JPH043726B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to a unit of a certain volume such as a tape cassette for a video tape recorder, a floppy disk, a video disk, a digital audio disk, a sheet of photosensitive material. This invention relates to a method for manufacturing a thermoplastic resin container suitable for accommodating products such as film, photographic paper, and IC printed boards.

[Prior art]

Thermoplastic resin containers with small volumes such as those mentioned above can be three-dimensionally molded by direct injection molding, but for cases that store items larger than a certain volume, such as tape cassettes for video tape recorders, In some cases, it is impossible to perform three-dimensional molding by direct injection molding, so a method of manufacturing a box from a spread plate is used.

Conventionally, the development plate for such synthetic resin containers is made by extruding a long synthetic resin plate from a T-die, printing it if necessary, and then cutting it into a plate of a certain size. , the part corresponding to the fold (hereinafter referred to as the "key line part") is compressed or cut, the notch part is punched out, and in some cases, the surface is made by foil stamping or embossing. Ta.

However, such conventional manufacturing methods require a large number of man-hours and are inefficient, lack uniformity in the strength of the silicon wire, surface shape, thickness of the developed plate, etc., and have a high incidence of defective products in terms of quality. In addition, because the wires, shaping, and cutting are done forcibly, wire cracks may occur, the surface of the wire grooves may become rough, and the appearance is poor due to debris adhering to the cut surface, resulting in cutting allowances and Since the notch allowance is discarded, there are inconveniences in terms of cost and industrial waste generation. Furthermore, in terms of quality, notches and other punched edges are crushed and cut scraps are generated, which fall off during use, and when storing video cassettes, for example, these adhere to the tape and drop out. (Sound skipping and image disturbance)
It was also impossible to partially change the thickness or create special shapes or fine letters or shapes for differentiation.

In order to overcome the drawbacks of the prior art as described above, one of the inventors of the present invention previously proposed producing a deployable plate for such a synthetic resin container by injection molding. No. 58-26007). In other words, it has been considered difficult to injection mold a deployable plate with a wide area beyond a certain level using resin, and no attempt has been made to do so. It has been found that by doing so, the drawbacks of the prior art as described above can be completely eliminated.

The developed plate formed by the above method has an average thickness of 0.3
~3mm, and has an area of, for example, 30cm x 30cm or more, so if the molten resin is not uniformly and quickly filled into the molding cavity from the gate during pouring,
Parts with different densities of resin occur, causing deformation after molding. Especially when printing on a development plate and heating it to quickly dry it, the deformation becomes severe. Also, flow marks, sink marks, silver streaks, and weld lines occur. , bubbles, burns, and other malfunctions may occur. Therefore, in order to prevent such failures, the position of the gate, the composition of the resin, the type of additives, etc. must be appropriately selected.

As a result of research to further improve the above-mentioned method, the inventor discovered that by manufacturing the expansion plate by in-mold vacuum injection molding, it was possible to create a precise shape that would not cause the above-mentioned failures. Succeeded in making a developing plate extremely quickly (patent application: January 23, 1981).

The inventors of the present invention have found that the method for forming a spread plate using the in-mold vacuum injection molding method described above has the following problems. In other words, after forming a developing plate in a mold, the mold is opened while being held on the movable mold side.
The expansion plate is ejected by protruding an ejector pin provided on the movable mold. In this case, marks from the ejector pins are formed on the molded product, which not only spoils the appearance of the molded product, but also makes it difficult to eject uniformly in the case of flat and relatively large plate-like products such as expansion plates. In this case, ejector pins must be installed in several locations, and care must be taken to ensure that the ejector pins are placed in locations where the puncture marks are not very noticeable. In addition, an ejector plate is required to move the ejector pin, and when the expansion plate has a large area or when molding multiple expansion plates at the same time, an ejector plate with a large area is required, and the injection molding equipment There is a problem with getting bigger.

Furthermore, when performing injection molding using split molds,
After molding, it is necessary to open the mold while holding the molded product on the movable mold side. Generally, for concave molded products,
If the movable mold is made convex, there is no problem because the molded product can be held in the movable mold and opened by the contraction of the molded product itself. In the case of a molded product, there is a problem in that it is difficult to always hold the molded product on the side of the movable mold because the shrinkage effect described above cannot be utilized.

