JPH10195219A - Polypropylene-based resin extruded foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject foam, capable of retaining a low density and a high closed-cell ratio even for a thick wall and useful for building materials, etc., by carrying out the extrusion foaming of a polypropylene-based resin composition having a specific elongational viscosity and a specified equilibrium compliance. SOLUTION: This polypropylene-based resin extruded foam is obtained by melt kneading (A) a polypropylene-based resin, preferably an ethylene (4-0.1 wt.%)-propylene (96-99.9wt.%) random copolymer with (B) a radically polymerizable monomer (styrene, etc.) and (C) a radical polymerization initiator (e.g. an organic peroxide) at a temperature for enabling the component A to melt and the component C to decompose, providing a modified polypropylene- based resin composition, capable of rapidly increasing the elongational viscosity, measured in a molten state and represented by the formula [η e is the elongational viscosity of a sample; σ e is the stress (N/m') based on the cross-sectional area of the sample; γ is the strain rate (sec<-> )] with increasing strain and having <1.2×10<-3> Pa<-1> Pa' equilibrium compliance measured at 210 deg.C and then carrying out the extrusion foaming of the resultant composition. The resultant foam has 10-100kg/m<3> density and >=60% closed-cell ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an extruded polypropylene resin foam. More specifically, it shows the excellent heat resistance and rigidity inherent to polypropylene resin, has a low density even if it is thick, has a uniform and fine cell structure with a high closed cell rate, and has various buffer packaging materials and building materials. The present invention relates to a polypropylene-based resin extruded foam which can be suitably used for such purposes.

[0002]

2. Description of the Related Art Polypropylene resins have been widely used in films, molded articles, fibers, etc. because of their excellent heat resistance, chemical resistance, electrical properties, etc., and have such excellent properties. Foams of polypropylene-based resin also have high industrial utility.

[0003] However, in general, a polypropylene resin is liable to break the cell membrane during extrusion foaming, and it is not easy to obtain a good foam having a high closed cell rate.

Under such circumstances, for example, Japanese Patent Publication No. 8-2
No. 521388 discloses a polypropylene sheet foam having a specific molecular weight, a molecular weight distribution and specific rheological properties.

However, a good foam can be obtained from the polypropylene only when it is intended to obtain a thin foam having a density of about 40 kg / m ³ and a thickness of about 5 mm. When attempting to obtain a thick extruded foam having a density of about 40 kg / m ³ and a thickness of about 10 mm or more using such polypropylene, the closed cell ratio is greatly reduced, and a good foam is obtained. There is a problem that is difficult.

Further, in order to prevent the decrease in the closed cell rate as described above, the production conditions have been changed. However, this cannot be an essential measure, and such production conditions have been further changed. In such a case, there is a problem that other undesirable phenomena occur, such as the extruded foam deforming in a wavy manner or the surface of the foam being peeled.

As described above, conventionally, a good foam having a relatively large thickness exceeding, for example, about 5 mm, a low density, and a high closed cell rate is not obtained. is there.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above prior art, and has a low density and a high closed cell ratio even if it is thick. An object of the present invention is to provide a polypropylene resin extruded foam suitably used.

[0009]

According to the present invention, the elongational viscosity measured in a molten state sharply increases with an increase in strain, and the equilibrium compliance measured at 210 ° C. is 1.2 × 10 ⁻³ Pa. Extruded and foamed a polypropylene resin composition having a density of less than ^-1 and a density of 10 to 100 kg / m.
³ and an extruded polypropylene resin foam having a closed cell ratio of 60% or more.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, in the extruded polypropylene resin foam of the present invention, the elongational viscosity measured in a molten state sharply increases with an increase in strain, and
1.2 × 10 equilibrium compliance measured at 10 ° C.
^It is obtained by extruding and foaming a polypropylene resin composition having a density of less than ^-3 Pa ^-1 , a density of 10 to 100 kg / m ³ , and a closed cell rate of 60% or more.

The polypropylene resin composition used as the base resin of the extruded foam of the present invention has a characteristic that the elongational viscosity measured in a molten state sharply increases with an increase in the amount of strain (hereinafter referred to as a specific resin). (Also referred to as elongational viscosity property).

Here, as a method for evaluating the elongational viscosity characteristic, a molded product of a strand-shaped resin composition having a diameter of about 3 mm is used as a sample, and the sample is completely melted by sandwiching both ends of the sample with a rotary clamp. Maintaining the temperature of the sample at a temperature (in the case of the polypropylene resin composition of the present invention, for example, about 180 ° C.), elongating the sample at a constant strain rate, and measuring the stress generated between the chucks with time. A method is employed in which the elongational viscosity is obtained from the relationship between the stress and the cross-sectional area of the sample at that time.

That is, the extensional viscosity is represented by the following equation.

[0014]

(Equation 1)

Next, the elongational viscosity determined as described above is plotted with time. At this time, the elongational viscosity is
It gradually increases as the measurement time elapses (as the strain amount increases), and from a certain measurement time (at a certain strain amount), the rate of increase in elongational viscosity increases more rapidly than before. Is said to have the specific elongational viscosity characteristics.

