JP2002011748A - Method for manufacturing resin foam for car part, and resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for a resin foam for a car part comprising a skin layer and a highly foamed core material molded from the same resin and having good appearance, lightweight properties, high rigidity and impact resistance. SOLUTION: The resin foam for the car part is manufactured through a process for injecting a part of a foamable resin composition, which consists of a specific propylene/ethylene block copolymer, an ethylene/1-octene random copolymer and foaming agent in a cavity having volume smaller than the total volume of a final product in such a state that a movable mold is fixed to fill the cavity, a process for filling the expanded cavity with the remaining foamable resin composition while the movable mold is allowed to retreat and a process for further allowing the movable mold to retreat to foam and mold the resin composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polypropylene resin foam used as an automobile part, and a resin foam obtained therefrom.

[0002]

BACKGROUND OF THE INVENTION Polypropylene resin has excellent physical properties and moldability, and furthermore, does not generate harmful gas when incinerated and is recyclable. Its use is expanding rapidly. Particularly, in the field of automobile parts, lightweight and highly rigid polypropylene resin products are provided.

[0003] As one of such products, an injection foamed molded article of a polypropylene resin is used. But,
A relatively high-viscosity resin is required in order to stabilize the foam cells during production. However, an injection-molded article of a high-viscosity resin generally tends to have a reduced appearance, particularly gloss. Therefore, in applications where appearance is prioritized, such as automobile parts, a molding method in which a pre-manufactured skin layer is loaded into a mold, and then a resin serving as a core material is foam-molded to integrate the two, or It is manufactured by a method of laminating a separately manufactured foam and a skin layer later.

However, the conventional manufacturing method using such a polypropylene resin foam as a core material not only complicates the parts manufacturing process but also uses a raw material resin whose foam and skin layer are different from each other. Therefore, it is difficult to recycle after use, and improvement from both sides is desired. Further, when the foam is used as an automobile part, a resin having high rigidity and high impact strength is required, and development of such a resin is also desired at the same time.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a resin foam for an automobile part in which a skin layer and a core material are molded from the same polypropylene resin composition. Further, the present invention provides a method for producing a resin foam for automobile parts, which has a good appearance on the surface, has good foam cells inside, and is lightweight and has high rigidity and impact resistance. It is to be. Another object of the present invention is to provide a resin foam for an automobile part obtained by such a production method.

[0006]

That is, a first invention according to the present invention comprises a propylene / ethylene block copolymer (A) of 75 to 85 parts by weight, an ethylene / 1-octene random copolymer (B) 15 ~ 25 parts by weight (where
(A) and (B) in a total amount of 100 parts by weight), and 0.1 to 6 parts by weight of a foaming agent (C). A primary injection step of injecting and filling a part of the cavity into the cavity with the movable mold fixed, and then secondary filling the remaining foamable resin composition into the enlarged cavity while retracting the movable mold This is a method for producing a resin foam for an automobile part, comprising: an injection step; and a foaming step of foaming and molding the foamable resin composition by further retracting the movable mold. Also,
A second invention is a resin foam for an automobile part manufactured by the above method.

The propylene / ethylene block copolymer (A) satisfies the following conditions (a) to (f). (A) The ratio (Mw / Mw) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in the propylene homopolymer portion
Mn) is 4 or more, and the ratio (Mz / M) of the Z-average molecular weight (Mz) to Mw in the (b) propylene homopolymer portion
w) is 3 to 10, and (c) the melt flow rate (230 ° C.) of the propylene homopolymer portion is 30 to 150 (g / 1).
0 min), (d) the isotactic pentad fraction of the propylene homopolymer portion is 97.5% or more, (e) the amount of the normal-temperature paraxylene-soluble portion is 7 to 13% by weight, and (f) the normal-temperature paraxylene. The soluble portion has an ethylene content of 24 to 30% by weight.

The above-mentioned ethylene / 1-octene random copolymer (B) satisfies the following conditions (g) to (i). (G) Density of 0.86-0.88 (g / c
m ³ ), (h) the melt flow rate (190 ° C.) is 3 to
70 (g / 10 min), (i) ethylene content of 70 to 90
Mol%.

