JP2000219766A - Foamed polypropylene resin molding and automotive interior furnishing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foamed polypropylene resin molding with its surface capable of lamination with or bonding to a skinning material by pressure- molding foamed resin particles obtained by foaming a polypropylene random copolymer. SOLUTION: A base resin is obtained which has a melting point of 140 deg.C or above and comprising a polypropylene random copolymer obtained by copolymerizing propylene with 0.05-10.0 wt.% comonomer selected from ethylene and a 4C or higher α-olefin. Foamed resin particles obtained by foaming this resin are packed into a mold and foamed by heating to obtain a molding having a difference of at least 5 J/g between the heat quantity in an endothermic peak in the first DSC curve (an endothermic peak in a DSC curve as obtained when 2-4 mg of a sample of the foamed molding is first heated to 220 deg.C at a rate of temperature rise of 10 deg.C/min on a differential scanning calorimeter) and the heat quantity in an endothermic curve in the second DSC curve (an endothermic peak as obtained when the molding heated to 220 deg.C is cooled to 40 deg.C at a rate of temperature fall of 10 deg.C/min and heated again to 220 deg.C).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamed molded article of a polypropylene resin and an interior material for an automobile.

[0002]

2. Description of the Related Art A foamed polyolefin resin article is widely used as an automobile member, mainly as a shock absorbing material because of its excellent shock absorbing property and light weight. Further, since polyolefin-based resins are excellent in recyclability, the range of use of polyolefin-based resin foams as interior materials for automobiles is expanding. However, since polyolefin resins having excellent foaming processability generally have low heat resistance, it is difficult to satisfy the heat resistance required for automotive interior materials, and the range of use of polyolefin resin foams as automotive interior materials is limited. I was Therefore, if the heat resistance of the polyolefin-based resin foam is improved, it can be widely used as an automobile interior material.

Therefore, the present inventors have attempted to produce a foamed molded article using foamed resin particles having a homopolypropylene resin having a melting point of 160 ° C. or higher as a base resin. This is because it is generally known that heat resistance can be improved by using a base resin having a high melting point.

[0004] However, the above-mentioned homopolypropylene resin having a high melting point must be released under a low-pressure atmosphere to obtain foamed resin particles, and the temperature condition must be set higher than that of a conventionally used resin. In addition, molding steam (steam) required when filling foamed resin particles into a mold and performing heat molding
The pressure had to be higher than the conventional resin. Therefore, when a homopolypropylene resin having a high melting point is used, the heat resistance is improved, but there has been a problem that existing production equipment conventionally used cannot be used.

[0005] Even if the equipment is renovated by investing a large amount of equipment, the appropriate temperature range in which the homopolypropylene resin can be foamed is narrow and the appropriate condition range of the hot molding in a mold or the like is extremely limited. Due to the narrow characteristic, there has been a problem that stable production is difficult. Further, the foam molded article of the homopolypropylene resin has a problem that it is brittle. Therefore, it has been desired to develop a foamed molded article having good heat resistance using a polypropylene random copolymer that is less brittle than a homopolypropylene resin as a base resin.

The present inventors have made intensive studies and, as a result, have arrived at the present invention. That is, an object of the present invention is to provide a foamed molded article having more excellent heat resistance even if it has the same melting point as a conventional foamed molded article using a polypropylene-based random copolymer as a base resin.

[0007]

The foamed polypropylene resin of the present invention comprises propylene and one or more comonomers selected from the group consisting of ethylene and α-olefins having 4 or more carbon atoms. Foamed resin particles obtained by foaming a polypropylene-based random copolymer obtained by copolymerization as a main component of a base resin and using a base resin having a melting point of 140 ° C. or higher as a raw material were obtained by heat molding. An endothermic peak in the first DSC curve of the polypropylene-based resin foam molded article (however, the foamed molded article having a sample amount of 2 to 4 mg was first heated at 10 ° C./min by a differential scanning calorimeter). From the calorific value of the DSC curve obtained when the temperature was raised to 220 ° C. at the temperature rate, the endothermic peak in the second DSC curve (however, the above-mentioned 220 ° C.)
The temperature of the foamed molded product having a sample amount of 2 to 4 mg raised to 40 ° C. was lowered by a differential scanning calorimeter at a rate of 10 ° C./min to 220 ° C. again at a rate of 10 ° C./min. The value obtained by subtracting the calorific value from the endothermic peak of the DSC curve obtained when the above is performed is 5 J / g or more.

