JP2000143856A - Extrusion expandable material comprising modified polypropyrene resin and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an expandable material comprising a polypropyrene resin having a beautiful surface, uniform inner foam having a high independent foam content, and excellent in processability, and its manufacturing method. SOLUTION: This polypropyrene resin extrusion expandable material comprising modified polypropyrene has an elongation viscosity measured in melt condition rapidly increasing with the quantity of strain, and the difference (Tt2-Tt1) of heat absorption initiation transition temp. (Tt1) and heat absorption termination transition temp. (Tt2) of not less than 20 deg.C in the peak melting heat absorption measured by a differential scanning calorimeter. This manufacturing method of polypropyrene resin extrusion expandable material comprises melting and kneading of a mixture of the modified polypropyrene resin and an expanding agent in an extruder, cooling the mixture to by not less than 2 deg.C lower than the melting peak temp. (Tm) of the modified polypropyrene resin measured by the differential scanning calorimeter, and then extrusion to a low pressure region for expansion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method and a device for measuring the elongational viscosity, which is measured in a molten state, sharply increases as the strain increases.
And from a modified polypropylene resin having a difference ((Tt2−Tt1)) between the endothermic onset transition temperature (Tt1) and the endothermic end transition temperature (Tt2) of 20 ° C. or more in the melting endothermic peak measured by the differential scanning calorimeter. And a method for producing the same.

[0002]

2. Description of the Related Art In general, a foam made of a thermoplastic resin is lightweight and has good heat insulating properties and good buffering properties against external stress. Therefore, it is widely used as a heat insulating material, a cushioning material, a core material, a food container and the like. It's being used. Above all, foams made of a polypropylene-based resin have good chemical resistance, impact resistance, and heat resistance, and are therefore particularly preferably used as cushioning materials. However, since the polypropylene-based resin is a crystalline resin, the viscosity and tensile strength at the time of melting are low, and when the resin is foamed, the strength of the cell wall is not sufficiently maintained at the time of foaming. Further, since this resin has a low gas barrier property, when the resin is foamed, the gas generated from the foaming agent is more easily scattered to the outside than the air bubbles. Therefore, it was difficult to obtain a low-density foam having a uniform surface, a high closed cell ratio, and excellent workability by foaming the polypropylene resin. Heretofore, as a method for producing an extruded foam, a crystalline substantially linear polyolefin has been used.
Press in a blowing agent having a boiling point in the range of 45 to + 70 ° C;
A production method of cooling and extruding to a temperature lower than the melting point of the polymer by 2 ° C. or more (Japanese Patent Publication No. 46-31755) and the like are disclosed.

However, even if these methods are used,
Still satisfactory foams are difficult to obtain.

[0004] As described above, there is still a method for producing a low-density foam having a beautiful surface with improved foamability of the polypropylene resin, uniform internal cells, high closed cell ratio and excellent workability. At present it has not been found.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a foam made of a modified polypropylene resin having uniform internal cells, a high closed cell ratio and excellent workability, and a beautiful surface, and a method for producing the same. .

[0006]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the elongational viscosity measured in a molten state sharply increases as the strain amount increases, and the differential scanning calorific value increases. In the melting endothermic peak measured by the meter,
Endothermic transition temperature (Tt1) and endothermic transition temperature (Tt1)
2) A mixture of a modified polypropylene resin having a difference ((Tt2−Tt1)) of 20 ° C. or more and a foaming agent is melt-kneaded in an extruder, and the mixture is measured by a differential scanning calorimeter. Peak temperature (T
m), the extruded foam obtained by extruding foam in the low pressure region after cooling at 2 ° C. or more has a high closed cell ratio, has a uniform cell diameter, and has excellent workability. They found that they were bodies and arrived at the present invention.