In the present invention, in the graph (curve) showing the relationship between the measurement time and the elongational viscosity, where the abscissa represents the logarithm of the time and the ordinate represents the logarithm of the elongational viscosity, the elongational viscosity is measured. In contrast to the slope of the straight line drawn from the initial part of the measurement, which rises relatively slowly with the passage of time, the straight line drawn from the part where the elongational viscosity rises most rapidly with the passage of the measurement time Is preferably 1.5 times or more, especially 2 times or more, from the viewpoint of further improving the properties of the obtained extruded foam. Although there is no particular upper limit on the ratio of the slopes of the two straight lines, it has been confirmed that the ratio is, for example, about 20 times.

The slope of each straight line drawn from the curve is obtained by the following equation.

Linear slope = Δ (logηe) / (Δlogt) For example, a graph (curve) Z representing the relationship between the elongational viscosity of the modified polypropylene resin composition obtained in Production Example 1 described below and the measurement time is shown in FIG. As shown in FIG. The curve Z shows that the modified polypropylene resin composition has a diameter of 3 mm and a length of 1 mm.
A sample molded into an 80 mm cylindrical rod was
It shows the relationship between the elongational viscosity (logηe) and the measurement time (logt) when elongated at 0 ° C. and a strain rate of 0.05 / sec.

In the curve Z of FIG. 1, the measurement time is about -1.
With respect to the slope (0.436) of the straight line X drawn from the flat part (the part where the elongational viscosity rises relatively slowly with the elapse of the measurement time) at the initial stage of the measurement, the measurement time Since the slope (1.85) of the straight line Y drawn from the portion where the elongational viscosity rises most steeply as the measurement time elapses is about 1.2 or more, it is about 4.2 times. It can be seen that the modified polypropylene resin composition obtained in Production Example 1 has an elongational viscosity that sharply increases with an increase in the amount of strain.

In the present invention, the conditions for measuring the elongational viscosity are not limited to the temperature of about 180 ° C., but may be higher than the temperature at which the polypropylene resin composition substantially melts, as described above. Yes, the temperature may be arbitrarily selected from a temperature range lower than the temperature at which the resin composition starts to thermally decompose. Usually, such a measurement temperature is 10 degrees lower than the melting point of the polypropylene-based resin composition in consideration of the melting point of the polypropylene-based resin composition itself and ease of measurement.
It is preferable to set the temperature in a temperature range higher by 50 ° C. The strain rate condition is generally 0.01 to 0.5 sec ^-1.
It is preferable to set within the range.

It is to be noted that a resin composition which exhibits the above-mentioned elongational viscosity property under any one of the measurement conditions within the range of the measurement temperature and the range of the strain rate condition is usually used. Such specific elongational viscosity characteristics are observed in the measurement under the measurement conditions within the entire range of these measurement temperature and strain rate conditions.

The polypropylene resin composition used as the base resin of the extruded foam of the present invention has a temperature of 210 ° C.
The equilibrium compliance measured at 1.2 × 10 ^-3 Pa
Another feature is that it is less than ^-1 .

Here, as a method for evaluating the equilibrium compliance, the following method is adopted.

That is, a molded article of the polypropylene-based resin composition is used as a sample, and the sample is sandwiched between two parallel disks, and the temperature is kept at 210 ± 1 ° C. to melt the sample. After the sample is sufficiently melted, the distance between the parallel disks is adjusted to 1.4 mm, and the resin composition protruding from the disk is removed. Then, at time t = 0, one of the disks is rotated with respect to the other so that the stress σc applied to the sample is maintained at a constant value of 100 N / m ² , and the amount of strain γ at that time is maintained for 300 seconds. (T) is measured over time.

Next, the creep compliance J (t) defined by the following equation is plotted with respect to the time t from the start of the application of the stress σc.

J (t) = γ (t) / σc = Jeo + t / η After a sufficient time has elapsed, the creep compliance J (t) has a linear relationship with the time t, and the equilibrium compliance Jeo is In the plot of the creep compliance J (t) and the time t, the portion where the two give a linear relationship is given as an intercept when the time t = 0 is extrapolated.

Thus, the equilibrium compliance of the polypropylene resin composition measured at 210 ° C. was 1.2 × 10 ⁻³ so that the obtained extruded foam had a low density and a high closed cell ratio. Less than Pa ⁻¹ ,
In terms of further improving the properties of such an extruded foam,
The equilibrium compliance is preferably 1 × 10 ⁻³ Pa ⁻¹ or less. The lower limit of the equilibrium compliance is not particularly limited, but is preferably about 1 × 10 ⁻⁵ Pa ⁻¹ or more.

The method for producing a polypropylene resin composition having a specific elongational viscosity characteristic and a specific equilibrium compliance used in the present invention is not particularly limited. For example, the polymerization method for producing a polypropylene resin composition is not limited. It is preferable to adopt a method in which the operation is performed in two or more stages and a method in which the resin composition is modified.

