JP2000026646A - Production of polypropylene resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain a thick-wall foam having a high expansion ratio, a beautiful appearance and a uniform cell structure by melt-kneading at least a PP resin, a specific amount of mica having a specified particle diameter, and a physical blowing agent under an elevated pressure and extruding the melt into a low-pressure zone. SOLUTION: 100 pts.wt. PP resin, 0.001-10 pts.wt. mica having a particle diameter of 1,000 μm or below, 2-1,000 μm, or 10-500 μm, and a physical blowing agent (e.g. isobutane) as essential components are melt-kneaded, and the melt is extruded into a low-pressure zone. It is desirable that the PP resin is a modified PP resin obtained by melt-kneading a starting PP resin (e.g. ethylene/ propylene random copolymer), isoprene, and a radical polymerization initiator [e.g. 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane] and featured in that the elongation viscosity as measured in a molten state steeply rises with an increasing strain.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polypropylene resin foam. More particularly, the present invention relates to a method for easily producing a thick foam having a high expansion ratio, a beautiful appearance, and a uniform cell structure from a polypropylene resin.

[0002]

2. Description of the Related Art As foams made of thermoplastic resins, for example, polystyrene foam, polyethylene foam, polypropylene foam, polyvinyl chloride foam and the like are known.
Since these foams are lightweight and have good heat insulating properties and good buffering properties against external stress, they are widely used in applications such as heat insulating materials, cushioning materials, core materials, packaging materials, and food containers.

[0003] Among foams made of thermoplastic resin,
Foams made of a polypropylene-based resin are preferably used particularly as a cushioning material because of their excellent chemical resistance, impact resistance and heat resistance. When the foam is used as a cushioning material or a heat insulator, it is often convenient for the foam to be manufactured to have a plate shape.

[0004] In order for the foam to be used as a cushioning material or a heat insulating material and exhibit good heat insulating properties and cushioning properties, it must be lightweight, have a high expansion ratio, have a fine cell diameter, and have a uniform cell structure. It is said that it is desirable.

However, since the polypropylene resin has a low viscosity and low tension when melted, the number of cells increases when an attempt is made to obtain a foam having a fine cell diameter and a uniform cell structure. Bubble becomes small and the bubble wall becomes thin. For this reason, the strength of the cell wall is not sufficiently maintained, and it is difficult to obtain a thick foam having a high expansion ratio like a polyethylene resin foam.

A method for obtaining a polypropylene resin foam is disclosed in, for example, Japanese Patent Publication No. 46-19854.
A method is disclosed in which a polypropylene-based resin and a chemical foaming agent are mixed in advance, crosslinked with an organic peroxide or ionizing radiation, and then foamed. However, such a manufacturing method requires special equipment, which leads to an increase in cost, and is not preferable from the viewpoint of recycling.

Further, for example, Japanese Patent Application Laid-Open No. Hei 5-506875.
Japanese Patent Application Laid-Open No. 62-121704 discloses a polypropylene having a long-chain branched structure by irradiation with an electron beam (a polypropylene having free-end long-chain branching and a strain-hardening elongational viscosity described in JP-A-62-121704). A method for producing a sheet-like foam from polypropylene) is disclosed.
However, according to this method, only a sheet-like foam having a thickness of 0.5 to 5 mm and a density of 0.05 to 0.5 g / cm ³ can be obtained.

[0008] As described above, at present, no method has been found for producing a thick foam having a high expansion ratio and a uniform cell structure from a polypropylene resin.

[0009]

Means for Solving the Problems The present inventors have solved the above-mentioned problems, and have developed a foamed foam having a high expansion ratio, a beautiful appearance, a uniform cell structure, and a large thickness from a polypropylene resin. As a result of intensive studies to provide a method for easily producing a mixture, a mixture obtained by adding a specific amount of mica having a specific particle size range to a polypropylene resin and a physical blowing agent is melt-kneaded under pressure, and a low-pressure region And found that the above problem could be solved, and completed the present invention.