[0008] The foamed polypropylene resin molded article of the present invention preferably has a melting point of 145 ° C to 160 ° C,
The density is preferably from 0.02 to 0.45 g / cm ³ . In addition, in the first DSC curve obtained by the above differential scanning calorimetry, the polypropylene resin foam molded article has an endothermic peak that does not appear in the second DSC curve on a higher temperature side than the endothermic peak of the second DSC curve. And the calorie of the endothermic peak on the high temperature side is preferably 4 J / g or more.

The automobile interior material of the present invention can be obtained by laminating or bonding a skin material on the surface of the above-mentioned polypropylene resin foam molded article.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The base resin of the polypropylene resin foam molded article of the present invention (hereinafter abbreviated as “foam molded article”) is propylene, a comonomer selected from the group consisting of ethylene and α-olefins having 4 or more carbon atoms. The main component is a polypropylene-based random copolymer obtained by copolymerizing one or more kinds. The propylene-based copolymer can be obtained by appropriately adjusting polymerization conditions and copolymerizing.

As the α-olefin having 4 or more carbon atoms, 1-butene, 1-pentene, 1-hexene, 3,3
-Dimethyl 1-butene, 4-methyl-pentene, 4,4
-Dimethyl-1-pentene, 1-octene and the like. The content of the ethylene or α-olefin in the copolymer is preferably 0.05 to 10.0% by weight. If the content exceeds 10.0% by weight, it becomes difficult to raise the melting point of the base resin to 140 ° C. or higher, and the heat resistance of the obtained foamed molding deteriorates. Conversely, when the content is 0.0
When the content is less than 5% by weight, the obtained foamed molded article becomes brittle and easily cracked. Therefore, from such a viewpoint, the content is more preferably 0.1 to 5.0% by weight.

The above-mentioned base resin may be mixed with other resins or elastomers as sub-components as long as the effects of the present invention are not impaired. As the other resin, for example,
High-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene and low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer Examples include various thermoplastic resins such as polyolefin resins such as polymers and polystyrene resins.

Examples of the elastomer include solid rubbers such as ethylene-propylene rubber, ethylene-1-butene rubber, propylene-1-butene rubber, styrene-butadiene rubber, and hydrogenated products thereof, isoprene rubber, neoprene rubber, and nitrile rubber. Or a styrene-butadiene block copolymer elastomer and a polystyrene-based elastomer such as a hydrogenated product thereof, and various elastomers can be used.

The addition amount of the above-mentioned subcomponent is preferably less than 50 parts by weight, more preferably less than 30 parts by weight, and particularly preferably less than 20 parts by weight based on 100 parts by weight of the polypropylene random copolymer. The smaller the amount of the subcomponent added, the easier it is to maintain high heat resistance of the foamed molded article.

The base resin of the present invention can contain various additives. Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a metal deactivator, a pigment, a dye, an inorganic substance, and a nucleating agent. Examples of the inorganic substance include zinc borate, talc, calcium carbonate, borax, and aluminum hydroxide. These additives are mixed in an amount of 20 parts by weight or less, preferably 5 parts by weight or less based on 100 parts by weight of the base resin. The amount of the additive is appropriately determined depending on the physical properties required for the foam molded article.

The above main components, subcomponents, and additives are generally mixed by melt-kneading. For example, using a kneader such as a roll, a screw, a Banbury mixer, a kneader, a blender, or a mill at a desired temperature. Kneaded. The kneaded base resin is further melt-kneaded with an extruder, extruded into strands, and cut into appropriate lengths after cooling, or cut into appropriate lengths and then cooled into pellets by means such as cooling. It is formed as resin particles for use.

The melting point (Tm) of the base resin must be 140 ° C. or higher. When the melting point is lower than 140 ° C., the heat resistance required as a foam molded article for automobile interior cannot be obtained. Further, the melting point of the base resin is preferably 160 ° C. or less. If the melting point exceeds 160 ° C., it may be difficult to perform heat molding stably in a mold or the like.

The melting point of the base resin is determined from a DSC curve obtained by differential scanning calorimetry. Specifically, a foamed molded product having a sample amount of 2 to 4 mg was first heated to 220 ° C. at a heating rate of 10 ° C./min by a differential scanning calorimeter, and the first measurement was performed. 2-4 mg of the sample heated to 10 ° C. was cooled to 40 ° C. at a rate of 10 ° C./min, and then again heated to 220 ° C. at a rate of 10 ° C./min to perform a second measurement. The vertex of the endothermic peak of the DSC curve obtained in the second measurement is defined as the melting point of the base resin.