That is, according to the present invention, the elongational viscosity measured in a molten state sharply increases as the strain amount increases, and the melting endothermic peak measured by a differential scanning calorimeter is:
Endothermic transition temperature (Tt1) and endothermic transition temperature (Tt1)
2) Extruding a polypropylene resin extruded foam made of a modified polypropylene resin (Claim 1) in which the difference ((Tt2−Tt1)) is 20 ° C. or more, and a mixture of the modified polypropylene resin and a foaming agent. Melt kneading in an extruder,
The extruded polypropylene resin foam, wherein the mixture is cooled by 2 ° C. or more below the melting peak temperature (Tm) of the modified polypropylene resin measured by a differential scanning calorimeter and then extruded into a low pressure region. Wherein the modified polypropylene resin is at least one monomer selected from a linear polypropylene resin, a styrene monomer, an isoprene monomer and a 1,3-butadiene monomer; The extruded polypropylene resin foam according to claim 1, which is a modified polypropylene resin obtained by melt-kneading a radical polymerization initiator (Claim 3), wherein the modified polypropylene resin is a linear polypropylene resin, styrene monomer , At least one monomer selected from isoprene monomer and 1,3-butadiene monomer, and a radical polymerization initiator are melt-kneaded. Erareru is a manufacturing method of polypropylene resin extruded foam according to claim 2, wherein the modified polypropylene resin (claim 4).

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Although the reason why the foamability of a polypropylene resin is remarkably improved in the present invention is not clear, it is considered that the temperature dependency of the melt viscosity is smaller than that of a normal polypropylene resin. The modified polypropylene resin, ie, the elongational viscosity measured in the molten state, rises sharply as the strain increases, and the endothermic transition temperature (Tt1) at the melting endothermic peak measured by a differential scanning calorimeter. Using a modified polypropylene resin having a difference in endothermic end transition temperature (Tt2) ((Tt2−Tt1)) of 20 ° C. or more, and supercooling by 2 ° C. or more from the melting peak temperature (Tm) of the modified polypropylene resin. It is presumed that this was due to the fact that foaming of the cell membrane during foaming was extremely suppressed by extruding and foaming in a state where the foaming was performed. That is, the foam of the present invention comprising a modified polypropylene resin having uniform internal cells, a high closed cell ratio, and excellent workability and having a beautiful surface has not been known at all, and is surprising. In the present invention, the characteristic that the elongational viscosity measured in a molten state sharply increases as the strain amount increases will be described below. As a method for evaluating this 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 between rotary clamps, and a temperature at which the sample is completely melted (for example, The temperature of this sample is maintained at about 180 ° C. in the case of the modified polypropylene resin in the invention, and the sample is elongated at a constant strain rate,
There is a method in which the stress generated between the chucks is measured over time, and the elongational viscosity is determined from the relationship between the stress and the cross-sectional area of the sample at that time. The temperature at which the sample is completely melted is a temperature that is arbitrarily selected from a temperature equal to or higher than the temperature at which the resin melts and lower than a temperature at which the resin starts to thermally decompose.
-250 ° C, more preferably 180-230 ° C. The constant strain rate is usually 0.01 to 0.5 / sec, and more preferably 0.1 to 0.5 / sec, since measurement can be easily performed.
It is selected from the range of 01 to 0.1 / sec. That is, the elongational viscosity is represented by the following equation.

[0009]

(Equation 1) (Where η _e is the elongational viscosity (poise), σ is the stress per sectional area (dynes / cm ² ), and γ is the strain rate (/ sec)
Is shown. Γ is given by

[0010]

(Equation 2) Where L indicates the length of the sample (cm) and t indicates the time (second). ) The elongational viscosity rises sharply as the strain amount increases when the obtained elongational viscosity is plotted over time (specifically, logη _E and l
ogt), the elongational viscosity gradually increases as the measurement time elapses, that is, as the strain amount increases. From a certain measurement time (at a certain strain amount), the elongational viscosity becomes higher than before. Rapidly increases (the slope of the graph increases).