That is, according to the present invention, when a foam is produced by melt-kneading at least a polypropylene resin, mica and a physical foaming agent under pressure and extruding the mixture into a low pressure region, the mica has a particle size of 1000 μm or less. Yes, 0.001 to 100 parts by weight of polypropylene resin
A method for producing a polypropylene-based resin foam, wherein 10 parts by weight are added (claim 1), wherein at least a polypropylene-based resin, mica, and a physical foaming agent are melt-kneaded under pressure and extruded into a low pressure region. Wherein the mica has a particle size of 2 to 1000 microns and is added in an amount of 0.001 to 10 parts based on 100 parts (parts by weight, hereinafter the same) of a polypropylene resin. The method for producing a polypropylene resin foam (claim 2), wherein the mica is melt-kneaded with at least a polypropylene resin, mica, and a physical foaming agent, and extruded to a low pressure range, thereby producing the foam. Has a particle size of 10 to 500 microns and is added in an amount of 0.001 to 10 parts based on 100 parts of the polypropylene resin. A method for producing a propylene-based resin foam (Claim 3), wherein the polypropylene-based resin was measured in a molten state obtained by adding and mixing isoprene and a radical polymerization initiator to a raw polypropylene-based resin and melt-kneading the mixture. 4. The method for producing a polypropylene-based resin foam according to claim 1, 2 or 3, wherein the elongational viscosity is a modified polypropylene-based resin that rapidly increases as the amount of strain increases. The expansion ratio of the body is 20 times or more.
Or a method for producing a polypropylene-based resin foam according to claim 4 (claim 5).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A polypropylene resin foam obtained by the production method of the present invention is prepared by melt-kneading a polypropylene resin, a specific amount of mica having a specific particle size range and a physical foaming agent under pressure, It is obtained by extruding into the area.

In the production of a general thermoplastic resin foam,
In order to obtain a foam having a uniform and fine cell structure, an inorganic nucleating agent or a chemical blowing agent that generates a gas by heating or reaction is used.
Submicron mica is used.

When a polypropylene-based resin foam is produced according to the present invention, a foam having a high expansion ratio, a beautiful appearance, a uniform cell structure, and a large thickness can be obtained. The reason is unknown, but is presumed as follows.

As in the conventional method, a mixture of a polypropylene resin and an inorganic nucleating agent or a chemical foaming agent that generates a gas by heating or reacting, and a physical foaming agent are melt-kneaded under pressure, and the mixture is melted and kneaded under low pressure. When extruding into the area, many bubbles will be generated starting from the nucleating agent or chemical blowing agent,
Foam breakage and corrugation (phenomenon where foams become wavy and uneven)
Adversely affects the foam due to the generation of It is considered that the appearance of the foam becomes heavily wavy, and the foaming ratio cannot be increased to 20 times or more due to foam breaking.

On the other hand, 1
In the case of the present invention, a mixture in which a specific amount of mica of 000 microns or less is added and a physical foaming agent are melt-kneaded under pressure and extruded to a low pressure region, the number of generated bubbles is limited, and the size of the foam increases in the thickness direction. It is considered that the foam is easy to be formed and the cell wall is not too thin, so that the strength is maintained, the expansion ratio is high, the appearance is beautiful, the cell structure is uniform, and a thick foam is obtained.

[0016] The polypropylene resin used in the present invention means that the unit composed of propylene monomer is 75 to 1 in total.
00% (% by weight, the same applies hereinafter), and 90 to 100%
And a resin in which the unit composed of the other copolymer component is 0 to 25%, and more preferably 0 to 10%. Such a polypropylene resin is preferable in terms of maintaining high crystallinity, high rigidity, and good chemical resistance, and specifically, for example, a propylene homopolymer, propylene and ethylene, α
-Random or block copolymers with olefin or diene monomers, and polypropylene resins with improved foamability.

Examples of the polypropylene resin having improved foaming properties include polypropylene resins such as propylene homopolymer and random or block copolymers of propylene with ethylene, α-olefin or diene monomer. Modified polypropylene resin that has free-end long-chain branching by electron beam irradiation and has been imparted with strain-hardening elongational viscosity to polypropylene resin before foamability is improved. A material that exhibits a fibril structure, such as polytetrafluoroethylene, is mixed with a raw polypropylene resin, and a polystyrene resin, an aromatic vinyl monomer, and a radical polymerization initiator are melted in the raw polypropylene resin. Modified polypropylene resin obtained by kneading, raw material polypropylene Modified polypropylene-based resin obtained by melt-kneading isoprene monomer and radical polymerization initiator in a lene-based resin, and elongational viscosity measured in the molten state increases sharply as strain increases. . The polypropylene resin may be used alone.
A combination of more than one species may be used. Among these, the above-mentioned various polypropylene resins having improved foaming properties, in particular, the elongational viscosities measured in a molten state obtained by melt-kneading an isoprene monomer and a radical polymerization initiator with the raw polypropylene resin. The modified polypropylene resin, which rises sharply as the amount of strain increases,
It is preferable because it has viscoelastic properties suitable for obtaining a thick foam.

Here, the characteristic (hereinafter, also referred to as "specific elongational viscosity characteristic") that the elongational viscosity measured in the molten state sharply increases as the strain amount increases will be described.

As a method for evaluating the specific elongational viscosity characteristic, for example, a strand-shaped resin molded product having a diameter of about 3 mm and a length of about 180 mm is used as a sample, and both ends of the sample are sandwiched with a rotary clamp to completely remove the sample. Maintain the melting temperature (for example, about 180 ° C. in the case of the modified polypropylene resin of the present invention), elongate at a constant strain rate, measure the stress generated between the chucks over time, The elongational viscosity is determined from the relationship with the cross-sectional area of the sample, and the method is evaluated based on the change over time.

