JPH068314A - Sheet forming preform and container manufacturing method - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the shape of the preform molded by injection molding used for sheet molding in order to improve the strength near the gate of a cup-shaped container used for retort foods and the like. [Composition] A preform for molding a sheet formed by an injection molding method, wherein a curved surface or a staircase having a hem diameter larger than the gate diameter and a gentle surface shape is provided on the surface opposite to the gate position. A protrusion is formed whose thickness gradually decreases from the center of the shape toward the skirt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preform used for forming a sheet of a cup-shaped container used for retort foods, and more particularly to a preform produced by an injection molding method.

[0002]

2. Description of the Related Art Conventionally, metal cans and glass containers have been used as storage containers for foods, but recently, plastic cup-shaped containers have also been used.
In many cases, these plastic cup-shaped containers have a multi-layered structure for protecting the contents, such as laminated sheets and multi-layer disc-shaped preforms such as vacuum forming, pressure forming and plug assist forming. The sheet is formed by the sheet forming method. Generally used preforms are mostly laminated sheets, and there are still few techniques for finalizing the injection-molded preforms according to the present invention, which were finalized in the development stage. The present applicant has proposed, in the specification of Japanese Patent Application No. 3-322495, that the wall thickness of a portion of the preform that greatly extends at the time of molding the container is increased.

[0003]

However, even in Japanese Patent Application No. 3-322494, no consideration was given to the strength in the vicinity of the gate at the time of injection molding of the preform in the container after molding, and for this reason In some cases, due to residual stress near the gate during preform injection molding at the bottom of the container and insufficient strength due to sink marks, the container may be damaged by an external impact force. Further, when molding into a container, if a preform formed by insert molding a sheet is used, it is difficult to uniformly spread as a whole,
There were partially extended portions and almost no extended portions, the impact resistance of the molded container was lowered, and in some cases, the sheet was torn. The present invention provides a container having a strong impact from the outside by improving the surface shape of the preform on the side opposite to the gate position.

[0004]

The first aspect of the present invention is, as shown in FIG. 1, a sheet-forming preform molded by an injection molding method, which is opposite to the position of the gate (11). A protrusion (12) having a diameter of the skirt larger than the gate diameter and a gradually curved surface or step-like shape with a gradually decreasing thickness from the center to the skirt is formed on the surface of A second aspect of the present invention is the sheet-forming preform, wherein the sheet-forming preform is a sheet-forming preform in which a resin layer is laminated on a surface of a sheet material by injection molding. The present invention of the present invention, on the surface of the opposite side of the gate position, the diameter of the skirt is larger than the gate diameter, and the projection whose thickness is gradually reduced from the center of the curved surface or step shape where the surface shape is gentle to the skirt. Preform for forming the formed sheet The sheet-forming preform is formed by the injection molding method, and the sheet-forming preform is placed in a container forming apparatus. Then, a plug corresponding to the protrusion is plug-assisted by a plug formed in the bottom to form a container. A fourth aspect of the present invention is a method for producing a container, wherein the sheet-forming preform is formed by laminating a resin layer on the surface of a sheet material by injection molding.

The above-mentioned sheet forming preform is a preform used in a sheet forming apparatus such as a vacuum forming method, a pressure forming method, and a plug assist forming method for forming a formed product. Thus, the sheet is formed into a shape that can be easily formed during the sheet forming of the main forming.

The gate used for injection molding the preform of the present invention is a direct gate or a center gate.

Further, as shown in FIG. 3, a projection having a gentle curved surface or a staircase means that the height of the projection (12) is the height of the projection (T ₂ ) = coefficient. (K ₁ ) × thickness (T ₁ ) of the preform, and the range of the coefficient (k ₁ ) is 0.
6 to 0.1, preferably 0.5 to 0.2, and the diameter (D ₂ ) of the skirt of the protrusion is such that the gate diameter (D ₁ ) + 2 ≦ the hem of the protrusion. Diameter (D ₂ ) ≦ gate diameter (D
₁ ) +20, preferably gate diameter (D ₁ ) + 5 ≦ diameter of the skirt of the protrusion (D ₂ ) ≦ gate diameter (D ₁ ) +15 (unit: mm).

The material of the preform may be a single layer or a multi-layer. In the case of a multi-layer, if the laminated sheet is mounted in a mold and molded by the insert injection molding method according to the required container characteristics, Also, various kinds of resins may be molded by a multilayer injection molding method.

The method of providing a projection on the surface of the molded product on the opposite side of the gate position to improve the strength in the vicinity of the gate according to the present invention is also applied to a preform for a biaxial stretch blow molding method. May be.

Further, the bottom of the plug used in the plug assist molding method may be provided with a recess corresponding to the projection of the sheet forming preform.

Further, as the resin laminated on the sheet material by injection molding, for example, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, etc. are used.

