JPH11156879A - Polypropylene resin in-mold foamed molded product and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polypropylene resin in-mold foamed molded product excellent in mechanical strength, and a stable producing method thereof. SOLUTION: In-mold foam molding is performed by using polypropylene resin foamed particles having two melting peaks in a DSC curve obtained when temp. is raised from 40 deg.C/min by a differential scanning calorimeter and characterized by that the melt calorie QH1 of the peak on a high temp. side among them is 4.5-8.0 cal/g. In this case, the calorie QH2 of the melt peak originating from the melt peak on the high temp. side of foamed particles is set to 7.0 cal/g or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene-based resin-type internal foam molded article used as a heat-insulating material, a shock-absorbing packaging material, a pass-through box, and in particular, a shock-absorbing material for the interior and exterior of vehicles such as automobile bumpers and pillars, and the like. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In-mold foamed articles obtained by filling foamed polypropylene resin particles in a mold and subjecting them to heat foaming are excellent in cushioning properties, heat insulating properties and compressive strength. Widely used as core materials for automobile bumpers. However, in recent years, in the field of automobiles, there has been a demand for a foamed molded article having higher mechanical properties due to an increase in safety consciousness.

Hitherto, the following are known as foams in polypropylene resin molds having excellent mechanical properties and methods for producing the same.

[0004] In Japanese Patent Publication No. 63-24618, a DSC curve obtained by differential scanning calorimetry of a foamed molded article in a polypropylene-based resin mold shows a characteristic peak peculiar to the polypropylene-based resin and a temperature at a peak of the peak. A molded article having a crystal structure in which a high-temperature peak that is higher than the temperature of the peak by 5 ° C. or more appears. However, only the temperature of the two melting peaks of the DSC curve of the compact is specified here, and the heat of crystal fusion of the high-temperature side peak which is most important for the mechanical strength of the compact is described. However, high mechanical strength is not necessarily obtained in the foamed molded article in a polypropylene resin mold disclosed herein.

In Japanese Patent Application Laid-Open No. 3-254930, foamed polypropylene resin particles having an endothermic peak at a high temperature side of 4.0 cal / g or more are compression-filled into a mold at a compression ratio of 5 to 40%. A method for obtaining a molded body by heating with steam is disclosed. However, here, only the heat of fusion of the high-temperature endothermic peak of the expanded particles is disclosed, and the crystal heat of fusion of the high-temperature peak in the molded product, which is most important for the mechanical strength of the molded product, is described. And the heat of fusion of the high-temperature endothermic peak of the expanded particles used in Examples was 4.0 to 4.0.
It is a relatively low range of 5.1 cal / g, and sufficient mechanical strength is not obtained irrespective of the fact that a polypropylene resin having a melting point of 150 ° C. is used as the base resin.

Further, Japanese Patent Application Laid-Open No. Hei 8-20662 discloses that 10 to 60% of expanded polypropylene resin particles having a heat of fusion at the high temperature side peak of more than 3.5 cal / g and not more than 6.0 cal / g. It discloses a method of compressively filling a mold at a compression ratio and heating it with steam to obtain a molded body. However, according to this method, when the high-temperature-side melting peak calorie of the expanded particles exceeds 5.0 cal / g, the strength of the molded body decreases, and a molded body having a stable high mechanical strength is not necessarily obtained. Not. Also here,
No mention is made of the heat of crystal fusion at the high temperature side peak in the molded article, which is most important for the mechanical strength of the molded article, and this method is limited to only compression filling molding.

[0007]

DISCLOSURE OF THE INVENTION The present invention has solved the above-mentioned drawbacks of the prior art, has improved the mechanical properties of a foamed molded article in a polypropylene-based resin mold, and has improved the mechanical properties. An object of the present invention is to provide a method capable of stably producing a foamed molded article in a polypropylene resin mold.

[0008]

The present invention SUMMARY OF], such circumstances result of intensive research in view of the out heat of two melting peaks with the polypropylene resin expanded particles, a relatively high specific melting peak heat QH ₁ on the high temperature side molded in a mold using a material obtained by adjusting to a range of, moreover, by increasing the melting peak heat QH ₂ on the high temperature side of the obtained molded article, mechanical strength of the foamed molded article is improved, also, the type The inventors have found that a molded body having high mechanical strength can be stably obtained by setting the temperature of the heated steam at the time of internal molding to a specific temperature range, and have completed the present invention.