The resin composition comprising the propylene / ethylene block copolymer (A) and the ethylene / 1-octene random copolymer (B) has a melt flow rate (230 ° C.) of 30 to 100 (g). / 10 minutes).

The foaming agent (C) comprises 30 to 65 parts by weight of a carbonate or bicarbonate and 35 to 70 parts by weight of an organic carboxylic acid (the total amount of both is 100 parts by weight). Desirably, it is a mixture.

[0011]

DETAILED DESCRIPTION OF THE INVENTION Next, the method for producing the resin foam for automobile parts according to the present invention and the respective constitutions of the resin foam for automobile parts obtained therefrom will be specifically explained.

Propylene / ethylene block copolymer
(A) The propylene / ethylene block copolymer, which is the main component of the raw material resin, is a polymer produced by block copolymerization of propylene and ethylene, and includes a portion insoluble in normal temperature paraxylene. It is composed of a certain propylene homopolymer portion, a propylene / ethylene random copolymer portion that is soluble in normal temperature para-xylene, and a polyethylene portion contained as required.

The propylene / ethylene block copolymer which can be used in the present invention contains the above-mentioned part soluble in normal temperature para-xylene in the range of 7 to 13% by weight, preferably 8 to 12% by weight. . The soluble portion is a propylene / ethylene random copolymer exhibiting rubber-like properties, and a foam having high impact strength and rigidity can be obtained when the content is within the above range. The ethylene content of the soluble portion is 24 to 30% by weight, preferably 25 to 28% by weight, and the propylene / ethylene random copolymer in this range has excellent low-temperature properties.

The propylene homopolymer portion in the propylene / ethylene block copolymer used in the present invention satisfies the following conditions (a) to (d):
This makes it possible to produce a foam molded article having an excellent balance between rigidity and impact resistance with good moldability.

(A) The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in the propylene homopolymer portion is 4 or more, preferably 8 to 25. When the value of Mw / Mn is in this range, since the molecular weight distribution is relatively wide and the melt tension is high, it is suitable for producing a foam in which cells having a uniform diameter are almost uniformly dispersed. The obtained molded body has a high mechanical strength and a small unevenness in the strength in the horizontal and vertical directions.

(B) Next, the weight average molecular weight (Mw) of the Z average molecular weight (Mz) in the propylene homopolymer portion
(Mz / Mw) to 3 to 10, preferably 4
８8. When the value of Mz / Mw is in this range, the foamed cells exhibit characteristics that are less likely to break during foam molding.

Here, Mw, Mn and Mz are values measured using gel permeation chromatography (GPC). For example, Waters 150C
Plmixed from Polymer Laboratories
B, the measurement temperature was 135 ° C., and o was used as the solvent.
Measurement is performed by supplying 400 μl of a sample having a polymer concentration of 0.15% by weight using dichlorobenzene. on the other hand,
The Mw, Mn, and Mz values of each sample can be obtained using a calibration curve prepared in advance using standard polystyrene.

The melt flow rate (MFR) in the propylene homopolymer portion is as per ASTM D-12.
The value measured at 230 ° C under a load of 2.16 kg is 30 to 150, preferably 50 to 120 (g
/ 10 minutes). When the MFR value is in this range, good injection moldability is exhibited.

Further, the propylene homopolymer portion has an isotactic pentad fraction (mmmm fraction) of 9%.
It is at least 7.5%, preferably at least 98.0%. When the propylene homopolymer portion has a high isotactic pentad fraction as described above, it is possible to produce a foam having high rigidity and high rigidity.

The isotactic pentad fraction
(Mmmm fraction)¹³Measured using C-NMR
Pentad unit in the polypropylene molecular chain.
Shows the proportion of sotactic chains present, propylene
At the center of a chain of 5 meso-bonded consecutive monomer units
It is the fraction of certain propylene monomer units. Specifically
Is ¹³Methyl carbon region observed in C-NMR spectrum
Fraction of mmmm peak in all absorption peaks in the region
It is a value calculated by:

The propylene / ethylene block copolymer having such properties is obtained, for example, by subjecting propylene to homopolymerization in the first step in the presence of a stereoregular polymerization catalyst, and performing propylene / ethylene polymerization in the second step. It can be produced by copolymerization and, if necessary, homopolymerization of ethylene as a third step.

