JP2003320580A - Molding method, mold structure, and molded article of foamed polypropylene resin sheet - Google Patents

Abstract

(57) [Summary] [Problem] In a continuous heating and molding of a foamed polypropylene resin sheet, a mold for suppressing a molding defect due to drawdown and obtaining a molded article with a beautiful appearance and molding using the same mold. Provide a way. SOLUTION: In a mold structure for heating a continuous polypropylene-based resin foam sheet in a heating furnace in which a heater is arranged, and guiding the sheet to a molding die position, at least one side end of the molding die. Is provided with a support member for supporting the foamed sheet.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polypropylene-based resin foam sheet, which is heated in a heating furnace in which a heater is placed, and then introduced to a molding die position and molded by a molding die to form a beautiful appearance. The present invention relates to a molding method for obtaining a body, a mold structure, and a molded body obtained by them.

[0002]

2. Description of the Related Art Conventionally, it has been difficult to form a polypropylene resin into an extruded foam sheet, but recent technological advances have made it possible to obtain a foam sheet. However, when a molded product such as a container, which is the final product, is obtained from a polypropylene-based resin foamed sheet (hereinafter referred to as “PP-based resin foamed sheet”), it is difficult to obtain a good molded product. . This is because the base resin in the PP-based resin foam sheet is a crystalline resin. When the crystalline resin has a melting point or lower, the sheet does not soften sufficiently and is difficult to stretch by molding. Further, when the temperature is higher than the melting point, it is sufficiently softened, but on the contrary, since the melt viscosity is low, the PP-based resin foam sheet itself absorbs heat and loses the foam layer when the temperature is too high. If the PP-based resin foam sheet is molded in this state, a thin portion will be formed in some parts of the molded product, and a good molded product cannot be obtained. For the above reasons, in the PP-based resin foam sheet, the temperature range in which it is softened by heating to a state suitable for its molding is extremely narrow, and it is difficult to obtain a good molded product. JP-A-6-218805 and the like disclose such a method for forming a PP-based resin foam sheet.

However, in the PP-based resin foamed sheet, since the viscosity when melted is low as described above, the phenomenon in which the sheet sags when heated (hereinafter referred to as "drawdown").
Called. ) Can be seen. One cause of drawdown is that when the PP-based resin foam sheet softens, it hangs down due to its own weight. Drawdown causes the following problems when molding a PP-based resin foam sheet.

Usually, when continuously forming a continuous sheet, the sheet is sandwiched by a clamp chain and intermittently transferred by a fixed length to pass a heating step and a forming step. In the molding step, the sheet transferred to a certain mold position is molded by the molding mold. During molding, if the drawdown amount is large, the deformation of the sheet at this part is large, and when the deformed sheet is molded, wrinkles occur in the molded body, the dimensional shape of the molded body changes, and the thin wall portion of the molded body Depending on the occurrence,
The appearance of the obtained molded product may be greatly impaired.

Further, the formed sheet is transferred to a subsequent process such as cutting with a cutter at the rear, or punching the molded body continuously by a punching machine provided at the rear. Therefore, the sheet at the position of the molding die is in a state where one side is not supported, as shown in FIG. Therefore, the above phenomenon tends to appear remarkably in this portion.

The degree of drawdown depends on the characteristics of the polypropylene foam sheet, such as the density, sheet width, and closed cell rate, and it is necessary to find molding conditions that do not cause molding defects due to drawdown during molding. Was difficult.

[0007]

PROBLEM TO BE SOLVED BY THE INVENTION The present invention provides a molding die and a molding method for suppressing a molding defect due to drawdown in a continuous heating molding of a polypropylene-based resin foamed sheet and obtaining a molded body having a beautiful appearance.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors defined a structure of a molding die in molding a PP-based resin foam sheet, thereby forming a molded article having a beautiful appearance. The present invention has been completed and the present invention has been completed.

That is, the present invention relates to a molding die structure used for guiding a continuous polypropylene-based resin foamed sheet to a molding die position after heating it in a heating furnace in which a heater is arranged, and forming a molding die. A molding die structure (claim 1), characterized in that a supporting member for supporting the foamed sheet is provided at least at one side end portion of the mold, and a mold having the molding die structure according to claim 1. A method for molding a polypropylene-based resin foam sheet, which is characterized by being used for molding (claim 2), which is obtained by melt-kneading a polypropylene-based resin as a base resin, a radical polymerization initiator, and an isoprene monomer. 3. A method for molding a polypropylene-based resin foam sheet according to claim 2, wherein a quality polypropylene-based resin is used (claim 3), and the method according to claim 2 or 3. Molded body obtained by the method (claim 4), relates.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of the present invention will be described with reference to the accompanying drawings. The implementation of the present invention is not limited to this.

