caught between them, and molding is performed in a state where excessive gas is dissolved on the surface of the preform to be molded. As it is known that crystallization proceeds when a gas dissolves in the resin, when such a preform is heated and stretch-molded (blow-molded), crystallization proceeds on the surface of the preform during heating and stretches. It is considered that cracks occur on the outer surface of the container during molding. Therefore, the gas pressure in the mold and the injection speed are adjusted so that the gas filled in the mold is sufficiently discharged, and thereby excessive gas is applied to the surface of the preform to be molded. By suppressing the melting of the resin and subjecting the preform thus obtained to stretch molding, crystallization of the polyester during stretch molding is suppressed, effectively preventing inconvenience due to crystallization such as cracks during stretch molding. In such a container, the outer surface of the body portion having the foamed region exhibits the infrared absorption characteristic having the absorbance ratio R of 1.30 or less.

Explanatory drawing for demonstrating the injection process employ | adopted when shape | molding the non-foaming gas impregnation resin molding of this invention. The figure which shows an example of the wall part cross-section in the foaming area | region of the foaming molding manufactured according to this invention. The figure which shows the other example of the wall part cross-section in the foaming area | region of the foaming molding manufactured according to this invention. The figure which shows an example of the cross-sectional structure along the maximum extending | stretching direction of the wall part in the foaming area | region of the extending | stretching molded object manufactured according to this invention. Explanatory drawing which shows simply the manufacturing process of the stretched foam plastic container of this invention. It is a figure for demonstrating the measurement principle of the light absorbency ratio R. FIG. It is a figure which shows an example of the chart of the infrared-light absorption spectrum measured by the total reflection absorption method.

<Non-foamed gas-impregnated resin molding and its production>
In the present invention, the non-foamed gas-impregnated resin molded body is molded by impregnating a resin melt with gas and injection-molding the gas-impregnated melt so as not to cause foaming.

  The resin used for the production of such a molded body is not particularly limited as long as it can be impregnated with an inert gas, and a known thermoplastic resin can be used. For example, low density polyethylene, high density polyethylene, polypropylene, poly 1-butene, poly 4-methyl-1-pentene or random of α-olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene Olefin resins such as block copolymers and cyclic olefin copolymers; ethylene / vinyl acetate copolymers, ethylene / vinyl alcohol copolymers, ethylene / vinyl chloride copolymers and other ethylene / vinyl copolymers; polystyrene Styrene resins such as acrylonitrile / styrene copolymer, ABS, α-methylstyrene / styrene copolymer; polyvinyl chloride, polyvinylidene chloride, vinyl chloride / vinylidene chloride copolymer, polymethyl acrylate, polymethacrylic acid Vinyl resins such as methyl; nylon 6, nylon Polyamide resins such as Ron 6-6, Nylon 6-10, Nylon 11 and Nylon 12; Polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their copolyesters; Polycarbonate resins; Polyphenylene oxide resins A biodegradable resin such as polylactic acid, or the like can be used alone or in a blend of two or more. In particular, when this molded body is used for molding a container, an olefin resin or a polyester resin is suitable, and among these, a polyester resin is most suitable for maximizing the advantages of the present invention.

  Moreover, inert gas functions as a foaming agent, and nitrogen gas, carbon dioxide gas, etc. are generally used.

  The above-described impregnation of the resin melt with the inert gas is performed by supplying the inert gas at a predetermined pressure to the resin held in the molten state by the resin kneading section (or plasticizing section) in the injection molding machine. Done. That is, according to this method, it is possible to impregnate the gas in an injection molding machine, and it is not necessary to impregnate the molded article after injection molding. it can. Further, by adjusting the amount of impregnation of the gas at this time, the number of foamed cells generated by heating can be adjusted. For example, as the gas pressure is increased and the kneading time under the gas pressure is increased, the amount of impregnation of the gas can be increased and the number of foam cells can be increased.

  In the present invention, the resin melt impregnated with gas as described above is injected and filled into a mold held at a high pressure. Referring to FIG. 1 for explaining this injection process, an injection mold indicated by 1 as a whole has a shell mold 3 and a core mold 5 that are cooled and held. , 5, a cavity 7 is formed, and the cavity 7 is filled with a resin melt from an injection nozzle 9. Further, the gas port 10 communicates with the cavity 7.