In a curve representing the relationship between the measurement time and the elongational viscosity obtained by taking the logarithm of the measurement time on the abscissa and the logarithm of the elongational viscosity on the ordinate, the elongational viscosity in the initial stage of measurement of the curve is the measurement time. The slope of the straight line drawn from the part where the elongational viscosity rises most steeply as the measurement time elapses is 1.2 times or more the slope of the straight line drawn from the part that rises relatively slowly with the passage of time. It is more preferably 1.5 times or more, particularly preferably 2.0 times or more. Note that the slope of each straight line drawn from the above curve is obtained by the following equation.

[0012]

(Equation 3) Next, the endothermic onset transition temperature (Tt1) and endothermic end transition temperature (Tt2) are determined by heating a polypropylene resin from 40 ° C. to 210 ° C. at a rate of 10 ° C./min with a differential scanning calorimeter, and then at 10 ° C./min. The relationship between the endothermic amount and the temperature based on the crystal melting when the temperature is cooled from 40 ° C. to 210 ° C. at 10 ° C./min after cooling to 40 ° C. is determined by the transition temperature measurement method of a differential scanning calorimeter. That is, the endothermic onset transition temperature (Tt1) is a temperature (Tt1 *) that is 5 ° C. lower than the tangent and the melting peak temperature (Tm) at the temperature of the flat portion before the endotherm starts in the relationship between the endothermic amount and the temperature in the differential scanning calorimeter. ) Is defined by the intersection of the tangents. The endothermic transition temperature (Tt)
2) is a temperature (Tt2 *) 5 ° C. higher than the tangent and the melting peak temperature (Tm) at the temperature of the flat portion after the endothermic end.
Is defined by the intersection of the tangents at. This relationship is shown in FIG. The value of (Tt2−Tt1) is preferably 50 ° C. or less.

[0013]

FIG. 1 As a specific example of the modified polypropylene resin of the present invention, for example, a linear polypropylene resin is irradiated with radiation or a linear polypropylene resin, a radical polymerization initiator, and a monomer are melt-mixed. And the like, and a polypropylene-based resin composition having a lightly crosslinked structure substantially free of a branched structure or a gel component obtained by such a method. Among these, linear polypropylene resin,
It is preferable because a modified polypropylene resin obtained by melt-mixing a radical polymerization initiator and a monomer can be produced at low cost.

As the linear polypropylene resin,
It may be any of a propylene homopolymer, a block copolymer and a random copolymer. Of these, propylene copolymers and propylene homopolymers containing 75% by weight or more of propylene are particularly preferred. The copolymerizable monomers in the polypropylene copolymer include, in addition to ethylene, 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-1,
3-methyl-hexene-1, octene-1, decene-1
Α-olefins having 4 to 12 carbon atoms; cycloolefins such as cyclopentene and norbornene. The melt flow index (MI) of the polypropylene resin is 230 according to JIS K7210.
It is preferably 0.2 or more from the viewpoint of processability under a load of 2.16 kg at a temperature of 20 ° C., and 20 or less, particularly from the viewpoint of maintaining the viscosity of the polypropylene resin composition at the time of melting to a degree suitable for foaming. It is preferably 10 or less.

Examples of the radical polymerization initiator include peroxides and azo compounds. In the present invention, the presence of a radical polymerization initiator having a hydrogen abstracting ability with respect to the polymer molecules of the polypropylene resin is preferable. .

As the radical polymerization initiator, peroxide,
And azo compounds. Specific examples include ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide; 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, , 1-bis (t-butylperoxy)
Peroxy ketals such as cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate and 2,2-bis (t-butylperoxy) butane; permethane hydroperoxide, 1,1,3 Hydroperoxides such as 2,3-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-butyl Dialkyl peroxides such as peroxy) hexyne-3;
Diacyl peroxides such as benzoyl peroxide; peroxydicarbonates such as di (3-methyl-3-methoxybutyl) peroxydicarbonate and di-2-methoxybutylperoxydicarbonate; t-butylperoxyoctate; t-butylperoxyisobutyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxyisopropyl carbonate,
2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-
One or more organic peroxides such as peroxyesters such as butylperoxybenzoate and di-t-butylperoxyisophthalate are exemplified. Among them, those having high hydrogen extraction ability are particularly preferable.
As such a radical polymerization initiator, for example, 1,
1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) Peroxyketals such as valerate and 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-
Dialkyl peroxides such as butyl peroxide and 2,5-dimethyl-2,5-di (t-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-
One or more of peroxyesters such as 2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate are listed. Can be

