JP4275250B2 - Polypropylene-based foamed container and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a polypropylene-based foamed container which is opaque and has a pearly luster, is excellent in heat resistance and rigidity, is excellent in design, heat retention and heat insulation, and a container obtained by the method.
[0002]
[Prior art]
Foamed containers made of thermoplastic resins are excellent in heat resistance, heat retention and the like, and are used for various applications. Among them, crystalline polypropylene has advantages such as higher mechanical strength, higher usable temperature, excellent chemical resistance and electrical insulation, and is opaque without blending pigments and inorganic fillers. It can give a feeling and pearl luster, and has advantages such as hygiene as a food container, manufacturing cost, and recycling and recycling.
[0003]
However, since it is difficult to obtain a foamed product due to its melting characteristics, a polypropylene resin requires a special foaming agent and a foaming device. In addition, a method for thermoforming a foamed sheet or a method for forming bubbles at the time of injection molding is known for producing a foam container, but it also requires a special apparatus and method, and generally from the viewpoint of cost. Not popular.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to economically produce a foamed container having excellent heat resistance and heat retention, and having an opaque feeling and pearly luster, without providing a foaming process such as forming a foamed sheet for polypropylene resin. It is to provide a method of obtaining.
[0005]
[Means for Solving the Problems]
The inventors of the present invention, by subjecting an unfoamed sheet containing a propylene-based polymer as a main component to vacuum-pressure forming at a specific temperature, pressure pressure, and plug stretching speed, achieve a fine without a special foaming step. The present invention has been completed by finding that a foam-molded product having bubbles and generating pearly luster can be obtained.
[0006]
That is, according to the first aspect of the present invention, an unfoamed sheet containing a propylene-based polymer as a main component is below a melting peak temperature (Tm ° C.) measured by a differential calorimeter (DSC) of the sheet, and an air pressure of 3 kg. / cm ² or more 50 kg / cm ² or less and is opaque process for producing a polypropylene-based foamed container having a pearly luster, characterized in that vacuum pressure forming below the plug drawing speed 250 mm / sec 1000 mm / sec.
[0007]
According to a second aspect of the present invention, the non-foamed sheet has a melt flow rate (230 ° C., 2.16 kg load) of 3 g / 10 min or more and less than 20 g / 10 min. It is a manufacturing method of a foaming container.
According to a third aspect of the present invention, the non-foamed sheet contains 1 to 50 parts by weight of an inorganic filler in 100 parts by weight of the resin component, and the melt flow rate (230 ° C., 2.16 kg load) is 1 g / 10 min or more and 20 g / It is a manufacturing method of the polypropylene-type foaming container which has opaque and pearl luster based on the said 1st invention which is less than 10 minutes.
A fourth aspect of the present invention is a polypropylene foam container having an opaque pearly luster obtained by the method of the first or second aspect.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Details of the present invention will be described below.
The propylene polymer used in the present invention is obtained by homopolymerization of propylene or polymerization of propylene and ethylene and / or α-olefin, and the production method is not particularly limited. For example, using a Ziegler-Natta catalyst, it can be produced by single-stage polymerization, multi-stage polymerization, or continuous multi-stage polymerization while controlling the polymerization conditions. Here, examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, and 4-methyl-1-pentene. Two or more kinds of these comonomers can be mixed and used for copolymerization with propylene. The polymerization can be performed by a slurry polymerization method, a gas phase polymerization method, a combination of a slurry polymerization method and a gas phase polymerization method, or the like.
[0009]
In addition, as the propylene-based resin used in the present invention, a mixture obtained by combining two or more components such as single-stage polymer products, single-stage polymer products and multi-stage polymer products, or multi-stage polymer products is also used. be able to.
[0010]
A known technique can be used as it is for mixing each component. For example, there are a method of mixing powders and granulated pellets obtained by polymerization in a batch system such as a mixer or a tumbler, and a method of continuously adding and mixing them to a pneumatic transport device using a measuring device. Melt mixing method is used to increase the degree of mixing, and powder and granulated pellets are melt-mixed with a melt-kneader such as a kneader, roll, brabender, extruder, etc., and pelletized with a granulator There is. Although not particularly limited, an extruder is generally used for improving the productivity in the melt mixing of the propylene-based resin. In particular, a twin-screw extruder having a rotor portion is preferable, and a tandem extruder of a type in which two extruders are connected in series is preferable when those having extremely different molecular weights and melt viscosities are melt-mixed.
[0011]
The sheet mainly composed of the propylene-based polymer used in the present invention is a sheet having a thickness of 0.1 mm to 10 mm, preferably 0.1 mm to 10 mm by a commonly used method such as T-die molding, injection molding, press molding, calendar molding, and the like. The sheet is 3 mm thick and is produced as a virtually unfoamed sheet that is not foamed by a chemical foaming agent, a volatile component, or gas. The sheet used in the present invention may have a multilayer structure by multilayer coextrusion, lamination, film bonding, sheet bonding, and the like.