  That is, a resin melt impregnated with an inert gas is injected and filled into the cavity 7 from the injection nozzle 9, and the resin melt in the cavity 7 is cooled and solidified, whereby the resin melt is formed by the cavity 7. In the present invention, when the resin melt is injected, nitrogen gas, carbon dioxide gas, air, or the like is supplied from the gas port 10 into the cavity 7 to increase the pressure inside the cavity 7. Keep it. By filling the melted resin impregnated with the gas into the cavity 7 held at a high pressure in this way, it is possible to effectively suppress bubble breakage when the molten resin flows in the cavity 7. The formation of a swirl mark can be prevented, and a molded product having a highly smooth surface can be obtained. Here, the smoothness of the surface of the mold cavity 7 is not particularly limited except for the necessary portions, and may be partially roughened in advance using a method such as sandblasting as necessary.

  Further, the gas in the cavity 7 is discharged from the gas port 10. It is also possible to obtain a molded body partially free of swirl marks by changing the timing of gas supply and discharge into the cavity 7 until the resin melt is injected and filled. In the present invention, the holding pressure is further applied by continuously injecting the resin melt. That is, this holding pressure can effectively prevent foaming in the cavity 7.

  As described above, in the present invention, the cavity 7 held under high pressure is filled with the gas-impregnated resin melt, and further the holding pressure is applied, so that there is no swirl mark and high surface smoothness. In addition, it is possible to obtain a non-foamed gas-impregnated resin molded article in which foaming is effectively suppressed while impregnating the gas which is a foaming agent. For example, the maximum height Pt (JIS B 0601) of this non-foamed gas-impregnated molded body is less than 10 μm, preferably 5 μm or less, and most preferably 1 μm or less, and is remarkably excellent in smoothness and visible light having a wavelength of 500 nm. The total light transmittance is 75% or more, and the transparency is remarkably excellent.

  In performing injection molding as described above, the pressure in the cavity 7 is not particularly limited, but is generally maintained in a range of 1.0 MPa or more, and the pressure in the cavity 7 is maintained at such pressure. It is preferable to injection-fill the resin melt. If this pressure is low, foam breakage during the flow of the resin melt cannot be effectively suppressed, swirl marks are generated, and the surface smoothness is low.

Further, the degree of holding pressure (holding pressure and time) is appropriately set according to the impregnation amount of the inert gas, the resin temperature, etc. so that foaming can be effectively suppressed. What is necessary is just to set so that a weight reduction rate may be 5% or less. The weight reduction rate of the preform can be experimentally obtained by the following formula.
Weight reduction rate = [(M ₀ −M ₁ ) / M ₀ ] × 100
In the formula, M ₀ represents the weight of the preform obtained by injecting under the condition setting so that there is no molding defect such as sink without impregnation with inert gas,
M ₁ represents the weight of a gas-impregnated preform obtained by impregnating with an inert gas,
It is represented by That is, the weight reduction rate decreases as the holding pressure increases, and the weight reduction rate decreases as the holding time increases. In the present invention, it is most preferable to set the pressure holding condition so that the weight reduction rate is 0%.

  Further, when the resin melt impregnated with the inert gas as described above is injected and filled into the cavity 7 held at a high pressure, the pressure and the injection are selected so that the gas does not dissolve into the resin melt as much as possible. It is preferable to adjust the speed. As described above, if the pressure and the injection speed are set higher than necessary, excessive gas is dissolved in the resin melt flowing in the mold and excessively applied to the surface of the preform to be molded. This is because the crystallization of the resin is promoted during the subsequent stretch molding. The specific pressure and injection speed may be set so that inconveniences such as cracks resulting from crystallization do not occur in the expanded foamed molded article that is finally experimented and finally molded.

<Heating foam>
In the present invention, by heating at least a part of the non-foamed gas-impregnated resin molded body obtained as described above, a foamed molded body having a foamed region in which foamed cells are distributed on the wall portion is obtained. Such a foamed molded article has no swirl mark and has high surface smoothness as described above. An example of the cross-sectional structure of the wall portion of the foam region (that is, the region corresponding to the heated region) of such a foamed molded product is shown in FIG.

  As can be understood from FIG. 2, the wall portion indicated by 20 as a whole is impregnated with an inert gas by the above heating, so that a large number of foamed cells A are generated. The heating temperature for foaming is equal to or higher than the glass transition point of the resin forming the molded body (wall portion 20), and the internal energy of the inert gas dissolved in the resin by such heating. An abrupt change in (free energy) is caused, phase separation is caused, and foaming occurs due to separation from the resin body as bubbles. Of course, this heating temperature should be not higher than the melting point, preferably not higher than 200 ° C., in order to prevent deformation of the molded body. If the heating temperature is too high, the cell diameter is difficult to control because of the rapid foaming after the heating, the appearance is deteriorated, and further, the crystallization of the body portion proceeds and the secondary formability is lowered.

