Plastic container and manufacturing method for the same

Abstract

To provide a container capable of being molded by adding a decorative pattern with fine irregularities to a surface of a plastic molded part regardless of a surface shape of a molding die, especially a smooth surface shape, and to provide a manufacturing method for the same.SOLUTION: When a container having a plastic molded part made of plastic and including a storage part for storing a stored item is manufactured by injection molding, the plastic molded part is molded under a molding condition that causes a swirl mark to occur by foam molding. This allows a decorative pattern with fine irregularities to be formed on a surface of the plastic molded part regardless of a surface condition of a mold used for molding. In particular, an irregularity display part has a whitened area and a transparent area, and the distribution of the whitened area and the transparent area gives it a marbled appearance.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a plastic container and a method for manufacturing the same. [Background technology]

[0002] In the technical field of plastic injection molding, development has traditionally been focused on accurately reproducing the shape formed in the mold. However, when swirl marks (also known as silver streaks) occur, shapes other than the shape formed in the mold are formed on the surface of the molded product.

[0003] Specifically, in the plastic molding process, the moisture contained in the plastic and the volatile gases that are generated when the raw plastic is melted are removed within the molding system. However, it is generally possible that not all moisture and volatile components can be removed. These volatile components cause bubbles to form during the plastic molding process. At the front of the plastic flow during the plastic molding process, a phenomenon known as fountain flow occurs, in which bubbles rise from the center of the front of the plastic flow and flow outward, causing the bubbles to burst when they come into contact with the cavity. The pattern that forms on the surface of the molded product when this happens is called a swirl mark (silver streak).

[0004] These swirl marks (silver streaks) occur on the surface of a molded product in a shape other than that formed in the mold, which goes against the main purpose described above and makes the molded product defective. For this reason, technological developments have been made to suppress the occurrence of swirl marks, as described in Patent Documents 1 to 3.

[0005] On the other hand, in injection molding, the molten plastic is pressed against the surface of the mold with a large injection pressure, so it is impossible to create controlled irregularities other than those on the surface of the mold. Therefore, in order to create a complex, finely textured pattern on the surface of a molded product, it is necessary to process the surface of the mold with the fine, complex irregularities that will form the desired design.

[0006] However, a mold with fine, complex recesses and protrusions cannot be used to create molded products with a smooth surface, and it becomes necessary to prepare a separate mold with the corresponding recesses and protrusions for each pattern. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-95043 [Patent Document 2] Patent No. 4292406 [Patent Document 3] Patent No. 7226363 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a container having a decorative pattern with fine irregularities on the surface of the plastic molded part, regardless of the surface condition of the mold used for molding.

[0009] Another object of the present invention is to provide a method for manufacturing a container that can mold a decorative pattern with fine irregularities on the surface of a plastic molded part, regardless of the surface shape of the molding mold, especially a smooth surface shape. [Means for solving the problem]

[0010] The present invention solves the above problem by providing a plastic container having a plastic molded part made of plastic with a storage section for storing items, characterized in that the surface of the plastic molded part has a textured display part, and the textured display part has fine protrusions made up of a large number of swirl marks.

[0011] When implementing the present invention, the uneven display portion has whitened areas and transparent areas, and the whitened areas are areas where the swirl marks are densely distributed and appear white due to diffused reflection of light, while the transparent areas are mixed with transparent areas where the swirl marks are sparsely distributed and light is not diffused and remains transparent, and the distribution of the whitened areas and transparent areas can give the display a marbled appearance. Furthermore, the whitened area can be configured so that continuous or discontinuous linear convex portions having a height and width of 0.02 mm or more and 1 mm or less occupy 30% or more of the surface of the plastic molded part.

[0012] The present invention also provides a method for manufacturing a plastic container, in which a container having a plastic molded part made of plastic and equipped with a storage section for storing items is manufactured by injection molding, characterized in that the plastic molded part is molded by foam molding under molding conditions that generate swirl marks, thereby forming a decorative pattern with fine irregularities on the surface of the plastic molded part regardless of the surface condition of the molding mold. It is also desirable that the surface of the mold is smooth. When this container manufacturing method is applied to manufacture a plurality of containers, the molding conditions can be made common to the molding of the plurality of containers. A foaming agent for foaming plastics, which has at least one of the following forms: gas, powder, granular pellets, and liquid, can be blended with the plastic and molded. [Effects of the Invention]

[0013] The present invention makes it possible to provide a container having a decorative pattern with fine irregularities on the surface of the plastic molded part, regardless of the surface condition of the mold used for molding.