[0012]
In the present invention, when molding a container suitable for applications that require heat resistance, rigidity, opacity, etc., it is preferable to use a sheet containing one or more inorganic fillers. Here, as the inorganic filler, calcium carbonate, kaolin (aluminum silicate), silica, pearlite, shirasu balloon, sericite, diatomaceous earth, calcium sulfite, calcined alumina, calcium silicate, crystalline zeolite, amorphous zeolite , Talc, mica, magnesium oxysulfate, potassium titanate fiber, fibrous calcium carbonate, glass fiber, clay, hydrated aluminum, hydrated gypsum, barium borate, borax, alumite, basic magnesium carbonate, water Examples thereof include calcium oxide and magnesium hydroxide. The compounding quantity in this case is the range of 1-50 weight part with respect to 100 weight part of resin.
[0013]
It is preferable not to add various nucleating agents to the sheet mainly composed of the propylene polymer according to the present invention. When a nucleating agent is blended, bubbles are less likely to be produced during molding of the container, and there is a possibility that no opacity or pearly luster will be produced or heat retaining properties cannot be expressed.
In addition, some of the inorganic fillers described above are used as nucleating agents, but generally the blending amount expected to have an effect as a filler is the amount blended as a nucleating agent (relative to the resin). Much higher than that of 0.01 to 1% by weight.
[0014]
The sheet used in the present invention has a melt flow rate (hereinafter abbreviated as MFR in the present specification) at a temperature of 230 ° C. and a load of 2.16 kgf, although not particularly limited, but 0.05 g / 10 min to 100 g / The range is 10 minutes, preferably 3 g / 10 minutes to 20 g / 10 minutes. Outside this range, there is a risk that bubbles will not be generated in the container, and cracking may easily occur during molding, resulting in poor productivity.
Even when an inorganic filler is blended, the MFR of the sheet is preferably in the range of 0.05 to 100 g / 10 minutes, more preferably in the range of 1 to 20 g / 10 minutes. Outside this range, the same problem as described above occurs.
[0015]
The vacuum / pressure forming machine used in the present invention is a molding machine of a type that is usually used, and is capable of performing pressure / vacuum forming by plug assist, and satisfies the resin temperature, pressure / air pressure, and plug stretching speed described below. If it is good.
[0016]
The conditions of vacuum / pressure forming are as follows: an unfoamed sheet is at a melting peak temperature (Tm ° C.) or less measured by a differential calorimeter (DSC) of the sheet, and an air pressure is 3 kg / cm ² or more and 50 kg / cm ² or less. It is necessary to carry out at a plug stretching speed of 250 mm / second or more and 1000 mm / second or less.
[0017]
The molding temperature here must be molded at a temperature equal to or lower than the melting peak temperature (Tm ° C.) of the sheet obtained by the following method. Preferably, the molding is performed at (Tm-30) ° C. or more and Tm ° C. or less, more preferably (Tm−15) ° C. or more and Tm ° C. or less. If the molding is performed at a temperature exceeding Tm ° C., the foamed state as seen in the present invention cannot be realized, and the container cannot have an opaque feeling or a pearly luster.
[0018]
The melting peak temperature (Tm) is obtained by a conventional method using a commercially available differential calorimeter (DSC) by cutting 10 mg of a sheet containing a propylene polymer as a main component to prepare a sample. That is, the sample is aged at 230 ° C. for 15 minutes in a nitrogen atmosphere, and then cooled at a temperature decrease rate of 10 ° C./min. After cooling to 20 ° C., it is heated again to 230 ° C. at a rate of 10 ° C./min, and the temperature at which the endothermic curve accompanying melting shows the maximum endothermic value is the melting peak temperature (Tm). . When the differential calorimetric curve accompanying melting shows a plurality of melting peaks or when the melting peaks show a plurality of overlapping shoulder peaks, or in the same way, the temperature at which the endothermic curve shows the maximum endothermic value is similarly expressed as Tm. ℃.
[0019]
The compressed air pressure at the time of molding in the present invention is 3 kg / cm ² or more and 50 kg / cm ² or less, more preferably 5 kg / cm ² or more and 30 kg / cm ² or less. If it is less than 3 kg / cm ² , the adhesion to the mold is poor, resulting in defects such as poor product shape and insufficient bubble formation. On the other hand, when the pressure exceeds 50 kg / cm ² , defective shaping due to perforation of the product or air leakage tends to occur.
[0020]
The plug stretching speed during molding in the present invention is 250 mm / second or more and 1000 mm / second or less, and more preferably 300 mm / second or more and 800 mm / second or less. If the plug speed is less than 250 mm / sec, sufficient bubble formation cannot be obtained, and shaping defects tend to occur. On the other hand, when the plug speed exceeds 1000 mm / sec, molding defects such as perforations are likely to occur.