As a method for modifying the resin composition,
For example, (A) a polypropylene resin, (B) a radical polymerizable monomer and (C) a radical polymerization initiator,
(A) a method of melt-kneading at a temperature at which the polypropylene-based resin can be melted and (C) a temperature at which the radical polymerization initiator can be decomposed, (A) a polypropylene-based resin in an aqueous medium,
After suspending the (B) radical polymerizable monomer and the (C) radical polymerization initiator, the reaction is carried out at a temperature at which the (C) radical polymerization initiator can be decomposed, and the oxygen concentration in the atmosphere is kept low. (A) a method of irradiating a low level radiation to a polypropylene-based resin under the conditions, (A) a polypropylene-based resin and (C) a radical polymerization under a temperature condition such that the main chain cleavage of the resin does not occur preferentially. A method of melt-kneading an initiator and the like can be used.

Among the above-mentioned modification methods, (A) a polypropylene-based resin which can easily obtain a modified polypropylene-based resin composition having stable physical properties;
A method of melt-kneading (B) a radical polymerizable monomer and (C) a radical polymerization initiator at a temperature at which (A) the polypropylene resin can be melted and at a temperature at which (C) the radical polymerization initiator can be decomposed. Particularly preferred.

The polypropylene resin composition used in the present invention includes, in addition to the resin composition such as the modified polypropylene resin composition obtained as described above, (A) a polypropylene resin such as a polypropylene resin described below. This is a concept that includes the resin itself.

The (A) polypropylene resin used in the present invention includes, for example, a homopolymer of propylene, a block copolymer of propylene and another monomer, and a random copolymer of propylene and another monomer. A substantially linear crystalline polymer such as a coalesced polymer may be mentioned, but from the viewpoint of high rigidity and low cost, the homopolymer of propylene is preferred, and both rigidity and impact resistance are high. For this reason, a block copolymer of the propylene and another monomer is preferred. When the polypropylene resin (A) is a block copolymer of propylene and another monomer or a random copolymer of propylene and another monomer, the high crystallinity characteristic of the polypropylene resin is used. In view of maintaining the properties, high rigidity and good chemical resistance, the propylene content is preferably at least 75% by weight, more preferably at least 90% by weight.

In the (A) polypropylene resin, the other monomer copolymerizable with propylene is selected from, for example, ethylene, α-olefin, cyclic olefin, diene monomer and vinyl monomer. Also, at least one monomer can be used. Among them, ethylene, α-olefin and diene monomers are preferred in that they are easily copolymerized with propylene and are inexpensive.

Representative examples of the α-olefin copolymerizable with the propylene include, for example, butene-1, isobutene, pentene-1, 3-methyl-butene-1, hexene-1, 3-methyl-pentene-1, 4-methyl-pentene-1, 3,4-dimethyl-butene-1, heptene-
Α-olefins having 4 to 12 carbon atoms such as 1,3-methyl-hexene-1, octene-1, decene-1 and the like.

Representative examples of the cyclic olefin copolymerizable with the propylene include, for example, cyclopentene, norbornene, 1,4,5,8-dimethano-1,2,3,
4,4a, 8,8a-6-octahydronaphthalene and the like.

Representative examples of the diene monomer copolymerizable with propylene include, for example, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene,
4-hexadiene, methyl-1,4-hexadiene, 7
-Methyl-1,6-octadiene and the like.

Representative examples of the vinyl monomer copolymerizable with propylene include vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, and the like.
Examples include methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, and maleic anhydride.

[0038] Among these monomers, ethylene and butene-1 are more preferable because they are inexpensive.

In the present invention, among the polypropylene resins (A), a homopolymer of propylene and a propylene content of 96 to 9 are preferred in terms of buffer characteristics.
An ethylene-propylene random copolymer having an ethylene content of 9.9% by weight and an ethylene content of 4 to 0.1% by weight is particularly preferably used.

(A) The melt flow index (230 ° C.) of the polypropylene resin is not particularly limited.
Considering that the polypropylene resin composition has a viscosity suitable for extrusion foaming, 0.01 to 8
g / 10 minutes, preferably about 0.01 to 4 g / 10 minutes.

Further, if necessary, other resins and rubbers may be added to the polypropylene resin (A) as long as the effects of the present invention are not impaired.

Specific examples of the resin or rubber which can be used by mixing with the above-mentioned (A) polypropylene resin include, for example, poly-α-polyethylene such as polyethylene, polybutene-1, polyisobutene, polypentene-1 and polymethylpentene-1. Olefins; polydiene polymers such as polybutadiene and polyisoprene; vinyl polymers such as polystyrene, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl acetate, polyethyl acrylate, polybutyl acrylate, and polymethyl methacrylate Rubbers such as ethylene-propylene rubber and ethylene-propylene-diene rubber;

The components which can be used by being mixed with the (A) polypropylene resin are used to maintain the crystallinity, rigidity, chemical resistance, heat resistance, etc., which are the characteristics of the (A) polypropylene resin. Is preferably 30% by weight or less of the total amount with the polypropylene resin.
It is more preferred that the content be not more than% by weight.