The present invention is characterized by using a molding die in which a supporting member for supporting the foamed sheet is provided at a side end portion of a molding die used for thermoforming a continuous polypropylene-based resin foamed sheet. The object of the present invention is to provide a molded product having a beautiful appearance without causing defective molding due to drawdown.

2 and 3 are schematic views showing an example of a molding die for carrying out the present invention. In this example, the support member is used for the lower mold of the molding die and is installed at the downstream side in the flow direction of the continuous polypropylene-based resin foam sheet, that is, at a position where the fold wrinkles due to drawdown are noticeable. When the molding die is fitted, the support member contacts the sheet before the die and supports the sheet from before fitting to during fitting.

By supporting the polypropylene resin foam sheet using this support member, the deformation of the sheet due to drawdown is corrected, wrinkles are generated in the molded body, the dimensional shape of the molded body is changed, and the molded body is changed. Suppresses molding defects such as a thin portion.

It is preferable that the sheet supporting member used in the present invention has a mechanism for moving up and down by using an air cylinder or the like, and has a function of closing at the same time as the die fitting. If this up-and-down mechanism is not provided, the support member may break the foamed sheet during mold fitting, causing defective molding. Specifically, a method of providing an air cylinder at the lower part of the support member to the lower mold, operating the air cylinder to raise it, and providing a tool for pressing the support member at the time of fitting the mold to the upper mold are mentioned. To be When this method is used, the support member is closed at the same time as the fitting, so that it is easy to handle without requiring special control in operation.

At this time, it is preferable that the protruding height of the vertical mechanism can be adjusted according to the height of the molded body. If the protruding height is too large, the drawdown may be promoted and the wrinkles may be generated. If the protruding height is too small, the effect of supporting the sheet cannot be obtained.
Further, when the lower die is a male die, if the protruding height is lower than that of the plug, the effect that the plug comes into contact with the seat first and the seat is similarly supported cannot be obtained.

In the practice of the present invention, when the drawdown is large on the entire surface of the sheet, the sheet supporting member may be provided not only on one side which is downstream of the sheet but also on both side surfaces of the mold, or may be provided so as to be surrounded by four sides. good.

Examples of heat molding used in the present invention include plug molding, matched mold molding, straight molding, drape molding, plug assist molding, plug assist reverse draw molding, air slip molding, snapback molding and reverse draw. Examples of the method include molding, free drawing molding, plug and ridge molding, and ridge molding.

The base resin of the polypropylene resin foamed sheet used in the present invention may be, for example, a method of irradiating a linear polypropylene resin with radiation, or a linear polypropylene resin, a radical polymerization initiator, a unit amount. A polypropylene resin containing a branched structure or a high molecular weight component obtained by a method such as melt-mixing the body, or a polypropylene resin having higher rigidity and higher heat resistance by adding a molecular structure and solid structure control technology. Or
A modified polypropylene resin such as a propylene / α, ω-diene copolymer produced by using a metallocene catalyst system and containing a specific amount of α, ω-diene may be mentioned.

Examples of the polypropylene resin used for the modified polypropylene resin include propylene homopolymers, block copolymers and random copolymers, and crystalline polymers. As a propylene copolymer, 75 parts by weight or more of propylene, particularly 90 parts by weight
It is preferable to contain more than one part by weight from the viewpoint of maintaining the crystallinity, rigidity, chemical resistance and the like which are characteristics of polypropylene resins. As the copolymerizable α-olefin, ethylene, butene-1, isobutene, pentene-
1,3-methyl-butene-1, hexene-1, 4-methyl-pentene-1,3,4-dimethyl-butene-1, heptene-1,3-methyl-hexene-1, octene-
1, α-olefin having 2 or 4 to 12 carbon atoms such as decene-1, cyclopentene, norbornene, 1,4
5,8-Dimethano-1,2,3,4,4a, 8,8a-
Cyclic olefins such as 6-octahydronaphthalene, 5
-Methylene-2-norbornene, 5-ethylidene-2-
Norbornene, 1,4-hexadiene, methyl-1,4
-Diene such as hexadiene, 7-methyl-1,6-octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride Examples thereof include one or more kinds of acids, vinyl monomers such as styrene, methylstyrene, vinyltoluene, and divinylbenzene. Of these, ethylene and butene-1 are preferable because they are inexpensive.

