JP2019137443A - Foaming container that color unevenness is inhibited - Google Patents

Abstract

To provide a foaming container where color unevenness is inhibited effectively in the foaming container formed by using thermoplastic resin.SOLUTION: In a foaming container which is made of thermoplastic resin and where a foaming region that a flatness shaped foaming cells are distributed in a container wall is formed in a drum portion, differences among L*values in the horizontal direction in a 2° view of C light in accordance with JISZ8722, in a same face and a same height over all of the foaming region formed in the drum portion are 4 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a foamed container that is formed using a thermoplastic resin and has a foamed region in which foamed cells are distributed in the body of the container.

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. In such an opaque container, it is not desirable to add a colorant from the viewpoint of resource reuse. Therefore, from the viewpoint of providing light shielding properties (opacity) without blending a colorant, various foamed containers in which the container wall is foamed using microcellular technology have been proposed.

  In such a foamed container, it is known that, depending on the distribution state of the foamed cells in the container wall, a light-shielding property is imparted and at the same time a highly glossy appearance (for example, pearl tone) is obtained (patent) Furthermore, when a colorant is dispersed in the resin forming the container wall, a very specific appearance can be obtained, for example, metal gloss even though no metal pigment is used. Is known to be expressed (see Patent Document 2).

  In other words, the foam container in which the foam cells are distributed is formed using a resin in which a colorant is dispersed, so that a unique appearance is obtained and a high decorative property is imparted. Even if it does not have, it has high commercial value.

  In the course of studying such a foam container, the present inventors have obtained knowledge that color unevenness may occur in the container body. In particular, in a colored foam container molded from a resin in which a colorant is dispersed, or a container having a body portion with a different transverse draw and different draw ratio, this color unevenness is at a level that cannot be ignored.

Patent No. 4839708 WO2013 / 146109

  Accordingly, an object of the present invention is to provide a foamed container in which uneven color in the circumferential direction is effectively suppressed.

  The present inventors have conducted many experiments on the cause of the color unevenness of the foam container, and as a result, the major cause of the color unevenness is not the dispersed state of the colorant, but the form and number of foamed cells, the skin layer The inventor found that there is variation in thickness and the like and completed the present invention.

  According to the present invention, a foamed container having a body portion having a transverse flat section and a different draw ratio is formed in the body portion, which is made of a thermoplastic resin and in which a foam-shaped foam cell is distributed inside the vessel wall. When the L * value in the C light 2 ° field of view in accordance with JISZ8722 is compared within the same plane and at the same height over the entire foamed region formed in the body portion, the difference is 4 or less. There is provided a foam container characterized in that.

In the foam container of the present invention,
(1) comprising a thermoplastic resin in which a colorant is dispersed;
(2) It is colored chromatic,
(3) The outer surface of the body is a smooth surface having a surface roughness Ra of 5 μm or less.
(4) It has a form of a bottle having a nozzle part for discharging contents whose diameter is smaller than that of the body part, and the foamed cells are not distributed in the nozzle part.
(5) The minimum diameter in the trunk horizontal cross section is 79% or less of the maximum diameter,
Is preferred.

  The foamed container of the present invention has a lateral direction in a C-light 2 ° field of view in accordance with JISZ8722 in the same plane and at the same height over the entire foamed region in which foamed cells are distributed in the body wall of the container. When comparing L * values, the difference is 4 or less. Thus, the fact that the variation in lightness shows a small value means that the same lightness is exhibited in any part of the foamed region, and as a result, the foamed container of the present invention has effective color unevenness in the foamed region. It has been suppressed. That is, regardless of whether or not a colorant is blended, color unevenness due to variation in brightness is effectively eliminated.

That is, the color unevenness recognized in the foamed container is considered to be caused by variations in the form and size of the foamed cells, the number of foamed cells in the thickness direction, and the like. These variations lead to variations in light transmittance, and in the foamed region, there are a portion where the light transmittance is large and a portion where the light transmittance is small. For example, the part where the foam cells overlap multiplely has a low light transmittance and a large amount of reflection, so the emitted color is visible brightly, but in the part where the degree of overlap of the foam cells is small, the light generated by the foam cells Since the degree of reflection and scattering is small and the amount of transmitted light is large (the amount of reflection is small), the color is visually perceived as dark. As a result, it is considered that color unevenness is recognized. Further, not only the overlapping of the foam cells but also the flatness of the foam cells, the degree of light reflection and scattering by the foam cells changes, and as a result, color unevenness may be affected. In particular, in a container in which a colorant is dispersed, in addition to light and darkness due to the degree of overlapping of foamed cells and the flatness of the foamed cells, the effect of light absorption by the colorant is added, so that color unevenness is more visible compared to the uncolored state. .
However, in the foamed container according to the present invention, as described above, the brightness in the circumferential direction on the front surface of the container is substantially constant, and as a result, uneven color in the circumferential direction is effectively suppressed and a uniform color is exhibited. , Its commercial value is extremely high.