Further, the polypropylene resin (A) may contain, if necessary, an antioxidant, a metal deactivator, a phosphorus-based processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent brightener, a metal soap, Stabilizers such as antacid adsorbents; crosslinking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing agents, pigments,
Additives such as dyes, flame retardants and antistatic agents may be added as long as the effects of the present invention are not impaired.

The (A) polypropylene resin containing kneading agents such as various other resins, rubbers, stabilizers and additives as necessary may be in the form of particles or pellets. The pod shape is not particularly limited.

When the above-mentioned kneading agent is used, the kneading agent may be added in advance to (A) the polypropylene-based resin, or may be added when (A) the polypropylene-based resin is melted. After the modified polypropylene resin composition is produced, it may be appropriately added to the modified polypropylene resin composition.

The radically polymerizable monomer (B) used in the present invention is selected from an aromatic vinyl compound and a conjugated diene compound in that it does not cause an appropriate decrease in melt viscosity during the modification. At least one is preferred.

Examples of the aromatic vinyl compound include styrene; methylstyrene such as o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, β-methylstyrene, dimethylstyrene, trimethylstyrene; Chlorostyrenes such as -chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, dichlorostyrene and trichlorostyrene; o-bromostyrene, m-bromostyrene, p-bromostyrene, dibromo Bromostyrenes such as styrene and tribromostyrene; o-fluorostyrene, m-fluorostyrene, p
-Fluorostyrene such as fluorostyrene, difluorostyrene and trifluorostyrene; nitrostyrene such as o-nitrostyrene, m-nitrostyrene, p-nitrostyrene, dinitrostyrene and trinitrostyrene; o-hydroxystyrene, m-hydroxystyrene , P-hydroxystyrene, dihydroxystyrene,
Vinylphenol such as trihydroxystyrene; o-
Divinylbenzene such as divinylbenzene, m-divinylbenzene and p-divinylbenzene; and isopropenylstyrene such as o-diisopropenylbenzene, m-diisopropenylbenzene and p-diisopropenylbenzene. Or a mixture of two or more. Among them, methylstyrene such as styrene, α-methylstyrene and p-methylstyrene, divinylbenzene, and a mixture of divinylbenzene isomers are preferred because they are inexpensive.

Examples of the conjugated diene compound include isoprene, 1,3-butadiene, chloroprene, 2-phenyl-1,3-butadiene and the like, and these may be used alone or in combination of two or more. be able to. Of these, isoprene and 1,
3-Butadiene is preferred because it is inexpensive.

The amount of the radical polymerizable monomer (B) used is
In order to sufficiently improve the foamability of the (A) polypropylene resin, it is preferably at least 3 parts by weight, especially at least 4 parts by weight, per 100 parts by weight of the (A) polypropylene resin. In order not to impair the inherent properties of the polypropylene resin such as good heat resistance, chemical resistance, and mechanical properties, (A) 15 parts by weight or less, especially 12 parts by weight, per 100 parts by weight of the polypropylene resin. It is preferable that the amount is not more than part by weight.

When the aromatic vinyl compound and the conjugated diene compound are used in combination, the ratio (weight ratio) of the amounts of the two is used.
Can be arbitrarily selected.

The radical polymerization initiator generally includes, for example, organic peroxides, azo compounds, inorganic peroxides and the like. Among the (C) radical polymerization initiators used in the present invention, among these, Organic peroxides are preferred.

Examples of the organic peroxide include ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide;
-Bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t
-Butylperoxy) valerate, 2,2-bis (t-
Peroxyketals such as butylperoxy) butane;
Permethane hydroperoxide, 1,1,3,3-
Hydroperoxides such as tetramethylbutyl hydroperoxide, 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) hexyne-3; diacyl peroxides such as benzoyl peroxide; di (3-methyl-3-methoxybutyl) peroxydicarbonate and di-2-methoxybutylperoxydicarbonate. Peroxydicarbonate; t-butylperoxyoctate, t-butylperoxyisobutyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butyl Peroxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, di-t-
Peroxyesters such as butyl peroxyisophthalate and the like can be mentioned, and these can be used alone or in combination of two or more. Among these, those having a particularly high hydrogen extraction ability are preferable.
-Bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t
-Butylperoxy) valerate, 2,2-bis (t-
Peroxyketals such as 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, 2,5-dimethyl- 2,5-di (t-
Dialkyl peroxides such as butylperoxy) hexyne-3; diacyl peroxides such as benzoyl peroxide; t-butylperoxyoctate;
-Butylperoxyisobutyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-
Trimethylhexanoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate,
It is preferable to use a peroxyester such as di-t-butylperoxyisophthalate alone or as a mixture of two or more.