That is, the present invention uses a differential scanning calorimeter of 40
The DSC curve obtained when the temperature was raised from 10 ° C. to 220 ° C. at a rate of 10 ° C./min. Had two melting peaks, and the heat of fusion QH of the high-temperature side peak among the two melting peaks.
_{The in-} mold foam molding is carried out using expanded polypropylene-based resin particles in which ₁ is 4.5 to 8.0 cal / g, and the calorific value Q of the melting peak derived from the high-temperature side melting peak of the expanded particles.
A foamed molded article in a polypropylene resin mold having H ₂ of 7.0 cal / g or more, and 40 ° C. with a differential scanning calorimeter
Has two melting peaks in the DSC curve obtained when the temperature is increased from 10 to 220 ° C. at a rate of 10 ° C./min, and the heat of fusion QH _{1 of the} high-temperature side peak of the two melting peaks.
Is filled with 4.5 to 8.0 cal / g of the polypropylene-based resin expanded particles in a molding die, and the temperature is higher than the low-temperature-side melting peak temperature + 2 ° C and the boundary temperature between two melting peaks -2 ° C or lower. Heating with steam at a temperature in the range, the calorific value Q of the melting peak derived from the high-temperature side melting peak of the expanded particles
The method for producing a foamed article in a polypropylene-based resin mold characterized in that the foamed article is molded so that H ₂ becomes 7.0 cal / g or more. A method for producing a foamed article in a polypropylene resin mold, which is obtained by applying a gas pressure of .18 atm or more, filling this into a molding die, and heating and molding with steam.

In the DSC curve obtained when the polypropylene resin expanded particles are heated at a rate of 10 ° C./min from 40 ° C. to 220 ° C. by a differential scanning calorimeter, the raw material resin of the polypropylene resin is inherently It has two melting peaks, a melting peak based on the melting in the crystalline state and a melting peak appearing on the higher temperature side.

The differential scanning calorimetry according to the present invention will be described. As a measuring device, a conventional differential scanning calorimeter, for example, Perkin-Elmer (Perkin-Elme)
r), DSC-2200H manufactured by Seiko Denshi Kogyo KK, and the like. In the present invention,
The melting peak calories on the low temperature side and the high temperature side of the expanded polypropylene resin particles and the in-mold expanded molded product are as shown in Samples 1 to 1.
With respect to 0 mg, the measurement is carried out at a heating rate of 10 ° C./min with the measuring device as described above.

FIG. 1 is a graph of the DSC curve of the expanded polypropylene resin particles used in Example 1 described below.
FIG. 2 shows a method of measuring a heat of fusion QH ₁ based on a high-temperature side peak among two melting peaks of expanded polypropylene resin particles. FIG. 2 shows a molded article of a polypropylene resin in-mold obtained in Example 1. of a graph of the DSC curve shows a method of measuring heat QH ₂ melting peaks in the polypropylene-based resin-mold molded product derived from the high temperature side melting peak of the polypropylene resin foamed beads.

The heat of fusion QH _{1 at the} peak on the high temperature side of the expanded polypropylene resin particles (the heat of fusion peak on the high temperature side in the total heat of fusion of the crystals of the expanded polypropylene resin particles) will be described with reference to FIG. A straight line d is drawn from the straight line a based on the melting start point (point c) to the straight line d from the boundary point (point b) between the low-temperature peak and the high-temperature peak.
Lower the perpendicular line e to the high temperature side peak and straight line d, the area surrounded with the perpendicular line e, and the high temperature side melting peak heat QH ₁ of PP beads.

Next, FIG. 2 shows the heat of fusion QH ₂ of the high-temperature side peak of the expanded foamed product in the polypropylene-based resin mold derived from the high-temperature side melting peak of the expanded polypropylene resin particles.
From the straight line a ′ based on the end of melting, a straight line d ′ is drawn to the melting start point (point c ′), and the low temperature side peak and the high temperature side peak of the expanded polypropylene resin particles used for in-mold molding are obtained. From the boundary point temperature (point b), the straight line d '
'Down the high temperature side peak and the straight line d' perpendicular e to, the area surrounding the perpendicular line e 'and the high-temperature side melting peak heat QH _2.

