JP4216404B2 - Propylene resin foamed container and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for producing a propylene-based resin foam container having excellent heat resistance and rigidity, design properties, heat retention properties, and heat insulation properties, and a foam container obtained by the method.
[0002]
[Prior art]
Crystalline polypropylene has advantages such as high mechanical strength, high usable temperature, excellent chemical resistance and electrical insulation, and is useful as a raw material resin for various molded products. However, it was difficult to obtain a foamed product due to the melting characteristics of the resin, and a special foaming agent and a foaming device were required.
[0003]
Also known are methods for producing foamed containers by methods such as thermoforming foamed sheets or forming bubbles during injection molding. In the case of polypropylene, special equipment is required due to the characteristics of the resin. Therefore, it is not popular because of cost.
[0004]
In general, a technique for thermoforming a crystalline plastic at a temperature below its melting point for the purpose of improving transparency and rigidity by stretching is known. However, as in the present invention, a foamed container is formed by thermoforming at a temperature below the melting point. The production method is not known so far. Conventionally, foamed containers are obtained by softening at a temperature equal to or higher than the melting point of the foamed sheet and then thermoformed by vacuum molding or vacuum / pressure forming. Functions such as lowering the foaming ratio and lowering the closed cell ratio There were problems that caused problems in molding such as reduction, perforation during thermoforming, drawdown, generation of wrinkles, and poor shaping.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to suppress productivity problems such as lowering of foaming ratio, lowering of closed cell ratio, and perforation during thermoforming, drawdown, generation of wrinkles, defective shaping, and productivity. Another object of the present invention is to provide a method for producing an excellent polypropylene-based foam container.
[0006]
[Means for Solving the Problems]
The present inventors have found that a foamed sheet containing a propylene-based polymer as a main component can be obtained by vacuum-pressure forming at a specific temperature, pressure pressure, and plug stretching speed to obtain a good foam container. Completed.
[0007]
That is, the present invention relates to a foamed sheet containing a propylene-based polymer as a main component, an air pressure of 1.5 kg / cm ² or more at a melting peak temperature (Tm ° C.) or less measured by a differential calorimeter (DSC) of the sheet. Vacuum-pressure forming at 50 kg / cm ² or less and a plug stretching speed of 250 mm / second or more and 1000 mm / second or less, and preferably the sheet has a melt flow rate (230 ° C., 2.16 kg load) of 0.1 to 20 g / 10 minutes. It is the manufacturing method of the propylene-type resin foam container to be used, and the propylene-type resin foam container obtained by the method.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
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]
The mixing method of each component can utilize a well-known technique as it is. 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 foamed sheet mainly composed of a propylene polymer used in the present invention is 0.1% by a method in which a resin mainly composed of a propylene polymer is used, for example, T-die molding, injection molding, press molding, calendar molding, etc. A sheet having a thickness of 10 mm to 10 mm, preferably a sheet having a thickness of 0.1 mm to 3 mm, which is foamed with a chemical foaming agent, a volatile component, gas, or the like.
The sheet used in the present invention may have a multilayer structure by multilayer coextrusion, lamination, film bonding, sheet bonding, and the like.
[0012]
The melt flow rate at a temperature of 230 ° C. and a load of 2.16 kgf (hereinafter sometimes abbreviated as MFR in the present specification) of a sheet mainly composed of a propylene-based polymer used in the present invention is particularly limited. Although it is not, it is the range of 0.1-20 g / 10min, More preferably, it is the range of 3-10 g / 10min. Outside this range, molding defects such as perforations, wrinkles, and poor shaping during thermoforming are likely to occur.
[0013]
An inorganic filler can also be blended in the foamed sheet mainly composed of the propylene-based polymer according to the present invention. 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, hydroxide Examples include calcium and magnesium hydroxide.
[0014]
The vacuum / pressure forming machine to be used in the present invention is a molding machine of a type that is usually used, and is capable of performing pressure / air vacuum forming by plug assist, and satisfies the following resin temperature, pressure / air pressure, and plug stretching speed. I just need it.
[0015]
The molding temperature at the time of vacuum / pressure forming is required to 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. Molding at a temperature exceeding Tm ° C is likely to cause functional problems such as a reduction in foaming ratio and a decrease in closed-cell ratio, as well as holes in thermoforming, drawdown, generation of wrinkles, molding defects, etc. .
[0016]
The melting peak temperature (Tm ° C.) 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. ℃.
[0017]
The compressed air pressure at the time of molding in the present invention is 1.5 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 1.5 kg / cm ² , the adhesion to the mold is poor, resulting in defects such as product shape defects. On the other hand, at pressures exceeding 50 kg / cm ² , defects such as product perforations, poor shaping due to air leakage, and reduced foaming ratio are likely to occur.
[0018]
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 / second, defects such as shaping defects are likely to occur. On the other hand, when the plug speed exceeds 1000 mm / sec, molding defects such as perforations are likely to occur.