The amount of the radical polymerization initiator (C) used should be at least 0.05 part by weight, preferably 0.1 part by weight, per 100 parts by weight of the polypropylene resin in order to obtain a sufficient modifying effect. Parts or more, and the melt viscosity of the resulting modified polypropylene-based resin composition is excessively reduced, or the economic efficiency is reduced, and it is difficult to obtain an extruded foam having a suitable shape and appearance. In order to eliminate the risk, it is preferable that the amount is 5 parts by weight or less, especially 2 parts by weight or less based on 100 parts by weight of the polypropylene resin (A).

(A) a polypropylene resin, (B)
There is no particular limitation on the mixing method and the melt-kneading method of the radical polymerizable monomer and (C) the radical polymerization initiator,
For example, (A) a polypropylene resin, (B) a radical polymerizable monomer and (C) a radical polymerization initiator, and other additives (kneading agents) added as necessary, and then melt-knead them. After melt-kneading (A) a polypropylene resin, (B) a radical polymerizable monomer and (C) a radical polymerization initiator,
And other additional materials added as needed,
They may be mixed simultaneously or separately, collectively or separately, and then melt-kneaded.

In the present invention, in order to obtain a modified polypropylene-based resin composition having desired properties, a temperature sufficient to melt the (A) polypropylene-based resin and to decompose the (C) radical polymerization initiator. It is important that these are melt-kneaded and reacted under the conditions.

In the present invention, the temperature at which (A) the polypropylene resin can be melted is a temperature range in which the crystal part of the resin melts and exhibits fluidity.
It refers to the temperature range above the melting point of the resin measured by differential scanning calorimetry (DSC).

In the present invention, the temperature at which (C) the radical polymerization initiator can be decomposed means that most of the radical polymerization initiator, for example, about 80% by weight or more of the radical polymerization initiator is substantially freed within the reaction time described later. Refers to the temperature range in which decomposition occurs.

Usually, the temperature at which the (A) polypropylene resin can be dissolved and the temperature at which the (C) radical polymerization initiator can be decomposed are in the range of about 170 to 300 ° C. Therefore, the melt kneading temperature for obtaining the modified polypropylene resin composition is 170 to 300 ° C.
It is preferable that the temperature is within the range, especially within the range of about 180 to 250 ° C. Under such conditions, the (A) polypropylene resin is sufficiently melted and hardly thermally decomposed. In addition, the time for the reaction is 0.1.
It is preferably about 5 to 60 minutes, especially about 1 to 10 minutes.

The apparatus used for the above-mentioned melt-kneading includes a kneader such as a roll, a co-kneader, a Banbury mixer, a Brabender, a single-screw extruder, a twin-screw extruder, a twin-screw surface renewer, and a twin-screw multi-circle Examples of such devices include a horizontal stirrer such as a plate device and a vertical stirrer such as a double helical ribbon stirrer, which can heat a resin to an appropriate temperature and knead each component while appropriately applying a shear stress. . Among these, a single-screw extruder and a twin-screw extruder are particularly preferred in terms of productivity and uniform denaturation. In addition, the melt-kneading may be repeated a plurality of times in order to sufficiently uniformly mix the components.

As a method for producing an extruded foam of the present invention, for example, (1) a (modified) polypropylene resin composition and a foaming agent are melt-kneaded in a melt extruder to form a foamable composition, and then the melt extruder is used. (2) a foaming agent is added or pressed into a molten (modified) polypropylene-based resin composition to form a foamable composition, and then a melt extruder is used. Examples include a method of obtaining an extruded foam by extruding.

For example, as an apparatus used for obtaining an extruded foam by the method (1) or (2), for example, a multi-screw extruder such as a single-screw extruder, a twin-screw extruder, one of these or one of them Any one such as a tandem type extruder in which two kinds are connected in series can be used. Further, an onerator for uniformly kneading and cooling the foamable composition, adjusting the speed at which the foamable composition is extruded from the die, an accumulator for cooling, and the like are suitably used as a part of an apparatus for extrusion foaming. .

When the method (1) is employed, it is preferable to use a pyrolytic foaming agent as the foaming agent. Examples of the thermal decomposition type blowing agent include N, N'-dinitrosopentamethylenetetramine, N, N'-dimethyl-
Nitroso-based blowing agents such as N, N'-dinitrosoterephthalamide; azo-based blowing agents such as azodicarbonamide and barium azodicarboxylate; A hydrazide-based blowing agent; trihydrazinotriazine and the like are preferably exemplified, and these can be used alone or in combination of two or more.

Addition amount (kneading amount) of the thermal decomposition type foaming agent
May be appropriately adjusted according to the type of the foaming agent and the target expansion ratio of the extruded foam, but within the range of 5 to 100 parts by weight based on 100 parts by weight of the (modified) polypropylene-based resin composition. Preferably, there is.

In order to control the cell diameter of the extruded foam, a foam nucleating agent such as talc or sodium bicarbonate-citric acid may be used. For example, pigments, stabilizers, fillers, flame retardants, antistatics Agents and the like may be used as needed within a range that does not impair the effects of the present invention.