[0021]
Various additives, compounding agents, and the like can be used for the sheet mainly composed of the propylene-based polymer according to the present invention as long as the characteristics are not impaired. Specific examples include antioxidants, heat stabilizers, UV absorbers, light stabilizers, weathering stabilizers, antistatic agents, antifogging agents, flame retardants, lubricants, slip agents, antiblocking agents, plasticizers, release agents. Examples include molds, colorants, dyes, pigments, and fragrances.
[0022]
Moreover, various thermoplastic resins etc. can be added to the sheet | seat which has the propylene-type polymer which concerns on this invention as a main component. The thermoplastic resin mentioned here includes high-pressure low-density polyethylene, linear ethylene-α-olefin copolymer, high-density polyethylene, polybutene, polyvinyl chloride, polystyrene, acrylic resin, ABS resin, polyamide, polyester, and polycarbonate. and so on.
[0023]
The container having fine bubbles by the propylene-based polymer obtained in the present invention is a container having a pearl luster and a high design property, and is used as a food container, a beverage container, a simple tableware, a packaging tray, a daily miscellaneous goods, a stationery, etc. it can. Further, taking advantage of the excellent cold resistance, heat resistance, and oil resistance of the propylene-based polymer, it is suitable for containers and trays of frozen foods, chilled foods, retort foods, and the like. Further, since it can be adapted to heating by a microwave oven, it is also suitable for containers for instant foods, lunch boxes, noodles and the like.
[0024]
【Example】
Next, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to the following Example.
In this example, the MFR of the sheet was measured according to JIS K6760 under the conditions of a temperature of 230 ° C. and a load of 2.16 kgf, and the melting point by DSC was determined in the same manner as the measurement method of the melting peak temperature (Tm ° C.). .
[0025]
Example 1
A propylene homopolymer of MFR 6.5 g / 10 min was heated and melted with a screw diameter 65 mmΦ extruder, extruded into a sheet from a 900 mm wide T-die, and a 2.0 mm thick sheet was produced by cooling by a touch roll method. The sheet MFR was 7.5 g / 10 min, and the melting point determined by DSC was 163.5 ° C. This sheet was vacuum-pressure molded using a cup-shaped mold having a diameter of 65 mm and a depth of 100 mm at a molding temperature of 155 ° C., a pneumatic pressure of 6 kgf / cm ² , and a plug stretching speed of 700 mm / second . The resulting molded article contained fine bubbles, had a pearly luster, and was opaque.
[0026]
Example 2
30 parts by weight of talc was contained in 100 parts by weight of a propylene homopolymer, and molded in the same manner as in Example 1 to produce an opaque sheet having a thickness of 2 mm. The sheet MFR was 5 g / 10 min, and the melting point determined by DSC was 164.2 ° C. This sheet was subjected to vacuum / pressure forming using the same mold as in Example 1 at a forming temperature of 158 ° C., a compressed air pressure of 6 kgf / cm ² , and a plug stretching speed of 700 mm / second . The obtained molded article contained fine bubbles and exhibited pearly luster.
[0027]
Comparative Example 1
The same propylene homopolymer-based sheet as in Example 1 was vacuum-pressure molded at a molding temperature of 168 ° C., a pneumatic pressure of 6 kgf / cm ² , and a plug stretching speed of 700 mm / second . Drawdown occurred during molding, wrinkles were formed in the product, and fine bubbles were not generated, so that only a translucent container was obtained.
[0028]
Comparative Example 2
The same propylene homopolymer system sheet as in Example 1 was vacuum-pressure molded at a molding temperature of 155 ° C., a pneumatic pressure of 2.8 kgf / cm ² , and a plug stretching speed of 700 mm / second . The obtained molded product was inadequately adhered to the mold and had a poor shape, bubbles were not sufficiently generated, and the appearance was poor.
[0029]
Comparative Example 3
The same propylene homopolymer system sheet as in Example 1 was vacuum-pressure molded at a molding temperature of 155 ° C., a pressure pressure of 6 kgf / cm ² , and a plug speed of 200 mm / second . The obtained molded article did not generate sufficient bubbles and had a poor appearance.

Claims (2)

The main component is a propylene polymer , 1 to 50 parts by weight of an inorganic filler is added to 100 parts by weight of a resin component, and the melt flow rate (230 ° C., 2.16 kg load) is 1 g / 10 min or more and less than 20 g / 10 min. The unfoamed sheet is a melting peak temperature (Tm ° C.) or less measured with a differential calorimeter (DSC) of the sheet, an air pressure of 3 kg / cm ² or more and 50 kg / cm ² or less, and a plug stretching speed of 250 mm / sec. A method for producing an opaque and pearly glossy polypropylene foam container, characterized by vacuum vacuum forming at 1000 mm / second or less.   An opaque, pearly glossy polypropylene foam container obtained by the method according to claim 1.