[0014] The present invention provides a method for manufacturing a container that can mold a decorative pattern with fine irregularities on the surface of a plastic molded part, regardless of the surface shape of the molding mold, especially a smooth surface shape. Furthermore, the decorative pattern can be changed without changing the shape of the mold. [Brief explanation of the drawings]

[0015] [Figure 1] 1A and 1B show a container according to an embodiment of the present invention, in which (A) is a plan view of the container and (B) is a front view of the container. [Figure 2] 1A and 1B are matrix diagrams showing the marble pattern on the surface of a container according to one embodiment of the present invention, where (A) is a matrix diagram of the front of the container, (B) is a matrix diagram of the left side of the container, and (C) is a matrix diagram of the back of the container. [Figure 3] (A) is an oblique view of a container according to an embodiment of the present invention, (B) is an oblique view of a container according to another embodiment of the present invention with a different pattern molded using the same mold as the container of (A), (A) is an oblique view of a container according to an embodiment of the present invention, (C) is a plan view of a container according to the embodiment of the present invention (A), (D) is an enlarged view of a key part of a container according to the embodiment of the present invention (A), (E) is an enlarged view of another key part of the same container, and (E) is an oblique view of a container molded using the same mold as the container of (A) with no swirl marks. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (1) Basic structure of the invention 1) Molding method: injection molding

[0017] The present invention can be implemented in the same manner as general injection molding. Injection molding involves a plastic melting process in which synthetic plastics such as thermoplastics are heated and melted, and a molding process in which the molten plastic (plastic melt) is forced into a mold under injection pressure, filling the mold and molding it.

[0018] The molding may be carried out by non-foam molding or by foam molding in which foamable plastic is molded by mixing a foaming agent therein to generate bubbles and obtain a porous molded product.

[0019] In the molding process, an injection molding apparatus is generally used that includes an injection device that applies injection pressure to force molten plastic into a mold, and a mold clamping device that fills the mold with the forced molten plastic to form it, and a similar apparatus can also be used when implementing the present invention. The molded product is a container having a storage section for storing an object to be stored. (2) Manufacturing method In carrying out the present invention, even in the case of non-foaming, a component that induces foaming (hereinafter referred to as a foaming component) is used in the molten plastic.

[0020] The foaming component may be a physical foaming agent such as nitrogen gas or carbon dioxide gas, or an organic chemical foaming agent such as ADCA, DPT, or OBSH that mainly generates N2 gas, or an inorganic chemical foaming agent such as bicarbonate that generates gas such as CO2 upon thermal decomposition. Any foaming component can be used.

[0021] Methods for imparting foamability to molding plastics include using a plastic containing a foaming component as a raw material, or mixing plastic with a foaming agent in an injection molding machine. Examples of plastics containing a foaming agent include plastics impregnated with a physical foaming agent and mixtures of plastic and a foaming agent (chemical foaming agent or microcapsules). The method of mixing plastic with a foaming agent in an injection molding machine can be suitably used when an inert gas is used as the foaming agent. (3) Swallow Mark

[0022] Plastic injection molding can produce surface defects such as sink marks and flow marks. One of these surface defects is swirl marks. When a foaming agent is added to plastic and injection molded, a foaming force equivalent to the volumetric shrinkage is generated inside the molded product, which can prevent sink marks on the surface of the molded product. However, bubbles from the foaming gas escape from the leading edge of the plastic flow and create swirl marks, which are tiny irregularities on the surface of the molded product, causing the surface to become rough. Swirl marks are thus considered a type of surface defect, and various improvements have been attempted to prevent their occurrence.

[0023] In the present invention, we propose to properly control the swirl marks that occur, thereby intentionally forming a large number of minute irregularities on the surface and using these as decorative patterns on the molded product.

[0024] The container of the present invention has a textured display portion on the surface of the plastic molded part, and this textured display portion has fine grooves consisting of numerous swirl marks. More specifically, the textured display portion has a whitened area and a transparent area. The whitened area is an area where the swirl marks are densely distributed and appear white due to diffused reflection of light. The transparent area is an area where the swirl marks are sparsely distributed and light is not diffused and transparency is maintained. The distribution of these whitened areas and transparent areas can give the container a marbled appearance.

[0025] To obtain a container having a textured display portion on its surface according to the present invention, a foaming agent is added in an amount of more than 0.01% but less than 3% by weight of the plastic. Preferably, the foaming agent is added in an amount of 1.3 or more, more preferably 1.5 or more, and preferably 2.5 or less.