[0019]
Various additives, compounding agents, and the like can be used in the foamed 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, nucleating agents, antifogging agents, flame retardants, lubricants, slip agents, antiblocking agents, Plasticizers, mold release agents, colorants, dyes, pigments, fragrances and the like can be mentioned.
[0020]
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. Here, as the thermoplastic resin, high pressure method low density polyethylene, linear ethylene-α-olefin copolymer, high density polyethylene, polybutene, polyvinyl chloride, polystyrene, acrylic resin, ABS resin, polyamide, polyester, polycarbonate and so on.
[0021]
The polypropylene-based foamed container obtained by the method of the present invention is excellent in heat resistance, cold resistance, heat insulation, heat retention, rigidity, impact resistance, chemical resistance, oil resistance, design, etc., food, beverages, chemicals, etc. It is suitable as a container and packaging material, or for daily necessities and tableware. In particular, it is suitable for microwave oven containers that could not be used with conventional polystyrene foam containers, and is useful as containers or trays for frozen foods, lunch boxes, chilled foods, noodles, and the like. In addition, it is useful as a container and tray for frozen desserts, meat, fresh fish, side dishes, eggs, dairy products, etc. due to its excellent heat retention and heat insulation.
[0022]
【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.). .
[0023]
Example 1
Using a homopolypropylene of MFR 8.0 g / 10 min, adding 2.0 parts of a decomposable foaming agent (manufactured by Eiwa Kasei Co., Ltd., Serpong) to 100 parts by weight of polypropylene, and melt-kneading with a single-screw extruder with a 40 mmφ diameter to give a width of 400 mm Was extruded from a T-die to obtain a sheet-like foam. The sheet MFR was 8.7 g / 10 min, the melting point determined by DSC was 163.5 ° C., and the expansion ratio was 2.1 times. The 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 obtained molded article had a pearly luster and was a good molded article having an expansion ratio of 2.2 times.
[0024]
Example 2
Using a block copolymerized polypropylene having an MFR of 6.5 g / 10 min, a foamed sheet was obtained in the same manner as in Example 1. The MFR of the sheet was 7.3 g / 10 min, the melting point determined by DSC was 162.5 ° C., and the expansion ratio was 2.5 times. 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 154 ° C., a pneumatic pressure of 6 kgf / cm ² , and a plug stretching speed of 700 mm / second . The obtained molded article had a pearly luster and was a good molded article having a foaming ratio of 2.7 times.
[0025]
Comparative Example 1
The foam sheet obtained in Example 1 was vacuum-pressure molded using the same mold at a molding temperature of 168 ° C., a pressure pressure of 6 kgf / cm ² , and a plug stretching speed of 700 mm / second . The obtained molded product was a molded product having a bad appearance with wrinkles and expanded foam cells.
[0026]
Comparative Example 2
The foam sheet obtained in Example 1 was vacuum-pressure molded using the same mold at a molding temperature of 155 ° C., a pressure pressure of 1.2 kgf / cm ² , and a plug stretching speed of 700 mm / second . The obtained molded product was a molded product with poor shape and poor appearance and stackability.
[0027]
Comparative Example 3
The foam sheet obtained in Example 1 was vacuum-pressure molded using the same mold at a molding temperature of 155 ° C., a pneumatic pressure of 6 kgf / cm ² , and a plug stretching speed of 1200 mm / second . The obtained molded product was unevenly thick, and a good molded product was not obtained.
[0028]
Comparative Example 4
The foam sheet obtained in Example 1 was vacuum-pressure molded using the same mold at a molding temperature of 155 ° C., a pressure pressure of 60 kgf / cm ² , and a plug stretching speed of 700 mm / sec . In the obtained molded product, the bubbles collapsed and the expansion ratio decreased to 1.5 times, and the molded product had a poor appearance.
[0029]
Comparative Example 5
The foam sheet obtained in Example 1 was vacuum-pressure molded using the same mold at a molding temperature of 155 ° C., a pneumatic pressure of 6 kgf / cm ² , and a plug stretching speed of 100 mm / second . The obtained molded product had poor shapeability and became a molded product with a poor appearance.

Claims (3)

A foamed sheet containing a propylene-based polymer as a main component is not more than a melting peak temperature (Tm ° C.) measured by a differential calorimeter (DSC) of the sheet, and an air pressure is 1.5 kg / cm ² or more and 50 kg / cm ² or less and A method for producing a propylene-based resin foamed container, characterized by vacuum-pressure forming at a plug stretching speed of 250 mm / second or more and 1000 mm / second or less. The method for producing a propylene-based resin foamed container according to claim 1, wherein the sheet has a melt flow rate (230 ° C, 2.16 kg load) of 0.1 to 20 g / 10 min. A propylene-based resin foamed container obtained by the method according to claim 1.