JP4399022B1 - Method for forming stretched synthetic resin sheet - Google Patents

Abstract

A method of forming a container having a recessed portion using an O-PET sheet or the like is proposed.
A stretched synthetic resin sheet softened by a heating device is disposed on a female mold, and an outer convex surface facing the inner concave surface of the female mold is the same as the concave surface shape of the female mold. A molding method in which a male mold having a convex surface shape is press-fitted into the female mold and the entire surface of the stretched synthetic resin sheet is uniformly pressed by the outer convex surface, and the male mold is elastic It was made to form with a member. In addition, before the step of press-fitting the male mold into the female mold, there may be included a step of bringing the stretched synthetic resin sheet along the inner concave surface of the female mold by a vacuum forming method in advance. And it attached to the surface of the outer side convex part of a male mold so that an elastic member may have a layer of desired thickness to the support member which constitutes a part of a male mold. The stretched synthetic resin sheet is an O-PET sheet, and the elastic member is made of silicon rubber or fluorine rubber.
[Selection] Figure 1

Description

  This invention relates to a method for molding a thermoplastic synthetic resin sheet, particularly a biaxially stretched synthetic resin sheet represented by O-PET, and is in close contact with the inner concave surface of a female mold having an undercut portion. A molding method for obtaining a molded product with high accuracy is proposed.

  Conventionally, various containers molded with a synthetic resin sheet have been used as containers for lunch boxes, sushi, oden and the like sold at convenience stores. This type of container is required to have a hermetic seal between the container body and the lid in order to prevent leakage of liquid components in the contents and drying. Therefore, a recessed groove is provided around one opening periphery of the container body or the lid so as to be fitted and engaged with the other opening periphery. The container body and the lid are securely adhered to each other by the recessed groove, and the sealing performance is ensured.

  As described above, when the concave groove is provided in the container, the portion becomes an undercut portion in the mold, and it is difficult to mold and take out by a normal method. Therefore, methods described in Patent Document 1 and Patent Document 2 have been proposed as a molding method using a mold having an undercut portion. The method described in Patent Document 1 uses a male mold in which an elastic member such as an O-ring that can be extruded in the radial direction is disposed at a position corresponding to a recessed groove (undercut portion) of the container on the molding surface. In the process of molding the heated and softened synthetic resin sheet between the male mold and the female mold, the air cylinder is actuated to lower the moving member and push the elastic member outward, A concave groove is formed on the inner peripheral surface of the slab.

  In addition, the method described in Patent Document 2 is related to the application of the present applicant, but in an apparatus for molding by a vacuum molding method, a plastic sheet in a softened state is vacuum sucked and molded into a desired shape. The main mold is fixed and the auxiliary mold can be separated from the undercut part. It is designed to rise obliquely outward and upward with a slight inclination angle.

  However, since the method described in Patent Document 1 uses an O-ring, there is a problem in durability such as an increase in diameter due to long-term use, and the O-ring has a circular cross section. It is difficult to mold a simple shape, and it may not always be suitable for molding a container that requires high dimensional accuracy.

  In addition, the methods described in the above documents employ a moving member (auxiliary mold) that is operated by an air cylinder for molding the undercut portion, and the configuration is complicated, and the mold is expensive. Challenges remain.

  By the way, as described above, the various containers described above are heated by a synthetic resin sheet to be softened, closely attached to a mold by vacuum suction or the like, and formed into a desired shape, or by a method of compressed air / vacuum forming. Often molded. In this case, as a synthetic resin sheet, a polystyrene (PS) sheet has often been conventionally used. However, in recent years, a container using polyethylene terephthalate (PET) has been proposed, and in particular, a PET sheet having biaxial stretchability ( The use of (O-PET) is being sought.

  The purpose of using the O-PET sheet in this way is that when the O-PET sheet is heated, the force to shrink shrinks and becomes hard, and even if it is thin, even if it is the same molded product, This is because the material cost can be reduced by about 30%. Moreover, it is excellent in transparency and heat resistance, and is optimal as a transparent lid such as a lunch box heated by a microwave oven.

JP-A-8-127062 JP 2001-301018 A

  However, when an O-PET sheet is used, in the conventional molding method, even if the sheet is softened by preheating, the sheet starts to be cured before it is sent to the mold. For this reason, the overall elongation at the time of molding is poor, the adhesion to the concavo-convex portion of the molding die is lowered, and molding that satisfies the required molding accuracy is difficult. In particular, when a container having a concave portion (undercut portion) as described above is molded, it is difficult to mold a container having a highly accurate concave portion because the sheet does not accurately adhere to the undercut portion of the mold. Met. In addition to the undercut portion, the adhesion to a corner portion having a small roundness was also low (see the portion surrounded by a circle in FIG. 4).

