JPH10101831A - Polypropylene-based resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polypropylene-based resin foam good in flatness. SOLUTION: This foam consists of a polypropylene-based resin wherein the base material resin has (a) a take-up speed which is between 0.5 and 10m/min. when a breakage occurs in the measurement of the melt tension at 190 deg.C and (b) the ratio of another take-up speed when a measurement is conducted similarly except at 230 deg.C to the above-mentioned take-up speed which falls into the range of 0.5 to 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polypropylene resin foam. The polypropylene resin foam of the present invention can be suitably used as various packaging materials and various product members including food packaging.

[0002]

2. Description of the Related Art Polypropylene resins are excellent in heat resistance, chemical resistance and the like, and are used in many fields. However, the polypropylene resin has a very low melt viscosity above the melting point of the crystalline melting point due to its crystallinity, and cannot easily retain foamed bubbles and easily break bubbles. It has been difficult to obtain a foam sheet that is a high foam sheet and has excellent mechanical properties and heat resistance having closed cells. And the density of the conventional polypropylene resin foam sheet is 0.5 g / c.
m ³ or more low foaming products or, alternatively, density 0.03 g / c
It was a highly foamed product of m ³ or less.

[0003] That is, a low-foamed sheet having a density of 0.5 g / cm ³ or more is produced by adding a decomposable or reactive foaming agent to a polypropylene-based resin and supplying it to a sheet forming and extruding apparatus. A highly foamed sheet having a microcellular structure of 0.03 g / cm ³ or less is disclosed, for example, in JP-B-46-41.
No. 474. This publication discloses that a crystalline polypropylene resin is dissolved in an activating liquid such as methylene chloride, fluorotrichloromethane, or perfluorocyclobutane, and the resulting solution has a vapor pressure higher than the vapor pressure of the solution.
Extruding from an area no higher than 0PSi to a substantially lower pressure area, thereby evaporating the activating liquid;
A method is described in which a solid polymer is precipitated, and the polymer is cooled to a temperature at which the orientation of the polymer is frozen and extruded and foamed to obtain a highly foamed sheet.

[0004] An intermediate foam of these two examples has a density of 0.
Although those having around 3 g / cm ³ are also found on the market, they are almost open cells and hardly any closed cells, so that it is hard to say that the foamed sheet has good mechanical properties. However, recently, the Z-average molecular weight Mz is at least 2.0 × 10 ⁶ , Mz / Mw is at least 3.0, and the molecular weight distribution curve by gel permeation chromatography indicates that the polymer region contains a branched polymer. By using a camel-type polypropylene resin having a shape with an overhanging curve, a density of 0.025
It has been found that a foam of about 0.5 g / cm ³ can be obtained by an inexpensive extrusion method such as a polystyrene resin foam sheet (Japanese Patent Application Laid-Open No. 6-192460).

[0005] The foam obtained by the method described in this publication is a foam having a high closed cell ratio and excellent heat resistance, heat insulation and mechanical properties. However, in the case of a sheet-like foam, a phenomenon that the surface of the sheet becomes wavy as the density becomes lower (hereinafter referred to as a corrugation phenomenon) occurs, and although a low-density foam sheet is obtained, there is a problem that the flatness is poor. Was. If the corrugation phenomenon becomes large, uneven heating may occur during thermoforming or the commercial value may be impaired. Further, in order to further adapt to an application requiring flatness, further improvement has been required.

As a method of suppressing such a corrugation phenomenon, there is a method of reducing a swell at the time of extrusion. An attempt to reduce the swell at the time of extrusion processing is found in JP-A-7-268121. In this publication, the melt tension is 6 gf or more, less than 20 gf and the ratio of the weight average molecular weight to the number average molecular weight is 7 or more, less than 20, and the melt tension is 1 gf or more and less than 6 gf. According to a foamed sheet obtained from an inorganic filler and a foaming agent, a swell is reduced according to a polypropylene resin mixture consisting of 10 to 90 parts by weight of a polypropylene resin having a weight average molecular weight and a number average molecular weight of 4 or more and less than 7. It is described that it is possible to obtain a beautiful sheet without a grime. The reduction of the swell in this publication is due to the fact that by mixing a polypropylene resin having a lower melt tension with the polypropylene resin used in the above-mentioned JP-A-6-192460, the melt viscosity as a mixture decreases. It is presumed.