The styrene monomer, isoprene monomer and 1,3-butadiene monomer may be used alone or in combination. When used in combination, the usage ratio is arbitrary. The amount of the monomer (or monomer mixture) is preferably 0.1 to 50 parts by weight based on 100 parts by weight of the raw material polypropylene resin. Further, the amount is preferably 0.1 to 20 parts by weight from the viewpoint of compatibility with the resin.

The amount of the radical polymerization initiator to be added is determined in view of optimizing the melt viscosity of the modified polypropylene resin and being economical.
It is preferably 0.05 to 5 parts by weight based on parts by weight.

The modified polypropylene resin 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, an antacid absorption. Additives such as stabilizers or cross-linking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants, antistatic agents, etc. as long as the object of the present invention is not hindered May be added.

At least one monomer selected from such a linear polypropylene resin, a styrene monomer, an isoprene monomer and a 1,3-butadiene monomer, a radical polymerization initiator and, if necessary, The mixing method and the melt-kneading method of other added materials to be added are not particularly limited, and examples thereof include a linear polypropylene resin, a styrene monomer, an isoprene monomer, and 1,3.
A mixture of at least one monomer selected from butadiene monomers, a radical polymerization initiator and other optional materials added as necessary, followed by melt-kneading, or mixing with a linear polypropylene resin. After melt-kneading additional materials added as necessary, at least one monomer selected from a styrene monomer, an isoprene monomer and a 1,3-butadiene monomer, a radical polymerization initiator May be mixed simultaneously or separately, collectively or separately, and then melt-kneaded.

The melt kneading apparatus includes a roll,
Kneaders such as co-kneaders, Banbury mixers, Brabenders, single-screw extruders, twin-screw extruders, twin-screw surface renewers,
Examples of such devices include a horizontal stirrer such as a multi-shaft disk device or a vertical stirrer such as a double helical ribbon stirrer, which can heat a polymer material to an appropriate temperature and knead it while applying an appropriate shear stress. Of these, especially uniaxial or 2
A screw extruder is preferred in terms of productivity. In addition, the melt-kneading may be repeated a plurality of times in order to sufficiently and uniformly mix the respective materials.

In the melting endothermic peak measured by the differential scanning calorimeter, the difference ((Tt2−Tt1)) between the endothermic transition temperature (Tt1) and the endothermic transition temperature (Tt2) is 20 ° C.
The modified polypropylene resin as described above can be produced by means such as manipulating the molecular weight distribution of the raw material linear polypropylene resin. In particular, as the molecular weight distribution increases, the temperature difference represented by (Tt2−Tt1) tends to increase. As a method of increasing the molecular weight distribution, when producing a modified polypropylene-based resin, using a linear polypropylene-based resin having a large molecular weight distribution, using a mixture of linear polypropylene-based resins having different molecular weights, a modification reaction, Utilizing such methods to broaden the molecular weight distribution. As a specific method for producing the foam, for example, a mixture composed of a modified polypropylene resin and a foaming agent is melt-kneaded in an extruder, and then the mixture is melted at a melting peak temperature of the modified polypropylene resin composition ( 2 ° C below Tm)
A method of obtaining a foam by cooling and extruding the above, a foaming agent is added or pressed into a modified polypropylene resin in a molten state, and then the mixture is subjected to a melting peak temperature (Tm) of the modified polypropylene resin. Under 2 ° C. or lower and extruding to obtain a foam. The extruder is not particularly limited as long as it can heat the modified polypropylene resin in a molten state and can knead it while giving an appropriate shear stress, and may be any of a single screw or a twin screw extruder. Further, these extruders may be used in combination with two, three or multiple stages in series. In particular, a two-stage tandem-type extruder is more preferable from the viewpoint of uniformity of the mixed composition of the modified polypropylene resin and the foaming agent and productivity.

