JPH04258644A - Foamed polypropylene sheet and its production - Google Patents

Abstract

PURPOSE:To improve thermal insulation and cushioning properties by melting a thermoplastic resin compsn. contg. a specified amt. of a syndiotactic PP in an extruder, forcing a low-boiling substance into the melt, and extruding it into the air under cooling. CONSTITUTION:At least 50wt.% syndiotactic PP which has an intrinsic viscosity (135 deg.C, a tetralin soln.) of 0.1-10.0 and comprises a propylene homopolymer having a syndiotactic pentad fraction of at least 0.6 or a propylene-alpha-olefin copolymer having a peak intensity around 20.2ppm in 13C-NMR measured using a 1,2,4-trichlorobenzene soln. of at least 0.3 times the peak intensity assignable to all the methyl groups of propylene units is mixed with another thermoplastic resin, if necessary, giving a thermoplastic resin compsn. After the compsn. is melted in an extruder, a low-boiling substance as a blowing agent is forced into the melt, which is then extruded under cooling through a die at the end of the extruder into the air, thus giving the title sheet.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene foam sheet and a method for producing the same.

0002

BACKGROUND OF THE INVENTION Foamed sheets made primarily of isotactic polypropylene are widely used, for example, as food containers and interior materials for automobiles. However, this foam sheet does not have a large expansion ratio, and therefore has problems such as insufficient heat insulation properties and poor cushioning properties.

0003

[Problems to be Solved by the Invention] Therefore, there is a demand for a polypropylene foam sheet with a high expansion ratio that has heat insulation and cushioning properties in addition to the heat resistance that polypropylene inherently has.

0004

[Means for Solving the Problems] The present inventors conducted intensive research on polypropylene foam sheets under the above-mentioned circumstances, and as a result, completed the present invention. That is, the present invention is a foamed sheet obtained by melting a thermoplastic resin in an extruder, pressurizing a low boiling point substance, and then releasing it into the atmosphere from a mold attached to the tip of the extruder while cooling.
The thermoplastic resin is syndiotactic polypropylene.
A foamed sheet containing 0% by weight or more and a method for producing the same.

Conventionally, syndiotactic polypropylene could only be obtained with low regularity and low molecular weight, but recently Yuen has made it possible to produce polypropylene with high syndiotacticity and large molecular weight. The physical properties of these materials were still not fully known, and it was also unknown what characteristics could be obtained by processing them.

[0006] The inventors of the present invention have investigated the above-mentioned foams of syndiotactic polypropylene or copolymers with high molecular weight and high syndiotacticity, and have found that they compare with isotactic polypropylene, which has been conventionally used as a raw material for foam sheets. The present invention was achieved by discovering that a foamed sheet with extremely excellent properties could be obtained by doing so. According to the present invention, a foamed sheet with a higher expansion ratio than conventional isotactic polypropylene can be easily obtained, and is extremely useful as a foamed sheet with excellent heat resistance and heat insulation properties.

In the present invention, a syndiotactic polypropylene or copolymer having a high molecular weight and high syndiotacticity can be used, and in addition to a homopolymer of polypropylene, a copolymer of propylene and other α-olefins can be used. Can be used for combination.

Other α-olefins used in the copolymerization in the method of the present invention include, in addition to ethylene, α-olefins having about 4 to 20 carbon atoms, preferably butene-1, butene-1,
Examples include pentene-1, hexene-1, octene-1, 4-methylpentene-1, etc., and the polymerization ratio to propylene is usually 20 wt% or less, more preferably 10 wt% or less of other olefins. Polymers can be used. The high molecular weight, high syndiotacticity syndiotactic polypropylene or copolymer used in the method of the present invention is described in J. A. EWEN literature (J.
Am. Chem. Soc. , 1988, 110, 625
An example is a catalyst system consisting of a transition metal compound having an asymmetrical ligand and aluminoxane as described in 5-6256), but even if the catalyst has a different structure, it can be used with syndiotactic polypropylene of high molecular weight and high syndiotacticity. Alternatively, any catalyst system that provides a copolymer can be used.