In this block copolymer, the branched olefin polymer is 0.1% by weight or less, preferably 0.0% by weight or less.
5% by weight or less may be contained. Since the branched olefin polymer acts as a nucleating agent for the propylene / ethylene block copolymer, the above-mentioned isotactic pentad fraction can be increased and the moldability can be improved. Examples of the polymer include 3-methyl-1-butene, 3,3-dimethyl-1-butene, 3-methyl-1-pentene, and 4-methyl-1-butene.
A branched olefin homopolymer or copolymer such as methyl-1-pentene and 3-methyl-1-pentene can be used, and among them, a 3-methyl-1-butene polymer is preferable.

Ethylene / 1-octene random copolymer
(B) The ethylene / 1-octene random copolymer that can be used in the present invention has an ethylene content of 70 to 90 mol%, preferably 75 to 85 mol%, and a density of 0.86 to 0.8 mol%.
0.88 (g / cm ³ ). A copolymer having an ethylene content and a density in this range has physical properties as an elastomer, and can increase the impact strength of a molded article.

The melt flow rate (MFR) of this ethylene / 1-octene random copolymer is ASTM D
The value measured at 190 ° C. under a load of 2.16 kg is 3 to 70 (g / 10 min), preferably 1
0 to 50 (g / 10 minutes). When the MFR value is in this range, the impact resistance can be improved without impairing the fluidity of the block copolymer, so that the impact strength is high,
A glossy molded article having excellent appearance can be obtained. In the present invention, the ethylene / 1-octene copolymer can be used alone, or can be used in combination with another elastomer.

The ethylene / 1-octene random copolymer is usually prepared by reacting ethylene and 1-octene in the presence of a transition metal catalyst.
It can be produced by copolymerizing octene with a gas phase or a liquid phase. There is no particular limitation on the polymerization catalyst, polymerization method and the like. For example, it can be produced by a polymerization method such as a gas phase method, a solution method, and a bulk polymerization method using a Ziegler type catalyst, a Phillips type catalyst, a metallocene type catalyst or the like.

Foaming agent (C) The foaming agent usable in the present invention is not particularly limited, and may be a solvent-type foaming agent or a decomposition-type foaming agent.

The solvent-type foaming agent is a substance which functions as a foaming agent by being generally injected from a cylinder portion of an injection molding machine, absorbed or dissolved in a molten raw material resin, and then evaporated in an injection mold. Propane, butane, neopentane,
Low-boiling aliphatic hydrocarbons such as heptane, isohexane, hexane, isoheptane and heptane, and low-boiling fluorine-containing hydrocarbons represented by Freon gas can be used.

The decomposable foaming agent is supplied to an injection molding machine after being previously blended with the raw material resin composition, and the foaming agent is decomposed under the cylinder temperature condition of the injection molding machine to form a gas such as carbon dioxide gas or nitrogen gas. Is a compound that generates It may be an inorganic foaming agent or an organic foaming agent. An organic acid or the like which promotes gas generation may be added in combination as a foaming aid.

The following compounds can be mentioned as specific examples of the decomposable foaming agent. (1) Inorganic foaming agents: sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate, ammonium nitrite, citric acid, sodium citrate.

(2) Organic foaming agents: N-nitroso compounds such as N, N'-dinitrosoterephthalamide, N, N'-dinitrosopentamethylenetetramine; azodicarbonamide, azobisisobutyronitrile, azo Azo compounds such as cyclohexylnitrile, azodiaminobenzene, and barium azodicarboxylate; benzenesulfonyl hydrazide, toluenesulfonyl hydrazide,
sulfonylhydrazide compounds such as p, p'-oxybis (benzenesulfenylhydrazide) and diphenylsulfone-3,3'-disulfonylhydrazide; calcium azide, 4,4'-diphenyldisulfonylazide, p-toluenesulfonylazide and the like Azide compounds.