  The heating as described above can be easily performed using, for example, an oil bath, an infrared heater, or the like. For example, the heating can be selectively performed as disclosed in Japanese Patent Application Laid-Open No. 2007-320082 (Patent Document 3) described above. By performing the heating, the foamed cells A can be generated only in the selectively heated region.

By the way, as shown in FIG. 2, a non-foamed skin layer 21 in which the foamed cells A do not exist is formed on the surface of the wall portion 20 having the foamed cells A inside. That is, after molding a non-foamed resin molded body impregnated with an inert gas, if this is kept under atmospheric pressure, the impregnated inert gas will be released from the surface, so the surface area of the molded body The amount of the inert gas at zero is zero or extremely low. For this reason, when it heats as mentioned above, the non-foamed skin layer 21 in which the foam cell A does not exist substantially is formed in the surface site | part.
In addition, the surface of the non-foamed skin layer 21 of such a foam molded body also has a high smoothness, like the surface of the non-foamed gas-impregnated resin molded body.

  As understood from the above description, the thickness of the non-foamed skin layer 21 can be adjusted by controlling the amount of gas released from the surface of the molded article after injection molding. For example, since the release of gas can be suppressed by performing heat foaming immediately after injection molding, the thickness of the non-foamed skin layer 21 can be made extremely thin. In this case, the thickness of the region 22 in the wall portion 20 where the foamed cells A are present (hereinafter sometimes referred to as a foamed layer) can be increased, which is advantageous in improving the light shielding property. . Further, as the time from injection molding to heating and foaming is increased, the amount of gas released increases, so that the thickness of the non-foamed skin layer 21 can be increased, which reduces gas barrier properties and strength reduction due to foaming. It is advantageous in terms of suppression.

  Moreover, the layer which the foaming cell A does not exist in the inside of the wall part 20 can also be formed by making the heating mentioned above into a short time and suppressing the heating inside the wall part 20. FIG. Such a layer structure is shown in FIG. That is, in the example of FIG. 3, the non-foamed core layer 23 in which the foam cell A does not exist is formed in the central portion of the wall portion 20, and the wall portion 20 is composed of the non-foamed skin layer 21 / foamed layer 22 / It has a five-layer structure of non-foaming core layer 23 / foaming layer 22 / non-foaming skin layer 21. Such a five-layer structure is particularly advantageous in improving gas barrier properties.

  Further, as shown in FIG. 2 and FIG. 3, the foam cell A formed inside the wall portion 20 (hereinafter sometimes referred to as a spherical foam cell) is substantially spherical, etc. It is distributed in the direction. In particular, in the present invention, foaming at the time of molding is suppressed by the above-described holding pressure at the time of injection molding, so that the diameter of the foamed cell A is particularly uniform and has a sharp particle size distribution.

The cell density of the spherical foam cell A (density in the foam layer 22) depends on the amount of the inert gas dissolved as described above. The larger the amount of the dissolved gas, the higher the cell density and the diameter of the spherical foam cell. The smaller the dissolved amount, the smaller the cell density and the larger the diameter of the foam cell A. The diameter of the spherical foamed cell A can be adjusted by the above heating time. For example, the longer the heating time for foaming, the larger the diameter of the spherical foamed cell A, and the shorter the heating time, the spherical foamed cell. Cell A has a small diameter. In the present invention, the above conditions are adjusted, and for example, the cell density of the spherical foam cell A in the foam layer 22 is set to about 10 ^{5 to} 10 ¹⁰ cells / cm ³ and the average diameter is set to about 3 to 50 μm. It is preferable to provide high light-shielding properties by stretch molding described later. Furthermore, when the average diameter of the spherical foam cell A is set in such a range, in the present invention, foaming during molding is prevented by holding pressure during injection molding, and a sharp particle size distribution is ensured. The standard deviation is 40 μm or less, in particular 20 μm or less.

<Extension molding>
The foamed molded product obtained above has no swirl mark, has a smooth surface, and has a foamed structure in which a large number of fine foam cells A are distributed in the foamed region. Not enough in terms. That is, the foam cell A formed in the foam region of the foam molded body has a spherical shape, and therefore the degree of overlap in the thickness direction is low and the degree of light transmission is large. For this purpose, the foam cell A is made flat by stretch molding, which causes multiple scattering and reflection of light in the foam amount region, lowering the light transmittance, and further increasing the light shielding performance per thickness. It can be granted.