  Such a foamed container of the present invention has not only lightness due to foaming but also a colored appearance peculiar to the foamed container, and color unevenness is effectively suppressed, and therefore, a field requiring decoration in particular. In particular, it is extremely useful for applications such as cosmetic containers.

It is a figure which shows the side cross section in the foaming area | region formed in the trunk | drum of the foaming container of this invention. The figure for demonstrating the principle of the foaming container of this invention. The figure which shows the example of the form of the foaming container of this invention. The figure which shows the other example of the form of the foaming container of this invention. The figure which shows the form of the preform used for manufacture of the foaming container of this invention.

<Foaming container>
The foam container of the present invention is formed of a thermoplastic resin, and the body of the container is internally foamed by physical foaming using microcellular technology or chemical foaming using a chemical agent as a foaming agent. A foamed region in which foamed cells are distributed is formed. Accordingly, the container as a whole exhibits a color emitted by the used colorant, and in the case where the colorant is not blended, it becomes cloudy, white or white due to an increase in light shielding property due to the distribution of the foamed cells. It has a pearl tone.
Microcellular foaming is a technique in which an inert gas is impregnated into a resin as a foaming agent, and this gas is grown into bubbles to physically form the foamed cells. It differs from chemical foaming using a compound that generates a gas such as nitrogen or carbon dioxide as a foaming agent in that it can control foaming so that it is distributed. In the present invention, these foaming agents are selectively used according to the required size and distribution of the foamed cells, and the foamed cells are generated by physical foaming or chemical foaming.

  Referring to FIG. 1 which shows a cross section (a vertical cross section along the maximum stretching direction) in the foaming region formed in the container body, a large number of resin matrices 3 forming the body wall 1 of this container Many foam cells 5 are distributed. In the case of a colored foam container, a colorant is dispersed in the resin matrix 3, whereby the entire container is colored in the color of the colorant. Moreover, when a coloring agent is not mix | blended, a cloudiness, white, or white pearl tone is exhibited.

  The foaming container of the present invention in which such a foaming region is formed on the body wall 1 is the same in the same surface and at the same height as measured on the outer surface of the body, and in the 2 ° visual field of C light according to JISZ8722. The difference in the L * value in the direction is 4 or less, particularly preferably 3 or less (that is, the variation in lightness on the outer surface of the foamed region is small), and thereby the color unevenness in the circumferential direction is effectively suppressed. Product value is significantly increased.

  By the way, the foaming container of this invention needs to be extended | stretched after foaming in order to make lightness variation small as mentioned above. That is, as can be understood from FIG. 1, since the foamed cells 5 are stretched after foaming, the plastics forming the resin matrix 3 are stretched. It has the flat shape extended so that it may become.

Referring to FIG. 2 for explaining the principle of eliminating light reflection variation and color unevenness, when the foamed cells 5 are distributed in the resin matrix 3, the portion where the foamed cells 5 are present is from the outer surface. Is reflected by the foamed cells 5, but the light penetrates into the resin matrix 3 and passes through the portions where the foamed cells 5 do not exist. Therefore, the reflectance of light is high in the portion where the foam cells 5 are densely present, but the reflectance of light is small in the portion where the foam cells 5 are sparse. As described above, when there is a portion with high light reflectance (portion where the foamed cells 5 are densely present) and a portion with low light reflectance (portion where the foamed cells 5 are sparse), color unevenness may occur. Become. In areas where the reflectance of light is high, the color is perceived brightly, and in areas where the reflectance of light is low, the amount of transmitted light is large and the color is perceived as dark. It will end up.
As described above, in the present invention, in order to prevent color unevenness in the foaming region, the variation in light reflectance is reduced so that the variation in brightness in the circumferential direction is within the above-described range. In this case, the smaller the variation in reflectance, the better the prevention of color unevenness. However, the variation in reflectance should be reduced to such an extent that the color unevenness cannot be visually recognized, and as a result, the difference in brightness L * is as described above. The range is set to 4 or less (preferably 3 or less).