[0026] If the amount of foaming agent is too small, it may not be possible to obtain good swirl marks as a decorative pattern, or the transmittance may be too large to produce a marbled appearance, making it difficult to distinguish these from surface defects.On the other hand, if the amount of foaming agent added is 3% or more, there will be too much foaming agent, which will cause the plastic to decompose and result in molding defects.

[0027] In the present invention, factors other than the amount of foaming agent that have a significant effect on the occurrence of swirl marks include the injection speed, secondary injection pressure, and plastic temperature. These factors will have different values ​​depending on the type of plastic and the shape of the molded product, so the specific values ​​are not very versatile, but in the example, the secondary injection pressure is low (normally 400 kgf, but in the example it is 50 kgf), the plastic temperature is high (normally 250 degrees, but in the example it is 270 degrees), and the injection speed is (normally 30 mm / sec, but in the example it is 5 mm / sec). The general trends can be seen as follows: The length of the swirl mark line is closely related to the size of the foam bubbles within the plastic. As the pressure increases, bubbles tend not to grow. When pressure is applied, the plastic softens and the gas (i.e., the bubbles) expand, increasing the size of the bubbles and causing them to grow. The number of swirl marks tends to be proportional to the number of bubbles produced during foaming. Therefore, creating more small bubbles increases the number of swirl marks.

[0028] In terms of temperature and speed, as mentioned above, when the temperature is high, the plastic becomes soft and the gas (i.e., the bubbles) expand, increasing the size of the bubbles and causing them to grow. Therefore, by lowering the temperature, more bubbles can be created.

[0029] If the speed is fast, the mold will be completely filled, and if it is low (the primary pressure has the same pushing-in effect as the secondary pressure), there will be fewer bubbles. If the speed is slow, there will be a tendency for the amount of bubbles to increase. The state of the marks that appear on the surface of the molded product can be summarized as follows, based on the phenomenon:

[0030] [Table 1]

[0031] (A) When the bubbles are large, the length of the swirl mark lines that appear on the surface will also be longer. Also, when there is a lot of foam, the lines of the swirl mark on the surface will overlap in a complex manner, creating a three-dimensional impression. (B) Even if the swirl mark line is long, if there are few swirl marks, the area of ​​the fabric on the surface of the molded product that can be seen will be larger, reducing the visual effect. (C) When the bubbles are small during foaming, the length of the swirl mark lines that appear on the surface will be short. When they become even shorter, the lines will change to dots. When there are many foaming bubbles in this state, the density of the lines will be high, and when the density of the dotted lines is high, the surface will have a matte, pear-skin texture, further widening the range of expression. (D) When the lines are short and the amount is small, the area of ​​the fabric visible on the surface of the molded product is larger, similar to (B), and the difference from the normal state is small. As a result of the above, the desirable state in the present invention is (A) and (C), which allows for maintaining a large amount of bubbles during foaming and creating new expressions by varying the size of the bubbles. That is, firstly, it is desirable to have many bubbles, and secondly, the length of the bubbles can be adjusted. Long bubbles can create interesting lines, while short bubbles can create a matte finish. The molding conditions must be changed depending on the shape of the mold and the plastic used, and can also be changed by changing the amount of foaming agent. [Example]

[0032] Examples are given below to enhance understanding of the present invention, but the present invention should not be understood as being limited to these examples. Manufacturing of the container of the example A cylindrical container with a bottom was molded according to a standard injection molding method. The injection molding machine used was Si180-6 manufactured by Toyo Machinery & Metal Co., Ltd., and molding was carried out under the following conditions. Injection speed: 5mm / sec Secondary injection pressure: 50Kgf Plastic temperature: 270 degrees Plastic: PETG Foaming agent: NaHCO3 Other additives: stearic acid Blending method: Dry (mix when plastic is melted) Shape of molded product: As shown in Figure 1 Table 2 shows examples in which the amount of foaming agent was changed during molding under the above conditions, and the evaluation results.

[0033] [Table 2] Next, the surface condition was evaluated. Surface condition evaluation method

[0034] The front of the molded product (container 1) was photographed, and the image was binarized to separate it into transparent areas without swirl marks and opaque areas with swirl marks. The area ratio of the transparent and opaque areas was then quantified using the binarized data. Table 3 shows the binarized results.