In the case of the above method (1), (reforming)
The polypropylene resin composition and the pyrolytic foaming agent are both supplied to, for example, a melt extruder, and a gas is generated by thermally decomposing the foaming agent while melt-kneading at an appropriate temperature to generate a gas. By discharging the (modified) polypropylene-based resin composition in a state from a die, an extruded foam can be formed. The melt-kneading temperature and the melt-kneading time in such a method may be appropriately adjusted depending on the type of the foaming agent used and the kneading conditions, and vary depending on the type of the polypropylene resin, but usually the melt-kneading temperature is about 130 to 400 ° C. Kneading time is 1
Preferably, it is about 60 minutes.

When the method (2) is adopted, it is preferable to use a volatile foaming agent as the foaming agent. Examples of the volatile foaming agent include aliphatic hydrocarbons such as propane, butane, pentane, hexane and heptane; alicyclic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane; chlorodifluoromethane, difluoromethane and trifluoromethane. , Trichlorofluoromethane, dichloromethane, dichlorofluoromethane, dichlorodifluoromethane, trichlorofluoromethane, chloromethane, chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane , Trifluoroethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, tetrachlorodifluoroethane, chloropen Fluoroethane, halogenated hydrocarbons such as perfluorocyclobutane; carbon dioxide, nitrogen, inorganic gases such as air; and water is preferably exemplified, and these can be used alone or in admixture of two or more thereof.

The addition amount (kneading amount) of the volatile foaming agent is as follows:
What is necessary is just to adjust suitably according to the kind of a foaming agent and the target expansion ratio of an extruded foam, but it is 5-100 weight part with respect to 100 weight part of (modified) polypropylene-type resin compositions. Is preferred.

Also in this method, for controlling the cell diameter of the extruded foam, for example, talc,
A foam nucleating agent such as sodium bicarbonate-citric acid may be used, and, for example, a pigment, a stabilizer, a filler, a flame retardant, an antistatic agent, and the like may be used as needed within a range that does not impair the effects of the present invention. Good.

In the case of the above method (2), for example, the (modified) polypropylene-based resin composition is melted in an extruder, a volatile foaming agent is pressed into the extruder, and the molten state is maintained at a high pressure. (Modified) polypropylene resin composition is kneaded, and a kneaded product of the sufficiently kneaded (modified) polypropylene resin composition and volatile foaming agent is discharged from a die to form an extruded foam. can do.
The melt-kneading temperature and the melt-kneading time in such a method may be appropriately adjusted depending on the type of the foaming agent used and the kneading conditions, and vary depending on the type of the polypropylene-based resin. The kneading time is preferably about 1 to 120 minutes.

The extruded foam of the present invention thus obtained is
Since its density is 10 to 100 kg / m ³ , it has excellent properties such as light weight, heat insulation, buffering of external stress, compressive strength, etc.
The density is 15 kg / m ³ or more, and preferably 1 kg / m ³ , because it can be more suitably used for cushioning materials, building materials and the like.
8 kg / m ³ or more, preferably 40 kg / m ³ or more.
/ M ³ or less, preferably 36 kg / m ³ or less.

The extruded foam of the present invention has excellent heat insulating properties, cushioning against external stress and compressive strength because its closed cell ratio is 60% or more.
It is preferable that the closed cell ratio is 70% or more from the viewpoint that a foam having a higher cushioning property can be obtained.

From these facts, it is particularly preferable that the extruded foam of the present invention has a density of 15 to 40 kg / m ³ and a closed cell ratio of 60% or more.

The shape of the extruded foam of the present invention is not particularly limited, and may be sheet-like, board-like or other plate-like, tube-like, bag-like-like hollow, cylindrical, elliptic, prismatic, or the like.
Various shapes such as a columnar shape such as a strand shape are exemplified. Among these, when the extruded foam of the present invention is used, for example, as a cushioning material or a core material, a relatively thick plate having a thickness of, for example, 8 mm or more has a high closed cell rate and a low It is preferable in terms of the density and the like.

The thickness (wall thickness) of the extruded foam of the present invention
There is no particular limitation, and it may be appropriately controlled according to the application.

As described above, the extruded polypropylene-based resin foam of the present invention exhibits the excellent heat resistance and rigidity inherently possessed by the polypropylene-based resin. Since it has a high cell structure, it can be suitably used for various buffer packaging materials and building materials.

[0077]

EXAMPLES Next, the polypropylene resin extruded foam of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to only these Examples.

Production Example 1 100 parts by weight of an ethylene-propylene random copolymer (ethylene content: 3% by weight, melt flow index at 230 ° C .: 0.4 g / 10 minutes), 10 parts by weight of styrene, and a radical polymerization initiator 0.5 parts by weight of α, α′-bis (t-butylperoxy-m-isopropyl) benzene (1 minute half-life temperature: 175 ° C.) was placed in a twin-screw extruder (LABOTEX, manufactured by Nippon Steel Corporation). The mixture was melt-kneaded at 200 ° C. for 5 minutes and extruded to obtain a rod-shaped modified polypropylene resin composition having a diameter of 4 mm. The rod-shaped molded product of the modified polypropylene-based resin composition was chopped to a thickness of 3 mm to obtain pellets of the modified polypropylene-based resin composition (hereinafter, referred to as resin A).