Of these foaming agents, carbonates or bicarbonates such as sodium bicarbonate are preferable, and in this case, it is preferable to use an organic carboxylic acid in combination as a foaming aid. The compounding ratio of the carbonate or bicarbonate to the organic carboxylic acid is preferably in the range of 30 to 65 parts by weight of the carbonate or bicarbonate and 35 to 70 parts by weight of the organic carboxylic acid. Here, the total amount of both becomes 100 parts by weight. In using the foaming agent and the foaming assistant, a masterbatch containing them may be prepared in advance, and the formulation may be blended with the propylene / ethylene block copolymer and the ethylene / 1-octene copolymer.

The onset foaming tree starting resin used in the production method of injection foaming body fat pair formation was present invention, propylene-ethylene block copolymer (A) and ethylene-1-octene random copolymer ( B) a resin composition comprising: (A)
Is 75 to 85 parts by weight, preferably 78 to 83 parts by weight,
(B) is 15 to 25 parts by weight, preferably 17 to 22 parts by weight. Here, the total amount of (A) and (B) is 100
Parts by weight. If the composition ratio of both is within this range,
A resin foam having high impact resistance and high rigidity can be manufactured.

[0033] The resin composition is ASTM D-123.
8 and the melt flow rate (MFR) measured at 230 ° C. under a load of 2.16 kg is 30 to 100 (g).
/ 10 minutes), preferably 50 to 90 (g / 10 minutes). When the MFR value is within this range, it is suitable for high-speed injection molding, it is easy to adjust the balance between rigidity and impact resistance of the foam, and it is easy for the foam cell to take a closed cell shape, and the cell shape is uniform. There is an advantage that it is easy to match.

The amount of the foaming agent (C) to be added is selected in consideration of the amount of gas generated from the foaming agent and a desired expansion ratio in accordance with the required physical properties of the foamed molded product. The amount is preferably 0.1 to 6 parts by weight, more preferably 0.5 to 2 parts by weight, based on 100 parts by weight of the total of the coalesced (A) and the ethylene / 1-octene random copolymer (B). From the foamable resin composition within this range, a foam molded article having uniform cell diameters and uniformly dispersed cells can be obtained.

The foamable resin composition comprising the propylene / ethylene block copolymer (A), the ethylene / 1-octene copolymer (B) and the blowing agent (C) does not impair the object of the present invention. Various additives can be added as needed within the range. Additives include nucleating agents, antioxidants, hydrochloric acid absorbers, heat stabilizers, weather stabilizers, light stabilizers, ultraviolet absorbers, lubricants, antistatic agents, flame retardants, pigments,
Dyes, dispersants, copper damage inhibitors, neutralizers, plasticizers, crosslinking agents,
Flowability improvers such as peroxides, weld strength improvers, natural oils, synthetic oils, waxes and the like can be added.

Method for Producing Resin Foam The method for producing a resin foam for automobile parts according to the present invention comprises a primary and secondary method for injection molding the foamable resin composition described above into an injection mold. It comprises at least three steps: an injection step and a foaming step of producing a foam by subsequent foam molding.

The molding die is composed of a fixed mold and a movable mold (core mold). When the fixed mold and the movable mold are in the mold-closed state closest to each other, a foaming material used as a raw material is interposed therebetween. A cavity close to the product shape having a smaller volume than the volume of the entire resin composition is formed. The volume of this cavity can be the volume where the skin layer is formed,
It is better to make it slightly larger than the volume where the skin layer is formed.

First, in the primary injection step, a part of the foamable resin composition is injected in a molten state and filled into a cavity adjusted to a volume smaller than the total volume of the foamable resin composition used for molding. . At this time, the portion of the resin composition that directly contacts the molding die is cooled to form a skin layer.

The temperature of the resin to be injected is 170 to 270
° C, preferably 180-260 ° C. The mold temperature of the fixed mold and the movable mold is 10 to 100 ° C, preferably 40 to 80 ° C. The pressure in the mold is 5-20MP
a, preferably 10 to 15 MPa. The injection is preferably performed at an injection pressure higher than the mold clamping pressure of the fixed mold and the movable mold. Usually, the injection pressure is 10 to 200 MPa, preferably 12 to 150 MPa. At this time, since the air in the cavity is exhausted, the movable mold is maintained in a fixed state.