The measurement temperature is not limited to 180 ° C., but is not less than the temperature at which the polypropylene resin substantially melts and is lower than the temperature at which the polypropylene resin starts to thermally decompose. It may be arbitrarily selected, and is preferably set in the range of usually 170 to 250 ° C. Further, it is generally preferable to set the strain rate in a range of 0.01 to 0.5 / sec.

If the resin has the specific elongational viscosity characteristic at any one point within the measurement temperature range and within the strain rate range, the resin generally has the total of the measurement temperature and strain rate. Within the range specific elongational viscosity properties are observed.

The elongational viscosity is represented by the following formula:

[0023]

(Equation 1)

(Where η _e is the elongational viscosity (poise), σ is the stress per sectional area (dynes / cm ² ),

[0025]

[Outside 1]

Indicates the strain rate (/ sec),

[0027]

[Outside 2]

Is the formula:

[0029]

(Equation 2)

(Where L is the length of the sample (cm), t
Represents time (seconds)).

The relationship between the elongational viscosity (η _e ) and the time (t) is plotted as a graph of log η _e and logt. At this time, the elongational viscosity gradually increases as the measurement time elapses (as the strain amount increases) (the slope of the graph does not substantially change), and at a certain measurement time (at a certain strain amount). ), The one in which the rate of increase in elongational viscosity increases sharply (the slope of the graph becomes larger) as compared to that before can be said to have specific elongational viscosity characteristics.

In the measurement of the elongational viscosity of the raw polypropylene resin before modification, the elongational viscosity gradually increases as the measurement time elapses, but a sharp increase in the elongational viscosity is hardly observed. In the measurement of elongational viscosity, the elongational viscosity of a modified polypropylene-based resin having a specific elongational viscosity gradually increases as the measurement time elapses (as the amount of strain increases). (When the amount of strain is increased) so that the rate of increase of the elongational viscosity increases more rapidly than before.

Also, logt is plotted on the horizontal axis, and logt is plotted on the vertical axis.
taking Jiita _e, in a graph plotting the relationship between measurement time and elongational viscosity, (which is gradually increased) relatively slowly has risen with the passage of elongational viscosity measurement time in measuring the initial graph With respect to the slope of the straight line drawn from the portion, the maximum slope of the straight line drawn from the portion where the elongational viscosity rises rapidly with the elapse of the measurement time is 1.2 times or more, and further, 1.
It is preferably at least 5 times, particularly preferably at least 2.0 times. Although the upper limit is not limited, usually, according to the method for producing a modified polypropylene resin in the present invention described later, a modified polypropylene resin having this value at most about 20 times can be produced.

The slope of each straight line drawn from the graph is expressed by the following equation: slope of straight line = Δ (log η _e ) / Δ (logt) (where η _e (poise) is elongational viscosity and t (second)) Represents the measurement time).

The modified polypropylene resin having the specific elongational viscosity characteristic usually has a measurement region where the elongational viscosity becomes lower as the measurement time elapses (the amount of strain increases) in the measurement of the elongational viscosity. Instead, the measurement sample eventually breaks elastically as if the rubber were cut.
On the other hand, in the case of the starting polypropylene resin, the elongational viscosity generally increases with the passage of the measurement time (increase in the amount of strain), but a sharp increase in the elongational viscosity is hardly observed. Further, in many cases, a phenomenon in which the elongational viscosity is reduced immediately before the measurement sample breaks is observed, followed by plastic breakage.

As an example, FIG. 1 shows the relationship between the elongational viscosity of the modified polypropylene resin and the measurement time in Example 1 described later.

FIG. 1 shows a modified polypropylene resin molded into a cylindrical rod having a diameter of 3 mm and a length of 180 mm.
It shows the relationship between the logarithm log _e of the elongational viscosity and the logarithm log of the measurement time when elongated at 80 ° C. at a strain rate of 0.05 / sec. In FIG. 1, the slope of a straight line drawn from a flat part (a part where the extensional viscosity rises relatively slowly as the measurement time elapses) in the initial stage of the measurement of the graph showing the relationship between the extensional viscosity and the measurement time is shown. From the relationship between the maximum slope (the value of each slope is shown in the figure) of the slope of a straight line drawn from a portion where the elongational viscosity sharply rises as the measurement time elapses in this curve, It can be seen that the elongational viscosity sharply increases as the strain rate increases.

Next, methods for producing the above-mentioned various modified polypropylene resins will be described.

The modified polypropylene resin having long-chain branching at the free end by electron beam irradiation and imparting a strain hardening elongational viscosity is linked to a raw polypropylene resin having no strain hardening elongational viscosity. Irradiate with high-energy ionizing radiation for a time sufficient to cause cleavage, but not enough to cause gelation, and hold it so that long-chain branching occurs. By deactivating the free radicals present in the polypropylene resin.