  Stretch molding is performed by a method known per se, for example, stretched by blow molding by heating the preform to a temperature not lower than the glass transition temperature of the resin and lower than the melting point, or vacuum molding typified by plug assist molding. Thereby, a bottle or a cup-shaped container having a foamed region (for example, a trunk) in which flat foamed cells are distributed is obtained. Alternatively, a stretched film can be produced by stretching a sheet-shaped foamed molded article, and a bag-like container can be obtained using the stretched film.

  That is, with reference to FIG. 4 which shows the cross section along the maximum extending | stretching direction of the wall part in the foaming area | region of an extending | stretching molded object, in this wall part 30, the foaming layer 31 in which many flat foam cells B are distributed is provided. The non-foamed skin layer 33 in which the foamed cells B are not distributed with an appropriate thickness is formed on the surface, and the foamed cells B are stretched along the maximum stretching direction. By making the spherical foam cell A into such a flat foam cell B by stretch molding, a certain degree of overlap can be secured over the entire foam region, and high light-shielding properties can be expressed. .

  In the present invention, foaming is performed so that the average major axis L (length along the maximum stretching direction) of the flat foam cell B is 400 μm or less, particularly 200 μm or less, and the thickness t is 50 μm or less, particularly 30 μm or less. It is preferable to perform stretching by setting stretching conditions such as a stretching ratio according to the size of the spherical foam cell A formed in the molded body. That is, by setting the size of the flat foam cell B within the above range, a high light-shielding property can be expressed over the entire foamed region, and a reduction in strength and a gas barrier property due to foaming can be effectively avoided. Moreover, it is advantageous also in reducing the weight reduction by foaming.

  For example, in blow molding that is stretched in the biaxial direction of the axial direction (height direction) and the circumferential direction, depending on the size of the spherical foam cell A formed on the foamed molded body (preform), etc. In plug-assist molding or the like in which stretching is performed in such a direction that the stretching ratio is about 2 to 4 times and stretching is performed in only one axial direction, the stretching in this direction becomes the maximum stretching direction, and It is preferable to perform stretching at the same stretching ratio so that the flat foam cell B having the above size is formed.

  In the separate collection of plastic molded products, the difference in specific gravity is used for each plastic type, but the weight reduction rate can be controlled in the same way as foamed molded products. There is an advantage that fractional collection can be performed using the difference in specific gravity.

  In the stretched molded product, the amount of gas impregnation, the heating conditions for foaming, the time from foaming to the time of foaming after injection molding are adjusted, and the thickness of the non-foamed skin layer 33 is 100 μm or less. The number of flat foam cells B that are thin and overlap in the thickness direction should be set to 17 or more, preferably 30 or more, and most preferably 50 or more. In addition, multiple reflection is amplified, for example, the total light transmittance for visible light having a wavelength of 500 nm is 15% or less, particularly 10% or less, and most preferably 5% or less. For example, when the total light transmittance is 5% or less, the light-shielding property is equivalent to that of a paper container, and it is extremely advantageous for accommodating contents that are likely to be altered by light, particularly in the field of containers. .

  In producing a stretched molded article by the above-described method, the glass transition point of the resin decreases linearly or exponentially as the amount of inert gas dissolved increases. 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, various conditions should be set so that a predetermined number of flat cells B overlap in the thickness direction in consideration of the dissolved amount of the inert gas.

<Stretched foam plastic container>
According to the above-described present invention, the stretched molded body finally obtained has not only a high light-shielding property but also the occurrence of swirl marks and a smooth surface. It is suitably used for the production of containers.

  That is, referring to FIG. 5 which briefly shows the manufacturing process of such a stretched foam plastic container, as described above, foaming by injection molding and partial heating is performed to form a foam preform 50 for a test tube. To do. The foam preform 50 includes a mouth part 51, a body part 53, and a bottom part 55. A screw part 51a and a support ring 51b are formed in the mouth part 51, and a portion below the support ring 51b is formed. It becomes the trunk | drum 53. FIG. The mouth portion refers to, for example, a screw portion of a bottle, a thick portion for preventing cap drop-off of a stopper type bottle, and a flange portion of a cup container.

  In the preform 50, the barrel portion 53 and the bottom portion 53 are foamed regions in which the above-described spherical foamed cells A are distributed by selective partial heating after injection molding, and the mouth portion 51 is formed of foamed cells. It is a non-foaming region that does not exist. That is, the preform 50 as a whole has high surface smoothness without a swirl mark, the mouth 51 is transparent, and the body 53 and the bottom 55 are opaque.

