JP3181077B2 - Method for producing foamed polypropylene resin sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foamed polypropylene resin sheet, and more particularly to a method for producing a foamed polypropylene resin sheet which is capable of being recycled after being formed into a molded product and which is excellent in heat resistance and heat insulation. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, with the spread of microwave ovens and the like, food containers having excellent heat resistance and heat insulation properties, and inexpensive food containers for instant cooked foods, which can be used as they are in microwave ovens, have been developed. Development is desired. BACKGROUND ART Conventionally, foamed polystyrene resin sheets have been widely used as food container materials because of their excellent moldability and low cost.

[0003] However, the foamed polystyrene resin sheet is excellent in heat insulation, but is insufficient in heat resistance and oil resistance for corrosion, so that it is difficult to use it as a material for a food container for a microwave oven, which is required. was there. In order to solve such a drawback, a sheet in which a heat-resistant polyethylene film or polyester film is bonded to a polystyrene resin foam sheet has been used. However, although heat resistance and oil resistance for corrosion are improved by this, there is a drawback that the sheet manufacturing process is complicated and the sheet manufacturing cost is increased.

On the other hand, heat-resistant food containers formed by processing a foamed sheet using a heat-resistant polypropylene resin have also been put to practical use. However, in general, a polypropylene resin has a low viscosity at the time of melting and a low take-off strength. Therefore, when a polypropylene resin is used, it is difficult to continuously produce a foamed sheet by a melt extrusion method.
In particular, when the foaming property of the molten resin composition is increased in order to lower the density of the foamed sheet, the take-off strength is further reduced. Is extremely difficult.

[0005] Therefore, the density of the foamed polypropylene resin sheet continuously produced by the melt extrusion method must be high, and the food container molded from the foamed sheet is required to have a high density.
Generally, the food has heat resistance, but the heat insulation property is insufficient.When foods and the like placed in the container are heated in a microwave oven, the outer wall surface of the container becomes hot immediately. There is a drawback that it is difficult.

Accordingly, polypropylene resins 100 to 9
0 to 100 parts by weight of the styrene resin,
And a styrene-based elastomer containing 10% by weight or more of an olefin component, having a density of 0.1 to 20 parts by weight.
A food container using a polypropylene resin foam sheet having a thickness of up to 0.5 g / ml and a thickness of 5 mm or less has been proposed (for example, Japanese Patent Application Laid-Open No. 1-278439), and has provided good results.

On the other hand, in recent years, it has been desired to recycle plastic, particularly from the viewpoint of resource recycling and environmental protection. However, since the above-mentioned foamed polypropylene resin sheet contains a polystyrene resin, a container formed by molding the same is used. When recycled, there is a disadvantage that it cannot be used as a general recycled polypropylene resin.

[0008]

The inventors of the present invention have conducted intensive studies on a method of manufacturing a foamed polypropylene resin sheet which can solve the above-mentioned drawbacks. As a result, a ring was provided in a circular die of a molten resin extruder. The present inventors have found that good results can be obtained by once dividing into two layers in an extruder, then combining them again, and then extruding them into the atmosphere, and reached the present invention. Therefore, an object of the present invention is to enable recycling as a polypropylene resin,
An object of the present invention is to provide a method for producing a foamed polypropylene resin sheet having excellent heat resistance and heat insulation.

The object of the present invention is to melt-knead a polypropylene resin together with a foaming agent in an extruder and then extrude the melt-kneaded foamable polypropylene resin composition from a circular die into the atmosphere. In the sheet manufacturing method, the melt-kneaded foamable polypropylene-based resin composition was provided in a circular die.
Heating the ring, dividing into two annular layers by the heated ring, combining the two layers again to form an annular single layer, and then extruding from a circular die into the atmosphere, the polypropylene-based resin foam sheet Has been achieved.

[0010] The polypropylene resin used in the present invention is not particularly limited, and can be appropriately selected from commercially available general-purpose polypropylene resins. From the viewpoint of obtaining, a polypropylene resin having an MI (melt index) of 3 to 8 is preferable.