The modified polypropylene resin obtained by mixing a material exhibiting a fibril structure, such as polytetrafluoroethylene, with the raw polypropylene resin is prepared by dry blending the polypropylene resin with polytetrafluoroethylene or the like or by using a twin-screw extruder. It is obtained by kneading.

The modified polypropylene resin obtained by melt-kneading the raw polypropylene resin with a polystyrene resin, an aromatic vinyl monomer and a radical polymerization initiator is a polypropylene resin, a polystyrene resin and an aromatic vinyl resin. It can be obtained by melt-kneading a monomer and a radical polymerization initiator using a Brabender or twin-screw extruder.

A modified polypropylene obtained by melt-kneading an isoprene monomer and a radical polymerization initiator in the raw material polypropylene resin, and having an elongational viscosity measured in a molten state that sharply increases as the strain increases. The resin is obtained by melt-kneading a polypropylene resin, an isoprene monomer and a radical polymerization initiator with a Brabender or a twin-screw extruder. This method will be described in detail below.

The raw material polypropylene resin (for example, propylene homopolymer, propylene and ethylene,
a polypropylene resin such as a random or block copolymer with an α-olefin or diene monomer) 1
The amount of the isoprene monomer to be added to 00 parts is 0.1 to 10
It is preferably 0 parts, more preferably 0.1 to 50 parts. If the amount of the isoprene monomer is less than 0.1 part, the effect of improving the foamability of the polypropylene resin becomes insufficient, and
If the amount is more than 00 parts, excellent chemical properties, physical properties, mechanical properties, etc. of the polypropylene resin are impaired, and a large amount of a radical initiator is required, which tends to be disadvantageous in cost. .

The radical polymerization initiator generally includes a peroxide or an azo compound. In the present invention, a compound such as a radical polymerization initiator having a hydrogen abstracting ability with respect to the polymer molecule of the polypropylene resin is used. The existence of is required.

The radical polymerization initiator generally includes peroxides, azo compounds and the like. In particular,
Ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide;
1,1-bis (t-butylperoxy) -3,3,5-
Such as trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate and 2,2-bis (t-butylperoxy) butane Peroxyketal; permethane hydroperoxide, 1,1,
3,3-tetramethylbutyl hydroperoxide,
Hydroperoxides such as diisopropylbenzene hydroperoxide and cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2,
5-di (t-butylperoxy) hexane, α, α'-
Bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t
Dialkyl peroxides such as -butylperoxy) hexine-3; diacyl peroxides such as benzoyl peroxide; di (3-methyl-3-methoxybutyl) peroxydicarbonate and di (2-methoxybutyl) peroxydicarbonate Peroxy dicarbonate such as t-butyl peroxy octate, t-butyl peroxy isobutyrate, t-butyl peroxy laurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t -Butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, di-t
Organic peroxides such as peroxyesters such as -butylperoxyisophthalate. Among them, those having a particularly high hydrogen abstracting ability are preferable. For example, 1,1-bis (t-butylperoxy) -3,
3,5-trimethylcyclohexane, 1,1-bis (t
-Butylperoxy) cyclohexane, n-butyl-
4,4-bis (t-butylperoxy) valerate,
Peroxyketals such as 2,2-bis (t-butylperoxy) butane; dicumyl peroxide, 2,5-
Dimethyl-2,5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, Dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3; diacyl peroxides such as benzoyl peroxide; t-butylperoxyoctate, t-butylperoxyiso Butyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-
Butyl peroxyisopropyl carbonate, 2,5-
One or two of peroxyesters such as dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate and di-t-butylperoxyisophthalate;
More than seeds.

The radical polymerization initiator is added in an amount of 0.1 to 10 based on 100 parts of the starting polypropylene resin.
Parts, more preferably 0.5 to 5 parts, from the viewpoint that the melt viscosity of the modified polypropylene resin does not excessively decrease and is economical. When the amount of the radical polymerization initiator is less than 0.1 part, the modifying effect tends not to be sufficiently obtained. When the amount exceeds 10 parts, a foam having a suitable shape and appearance is obtained. It tends not to be obtained.

The method of mixing and melt-kneading the raw material polypropylene-based resin, isoprene monomer, radical polymerization initiator and other additives to be added as required are not particularly limited. The polypropylene resin, the isoprene monomer, the radical polymerization initiator and the additives optionally added may be mixed and then melt-kneaded, or the raw polypropylene resin may be melt-kneaded and then mixed with isoprene alone. Mers,
The radical polymerization initiator and the additives optionally added may be mixed simultaneously or separately, collectively or separately, and then melt-kneaded.