As the foaming agent, for example, propane,
Aliphatic hydrocarbons such as butane, pentane, hexane and heptane; alicyclic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane; chlorodifluoromethane, difluoromethane, trifluoromethane, trichlorofluoromethane, dichloromethane, dichlorofluoromethane, Dichlorodifluoromethane, trichlorofluoromethane, chloromethane, chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, dichlorotetrafluoroethane, trichloro Trifluoroethane, tetrachlorodifluoroethane, chloropentafluoroethane, perfluorocyclobutane What halogenated hydrocarbons; carbon dioxide, nitrogen, inorganic gases such as air; one or two or more of such water.

The addition amount (kneading amount) of the blowing agent varies depending on the type of the blowing agent and the target expansion ratio, but may be in the range of 2 to 30 parts by weight with respect to 100 parts by weight of the modified polypropylene resin. preferable.

In order to control the cell diameter of the foam to an appropriate size, if necessary, sodium bicarbonate may be used.
A foam nucleating agent such as citric acid or talc or mica may be used in combination. Usually, the addition amount of the foaming nucleating agent used as needed is preferably 0.01 to 1 part by weight based on 100 parts by weight of the modified polypropylene resin composition.

The foam of the present invention and the foam obtained by the production method of the present invention are low-density foams having a uniform internal cell state, light weight, beautiful appearance, and a high closed cell ratio, and a packaging material, a cushioning material. It is useful in materials, thermal insulation, and other uses.

[0027]

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to only these examples. The evaluation methods used in the examples and comparative examples are summarized below. (Relationship between Elongational Viscosity Measured in Melted State of Polypropylene-Based Resin and Measurement Time (Strain Amount)) A pellet of polypropylene-based resin is filled into a capillary having an orifice having a diameter of 3 mm, melted at 200 ° C., and extruded. And a strand-like sample having a length of about 180 mm.
Using this sample, at 180 ° C. and a strain rate of 0.05 / sec, using a Merten rheometer manufactured by Toyo Seiki Co., Ltd.
The relationship between the elongational viscosity and the measurement time (strain amount) is measured. Note that the stress per cross-sectional area was determined by dividing the stress by the cross-sectional area of the sample measured with the charge-coupled device.

Next, the obtained values (elongational viscosity and measurement time) were plotted on a graph in which the horizontal axis represents logarithm of time and the vertical axis represents logarithm of elongational viscosity.

When the obtained correlation line indicates that the modified polypropylene resin of the present invention is used as a sample, the elongational viscosity increases with a gentle slope immediately after the start of the measurement, and the elongational viscosity rapidly increases from a certain position. However, the ratio of the slope of the portion where the extensional viscosity rises sharply (the slope of the straight line drawn from the portion where the extensional viscosity rises most steeply as the measurement time elapses) to the gentle slope at the beginning of the measurement ( (Specific elongational viscosity ratio). (Endothermic transition temperature (Tt1) and endothermic transition temperature (Tt1)
t2) Measurement) 5 mg of a polypropylene resin is sealed in an aluminum pan, and a differential scanning calorimeter (DS manufactured by Seiko
C SSC-5000) at a heating rate of 10 ° C / min.
After heating from 0 ° C to 210 ° C, 4 ° C at 10 ° C / min
It was cooled to 0 ° C and heated again to 210 ° C at 10 ° C / min. The endothermic transition temperature (Tt1) and the endothermic transition temperature (Tt2) determined by the transition temperature measurement method of the differential scanning calorimeter were obtained from the relationship between the endothermic amount and the temperature during the second heating. That is, the endothermic onset transition temperature (Tt1) is a temperature (Tt1 *) that is 5 ° C. lower than the tangent and the melting peak temperature (Tm) at the temperature of the flat portion before the endotherm starts in the relationship between the endothermic amount and the temperature in the differential scanning calorimeter. From the intersection of the tangents at. Endothermic end transition temperature (Tt2)
Was obtained from the intersection of the tangent at the temperature of the flat portion after the endotherm was completed and the tangent at a temperature (Tt2 *) 5 ° C. higher than the melting peak temperature (Tm). (Expansion ratio) The expansion ratio was determined by dividing the resin density by the foam density. (Closed cell ratio) The appearance of the foam was measured by an air pycnometer according to the method described in ASTM D-2856. (Appearance of foam) The appearance of the foam was visually judged according to the following criteria.