FIG. 1 is a drawing showing an example of a DSC curve of a base resin obtained in the second measurement of the foamed molded article, where c is an endothermic peak, Tm is a melting point, and Tm is a melting point.
e indicates the melting end temperature, respectively. As the differential scanning calorimeter, "Shimadzu Flux Differential Scanning Calorimeter DSC-50" manufactured by Shimadzu Corporation was used (the same applies to the measurement of the following DSC curve).

The expanded molded article of the present invention has a 1
It is necessary that the value obtained by subtracting the endothermic peak calorie in the second DSC curve from the second peak calorie is 5 J / g or more. By making the difference between the endothermic peak calories 5 J / g or more, even if the melting point of the base resin is the same, the difference in the endothermic peak calories is less than 5 J / g when compared with a foamed molded article having less heat resistance. An excellent foam molded article can be obtained. In the present invention, the difference between the above-mentioned endothermic peaks can be reduced to 5 J / g by using a polypropylene random copolymer selected according to the criteria described later.

The above-mentioned first endothermic peak calorific value is obtained when a foamed molded product having a sample amount of 2 to 4 mg is first heated to 220 ° C. at a rate of 10 ° C./min by a differential scanning calorimeter. DSC curve (hereinafter, "first DSC curve"
Abbreviated. )), The second DS above
The endothermic peak of the C curve means that the foamed molded body having a sample amount of 2 to 4 mg heated to 220 ° C. was cooled to 40 ° C. by a differential scanning calorimeter at a temperature decreasing rate of 10 ° C./min, and then 10 ° C./min. This is a heat collection peak of a DSC curve (hereinafter abbreviated as “second DSC curve”) obtained when the temperature is raised to 220 ° C. at a rate of temperature rise per minute.

FIG. 2 is a drawing showing an example of the DSC curve obtained in the first measurement of the foam molded article. In FIG. 2, a is an endothermic peak appearing on the low temperature side, and b is a second DS curve which appears on the first DSC curve.
An endothermic peak which does not appear in the C curve and which appears on the higher temperature side than the endothermic peak c of the second DSC curve in FIG. 1, TE is the melting end temperature, and is the endothermic peak on the higher temperature side of the endothermic peak b. Shows the temperature when the setting returns to the baseline position.

As shown in FIG. 2, the first endothermic peak calorific value in the DSC curve is a point α at 80 ° C. on the DSC curve.
And a straight line connecting the point β on the DSC curve indicating the melting end temperature TE of the foam molded article, and a straight line connecting the points α and β and a portion surrounded by the DSC curve (a hatched portion in FIG. 2) This is the corresponding amount of heat. Similarly, as shown in FIG. 1, the second endothermic peak calorie in the DSC curve is a point α at 80 ° C. on the DSC curve and the melting end temperature Te of the base resin.
Is a heat amount corresponding to a straight line connecting the point α and the point β on the DSC curve indicating the point (α) and a portion (hatched portion in FIG. 1) surrounded by the DSC curve.

As a main component of a base resin capable of obtaining a foamed molded product having a value obtained by subtracting the endothermic peak calorific value in the second DSC curve from the endothermic peak calorific value in the first DSC curve is 5 J / g or more. The polypropylene-based random copolymer that can be used is selected according to the following criteria.

First, a polypropylene random copolymer was used as a sample, and the sample amount of 2 to 4 mg was heated from room temperature to 220 ° C. at a heating rate of 10 ° C./min by a differential scanning calorimeter to perform a first measurement. Next, the temperature was lowered from 220 ° C. to 10
The second DS obtained by lowering the temperature to 40 ° C. at a rate of 10 ° C./min and then increasing the temperature from 40 ° C. to 220 ° C. at a rate of 10 ° C./min.
The endothermic peak calorie (B) and peak temperature (C) of the C curve are measured.

Next, the same polypropylene random copolymer prepared separately from the above was used as a sample.
４4 mg by a differential scanning calorimeter from a room temperature to a temperature 5 ° C. lower than the peak temperature (C) at a rate of 10 ° C./min, hold at that temperature for 20 minutes, and then decrease the temperature by 10 ° C.
/ Min at 40 ° C / min.
The endothermic peak calorie (A) of the second DSC curve obtained when the temperature is raised to 20 ° C. is measured.