The heating temperature during the melt-kneading is from 130 to 1
A temperature of 40 ° C. is preferred from the viewpoint that the raw polypropylene resin is sufficiently melted and hardly thermally decomposed.
The time for melt-kneading (the time after mixing the radical polymerization initiator and the isoprene monomer) is generally 30 to
Preferably, it is 60 seconds.

Examples of the melt kneading apparatus include kneaders such as rolls, conneaders, Banbury mixers, Brabenders, single-screw extruders, and twin-screw extruders, horizontal-shape renewing machines, and twin-screw multi-disc machines. There is a device such as a stirrer, a vertical stirrer such as a double helical ribbon stirrer, which can heat a polymer material to an appropriate temperature and knead while applying an appropriate shear stress. Among these, a single-screw or twin-screw extruder is particularly preferred from the viewpoint of productivity. In addition, the melt-kneading may be repeated a plurality of times in order to sufficiently uniformly mix the respective materials.

The mica used in the present invention has a particle size of 10
It is less than 00 microns, even 2 to 1000 microns, especially 10 to 500 microns. The particle size is 100
If the thickness exceeds 0 micron, the generated bubbles become coarse, and a foam having a uniform cell structure cannot be obtained. In addition,
When the particle size is 2 μm or more, and more preferably 10 μm or more, the number of generated bubbles is reduced, the thickness of the cell film is increased, and the foam is hardly broken, and the foam has a wavy surface. The corrugation that occurs and becomes uneven is less likely to occur, which is preferable in obtaining a thick foam.

The amount of the mica is 0.001 to 10 parts, preferably 0.01 to 1 part, per 100 parts of the polypropylene resin. When the amount of added mica is less than 0.001 part, coarse cells are generated to make the cell structure non-uniform, and when it exceeds 10 parts, foam is broken and a thick foam is obtained. In addition, the extrusion becomes unstable, and the cost is disadvantageous.

The physical blowing agent used in the present invention includes a liquefied gas consisting of a hydrocarbon or halogenated hydrocarbon having a boiling point generally lower than the melting point of the base resin used in the production of foam, chlorine atom and Inorganic gas containing no fluorine atom in the molecule, water, alcohol, etc.

Specific examples of the physical foaming agent include aliphatic hydrocarbons such as propane, butane, pentane, hexane and heptane, cyclobutane, cyclopentane, and the like.
Alicyclic hydrocarbons such as cyclohexane, trichlorofluoromethane, dichlorodifluoromethane, chlorodifluoromethane, dichlorotetrafluoroethane, 1,1-
Halogenated hydrocarbons such as difluoro-1-chloroethane, 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, methyl chloride, ethyl chloride, methylene chloride, carbon dioxide, nitrogen, air,
Inorganic gas such as argon, water, alcohol and the like can be mentioned. These may be used alone or in combination of two or more.

Of these, propane or butane is suitable for producing a thick foam because of its good solubility in a polypropylene resin, and is preferable from the viewpoint of no ozone layer destruction and environmental compatibility.

The amount of the physical foaming agent varies depending on the type of the foaming agent and the target expansion ratio, but is usually 0.5 to 100 parts, more preferably 3 to 50 parts, per 100 parts of the polypropylene resin. Is preferred. The amount added is 0.5
If the amount is less than 100 parts, the expansion ratio becomes low, and it becomes difficult to obtain a thick foam. If the amount exceeds 100 parts, the extrusion agent tends to be unstable because the blowing agent is not completely dissolved.

When a foam is produced by the production method of the present invention, in addition to the polypropylene resin, mica, and a physical foaming agent, stabilizers such as antioxidants, metal deactivators, and ultraviolet stabilizers, lubricants, Plasticizers, pigments, dyes, flame retardants,
An additive such as an antistatic agent may be used. When these components are used, the content is preferably 10 parts or less with respect to the polypropylene resin. In addition, in order to obtain a clear effect by using these components, each of the components is required to be 0.1 to 0.1.
001 parts or more are preferable.

In the present invention, a foam is produced by melt-kneading at least the above polypropylene resin, mica and a physical foaming agent under pressure, and extruding the mixture into a low pressure region.

For the melt kneading under pressure, for example, a kneading cooling device such as a single-screw extruder, a twin-screw extruder, an onlator or the like, a plurality of these devices are connected, or a stirring mechanism such as a double helical ribbon stirrer is provided. An apparatus such as a pressure vessel capable of heating a polymer material to an appropriate temperature and kneading while applying an appropriate shear stress under pressure is used, but is not limited thereto.

The melt-kneading under pressure is carried out by mixing a mixture containing the polypropylene resin, mica and a physical foaming agent at a temperature of 130 to 300 ° C. where the polypropylene resin is melted, further at 160 to 250 ° C., and 0.1 to 30 MPa. Usually, the mixture is melt-kneaded under a pressure of 0.5 to 20 MPa.

The kneading is performed for 1 to 240 minutes in order to uniformly dissolve the physical foaming agent in the polypropylene resin.