  As described above, in the present invention, in order to prevent color unevenness visually recognized from the outside, the variation in reflectance is reduced. As understood from the above description, this reflectance In order to reduce the variation, it is necessary to uniformly distribute the foamed cells 5 so that there is no density. For this reason, the form of the foam cell 5 has become a flat shape stretched in the stretching direction as shown in FIG. 1 by stretch molding. In the case of not being stretch-molded, the foam cell 5 has a shape close to a sphere, but in this case, the area of the gap between adjacent foam cells 5 (the portion where the foam cell does not exist) is large. Since the foam cell 5 becomes larger than the area occupied by the foam cell 5, the density of the foam cell 5 increases, and the variation in reflectance cannot be reduced to the above-described range.

Therefore, in the present invention, the foam cell 5 is stretched into a flat shape by stretch molding. For example, when viewed from the side cross-section of FIG. 1, the aspect ratio of the foam cell 5 (stretching direction length L / thickness t). Is preferably in the range of 1.5 or more. When this aspect ratio is small, the stretching is insufficient, the multiple reflection by the foam cell 5 when light is incident becomes significant, and the regular reflection is reduced. As a result, the variation in reflectance is reduced to the above-mentioned range. It is difficult to suppress.
If the aspect ratio becomes unnecessarily large due to unnecessarily stretching, depending on the shape of the container, it may be difficult to keep the aspect ratio of the foam cell 5 within a certain range over the entire foam region. For example, a part that is not sufficiently stretched by stretching or a part that is excessively stretched occurs, and as a whole, a large variation in aspect ratio occurs, and a variation in reflectance is kept small. Can be difficult. Therefore, it is desirable that the expansion is suppressed so that the aspect ratio of the foam cell 5 is 20 or less.
The aspect ratio is the ratio (L / t) between the length L in the stretching direction and the thickness t (L / t). Stretch molding into the shape of the container is usually biaxial: axial stretching and circumferential stretching. Since the above-described aspect ratio is performed by stretching, it is necessary that the above aspect ratio is satisfied for both the length in the axial direction and the length in the circumferential direction.

In the colored foam container of the present invention, it is preferable that foaming is adjusted so that the number of foam cells 5 distributed in the thickness d direction of the body wall 1 is 5 or more, particularly 10 or more. .
That is, even if the aspect ratio is increased and the gap between the foamed cells 5 is smaller than that of the foamed cells 5, the gap is not necessarily reduced by mechanical processing, and therefore variations are inevitably caused. In order to suppress the variation in reflectance caused by the variation in the size of the gap to a level that can be ignored, the number of the foam cells 5 distributed in the thickness d direction of the body wall 1 is increased as described above. Is preferred.

In addition, the thickness d of the body wall 1 of the colored foam container of the present invention may be in an appropriate range depending on the application, but the number of foam cells 5 distributed in the direction of the thickness d as described above in particular. From the viewpoint of increasing the thickness, the thickness d is preferably set to 200 μm or more, particularly 300 μm or more.
Generally, when the lightness L * of the reflectance is adjusted by adjusting the aspect ratio and the number of the foam cells 5 in the direction of thickness d as described above, the average reflectance in the foamed region is about 30 to 90%. In addition, the total light transmittance is 70% or less, and the colorant and the foamed cell 5 exhibit high reflectance and light shielding properties. The total light transmittance is measured at a wavelength at which the colorant to be blended does not show activity, that is, the absorption coefficient a = 0.

  Furthermore, in the colored foam container of the present invention, as described in Patent Document 2, a thin skin layer 7 (for example, a thickness of 200 μm or less) in which the foam cells 5 are not distributed is formed on the outer surface of the container wall 1. Preferably, the formation of the skin layer 7 avoids the formation of surface irregularities due to foaming, and the outer surface thereof is a smooth surface, for example, a smooth surface having an average surface roughness Ra (JIS B 0601) of 5 μm or less. It is most preferable to maximize the decoration effect by coloring. That is, the presence of the skin layer 7 and the smooth surface effectively expresses regular reflection, multiple reflection, light scattering, and light interference in the flat foam cell 5, and further the skin layer. 7 together with the nail polish effect (the refractive index of the light on the surface is uniform), the coloration by the colorant is also added, and a glossy appearance can be expressed.

In addition, the patent document 2 which concerns on the patent by this applicant has an indication about the above skin layers and smooth surfaces. However, this Patent Document 1 does not consider variations in aspect ratio and the like, and as a result, the difference in lightness L * in the foamed region exceeds 4, and color unevenness occurs at a level that cannot be ignored. However, the decorativeness as high as the colored foam container of the present invention is not obtained.
As can be understood from the above description, in order to reduce the variation in the reflectance of light over the entire foamed region, there is little variation in the shape and size of the foamed cells, and further, the distribution is distributed in the thickness direction of the container wall. It is also necessary to reduce the variation in the number of foamed cells, and it is not necessary that the average value of these is within a certain range. If there is a variation in the number of cells that are distributed in the shape, size, and thickness direction of the foam cell, this will cause variations in the light transmission, and this will result in variations in reflectance, resulting in color unevenness. It becomes.
Therefore, in the present invention, it is possible to generate the foamed cell 5 by chemical foaming. However, physical foaming by the microcellular technology capable of easily adjusting the shape and size of the foamed cell 5 is particularly possible. It is preferably applied.