In this measurement, the endothermic peak calorific value (A)
-If a propylene random copolymer having an endothermic peak calorie (B) of 10 J / g or more is selected as a main component of the base resin, the foam molded article of the present invention can be obtained. Examples of the propylene random copolymer exhibiting such physical properties include “Idemitsu Polypro F714NP” and “Idemitsu Polypro J740GP” manufactured by Idemitsu Petrochemical Co., Ltd.

The density of the foamed molded article of the present invention is usually 0.1.
006~0.6g / cm ³ of but is selected according to the application within the scope, it is preferably 0.020~0.45g / cm ^3, a 0.040~0.30g / cm ³ Is more preferable, and particularly preferably 0.050 to 0.20 g / cm ³ . The density of the foamed molding is 0.020 g /
If it is less than ³ cm ³ , it may be inferior in shock absorbing properties and thus may be less suitable as an automobile interior material. If it exceeds 0.45 g / cm ^{3, it} may be too hard to be used as an automobile interior material.

The density of the foamed molded article is obtained by calculating a volume V (cm ³ ) from the outer dimensions of the foamed molded article, and calculating the volume V (cm ³ ).
And the weight W (g) of the molded body is determined by the following equation. Density of foam (g / cm ³ ) = W / V

The foamed molded article of the present invention is obtained by the first DS
It is preferable that the C curve has a crystal structure in which an endothermic peak not appearing in the second DSC curve appears at a higher temperature side than the endothermic peak of the second DSC curve. When the peak on the high temperature side of the first DSC curve does not appear, the moldability is deteriorated, and there is a possibility that a foamed molded article having good quality and a high closed cell rate cannot be obtained.

Hereinafter, the endothermic peak appearing on the high temperature side and the endothermic peak appearing on the low temperature side in the first DSC curve will be described. FIG. 2 showing an example of a first DSC curve
In the above, the endothermic peak a that appears on the low temperature side (hereinafter, referred to as “inherent peak”) a is due to the endothermic time of the melting of the polypropylene copolymer which is the main component of the base resin. On the other hand, the endothermic peak b which appears on the high temperature side (hereinafter, referred to as “high temperature peak”) has a specific property that it appears on the first DSC curve but does not appear on the second DSC curve.

The appearance of the high temperature peak b is caused by the fact that the crystal of the polypropylene random copolymer is heated and melted, and is a phenomenon associated with the crystal structure. Accordingly, the size and shape of the high-temperature peak b change depending on the crystal structure, and the high-temperature peak b may not appear. However, the appearance of the high-temperature peak b is not due to the crystal structure of the base resin itself, but to the characteristic crystal structure of the foamed resin particles as a result of passing through the heat history. That is, the unique peak a is the same as that of the first DSC curve and the second DSC curve.
Since it also appears on the curve, it can be considered that it is caused by the crystal structure or the like of the base resin itself. On the other hand, the high temperature peak “b” appears in the first DSC curve in which the expanded resin particles maintain the expanded state, but after heating once to 220 ° C. and completely melting, the rate of 10 ° C./min. After the temperature was lowered to 40 ° C., the temperature was raised again under the same conditions as the first time.
It does not appear in the second DSC curve. Therefore, the high temperature peak b
Can be considered to be attributable to the unique crystal structure of the foamed resin particles as a result of undergoing the thermal history of foaming. In addition, most of the specific crystal structure is carried over to a foam molded article obtained by subjecting the foamed resin particles to heat molding.

High temperature peak b appearing in the first DSC curve
Is preferably 5 ° C. or higher, and the difference between the temperature at the top of the peak and the temperature at the top of the unique peak a appearing in the second DSC curve is preferably 10 ° C. or more.
C. or higher is particularly preferred. When the temperature difference is small, the closed cell ratio of the obtained foamed resin particles tends to be small, and a foamed molded product obtained by molding the foamed resin particles having a small closed cell ratio is inferior in mechanical properties, which is not preferable. . FIG.
In FIG. 2, two endothermic peaks a and b are drawn as smooth curves. However, the DSC curve is not always such a smooth curve.
In some cases, two endothermic peaks appearing on the curve, an intrinsic peak and a high-temperature peak, appear on the DSC curve.