[0015] Foamed polypropylene resin used in the present invention
Heat of fusion QH of peak at high temperature side of particle ₁Are 4.5-8.
0 cal / g, preferably 5.0-7.0 cal / g
is there. Heat of fusion QH at peak on high temperature side of expanded particles₁Is 4.
Good molded product is obtained even when less than 5 cal / g
However, in this case, the high-
Heat quantity QH_TwoIs not high enough and has sufficient mechanical strength
Does not appear. Heat of fusion QH at peak on high temperature side of expanded particles
₁Is 4.5 cal / g or more, so that the compressive strength
The in-mold foam molded article excellent in the above can be obtained. Also, departure
Heat of fusion QH at peak on high temperature side of foam particles₁Is 8.0 cal
/ G, internal fusion increases during in-mold molding.
The temperature of the steam must be raised in order to
Is melted, and the heat of fusion QH_Two
, The compressive strength of the compact tends to decrease
is there. Therefore, the high-temperature side of polypropylene-based resin expanded particles
Heat of fusion QH of peak₁To 4.5-8.0 cal / g
By doing so, it is possible to obtain an in-mold foam molded article with excellent compressive strength
Rukoto can.

The calorific value Q of the melting peak derived from the high-temperature side melting peak of the expanded polypropylene resin particles in the expanded polypropylene resin molded article according to the present invention.
H ₂ is 7.0cal / g or more. When the calorific value QH ₂ of the melting peak in the molded article derived from the high-temperature side melting peak of the expanded particles is less than 7.0 cal / g, the amount of crystals in the high-temperature side melting peak region required for developing mechanical strength is small. The compressive strength of the compact tends to decrease. Since the amount of crystals of the high-temperature side melting peak area necessary mechanical strength development the more heat QH ₂ melting peaks in-mold foamed article from a high temperature side melting peak of the expanded particles is increased,
The mechanical strength of the molded body is improved.

The calorific value QH _{2 of the} melting peak derived from the high-temperature side melting peak of the expanded polypropylene resin particles is 7.0 ca.
polypropylene resin mold expansion-molded article according to the present invention which is a l / g or more, a heat of fusion QH ₁ on the high temperature side peak as described above polypropylene resin foamed beads is 4.5~8.0cal / g After filling in a molding die, it can be obtained by heating and molding with steam having a temperature in a range of not less than a low-temperature side melting peak temperature + 2 ° C and a boundary temperature between two melting peaks -2 ° C or less.

As described above, in the in-mold molding method of the expanded polypropylene resin particles according to the present invention, the heating steam temperature is set to be equal to or higher than the melting peak temperature on the low temperature side of the expanded particles + 2 ° C. and between the low temperature side and the high temperature side. The boundary temperature between the two melting peaks is set to −2 ° C. or less. When the steam temperature is lower than the low-temperature-side melting peak temperature + 2 ° C., the high-temperature-side melting peak calorific value QH ₂ of the in-mold foam molded article is not sufficiently increased, and a high compressive strength cannot be obtained. On the other hand, when the water vapor temperature is higher than the boundary temperature between the two melting peaks, −2 ° C., the high-temperature side melting peak calorific value QH _{2 of the in-} mold foam molded article decreases, and the compressive strength decreases. By setting the heating steam temperature during the in-mold molding of the polypropylene resin pre-expanded particles within the above temperature range, the amount of crystals in the high-temperature region of the obtained in-mold foam molded product increases, and the molded product having a high compressive strength stably. Can be obtained.

In the in-mold foam molding method of the present invention, the expanded polypropylene resin particles to be used are added in advance by 1.1.
By applying a gas pressure of 8 atm or more, a molded body having better surface properties can be obtained.