  Therefore, in the stretched and foamed plastic container 60 obtained by blow-molding the preform 50 as described above, the mouth portion 61 (corresponding to the mouth portion 51 of the preform 50) provided with the screw portion 61a and the support ring 61b; A large number of flat foam cells B are distributed and have an inflated body 63 and a bottom 65.

  The mouth portion 61 of such an expanded foamed plastic container 60 exhibits high transparency, and as understood from the above description, the total light transmittance for visible light having a wavelength of 500 nm is 75% or more. Yes. The transparent mouth 61 does not have a swirl mark and has high surface smoothness, and its maximum height Pt (JIS B 0601) is less than 10 μm, preferably 5 μm or less, most preferably 1 μm or less. In addition, the mouth portion 61 provided with the screw portion 61a is required to have high strength in order to prevent breakage and deformation during screw engagement with the cap and ensure high sealing performance. No. 60 satisfies the above requirement sufficiently because no foam cell is generated in the mouth portion 61 and there is no swirl mark and the surface smoothness is high.

In addition, the body portion 63 and the bottom portion 65, which are foamed regions, exhibit high light shielding properties. For example, as described above, the non-foamed skin layer is extremely thin, and the number of flat foam cells B in the thickness direction is increased. Thus, the total light transmittance in this region is 15% or less, particularly 10% or less, more preferably 5% or less, and a high light shielding property at the paper container level can be imparted. Further, the trunk portion 63 and the bottom portion 65 have no swirl marks and have the same high surface smoothness as described above, so that they are glossy while being foamed, and have very good appearance characteristics.
Furthermore, when high light-shielding properties are not required, excellent gloss and appearance characteristics are also effective in terms of decorativeness. In this case, the total light transmittance in the foamed region is 20 to 40%. It only has to be about.

  Furthermore, in the stretched and foamed plastic container 60 described above, only the trunk portion 63 can be made a foamed region and the bottom portion 65 can be made a non-foamed region together with the mouth portion 61 by partial heating when the foamed preform 50 is manufactured. In particular, an erecting member may be provided at the bottom of the foamed plastic container 60 to improve erecting stability. In such a case, even if the bottom 65 is set as a non-foamed region (transparent region), it is shielded by the eaves member. Since sex can be imparted, no particular problem arises.

In the stretched and foamed polyester container of the present invention manufactured by the above-described method using a polyester resin such as polyethylene terephthalate as the resin, in particular, the pressure inside the mold and the injection speed during injection molding are such that the gas on the preform surface When it is set to effectively prevent melting (for example, the speed at which the resin is filled in the mold cavity is set to be slow), all of the infrared light and the germanium (Ge) prism are used. When the infrared absorption spectrum of the reflected light is analyzed from the outer surface of the body portion by the reflection method (incident angle 45 degrees), the following formula:
R = I ₁₃₄₀ / I ₁₄₀₉ (1)
_Where I ₁₃₄₀ represents the absorbance of the peak corresponding to the longitudinal vibration mode of CH ₂ in the region where the wave number is 1340 ± 2 cm ⁻¹ .
I ₁₄₀₉ indicates the absorbance of the reference peak in the region where the wave number is 1409 ± 2 cm ⁻¹ .
The absorbance ratio R defined by is 1.30 or less, particularly 1.25 or less.

That is, referring to FIG. 6 for explaining the measurement principle, when the Ge prism is pressed against the surface of the sample (the outer surface of the body of the container) and infrared light is incident under the total reflection condition, the sample surface (ie, When the infrared light is reflected at the boundary between the prism and the sample), the infrared light penetrates the surface of the sample (evanescence light) to a slight extent, and absorption occurs there. Infrared light incident on the outer surface of the sample slightly permeates from the outer surface to the inside when reflected by the surface of the outer surface layer. It is a layer. Therefore, the infrared absorption spectrum of the reflected light is not affected by scattering by the foam cell, and the infrared absorption spectrum information on the sample surface as shown in FIG. 7 can be obtained by analyzing the reflected light. In such an infrared absorption spectrum, in polyester, the peak intensity of absorbance I ₁₃₄₀ increases as the degree of crystallinity increases, while the absorbance I ₁₄₀₉ of the reference peak depends on the orientation and crystallinity of the polyester. It is known not to.