The present inventors conducted further studies to solve the above problems, and as a result, they were able to solve these problems by adopting an air blow system and a gas vent slit, and achieved the present invention.

[Purpose of the invention]

Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide a thermally developed plate that can be manufactured by in-mold vacuum injection molding without forming ejector pin puncture marks. An object of the present invention is to provide a method for manufacturing a container made of plastic resin.

Another object of the present invention is to use a thermoplastic resin that makes it possible to securely hold the molded expansion plate in a movable mold and open the mold when manufacturing the expansion plate by in-mold vacuum injection molding. An object of the present invention is to provide a method for manufacturing containers.

Another object of the present invention is to produce, by injection molding, a developing plate for a thermoplastic resin container that has an almost uniform density and a precise shape, regardless of the position and number of gates, the composition of the resin, etc. An object of the present invention is to provide a method for manufacturing a thermoplastic resin container.

A further object of the present invention is to provide a method for manufacturing a thermoplastic resin container that greatly reduces failures such as flow marks, sink marks, silver streaks, weld lines, bubbles, and burns, and has high iso-impact strength.

The above objects of the present invention are achieved by the present invention described below.

[Structure of the invention]

That is, the present invention provides a method for producing a thermoplastic resin container, which is mainly made of a thermoplastic resin and includes producing a developing plate having a diagonal line portion and a cutout portion by an in-mold vacuum injection molding method, and manufacturing the same into a box. In this method, the mold is composed of a fixed mold and a movable mold, a gas vent slit is provided in the mold in which the cavity for molding the expansion plate is formed, and the expansion plate is kept under negative pressure from the gas vent after molding. Therefore, this method of manufacturing a thermoplastic resin container is characterized in that the mold is opened while the expansion plate is held on the mold side, and then the molded product is ejected by blowing air from the gas vent slit.

Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings.

In the present invention, as shown in FIG.
is manufactured by box-making the expansion plate 2 shown in FIG.

In FIG. 2, the unfolding plate 2 includes a front part 4, a back part 5, a left side part 6, a right side part 7, a bottom part 8, a left side overlapped part 9, a right side overlapped part 10, flaps 11 and 11a, and a case. The thermoplastic resin container 1 as shown in FIG. 1 is formed by forming the wire portion 12 into a box. In FIG. 1, the correspondence of each part of the expansion plate in FIG. 2 is indicated except for the flaps 11, 11a and the highlighted portion 12.

Conventionally, a thermoplastic resin container 1 as shown in FIG.
In the case of a case that stores items over a certain volume, print on a synthetic resin flat plate of a certain thickness extruded into a long length from a T-die in multiple impositions, dry it, and then cut it. After cutting out the notch indicated by the diagonal lines in Fig. 2, shaping it, or punching it out with a diamond wire attached, or making the notch into a rectangular plate with no cutout, the diamond wire portion 12 is compressed and shaped. Or notches 13, 1 formed by cutting and then shaded
4, 15, and 16 are punched, and in some cases, the front part 4, etc. is stamped to create a development plate,
This was made into a box.

According to the present invention, a developing plate 2 as shown in FIG.
is made from the beginning by in-mold vacuum molding into a polygonal shape with a notch and a shape with unevenness on the diagonal line part 12 and, in some cases, on the front part, etc., and if necessary, it is printed on this. After performing the above steps, it is made into a box to create a thermoplastic resin container 1 as shown in FIG.

In the method of the present invention, various thermoplastic resins can be used as the thermoplastic resin used in in-mold vacuum injection molding, but in particular polyolefin thermoplastic resins (including copolymers with other thermoplastic resins) or Polystyrene thermoplastic resin, ABS thermoplastic resin, or a mixed resin of two or more of these thermoplastic resins are used, and various polypropylene resins, especially propylene containing 0.01 to 2 parts by weight of various nucleating agents, are used.
Ethylene random copolymer resin is suitable in terms of cost, printability, manufacturing accuracy, dimensional stability, silicon wire strength, surface strength, rigidity, suitability for injection molding, etc. These thermoplastic resins contain various blowing agents and white pigments (titanium oxide, talc, mica, calcium carbonate,
clay, etc.), various carbon blacks, various colored pigments, various metal powders (aluminum powder, tin powder, aluminum paste, etc.), various metal fibers, various organic or inorganic fibers such as glass fibers, carbon fibers, etc. Various additives such as various coloring dyes, various antistatic agents, various silicones, surfactants, lubricants such as sodium stearate, and antioxidants can be added.

