JP2004268542A - Manufacturing method for thermoplastic resin vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method which enables manufacture with high efficiency of a thermoplastic resin vessel of which the whole, including a flange, has a sufficient heat resistance as occasion demands, in addition to that it is free of a problem in a manufacturing method wherein first a sheet is extruded. <P>SOLUTION: A preform is prepared by injection molding and a flange part of the preform is crystalLized. In a thermoforming process, subsequently, the preform is formed in a forming shape of a female forming tool member heated to a crystallization start temperature or above and a melting point or below, by air-pressure forming and/or vacuum forming, and is also fixed thermally. Then, it is shrunk back for shaping into a forming shape of a plug member and also cooled down. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a cup-shaped thermoplastic resin container that can be conveniently used as a container for food and drink.
[0002]
[Prior art]
As is well known, cup-shaped thermoplastic resin containers having a flange, a cylindrical side wall depending from the inner edge of the flange, and a bottom wall closing the lower end of the side wall are widely used as containers for food and drink. Such containers are generally made by extruding a thermoplastic resin sheet, then heating and softening the sheet to simultaneously compress and / or vacuum form multiple areas of the sheet to the required cup shape and then into the cup shape. The molded part is manufactured by cutting it at a part surrounding it and separating it from the sheet.
[0003]
However, in the manufacturing method as described above, the remaining portion of the sheet (so-called skeleton portion) from which the cup-shaped portion has been cut occupies a considerable portion of the sheet, usually 40 to 60%, and the remaining portion is discarded wastefully. Therefore, the material yield is significantly reduced. The remainder of the sheet is also intended to be melted and reused, but reuse reduces the material quality and to avoid excessive degradation of material quality, reuse is not the entire remainder of the sheet. It must be limited to only a part. When the sheet layer is a multilayer sheet containing an additional layer such as a gas barrier layer together with the main layer, it is practically impossible to reuse the remainder of the sheet. In addition, the thickness of the container strongly depends on the thickness of the sheet, and it is difficult to select an appropriate thickness distribution for the container. Furthermore, for the convenience of the manufacturing process, it is desired that the sheet can be wound in a roll shape, and therefore the thickness of the sheet is limited to, for example, 1.2 mm or less, and thus the thickness of the bottom wall of the container, Therefore, the strength tends to be too low.
[0004]
In Patent Document 1 below, a thermoplastic resin preform (so-called preform) having a thermoforming main portion and a flange portion is formed by injection molding, and then the thermoforming main portion of the pre-formed body is plug-assisted vacuum and A manufacturing method for forming a cup-shaped thermoplastic resin container by pressure forming is disclosed.
[0005]
Further, in Patent Document 2 below, a thermoplastic resin preform having a thermoformed main portion and a flange portion is formed by injection molding, and then the thermoformed main portion of the preform is subjected to matched mold vacuum forming to form a cup. A method of manufacturing a shaped thermoplastic resin container is disclosed. At the time of matched mold vacuum forming, one mold member is heated to a temperature higher than the crystal start temperature, and thus the thermoplastic container formed into a cup shape is heat-set.
[0006]
[Patent Document 1]
JP-A-5-69478 [Patent Document 2]
Japanese Examined Patent Publication No. 7-67737 [0007]
[Problems to be solved by the invention]
In the manufacturing methods disclosed in Patent Document 1 and Patent Document 2, there is no problem as described above in the manufacturing method in which a sheet is first extruded. However, these production methods are still not fully satisfactory and have the following problems to be solved. In the manufacturing method disclosed in Patent Document 1, the thermoplastic resin is not thermally fixed, and therefore the manufactured thermoplastic resin container is inferior in heat resistance. According to the manufacturing method disclosed in Patent Document 2, the heat resistance is improved because the thermoplastic resin is heat-set, but the thermoforming of the thermoforming main part is heated to a temperature higher than the crystallization start temperature. Comparison of the time required for heat setting and the time required for cooling the thermoformed container due to the close fitting of the other mold member with the other mold member having a temperature lower than the crystallization start temperature. Manufacturing efficiency is low.
[0008]
Furthermore, in any of the manufacturing method disclosed in Patent Document 1 and the manufacturing method disclosed in Patent Document 2, the flange of the thermoplastic resin container to be finally molded is subjected to heat treatment. In many cases, the heat resistance of the flange is insufficient.
[0009]
The present invention has been made in view of the above-mentioned facts, and its first technical problem is that it has sufficient heat resistance in addition to the above-described problem in the manufacturing method in which a sheet is first extruded. It is an object of the present invention to provide a new and improved production method capable of producing a thermoplastic resin container with high efficiency.