Next, in the secondary injection step, the residual resin composition is injected and filled into the enlarged cavity while the movable mold is retracted. As a method of retreating the movable mold, a method of increasing the injection pressure of the resin higher than the mold clamping pressure and increasing the cavity volume by the resin pressure may be adopted, or the mold position is controlled by computer control. The method can be used. The retracting speed of the movable type is desirably controlled to 0.1 to 10 (mm / sec), preferably 0.5 to 3 (mm / sec).
The resin temperature, the mold temperature, the pressure in the mold, and the injection pressure can be substantially the same as those in the primary injection step.

Here, if the volume of the cavity is represented by using the length of the cavity cross section as an index, the length of the cavity cross section in the primary injection step is represented by L ₀ (hereinafter, clearance L _0).
), And the length of the cavity cross section at the end of the injection of the resin composition in the secondary injection step is described as L ₁ (hereinafter sometimes referred to as clearance L ₁ ). If the volume of the cavity in the primary injection step is tentatively expressed by a ratio L ₀ / L ₁ (hereinafter sometimes referred to as a clearance ratio L ₀ / L ₁ ), L ₀ / L ₁ is 0.1 or more. It is desirably less than 1, preferably 0.4 to 0.7. L
₀ / the value of L ₁ is within that range, it is possible to easily and efficiently form a skin layer having a good appearance.

The time from the start of resin injection in the primary injection step to the end of injection in the secondary injection step (hereinafter referred to as
The injection time is 0.1 to 10 seconds, preferably 0.1 to 10 seconds.
5 to 3 seconds. The secondary injection step is preferably performed continuously after the primary injection step, that is, the resin injection is preferably performed continuously through the primary injection step and the secondary injection step. In the primary injection step and the secondary injection step, since the injection pressure and the filling pressure are always applied to the cavity, no or almost no resin foaming phenomenon occurs.

Thereafter, in the foaming step, when the movable mold is further retracted in a state where the injection of the foamable resin composition is stopped, the inside of the cavity is depressurized and the foaming of the resin proceeds to obtain a foamed molded article. . At this time, since the portion of the resin that is in contact with the mold is cooled, foaming does not occur at all or hardly occurs, so that a skin layer is formed and a foam layer is formed inside. This molding method is a so-called core back method. In the foaming process,
May be referred to as the clearance L ₂ after a length L ₂ of the cavity in cross-section at the time was the most retracted movable die.

The mold temperature may be the same as the condition of the secondary injection step, and the retreat speed of the movable mold is 0.1 to 10 (mm / mm).
s), preferably 0.5 to 3 (mm / s). The time from the start to the end of the retraction of the movable mold in the foaming step (hereinafter, sometimes referred to as the foaming time) is 0.
1 to 5 seconds, preferably 0.5 to 3 seconds is desirable. By adopting such conditions, it is possible to easily and efficiently produce a foam molded article having a good appearance.

The retracting of the movable mold in the foaming step can be carried out continuously from the secondary injection step, or at the end of the secondary injection step, ie, at the end of the injection of the foamable resin composition, from 0.1 to 0.1. A method of stopping the retraction for 5 seconds, preferably 0.5 to 3 seconds, and then resuming the retraction after that can be adopted. By providing the stop time, the thickness of the skin layer can be controlled. If the stop time is lengthened, the skin layer can be thickened, and as a result, mechanical properties such as rigidity can be improved. The end point of the retraction is determined by the desired expansion ratio, and when the expansion ratio is increased, the retraction distance may be increased.

After the foaming step, the foamed molded article can be taken out by cooling as it is, or 0.1 to 60
After cooling for 2 seconds, preferably 1 to 10 seconds, the movable mold can be advanced to close the mold, compressed, adjusted to a predetermined size, and then removed. When compressed, the volume decreases and the surface of the foam molded body that did not come into contact with the mold is re-contacted with the inner surface of the mold, so that the cooling efficiency is improved and the shape is regulated in the mold. Can be prevented, and a good appearance can be obtained.

[0047] In the production method according to the present invention is to start the injection from the state of the clearance L ₀ between both molds, the volume of the cavity in comparison with the case of starting the injection from conventional methods state clearance L ₁ of The smaller the size, the faster the flow speed of the resin in the cavity, and the blowing of the foaming gas during the flow which causes silver streaks is prevented. In addition, since the foamable resin composition is filled quickly, cooling proceeds quickly, and a skin layer having excellent appearance is formed. In the conventional method, the inside (core layer) of the foam structure is hardly cooled, while the skin layer is cooled quickly, so that it is difficult to adjust the expansion ratio. However, in the present invention, it is possible to increase the expansion ratio. It is possible to obtain a foam molded article which is free from deformation distortion.