As the modified polypropylene resin, a modified polypropylene resin obtained by melting and mixing a linear polypropylene resin, a radical polymerization initiator and a monomer is preferable because it can be produced at a low cost.

As the above-mentioned monomer, for example, styrene monomer, isoprene monomer and 1,3-butadiene monomer are preferable, and these may be used alone or in combination. Among these, the isoprene monomer is particularly preferable because it is inexpensive, easy to handle, and the reaction is likely to proceed uniformly.

The amount of the above-mentioned monomer added is preferably 0.05 to 20 parts by weight, and 0.1 to 10 parts by weight, based on 100 parts by weight of the polypropylene resin, from the viewpoint of reaction efficiency in melt-kneading. preferable.

Monomers copolymerizable with the above monomers, such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, Acrylic acid metal salts, methacrylic acid metal salts, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, acrylic acid esters such as stearyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylic acid 2-ethylhexyl acid, methacrylic acid esters such as stearyl methacrylate, and the like may be used in combination.

The radical polymerization initiator generally includes peroxides and azo compounds. In order for the graft reaction to occur between the polypropylene resin and the monomer (polymer consisting of) or the polypropylene resin,
What has a so-called hydrogen abstraction capability is required, and generally, organic peroxides such as ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxydicarbonate, and peroxyester can be mentioned. . Of these, those having a particularly high hydrogen abstraction ability are preferable, and for example, 1,1-bis (t-butylperoxy)
3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl 4,4-bis (t-butylperoxy) valerate,
Peroxyketals such as 2,2-bis (t-butylperoxy) butane, dicumyl peroxide, 2,5-
Dimethyl-2,5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, Dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, diacyl peroxides such as benzoyl peroxide, t-butylperoxyoctate, t-butylperoxyiso Butyrate, t-butylperoxylaurate, t-butylperoxy 3,5,5-trimethylhexanoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5di (benzoylperoxy) Hexane,
One or more of peroxyesters such as t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate may be used.

The amount of the radical polymerization initiator added is 0.05 to 100 parts by weight of the polypropylene resin.
10 parts by weight, particularly 0.1 to 2 parts by weight is preferable from the viewpoint of preventing the melt viscosity of the modified polypropylene resin from excessively decreasing and being economical.

As a device for reacting the polypropylene resin, the isoprene monomer and the radical polymerization initiator, a kneader such as a roll, a co-kneader, a Banbury mixer, a Brabender, a single screw extruder or a twin screw extruder, A biaxial surface renewing machine, a biaxial multi-disc device or other horizontal type agitator, a double helical ribbon agitator or other vertical type agitator, etc. may be mentioned. Of these, an extruder is particularly preferable in terms of productivity.

The order and method of mixing and kneading (stirring) the polypropylene resin, the isoprene monomer and the radical polymerization initiator are not particularly limited. The polypropylene resin, the isoprene monomer and the radical polymerization initiator may be mixed and then melt-kneaded (stirred), or the polypropylene resin may be melt-kneaded (stirred) and then the isoprene monomer or the radical initiator may be added. You may mix simultaneously or separately. When they are mixed simultaneously or separately, they may be mixed all at once or may be mixed separately. The temperature of the kneading (stirring) machine is preferably 130 to 400 ° C. because the polypropylene resin melts and is not thermally decomposed. The time is generally 1 to 60 minutes.

If necessary, polypropylene resin may be used.
To the extent that the effects of the present invention are not impaired, antioxidants, metal deactivators, phosphorus-based processing stabilizers, UV absorbers, UV stabilizers, optical brighteners, metal soaps, stabilizers such as antacid adsorbents,
Additives such as cross-linking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing materials, pigments, dyes, flame retardants and antistatic agents may be used.

The foamed sheet made of polypropylene resin used in the present invention is prepared by, for example, pressurizing a foaming agent into a melted polypropylene resin and then adjusting the temperature to the optimum foaming temperature in an extruder to obtain a low pressure region from a die. It can be manufactured by extrusion.

As the extruder, a tandem type extruder in which two single-screw extruders are vertically connected, a twin-screw extruder in which a gear pump is attached to the tip, and the like can be used.

In the case of a tandem type extruder, the resin is melted and the molten resin and the foaming agent are kneaded in the first extruder, and in the subsequent extruder, the mixture of the molten resin and the foaming agent is heated to a temperature range suitable for extrusion foaming. The purpose is to cool.