In addition, when performing in-mold vacuum injection molding in the method of the present invention, there is an injection port (gate) for molten thermoplastic resin.
is not limited to one location, but can be provided at multiple locations. By doing so, the flow of the thermoplastic resin improves during injection molding, and it is possible to prevent the occurrence of a boundary line where the flow of the thermoplastic resin joins, which is called a weld line. These injection ports (gates)
In terms of the appearance of the container, and as shown in Figure 3, in a structure in which the diagonal lines are provided only on the surface of the container, X _{1 and} , Y ₂ , X ₃ , Y ₁ , Y ₃ , preferably in the vicinity of horizontally or vertically symmetrical positions where the thermoplastic resin can flow in approximately the same amount of time in all four corners. In particular, if the injection port (gate) for the thermoplastic resin is to be provided at only one location, it is particularly desirable to provide it at the position X ₂ Y ₂ in FIG. Also, if you want to put it in two places, put it in the positions Y ₁ and Y ₃ in Figure 2.

Another example of creating two locations is X ₁ and
It is also desirable to add one at the X ₃ position. There are various known shapes of the resin injection port (gate), which will be described later, but a pin gate is preferred from the viewpoint of leaving no marks on the appearance. Another desirable position for the resin injection port (gate) is when using a side gate, etc., in the notch 1 of the development plate shown in Figure 2.
3, 14, 15, and 16 are desirable, and other desirable locations for using pin gates or other gates include locations where the resin injection port does not appear on the surface after forming the box, for example, the locations shown in Figure 2. The right and left side overlapping portions 9, 10 or flaps 11 of the unfolding plate shown in FIG.
It is desirable to provide at one or more locations on the front and back ends of 11a, preferably in the vicinity of the left and right or vertically symmetrical positions as described above.

In any case, in the present invention, the number of resin injection ports (gates) is determined depending on the shape of the developing plate, the fluidity (melt index) of the thermoplastic resin, the ease of generating gate marks, the ease of generating weld lines, etc. Since the position and shape change, the present invention is not limited to the above description. Resin injection ports (gates) can be placed in any position on the expansion plate, in any number and shape, and are suitable for injection molding and can be formed into a container when molded into a box. It is desirable to prevent the resin from appearing on the surface (visible surface), both from the viewpoint of appearance and the fluidity of the resin.

FIG. 4 is a schematic cross-sectional view showing an example of an apparatus used for in-mold vacuum injection molding according to the present invention. Although this example illustrates a mold having one cavity for molding a development plate, the present invention is not limited to this, and may include a mold in which a plurality of cavities are formed on one side of a fixed mold, There are double-stacked molds in which cavities are formed on both sides of a fixed mold so that molten resin can be supplied to both cavities at the same time from one injection tube, and there are also double-stacked molds in which cavities are formed on both sides of a fixed mold so that molten resin can be supplied to both cavities at the same time. It is possible to use a multi-layer mold that allows the molten resin to be supplied from a cylinder. In either case, the exhaust means described below can be used.

The injection molding apparatus illustrated in FIG. 4 includes a fixed mold consisting of a fixed side mounting plate 21 and a fixed side mold plate 22,
It consists of a movable mold consisting of a movable mold mounting plate 23, a movable mold plate 24, and a core 25.

A bush 26 for supplying molten resin from an injection tube (not shown) is provided on the fixed side mounting plate 21 of the fixed mold, and a runner 27 and 2 are provided on the fixed side mold plate 22.
7a, 27b, and gates 28a, 28b for guiding the molten resin to the cavity 29 for molding the expansion plate.

A suitable number of core inserts 30a, 30b, 30c are arranged on the side of the core 25 of the movable mold facing the fixed mold, and form a cavity 29 for molding a development plate between the core 25 and the mold plate 22. There are as many core inlets as there are areas partitioned by the lines 12 of the expansion plate shown in FIG. 2, and gas vent slits 31 are formed on the contact surface of each core insert (the gas The vent slit 31 extends perpendicularly to the core surface with a gap of approximately 0.01 mm). The gas vent slit 31 opens at the base of the wire-forming protrusion 32, as shown in a partially enlarged sectional view in FIG.