The calorie at the high temperature peak of the foamed molded article of the present invention (hereinafter, abbreviated as “high temperature peak calorie”) is 4 J / g.
It is preferable that it is above. The high temperature peak calorie is 4 J / g
If it is less than 1, the mechanical properties such as the bending strength and the compressive strength of the foamed molded article are significantly reduced, and the heat resistance may be reduced.
From such a viewpoint, the high-temperature peak calorie is more preferably 10 J / g or more. However, if the high-temperature peak calorific value becomes too large, the temperature of steam used for molding the foamed molded article must be increased, or the voids between the foamed resin particles constituting the foamed molded article increase, and The appearance of the molded article tends to be poor. From such a viewpoint, the upper limit of the high-temperature peak calorific value is preferably set to 40 J / g.

The high-temperature peak calorific value is DS as shown in FIG.
The point α at 80 ° C. on the C curve and the melting end temperature TE of the resin
Draw a straight line connecting the point β on the DSC curve indicating
DS corresponding to the valley between the characteristic peak a and the high temperature peak b
From the point γ on the C curve, a line parallel to the vertical axis of the graph is drawn to a straight line connecting the points α and β, and the intersection thereof is defined as a point δ. , A straight line connecting the point γ and the point δ, and a heat amount corresponding to a portion surrounded by a DSC curve connecting the point γ and the point β.

The foamed molded article of the present invention can be obtained by filling foamed resin particles having predetermined characteristics in a mold, and pressurizing heated steam or the like to foam by heating. The foamed resin particles are dispersed in a dispersion medium together with a dispersant added as necessary, in the presence of a foaming agent, in the presence of a foaming agent, and the resin particles are softened. The resin particles are heated to a point or more to impregnate the resin particles with the foaming agent, and thereafter, one end located below in the closed container is opened, and the resin particles are kept at a pressure equal to or higher than the vapor pressure of the foaming agent. And the dispersion medium are simultaneously released under a lower pressure atmosphere than the inside of the container (usually under atmospheric pressure) to foam the resin particles.

As the foaming agent, there are usually used aliphatic hydrocarbons such as propane, butane, pentane, hexane and heptane, cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane, chlorofluoromethane, trifluoromethane, ,
Volatile blowing agents such as halogenated hydrocarbons such as 1-difluoroethane, 1,2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride and methylene chloride; and inorganic materials such as nitrogen, carbon dioxide, argon and air. A gas-based blowing agent or a mixture thereof is used. Among these, an inorganic gas-based blowing agent is preferable because it does not destroy the ozone layer and is inexpensive, and nitrogen, air, and carbon dioxide are particularly preferable.

The amount of the foaming agent used is usually 2 parts per 100 parts by weight of resin particles in the case of volatile foaming agents such as aliphatic hydrocarbons, cycloaliphatic hydrocarbons and halogenated hydrocarbons. ５０50 parts by weight. In the case of an inorganic gas-based foaming agent such as nitrogen or air, the foaming agent is usually placed in a closed container so that the pressure in the closed container immediately before the start of foaming (release) is in a pressure range of 1 to 60 kgf / cm ² G. Press into. The use amount (or press-fit amount) of these foaming agents is appropriately selected from the relationship between the desired expansion ratio of the foamed resin particles and the desired high-temperature peak calorific value.

The dispersion medium for dispersing the base resin particles is not particularly limited as long as it does not dissolve the resin particles. Examples of such a dispersion medium include water, ethylene glycol, glycerin, methanol, ethanol, and the like, but water is usually used.

To disperse the base resin particles in the dispersion medium,
Add a dispersant as needed. As the dispersant, magnesium, basic zinc carbonate, calcium carbonate, kaolin, mica, clay and the like are used. Usually, these are added to the dispersion medium at a ratio of 0.2 to 2 parts by weight based on 100 parts by weight of the base resin.

As described above, the foam molded article of the present invention preferably has a crystal structure in which a high-temperature peak appears as an endothermic peak in the first DSC curve, and the calorific value of the high-temperature peak is 4 J / g or more. . A foamed molded article having such characteristics is obtained by molding using foamed resin particles in which a unique peak and a high-temperature peak appear on the first DSC curve and the calorific value of the high-temperature peak is 4 J / g or more. be able to. The expanded resin particles can be obtained by holding the base resin particles in a closed container at a predetermined temperature for a predetermined time, as described below. The high-temperature peak calorie of the foamed resin particles can be obtained from the first DSC curve of the foamed resin particles in the same manner as the method for obtaining the high-temperature peak calorie of the foamed molded product. Indicates a value approximately equal to.