In the case of a twin-screw extruder having a gear pump at the tip, the resin and the foaming agent are mixed more uniformly. Further, when the gear pump is attached, the extrusion pressure and the discharge amount are stable, so that stable extrusion can be realized.
Since melt-kneading and cooling can be performed at the same time, there is also an advantage that space can be saved as compared with a tandem type extruder.

As the cell regulator (foam nucleating agent), an inorganic substance such as a pyrolytic chemical foaming agent or talc can be used as the cell regulator.

The thermal decomposition type chemical foaming agent is classified into an endothermic type chemical foaming agent and an exothermic type chemical foaming agent. There is an endothermic chemical foaming agent alone or in combination with a weak acid. Examples of the inorganic carbon dioxide generator include carbonates or bicarbonates of alkali metals or alkaline earth metals, as well as ammonium carbonate and ammonium bicarbonate. Further, these may be a mixture of two or more kinds.

As weak acids, oxalic acid, malonic acid, maleic acid, fumaric acid, succinic acid, itaconic acid, citraconic acid, adipic acid, formic acid, acetic acid, propionic acid, butyric acid,
Stearic acid, oleic acid, caprylic acid, enanthic acid,
Organic acids such as caproic acid, valeric acid, lactic acid, tartaric acid, citric acid, phthalic acid, benzoic acid, benzenesulfonic acid, toluenesulfonic acid, chloroacetic acid, diglycolic acid, inorganic acids such as boric acid and acidic acids such as potassium potassium tartrate Examples thereof include salts, and citric acid is preferably used from the viewpoint of improving the performance of the chemical foaming agent. The weak acid may be a mixture of two or more kinds. Examples of the exothermic chemical foaming agent include azodicarbonamide, azobisformamide, azobisisobutyronitrile, N, N'-dinitropentatetramine and the like, and azodicarbonamide is preferable from the viewpoint of controlling the decomposition temperature. In addition, when a nitrogen atom-containing bubble control agent is used, there is a coloring problem such that the foamed sheet becomes yellowish.
Among the above-mentioned foam control agents, a combination of sodium bicarbonate and citric acid is preferable.

Although a powdery or masterbatch type air-conditioning agent is available, a masterbatch is preferred from the viewpoint of easy handling.

In the present invention, preferred volatile foaming agents include inorganic gases such as water, carbon dioxide and nitrogen. Two or more of these inorganic gases may be used in combination. In addition, aliphatic hydrocarbons such as propane, butane, isobutane, pentane, hexane, heptane, alicyclic hydrocarbons such as cyclobutane, cyclopentane, cyclohexane, chlorodifluoromethane, dichloromethane, dichlorofluoromethane, dichlorodifluoromethane Halogenated hydrocarbons such as trichlorofluoromethane, chloroethane, dichlorotrifluoroethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, tetrachlorodifluoroethane and perfluorocyclobutane can also be used. Inorganic gas and these aliphatic hydrocarbons, alicyclic hydrocarbons, and halogen-based hydrocarbons may be used in combination.

The amount of the foaming agent added is selected according to the type of the foaming agent and the target expansion ratio, but generally 0.1 to 10 parts by weight is preferable with respect to 100 parts by weight of the resin.

In order to obtain a desired cell structure, the foamed sheet of the present invention may promote surface cooling of the foamed sheet, for example, by blowing air after extrusion foaming, and at the time of mandrel molding. Alternatively, stretching may be performed by changing the take-up speed or the mandrel diameter.

The density of the foamed sheet in the present invention is preferably 0.091 to 0.45 g / cm ³ , and more preferably 0.120 to 0.320 g / cm ³ . When it is less than 0.091 g / cm ^3, the rigidity of the foamed sheet is low, and the rigidity of the molded product of the foamed sheet is also low. The density of the foam sheet is 0.45g / cm ³
If it is larger than the above range, the heat insulation of the molded article is low and the cost is high, which is not preferable.

In the foamed sheet of the present invention, a non-foamed layer made of a thermoplastic resin is formed on one surface or both surfaces of the foamed sheet for the purpose of improving surface properties, rigidity and heat moldability. Good.

As the thermoplastic resin, polystyrene resin, modified polyphenylene ether resin, polyethylene resin, polypropylene resin, polyethylene terephthalate resin, polybutylene terephthalate, polyamide resin, polyarylate resin, polyimide resin, Polyether sulfone resin, polysulfone resin, polyester resin, acrylic resin, polyvinyl chloride resin, polycarbonate resin, etc. can be used. These may be used alone or in combination of two or more, and polypropylene resin is preferable from the viewpoint of adhesiveness to the foamed sheet. The method for forming the non-foamed layer is not particularly limited, and may be formed by forming a foamed sheet and then laminating a separately prepared non-foamed film using heat or an adhesive. Alternatively, a non-foamed film may be directly extruded from a T die onto a sheet and laminated to form a sheet. As the non-foamed film, a biaxially oriented polypropylene resin film is particularly preferable from the viewpoint of rigidity and gloss.