After the above-described melt-kneading under pressure, the mixture is passed through a mouthpiece in a low-pressure range, usually 0 to 0 in absolute pressure.
It is extruded into a region of 0.5 MPa to obtain a foam.

Foams of various shapes can be obtained depending on the shape of a die used for extrusion, etc., and the thickness of the foamed material is 2 mm through a die having a rectangular opening shape (hereinafter also referred to as a rectangular die).
A plate-like foam having a thickness of 0 mm or more can also be produced.

The cell diameter of the foam varies depending on the type and amount of the foaming agent, the shape of the die used, and the like, but is 5 μm to 10 mm, and more preferably 0.1 mm to 5 mm.
mm.

The expansion ratio of the foam is preferably 10 times or more, and more preferably 20 times or more, in terms of lightness, heat insulation, cushioning, and compressive strength.

[0065]

EXAMPLES The method for producing a polypropylene-based resin foam of the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

The evaluation methods in Examples and Comparative Examples are summarized below.

(Expansion Ratio) The foam density was calculated from the weight and volume of the obtained foam, and the expansion ratio was calculated from the resin density before foaming / the foam density.

(Foam Thickness) The foam was cut in a direction perpendicular to the extrusion direction of the obtained foam, that is, in the width direction, and the thickness was measured.

(Cross-section magnification) The foam was cut in a direction perpendicular to the extrusion direction of the obtained foam, that is, in the width direction, and its cross-sectional area was measured and calculated as a magnification relative to the opening area of the rectangular die.

(Cell Structure) The cells of the foam were cut in a direction perpendicular to the extrusion direction of the manufactured foam, that is, in the width direction, and the cross section was taken as the observation site, and the cross section of the cell membrane included in the observation site was taken as the observation site. Colored with water-based black magic ink, and the number of bubbles in the visual field was 5 at the center of the cross section with an optical microscope.
Observation was performed at a magnification of 10 to 1000 times so as to reduce the number to about 0, the diameter of any 10 bubbles in the visual field was measured, and the uniformity of the cell structure was evaluated based on the following evaluation criteria.

：: The ratio of the measured maximum bubble diameter to the minimum bubble diameter is less than 2. Δ: The ratio of the measured maximum bubble diameter to the minimum bubble diameter is 2
It is 10. X: The ratio of the measured maximum bubble diameter to the minimum bubble diameter is 10
Beyond.

(Extended Viscosity Characteristics) A modified polypropylene resin (hereinafter also referred to as isoprene-modified PP) obtained by adding and mixing isoprene and a radical polymerization initiator to a raw polypropylene resin or a raw polypropylene resin A resin pellet was filled in a capillograph provided with an orifice having a diameter of 3 mm, melted at 200 ° C., and extruded to obtain a strand-shaped sample having a length of about 180 mm. Using this sample, using a Melten rheometer manufactured by Toyo Seiki Co., Ltd. at 180 ° C. and a strain rate of 0.0
At 5 / sec, the relationship between the elongational viscosity and the measurement time (strain amount) is measured. At this time, the elongational viscosity was measured by dividing the stress by the cross-sectional area of the sample measured by a charge-coupled device (CCD). That is, the extensional viscosity is given by the following equation:

[0073]

(Equation 3)

(Where η _e is the elongational viscosity (poise), σ is the stress per sectional area (dynes / cm ² ),

[0075]

[Outside 3]

Indicates the strain rate (/ sec),

[0077]

[Outside 4]

The formula is:

[0079]

(Equation 4)

(Where L is the length (cm) of the sample, t
Represents time (seconds)).

Example 1 100 parts of ethylene-propylene random copolymer (manufactured by Mitsui Chemicals, Inc., random PP Hypol B230, ethylene content 3%), 1,1-
Bis (t-butylperoxy) -3,3,5-trimethylcyclohexane 0.5 part, stabilizer (Nippon Ciba Geigy)
(Irganox B225, manufactured by Co., Ltd.) 0.2 parts of a mixture obtained by stirring and mixing with a ribbon blender were mixed by a measuring feeder.
It is supplied to a twin screw extruder (TEX44XCT-38) manufactured by Nippon Steel Works, and 2.5 parts of isoprene is supplied from the middle of the extruder using a liquid addition pump, and is melt-kneaded in the twin screw extruder.
By melt extrusion, pellets of a modified polypropylene resin (isoprene-modified PP) were obtained.

Using the obtained isoprene-modified PP, elongational viscosity characteristics were determined in accordance with the above method, and the relationship between the obtained elongational viscosity (η _e ) and the measurement time (t) was determined by log η _e and l
and plotted on a graph with ogt.