If necessary, an inorganic pigment such as talc, calcium carbonate or titanium oxide, a plasticizer or a stabilizer may be added to such a polypropylene resin.
The foaming agent used in the present invention can be appropriately selected and used from a physical foaming agent of a polypropylene resin or a foaming agent known as a chemical foaming agent.

Specific examples of the physical foaming agent include, for example,
Hydrocarbon compounds such as propane, butane, hexane, heptane, freon-11, freon-12, freon-1
13, fluorochloro-substituted hydrocarbons such as Freon-114 (Freon is a trade name of DuPont),
Examples thereof include halogenated hydrocarbon compounds such as methyl chloride and methylene chloride, and examples of the chemical blowing agent include organic thermal decomposition type blowing agents such as azodicarbonamide, bicarbonate, and bicarbonate. Combinations with organic acids such as citric acid can be mentioned. The above foaming agents can be used alone or in combination of two or more.

Next, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing one example of the manufacturing method of the present invention, and FIG. 2 is a cross-sectional view taken along the line AA ′ shown in FIG. As shown in the figure, a foaming agent and a polypropylene-based resin composition (here, simply referred to as a resin) are extruded (not shown).
After being melted and kneaded by being deployed to the annular layer by a mandrel 4 of the circular die (hereinafter referred to as die) 1, further ring is heated is provided in the resin flow passage 5 2
Into two annular layers.

[0014] At this time, since the are heated ring 2, the higher temperature of the resin in the vicinity of the contact with the surface of the ring 2, the resin of the viscosity of the resin on the other element in the vicinity of the contact with the ring second surface Lower than the viscosity. Therefore, foaming is promoted in the resin portion having a reduced viscosity due to contact with the ring 2 than in other resin portions having a high viscosity, so that a resin layer having a low density is formed.

After passing through the ring 2, the resin is united, again formed into one annular layer, extruded from the die orifice 6 into the atmosphere, and formed into a tube to form a resin tube 7. Therefore, the tube 7, pick-up property becomes good tube the viscosity table (Table) plane layer and back layer is higher than the middle tier.

In particular, when the resin is extruded from the die orifice 6 in the direction of gravity and blow-up to form a resin tube 7, which is hung on a plug 10 and taken up in a sheet tube shape, Since the resin tube does not sag compared to the case of extruding into
There is no partial stagnation on the upper surface of the plug, and it is easy to continuously pull it out in a sheet tube shape.

From the viewpoint of increasing the density of the front and back layers of the resin tube to increase the strength of the resin foam sheet,
It is preferable to provide the outer cooling air ring 8 and the inner cooling air ring 9 in the blow-up step, and rapidly cool the front and back surfaces of the resin tube by air.

In the present invention, the resin is extruded at a density of 0.1 to 0.1 by controlling the resin extrusion temperature, ring temperature, amount of foaming agent, resin tube take-up speed, and cooling conditions using air.
Polypropylene resin foam sheet in the range of 5 g / ml and thickness of 1 to 3 mm (hereinafter referred to as resin foam sheet)
It is preferred to produce

When the density of the resin foam sheet is 0.1 g / ml or less, not only the strength of a molded product using the sheet is inferior, but also the appearance of the surface becomes poor, and 0.5 g / ml.
If the above is set, the heat insulating property of the molded product is deteriorated, and neither is preferable. The thickness of the resin foam sheet is 3 mm
When the above is set, the heat capacity of the sheet becomes large, and a long time is required for the thermoforming, so that the forming efficiency is lowered. When the thickness is 1 mm or less, the strength of the formed product is insufficient, and neither is preferable.

[0020]

As described in detail above, according to the production method of the present invention, the heating ring provided in the circular die can strongly maintain the take-up strength of the foamed polypropylene resin sheet, and can be used as a molded product. The density of the resin foam sheet can be reduced. Therefore, it is possible to continuously produce a polypropylene resin foam sheet that is recyclable and excellent in heat resistance and heat insulation without adding a polystyrene resin or the like as in the related art.