The production of foamed resin particles which can be used for producing a foamed molded article having the above characteristics is carried out by dividing the base resin particles into two stages of a predetermined holding temperature Ta and Tb in a closed container and holding each for a predetermined time. Do. According to such means, it is easy to control the high-temperature peak calorie of the expanded resin particles and the expanded molded article to 4 J / g or more.

The holding temperature Ta is [melting point Tm-15 ° C.]
The temperature arbitrarily selected and the holding temperature Tb in the range of less than to [Te] are [melting point Tm−15 ° C.] to [melting end temperature Te +
5 ° C.], and the holding time at each temperature is an arbitrarily selected time within a range of 10 to 60 minutes. Specifically, the temperature of the dispersion medium in the closed container is raised to the temperature Ta without being raised to the melting end temperature Te or higher, and the temperature is kept within the range of 10 to 60 minutes at the temperature Ta, and then the temperature Tb And maintained within the range of 10 to 60 minutes, and then released under atmospheric pressure to foam. By foaming in this manner, foamed resin particles having a crystal structure in which a high-temperature peak appears on a DSC curve can be obtained. The magnitude of the high-temperature peak calorific value of the foamed resin particles mainly depends on the temperature Ta and the holding time at the temperature Ta, the temperature Tb and the holding time at the temperature Tb, and the heating rate.

The above temperature range is a temperature range when an inorganic gas-based blowing agent is used as a blowing agent. When an organic volatile blowing agent is used as a blowing agent, the temperature range depends on the type and amount of the organic volatile blowing agent. The appropriate temperature range tends to shift to a lower temperature than the above temperature range.

The foamed molded article of the present invention is subjected to a pretreatment such as application of an internal pressure, if necessary, to the foamed resin particles, and then filled in a molding die which can be opened and closed but cannot be sealed. Then, by injecting about 2.0 to 6.0 kg / cm ² G of steam, the foamed resin particles are heated to cause secondary foaming and are fused to each other, and then cooled to be obtained. it can.

Further, the foamed molded article of the present invention can be obtained by a continuous molding method (for example, Japanese Patent Application Laid-Open Nos. 9-104026 and 9-10402).
7, and the molding method described in JP-A-10-180888). The continuous molding method,
After increasing the internal pressure of the foam as required, the foamed resin particles are continuously supplied between the belts that move continuously up and down in the passage, so that the foamed resin particles expand when passing through the heating area. This is a method of fusing, cooling when passing through a cooling area provided thereafter, and then taking out the obtained foam molded article from the passage and sequentially cutting it into appropriate lengths.
The application of the internal pressure of the expanded resin particles is performed by supplying pressurized air in a closed container to increase the internal pressure of the expanded resin particles to a predetermined pressure.

The foam molded article of the present invention produced by the above method preferably has an open cell ratio of 40% or less based on Procedure C of ASTM-D2856-70,
%, More preferably 25% or less, particularly preferably 25% or less. This is because the smaller the open cell ratio is, the more a foam molded article having excellent mechanical strength can be obtained.

The in-mold molded product of the present invention is integrated with a shock absorbing material such as an automobile bumper core material and a skin material to form a dashboard, console box, console lid, instrument panel, door panel, door trim, and the like. It can be suitably used as an automobile interior material such as a ceiling material, an automobile interior material of a pillar portion, a sun visor, an armrest, and a headrest. In addition to automotive applications, core materials for helmets, heat insulating materials, structural materials for ships and airplanes,
It can be widely used for cushioning materials and building materials.

[0049]

The present invention will be described below in more detail with reference to examples and comparative examples. [Examples 1 to 3] To a variety of polypropylene random copolymers having the characteristics shown in Table 1, "Zinc borate 2335" manufactured by Tomita Pharmaceutical Co., Ltd. was added as a foaming aid so as to contain 500 ppm and melted in an extruder. The mixture was extruded into a strand from a die, quenched in water, cut into a predetermined length, and granulated into pellets (about 2 mg per pellet). Table 1 shows that α was copolymerized with propylene.
-The type of olefin, the content (wt%) of the α-olefin, the MFR (g / 10 min), the melting point Tm (° C), and the endothermic peak calorie (A)-the endothermic peak calorie (B) (“the endothermic peak calorie” Difference (A)-(B) ").