In the colored foam container of the present invention described above, the resin used for the molding, that is, the resin of the matrix 3 is not particularly limited as long as chemical foaming or physical foaming is possible. A known thermoplastic resin that can be foamed by a cellular material is preferably 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 (PET), polybutylene terephthalate, polyethylene naphthalate, and copolymerized polyesters thereof; Polycarbonate resin; Nylene oxide resin; biodegradable resin such as polylactic acid; and the like can be used. Of course, blends of these thermoplastic resins can also be used.
In the present invention, the most preferable resin is a polyester resin typified by PET from the viewpoint of the form of the foamed cell 5 and stretch moldability for adjusting the number of cells.

Moreover, it does not restrict | limit especially as a coloring agent mix | blended with the said resin for coloring, A various pigment can be used according to the target color.
In addition, expensive pigments called so-called metallic pigments, for example, metal powder pigments such as copper powder, aluminum powder, zinc powder, gold powder, and silver powder, and flaky pigments such as mica, flaky titanium, and flaky stainless steel Alternatively, by using a pigment (bright pigment) in which the surface of such a scaly pigment is coated with fine metal particles such as cobalt, nickel, titanium, etc., and using these in combination with pigments of other colors as appropriate, metallic However, according to the present invention, it is possible to obtain a highly decorative appearance having a metallic luster without using such a metallic pigment, so that the cost can be reduced. Therefore, it is not necessary to dare to use such an expensive pigment. That is, in the foamed region where the foamed cells 5 are distributed, gloss or luster due to light scattering, reflection, interference, and a manicure effect by the skin layer is added to show a metal color corresponding to the color. For example, when a gold color is to be obtained, a golden color can be obtained by using an orange-green pigment.

  The foam container of the present invention may not contain a colorant. However, in order to maximize the effects of the present invention, it is preferable to use a colorant, particularly a chromatic pigment, and titanium oxide. It is desirable to avoid the use of white pigments such as That is, when colored in white, even if the above-described color unevenness occurs, it is difficult to visually recognize the color unevenness, and even if the variation in light reflectance is reduced, there is not much merit. It is.

  The above-mentioned colorant is generally used in an amount of 2.5 to 20 parts by weight, particularly 5 to 10 parts by weight per 100 parts by weight of the resin described above in the state of a colored masterbatch.

In the colored foam container of the present invention, the difference in the lightness L * at the outer surface of the foamed region is 4 or less, preferably 3 or less, by adjusting the form and distribution state of the foamed cells 5 that are stretched and flattened. As long as the shape is not particularly limited, for example, the shape having the skin layer 7 shown in FIG. 1 is a non-laminate structure, and the growth and expansion of bubbles in the body wall 1 It is formed by.
Moreover, it is preferable that it has the shape of a bottle at the point of utilizing the decorating property by a uniform color to the maximum.

  Examples of the form of such a bottle are not limited to this, but representative examples include those having the form shown in FIGS. 3 and 4. In addition, although these figures show a side view (A) and a top view (B), the cap which should be mounted | worn with a bottle is abbreviate | omitted in any.

  The bottle of FIG. 3 (shown as 10 as a whole) is provided with a small-diameter content discharge nozzle 13 at the top of the body 11. The nozzle 13 has a screw 13a for attaching a cap on its outer surface, a support ring 13b used for transportation, and the like, and is connected to the body 11 via a shoulder 15 projecting in the horizontal direction. ing. Further, the lower end of the body portion 11 is closed by the bottom portion 17.

In such a bottle, it is possible to make a part of the body part 11 a foamed region in which the flat foamed cells 5 are partially distributed. Usually, however, color unevenness in the foamed region is suppressed. In order to make full use of the effect, the entire body 11 is a foamed region, and flat foamed cells 5 are distributed in the wall.
Further, the shoulder 15 connecting the nozzle 13 and the body 11 and the bottom 17 closing the body 11 are also foamed regions, and flat foam cells 5 are distributed on the wall. However, the nozzle 13 is a non-foaming region, and the foamed cells 5 are not distributed on this wall portion. This is because the nozzle 13 includes the screw 13a and the support ring 13b, and thus it is necessary to avoid strength reduction due to foaming. Moreover, since this part is normally an unstretched part, the flat foam cell 5 cannot be formed.