The movable template 24 has a gas vent slit 31.
gas vent holes 33 communicating with the gas vent holes 33 and gas vents and holes 34 connecting each gas vent hole 33 to a vacuum device (e.g., a vacuum pump) are provided, and an outlet 35 of the gas vent hole 34 is configured to Connected to a suitable vacuum device or pressurized gas supply.

Note that 35 is a packing (O-ring) made of an elastic material such as rubber, and is provided to isolate the vacuum system inside the mold from the outside air.

In addition, passages for heat medium and cooling medium are provided in the mold to maintain the mold at an appropriate temperature when supplying molten resin (during injection), and to cool the mold during molding. There is.

When carrying out the present invention using an in-mold vacuum injection molding apparatus as exemplified in FIG. It can be carried out.

Injection control cycle (1) Close the fixed mold and movable mold and start mold clamping. (In this case, the injection tube is attached to the bush 26 of the fixed mold.) (2) Connect the gas vent outlet 35 to a vacuum device and start evacuation of the cavity.

(3) When mold clamping is completed, cavity exhaust is completed,
Injection is performed, and the molten resin is guided from the injection tube through the runner 27 to the cavity 29.

(4) Start cooling the cavity and complete molding.

(5) Start opening the mold with the gas vent hole outlet connected to the vacuum device (move the movable mold. In this case, the molded product is receiving negative pressure from the gas vent slit, so it is held in the movable mold. (6) When the mold opening is completed, switch the gas vent hole outlet 35 from the vacuum device to the pressurized gas supply device, switch the air to the gas supply device, blow air from the gas vent slit, and use the gas blow. to eject the molded product.

(7) Next, start mold clamping and close the gas vent hole exit 35.
Switch from the pressure device to the vacuum device and repeat the above operation.

Since the developing plate of the present invention is manufactured as described above, a homogeneous and precise molded product can be obtained in an extremely short time, and since the molded product is ejected by air blowing, the ejector pin It is possible to obtain a developing plate with a good appearance without producing any puncture marks. Further, since the molded product is kept under negative pressure by the air vent slit, a flat molded product such as a developing plate can be reliably held on the movable mold side when the mold is opened.

In the present invention, a thermoplastic resin container is obtained by box-manufacturing the expandable plate produced as described above. Various printing methods (silk screen printing, offset printing, flexo printing, gravure printing, tampo printing,
Electrostatic transfer printing, hot stamping (= foil stamping),
(transfer printing, inkjet printing, rotating roll printing, etc.) to create a printing layer of one or more colors per type (if necessary, a primer coating or a protective layer to protect the printed surface may be applied to improve printability). After that, it is possible to fix the printing layer to the developing plate by using cold air, hot air, various types of air, infrared irradiation, ultraviolet irradiation, electron irradiation, etc.Assembling a continuous printing line after vacuum injection molding in the mold reduces the production cost, Decrease in inventory,
This is effective in terms of reducing printing man-hours, etc.

When manufacturing a thermoplastic resin container 1 as shown in FIG. 1 by the method of the present invention, it is preferable that the expansion plate 2 as shown in FIG. 2 has a cross-sectional shape as shown in FIG. 3. Plate thickness t is about 0.3mm to 3mm
The average thickness of the developed plate is t.
By thinning the plate by 5% or more, preferably 15% or more, most preferably 30% or more, the printing ink can be rapidly applied to the plate by drying or chemical reaction after printing. Even if it is fixed, there is little warping or twisting, making it easier to form boxes.
In the present invention, the thickness of the developing plate 2, which is an injection molded product, is limited to 0.3 to 3 mm in order to ensure cooling efficiency, prevention of warpage, sink marks, and twisting, and to ensure strength. In order to ensure the fluidity of the thermoplastic resin and at the same time to facilitate box manufacturing, it is necessary to reduce the thickness by at least 5%, preferably at least 15%, and most preferably at least 30% with respect to the plate thickness t. It is necessary to ensure a thickness of 0.1 mm or more.