1000 g of the above pellets were dispersed in 3000 cc of water in a closed container (volume: 5 liters), and the amount of dry ice (CO ₂ ) shown in Table 1 was used as a foaming agent.
And 5 g of kaolin as a dispersant and 0.05% of sodium dodecylbenzenesulfonate as a surfactant.
g, and the mixture was stirred in an airtight container without heating to a temperature equal to or higher than the melting end temperature Te of the base resin.
And held for 15 minutes. Next, after the temperature was raised to the foaming temperature Tb shown in Table 1 and maintained for 15 minutes without increasing to the temperature equal to or higher than the melting end temperature Te of the base resin, “equilibrium” of the foaming agent was performed by introducing pressurized nitrogen. Back pressure of "vapor pressure + 10 kg / cm ² G"
By releasing one end located below the container while maintaining the pressure, the base resin particles and water were simultaneously released, and the base resin particles were expanded to obtain expanded resin particles.

Next, after the foamed resin particles are dried in an oven at 60 ° C. for 24 hours, they can be closed but not sealed without increasing the internal pressure (the size of the molding space is 300 mm). × 300 mm × 50 mm), and superheated steam having a pressure shown in Table 2 was pressed into a mold and heated to perform molding. After cooling, remove the molded body from the mold to 6
The foam was dried in an oven at 0 ° C. for 24 hours to obtain a foamed molded product of the present invention.

[Comparative Example 1] Using a polypropylene random copolymer having the characteristics shown in Table 1, the base resin particles were foamed under the conditions shown in Table 1 in the same manner as in Examples 1 to 3 to obtain a foamed resin. Particles were obtained. Next, after drying in the same manner as in Examples 1 to 3, superheated steam having the pressure shown in Table 2 was pressed into the mold and heated to mold, and then the molded body was dried in an oven at 60 ° C. for 24 hours. To obtain a foam molded article.

The high-temperature peak calorie and bulk density of the foamed resin particles obtained in Examples 1 to 3 and Comparative Example 1 were measured. Table 1 shows the results. For the bulk density of the expanded resin particles, a container having an opening at the top with a capacity of 1000 cm ³ is prepared, and the expanded resin particles are filled in the container under normal temperature and pressure, and the expanded resin particles having passed through the opening of the container are prepared. , The height of the foamed resin particles is made to substantially match the opening of the container, and the weight (g) of the foamed resin particles in the container at that time is 1000 cm.
It was determined by dividing by ³ .

The foamed molded articles obtained in Examples 1 to 3 and Comparative Example 1 had high-temperature peak calories, densities,
Endothermic peak calories of the second and second DSC curves, and
The amount of deflection of the foam molded article at a high temperature was measured. Table 2 shows the results.

The method for measuring the amount of deflection under high temperature is as follows. As shown in FIG. 3, the distance between the centers is 150
mm, and the upper end is rounded so as to have a radius of curvature R = 1 mm, a length of 85 mm and a width of 60 mm.
Two support plates 2 and 2 having a thickness of 2 mm and a thickness of 2 mm were prepared. Next, on the support plates 2 and 2, the test piece 1 cut out from the surface layer portion of the obtained foamed molded product at a length of 200 mm, a width of 40 mm, and a thickness of 10 mm, the surface of the molded body facing upward, and They were straddled evenly so that the longitudinal direction was orthogonal to the support plates 2 and 2. Next, on the test piece 1, 2
A radius of 3 m at a position substantially at the center between the two support plates 2 and 2
The columnar weight 3 (weight: 5 g) having a length of 60 mm and a length of 60 mm is placed on the supporting plate 2, 2 in such a manner that the columnar weight 3 is laid sideways so as to be parallel to the supporting plates 2, 2.
It was left for 22 hours in an atmosphere at a temperature of ° C.