In FIG. 1, which shows the elongational viscosity characteristics of the isoprene-modified PP, the elongational viscosity increased gradually with a gentle slope for about 10 seconds immediately after the start of the measurement. ing. The flat part at the beginning of the measurement of the slope of the portion where the elongational viscosity is rapidly rising (the maximum slope of the slope of the straight line drawn from the portion where the elongational viscosity is rapidly rising over the measurement time) To the slope (the slope of a straight line drawn from a portion where the extensional viscosity rises relatively slowly with the elapse of the measurement time) (hereinafter sometimes referred to as a “specific extensional viscosity ratio”), 8.6.

In FIG. 2, the elongational viscosity characteristics of the starting polypropylene resin were determined and plotted on a graph in the same manner as in the case of the isoprene-modified PP. Could not be asked.

To 100 parts of the obtained isoprene-modified PP was added 0.1 part of mica (Mica B-82, manufactured by Mika Yamaguchi Co., Ltd., particle size: 82 μm), followed by mixing with a ribbon blender.

This mixture was subjected to a tandem type extruder (first-stage extruder (cylinder diameter 65 mm) equipped with an onlator.
φ), a second-stage extruder (cylinder diameter 90 mmφ), an onlator (a kneading and cooling device, a cylinder diameter 150 mm) was supplied to a foaming extruder connected by a continuous pipe, and melted at 230 ° C. in the first-stage extruder. Thereafter, 15 parts of isobutane gas as a foaming agent was injected into 100 parts of the molten resin and kneaded, and the mixture was cooled in a second-stage extruder so that the resin temperature became 140 ° C., and further introduced into an onlator.
Kneading at 60 ° C, slit width 60mm, slit thickness 3
The sheet was extruded from a rectangular die having a thickness of 2 mm to obtain a plate-like foam. The obtained foam had a beautiful appearance.

The expansion ratio of the obtained foam, the thickness of the foam,
The cross-sectional magnification and the cell structure were evaluated according to the above-described evaluation methods.

Table 1 shows the results.

Example 2 Isoprene-modified PP obtained in the same manner as in Example 1
To 100 parts, add 0.05 parts of blend oil (Super Ease manufactured by Koshigaya Kasei Kogyo Co., Ltd.) and 0.01 parts of mica (Mica A-21S, manufactured by Mika Yamaguchi Mfg. Co., Ltd., particle size 21 microns). And mixed with a ribbon blender.

Using the obtained mixture, a plate-like foam was obtained in the same manner as in Example 1. The obtained foam had a beautiful appearance.

The expansion ratio, foam thickness of the obtained foam,
The cross-sectional magnification and the cell structure were evaluated according to the above-described evaluation methods.

Table 1 shows the results.

Example 3 A high melt strength polypropylene resin, PF-814 (manufactured by Montel Co., Ltd.,
No. 121704, 100 parts of polypropylene having free-end long-chain branching and strain-hardening elongational viscosity according to the production method described in JP-A-121704, and blend oil (Koshigaya Chemical Industry)
0.05 parts, mica (manufactured by Mika Yamaguchi Corporation, mica A-41, particle size 41 microns)
0.05 parts were added and mixed with a ribbon blender.

Using the resulting mixture, a plate-like foam was obtained in the same manner as in Example 1. The obtained foam had a beautiful appearance.

The expansion ratio, foam thickness of the obtained foam,
The cross-sectional magnification and the cell structure were evaluated according to the above-described evaluation methods.

The results are shown in Table 1.

Example 4 1000 g of PF-814 and 0.5 g of mica (mica A-21S, manufactured by Mika Yamaguchi Corporation, particle size: 21 microns)
Were sealed in a pressure-resistant container having a capacity of 3000 cm ³ and a valve for discharging the contents and a rectangular die attached to the end. 100 g of isobutane gas was injected as a foaming agent and heated at 200 ° C. for 3 hours. At that time, the pressure inside the pressure vessel was about 1 MPa. In this state, the stirring shaft with the anchor blade was rotated at a speed of 10 rpm for 1 hour to melt-knead the mixture of PF814, mica and isobutane. Thereafter, the temperature was lowered to 155 ° C., the valve was opened, and nitrogen gas was fed into the pressure-resistant container at a pressure of 5 MPa. As a result, the foam was extruded through a rectangular die having a slit width of 10 mm and a slit thickness of 1.5 mm. The obtained foam had a beautiful appearance.

The expansion ratio, thickness of the foam,
The cross-sectional magnification and the cell structure were evaluated according to the above-described evaluation methods.

Table 1 shows the results.

[0100]

[Table 1]

Comparative Example 1 Isoprene-modified PP obtained in the same manner as in Example 1.
To 100 parts, 0.05 part of blended oil (Super Ease manufactured by Koshigaya Chemical Co., Ltd.) and 0.05 part of calcium carbonate (Super 2000, manufactured by Maruo Calcium Co., Ltd., particle size: 1.1 micron) are added. Mix in a ribbon blender.