The present invention has been invented to solve the above problems, and proposes a new molding method in the case of molding a container having a recessed portion using, for example, a stretched synthetic resin sheet such as an O-PET sheet. To do.

In order to solve the above problems, in the present invention, as a method for forming a stretched synthetic resin sheet, a stretched synthetic resin sheet softened by a heating device is disposed on a female mold, and the inner concave surface of the female mold is arranged. A male mold having a convex surface shape whose opposing outer convex surface is the same as the concave surface shape of the female mold is press-fitted into the female mold, and the entire surface of the stretched synthetic resin sheet is formed by the outer convex surface. The male mold is formed of an elastic member, and the female mold is composed of a fixed mold and a movable mold provided at the peripheral edge of the opening. A means in which a male mold is press-fitted into the female mold and the entire surface of the stretched synthetic resin sheet is pressed uniformly, and then the moving mold is advanced into the inner recess of the female mold to form an undercut portion. Adopted.

Furthermore, after the stretched synthetic resin sheet softened by the heating device is disposed on the female mold, and before the step of press-fitting the male mold into the female mold, the vacuum molding method is used in advance. The means of including the process of making the said stretched synthetic resin sheet along the inner side recessed surface of a female metal mold | die was employ | adopted.

Further , instead of the vacuum forming method, a means of applying a pressure forming method or a pressure / vacuum forming method was adopted.

And with respect to the support member that constitutes a part of the male mold , the male mold has a convex surface shape that is opposite to the inner concave surface of the female mold and has the same shape as the concave surface of the female mold. The means that the elastic member was attached to the surface of the outer convex portion so as to have a layer having a desired thickness was adopted.

Moreover, the means that the said stretched synthetic resin sheet was an O-PET sheet was employ | adopted.

And the means that the said elastic member consists of silicone rubber or fluorine rubber as an elastic material was employ | adopted.

Furthermore, the means that the said elastic member was obtained by inject | pouring and hardening one of the said elastic materials to the said female metal mold | die was employ | adopted.

In the present invention described above, the outer convex surface of the male mold is formed of an elastic member having a convex surface shape that is the same shape as the concave surface shape of the female mold. After softening, the male die is press-fitted, thereby causing the sliding characteristics and elasticity of the elastic member to act and press the entire surface of the sheet evenly. Thus, the sheet can be completely adhered along the inner concave surface of the female mold, and can be molded with high accuracy. Further, the female mold is composed of a fixed mold and a movable mold provided at the peripheral edge of the opening, and the male mold is press-fitted into the female mold so that the entire surface of the stretched synthetic resin sheet is evenly distributed. After pressing, when the moving mold is advanced into the inner recess of the female mold to form an undercut portion, damage due to wear that occurs when the elastic member enters the undercut portion can be prevented, so higher accuracy Thus, it became possible to form a recess.

In addition, since the stretched synthetic resin sheet softened by the heating device is preliminarily fitted into the concave surface shape of the female mold by a vacuum forming method, the male mold is press-fitted, and similarly, the sheet is a female mold. It can adhere | attach completely along the inner side recessed surface, and can shape | mold with high precision.

Further, even if a compressed air forming method or a compressed air / vacuum forming method is applied instead of the vacuum forming method, an equivalent effect can be obtained, and the range of application is expanded.

Since the elastic member is attached to the surface of the outer convex portion of the male mold so as to have a desired thickness, the elastic member is reliably supported by the support member and can be press-fitted. At the same time, since the desired thickness is obtained, the elasticity of the elastic member can be ensured and the pressing force during press-fitting can be maintained.

Further, even when an O-PET sheet is employed as the stretched synthetic resin sheet, unlike the conventional case, it is possible to mold a highly accurate molded product by the above action. By using an O-PET sheet, it is possible to obtain a molded product having the same strength even if it is thinner than before, so that it has become possible to reduce the material cost by about 30%. Furthermore, since the O-PET sheet is excellent in transparency and heat resistance, the O-PET sheet can be widely used for a lunch container that is often heated in a microwave oven.

In addition, when silicon rubber or the like is used as the elastic material, the slip characteristics and elasticity of the elastic member are ensured during press-fitting, and molding along the inner concave surface of the female mold is possible.

Further, since the elastic member is obtained by injecting and curing an elastic material such as silicon rubber into the female die, the convex surface shape of the elastic member is made the same shape as the concave surface shape of the female die. And high accuracy during molding can be maintained.