The amount of deflection (D) of the molded body under high temperature is as follows.
It is calculated by the formula. D = L₁ -L_Two Where L_Two Immediately after being left in the above high temperature atmosphere for 22 hours
A lower surface of a test piece at a central portion between the support plates 2 and 2,
The shortest length from the upper surface of the pedestal 4 having a horizontal plane, L ₁ Is high temperature
It is the same shortest length immediately before being placed in the atmosphere. Also, this implementation
L in Examples, Comparative Examples and Reference Examples described later.₁ Are both
85 mm. FIG. 3B shows the state shown in FIG.
It is the drawing which looked at a state from the top.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

As described above, the present invention provides a copolymer obtained by copolymerizing propylene with one or more comonomers selected from the group consisting of ethylene and α-olefins having 4 or more carbon atoms. The obtained polypropylene-based random copolymer is used as a main component of the base resin, and a base resin having a melting point of 140 ° C. or higher determined from a DSC curve of the base resin is used as a raw material, and the base resin is further foamed. When the value obtained by subtracting the endothermic peak calorie in the second DSC curve from the endothermic peak calorie in the first DSC curve of the foamed molded article obtained by molding is 5 J / g or more, shock absorption and light weight In addition to excellent heat resistance, polypropylene resin foam molding that can be molded under almost the same molding conditions as conventional polypropylene resin and has better heat resistance than conventional foam molded products with the same melting point It became possible to provide a body.

The foam molded article of the present invention has a crystal structure in which a high-temperature peak appears as an endothermic peak in the first DSC curve, and the heat quantity of the high-temperature peak is 4 J / g or more. Thereby, a foam molded article having excellent mechanical strength can be obtained.

An automobile interior material obtained by laminating or adhering a skin material on the surface of the foamed molded article of the polypropylene resin of the present invention is excellent not only in shock absorption and lightness but also in heat resistance. Small dents and deflections due to load at high temperature.

[Brief description of the drawings]

FIG. 1 is a drawing showing an example of a second DSC curve of a foam molded article.

FIG. 2 is a drawing of a first DSC curve of a foam molded article.

FIG. 3A is a front view of a method for measuring the amount of deflection under a high temperature. FIG. 3B is a plan view of a method for measuring the amount of deflection at a high temperature.

[Explanation of symbols]

a It is an endothermic peak on the low temperature side that appears in the first DSC curve of the foam molded article. b It is an endothermic peak on the high temperature side that appears in the first DSC curve of the foam molded article. c It is an endothermic peak appearing in the second DSC curve of the foam molded article.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 31:58 C08L 23:14 (72) Inventor Toshio 282-1 Togamicho, Utsunomiya-shi, Tochigi Pref. Room 103 F-term (reference) 4F074 AA24A AA25A AB02 AB03 BA32 BA33 BA35 BA36 BA37 BA39 BA40 BA44 BA45 BA47 BA48 BA53 BA67 CA24 CE02 DA02 DA33 DA35 DA59 4F212 AA09 AA09C AA11C AC01 AG03 AG20 AH26 UA01 UB01 UC01 UF01

Claims (5)

[Claims] 1. A polypropylene-based random copolymer obtained by copolymerizing propylene with one or more comonomers selected from the group consisting of ethylene and α-olefins having 4 or more carbon atoms. A polypropylene resin foam molded article obtained by heating and molding foamed resin particles obtained by foaming a foamed resin particle which is a main component of a material resin and having a melting point of 140 ° C. or higher as a raw material, Endothermic peak in the first DSC curve (however, sample amount is 2 to 4 m
g of the foamed molded product was first measured with a differential scanning calorimeter.
Endothermic peak of the DSC curve obtained when the temperature was raised to 220 ° C. at a temperature rising rate of 200 ° C./min.
Endothermic peak in the curve (however, after the foamed molded article of 2 to 4 mg in sample amount heated to 220 ° C. was cooled to 40 ° C. by a differential scanning calorimeter at a cooling rate of 10 ° C./min, then again to 10 ° C./min. An endothermic peak of a DSC curve obtained when the temperature is raised to 220 ° C. at a heating rate of 5), wherein the value obtained by subtracting the calorific value is 5 J / g or more. 2. The foamed polypropylene resin article according to claim 1, wherein the melting point of the base resin is 145 ° C. to 160 ° C. 3. The foamed polypropylene resin article according to claim 1, wherein the density is 0.02 to 0.45 g / cm ³ . 4. The first DSC curve obtained by the differential scanning calorimetry has a crystal structure in which an endothermic peak not appearing in the second DSC curve appears on a higher temperature side than the endothermic peak of the second DSC curve. The foamed polypropylene resin article according to any one of claims 1 to 3, wherein the heat quantity at the endothermic peak on the high temperature side is 4 J / g or more. 5. An automobile interior material comprising a skin material laminated or adhered to the surface of the foamed polypropylene resin article according to any one of claims 1 to 4.