Examples of the transition metal compound having an asymmetric ligand include isopropyl (cyclopentadienyl-1-fluorenyl) hafnium dichloride, or isopropyl (cyclopentadienyl-1-fluorenyl) described in the above-mentioned literature.
Examples include fluorenyl) zirconium dichloride, and aluminoxane is an alkyl aluminum treated with a small amount of water, in which aluminum and oxygen are alternately bonded to form a dimer to 50-mer, preferably a pentamer or more. It is thought that each aluminum has an alkyl group bonded to it. This aluminoxane exists in linear or cyclic forms. The ratio of aluminoxane to the above transition metal compound is 10
~1,000,000 times by mole, usually 50 to 5,000 times by mole.

The polymerization method is not particularly limited as long as it is a known polymerization method and polymerization conditions for polymerizing or copolymerizing isotactic or syndiotactic polypropylene, and solvent polymerization using an inert medium or substantially Bulk polymerization methods and gas phase polymerization methods without the presence of an inert medium can also be used. The polymerization temperature is -100 to 200°C,
The polymerization pressure is generally from normal pressure to 100 kg/cm2. Preferably -100 to 100°C and normal pressure to 50 kg/cm2.

[0011] The preferred molecular weight of the syndiotactic polypropylene or copolymer used in the present invention is generally about 0.1 to 10.0 as the intrinsic viscosity measured in a tetralin solution at 135°C. . Regarding the degree of syndiotactic structure, the syndiotactic pentad fraction in the propylene homopolymer is 0.6 or more, preferably 0.7 or more. In addition, in copolymers with other α-olefins, the peak intensity observed at about 20.2 ppm in 13C-NMR measured with a 1,2,4-trichlorobenzene solution is the peak attributable to all methyl groups in the propylene unit. The strength is 0.3 or more, preferably 0.5 or more. If it is less than 0.3, the physical properties will be poor, which is not preferable.

[0012] During foam extrusion, other polyolefins may be included depending on the purpose. Other polyolefins to be used in combination include isotactic polypropylene, copolymers of isotactic propylene and other α-olefins, and commercially available polypropylenes as α-olefin copolymers. Alternatively, polyethylene, polybutene, or even copolymers thereof can be used, and in some cases, materials such as ethylene-propylene rubber can also be used, and the physical properties such as impact resistance and processing of the foam obtained by adding these can be used. You can also improve your gender.

[0013] Regarding the method of manufacturing foamed sheets according to the method of the present invention, methods used for manufacturing ordinary thermoplastic resin, especially polypropylene foamed sheets can be used, such as those described in JP-A-55-27320 and JP-A-55 -45714
, JP-A No. 63-288731, etc. can be used.

[0014] In order to obtain the foamed sheet referred to in the present invention, a low-boiling point substance is mixed, and the low-boiling point substance may be one commonly used as a blowing agent for thermoplastic resins, such as propane, butane, pentane, etc. , hydrocarbon compounds such as hexane, Freon-22, Freon-123, Freon-134,
Typical examples include Freon 12, Freon 11, Freon 114, halogenated hydrocarbon compounds such as methyl chloride and methylene chloride, petroleum ether, carbon dioxide gas, and nitrogen gas.

The amount of low boiling point material to be injected is selected depending on the desired thickness and apparent density of the foamed sheet.
The amount is 0.01 to 0.1 mol, preferably 0.02 to 0.08 mol, per 00 g. If the amount of low boiling point material injected is less than 0.01 mol, the extruded sheet is likely to tear. Furthermore, if the injection amount exceeds 0.1 mol, when the resin is released from the annular slit of the mold attached to the tip of the extruder, there will be many holes in the sheet, and the quality difference will increase in the width direction of the sheet.

The expansion ratio varies depending on the use and may be adjusted according to the purpose, but is usually 2 to 10 times. Also,
In the present invention, there is no problem in adding a small amount of an inorganic substance such as talc, silica gel, or calcium carbonate, or a chemical blowing agent as a cell conditioner.

Regarding the method for manufacturing the foam sheet of the present invention,
In this example, polypropylene with a syndiotactic structure and talc are fed from a hopper and mixed in an extruder heated to 150 to 220°C, and low-boiling materials are added to the extruder. Press-fit to uniformly mix resin and low boiling point substances. The mixture is continuously supplied to a second extruder, cooled to 100 to 160°C, and discharged into the atmosphere through an annular slit in a mold attached to the tip of the extruder. A foamed sheet is obtained by successively drawing the foamed sheet along a sizing drum while cooling the inner and outer surfaces of the foamed sheet.

