JPH06340761A - Production of polypropylene-based resin foam - Google Patents

Abstract

PURPOSE:To produce a polypropylene-based resin foam having high temperature elongation and high temperature bond strength and excellent secondary processability. CONSTITUTION:A polypropylene-based resin is mixed with a blowing agent of thermal decomposition type and a cross-linking promoter composed of an aromatic polyfunctional monomer, molded into a sheetlike shape, cross-linked by electron beams and the sheet is heated and foamed by using a molten salt of a nitrite, a nitrate or their mixture.

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 polypropylene resin foam used as a door material or an automobile ceiling material.

[0002]

2. Description of the Related Art Recently, polypropylene resin foams have been
Bonded to a soft vinyl chloride sheet etc. with an adhesive such as polyester series, urethane series etc., and subjected to secondary molding such as vacuum molding, stamping molding, press molding, etc. and used for molded ceiling materials, door materials, instrumental panels etc. It is like this.

As a method for producing a foam of a polyolefin resin, conventionally, a polyolefin resin and a thermal decomposition type foaming agent are blended, a sheet is prepared by melt-kneading extrusion, and the sheet is crosslinked by an electron beam or radiation. A method of heating to obtain a foam is known.

By the way, polypropylene has a larger G value for cleavage than a G value for cross-linking, and it is said that effective cross-linking does not easily occur with a resin alone even if it is simply irradiated with an electron beam or radiation. Therefore, it has been conventionally known to blend a polyfunctional monomer as a crosslinking accelerator for crosslinking polypropylene. Polyfunctional monomers include bifunctional ones,
There are various types such as those having different numbers of functional groups such as trifunctional ones, those having a linear molecular structure, and those having an aromatic ring. The cross-linking efficiency and the mechanical properties of the resulting foam differ depending on the type of polyfunctional monomer used. Therefore, in JP-A-4-292642, a difunctional or trifunctional monomer having an ethylenically unsaturated bond is used in order to obtain a foam having excellent tensile elongation without deteriorating mechanical properties and heat resistance. It is proposed to use them by mixing them at a specific ratio.

[0005]

However, when the foam obtained by the conventional method is laminated with the vinyl chloride film or the like as described above and the secondary molding processing such as vacuum molding, stamping molding and press molding is performed, The adhesive strength between the vinyl chloride film and the foam becomes extremely small at the secondary molding temperature of 130 ° C. or higher, and there is a phenomenon of peeling at the interface between the foam and the adhesive, resulting in poor secondary moldability. There was a problem. Further, in the secondary molding process, if the elongation at the processing temperature (hereinafter referred to as high temperature elongation) is small, problems such as the foam not being shaped according to the mold and the foam breaking may occur. Must also be satisfied at the same time. The present invention has been made in view of the above problems, high temperature elongation,
It is an object of the present invention to provide a method for producing a polypropylene-based resin foam having a high adhesiveness at high temperature and excellent suitability for secondary molding.

[0006]

Means for Solving the Problems The present invention uses an aromatic polyfunctional monomer as a crosslinking accelerator, and when heat-foaming a sheet, one kind or a mixture of two or more kinds selected from nitrite and nitrate. It has been found that a foam having excellent suitability for secondary molding can be obtained by using a molten salt.

The present invention will be described in detail below. The polypropylene-based resin refers to a homopolymer of propylene or a copolymer containing the same monomer as a main component. Polyethylene or a modified product thereof may be used in combination for the reasons of moldability and performance. As the thermal decomposition type foaming agent, those usually used can be used, and azodicarbamide, dinitrosopentamethylenetetramine, allophanic acid amide and the like are used, but azodicarbamide is suitable.

A polyfunctional monomer is mainly used as the crosslinking accelerator. The aromatic polyfunctional monomer used in the present invention may be any bifunctional or higher organic compound in which a plurality of functional groups having an ethylenically unsaturated bond are bonded to a skeleton having a benzene ring, for example, divinylbenzene. , Methyl vinyl benzene, ethyl vinyl benzene,
Examples include trivinylbenzene, diallyl phthalate, triallyl phthalate, diallyl melitate, triallyl melitate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1,6 hexanediol dimethacrylate, and triallyl isocyanurate. It is not limited to.
These may be used alone or in combination. Among these, divinylbenzene, diallyl phthalate and triallyl melitate are particularly suitable. These may be used alone or in combination of two or more. In addition to these, additives used in ordinary blending such as an antiaging agent, a stabilizer, and a viscosity reducing agent may be used as necessary. Each of the above compositions may be premixed or added separately to the molding machine.

The molding machine does not have to be a specific one, and a normal single-screw extruder, twin-screw extruder or the like is used. The raw material composition is melt-kneaded in a molding machine, molded into a sheet, and the obtained sheet is crosslinked with an electron beam or radiation and then heated to obtain a foam. In the present invention, heating is performed in a salt bath. The nitrite, nitrate or a mixture thereof is heat-melted at an elevated temperature, and the sheet is directly heated by the melt in the melt surface or in the melt. The nitrite and nitrate are not particularly limited, but sodium nitrite, potassium nitrite, sodium nitrate, potassium nitrate and the like are preferably used. The bath temperature is usually 160 to 290 ° C.

[0010]

In the present invention, an aromatic polyfunctional monomer is used as a crosslinking accelerator, and a molten salt of nitrite, nitrate or a mixture thereof is used in the foaming process, so that high-temperature elongation is excellent and soft vinyl chloride is obtained. It is possible to produce a foam having a high peel strength with a sheet or the like at high temperature.