The twin-screw extruder is of the same-direction twin-screw type, has a cylinder bore of 32 mmφ, and has a maximum effective screw length (L / D) of 25.5.
The twin-screw extruder was heated at a set temperature of the cylinder section of 200 ° C. and a set temperature of the feed section of 180 ° C., and the rotation speed of the screw was set at 100 rpm for each axis.

Production Example 2 In Production Example 1, 100 parts by weight of the ethylene-propylene random copolymer was added to a propylene homopolymer (melt flow index at 230 ° C .: 0.5 g / 10 min).
0 parts by weight, and the amount of α, α'-bis (t-butylperoxy-m-isopropyl) benzene was changed from 0.5 parts by weight to 1.8 parts by weight and melt-kneaded at 200 ° C. for 5 minutes. Otherwise in the same manner as in Production Example 1, pellets of a modified polypropylene resin composition (hereinafter referred to as resin B) were obtained.

Production Example 3 In Production Example 1, 10 parts by weight of styrene was added to isoprene 5
Parts by weight and the amount of α, α'-bis (t-butylperoxy-m-isopropyl) benzene was changed from 0.5 part by weight to 1 part by weight in the same manner as in Production Example 1 except that the modified polypropylene was used. A pellet of the resin composition (hereinafter referred to as resin C) was obtained.

Comparative Production Example 1 In Production Example 1, 100 parts by weight of the ethylene-propylene random copolymer was mixed with propylene homopolymer (melt flow index at 230 ° C .: 0.5 g / 10 min).
0 parts by weight, and the amount of α, α'-bis (t-butylperoxy-m-isopropyl) benzene was changed from 0.5 parts by weight to 2.3 parts by weight and melt-kneaded at 200 ° C. for 5 minutes. Otherwise, pellets of the modified polypropylene resin composition (hereinafter referred to as resin D) were obtained in the same manner as in Production Example 1.

Comparative Production Example 2 Production Example 1 was repeated except that the amount of α, α'-bis (t-butylperoxy-m-isopropyl) benzene was changed from 0.5 parts by weight to 5.2 parts by weight. In the same manner as in Example 1, pellets of the modified polypropylene resin composition (hereinafter referred to as resin E) were obtained.

Next, the resins A to E obtained in Production Examples 1 to 3 and Comparative Examples 1 to 2 and a propylene homopolymer having a linear molecular structure (melt flow index at 230 ° C .: 0.5 g / 10 min, hereinafter, resin F
And a propylene homopolymer having a long-chain branched structure in the resin (PF-814, 2 manufactured by Himont)
Melt flow index at 30 ° C .: 4 g / 10 minutes,
(Hereinafter referred to as resin G), the elongational viscosity characteristics and the equilibrium compliance were examined. Table 1 shows the results.

(Characteristics of Elongational Viscosity) Pellets of resin (A to G) were filled in a capillograph provided with an orifice having a diameter of 3 mm, melted at 200 ° C., and extruded to obtain a strand-like sample having a length of about 180 mm. Make it. This sample was measured at 180 ° C. and a strain rate of 0.05 / sec using a Melten rheometer (manufactured by Toyo Seiki Co., Ltd.).
At c, the relationship between the elongational viscosity and the measurement time (strain amount) is measured.

At this time, the elongational viscosity is determined 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 represented by the following equation.

[0088]

(Equation 2)

FIG. 1 shows the elongational viscosity (l) of the resin A in the molten state.
3 shows a graph (curve) Z representing the relationship between the measurement time (strain, logt) and the measurement time (strain amount, logt). The curve Z in FIG. 1 rises with a gentle slope immediately after the start of the measurement, but rises sharply thereafter. The slope (1.85) of the straight line Y drawn from the portion where the measurement time rises rapidly by about 1.2 or more (the portion where the elongational viscosity rises most rapidly with the passage of the measurement time). The measurement time is about -1
The ratio of the straight line X (0.436) drawn from the flat part (the part where the elongational viscosity rises relatively slowly with the elapse of the measurement time) at the initial stage of the measurement of 1.2 (hereinafter referred to as a specific ratio) Elongational viscosity).

The specific elongational viscosity ratio of the resins B to G is determined in the same manner as the resin A.

(Equilibrium compliance) The pellets of the resins A to G were heated at 190 ° C. under no pressure for 5 minutes at 50 kPa.
It is pressed at a pressure of g / cm ³ for 2 minutes and formed into a sheet having a thickness of 1.5 mm. Punch from this sheet with a diameter of 25
A mm disk is punched out to obtain a measurement sample.