[0012]

In the sheet forming preform of the present invention, since the diameter of the hem is larger than the gate diameter and the projection is formed in a gentle curved surface or step shape on the surface opposite to the gate position, injection is performed. Residual stress near the gate at the time of molding is relaxed, and cracks due to residual stress are less likely to occur near the gate of the molded preform. In addition, since the protrusions are formed, sink marks (dents) due to molding shrinkage on the surface opposite to the gate position, which was a problem with conventional molded products, are less likely to occur. Since the thickness change near the gate is gradual, it does not become partially thin like the conventional preform, and as a result, the impact resistance strength against external impact near the gate of the molded product is improved. , Improved compared to conventional molded products. Further, when a container is molded by the Bragg assist molding method using a plug having a recess corresponding to the protrusion of the sheet-forming preform on the bottom, the protrusion of the sheet-forming preform and the recess of the plug are Since the preform is stretched in the fitted state, the sheet forming preform is stretched uniformly throughout, and the wall thickness of the molded container does not become partially thin, and the impact resistance of the container Is improved.

[0013]

【Example】

Example 1 FIG. 1 is a partially cutaway perspective view of the sheet-forming preform of the present example, and FIG. 2 is a cup-shaped container manufactured using the sheet-forming preform. 4 is a side cross-sectional view of FIG. 4, and FIG. 4 is a cross-sectional view showing the shape and material near the gate of the sheet-forming preform produced in this example. Next, this embodiment will be described in detail with reference to the drawings.

First, a laminated film for giving a gas barrier property to a container was produced. This is obtained by laminating a 30 μm thick polyvinylidene chloride film on a 25 μm thick biaxially stretched polyethylene terephthalate film with a urethane adhesive by a dry lamination method, and further,
A 30 μm thick unstretched polypropylene film was laminated on the surface of the ethylene / vinyl alcohol copolymer film with a urethane adhesive by a dry lamination method,
A laminated film of a polyethylene terephthalate layer / ethylene / vinyl alcohol copolymer resin layer / polypropylene layer was prepared and punched into a disk shape having a diameter of 108 mm with a punching machine.

Next, in order to manufacture the sheet-forming preform of this embodiment shown in FIG. 4, a disc-shaped laminated film prepared in a mold attached to an injection molding machine was used as a mold with a polyethylene terephthalate layer surface. The cavity surface is attached by suction, and the molten polypropylene resin of the preform base material is injected into the polypropylene layer from the gate and integrally molded with the laminated film to form the shape shown in FIG. 1 with an outer diameter of 108 mm and a thickness of 2.6 mm. Laminated film (24) and substrate (2
A sheet forming preform (20) made of the polypropylene of 3) was produced. Gate diameter at this time (21)
Is 5 mm, and the protrusion (22) provided on the surface of the molded product on the side opposite to the gate has a hem diameter of 24 mm.
The height was 1.27 mm (k ₁ = 0.49), and the cross-sectional shape was a gently curved surface as shown in FIG.

Next, using the produced sheet-forming preform of this example, the outer diameter of the upper end shown in FIG. 2 was 89 by the method for producing a multi-layer thin-walled container described in Japanese Patent Application No. 3-268209. A cup-shaped container having a diameter of 0.3 mm, an outer diameter of the lower end of 60 mm, and a height of 58 mm was produced. Separately from this,
For comparison, a conventional preform was used to prepare a cup-shaped container having the same shape as that of the example.

Then, in order to evaluate the impact resistance in the vicinity of the gate of the two types of cup-shaped containers produced, 200 m of water was used.
1 Fill, cover the container with a metal lid, and open the container opening (42)
The outer flange (43) of the above was wrapped and sealed. After the filled container was stored at 5 ° C, the bottom of the gate (11) at the bottom (41) was continuously vertically dropped from the height of 1 m onto the concrete floor to check the number of cracks. The results are shown in Tables 1 and 2.

[0018]

[Table 1]

[0019]

[Table 2]

From the results shown in Table 2, in the cup-shaped containers using the conventional preform, cracks occurred in the vicinity of the gates of all the containers up to 4 times, but the cups using the preform of this example were cracked. As shown in Table 1, 20
Only one of the books cracked near the gate at the 4th time, but the other containers did not crack at the 5th time.

<Embodiment 2> FIG. 5 is a cross-sectional view showing the shape and material in the vicinity of the gate of the sheet-forming preform produced in this embodiment, and the overall shape is the same as in Embodiment 1. Next, this embodiment will be described in detail with reference to the drawings.

First, in order to produce the sheet-forming preform (30) of this embodiment shown in FIG. 5, a base material (31) was prepared using a multi-layer injection molding machine equipped with three injection devices.
Resin and Adhesive Resin Layer for Forming (34)
The maleic anhydride-modified polyolefin forming the resin and the ethylene / vinyl alcohol copolymer resin of the barrier resin layer (35) are sequentially injected into the mold cavity, and the shape shown in FIG. 1 has an outer diameter of 108 mm and a thickness of 108 mm. A sheet-forming preform (20) of 2.6 mm and 5 layers of three kinds of resin was produced. The gate diameter (31) at this time was 5 mm, and the protrusion (3) provided on the surface of the molded product on the opposite side of the gate position.
2) has an outer diameter of 12 mm and a height of 0.52 mm
At (k ₁ = 0.2), the cross-sectional shape was a gently curved surface, as shown in FIG.