  Therefore, in the bottle, the nozzle 13 in which the foamed cells 5 are not distributed, and the body portion 11 and the shoulder portion 15 in which the foamed cells are distributed, are considerably different in color. For example, when a brown coloring pigment is blended, the nozzle 11 is brown, but the body 11 and the shoulder 15 are gold. This is as described in Patent Document 2.

The bottle shown in FIG. 3 has a form in which the effects of the present invention can be utilized. As shown in FIG. 3B, the barrel 11 has an elliptical cross section. It has an elliptic cylinder shape as a whole. That is, the bottle having such a shape has a shape having a major axis surface region x and a minor axis surface region y.
According to the study by the present inventors, color unevenness tends to be prominent in such a bottle. In particular, when the shape is such that the ratio of the minimum diameter d2 to the maximum diameter d1 is 79% or less, the color unevenness is clearly recognized. That is, as can be understood from FIG. 3B, the portion having the minimum diameter d2 (the central portion of the major axis surface region X) is a low-stretched portion, and the portion having the maximum diameter d1 (the central portion of the minor axis surface region Y). ) Is a highly stretched part. For this reason, the form (aspect ratio) of the foamed cell 5 is composed of the central portion of the long axis surface region X (end portion of the short axis surface region Y) and the central portion of the short axis surface region Y (end portion of the long axis surface region X). As a result, in the long axis plane region X, the central portion is dark and the end portion is bright, and the color unevenness becomes noticeable due to such a light / dark difference. .
However, in the present invention, the flat foam cell 5 has a uniform shape and the like, and the light reflection variation is adjusted to be small. The difference is also effectively eliminated, and the color unevenness is effectively suppressed. (For example, when forming a bottle by blow molding of a preform described later, blow molding is performed by forming a temperature distribution so that the temperature of the highly stretched portion of the preform is low and the temperature of the low stretched portion is high. Thus, the variation in light reflection can be adjusted to be small.)

  In the present invention, the shoulder portion 15 is also a foamed region, but it is not necessary to adjust the variation of the reflected light in this portion. This is because this portion is not as conspicuous as the body portion 11 and does not affect the appearance characteristics so much even if some color unevenness occurs. Similarly, although the bottom portion 17 is also a foamed region, this portion is a portion that cannot be seen from the outside, and color unevenness can be completely ignored, so that it is not necessary to adjust the variation in reflected light.

Moreover, the bottle of FIG. 4 has a rectangular flat cross section so that it may be understood from FIG. 4 (B).
Such a rectangular bottle has four surfaces x, and a corner y is formed at a portion where the two surfaces x are continuous, and there are four such corners y. That is, the length of the straight line connecting the two corner portions y located on the diagonal line is the major axis d1, and the length of the surface x having the two corner portions y at both ends is the minor axis d2.
When a preform is formed by stretching a preform having a circular body section, the corner portion y becomes a highly stretched portion, the foam cell 5 is stretched most, becomes a bright portion, and the surface x The central portion becomes a low stretched portion, the extent of expansion of the foam cell 5 is small, and the dark portion becomes dark. For this reason, it is necessary to avoid color unevenness due to such a light / dark difference.

<Manufacture of foam containers>
The foam container of the present invention in which the variation in reflectance in the foam region formed in the body portion is suppressed and the generation of color unevenness is effectively suppressed is to reduce the variation in the form of the foam cell 5 and the like. Manufacturing according to a known method proposed by the present applicant (see, for example, Patent Documents 1 and 2), except that foaming conditions and stretching conditions are set according to the form of the container. can do.

  That is, in order to manufacture the various types of containers described above, a container preform 50 having a form as shown in FIG. 5 is prepared.

The preform 50 has a test tube shape as a whole, and includes a neck portion 51 corresponding to the above-described bottle nozzle 13 and a cylindrical forming portion 53 connected to the neck portion 51.
The neck portion 51 is a portion that is not stretch-molded, and has a screw 51 a and a support ring 51 b on the outer surface. The molding portion 53 is a portion that is stretch-molded, and its lower end is closed by the bottom wall 55. . That is, by stretching and forming the molding part 53 using a predetermined mold while holding the neck part 51, for example, the body part 11, the shoulder part 15 and the bottom part of the bottle shown in FIGS. 17 can be formed.
In addition, the thickness of the said shaping | molding part 53 shall consider the thinning in the extending | stretching process mentioned later so that the thickness of the trunk | drum wall of the target container may be obtained.

  Incidentally, the preform 50 of FIG. 5 is obtained by injection molding the above-described blend of resin and colorant (molding resin composition). An inert gas (for example, nitrogen gas or carbon dioxide gas) as an agent is impregnated.