The mechanical strength of the foamed molded article in a polypropylene resin mold according to the present invention produced as described above is as follows:
Specifically, in the measurement of the compression strength of a foamed article in a polypropylene-based resin mold having a density of 25 to 100 g / L according to NDS-Z0504, the strength at a compressibility of 50% satisfies the following formula (1). I do. Y ≧ 0.15X−2.0 (1) [wherein, Y represents the compressive strength (Kg / cm ² ), and X represents the density of the compact (g / L). ]

[0021]

DETAILED DESCRIPTION OF THE INVENTION Examples of the polypropylene resin used in the present invention include propylene homopolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-propylene-butene random copolymer, propylene-chlorinated vinyl. Copolymers, propylene-butene copolymers, propylene-maleic anhydride copolymers and the like are mentioned, and those produced by a stereoregular polymerization method are preferred. These may be used alone or as a mixture of two or more. The proportion of the propylene component in the polypropylene resin is 50% by weight or more, preferably 8% by weight.
0% by weight or more.

These propylene resins are preferably in a non-crosslinked state, but may be crosslinked by peroxide or radiation. Further, other thermoplastic resins that can be used in combination with the propylene-based resin, for example, low-density polyethylene, linear low-density polyethylene, polystyrene, polybutene, ionomers, and the like may be mixed and used within a range in which the properties of the propylene-based resin are not lost. . For example, when low-density polyethylene, linear low-density polyethylene, polystyrene, polybutene, and an ionomer are used in combination, 5 to 20 parts with respect to 100 parts (parts by weight, hereinafter the same) of the polypropylene-based resin; 5 to 10 parts are more preferred. Also, when a thermoplastic resin other than the above is used in combination, the content is preferably 20 parts or less based on 100 parts of the polypropylene resin.

These polypropylene resins are usually
Extruders, kneaders, Banbury mixers, rolls, etc., are melted in advance so as to be easily used for prefoaming, and are formed in a desired particle shape such as a columnar shape, an elliptical shape, a spherical shape, a cubic shape, and a rectangular parallelepiped. The average particle size of the particles is 0.1 to 10
mm, preferably 0.7 to 5 mm.

The expanded polypropylene resin particles used in the present invention have two melting peaks as measured by the DSC method, and have a heat of fusion QH ₁ of 4.5 to 8 based on the higher temperature peak of the two melting peaks. 0.0 cal / g. The relationship between the two melting peaks is not particularly limited, but the difference between the two melting peaks is 10 to 25 ° C.
It is preferable because fusion during molding heating is facilitated.
The two melting peak temperatures vary depending on the molecular structure of the resin, the heat history of the resin, the amount of the foaming agent, the foaming temperature, the foaming pressure, and the like. However, when foaming is performed at a higher temperature, the temperature difference between the two melt peaks increases. The melting peak on the low temperature side is 125 to 15
In the range of 5 ° C., the melting peak on the high temperature side is usually 145.
It is in the range of １７175 ° C. and varies depending on the type of propylene resin used.

The heat of fusion based on the high temperature side peak is 4.
There is no particular limitation on the method for producing the foamed polypropylene resin particles of 5 to 8.0 cal / g. For example, a volatile foaming agent is added to the polypropylene resin particles in a pressure vessel and dispersed in water with stirring. After heating to a predetermined foaming temperature under pressure, a method such as releasing the aqueous dispersion to a low pressure region may be used. The high-temperature-side melting peak calorific value varies depending on the molecular structure of the resin, but generally decreases as the foaming temperature increases.

When the melting point (melting peak temperature) of the polypropylene resin particles is set to TM ° C., the expanded particles used in the present invention depend on the type of the propylene resin, the amount of the blowing agent used, the expansion ratio of the target expanded particles, and the like. , Can be easily obtained by setting the foaming temperature in the range of approximately (TM-20) to (TM) ° C.

The volatile blowing agent for impregnating the propylene resin particles used in the present invention includes, for example, propane,
Aliphatic hydrocarbons such as butane, pentane and hexane;
Aliphatic hydrides such as cyclopentane and cyclobutane; and halogenated hydrocarbons such as trichlorotrifluoromethane, dichlorodifluoromethane, dichlorotetrafluoromethane, trichlorotrifluoroethane, methyl chloride, methylene chloride, and ethyl chloride. These blowing agents may be used alone,
Also, two or more kinds may be used in combination. The amount of the propylene-based resin particles is not particularly limited and may be appropriately used depending on the desired degree of expansion of the expanded propylene-based resin particles. The amount is usually 5 to 50 parts based on 100 parts of the propylene-based resin particles.