As understood from the above description, the absorbance ratio R (I ₁₃₄₀ / I ₁₄₀₉ ) shows a value of 1.30 or less, particularly 1.25 or less, which means that crystallization on the outer surface of the body wall is It means being suppressed.
For example, in a conventionally known stretched polyester container made of polyester, an inert gas such as carbon dioxide gas present in a preform during blow molding promotes crystallization of the polyester, and as a result, the absorbance ratio R (I ₁₃₄₀₎ described above. / I ₁₄₀₉ ) becomes a value higher than 1.3, and it is difficult to prevent surface cracks due to stretch molding.
However, in the stretched foamed polyester container of the present invention in which the absorbance ratio R (I ₁₃₄₀ / I ₁₄₀₉ ) is controlled to a low value, crystallization of the polyester is suppressed, so that the surface derived from stretch molding (blow molding) This has the advantage that cracking of the steel is effectively suppressed.

The invention is illustrated in the following examples.
In the following experimental examples, the effect of preventing swirl marks by injection filling into a mold held at a high pressure was evaluated.

Example 1
In a mold cavity maintained at a temperature of 30 ° C., a PET resin for bottles having an inherent viscosity (IV) of 0.84 dL / g containing 0.1% of nitrogen gas in a mold cavity maintained at 1 MPa with nitrogen gas. After injection, a holding pressure of 50 MPa was applied for 18 seconds, and after 12 seconds, the mold was opened. Thus, a test tube-shaped container preform in which gas was dissolved but not foamed was obtained.

The surface roughness of the mouth portion of this preform was measured with a surface roughness shape measuring device Surfcom 570A (manufactured by Tokyo Seimitsu Co., Ltd.) based on JISB0601, and evaluated with an average value of 4 positions every 90 degrees. However, the average maximum height was 0.8 μm (reference length 2.5 mm), and it was confirmed that the surface was smooth. Further, it was confirmed visually that the preform body had no swirl mark and the surface was smooth. Furthermore, using a spectrophotometer UV-3100PC (manufactured by Shimadzu Corporation), the total light transmittance of the mouth cut into ¼ in the wavelength range of 300 to 800 nm was measured by an integrating sphere measurement method. As a representative, the total light transmittance at a wavelength of 500 nm was 85%, and the light transmittance was good.
Further, the preform was heated and blow-molded to obtain a blow bottle. The mouth of this blow bottle was transparent (total light transmittance 85%) and smooth (Pt = 0.8 μm) as before blow molding. Further, the total light transmittance of the body portion was 9.0%, and the light shielding performance was excellent.

(Example 2)
Except that the mold cavity pressure before injection was 3 MPa, the preform was injected in the same manner as in Example 1 to obtain a preform in which gas was dissolved but not foamed. When the surface roughness of the mouth of the preform thus obtained was evaluated in the same manner as in Example 1, the average maximum height was 0.6 μm (reference length 2.5 mm), and the surface was smooth. It was confirmed that there was. Further, it was confirmed visually that the preform body had no swirl mark and the surface was smooth. Further, the total light transmittance at the mouth was 86%, and the light transmittance was good.
Furthermore, this preform was heated and blow-molded to obtain a blow bottle. The mouth of this blow bottle was transparent (total light transmittance 86%) and smooth (Pt = 0.6 μm) as before blow molding. Further, the total light transmittance of the body portion was 8.7%, and the light shielding performance was excellent.

(Comparative Example 1)
A preform was injected in the same manner as in Example 1 except that the mold cavity pressure before injection was atmospheric pressure, and a preform in which the gas was dissolved but not foamed was obtained. The surface roughness of the mouth portion of the preform thus obtained was evaluated in the same manner as in Example 1. As a result, the average maximum height was 10 μm (reference length 2.5 mm), and the entire preform was swirled. Was confirmed. Further, the total light transmittance at the mouth was 74%, which was opaque.

(Comparative Example 2)
The mold preform pressure before injection was set to atmospheric pressure, and injection was performed without applying pressure to obtain a foamed preform with a weight reduction rate of 10%. When the surface roughness of the mouth of the foamed preform thus obtained was evaluated in the same manner as in Example 1, the average maximum height was 15 μm (reference length 2.5 mm), and the entire preform was swirled. The mark was confirmed. Further, the total light transmittance of the mouth was 25%, and it was opaque.

(Comparative Example 3)
The preform was injected in the same manner as in Example 1 except that the holding pressure cooling time after injection was 2 seconds, and the surface roughness of the mouth of the preform thus obtained was the same as in Example 1. The average maximum height was 0.8 μm (reference length 2.5 mm), and the surface was smooth, but the pressure holding cooling time was insufficient, so the preform was removed from the mold. At the time, both the mouth and torso were foamed. Further, the total light transmittance at the mouth was 80%.