The preform 50 impregnated with an inert gas can be performed by placing a preform that has not been impregnated with a preformed inert gas in a high-pressure inert gas atmosphere with or without heating. . The higher the temperature, the smaller the amount of gas dissolved, but the faster the impregnation rate. The lower the temperature, the larger the amount of gas dissolved, but the impregnation takes time.
Also, a preform impregnated with an inert gas can be obtained by supplying an inert gas at a high pressure to a melt-kneading part in a molding machine and subjecting the molding resin composition dissolved with the inert gas to injection molding as it is. You can also. In this case, in order to prevent the foaming in the injection molding machine and obtain a preform having no appearance defect such as a swirl mark, it is maintained at a high pressure as proposed by the present applicant in WO2009 / 119549, for example. It is preferable to perform molding by injection-filling a molding resin composition in which an inert gas is dissolved while holding pressure in the mold cavity.

After obtaining the gas-impregnated preform 50 thus obtained, for example, when forming the skin layer 7 in FIG. 1 described above, the gas-impregnated preform is kept under normal pressure (atmospheric pressure) for a predetermined time. To release the inert gas from the surface. As a result, a thin skin layer in which the inert gas is not dissolved or the inert gas concentration is low is formed on the surface layer portion of the preform 50, and the foamed cells described above are distributed in the skin layer. It corresponds to the non-skin layer 7. The thickness of the skin layer 7 can be adjusted by the opening time under atmospheric pressure (substantially, the time until the next heating and foaming). That is, the longer the opening time, the thicker the skin layer 7 becomes, and the shorter the opening time, the thinner the skin layer 7.
Note that the skin layer 7 only needs to be formed only on the outer surface of the body portion 11 that becomes the foam region, and does not bother to form the entire preform. Therefore, only the portion that becomes the foam region of the body portion 11 is exposed to the atmosphere. It is possible to selectively release the gas only to the outer surface of the body portion 11 of the portion that becomes the foaming region by adopting a means such as exposing the other portion so as not to be exposed to the atmosphere.

Foaming is performed subsequent to the gas releasing step performed for forming the skin layer 7 as described above.
In this foaming step, cells are generated and grown by the expansion of the inert gas by selectively heating the portion that will be the foaming region of the finally obtained container (for example, the bottles of FIGS. 3 to 4). Foaming is performed. Therefore, in order to obtain the container of the form of FIGS. 3-4, the neck part 51 corresponding to the nozzle 13 is not heated, and a foam cell is not formed in this part.

The heating temperature for foaming is equal to or higher than the glass transition point (Tg) of the resin, but it is necessary to be lower than the melting point of the resin in order to prevent thermal deformation of the preform. The higher the heating temperature and the longer the heating time, the more large cells are formed. Therefore, the cell density and the cell size are adjusted using this. For example, in the boundary portion between the body portion 11 and the shoulder portion 15 in FIGS. 3 and 4, the above-described foamed cell 5 (see FIG. 1) tends to be sparse, so that the heating temperature of the corresponding portion is selectively increased. Alternatively, it is preferable to lengthen the heating time for foaming selectively. Moreover, since the center part (end part of the short-axis surface area | region Y) of the long-axis surface area | region X of the elliptical bottle of FIG. 3 is a low extending | stretching part and the foaming cell 5 tends to become sparse, it respond | corresponds to this too. It is preferable that the portion is also set so that the foamed cell becomes larger by selectively raising the heating temperature or heating for a long time. Similarly, the central part of the surface x of the rectangular bottle in FIG. 4 is a low-stretched part, and the foamed cells 5 tend to be sparse. Therefore, the preform temperature of the part corresponding to this part is increased to perform blow molding. Is preferred. Further, in the bottles shown in FIGS. 3 and 4, a portion to be a highly stretched portion, for example, a central portion of the long-axis surface region X of the bottle in FIG. 3 or a portion corresponding to the corner portion y of the bottle in FIG. Blow molding can also be performed by cooling the temperature to a low temperature.
In addition, the heating for foaming is selectively performed on the portion to be the foaming region by blowing hot air, external heating with an infrared heater or the like, immersion in an oil bath, or the like.

By heating the preform 50 impregnated with the gas in this way, a foamed preform in which foamed cells are distributed in the molded part is obtained.
The foamed cells distributed in the foamed region of the foamed preform are in a spherical shape or a state close to a spherical shape and are not flattened, and thus variation in light reflectance is not suppressed. Moreover, in the foaming area | region of the foam preform obtained here, since a cell is spherical and there are many irregular reflections, it becomes a whitish color and lacks gloss.