A plate-like foam was obtained in the same manner as in Example 1 using the obtained mixture.

The expansion ratio of the obtained foam, the thickness of the foam,
The cross-sectional magnification and the cell structure were evaluated according to the above-described evaluation methods.

Table 2 shows the results.

The obtained foam was corrugated and had a cross-sectional enlargement ratio of only 9 times. Looking at the cross section of the foam, coarse cells and fine cells were mixed, and the distribution of cell diameters was uneven.

Comparative Example 2 Isoprene-modified PP obtained in the same manner as in Example 1.
To 100 parts, add 0.05 parts of blended oil (Super Ease manufactured by Koshigaya Kasei Kogyo Co., Ltd.) and 30 parts of mica (Mica B-82, manufactured by Mika Yamaguchi Mfg. Co., Ltd., particle size 82 microns), and add ribbon. Mix in blender.

The obtained mixture was extruded in the same manner as in Example 1, but the extrusion was not stable.
The foam did not become plate-like.

Comparative Example 3 Isoprene-modified PP obtained in the same manner as in Example 1.
100 parts of mica (Mica C-Made by Mica Yamaguchi Corporation)
113, particle size 1700 microns (1.7 mm)) 0.1
Parts were added and mixed with a ribbon blender.

A plate-like foam was obtained in the same manner as in Example 1 using the obtained mixture.

The foaming ratio, foam thickness, and
The cross-sectional magnification and the cell structure were evaluated according to the above-described evaluation methods.

Table 2 shows the results.

From Table 2, it can be seen that the expansion ratio is 35 times and the foam thickness is 2
A foam having a cross-sectional area of 5 mm and a cross-sectional area of 19 times the rectangular die area was obtained. However, when the cross-section of the foam was viewed, extremely coarse cells having a cell diameter of about 10 mm were scattered, and the cell structure was not uniform. Was.

Comparative Example 4 1000 g of PF-814 and azodicarbonamide, a chemical blowing agent that generates a gas upon heating (17 micron, Cell Mike CE, manufactured by Sankyo Chemical Co., Ltd.)
A plate-like foam was obtained in the same manner as in Example 4 using 0.5 g.

The expansion ratio of the obtained foam, the thickness of the foam,
The cross-sectional magnification and the cell structure were evaluated according to the above-described evaluation methods.

Table 2 shows the results.

The foam obtained was corrugated and had a cross-sectional magnification of only 12 times. Looking at the cross section of the foam, coarse cells and fine cells were mixed, and the cell structure was uneven.

[0117]

[Table 2]

[0118]

According to the present invention, a mixture obtained by adding a specific amount of mica having a specific particle size range to a polypropylene resin and a physical foaming agent are melt-kneaded under pressure and extruded into a low-pressure region to obtain a low-density and appearance. Beautiful, uniform cell structure,
A thick foam is obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing elongational viscosity characteristics of isoprene-modified PP used in Examples of the present invention.

FIG. 2 is a graph showing the elongational viscosity characteristics of a raw material polypropylene resin as a raw material of isoprene-modified PP used in Examples of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F074 AA24 AA40 AC36 AE01 BA38 CA22 CC22X DA02 DA14 DA59 4J002 BB121 BB141 DJ059 EA016 EA018 EA028 EB008 EK007 EQ017 FD157 FD328

Claims (5)

[Claims] 1. A method for producing a foam by melt-kneading at least a polypropylene resin, mica, and a physical foaming agent under pressure and extruding the mixture into a low pressure region, wherein the mica has a particle size of 1000 microns or less; A method for producing a polypropylene resin foam, wherein 0.001 to 10 parts by weight is added to 100 parts by weight of the resin. 2. A method for producing a foam by melt-kneading at least a polypropylene resin, mica, and a physical foaming agent under pressure and extruding the foamed material into a low pressure region, wherein the mica has a particle size of 2 to 1000 microns, A method for producing a polypropylene resin foam, wherein 0.001 to 10 parts by weight is added to 100 parts by weight of the polypropylene resin. 3. A method for producing a foam by melt-kneading at least a polypropylene resin, mica, and a physical foaming agent under pressure, and extruding the foamed material into a low pressure region, wherein the mica has a particle size of 10 to 500 microns, A method for producing a polypropylene resin foam, wherein 0.001 to 10 parts by weight is added to 100 parts by weight of the polypropylene resin. 4. The elongational viscosity of the polypropylene-based resin obtained by adding isoprene and a radical polymerization initiator to a raw polypropylene-based resin, followed by melt-kneading, and the elongational viscosity measured in a molten state increases rapidly as the amount of strain increases. 4. A modified polypropylene resin which rises to a high temperature.
The method for producing a polypropylene resin foam according to the above. 5. The method for producing a polypropylene resin foam according to claim 1, wherein the expansion ratio of the polypropylene resin foam is 20 times or more.