[0035] This container 1 is a plastic container with a mouth 2 and a cylindrical body 3 with a bottom suitable for storing liquid or viscous contents. The mouth 2 and body 3 are molded plastic parts, but the mouth 2, which includes the screw part of the container, is hidden when the lid is on, so it was excluded from this processing, and only the body 3 was processed. Through binarization, transparent parts are displayed as black and opaque parts as white. Image binarization and area digitization can be easily performed using commercially available software such as Adobe Photoshop (registered trademark) or free software such as ImageJ.

[0036] [Table 3] Software used: ImageJ (Version 1.8.0 Developer / Manufacturer: Bharti Airtel Ltd)

[0037] (Marbled texture evaluation) Next, an evaluation of the marble effect was carried out by creating a matrix diagram (see Figure 2). The whitened area (i.e., the opaque area) is an area where the distribution density of the swirl marks is high and the area appears white due to diffuse reflection of light. The transmission area (i.e., the transmission portion) is an area in which the distribution density of the swirl marks is sparse, and light is not diffusely reflected and transparency is maintained, The distribution of the whitened regions and the transparent regions gives the film a marbled appearance.

[0038] In other words, marbled refers to a surface condition in which two or more differently appearing colors, glosses, transparencies, or textures are mixed together in uneven shapes, and the size and density of the shapes are irregularly distributed. This was evaluated using the example shown in the second row of Table 3 (transparent portion: 64%) as an example. (Evaluation method)

[0039] 1) An opaque liquid was poured into the container, and a photograph was taken to prevent reflections from the back side. This photograph was taken by rotating the container in 30 mm increments and taking a photograph of the expanded state of the 30 mm wide part on the front side. 2) The photographs of the unfolded state were binarized and divided into a matrix of 3 mm squares. 3) The numerical value of the whitened area (= the opaque area mentioned above) was entered in each cell of the matrix, and a matrix diagram (see Figure 2) was created in which numerical values ​​above 50% were displayed in black. 4) In Figure 2, check the number of specific cells. If there is one, preferably several, and even more preferably several tens of specific cells, the marbled effect can be enhanced. Here, a specific cell refers to a cell with three adjacent cells in four directions that have different numerical values ​​(cells with different black and white).

[0040] In the matrix diagram in Figure 2, there are multiple specific cells, so it can be evaluated as having a marbled appearance. Note that the matrix diagram in Figure 2 is displayed according to the external shapes of the front, left side, and back of the container 1, and since this is sufficient for evaluating the marbled appearance of the Swirlmark, the right side has been omitted from the illustration.

[0041] (Summary) In the embodiment of the present invention, even when a mold with smooth inner and outer surfaces is used, various Swalmart marble patterns can be imparted to the surface of the container 1, as shown in Figure 3. Therefore, regardless of the surface shape of the mold for the molded product, especially a smooth surface shape, various decorative patterns with fine irregularities can be added to the surface of the plastic molded product to produce a molded product. [Explanation of symbols]

[0042] 1: Container 2: Mouth 3: Torso

Claims

1. A container having a plastic molded part made of plastic and having a storage part for storing an object, A textured display portion is provided on the surface of the plastic molded portion, The plastic container is characterized in that the uneven display portion has minute protrusions consisting of a large number of swirl marks.

2. the relief display portion has a whitened area and a transparent area, The whitened area is an area where the distribution density of the swirl marks is high and the area appears white due to diffuse reflection of light, The transmission area includes a mixture of transmission areas in which the distribution density of the swirl marks is sparse and light is not diffused and transparency is maintained, 2. The container according to claim 1, wherein the distribution of the whitened regions and the transparent regions gives the container a marbled appearance.

3. 3. The container according to claim 2, wherein the whitened area is characterized in that the continuous or discontinuous linear convex portions having a height and width of 0.02 mm or more and 1 mm or less occupy 30% or more of the surface of the plastic molded portion.

4. A method for manufacturing a container, which is manufactured by injection molding, has a plastic molded part made of plastic and has a storage part for storing an object, By molding the plastic molded part under molding conditions that cause swirl marks during foam molding, A method for manufacturing a plastic container, characterized in that a decorative pattern with fine irregularities is formed on the surface of the plastic molded part regardless of the surface condition of the mold used for molding.

5. 5. The method for manufacturing a plastic container according to claim 4, wherein the surface of the mold is smooth.

6. When a plurality of containers are manufactured by applying the container manufacturing method according to claim 4 or 5, A method for manufacturing a plastic container, characterized in that the molding conditions are common to the molding of the plurality of containers.

7. 6. A method for manufacturing a plastic container according to claim 4 or 5, characterized in that a foaming agent for foaming plastic, which has at least one form of gas, powder, granular pellets, and liquid, is blended with the plastic and molded.

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