A foamed container is obtained by stretching the foamed preform as described above. In order to ensure a color that is particularly excellent in decorating properties and has metallic luster, it is also described in, for example, Patent Document 2. As described above, for example, the cell density of the spherical foam cell 5a is adjusted to about 1 × 10 ^{5 to} 1 × 10 ⁸ cells / cm ³ by adjusting the amount of gas dissolved and the foaming conditions (heating temperature) described above. The average diameter (equivalent circle diameter) is set so as to be about 5 to 50 μm, and further, the thickness of the molded part 53 of the preform is set to a certain thickness or more, and the number of foam cells distributed in the thickness direction at this time Is preferably 5 or more.

Stretch molding performed on the above foam preform is performed by a method known per se, for example, by biaxial stretch 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. (Axial direction stretching by a stretch rod and circumferential direction stretching by blowing a blow fluid such as air into the preform), a foaming region in which flat foam cells 5 as shown in FIG. 1 are distributed In the present invention, since the variation in the reflectance in the foamed region formed in the container body is reduced, the flat shape having the aspect ratio as described above particularly in the container circumferential direction is formed. It is necessary to distribute the foamed cells 5 evenly without unevenness.
For this reason, in the present invention, in addition to the density of the foamed cells formed on the preform 50, the average diameter, the thickness of the body wall, etc., for example, the axial stretch ratio and the circumferential stretch ratio are all 1. It is necessary to stretch uniformly so that it may be 1 to 4.0 times and the entire body foam region has such a stretching ratio.

This adjustment of the draw ratio can be easily performed by setting the form of the molding part 53 of the preform 50 according to the form of the container finally obtained.
For example, as the body diameter of the preform 50 is smaller than the body diameter of the container, the circumferential stretch ratio increases, and as the body height is smaller than the body height of the container, the axial direction Since the stretch ratio becomes large, the aspect ratio of the flat foam cell 5 shown in FIG. 1 is adjusted to a predetermined range by adjusting the stretch ratio using this, and the lightness L in the foam region is adjusted. * Difference can be reduced within a predetermined range.

The foamed container of the present invention obtained in this way has a foamed region that is uniformly colored and has high decorating properties. In particular, a container exhibiting metallic luster has the highest quality and the highest decorativeness, and is extremely useful as a container for cosmetics and the like that particularly require a high-class feeling.
Of course, since the foamed container of the present invention has a light shielding property, it is effectively applied to contain contents that are altered by light, and the foamed cell is excellent in terms of lightness and heat insulation. .
In particular, the present invention is preferably applied to an elliptical bottle (or a rectangular bottle) having a flat section with a flatness ratio of 0.21 or more.
In addition, the flatness rate in an elliptical bottle and a rectangular bottle is represented by the following formula with reference to FIG.3 and FIG.4.
Flatness ratio = 1-d2 / d1

  The invention is illustrated by the following experimental examples.

<Preform molding method>
Commercially available PET resin for bottles (inherent viscosity: 0.84 dl / g) sufficiently dried by a dehumidifying dryer is supplied to the hopper of the injection molding machine, and further nitrogen gas is supplied from the middle of the heating cylinder of the injection molding machine. Test tube impregnated with gas by kneading and dissolving with resin, pressurizing the inside of the mold with air in advance to prevent foaming in the mold, adjusting the holding pressure and time to prevent foaming, injection molding A container preform having a shape (weight 26 g, barrel thickness 3.8 mm) was obtained.
In this example, a commercially available brown masterbatch was used in an amount of 5 parts by mass per 100 parts by mass of PET resin, and a preform was injection molded.

<Bottle molding method>
With respect to the gas impregnated preform obtained by injection molding, the outer surface of the preform was heated to 100 ° C. with a quartz heater, and then blow molded to obtain a colored foam container.

<Blow mold>
An elliptical mold and a rectangular mold having the following specifications were prepared.
Oval mold (see Fig. 3);
Vertical magnification for the preform: 1.1 times Horizontal magnification for the preform:
Double the minor axis side (minor axis 47mm)
Major axis side: 3 times (major axis 70mm)
Oval die (see Fig. 3);
Vertical magnification for the preform: 1.1 times Horizontal magnification for the preform:
Double the minor axis side (minor axis 47mm)
Long diameter side: 3.5 times (major diameter 82mm)
Rectangular mold (see Fig. 4):
Vertical magnification for the preform: 1.1 times Horizontal magnification for the preform:
Horizontal magnification viewed diagonally 2.1 times (horizontal magnification corresponding to major axis d1)
Length corresponding to side x: 35 mm

<Bottle evaluation method>
L * difference;
The L * value was measured for the obtained foamed container using an SM color computer (SM-4 manufactured by Suga Test Instruments Co., Ltd.) with a spot diameter of 5 mm and a C light 2 ° field of view.
In the case of a rectangular container, a point 12.5 mm apart in the lateral direction was measured in the same plane and at the same height as the center of the body of the bottle, and the L * difference was calculated.
In the case of an elliptical container, the points near the apex on the major axis side and the minor axis side at a half of the bottle height were measured and compared.
appearance;
About the obtained foamed container, the brightness difference (color unevenness) of the external appearance of a trunk | drum was determined visually and evaluated by the following references | standards.
◯: Color unevenness is not recognized at all.
X: Color unevenness is visible.