When the polypropylene-based resin composition is extruded from the die in the direction of gravity, blow-up and taken up while being hung on a plug, and formed into a sheet tube, sagging due to gravity, cutting, or partial cutting may occur. Therefore, the seat tube can be manufactured particularly favorably.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

Embodiment 1 FIG. To 100 parts by weight of a polypropylene resin (MI is 5.5), 1 part by weight of fine powder talc was added and dispersed as a cell regulator. The obtained propylene-based resin composition was charged into a 45 mmΦ extruder heated to 230 ° C. and melt-kneaded. Next, 13 parts by weight of butane as a foaming agent was press-mixed into the obtained melt-kneaded product from an injection port provided in the middle of the extruder, and mixed.

The obtained molten mixture of the blowing agent is supplied to an extruder having a diameter of 65 mm, the temperature of the mixture is adjusted to 170 ° C., and then the mixture is passed through a resin flow path 5 in a die 1 provided at the tip of the extruder. After being guided and passed between the rings 2 provided so as to divide the resin flow path 5, it was extruded into the atmosphere in the direction of gravity from an annular orifice 6 having a diameter of 90 mm to form a tube.

Air at 20 ° C. is blown from the inner cooling air ring 9 and the outer cooling air ring 8 onto the front and back surfaces of the extruded resin tube 7 to rapidly cool the resin tube 7 and then blow up to form a sheet tube. Then, the inside of the sheet tube was hung on the end of a plug having a diameter of 204 mm and pulled off to prepare a polypropylene resin foam sheet having a thickness of 1.4 mm, a density of 0.3 g / ml, and a width of 640 mm.

Using the resin foamed sheet of the present invention thus obtained, a container having a major axis of 173 mm, a minor axis of 120 mm, a depth of 30 mm and an elliptical cross section as shown in FIG. ) Was molded. Using the obtained container, a practical handling test of the following container was performed, and the resin foam sheet was evaluated.

As a model food, 200 ml of a liquid obtained by diluting curry (Jawa Curry: trade name of House Foods Industry Co., Ltd.) 10 times with water was put into a microwave oven (MOR).
-A80: Inserted in Hitachi Heat Instruments Co., Ltd.) and heated for 15 minutes. Immediately after the heating, the container was taken out with bare hands. As a result, the container was not heated and no deformation or deterioration of the container was observed.

Comparative Example 1 Except that the ring in the die 1 was removed, the thickness was 1.4 mm and the width was 6
When a polypropylene resin foam sheet of 40 mm was produced, the density was 0.6 g / ml. Using the obtained resin foam sheet, a container was formed in exactly the same manner as in Example 1. Using the obtained container, a practical handling test was performed in exactly the same manner as in Example 1. As a result, the container wall was hot and could not be taken out of the microwave oven with bare hands.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view taken along line A-A 'of FIG.

FIG. 3 is a perspective view of a container formed using a resin foam sheet manufactured in Examples and Comparative Examples.

[Description of Signs] 1 die 2 ring 3 heating mechanism 4 mandrel 5 resin flow path 6 die orifice 7 resin tube 8 outer cooling air ring 9 inner cooling air ring 10 plug 11 air exhaust pipe 12 cavity

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-14470 (JP, A) JP-A 1-278539 (JP, A) JP-A 2-84314 (JP, A) (58) Investigation Field (Int. Cl. ⁷ , DB name) B29C 47/00-47/96

Claims (3)

(57) [Claims] 1. A method for producing a foamed polypropylene resin sheet, comprising: melt-kneading a polypropylene-based resin together with a foaming agent in an extruder; and extruding the melt-kneaded foamable polypropylene-based resin composition from a circular die into the atmosphere. The melt-kneaded foamable polypropylene resin composition is heated by heating a ring provided in a circular die.
A method for producing a foamed polypropylene resin sheet, comprising dividing into two annular layers by a heated ring, combining the two layers again into one annular layer, and then extruding the same from a circular die into the atmosphere. 2. A foamable polypropylene tree melt-kneaded.
The fat composition is blown from the circular die in the direction of gravity.
While extruding into a tube while
Claims that we take over while putting hive on plug
Item 1. A method for producing a foamed polypropylene resin sheet according to item 1.
Law. 3. A foamed polypropylene resin sheet obtained.
The density is 0.1 to 0.5 g / ml and the thickness is 1 to 3
3. The method according to claim 1, wherein the molding conditions are controlled so that
The method for producing a polypropylene resin foam sheet according to the above.