  Hereinafter, preferred embodiments of a molding method and a molding apparatus of a stretched synthetic resin sheet (for example, a biaxially stretched synthetic resin sheet represented by an O-PET sheet) according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a first embodiment. In FIG. 1, reference numeral 1 denotes a female mold for molding a molded product (for example, a lid) having a desired recessed portion, and the outer shape of the finished molded product. An inner recess 1a having the same inner shape is formed, and an undercut portion 1b having a shape corresponding to a recessed portion that can be fitted and engaged with the opening periphery of the container body to be combined is formed on the opening periphery. 2 is a male mold that is paired with the female mold 1, and the outer convex portion 2 a surface facing the inner concave portion 1 a surface of the female mold 1 has the same shape as the concave surface shape of the female mold 1. It has a convex surface shape, and is attached to an appropriate support member 2b so as to have a layer of the elastic member 2c with a desired thickness on the surface of the outer convex portion 2a.

  The male mold 2 is press-fitted into the female mold 1 at the time of molding (in the direction of the arrow). At the end of the male mold 2, the space provided between both molds is the heat-softened synthetic resin sheet (S) to be molded. ), And the elastic member 2c that is press-fitted presses the entire surface of the synthetic resin sheet (S) that is in close contact with the female mold 1 at the time of molding. However, the present invention is not limited to this, and even if the above-mentioned interval is eliminated (set to zero) and the convex surface shape is exactly the same as the concave surface shape of the female mold 1, it is contracted and rebounded by its elasticity when pressed. Therefore, the same effect can be obtained.

  Further, as the elastic member 2c, a general rubber-like elastic material can be widely used. In this case, since it is necessary to press the female mold 1 so as to be in close contact with the press-fitting, it is preferable that it has a property that is soft but does not easily change its shape, and has elasticity, releasability, and sliding characteristics. From the viewpoint, it is desirable to employ silicon rubber or fluorine rubber.

  The support member 2b to which the elastic member 2c is attached is connected to a cylinder (not shown) and moves the male mold 2 up and down. That is, the gist of the present invention is to form and mold a male mold with a predetermined elastic member 2c. In order to move the male mold 2 up and down, it is supported by a predetermined support member 2b. However, it is necessary to provide the elastic member 2c with elasticity by providing a layer of an elastic member having a predetermined thickness or more with the convex surface shape on the support member 2b. If this thickness is too thin, the elasticity of the elastic member cannot be exhibited. Therefore, a thickness is selected so that at least the elasticity effectively acts on the molding surface.

  Here, first, the manufacturing method of the elastic member 2c will be described by taking as an example the case where silicon rubber is used as the elastic material. First, a female die 1 having a recess 1a having the same inner shape as the outer shape of a lid that is a molding target is prepared. Then, as shown in FIG. 2, a mixture of liquid silicone rubber and a curing agent is injected into this and cured. When this is released, it is possible to obtain an elastic member 2 c having a convex surface shape that is exactly the same as the concave surface shape of the female mold 1. If the elastic member 2c is appropriately attached to the above-described support member 2b so as to have a desired thickness, the male mold 1 is obtained.

  Next, the molding method according to the present invention will be described. In the method of the present invention, the female mold 1 and the male mold 2 having the above-described configuration are used as a pair of molds. In FIG. 1 (A), as in the conventional vacuum forming method, an O-PET sheet (S) that has been heated and softened in advance by a preheating device is placed on the female mold 1, and the surface of the inner recess 1a is removed. The sheet (S) is placed along the surface of the inner recess 1 a of the female mold 1 by creating a vacuum state by suction. At this time, due to the nature of the O-PET sheet, the O-PET sheet does not completely adhere to the inner recess 1a surface of the female mold 1, and a small gap is generated particularly in the undercut portion 1b and the corner portion. Subsequently, the male mold 2 having the elastic member 2 c is press-fitted into the female mold 1, and a pressing force is applied to the entire surface of the sheet (S) by the elastic member 2 c, so that the male mold 2 is firmly attached to the female mold 1. That is, since the elastic member 2c has a convex surface shape that is exactly the same as the concave surface shape of the female mold 1, the entire surface of the elastic member 2c is pressed evenly without damaging the O-PET sheet due to the slip characteristics and elasticity of the surface. However, it can enter the undercut portion 1b and the corner portion, and as shown in FIG. 1 (B), the gap can be eliminated and can be brought into close contact with the inner concave surface of the female mold 1 with high accuracy. And if a sheet | seat is hardened | cured completely after fixed time progress, if a cooling, taking out, etc. are performed by a conventional method, the cover body which has a desired recessed part can be obtained easily.

  In the initial stage, the same action and effect can be obtained by applying a pressure forming method or a pressure / vacuum forming method instead of the vacuum forming method.