○: Shrinkage and swelling of foam surface less than 10% ×: Shrinkage and swelling of foam surface 20% or more (Example 1) Ethylene random polypropylene (Hypol manufactured by Grand Polymer Co., Ltd.) B230, MI = 0.
5 g / 10 minutes, ethylene content: 3% by weight) 100 parts by weight, 1,1-di (t-butylperoxy) -3,3,5-trimethylcyclohexane (manufactured by NOF Corporation, as a radical polymerization initiator, 0.5 parts by weight of Perhexa 3M, 1 minute half-life temperature 147 ° C.), 0.2 parts by weight of stabilizer (Irganox B225 manufactured by Ciba-Geigy), 0.05 parts by weight of blend oil (SuperEase manufactured by Koshigaya Chemical Co., Ltd.) Parts of the mixture were stirred and mixed with a super floater.
The mixture was put into a hopper opening of a 44 mm twin-screw extruder at 50 kg / hr using a measuring feeder, and an attached liquid feed pump (manufactured by Nikkiso Co., Ltd.) was supplied at a rate of 1.25 kg / hr of isoprene. Diaphragm: Model C22X-
08F-14D1D, discharge pressure 50 kgf / cm 2) from the middle of the extruder cylinder to about 2.5 isoprene.
Parts by weight were press-fitted. The mixture was extruded at a rotation speed of 150 rpm at 180 ° C. before injecting isoprene and at 200 ° C. after injecting to produce a modified polypropylene resin. The melting peak temperature Tm of the modified polypropylene resin is 144
° C.

Based on 100 parts by weight of the modified polypropylene resin, 0.05 parts by weight of the blended oil and mica (A21S; YAMAGUCHI MI) as a cell nucleating agent.
0.02 parts by weight (manufactured by CA POWDER) were added and mixed with a super floater. Then, the mixture is fed to a 65-90 mmφ tandem type extruder, the rotation speed of the first stage extruder (65 mmφ) is set to 80 rpm, the temperature is set to 200 ° C., and the mixture is melted. 18 parts by weight were press-mixed with 100 parts by weight of the resin composition. Next, the mixture is fed to a second-stage extruder (90 mmφ) set at a rotation speed of 10 rpm and a temperature of 140 ° C. Then, the mixture was fed to a cooler having a rotation speed of 7 rpm, a temperature of 136 ° C. and a length of 1.5 m and an inner diameter of 155 mmφ, stayed in the cooling mixer for 10 minutes, a discharge amount of 50 kg / hr, a width of 50 mm and a die gap of 2 mm. The mixture was discharged from a slit die having a land length of 20 mm, and passed through a sizing having a width of 250 mm and a length of 250 mm while maintaining an interval of 25 mm to obtain an extruded foam.

[0032] (Example 2) isoprene monomer styrene monomer 10 parts by weight, the radical polymerization initiator alpha, alpha ^`- bis (t-butylperoxy -m- isopropyl) benzene (NOF Corporation Same as Example 1 except that the product was changed to 1.0 parts by weight (manufactured by Perbutyl P, 1 minute half-life temperature: 175 ° C.). Melting peak temperature Tm of modified polypropylene resin
Was 144 ° C.

Example 3 The isoprene monomer was 1,3-
Same as Example 1 except that butadiene monomer was used. The melting peak temperature Tm of the modified polypropylene resin is 14
3 ° C.

(Example 4) 65-90 in Example 1
isoprene 1 in the first stage extruder of a mmφ tandem extruder.
Same as Example 1 except that the weight part was additionally press-fitted. The melting peak temperature Tm of the modified polypropylene resin was 144 ° C.