Next, using the produced sheet-forming preform of this embodiment, the outer diameter of the upper end shown in FIG. 2 was 89.3 mm by the same manufacturing method as that of the first embodiment.
A cup-shaped container having an outer diameter of the lower end of 60 mm and a height of 58 mm was produced.

Then, in order to evaluate the impact resistance in the vicinity of the gate of the prepared cup-shaped container, 200 ml of water was filled, the container was covered with a metal lid, and the flange (43) outside the container opening (42) was placed. Tighten and seal, and fill the filled container with 5
After storing at ° C, the bottom (41) of the gate (1
1) The number of cracks in the vicinity was checked. The results are shown in Table 3.

[0025]

[Table 3]

From the results shown in Table 3, it was found that some cup-shaped containers using the preform of this example had cracks in the vicinity of the gate 3 times, 4 times and 5 times. When the state was compared with a cup-shaped container using a conventional preform, it was found that the impact strength was significantly improved.

<Embodiment 3> FIG. 6 is a cross-sectional view of a plug for molding the sheet-forming preform of this embodiment by a plug assist molding method and the multilayer sheet-forming preform used in Embodiment 2. FIG. As shown in FIG. 6, the bottom of the plug has a recess corresponding to the protrusion of the sheet-forming preform.

Next, using the produced sheet-forming preform of this embodiment, the outer diameter of the upper end shown in FIG. 2 was 89.3 mm by the same manufacturing method as that of the first embodiment.
A cup-shaped container having an outer diameter of the lower end of 60 mm and a height of 58 mm was produced.

Then, in order to evaluate the impact resistance in the vicinity of the gate of the prepared cup-shaped container, 200 ml of water was filled, the container was covered with a metal lid, and the flange (43) outside the container opening (42) was placed. Tighten and seal, and fill the filled container with 5
After storing at ° C, the bottom (41) of the gate (1
1) The number of cracks in the vicinity was checked. The results are shown in Table 4.

[0030]

[Table 4]

As can be seen from the results in Table 4, the cup-shaped container formed by using the preform of this embodiment and using the plug provided with the recess corresponding to the projection of the sheet on the bottom is different from that of the second embodiment. It was found that the number of cracks also decreased and the impact resistance was improved.

[0032]

EFFECTS OF THE INVENTION When the sheet-forming preform of the present invention is used, since the diameter of the hem is larger than the gate diameter and the projection is formed in a gentle shape on the surface opposite to the gate position. , The residual stress near the gate during injection molding is relaxed, and cracks due to the residual stress are less likely to occur near the gate of the molded preform, and the surface on the opposite side of the gate position, which was a problem in conventional molded products In addition, there is no shrinkage of molding, and when the preform is formed into a sheet, it does not become partially thin like a conventional preform, and it is resistant to external impact near the gate of the molded product. Impact strength is improved compared to conventional molded products.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an embodiment of a sheet-forming preform according to the present invention.

FIG. 2 is a side sectional view of a cup-shaped container showing an example manufactured using the sheet-forming preform according to the present invention.

FIG. 3 is a cross-sectional view showing the shape near the gate of the sheet-forming preform according to the present invention.

FIG. 4 is a cross-sectional view showing the shape and material near the gate of the sheet-forming preform produced in Example 1.

5 is a cross-sectional view showing the shape and material near the gate of the sheet-forming preform produced in Example 2. FIG.

6 is a cross-sectional view of a plug for molding the sheet-forming preform of Example 3 by a plug-assist molding method and a cross-sectional view of the multilayer sheet-forming preform used in Example 2. FIG.

[Explanation of symbols]

 10, 20, 30 ... Preform 11, 21, 31 ... Gate 12, 22, 32 ... Projection 23, 33 ... Base material 24 ... Laminated sheet 34 ... Adhesive resin 35 ... Barrier resin 40 ... Cup-shaped container 41 ... Bottom 42 ... Opening 43 ... Flange 50 ... Plug 51 ... Recess

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Claims (4)

[Claims] 1. A preform for molding a sheet, which is molded by an injection molding method, the surface of which is opposite to the position of the gate,
A preform for sheet molding, characterized in that a protrusion having a diameter of the hem portion larger than the gate diameter and having a gradually curved surface or a step-like shape having a gradually decreasing thickness from the center toward the hem portion is formed. 2. The sheet-forming preform according to claim 1, wherein the sheet-forming preform is formed by laminating a resin layer on the surface of a sheet material by injection molding. 3. A projection on the surface opposite to the gate position, in which the diameter of the skirt is larger than the gate diameter, and the surface shape is gentle, or the thickness gradually decreases from the center to the skirt. The formed sheet-forming preform is formed by an injection molding method, the sheet-forming preform is placed in a container forming apparatus, and then a plug having a recess corresponding to the protrusion formed on the bottom is used as a plug assist. And then molded into a container. 4. The method for producing a container according to claim 3, wherein the sheet-forming preform is formed by laminating a resin layer on the surface of a sheet material by injection molding.