The molded article obtained by the method of the present invention is a cushioning material such as a fruit packaging tray for apples or pears, a food container,
It can be used for applications such as heat insulating materials and automobile members such as automobile ceiling materials.

[0044]

EXAMPLES The present invention will be described below in more detail with reference to specific examples, but the present invention is not limited to these examples.

The sheet support member installed in the lower molding die is
Aluminum was used as the material, and it was formed in the shape as shown in FIG. An air cylinder is provided below the support member, and is lifted upward by injecting air. The protrusion force of the support member can be adjusted by the air pressure of the air cylinder. In addition, the metal mold was provided with a pad made of aluminum at a position above the supporting member so that the supporting member was closed at the same time as the fitting was fitted on the molding die.

The following polypropylene-based resin foam sheets were used in Examples and Comparative Examples.

(Foamed sheet A) A sheet width 1035 was obtained by extrusion-foaming with a tandem extruder using a modified polypropylene obtained by isoprene melt graft modification.
mm, sheet thickness 1.7 mm, sheet density 0.17 g /
A polypropylene-based resin foam sheet having a cm ³ (measured according to JIS-K6767) was obtained.

(Foamed sheet B) Commercially available polypropylene for foaming produced by irradiating an electron beam (P, manufactured by Sun Allomer Co., Ltd.
rofax PF-814) is extruded and foamed by a tandem extruder to obtain a sheet width of 1035 mm, a sheet thickness of 1.6 mm, and a sheet density of 0.18 g / cm ³ (JI
(Measured according to S-K6767), to obtain a polypropylene resin foam sheet.

A continuous molding machine (FLC 415-manufactured by Asano Laboratory Co., Ltd.) is used for continuous heating molding of a polypropylene resin foam sheet.
PB4-C3-S) and the mold size is 21
In a rectangular container having a size of 0 mm × 180 mm × H30 mm, a total of 20 metal molds were used, 4 in the sheet flow direction and 5 in the sheet width direction. For the molding, matched mold molding was performed using the upper mold as a female mold and the lower mold as a male mold.

The appearance of the obtained molded product was evaluated according to the following criteria. ⊚: No wrinkles due to drawdown, and the appearance is extremely beautiful. ◯: No wrinkles due to drawdown and beautiful appearance. Poor: Wrinkles were generated due to drawdown, and there were problems in appearance and practical use.

(Examples 1 and 2) Using the foamed sheet A,
The function of the seat support member is activated to set the upper heater temperature to 3
Molding was performed at 90 ° C. and a lower heater set temperature of 330 ° C. (Claim 1), and the foamed sheet B was similarly molded (Example 2).

Comparative Examples 1 and 2 Using the foamed sheet A,
Molding was performed at an upper heater set temperature of 390 ° C. and a lower heater set temperature of 330 ° C. without activating the function of the sheet supporting member (Comparative Example 1), and similarly performed using the foamed sheet B (Comparative Example 2). did.

The results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1.

[0054]

[Table 1]

[0055]

According to the present invention, it is possible to obtain a molded article having a beautiful appearance by suppressing molding failure due to drawdown in the continuous heating molding of a polypropylene resin foam sheet.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of use of a conventional molding die structure.

FIG. 2 is a schematic view showing an example of use of the molding die structure according to the present invention.

FIG. 3 shows an example of a molding die structure according to the present invention.

[Explanation of symbols]

1 Seat support member 2 Air cylinder 3 Mold 4 Upper heater 5 Lower heater 6 heater shutter 7 Upper mold 8 Lower mold 9 foam sheet

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Claims (4)

[Claims] 1. A molding die structure used for guiding and molding a continuous polypropylene-based resin foam sheet in a molding furnace after heating it in a heating furnace in which a heater is arranged. A molding die structure, wherein a supporting member for supporting a foamed sheet is provided at least at one end. 2. A method for molding a polypropylene-based resin foam sheet, which comprises molding using a mold having a mold structure according to claim 1. 3. The polypropylene according to claim 2, wherein a polypropylene resin, a radical polymerization initiator, and a modified polypropylene resin obtained by melt-kneading an isoprene monomer are used as the base resin. Method for molding resin foam sheet. 4. A molded body obtained by the molding method according to claim 2 or 3.