In the present invention, a specific foamable resin composition is used, and the above-mentioned molding conditions are employed, so that a skin layer having a good appearance can be easily formed, and the crystallization of the resin composition can be easily achieved. This makes it easier to increase the foaming ratio by suppressing the expansion ratio, and furthermore, it is possible to easily produce a lightweight and rigid foam molded article having good foam cells.

Next, the method for producing a resin foam according to the present invention will be described in more detail with reference to the drawings. FIG. 1 shows a sectional view of a molding die during a primary injection step, and FIG.
Shows a sectional view of the molding die at the end of the secondary injection step, and FIG. 3 shows a sectional view of the molding die at the end of the foaming step. In the figure, 1 is a fixed mold, 2 is a movable mold, and 3 is a cavity.

FIG. 1 shows a state in which the movable mold 2 is closest to the fixed mold 1 in the primary injection step, and the volume of the cavity 3 formed between the movable mold 2 and the fixed mold 1 is the smallest. It is in. At this time, the volume of the cavity 3 is smaller than the total volume of the foamable resin composition used for injection,
Sectional length of the cavity 3 is in a state of clearance L _0.

From the state of the clearance L ₀ , the movable mold 2
The foamable resin composition 5 is injected into the cavity 3 from an injection nozzle (not shown) through a sprue 4 in a state where the foamable resin composition 5 is fixed so as not to recede, and the cavity 3 is filled with the foamable resin composition 5. At this time, the injection of the resin 5 is preferably performed at an injection pressure higher than the mold clamping pressure of the movable mold 2 and the fixed mold 1. In this case, too, since the air in the cavity 3 is exhausted, the movable mold 2 is fixed. Maintained in state. Since the volume of the cavity 3 is small, the surface of the filled resin composition is rapidly cooled to form a skin layer.

FIG. 2 shows that when the foamable resin composition is injected at an injection pressure higher than the mold clamping pressure in the secondary injection step, the volume of the cavity 3 increases due to the high resin pressure, and This shows a state in which the injection of the composition 5 is continued and the entire amount of the resin composition 5 has been filled.
In this case, the cavity 3 is in a position of clearance L _1, the volume of the cavity 3 is increased compared to FIG. 1,
The clearance is in a state of L ₀ <L ₁ . In the steps so far, the resin composition 5 is still in a softened state, but since the injection pressure and the filling pressure are applied to the resin, no or almost no foaming occurs.

[0053] Figure 3 is retracting the movable die 2 in the foaming process, the cross-sectional length of the cavity 3 shows a state of the clearance L _2. The volume of the cavity 3 is increased as compared with FIG. 2, and the clearance is L ₁ <L ₂ . At this time, the pressure in the cavity 3 is reduced, and the foaming of the resin composition 5 proceeds to form a foam. After the completion of the foaming, the foamed molded body 6 can be taken out by cooling as it is, or the movable mold 2 can be moved forward to close the mold.

Resin Foam for Automotive Parts According to the method for producing a resin foam of the present invention, a foam having a highly foamed core formed inside and a skin layer formed on the surface is obtained. The expansion ratio is not particularly limited because it is adjusted depending on the application. However, when the expansion ratio is usually 1.05 to 5 times, preferably 1.3 to 2 times, the desired strength as the core material is obtained and the shape is maintained. The thickness of the skin layer is usually 0.1.
The thickness is desirably adjusted to 25 to 1 mm, preferably 0.5 to 0.8 mm, and the thickness can be changed depending on molding conditions. As a whole, it is a resin foam having good surface characteristics, light weight, high rigidity and impact resistance.

Since this resin foam is formed from the above-described resin composition, it does not generate harmful gas even if it is incinerated. Further, since the inner and surface layers are made of the same material, it can be easily recycled. Can be done.
Therefore, this resin foam can be suitably used for automobile interior parts such as door trims and instrument panels, and automobile exterior parts such as side protect malls, bumpers, soft fascias, and mudguards.