[0010]
The second technical problem of the present invention is to provide a new and improved production method capable of producing a thermoplastic resin container having sufficient heat resistance in the flange.
[0011]
[Means for Solving the Problems]
As a result of diligent study, the inventors of the present invention formed the preformed body into a molded shape of a female mold member heated to a temperature higher than the crystallization start temperature and lower than the melting point in the thermoforming step, It has been found that the first technical problem described above can be achieved by fixing and then shrinking back to a molded shape of the plug member and shaping and cooling.
[0012]
That is, according to the first aspect of the present invention, as a manufacturing method for achieving the first technical problem, an injection molding step of molding a thermoplastic resin preform by injection molding, and a heat treatment of the preform. In a method for manufacturing a thermoplastic resin container, including a thermoforming step of molding and molding a cup-shaped thermoplastic resin container,
In the thermoforming step, the preformed body is compressed and / or vacuum-molded into a molded shape of a female mold member heated above the crystallization start temperature and below the melting point and heat-set, and then the molded shape of the plug member The manufacturing method is characterized in that it includes shrinking and shaping and cooling.
[0013]
Furthermore, as a result of intensive studies, the present inventors have heated the flange part to a temperature above the glass transition point temperature and below the melting point and pressurized and crystallized, or the flange part of the preform has a temperature above the crystallization start temperature. And it discovered that said 2nd technical subject could be achieved by heating to below melting | fusing point and crystallizing.
[0014]
That is, according to the second aspect of the present invention, as a manufacturing method for achieving the second technical problem, the thermoformed main part in the pre-formed body composed of the thermoformed main part and the flange part is heated. In the method of manufacturing a thermoplastic resin container including a thermoforming step of forming and molding a cup-shaped thermoplastic resin container,
Including a flange crystallization step in which the flange portion is heated to a temperature not lower than the glass transition point and not higher than the melting point and pressurized to be crystallized, or the flange portion is heated not lower than the crystallization start temperature and not higher than the melting point. There is provided a manufacturing method characterized by including a flange crystallization step for crystallizing.
[0015]
In the thermoforming step, prior to pressure forming and / or vacuum forming the preform into the shape of the female mold member, the preform is brought to a temperature above the glass transition temperature and below the crystallization start temperature. Heating is preferred. Preferably, the flange crystallization step is performed after the injection molding step and before the thermoforming step. It is preferable to include a trimming step of trimming the flange portion to a required shape after the thermoforming step. The preform may have a multilayer structure.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, with reference to an accompanying drawing, a suitable embodiment of a manufacturing method of a thermoplastic resin container constituted according to the present invention is described in detail.
[0017]
In a preferred embodiment of the production method according to the present invention, first, an appropriate thermoplastic resin is injection-molded to form a preform 2 in the form shown in FIG. The injection molding mode itself may be a well-known form. The illustrated pre-formed body 2 includes a substantially disk-shaped thermoformed main portion 4 and an annular flange portion 6 positioned around the thermoformed main portion 4. The flange part 6 is comparatively thick, for example, has a thickness of about 1.8 mm.
[0018]
Examples of the thermoplastic resin that can be suitably used for injection molding the preform 2 include, but are not limited to, a polyester resin, a polyolefin resin, a polystyrene resin, a polyamide resin, and the like. A polycarbonate resin can be mentioned.
[0019]
In the production method of the present invention, various polyester resins can be suitably used, and particularly, a polyester resin in which excellent transparency and impact resistance can be obtained by stretching and heat setting acts effectively is desirable. A polyester mainly composed of polyethylene terephthalate, polypropylene terephthalate, and polylactic acid having a glass transition temperature of room temperature or higher and crystallinity can be particularly preferably used. In particular, polyethylene terephthalate in which ethylene terephthalate units occupy 80 mol% or more, particularly 90 mol% or more is preferable from the viewpoint of economy, moldability, and molded article physical properties. As a copolymerization component when such polyethylene terephthalate is used, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like are preferable. Polyethylene terephthalate is most preferred as the thermoplastic polyester resin, but is not limited thereto, polyethylene / butylene terephthalate, polyethylene terephthalate / 2,6-naphthalate, polyethylene terephthalate / isophthalate, and these and polybutylene terephthalate, Polybutylene terephthalate / isophthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate / adipate, polyethylene-2,6-naphthalate / isophthalate, polybutylene terephthalate / adipate, or a blend of two or more thereof. Can be used. Polyester has an intrinsic viscosity [IV] of 0.5 using a phenol / tetrachloroethane mixed solvent as a solvent in terms of preform moldability, moldability in container molding, mechanical properties of the container, and heat resistance. In particular, those in the range of 0.6 to 1.5 are preferable. Polyester can be blended with at least one of ethylene-based polymer, thermoplastic elastomer, polyarylate, polycarbonate and the like as a modified resin component. This modified resin component is generally used in an amount of up to 60 parts by weight, particularly preferably 3 to 20 parts by weight, per 100 parts by weight of polyester.