[0035] (Example 5) Ethylene random polypropylene of Example 1 was changed to homopolypropylene (Grand Polymer Co., Ltd. F109BA, MI = 6g / 10 minutes), a radical initiator alpha, alpha ^`- bis ( t-butylperoxy-m-isopropyl) benzene (manufactured by NOF CORPORATION, perbutyl P, 1 minute half-life temperature 175 ° C)
Same as Example 1 except for changing to 0.5 parts by weight. The melting peak temperature Tm of the modified polypropylene resin is 164 ° C.
Met.

Comparative Example 1 Example 1 was repeated except that the ethylene random polypropylene of Example 1 was used without modification.
Same as. The melting peak temperature Tm of ethylene random polypropylene was 143 ° C.

(Comparative Example 2) Modified homopolypropylene (PF814 manufactured by Montell Co., MI = 2 g / 10 min.)
Was used directly without modification, and the second-stage extruder and the cooler of the 65-90 tandem extruder were set at 152 ° C., the same as Example 1. The melting peak temperature Tm of the homopolypropylene was 161 ° C.

Table 1 shows the compounding tables of the respective polypropylene resins used in the Examples and Comparative Examples, and Tables 2 and 3 show the resin properties and foaming results.

FIG. 2 shows the relationship between the elongational viscosity of the modified polypropylene resin used in Example 1 and the measurement time.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

FIG. 2

[0044]

The extensional viscosity measured in the molten state sharply rises as the strain increases, and the endothermic transition temperature (Tt1) and the endothermic transition at the melting endothermic peak measured by a differential scanning calorimeter. Difference in temperature (Tt2) ((Tt2
2-Tt1)) a modified polypropylene resin having a temperature of 20 ° C. or higher and a mixture of the resin and a foaming agent are melt-kneaded in an extruder, and the mixture is melted at a melting peak temperature (Tm) of the modified polypropylene resin. The foam obtained by extruding and foaming in a low-pressure region while cooling at a temperature of 2 ° C. or more below has uniform internal cells, a high closed cell ratio, and excellent workability. It is a foam and is useful in packaging materials, cushioning materials, heat insulating materials, and other uses.

[Brief description of the drawings]

FIG. 1 is a diagram showing how to determine an endothermic transition temperature Tt1 and an endothermic transition temperature Tt2 in the present invention.

FIG. 2 is a graph showing the elongational viscosity characteristics of the modified polypropylene resin used in Example 1 of the present invention and the unmodified polypropylene resin of Comparative Example 1.

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Claims (4)

[Claims] An elongational viscosity measured in a molten state sharply rises with an increase in strain, and an endothermic transition temperature (Tt1) and an endothermic end transition at a melting endothermic peak measured by a differential scanning calorimeter. Difference in temperature (Tt2) ((Tt2
2-Tt1)) A polypropylene resin extruded foam comprising a modified polypropylene resin having a temperature of 20 ° C or higher. 2. A mixture comprising the modified polypropylene resin according to claim 1 and a foaming agent is melt-kneaded in an extruder,
2. The polypropylene-based mixture according to claim 1, wherein the mixture is cooled to at least 2 ° C. below a melting peak temperature (Tm) of the modified polypropylene-based resin measured by a differential scanning calorimeter and then extruded into a low-pressure region. A method for producing a resin extruded foam. 3. The modified polypropylene resin is at least one monomer selected from a linear polypropylene resin, a styrene monomer, an isoprene monomer and a 1,3-butadiene monomer, and a radical polymerization initiator. 2. The extruded polypropylene resin foam according to claim 1, which is a modified polypropylene resin obtained by melt-kneading. 4. The modified polypropylene resin is at least one monomer selected from a linear polypropylene resin, a styrene monomer, an isoprene monomer and a 1,3-butadiene monomer, and a radical polymerization initiator. 3. The method for producing an extruded polypropylene resin foam according to claim 2, wherein the foam is a modified polypropylene resin obtained by melt-kneading.