[0011]

EXAMPLES The present invention will be described in more detail by the following examples. 1. Examples 1, 2, 3, 4, 5 Random copolymer polypropylene having an ethylene content of 3.2% by weight, MI = 1.0, m.p. p. = 70 ° C or 60 parts at 148 ° C, MI = 2.0, m.p. p. = 120
30 parts or 40 parts of LLDPE at 0 ° C., 15 parts of azodicarboxamide as a foaming agent, 0.5 part of a phenolic antioxidant as a stabilizer, triallyl melitate or divinylbenzene as a crosslinking accelerator, Alternatively, a predetermined number of diallyl phthalates were mixed and fed to a twin-screw extruder to be molded to obtain a sheet. Electron beam on the sheet with a degree of crosslinking of 40
%, And the solution was bubbled in a salt bath. As the salt bath composition, in Examples 1 to 3, sodium nitrate and sodium nitrite were mixed at a weight ratio of 1: 1 and in Examples 4 to 5, sodium nitrate and potassium nitrite were mixed at a weight ratio of 7: 3. . The bath temperature was 190 ° C. in Example 1 and 2 in Examples 2-5.
It was set to 20 ° C. The expansion ratio was determined by the standard specific gravity liquid method.
The elongation of the obtained foam was measured at 150 ° C. The obtained foam was adhered to an ABS resin-containing soft vinyl chloride sheet with a polyester adhesive, and the peel strength was measured at 150 ° C. The peel strength was determined by a method in which an adhesive product obtained by adhering a foam to a vinyl chloride sheet was cut into 25 mm wide strips, and the peel strength was measured at a speed of 200 mm per minute. Tensilon manufactured by Toyo Seiki was used for measuring the elongation and the peel strength. In Examples 3 and 4, the peel strength was measured in the same manner as in the case of the polyester adhesive, even if the adhesive was a urethane adhesive or an emulsion adhesive. The results are shown in Table 1. In the table, M and T in the columns of elongation and peel strength indicate the machine direction and the width direction. Example 1
In Nos. 5 to 5, because the adhesion was strong, the foam layer did not peel off at the interface and the material of the foam layer was destroyed. The results for urethane-based and emulsion-based adhesives were also at the same level as those for polyester-based adhesives.

[0012]

[Table 1]

2. Comparative Examples 1, 2, 3, 4, 5 Examples 1-5, except that in Examples 1, 2, 3, 4, 5 foaming was done using a hot air oven instead of a salt bath.
The same treatment and measurement were performed. For Comparative Examples 3 and 4, the peel strength was measured in the same manner as in the case of the polyester adhesive, even if the adhesive was a urethane adhesive or an emulsion adhesive. The results are shown in Table 2.
Shown in. In each of Comparative Examples 1 to 5, interfacial peeling occurred. The results for urethane-based and emulsion-based adhesives were also at the same level as those for polyester-based adhesives.

[0014]

[Table 2]

3. Comparative Examples 6, 7, 8, 9, 10, 11 Random copolymerized polypropylene having an ethylene content of 3.2% by weight, MI = 0.5, m.p. p. = 60 ° C. for 148 ° C., MI = 2.0, m.p. p. = LLDP of 120 ° C
40 parts E and 15 azodicarbamide as a foaming agent
Parts, 0.5 parts of a phenolic antioxidant as a stabilizer, ethylene glycol dimethacrylate, or 1,6 hexanediol dimethacrylate or trimethylolpropane triacrylate as a non-aromatic crosslinking accelerator. Parts were mixed and fed to a twin-screw extruder to be molded to obtain a sheet. The sheet was irradiated with an electron beam so that the degree of crosslinking was 40%, and the obtained sheet was foamed in a salt bath or a hot air oven. In Comparative Examples 6 to 8, a salt bath at 190 ° C. in which sodium nitrate and potassium nitrite were mixed at a weight ratio of 7: 3 was used. In Comparative Examples 9 to 11, heating was performed in a hot air oven at 330 ° C. for 1 to 2 minutes for foaming. The expansion ratio was determined by the standard specific gravity liquid method. The elongation of the obtained foam was measured at 150 ° C. The resulting foam was adhered to an ABS resin-containing soft vinyl chloride sheet with a polyester adhesive, and the peel strength was measured at 150 ° C. The peel strength was determined by a method in which an adhesive product obtained by adhering a foam to a vinyl chloride sheet was cut into 25 mm wide strips and the peel strength was measured at a speed of 200 mm / min. Tensilon manufactured by Toyo Seiki was used for measuring the elongation and the peel strength. The results are shown in Table 3. In the table, M and T in the columns of elongation and peel strength indicate the machine direction and the width direction. Comparative Example 6-
In No. 11, the interface layer was not peeled off and the foam layer was destroyed, but the high temperature elongation was insufficient.

[0016]

[Table 3]

[0017]

As described above in detail, according to the present invention,
By using an aromatic polyfunctional monomer as a crosslinking accelerator and heating and foaming in a salt bath, a foam having excellent secondary processability can be produced.

Claims (2)

[Claims] 1. A polypropylene resin, a pyrolytic foaming agent, and a crosslinking accelerator are mixed and molded into a sheet with a molding machine, and the sheet is crosslinked with an electron beam or radiation.
In the method for producing a foam by heating at a temperature higher than the decomposition temperature of the foaming agent in the foaming step, 1) using an aromatic polyfunctional monomer as a crosslinking accelerator, and 2) selecting one of nitrite and nitrate in the foaming step. A method for producing a polypropylene-based resin foam, which comprises using a molten salt of one kind or a mixture of two or more kinds. 2. The method according to claim 1, wherein the crosslinking accelerator is one kind or a mixture of two or more kinds selected from divinylbenzene, diallyl phthalate and triallyl melitate.