For the measurement, a dynamic stress rheometer (DSR) (manufactured by Rheometrics) is used.
At this time, a parallel disk having a diameter of 25 mm is used as a fixture, and the temperature is maintained at 210 ± 1 ° C. After the sample is sufficiently melted between the parallel disks, the distance between the parallel disks is adjusted to 1.4 mm to remove the resin protruding from the parallel disks. Then, while rotating the plate on one side in one direction with a stress σc = 100 N / m ² with respect to the other plate,
The change with time of the distortion amount γ (t) at that time is measured over 300 seconds.

At this time, if the creep compliance J (t) (Pa ⁻¹ ) defined by the following equation is plotted against the time t from the start of applying the stress σc, a sufficient time elapses. , The creep compliance J (t) can be considered linear with respect to time t,
The equilibrium compliance Jeo represents the straight line at time t = 0.
Is obtained as the intercept when extrapolated to

J (t) = γ (t) / σc = Jeo + t / η

[0095]

[Table 1]

The resins E and F did not show any specific elongational viscosity characteristics.

Examples 1 to 3 and Comparative Examples 1 to 4 Plate-like extruded foams were prepared by using the pellets of resins A to G by the following method.

100 parts by weight of pellets of resins A to G shown in Table 2, 0.05 parts by weight of blend oil (Super Ease, manufactured by Koshigaya Chemical Industry Co., Ltd.) and sodium bicarbonate-citric acid (Eiwa Chemical Co., Ltd.) as a foam nucleating agent Cerbon S manufactured by
G / K) 0.15 parts by weight using a ribbon blender
Mix for minutes. This mixture is supplied to a tandem-type extruder (first-stage extruder cylinder diameter: 65 mmφ, second-stage extruder cylinder diameter: 90 mmφ), and the mixture is fed into the first-stage extruder.
After melting at 30 ° C., 15 parts by weight of butane gas (iso-rich butane gas, normal butane / isobutane (weight ratio): 15/85) as a foaming agent was injected and kneaded by 15 parts by weight with respect to 100 parts by weight of resins A to G. In the second-stage extruder, the resin was cooled to 145 ° C.
It was extruded from a rectangular die having a slit of 1.0 mm in height to obtain a plate-like extruded foam.

With respect to the obtained extruded plate-like foam, the closed cell ratio, the density and the minimum thickness of the cross section were examined in accordance with the following methods. Table 2 shows the results.

(A) Closed cell rate Multi-pycnometer (product name, Yuasa Ionics Co., Ltd.)
And a method described in ASTM D-2856.

(B) Density The density is obtained by dividing the weight by the volume obtained by the submersion method.

(C) Minimum thickness of cross section A plate-shaped extruded foam is cut perpendicularly to the extrusion direction using a cutter, and the thickness of the thinnest portion 5 mm or more inside from the end is measured with a vernier caliper.

[0103]

[Table 2]

From the results shown in Table 2, it was found that the resin exhibited specific elongational viscosity characteristics and had an equilibrium compliance of 1.2 × 10
Extruded foams of Examples 1 to 3 obtained using a polypropylene-based resin composition of less than ^-3 Pa ^-1 have a thickness of 20 m
It can be seen that despite having a large cell diameter of at least m, the cell has both a high closed cell rate of at least 70% and a low density of less than 30 kg / m ³ .

[0105]

The extruded polypropylene-based resin foam of the present invention exhibits excellent heat resistance and rigidity inherently possessed by the polypropylene-based resin, has a low density even when thick, and has a uniform and fine closed cell rate. It has a cell structure.

Therefore, the extruded polypropylene resin foam of the present invention can be suitably used for various buffer packaging materials and building materials.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the elongational viscosity (logηe) of a resin A obtained in Production Example 1 in a molten state and a measurement time (logt).

Claims (4)

[Claims] ^1. A polypropylene resin composition whose elongational viscosity measured in a molten state sharply rises with an increase in strain and whose equilibrium compliance measured at 210 ° C. is less than 1.2 × 10 ⁻³ Pa ^−1. The product is extruded and foamed, has a density of 10 to 100 kg / m ³ and a closed cell ratio of 60
% Extruded polypropylene resin foam. 2. The extruded polypropylene resin foam according to claim 1, which has a density of 15 to 40 kg / m ³ and a closed cell ratio of 60% or more. 3. A plate having a thickness of 8 mm or more.
Or an extruded polypropylene resin foam according to item 2. 4. The method according to claim 1, wherein the polypropylene resin composition comprises (A)
The polypropylene resin, (B) the radical polymerizable monomer and (C) the radical polymerization initiator are mixed at a temperature at which the (A) polypropylene resin can melt and at a temperature at which the (C) radical polymerization initiator can decompose. Modified by melt kneading, elongational viscosity measured in the molten state sharply increases with increasing strain, and equilibrium compliance measured at 210 ° C. is less than 1.2 × 10 ⁻³ Pa ⁻¹ 4. The extruded polypropylene resin foam according to claim 1, which is a polypropylene resin composition.