  The experimental results of the above examples and comparative examples are summarized in Table 1 below.

In the following examples, the moldability was evaluated by controlling the value of the absorbance ratio R (I ₁₃₄₀ / I ₁₄₀₉ ) while suppressing orientational crystallization during stretch molding.

Measurement of the absorbance ratio R (I ₁₃₄₀ / I ₁₄₀₉ );
The measurement was performed under the following conditions using a Fourier transform infrared spectrophotometer (FTS7000e, manufactured by Varian) and a single reflection ATR (Silver Gate, manufactured by Systems Engineering) using a Ge prism.
Incident angle: 45 degrees Measurement area: about 0.385 mm ²
Resolution: 4cm ^-1
Measurement wave number range: 700 to 4000 cm ⁻¹
Integration count: 64 times

  The measurement was performed by measuring the outer surface of the body part having a height of 5 cm to 16 cm from the bottom of the bottle and evaluating the maximum absorbance ratio R.

(Example 3)
PET resin for bottles (intrinsic viscosity: 0.84 dl / g) is supplied to an injection molding machine, and further, 0.1% by weight of nitrogen gas is supplied from the middle of the heating cylinder of the injection molding machine to knead and dissolve with PET resin. , Injected into the mold cavity over 0.46 seconds, then applied with a holding pressure of 50 MPa for 18 seconds, cooled and solidified, impregnated with gas but in a substantially non-foamed test tube shape 25 g container preform Got. By quickly filling the cavity with resin, it was possible to suppress foaming in the cavity and visually confirm that there was no foaming throughout the preform. Further, when visually observed, swirl marks were observed throughout the preform.

Further, the preform was heated and blow-molded to obtain a blow bottle having an internal volume of about 500 ml. The obtained bottle body outer surface is irradiated with infrared light at an incident angle of 45 degrees with respect to the outer surface by a total reflection absorption method using infrared light and a germanium prism, and an absorbance ratio R (I _1340). / I ₁₄₀₉ ), the absorbance ratio R was 0.68.

(Comparative Example 4)
In order to further improve the swirl mark, a preform was molded in the same manner as in Example 3 except that the mold cavity was filled with 3 MPa of air. When the obtained preform was observed, it was visually confirmed that there was no swirl mark and the surface was smooth.
Further, the preform was heated and blow-molded to obtain a blow bottle having an internal volume of about 500 ml. The obtained bottle had many cracks parallel to the circumferential direction in the body portion, and the appearance was impaired. Further, when the absorbance ratio R was evaluated, it was a high value of 1.43.

Example 4
A preform was molded in the same manner as in Comparative Example 4 except that the injection time was 0.83 seconds. When the obtained preform was observed, it was visually confirmed that there was no swirl mark and the surface was smooth.
Further, the preform was heated and blow-molded to obtain a blow bottle having an internal volume of about 500 ml. The resulting bottle was smooth and free from cracks and had a good appearance. Further, when the absorbance ratio R was evaluated, it was suppressed to a low value of 1.06.

(Example 5)
A preform was molded in the same manner as in Comparative Example 4 except that the injection time was 1.54 seconds. When the obtained preform was observed, it was visually confirmed that there was no swirl mark and the surface was smooth.
Further, the preform was heated and blow-molded to obtain a blow bottle having an internal volume of about 500 ml. The resulting bottle was smooth and free from cracks and had a good appearance. Moreover, when the absorbance ratio R was evaluated, it was suppressed to a low value of 0.85.

(Example 6)
A preform was molded in the same manner as in Comparative Example 4 except that the injection time was 2.35 seconds. When the obtained preform was observed, it was visually confirmed that there was no swirl mark and the surface was smooth.
Further, the preform was heated and blow-molded to obtain a blow bottle having an internal volume of about 500 ml. The resulting bottle was smooth and free from cracks and had a good appearance. Moreover, when the absorbance ratio R was evaluated, it was suppressed to a low value of 0.81.

(Comparative Example 5)
A preform was molded in the same manner as in Comparative Example 4 except that the pressure in the mold cavity was changed to 5 MPa. When the obtained preform was observed, it was visually confirmed that there was no swirl mark and the surface was smooth.
Further, the preform was heated and blow-molded to obtain a blow bottle having an internal volume of about 500 ml. The obtained bottle had many cracks parallel to the circumferential direction in the body portion, and the appearance was impaired. Further, when the absorbance ratio R was evaluated, it was a high value of 1.52.