[0020]
Examples of polyolefin resin include low-medium-high density polyethylene, isotactic polypropylene, syndiotactic polypropylene, propylene-ethylene copolymer, ethylene-vinyl acetate copolymer, ethylenically unsaturated carboxylic acid or anhydride thereof. Examples thereof include olefin resins graft-modified with products.
[0021]
Examples of polycarbonate resins include carbonate resins derived from bicyclic dihydric phenols and phosgene. Bisphenols such as 2,2′-bis (4-hydroxyphenyl) propane (bisphenol A), Polycarbonates derived from 2,2′-bis (4-hydroxyphenyl) butane (bisphenol B), 1,2-bis (4-hydroxyphenyl) ethane and the like are preferred.
[0022]
The thermoplastic resins used in the production method of the present invention include known compounding agents such as antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents, fillers, lubricants, inorganic to organic types. A coloring agent etc. can be mix | blended.
[0023]
The description will be continued with reference to FIG. 2. The preform 2 taken out from the injection molding apparatus (not shown) is heated to a required thermoforming temperature, and then the whole is formed into a thermoforming apparatus denoted by numeral 8. Supplied. In particular, when the preform 2 is obtained in a substantially amorphous state such as a polyester resin, the heating temperature of the preform 2 is not less than the glass transition temperature (Tg) and not more than the crystallization start temperature (Tic). Preferably there is. If the heating temperature is lower than the glass transition temperature (Tg), an excessive force is required for thermoforming. On the other hand, when the crystallization start temperature (Tic) is exceeded, spherulites are formed and transparency tends to be impaired. As for the glass transition temperature (Tg) and crystallization start temperature (Tic) used in the specification, about 10 mg is arbitrarily sampled from the molded article to be measured, and a differential scanning calorimeter (DSC) is used. Based on a DSC curve obtained by holding at 300 ° C. for 3 minutes in a nitrogen gas atmosphere, rapidly cooling to room temperature, and heating at a heating rate of 20 ° C. per minute.
[0024]
The illustrated thermoforming apparatus 8 includes a female mold member 10, a pressurizing / clamping member 12, and a plug member 14. The female mold member 10 is formed with a molding cavity 16 extending downward from the upper surface thereof. The upper part of the inner peripheral surface of the molding cavity 16 has a cylindrical shape, the middle part and the lower part of the inner peripheral surface have an inverted truncated cone shape whose inner diameter is gradually reduced downward, and the bottom surface is a substantially horizontal circular shape. It is. The female mold member 10 is also formed with a communication hole 18 penetrating the bottom wall. The pressurizing / clamping member 12 has an annular shape, and the inner diameter of the opening disposed in the center thereof is substantially the same as the inner diameter of the upper end of the molding cavity 16 in which the female mold member 10 is formed. . The plug member 14 has a columnar upper part and an inverted truncated cone-columnar lower part whose outer diameter is gradually reduced downward. The plug member 14 is formed with a communication hole 20 extending in the axial direction.
[0025]
As shown in FIG. 2, the pre-formed body 2 heated to the required thermoforming temperature is placed on the upper surface of the female mold member 10, and the thermoforming main portion 4 is positioned corresponding to the forming cavity 16. . Thereafter, as shown in FIG. 3, the pressurizing / clamping member 12 is lowered, and the flange portion of the preform 2 is formed between the upper surface of the female mold member 10 and the lower surface of the pressurizing / clamping member 12. 6 is pressurized and tightened. And when giving heat resistance to the flange part 6, the flange part 6 is locally heated to crystallization start temperature (Tic)-below melting | fusing point (Tm), and is crystallized. Further, according to the experience of the present inventors, when the flange portion 6 heated to the glass transition temperature or higher is pressurized with a considerable pressure, for example, a pressure of about 4.5 to 13 MPa, the flange portion 6 is stretched. As a result, the thickness of the flange portion 6 is reduced to about 1/3 to 1/2, for example, and is oriented and crystallized due to the flow of the resin. Further, the flange portion 6 is brought into contact with the upper surface of the female mold member 10 heated to a temperature lower than the crystallization start temperature (Tic) to the melting point (Tm), thereby reducing the molding strain caused by the flow orientation of the resin and heat resistance. Crystallization is performed to provide And the heat resistance and intensity | strength of the flange part 6 are improved by relaxation of this crystallization and a shaping | molding distortion. In order to promote the flow of the resin in the flange portion 6, prior to pressurizing and tightening the flange portion 6, the upper surface and lower surface of the flange portion 6, the lower surface of the pressurizing / clamping member 12, or the female mold member 10. It is preferable to apply an appropriate lubricant such as silicone oil to any one of the upper surfaces. In the illustrated embodiment, when the pressure / clamping member 12 is lowered and the flange part 6 is pressurized / clamped, the flange part 6 is crystallized. 6 is performed, and the crystallization process of the flange portion 6 is performed.