<Example 1>
Using an elliptical die (A) with a flatness ratio of 0.33, after completion of preform heating, immediately before blow molding, per one apex with an air nozzle against the part corresponding to the apex on the long diameter side in the flat cross section of the bottle body It was locally cooled at a flow rate of 4 L / min for 7 seconds and blow-molded. The appearance of the obtained bottle body was uniform, and the difference in L * value was measured to be 4.0.
The results for the difference in appearance and L * value are shown in Table 1.

<Example 2>
Using an elliptical die with a flatness ratio of 0.43, after completion of preform heating, immediately before blow molding, per one apex with an air nozzle against the part corresponding to the apex on the long diameter side in the flat cross section of the bottle body It was locally cooled at a flow rate of 6 L / min for 7 seconds and blow-molded. The appearance of the body of the obtained bottle was uniform, and the difference in L * value was measured to be 3.8.
The results for the difference in appearance and L * value are shown in Table 1.

<Example 3>
Using a rectangular mold, immediately after completion of preform heating, immediately before blow molding, for 7 seconds at a flow rate of 7.5 L / min per apex with an air nozzle for the part corresponding to the apex in the flat section of the bottle body , Locally cooled and blow molded. The appearance of the obtained bottle body was uniform, and the difference in L * value measured was 3.1.
The results for the difference in appearance and L * value are shown in Table 1.

<Comparative Example 1>
The bottle was molded in the same manner as in Example 1 except that the air flow rate was 0 L / min (no cooling). Dark vertical streak-like color unevenness was observed at the center of the short side of the bottle body obtained, and the difference in L * value was measured to be 8.1.
The results for the difference in appearance and L * value are shown in Table 1.

<Comparative example 2>
The bottle was molded in the same manner as in Example 2 except that the air flow rate was 0 L / min (no cooling). Dark vertical streak-like color unevenness was observed at the center of the short side of the obtained bottle body, and the difference in L * value was measured to be 9.8.
The results for the difference in appearance and L * value are shown in Table 1.

<Comparative Example 3>
The bottle was molded in the same manner as in Example 3 except that the air flow rate was 0 L / min (no cooling). A dark vertical stripe-like color unevenness was observed at the center of the body of the bottle, and the difference in L * value was measured to be 5.9.
The results for the difference in appearance and L * value are shown in Table 1.

<Comparative Example 4>
The bottle was molded in the same manner as in Example 3 except that the air flow rate was 5 L / min. A dark vertical stripe-like color unevenness was observed at the center of the body of the bottle, and the difference in L * value was measured to be 4.6.
The results for the difference in appearance and L * value are shown in Table 1.

<Comparative Example 5>
The bottle was molded in the same manner as in Example 3 except that the air flow rate was 10 L / min. Bright vertical streak-like color unevenness was observed at the center of the body of the bottle, and the difference in L * value was measured to be 4.5.
The results for the difference in appearance and L * value are shown in Table 1.

1: body wall 3: resin matrix 5: flat foam cell 7: skin layer 11: body part 13: nozzle 15: shoulder part 50: gas impregnated preform 51: neck part 53: molding part

Claims (6)

  In a foamed container having a body part having a transverse cross section and a different stretch ratio, the foam part is formed of a thermoplastic resin and having a foamed region in which flat foam cells are distributed inside the vessel wall. When the L * values in the C-light 2 ° field of view conforming to JISZ8722 are compared within the same plane and at the same height over the entire foamed region, the difference is 4 or less. Foam container.   The foaming container according to claim 1, comprising a thermoplastic resin in which a colorant is dispersed.   The foaming container according to claim 2, which is colored chromatic.   The foaming container according to any one of claims 1 to 3, wherein an outer surface of the body portion is a smooth surface having a surface roughness Ra of 5 µm or less.   It has the form of the bottle which has the nozzle part for discharge | emissioning the content of a small diameter compared with the said trunk | drum, The said foaming cell is not distributed in this nozzle part. The foam container of crab.   The foaming container according to any one of claims 1 to 5, wherein the minimum diameter in the horizontal cross section of the trunk portion is 79% or less of the maximum diameter.