(Example 7)
A preform was molded in the same manner as in Comparative Example 5 except that the injection time was 1.54 seconds. When the obtained preform was observed, it was visually confirmed that there was no swirl mark and the surface was smooth.
Further, the preform was heated and blow-molded to obtain a blow bottle having an internal volume of about 500 ml. The resulting bottle was smooth and free from cracks and had a good appearance. Further, when the absorbance ratio R was evaluated, it was suppressed to a low value of 0.76.

(Example 8)
A preform was molded in the same manner as in Comparative Example 5 except that the injection time was 2.35 seconds. When the obtained preform was observed, it was visually confirmed that there was no swirl mark and the surface was smooth.
Further, the preform was heated and blow-molded to obtain a blow bottle having an internal volume of about 500 ml. The resulting bottle was smooth and free from cracks and had a good appearance. Further, when the absorbance ratio R was evaluated, it was suppressed to a low value of 0.88.

(Comparative Example 6)
A preform was molded in the same manner as in Example 7 except that the pressure in the mold cavity was 7 MPa. When the obtained preform was observed, it was visually confirmed that there was no swirl mark and the surface was smooth.
Further, the preform was heated and blow-molded to obtain a blow bottle having an internal volume of about 500 ml. The obtained bottle had many cracks parallel to the circumferential direction in the body portion, and the appearance was impaired. Further, when the absorbance ratio R was evaluated, it was a high value of 1.34.

  The experimental results of the above examples and comparative examples are summarized in Table 2 below.

1: Injection mold 3: Shell mold 5: Core mold 7: Cavity 9: Injection nozzle 10: Gas port

Claims (12)

  Non-foamed gas-impregnated resin characterized by injection-filling a resin melt impregnated with an inert gas into a mold cavity held at a high pressure so as not to cause foaming and cooling and solidifying. Manufacturing method of a molded object.   The method for producing a non-foamed gas-impregnated resin molded article according to claim 1, wherein a melt of a polyester resin is used as the resin melt.   A non-foamed gas-impregnated resin molded body obtained by injection molding a resin melt impregnated with an inert gas, wherein the non-foamed gas has a smooth surface at least partially Impregnated resin molding.   The non-foamed gas-impregnated resin molded article according to claim 3, which has a smooth surface having a maximum height Pt (JIS B 0601) of less than 10 µm.   The non-foamed gas-impregnated resin molded article according to claim 3 or 4, having a total light transmittance of 75% or more.   The non-foamed gas-impregnated resin molded body according to any one of claims 3 to 5, which is a preform for container molding.   A stretched foam molded article, wherein at least a part of the non-foamed gas-impregnated resin molded body according to any one of claims 3 to 6 is heated to obtain a foamed molded article, and the foamed molded article is stretch-molded. Production method. In the stretched and foamed plastic container comprising a mouth part, a body part and a bottom part, and at least a part of the body part is a foamed region having foam cells,
A stretched foamed plastic container having a smooth surface with a maximum height Pt (JIS B 0601) of less than 10 μm at least in a non-foamed region having no foamed cells.   The stretched and foamed plastic container according to claim 8, wherein the mouth is a transparent region having a total light transmittance of 75% or more, and no swirl mark is present in the mouth.   The stretched foamed plastic container according to claim 8 or 9, wherein in the foamed region, the thickness of the non-foamed skin layer in which foam cells existing on the surface of the wall portion do not exist is suppressed to 100 µm or less.   The stretched foamed plastic container according to any one of claims 8 to 10, wherein the total light transmittance in the foamed region is 40% or less. Made of polyester resin, the outer surface of the foamed region of the body portion was irradiated with infrared light at an incident angle of 45 degrees with respect to the outer surface by a total reflection absorption method using infrared light and a germanium prism. When the reflected light is the following formula:
R = I ₁₃₄₀ / I _1409
Where I ₁₃₄₀ represents the absorbance of the peak corresponding to the longitudinal vibration mode of CH ₂ in the region where the wave number is 1340 ± 2 cm ⁻¹ .
I ₁₄₀₉ indicates the absorbance of the reference peak in the region where the wave number is 1409 ± 2 cm ⁻¹ .
The stretched and foamed plastic container according to any one of claims 8 to 11, which exhibits an infrared absorption characteristic in which an absorbance ratio R defined by the formula (1) is 1.30 or less.

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