[0026]
Next, thermoforming of the thermoforming main portion 4 of the preform 2 is performed. This thermoforming is carried out in two stages, ie, compressed air and vacuum forming followed by shrink back. In the first stage of the thermoforming process, the plug member 14 is gradually lowered. As understood by comparing and referring to FIGS. 3 and 4, when the plug member 14 is gradually lowered, the thermoforming main portion 4 of the pre-formed body 2 is gradually stretched accordingly. Further, the communication hole 20 of the plug member 14 communicates with a compressed air source (not shown), and the communication hole 18 of the female mold member 10 communicates with a vacuum source (not shown), and thus compressed air. Both the pressure forming by pressure and the vacuum forming by vacuum suction are performed, and the thermoforming main portion 4 of the pre-formed body 2 is formed into a shape corresponding to the forming shape of the female mold member 10, that is, the inner surface of the forming cavity 16. . In the illustrated embodiment, the pressure forming is performed by communicating the communication hole 20 of the plug member 14 with a compressed air source, and the vacuum molding is performed by communicating the communication hole 18 of the female mold member 10 with a vacuum source. However, if desired, only one of pressure forming and vacuum forming can be performed. The compressed air and / or vacuum forming may be started at any time after the plug member 14 starts to descend, at the same time as the plug member 14 descends, or after the plug member 14 finishes descending. At this time, the temperature of the plug member 14 can be arbitrarily set as long as it does not affect the quality of the molded body. For example, when the preform 2 is made of a polyester resin, a range from near room temperature to the crystallization start temperature (Tic) of the thermoplastic resin is preferable. If the temperature is lower than room temperature, condensation may occur on the surface of the plug member 14, and if the crystallization start temperature (Tic) is exceeded, the preform 2 may be partially heated and stretched too much. It is. The draw ratio in compressed air and / or vacuum forming is the ratio to / t1 between the thickness to 1 before processing and the thickness t1 after processing in terms of imparting impact resistance and transparency (change in specific gravity before and after forming is small). In this case, it is preferably 3 or more, particularly 4 to 10). If it is less than 3, stretching is insufficient, so that spherulites are likely to be generated, and this is not preferable in terms of inferior impact resistance and transparency. When the draw ratio exceeds 10, the orientation crystallization becomes too strong, and the pressure air at the time of heat setting to be described later must be made high.
[0027]
In the above-described compressed air and / or vacuum forming, the female mold member 10 is heated by an appropriate heating means (not shown) such as an electric resistance heater, and the inner surface of the molding cavity 16 is crystallized from a thermoplastic resin. It is set to a temperature not lower than the start temperature and not higher than the melting point, for example, about 180 ° C. Accordingly, the thermoformed main portion 4 formed by compressed air and / or vacuum forming is heated and heat-set by being brought into contact with the inner surface of the forming cavity 16 of the female mold member 10 substantially simultaneously with the compressed air and / or vacuum forming. The heat setting temperature is higher than the crystallization start temperature (Tic) of the thermoplastic resin, but is preferably not higher than the melting point (Tm), particularly preferably not higher than the melting point (Tm) −10 ° C. When the heat setting temperature exceeds the melting point (Tm), the thermoforming main part 4 tends to be welded to the female mold member 10.
[0028]
Following compressed air and / or vacuum forming and heat setting, a second stage in the thermoforming process is performed. In this second stage, as shown in FIG. 5, the communication hole 18 of the female mold 10 is communicated with the compressed air source, and the communication hole 20 of the plug member 14 is communicated with the vacuum source. Accordingly, the thermoforming main portion 4 is shrunk back to the molding shape of the plug member 14, that is, the outer shape of the plug member 14, by the compressed air pressurization and the vacuum suction, and is shaped into the final shape, that is, the container 22, and also the plug member. It is cooled by being brought into contact with 14. If desired, the plug member 14 can be actively cooled during shrinkback to facilitate cooling of the container 22.