In addition, although the cross-sectional shape of FIG. 3 shows the case where the C line is formed only on one side of the expansion plate, the C line may be provided at symmetrical positions on both sides depending on the case.

Emboss processing, (texturing) grooves, and unevenness are applied to the front and back surfaces or the outer or inner surfaces of the front section 4, back section 5, left side section 6, right side section 7, bottom section 8, etc. before manufacturing the box. It is also selectively applied to improve the appearance and ease of handling. In conventional manufacturing methods, these were performed by embossing, but in the method of the present invention, these surface treatments can also be performed during in-mold vacuum injection molding.

〔Example〕

Next, in order to further clarify the effects of the present invention, examples are listed below.

(1) A two-stage, four-cavity mold for vacuum injection molding in a spread plate mold as shown in FIG. 6 was used.

FIG. 6 is a schematic diagram showing the mold in an open state, and four development plates can be molded at the same time.
The mold consists of a fixed mold 41 and a movable mold consisting of an intermediate plate 42 and a movable core 43.

The fixed mold 41 includes a sprue bush insertion opening 44 for the intermediate plate, two cavities 45a and 45b for molding the expansion plate, and gas vent holes 46 and gas vent slits 47 for vacuum and air blow as explained in FIG. is provided. These operating mechanisms are as described with respect to FIG. 4, and are coupled by a gas vent outlet 48 to an external vacuum system or pressurized gas supply system according to the injection control pattern described above.

The intermediate plate 42 is provided with a spool bush 49 provided with a spool for molten resin, a manifold 50 for molten resin, and a gate 51.

The movable plate 43 is provided with a developing plate molding cavity 45, a gas vent hole 46, and a gas vent slit 47, similar to the fixed mold 41 (simultaneously). It acts on

During use, the fixed mold and movable mold are closed, the injection tube 52 is set, and the vacuum operation → injection → molding → mold opening →
Four development plates are simultaneously molded using an injection control pattern of gas blow (molded product eject) → opening/closing and vacuum operation.

In addition, in this apparatus, after the first injection molding is completed, molten resin exists in the manifold 50 and is maintained in a molten state, and the next time the vacuum operation is performed, the molten resin passes through the gate 51. At the same time as being supplied to the cavity 47, new molten resin is supplied from the injection tube 52. In this case, gate 51
The diameter of the tube is very small, and when an external exhaust force is applied, molten resin can pass through the tube, but when there is no exhaust force, there is almost no leakage of the molten resin. Furthermore, the gap in gas vent slit 47 is extremely small (as in FIG. 4), allowing air to pass through, but not molten resin supplied to cavity 45 by vacuum operation.

Also in this case, when the mold is opened, the gas vent cavity is connected to the vacuum system, and the back side of the molded product is kept under negative pressure to hold it on the fixed mold 41 and movable core 43 side. There is.

In this case, the mold was designed so that the dimensions of the expansion plate were as follows. The thermoplastic resin injection ports (gates) were located at two locations, Y ₁ and Y ₃ on the inside of the development plate (inner bottom surface in contact with the product) as shown in Figure 2.

Vertical and horizontal dimensions of the expansion plate: The longest part is 247mm x 237mm Thickness of the expansion plate: 0.9mm Dimensions of the lined part: Width 1.5mm, depth 0.25mm Cross-sectional shape of the lined part: As shown in Figure 3 Notch Dimensions of parts 13 and 14: Length approximately 70 mm, width 20 mm Dimensions of cutout parts 15 and 16: Polygon with the longest part being 37 mm x 28 mm (2) Using this mold, molten thermoplastic resin with the following composition was molded. In-mold vacuum injection molding: Polypropylene resin manufactured by Mitsui Petrochemical Co., Ltd. (MI-
40g/10min) ...97.8% by weight Dimethylpolysiloxane manufactured by Shin-Etsu Silicone Co., Ltd.
KF-96 (product name) ...0.1% by weight Titanium oxide ...2% by weight Electroslipper, an antistatic agent manufactured by Kao Soap Co., Ltd.
……0.1% by weight (3) Assemble the injection molded expansion plates and weld the overlapping parts using an ultrasonic welder to determine the approximate dimensions.
A case for a videotape cassette measuring 192mm x 105mm x 28mm was manufactured.