In preparing the aqueous dispersion, as a dispersant, for example, tribasic calcium phosphate, basic magnesium carbonate, calcium carbonate, or the like, or a small amount of a surfactant, for example, sodium dodecylbenzenesulfonate or sodium n-paraffin sulfonate. , Α-olefin sodium sulfonate and the like are used in combination as a dispersing aid. The dispersant and the surfactant as a dispersing agent as described above vary depending on the type and the amount of the propylene-based resin particles used and the amount used,
Usually, 0.2 to 3 in the case of a dispersant with respect to 100 parts of water.
Parts, in the case of a surfactant, 0.001 to 0.1 part.

The propylene resin particles containing the volatile blowing agent are usually added in an amount of 20 to 100 parts per 100 parts of water in order to improve the dispersibility in water. preferable.

The aqueous dispersion prepared as described above is
After being heated under pressure, the propylene-based resin particles are released under a low pressure through an opening orifice having a diameter of 2 to 10 mm to foam the propylene-based resin particles. can get.

The aqueous dispersion is heated in advance in a pressure vessel as described above under pressure to the foaming temperature. The heating temperature depends on the type of propylene-based resin particles used and the DSC of the intended propylene-based resin foamed particles. It depends on which value the calorie of the melting peak on the high temperature side measured by the method is selected, so it is not uniquely determined, but as described above, the propylene resin particles used are measured by the DSC method. The melting point (melting peak) is TM
-20) to (TM) ° C. On the other hand, the foaming pressure is selected mainly according to a predetermined foaming ratio, but is generally about 10 to 50 kg / cm ² -G.

The structure of the pressure vessel is not particularly limited.
Any material can be used as long as it can withstand the pressure and temperature described above. Specific examples of the pressure-resistant container include, for example, an autoclave-type pressure-resistant container.

As a method of molding the expanded foamed article in the polypropylene resin mold according to the present invention, the expanded foamed polypropylene resin particles are filled in a mold that can be closed but cannot be sealed, heated with steam or the like, Are heat-fused with each other and molded according to a mold. Further, in the molding of the present invention, a gas pressure of 1.18 atm or more may be applied before filling the foamed particles into the mold. In this case, the polypropylene resin foamed particles are compressed under the pressure of inorganic gas. , A gas pressure of 1.18 atm or more can be applied.

[0034]

Next, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Production of expanded polypropylene resin particles]
Ethylene-propylene random copolymer (Grand Polymer Co., Ltd. product, ethylene content 2.4% by weight, M
I (melt flow index) = 7) pellets (one particle weight: about 1.8 mg, DSC melting point TM = 152.5)
C) 100 parts, isobutane 5 to 15 parts, powdered basic tribasic calcium phosphate 2.0 parts as a dispersant and n
-0.05 parts of sodium paraffin sulfonate were placed in a pressure vessel together with 300 parts of water, and each was heated to a predetermined temperature.
The pressure in the container at this time is about 12 to 17 kg / cm ² -G
Met. Subsequently, while isobutane is being pressed into the pressure in the container, a predetermined foaming pressure of 16 to 23 kg / cm ² -G is applied.
Was adjusted. When a predetermined foaming pressure is delivered, while maintaining the pressure inside the container, the valve at the lower part of the pressure-resistant container is opened, and the aqueous dispersion is discharged under atmospheric pressure through an orifice plate having an opening diameter of 4.4 mmφ to perform foaming. Six types of expanded polypropylene resin particles 1 to 6 were obtained.

The obtained expanded particles have an expansion ratio of 10.0 to
16.0 fold, melting peak heat QH ₁ based on the high temperature side of the melting peak measured by DSC method was as shown in Table 1.

[0037]

[Table 1]

[Production of foamed molded article in polypropylene resin mold] The foamed polypropylene particles obtained as described above are put in a pressure vessel, at a temperature of 70 ° C. and a pressure of 7.2 kg / c.
What was processed for 1 hour at m ² -G was 290 × 270 × 6
Filled into a 0 mm block mold, about 3.5 kg / cm ²
-G to 5.0 kg / cm ² -Heat molding at a steam pressure of -G, no fusing, no problem in surface appearance, Examples 1 to
4 and Comparative Examples 1-4 were obtained. For the obtained foamed molded article in a polypropylene resin mold, the peak heat of fusion QH ₂ , the density, and the strength at the time of 50% compression were measured, and the results are shown in Table 2.