[0007] However, mixing a general polypropylene resin having a low melt tension with a polypropylene resin having a high melt tension having such a long chain branch makes it difficult to obtain a high melt tension having viscoelastic properties suitable for foaming. It is considered that the excellent foamability of the polypropylene resin is impaired, and as a result, a low-density foam cannot be obtained. In the embodiments of the above publications, 1.5 to 1.
A foam sheet having an expansion ratio of 6 times is described, and it is considered that there is no difference from the expansion ratio of a conventional polypropylene resin foam sheet because of the above background.

[0008]

Thus, according to the present invention, the base resin has (a) a take-off speed of 0.5 to 10 m / min at the time of cutting when measuring the melt tension at 190 ° C., (B) 230 for the take-off speed at 190 ° C.
A polypropylene-based resin foam characterized by comprising a polypropylene-based resin having a take-up speed ratio of 0.5 to 5 at the time of cutting when measuring a melt tension at 0 ° C.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The polypropylene resin used as the base resin of the present invention has a take-off speed of 0.5 to 10 m when cut at a melt tension measurement at 190 ° C.
/ Min and the ratio to the take-off speed at the time of cutting in the melt tension measurement at 230 ° C (take-off speed at the time of cut at 230 ° C / take-off speed at the time of cut at 190 ° C) is 0.5 to 5. .

Here, the melt tension (also referred to as melt strength) and the take-off speed at the time of cutting in the present invention are values obtained by measuring as follows. The apparatus used was a Capillograph manufactured by Toyo Seiki Seisaku-Sho, Ltd. The orifice attached to the apparatus had a diameter of 1.0 mm, a length of 5.0 mm, and an inflow angle of 45 °. From the orifice, a molten polypropylene resin heated to 230 ° C. and 190 ° C. is extruded at an extrusion speed of 10 mm / min, and the extrudate is gradually increased from a low speed until the extrudate is cut. The load with respect to the average diameter of the extrudate was defined as the melt tension, and the speed immediately before cutting was defined as the take-up speed at the time of cutting.

When the take-off speed at the time of cutting in the measurement of the melt tension at 190 ° C. is more than 10 m / min, the obtained foam is not preferable because the cells are nonuniform and open cells. On the other hand, when it is smaller than 0.5 m / min, a foam having fine bubbles cannot be obtained, which is not preferable. The take-up speed is more preferably 1.5 to 5.0 m / min. When the take-up speed at the time of cutting at 230 ° C./the take-up speed at the time of cutting at 190 ° C. is larger than 5, the change in the resin properties such as the tension and the melt viscosity due to the temperature change becomes large. As a result, it is difficult to control the temperature to a temperature range suitable for foaming, and only foams having a high open cell ratio or a poor surface state are obtained, which is not preferable. On the other hand, if it is smaller than 0.5, the extrusion load is increased, and the productivity is undesirably reduced. The take-off speed at the time of cutting at 230 ° C. /
The take-off speed at the time of cutting at 190 ° C. is more preferably 1.0 to 3.0.

It is more preferable that the melt tension at 190 ° C. is 3 to 15 gf, since corrugation generated during foam formation can be reduced. Particularly preferred melt tension is 5 to 13 gf. In addition, the melt tension means a tension immediately before the extrudate extruded at 190 ° C. is cut. Pickup speed is 50
If the extrudate is not cut even at m / min, the tension at that point is taken as melt tension.

In the present invention, any polypropylene resin that satisfies the above relationship can be used. For example, a resin in which an ultrahigh molecular weight component due to branching is adjusted by using a method of giving a branched structure to a polypropylene resin described in U.S. Pat. No. 4,916,198 and Japanese Patent Publication No. 7-45551. Can be

More specifically, there may be mentioned a homopolymer of polypropylene and a copolymer of propylene with another olefin. Other olefins include ethylene, butene, and the like. Further, the copolymer may be a block copolymer or a random copolymer. Further, other known resins may be added as long as the effects of the present invention are not impaired.

A foaming agent is added to the base resin, and the resin is subjected to an extrusion foaming process. As an extruder that can be used for extrusion foam molding, any apparatus generally used in the art can be used. After the base resin is sufficiently melted by the first extruder, the melt may be transferred to the second extruder and extruded and foamed by the second extruder. Here, the foaming agent is not particularly limited, and a decomposition-type foaming agent, a gaseous or volatile foaming agent can be used.