When the number of boxes manufactured is 300,000, the manufacturing cost is reduced to 60% compared to the conventional manufacturing method that includes cutting and punching processes, and the incidence of defective products is 11% compared to the conventional method. In the method of the present invention, it was 1%.

Furthermore, according to the method of the present invention, the molded product does not have any marks at the time of ejecting and has a good appearance, and throughout the entire process, when the mold is opened, the molded product is reliably placed in the core with the cavity formed or in the mold. held to the side. Furthermore, since the present invention uses in-mold vacuum injection molding, it reduces man-hours, lowers manufacturing costs, stabilizes the process, improves quality in terms of appearance, precision, finished surface, etc., and automates work. , significant effects such as reduction of industrial waste can be obtained.

The present invention is not limited to the embodiments, and can be widely applied, for example, as shown below.

(1) The shape of the expansion plate is not symmetrical; for example, the shape of the front part and the shape of the back part may be different.

(2) Even if the thickness of the side part is the same as the remaining thickness of the wire part, the strength can be maintained by overlapping joints.

(3) The shape of the notch can be various shapes such as rectangle, square, trapezoid, semicircle, semiellipse, equilateral triangle, isosceles triangle, and arrow shape.

(4) The remaining thickness of the wire part may be partially thickened to improve the flow of resin during vacuum injection molding within the mold.

(5) The surface of the mold is processed to have a transparent window in one or more places on the development plate, and the product name, company name, picture, etc. are printed on the inside and outside surfaces of the case, and the surface of the mold is treated with silk, sand, rope, etc.
It can have shapes (texturing) such as vertical stripes, horizontal stripes, lattice patterns, and fine-grain surface textures.
More than 210 types of "Bearon Shibo" published by Tokyo Bearon Co., Ltd. are presented as specific grain processing samples.

(6) For injection molding, the thermoplastic resin can be a copolymer or a mixed resin of two or more thermoplastic resins.

(7) Thermoplastic resins contain 1 color pigment or color dye.
A species or multiple species can be added.

(8) After in-mold vacuum injection molding of the development plate, printing and labeling processes can be selectively added before and after the box manufacturing process to add marks and letters.

[Brief explanation of drawings]

Fig. 1 is an external view showing an example of a thermoplastic resin container manufactured according to the present invention, Fig. 2 is a plan view of a developing plate, Fig. 3 is a sectional view of the A-B plane of the developing plate in Fig. 2; FIG. 4 is a schematic sectional view showing an example of an in-mold vacuum injection molding apparatus used in the present invention, and FIG. 5 is a partially enlarged schematic sectional view of a gas vent slit used in an embodiment of the present invention. FIG. 6 is a schematic sectional view of an apparatus used in an embodiment of the present invention. 1...Thermoplastic resin container, 2...Development plate, 12...
Key wire, 13, 14, 15, 16...notch, X ₁ ,
_{X2Y2 , _ _ _} 2
7a, 27b... hot water guide, 28a, 28b... gate,
29...Cavity for forming the expansion plate, 31...Gas vent slit, 32...Protrusion for forming the wire, 3
3, 34...Gas vent hole, 41...Fixed mold, 42
...Intermediate core, 43...Movable core, 45...Cavity for molding expansion plate, 46...Gas vent hole, 47
...Gas vent slit, 50...Manifold for molten resin, 51...Gate.

Claims (1)

[Scope of Claims] 1. A container made of a thermoplastic resin, which is made of a thermoplastic resin and is made by producing a spread plate having a diagonal line part and a cutout part by an in-mold vacuum injection molding method, and then manufacturing the same into a box. In the manufacturing method, the mold is composed of a fixed mold and a movable mold, a gas vent slit is provided in the mold in which a cavity for molding the expansion plate is formed, and after molding, the expansion plate is inserted through the gas vent slit. A method for manufacturing a thermoplastic resin container, which comprises opening the mold while holding it on the mold side by maintaining a negative pressure, and then ejecting the molded product by blowing air through the gas vent slit. 2. The average thickness of the developed plate is 0.3 to 3 mm, and the average thickness of the C line part is 5% or more thinner than the average thickness of the developed plate.
The method for manufacturing a thermoplastic resin container according to claim 1, wherein the average thickness of the wire portion is 0.15 to 1.5 mm.