  Alternatively, the O-PET sheet (S) heated and softened in the same manner as in the conventional press molding method, omitting the step of causing the sheet (S) to follow the inner recess 1a surface of the female mold 1 by the vacuum forming method. Is placed on the female mold 1, and then the male mold 2 having the elastic member 2c is immediately press-fitted into the female mold 1, and a pressing force is applied to the entire surface of the sheet (S) by the elastic member 2c. You may do it. Also by such a method, the sheet (S) can be securely adhered to the female mold 1.

  Next, FIG. 3 shows a second embodiment. In FIG. 3, reference numeral 11 denotes a female mold for molding a molded product (for example, a lid) having a desired recessed portion. An inner recess 11a having the same inner shape as the outer shape is formed, and an undercut portion 11b having a shape corresponding to a recessed portion that can be fitted and engaged with the opening periphery of the container body to be combined is formed on the opening periphery. ing. The female mold 11 is composed of a fixed mold 11c that forms most of the female mold 11 and a moving mold 11d provided at the peripheral edge of the opening. The moving mold 11d is horizontally (arrow direction) by a cylinder (not shown). And the undercut portion 11b is formed by projecting into the inner concave portion 11a.

  Reference numeral 12 denotes a male mold that is paired with the female mold 11, and the outer convex portion 12 a surface facing the inner concave portion 11 a surface of the female mold 11 is a convex having the same shape as the concave surface shape of the female mold 11. It has a part surface shape, and is attached to an appropriate support member 12b so as to have a layer of the elastic member 12c with a desired thickness on the surface of the outer convex portion 12a.

  The configuration and operation of the male mold 12 are basically the same as those of the male mold 2 shown in the first embodiment described above. The elastic member 12c may be made of silicon rubber or fluorine. It is preferable to employ a system rubber. The manufacturing method is the same, and liquid rubber or the like and a curing agent are injected into a predetermined-shaped female die, cured, and released to release the elastic member 12c. Attach to 12b.

  Next, a molding method when the female mold 11 and the male mold 12 having the above-described configuration are used as a pair of molds will be described with reference to FIG. In FIG. 3 (A), the O-PET sheet (S) heated and softened in advance by the preheating device is placed on the female mold 11 and sucked from the surface of the inner recess 11a, as in the conventional vacuum forming method. Then, the sheet (S) is made to conform to the surface of the inner recess 11a of the female mold 11 by creating a vacuum state. At this time, the moving mold 11d is in the retracted position, and the undercut portion 11b is not formed. In addition, due to the nature of the O-PET sheet, the O-PET sheet is not completely in close contact with the inner recess 11a surface of the female die 11, and a small gap is generated at the corner or the like. Subsequently, the male mold 12 having the elastic member 12 c is press-fitted into the female mold 11, and a pressing force is applied to the entire surface of the sheet (S) by the elastic member 12 c, so that the male mold 12 is in close contact with the female mold 11. That is, since the elastic member 12c has the same convex surface shape as the concave surface shape of the female die 11, the entire surface of the elastic member 12c is pressed evenly without damaging the O-PET sheet due to the slip characteristics and elasticity of the surface. As shown in FIG. 3B, the gap can be eliminated and the female mold can be closely adhered along the surface of the inner recess 11a. When the movable mold 11d is advanced in the direction of the arrow in this state, the movable mold 11d is inserted into the concave portion 12d of the male mold 12 to push the sheet (S), and as shown in FIG. The part 11b is formed. In this case, the pressing force of the moving mold 11d and the elastic force of the elastic member 12c interact with each other, and the sheet (S) is formed along the shape of the undercut portion 11b formed by the advancement of the moving mold 11d. It is possible to form a concave portion with high accuracy by closely adhering without any gap. And if a sheet | seat is fully hardened | cured after progress for a fixed time, if the movable metal mold | die 11d is retracted to the original position and taken out, the cover body which has a desired recessed part can be obtained easily.

  In the initial stage, the same action and effect can be obtained by applying a pressure forming method or a pressure / vacuum forming method instead of the vacuum forming method.

  Alternatively, the O-PET sheet (S) heated and softened in the same manner as in the conventional press molding method, omitting the step of bringing the sheet (S) along the inner recess 11a surface of the female mold 11 by the vacuum forming method. Is placed on the female die 11, and then the male die 12 having the elastic member 12c is immediately press-fitted into the female die 11, and the pressing force is applied to the entire surface of the sheet (S) by the elastic member 12c. Further, the movable mold 11d may be further advanced to be molded. Also by such a method, the sheet (S) can be securely adhered to the female die 11.