[0056]

EXAMPLES Next, the present invention will be described with reference to examples, but the present invention is not limited to these examples. First, methods for measuring the expansion ratio, appearance, elastic gradient, and high-speed penetration impact measured for evaluating the molded articles obtained in the examples and comparative examples will be described.

(1) Expansion ratio The specific gravity (dc0) of the unfoamed product and the specific gravity (dc1) of the foamed molded article were determined by the underwater substitution method, and the ratio dc0 /
The expansion ratio was determined from dc1. At that time, the measurement was performed on the foamed molded article including the skin layer.

(2) Appearance The surface of the foam molded article was visually observed and evaluated according to the following criteria. [Silver streak] ：: Almost no observation. ×: Silver streaks are observed on the surface of the molded product. [Hike] ○: Not at all. Δ: There is a little. X: Depression is observed on the surface of the molded body.

(3) Elastic gradient A test piece of 50 × 150 mm was supported at both ends with a span of 100 mm, and a load was applied to the center at a speed of 50 (mm / min) to form a load / deflection curve. The load at the time of 1 cm deformation from the straight line portion was expressed as an elastic gradient in N / cm.

(4) High-Speed Penetration Impact Using a high-rate impact tester manufactured by Rheometrics, a hemispherical striker having a tip diameter of 12.6 mm was vertically applied to the test specimen at 4 ° C. in an atmosphere of 23 ° C.
The collision was performed at the speed of s), and the penetrating fracture energy (J) was obtained and shown.

Example 1 80 parts by weight of a propylene / ethylene block copolymer, an ethylene / 1-octene random copolymer (ethylene content: 85 mol%, density: 0.87
(G / cm ³ ), 20 parts by weight of MFR35 (g / 10 minutes), a blowing agent masterbatch (25% by weight of sodium hydrogen carbonate, 25% by weight of citric acid, and low-density polyethylene 5)
(0% by weight) and 1.8 parts by weight, and then injection-molded under the following conditions to obtain a foam molded article. The physical properties of this foam molded article were evaluated by the above-mentioned methods, and the results were shown in Table 1.
It was shown to.

The properties of the propylene / ethylene block copolymer used were as follows. Propylene content = 94 mol%, ethylene content = 6 mol%, Mw / Mn of propylene homopolymer = 6.5, M
z / Mw = 7, MFR = 80 (g / 10 min), mmmm
Fraction = 98.0%, ratio of the normal-temperature paraxylene-soluble portion = 10% by weight, ethylene content of the normal-temperature paraxylene-soluble portion = 28% by weight Further, the propylene / ethylene block copolymer and ethylene / 1-octene MFR of a mixture with a random copolymer
Was 68 (g / 10 minutes).

The molding conditions were as follows. Injection molding machine: A modified version of IS450GS (trademark) manufactured by Toshiba Corporation Molded product size: 50 cm long, 30 cm wide, 3 mm thick plate Gate structure: Bubble gate, 1 point gate at the center of molded product Injection temperature: 200 ° C Mold pressure: 12 MPa Injection pressure: 15 MPa Injection time: 2.0 seconds Foaming time: 1.0 second Mold surface temperature: 50 ° C.

Retraction speed of movable type in secondary injection step:
0 mm / sec Retraction stop time after the end of the secondary injection step: 2.0 seconds Retraction speed of the movable mold in the foaming step: 1.0 mm / sec Mold clearance (L ₀ ) in the primary injection step (initial):
1.0 mm Mold clearance after secondary injection process (L ₁ ):
2.0 mm Mold clearance (L ₂ ) after completion of the foaming step: 3.0
mm Cooling time: 30 seconds

In the above conditions, the injection time is the time from the start of the injection to the end of the injection of the entire amount of the raw material, and the cooling time is the time from the end of the retreat of the movable mold in the foaming process to the removal of the foam molded article from the mold. It is.

Comparative Example 1 (Injection Core Back Method) The same method as in Example 1 was repeated except that the injection molding conditions were changed as follows. That is, the initial mold clearance (L ₀ ) was set to 2.0 mm, the entire amount of the resin composition was filled at once with the clearance kept, and after the filling was completed, the core was backed up to 3.0 mm to obtain a foam molded article. . The cooling time was 60 seconds. The obtained results are also shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated, except that a composition containing no ethylene / 1-octene copolymer was used. The obtained results are also shown in Table 1.