[0018]

[Example] This will be explained below using an example. Example 1 2 g of isopropyl (cyclopentadienyl-1-fluorenyl) zirconium dichloride obtained by lithiation of isopropylcyclopentadienyl-1-fluorene synthesized according to a conventional method, reaction with zirconium tetrachloride, and recrystallization and Tosoh.・Using 600 g of methylaluminoxane (polymerization degree 16.1) manufactured by Akzo Co., Ltd., internal volume 200
Polymerization pressure 3kg/cm2 in a 0L polymerization pot, 2 at 20℃
Polymerized for hours, then deashed with methanol and acetone methyl acetate, washed with an aqueous hydrochloric acid solution, and then filtered to 61k
g of syndiotactic polypropylene was obtained. According to 13C-NMR, this polypropylene has a syndiotactic pentad fraction of 0.928, and an intrinsic viscosity (hereinafter abbreviated as [η]) measured in a tetralin solution at 135°C.
is 1.38, the ratio of the weight average molecular weight to the number average molecular weight measured with 1,2,4-trichlorobenzene (hereinafter referred to as MW/M
N) was 2.1, and the melting point measured with a differential scanning calorimeter was 149°C.

100 parts by weight of this polypropylene and 1.0 parts by weight of talc (manufactured by Nippon Talc) as a bubble regulator were added and melted and kneaded at a temperature of 180°C. After that, Freon-22 was added in a proportion of 0.055 mol per 100 g of resin. I pressed it in. This mixture was cooled to 125° C. in a second extruder and discharged into the atmosphere through an annular slit of a die to obtain a foamed sheet. The thickness of the obtained foamed sheet was 0.5 mm, and the apparent density was 0.22 g/cc.

Example 2 Foaming and extrusion was carried out in the same manner as in Example 1 except that the syndiotactic pentad fraction of polypropylene was changed to 0.65. The thickness of the obtained foam sheet was 0.5 mm.
The apparent density was 0.35 g/cc.

Example 3 The resins used in the method of Example 1 were mixed with 60 parts by weight of syndiotactic polypropylene, 25 parts by weight of low-density polyethylene (Mirason 11 manufactured by Mitsui Petrochemicals Co., Ltd.), and high-density polyethylene (Hizex manufactured by Mitsui Petrochemicals Co., Ltd.). 33
Foaming and extrusion was carried out in the same manner as in Example 1 except that the amount was changed to 15 parts by weight (00F). The thickness of the obtained foam sheet is 0.5m
m, and the apparent density was 0.15 g/cc.

Comparative Example 1 Foaming and extrusion was carried out in the same manner as in Example 1 except that the polypropylene was changed to a normal isotactic type polypropylene (Mitsui Noblen JHH; manufactured by Mitsui Toatsu Chemical Co., Ltd.). When the resin released into the atmosphere was collected through the annular slit of the die, it was easy to cut, creating holes in the sheet and making it difficult to collect the resin.

[0023]

As described above, according to the present invention, a foamed sheet having a high expansion ratio can be obtained. It is possible to provide a foamed sheet that has the heat resistance inherent to polypropylene and also has heat insulation properties, cushioning properties, etc. For example, the foamed sheet obtained by the present invention can be processed into containers of various shapes and interior materials for automobiles by vacuum or pressure forming, and is suitable for molded products that take advantage of heat resistance, heat insulation, cushioning properties, etc.

Claims (2)

[Claims] Claim 1: A foamed sheet obtained by melting a thermoplastic resin in an extruder, pressurizing a low boiling point material, and then releasing it into the atmosphere from a mold attached to the tip of the extruder while cooling. A foamed sheet characterized in that the resin contains 50% by weight or more of syndiotactic polypropylene. [Claim 2] A thermoplastic resin containing 50% by weight or more of syndiotactic polypropylene is melted in an extruder, a low boiling point substance is press-injected, and then, while cooling, it is melted in the atmosphere from a mold attached to the tip of the extruder. 2. The method for producing a foamed sheet according to claim 1, wherein the foamed sheet is produced by discharging the foamed sheet.