  In the case of the above-described first embodiment, as shown in FIG. 2B, when the male mold 2 having the elastic member 2c is press-fitted into the female mold 1, the surface of the elastic member 2c The sheet (S) is evenly pressed by the slip characteristics and elasticity, and enters the undercut portion 1b to form a recessed portion. At this time, if such a molding operation is repeated, the protruding portion corresponding to the undercut portion 1b of the elastic member 2c of the male mold 1 may be gradually worn. If it does so, the precision of formation of the recessed part by the penetration | invasion of the elastic member 2c in this part will fall, and the case where a shaping | molding precision cannot be maintained high arises. On the other hand, according to the second embodiment, since the undercut portion 11b is formed by the advancement of the moving mold 11d, the burden on the elastic member 12c is reduced, and wear of the protruding portion is prevented. It can be done.

  In each of the above embodiments, the case where an O-PET sheet is used has been described as an example. However, the molding method according to the present invention is not limited to an O-PET sheet, and other biaxially stretched synthetic resin sheets, 1 The present invention can be widely applied to axially stretched synthetic resin sheets. However, in particular, when applied to an O-PET sheet, which has been difficult to form conventionally, it is possible to obtain a lid that is thinner and has the same strength as the conventional one, and the material cost can be reduced by about 30%. Is. In addition, since the O-PET sheet is excellent in transparency and heat resistance, the O-PET sheet can be widely used for a lid of a lunch box that is often heated in a microwave oven.

  Furthermore, since the elastic member to be a male mold is produced by pouring silicon rubber into a female mold and curing it, it is possible to produce a male mold that accurately corresponds to the female mold. Recesses can be molded with high accuracy. Therefore, it is a molding method that can be widely applied to the production of lids for various containers that require sealing properties.

It is explanatory sectional drawing of 1st Embodiment of the shaping | molding method of the sheet | seat which concerns on this invention. It is explanatory drawing sectional drawing in the case of manufacturing a silicon | silicone elastic member. It is explanatory sectional drawing of 2nd Embodiment of the shaping | molding method of the sheet | seat based on this invention. It is explanatory sectional drawing which shows the adhesiveness with respect to the metal mold | die of the case in the case of being based on the conventional forming method.

DESCRIPTION OF SYMBOLS 1 Female die 1a Inner recessed part 1b Undercut part 2 Male mold 2a Outer convex part 2b Support member 2c Elastic member 11 Female mold 11a Inner recessed part 11b Undercut part 11c Fixed mold 11d Moving mold 12 Male mold 12a Outside Convex part 12b Support member 12c Elastic member 12d Concave part

Claims (7)

A stretched synthetic resin sheet softened by a heating device is disposed on a female die, and an outer convex surface facing the inner concave surface of the female die is a convex portion having the same shape as the concave surface shape of the female die. A molding method in which a male mold having a surface shape is press-fitted into the female mold and the entire surface of the stretched synthetic resin sheet is uniformly pressed by the outer convex surface, wherein the male mold is formed of an elastic member. The female mold is composed of a fixed mold and a movable mold provided at the peripheral edge of the opening. The male mold is press-fitted into the female mold so that the entire surface of the stretched synthetic resin sheet is evenly distributed. After the pressing, the moving mold is advanced into the inner recess of the female mold to form an undercut portion . The stretched synthetic resin sheet softened by the heating device is disposed on the female mold, and before the step of press-fitting the male mold into the female mold, the stretch is performed in advance by a vacuum molding method. The method for forming a stretched synthetic resin sheet according to claim 1, comprising a step of causing the synthetic resin sheet to lie along the inner concave surface of the female mold. 3. The method for forming a stretched synthetic resin sheet according to claim 2, wherein a compressed air forming method or a compressed air / vacuum forming method is applied instead of the vacuum forming method. The male mold is opposed to the inner concave surface of the female mold of the male mold with respect to the support member constituting a part of the male mold, and is a convex portion having the same shape as the concave surface of the female mold. The method for forming a stretched synthetic resin sheet according to any one of claims 1 to 3, wherein the elastic member is attached to the surface of the outer convex portion having a surface shape so as to have a layer having a desired thickness. . The method for forming a stretched synthetic resin sheet according to any one of claims 1 to 4 , wherein the stretched synthetic resin sheet is an O-PET sheet. The method for molding a stretched synthetic resin sheet according to any one of claims 1 to 5 , wherein the elastic member is made of silicon rubber or fluorine rubber as an elastic material. The method for molding a stretched synthetic resin sheet according to any one of claims 1 to 6 , wherein the elastic member is obtained by injecting and curing any one of the elastic materials into the female mold.

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