[0068]

[Table 1]

[0069]

According to the method for producing a resin foam for automobile parts of the present invention, a foam having a structure composed of an inner foam layer and a surface skin layer formed of the same material as a whole can be produced. High foam with good foam cells, the surface skin layer has a good appearance. In this production method, the expansion ratio and the thickness of the surface layer can be easily adjusted, and the production efficiency is high.

The resin foam for automobile parts obtained by this production method is easy to recycle and use since the inner foam layer and the surface skin layer are formed of the same resin composition, and the flow mark, sink marks, etc. It has a good appearance that is hardly seen, and is lightweight as a whole and has excellent rigidity and impact resistance. Therefore, it is suitable for interior and exterior parts for automobiles.

[Brief description of the drawings]

FIG. 1 shows a sectional view of a molding die during a primary injection step.

FIG. 2 is a sectional view of a molding die at the end of a secondary injection step.

FIG. 3 shows a sectional view of a molding die at the end of a foaming step.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fixed mold 2 movable mold 3 cavity 4 sprue 5 foamable resin composition 6 foam molded article

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsushi Yamada 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Kenji Hikita 1-4-1 Chuo, Wako-shi, Saitama Inside the Honda R & D Co., Ltd. 4F206 AA04H AA11F AA11K AB02 AG20 AH26 JA04 JF01 JL02 JM05 JN25 JQ81 4J002 BB052 BP021 DE206 DE226 DF036 EA016 EB066 EF066 EG026 EQ016 EQ026 EQ036 ES006 FD326 GN00

Claims (4)

[Claims] (1) 75 to 85 parts by weight of a propylene / ethylene block copolymer (A) and 15 to 25 parts by weight of an ethylene / 1-octene random copolymer (B) (wherein (A)
And (B) are 100 parts by weight), and a foaming resin composition comprising 0.1 to 6 parts by weight of a foaming agent (C), a cavity having a volume smaller than the total volume of the final product. A primary injection step of injecting and filling a part of the movable mold in a fixed state thereof, and then a secondary injection step of filling the remaining foamable resin composition into the enlarged cavity while retracting the movable mold. And a foaming step of foaming and molding the foamable resin composition by further retracting the movable mold, wherein the propylene / ethylene block copolymer (A) has the following conditions (a) to ( f) is satisfied,
(A) The ratio (Mw / Mw) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in the propylene homopolymer portion
Mn) is 4 or more, and the ratio (Mz / M) of the Z-average molecular weight (Mz) to Mw in the (b) propylene homopolymer portion
w) is 3 to 10, and (c) the melt flow rate (230 ° C.) of the propylene homopolymer portion is 30 to 150 (g / 1).
0 min), (d) the isotactic pentad fraction of the propylene homopolymer portion is 97.5% or more, (e) the amount of the normal-temperature paraxylene-soluble portion is 7 to 13% by weight, and (f) the normal-temperature paraxylene. The ethylene content of the soluble portion is 24 to 30% by weight, and the ethylene / 1-octene random copolymer (B) satisfies the following conditions (g) to (i):
(G) a density of 0.86 to 0.88 (g / cm ³ );
(H) Melt flow rate (190 ° C.) is 3 to 70 (g)
/ 10 minutes), and (i) a method for producing a resin foam for automobile parts, wherein the ethylene content is 70 to 90 mol%. 2. The resin composition comprising the propylene / ethylene block copolymer (A) and the ethylene / 1-octene random copolymer (B) has a melt flow rate (230 ° C.) of 30 to 100. (G / 10 minutes), The manufacturing method of the resin foam for automotive parts according to claim 1 characterized by the above-mentioned. 3. A method according to claim 1, wherein said blowing agent (C) comprises 30 to 65 parts by weight of a carbonate or bicarbonate and 35 to 70 parts by weight of an organic carboxylic acid (the total amount of both is 100 parts by weight). The method for producing a resin foam for an automobile part according to claim 1, wherein the method comprises: 4. A resin foam for an automobile part produced by the method according to claim 1.