[0039]

[Table 2]

FIG. 3 is a graph showing the relationship between the 50% compressive strength and the density of the molded articles of the above Examples and Comparative Examples. FIG. 3 shows, as an example of a conventional foamed molded article in a polypropylene-based resin mold, the compressive strength, density and density of the molded articles disclosed in JP-A-3-25493 and JP-A-8-20662. The relationship was also shown.

[0041]

As described above, the foamed molded article in the polypropylene resin mold of the present invention has higher compressive strength than the conventional foamed molded article in the polypropylene resin mold.
5X-2.0 [where Y is the compressive strength (Kg / cm
² ), X is the green density (g / L). Is satisfied. Further, according to the production method of the present invention, it is possible to stably produce a foamed molded article in a polypropylene resin mold having high compressive strength.

[Brief description of the drawings]

FIG. 1 is a graph showing a DSC curve of expanded ethylene-propylene random copolymer particles used in Example 1,
Method of measuring the heat of fusion QH ₁ on the high temperature side peak of the polypropylene resin foamed beads is a diagram showing a.

FIG. 2 is a graph of a DSC curve of the molded article obtained in Example 1, which shows a method for measuring the heat of fusion QH ₂ of the high-temperature peak in the molded article derived from the high-temperature peak of the foamed particles.

FIG. 3 is a graph showing the relationship between the strength at the time of 50% compression and the density of a foamed molded article in a polypropylene-based resin mold according to an example of the present invention, a comparative example, and a conventional polypropylene-based resin molded article.

Claims (7)

[Claims] 1. From 40 ° C. to 220 ° C. with a differential scanning calorimeter
In the DSC curve obtained when the temperature was raised at a rate of 10 ° C./min, there were two melting peaks, and the heat of fusion QH ₁ of the high-temperature side peak of the two melting peaks was 4.5 to 4.5.
8.0cal / g and is using the polypropylene resin expanded particles becomes to mold foaming, the foamed heat QH ₂ melting peaks derived from the high temperature side melting peak of the particles 7.0
cal / g or more foamed molded article in a polypropylene resin mold. 2. The heat of fusion QH ₁ at the high temperature side peak is 5.0.
The foamed molded article in a polypropylene resin mold according to claim 1, wherein the molded article is molded using polypropylene resin foamed particles having a particle size of from 7.0 to 7.0 cal / g. 3. The ND having a density of 25 to 100 g / L.
A foamed molded article in a polypropylene resin mold having a strength at a compressibility of 50% that satisfies the following formula (1) in the measurement of compression strength in accordance with S-Z0504. Y ≧ 0.15X−2.0 (1) [wherein, Y represents the compressive strength (Kg / cm ² ), and X represents the density of the compact (g / L). ] 4. The foam according to claim 1, wherein the expanded polypropylene resin particles are an ethylene-propylene random copolymer.
4. The foamed molded article in a polypropylene resin mold according to 2 or 3. 5. The polypropylene-based resin-type internal foam molded article according to claim 1, which is a shock absorbing material for interior and exterior of a vehicle. 6. From 40 ° C. to 220 ° C. by a differential scanning calorimeter.
In the DSC curve obtained when the temperature was raised at a rate of 10 ° C./min, there were two melting peaks, and the heat of fusion QH ₁ of the high-temperature side peak of the two melting peaks was 4.5 to 4.5.
After the foamed polypropylene resin particles of 8.0 cal / g were filled in a molding die, the melting peak temperature on the low temperature side +2
When heated with steam at a temperature of not less than 2 ° C. and a boundary temperature between two melting peaks and not more than −2 ° C., the calorific value QH _{2 of the} melting peak derived from the high-temperature side melting peak of the expanded particles in the obtained molded product is 7 A method for producing a foamed article in a polypropylene-based resin mold, wherein the foamed article is molded so as to have a caliper of 0.0 cal / g or more. 7. The foamed polypropylene resin particles are provided with a gas pressure of 1.18 atm or more with an inorganic gas, filled in a molding die, and heated with steam to be molded. A method for producing a polypropylene resin in-mold molded article of the above.