[0029]
After the container 22 is sufficiently cooled, the container 22 is taken out from the thermoforming device 8. The taken out container 22 has an annular flange 24, a side wall 26 that hangs down from the inner periphery of the flange 24, and a bottom wall 28 that closes the lower end of the side wall 26. Further, in the illustrated embodiment, as shown in FIG. 6, the flange 24 which has been pressure-stretched is trimmed to have a required outer diameter. Trimming of the flange 24 can be accomplished in a known manner.
[0030]
The preferred embodiments of the manufacturing method configured according to the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such embodiments and does not depart from the scope of the present invention. It should be understood that various variations and modifications are possible. For example, in the above-described embodiment, the preform 2 formed from a single thermoplastic resin is injection-molded, and then the preform 2 is thermoformed. If desired, the main thermoplastic resin and the main It is also possible to produce a container by injection molding a preform having a multilayer structure composed of an additional thermoplastic resin wrapped in a thermoplastic resin, and thermoforming the preform. Examples of the additional thermoplastic resin include a resin excellent in gas barrier properties, a recycled resin, an oxygen-absorbing resin, and a moisture-resistant resin.
[0031]
【The invention's effect】
In the first aspect of the present invention, a thermoplastic resin container having sufficient heat resistance can be produced with high efficiency, in addition to no problems in the production method of first extruding a sheet.
[0032]
In the second aspect of the present invention, a thermoplastic resin container having sufficient heat resistance can be manufactured.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a pre-formed body that has been injection-molded.
FIG. 2 is a cross-sectional view showing a state in which a preform is supplied to a thermoforming apparatus.
FIG. 3 is a cross-sectional view showing a manner in which a flange portion of a pre-formed body is stretched under pressure.
FIG. 4 is a cross-sectional view showing a manner in which a main part of a thermoformed main body is compressed and vacuum formed.
FIG. 5 is a cross-sectional view showing a manner of shrinking back a thermoformed main part of a pre-formed body.
FIG. 6 is a cross-sectional view showing a container completed by trimming a flange.
[Explanation of symbols]
2: Pre-formed body 4: Thermoforming main part 6: Flange part 8: Thermoforming apparatus 10: Female mold member 12: Pressure / clamping member 14: Plug member 22: Container

Claims (11)

In a method for producing a thermoplastic resin container comprising an injection molding step of molding a thermoplastic resin preform by injection molding, and a thermoforming step of thermoforming the preform and molding a cup-shaped thermoplastic resin container,
In the thermoforming step, the preformed body is compressed and / or vacuum formed into a molded shape of a female mold member heated above the crystallization start temperature and below the melting point and heat-set, and then the molded shape of the plug member A manufacturing method comprising: shrinking back to form and cooling. In the thermoforming step, prior to pressure forming and / or vacuum forming the preform into the shape of the female mold member, the preform is brought to a temperature above the glass transition temperature and below the crystallization start temperature. The manufacturing method of Claim 1 which heats. The preform is composed of a thermoforming main portion and a flange portion, and includes a flange portion crystallization step in which the flange portion is heated to a temperature not lower than the glass transition temperature and not higher than the melting point, and is stretched under pressure to be crystallized. The manufacturing method of Claim 1 or 2. The said preform is comprised from the thermoforming main part and the flange part, The flange part crystallization process which heats this flange part more than crystallization start temperature and below melting | fusing point is made to crystallize. Or the manufacturing method of 2. The manufacturing method according to claim 3 or 4, wherein the flange crystallization step is performed after the injection molding step and before the thermoforming step. The manufacturing method according to any one of claims 3 to 5, further comprising a trimming step of trimming the flange portion to a required shape after the thermoforming step. In the method for manufacturing a thermoplastic resin container, including a thermoforming step of forming a cup-shaped thermoplastic resin container by thermoforming the thermoformed main part in a pre-formed body composed of a thermoformed main part and a flange part,
A manufacturing method comprising a flange portion crystallization step in which the flange portion is heated to a temperature not lower than the glass transition point and not higher than a melting point, and is stretched under pressure to be crystallized. In the method for manufacturing a thermoplastic resin container, including a thermoforming step of forming a cup-shaped thermoplastic resin container by thermoforming the thermoformed main part in a pre-formed body composed of a thermoformed main part and a flange part,
A manufacturing method comprising a flange portion crystallization step in which the flange portion is heated to a temperature not lower than a crystallization start temperature and not higher than a melting point to be crystallized. 9. The manufacturing method according to claim 7, wherein the flange crystallization step is performed before the thermoforming step. The manufacturing method according to any one of claims 7 to 9, further comprising a trimming step of trimming the flange portion to a required shape after the thermoforming step. The manufacturing method according to claim 1, wherein the preform has a multilayer structure.

Images