Examples of the decomposable blowing agent include inorganic decomposable blowing agents such as ammonium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium nitrite, calcium azide, sodium azide, sodium borohydride, azodicarbonamide, azobis Azo compounds such as sulfformamide, azobisisobutyronitrile and diazoaminobenzene, nitroso compounds such as N, N'-dinitrosopentamethylenetetramine and N, N'-dimethyl-N, N'-dinitrosoterephthalamide; Benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide,
p, p'-Oxybisbenzenesulfonylsemicarbazide, p-toluenesulfonylsemicarbazide, trihydrazinotriazine, barium azodicarboxylate and the like. Further, in order to adjust the decomposition temperature, the amount of generated gas, and the decomposition rate, a known foaming aid can be added.

Examples of the gaseous foaming agent include carbon dioxide, propane, neopentane, methyl ether, methane difluoride, n-butane and i-butane. on the other hand,
Examples of the volatile foaming agent include ether, petroleum ether, acetone, pentane, hexane, isohexane, heptane, isoheptane, benzene, and toluene.

The above foaming agents may be used alone or in combination. Of these foaming agents, butane is particularly preferred. Further, if necessary, a bubble regulator (inorganic powder such as talc and silica, an acid salt such as a polycarboxylic acid, a reaction mixture of a polycarboxylic acid with sodium carbonate or sodium bicarbonate, etc.), an ultraviolet absorber, An antioxidant, a coloring agent, a crosslinking aid, a flame retardant, and the like may be added.

Extrusion foaming is carried out by extruding the molten resin while melting the resin in an extruder and adjusting the die to a temperature most suitable for foaming. The sheet-like foam can be obtained by directly extruding the sheet-like foam or a cylindrical shape from the extruder, and then cutting the sheet-like foam along an arbitrary line. Foam extruded by the above method,
Thickness 0.5-6.0mm, density 0.025-0.5g /
It is preferably a sheet of cm ³ .

The foam of the present invention can be suitably used as various packaging materials and various product members including food packaging.

[0021]

EXAMPLES Table 1 shows the melt tension of the polypropylene resins used in Examples and Comparative Examples at 190 ° C. and 230 ° C. and the measured values of the take-off speed at the time of cutting.

[0022]

[Table 1]

Examples 1 to 3 and Comparative Examples 1 to 4 As a base resin, a certain amount of a cell regulator (HK-70, manufactured by Boehringer Ingelheim Chemicals Co., Ltd.) was mixed with the polypropylene resin shown in Table 1. The mixture is caliber φ
The mixture was supplied to a 50-φ65 mm foam extruder. Butane is injected as a foaming agent in the central zone of the first extruder, melted and kneaded in the first extruder, and then the resin is conveyed to the second extruder, where it is kept in a mold having a diameter of φ80 mm maintained at a temperature most suitable for foaming. A tubular foam was obtained by injecting and then extruding through a slit with a die gap of 0.8 mm. Furthermore, outer diameter 205m
The sheet was taken along a sizing drum of length m, and cut at one point on the circumference with a cutter to obtain a sheet-like foam. Table 2 shows the properties of the obtained sheet-like foam.

[0024]

[Table 2]

As is apparent from Table 2, the sheet-like foam using the resin satisfying the conditions of the present invention as a base resin has a flatness while the density is 0.025 to 0.5 g / cm ³ . It can be seen that is improved.

[0026]

According to the polypropylene resin foam of the present invention, the base resin has (a) a take-up speed of 0.5 to 10 m / min at the time of cutting when measuring the melt tension at 190 ° C., b) 230 for the take-off speed at 190 ° C.
It is made of a polypropylene resin whose take-off speed ratio at the time of cutting when measuring the melt tension at 0.5 ° C. is 0.5 to 5; Since an appropriate temperature can be set widely, a uniform and beautiful foam having good flatness can be obtained.

Further, the melt tension is adjusted to 3 to 15 gf (1
(Measured at 90 ° C.), it is possible to reduce the corrugation generated during foam formation.

Claims (2)

[Claims] The base resin has a take-off speed of 0.5 to 1 at the time of cutting (a) measuring a melt tension at 190 ° C.
0 m / min, and (b) a polypropylene-based resin having a ratio of the take-up speed at the time of cutting when measuring the melt tension at 230 ° C. to the take-up speed at 190 ° C. of 0.5 to 5 Polypropylene-based resin foam. 2. The foam according to claim 1, wherein the base resin has a melt tension at 190 ° C. of 3 to 15 gf.