JPH10316791A - Pre-expanded polypropylene resin particle and in-mold foamed molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide pre-expanded particles which can be fused together by heating with a conventional die and a molding machine to give an in-mold expanded molding showing high compressive strength as well as lightweight properties. SOLUTION: The pre-expanded polypropylene resin particles are made from a base resin being an ethylene/propylene random copolymer having a melting point of 1490-157 deg.C, an MI of 1-20 g/10 min and a half-crystallization temperature of 45 sec or below, an ethylene/propylene/1-butene random copolymer having a melting point of 149-157 deg.C, an MI of 1-20 g/10 min and a half-crystallization time of 55 sec or below or a propylene/1-butene random copolymer having a melting point of 149-157 deg.C, an MI of 1-20 g/10 min and a half-crystallization time of 60 sec or below and satisfies the formula: 0.25<=β/(α+β)<=0.60 (wherein α is the melting heat of the endothermic peak attributable to the crystalline state inherent in the base resin in a DSC curve as observed when the sample is heated from 40 deg.C to 200 deg.C at a rate of temperature increase of 10 deg.C/min with a differential scanning calorimeter, and βis the melting heat of the endothermic peak appearing at a temperature higher than that of the former peak.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to pre-expanded polypropylene resin particles capable of producing expanded molded articles having excellent mechanical properties such as compressive strength, and excellent mechanical properties formed by using the pre-expanded particles. The present invention relates to an in-mold foam molded article.

[0002]

2. Description of the Related Art In an in-mold foamed product obtained by filling pre-expanded particles in a mold and heat-sealing with a heating medium such as steam, a polyolefin resin such as a polyethylene resin or a polypropylene resin is foamed in the mold. The molded article is superior in heat resistance, chemical resistance, impact resistance, recovery after compression, and the like, as compared with the foam molded article in a polystyrene resin mold. Furthermore, the polypropylene resin molded foam inside is superior in heat resistance and compressive strength to the polyethylene resin molded foam, and is widely used for cushioning materials, automobile parts, building materials, heat insulating materials, etc. ing. On the other hand, in applications such as automobile bumper core materials and automobile side bump pads, in addition to the general properties of the above-mentioned polypropylene resin, further excellent rigidity (high compressive strength) is required.

[0003] In order to improve the compressive strength of the in-mold foam molded article of a polypropylene resin, it is common to lower the expansion ratio of the in-mold foam molded article or to use a base resin having a low comonomer content. However, lowering the expansion ratio of the in-mold foam molded article leads to an increase in weight, which goes against the recent demand for weight reduction. On the other hand, when a polypropylene-based resin having a low comonomer content is used as the base resin, the melting point of the base resin increases.For example, in order to heat and fuse the pre-expanded particles with steam to form an in-mold foam molded article, In addition to using high-pressure (high-temperature) steam, not only is it disadvantageous in terms of energy costs, it is also necessary to improve the pressure resistance of the molding die and the clamping pressure of the molding machine. And increase costs.

In order to solve this problem, the 1-butene content is 3 to 12% by weight, and the latent heat of crystallization is 17 to 2%.
Bulk density 0.015 to 0.09 g / c using 5 cal / g propylene-1-butene random copolymer as a base resin
m ³ and is pre-expanded particles (Kokoku No. 7-68402),
Melting point is 153 ° C or less and Vicat softening point is 132
Pre-expanded particles (JP-A-5-32815) using a propylene-based random copolymer having a base resin of not less than ℃, a tensile yield point strength of 250 to 300 kg / cm ² , and an organoaluminum-based nucleating agent. Pre-expanded particles containing a polypropylene resin as a base resin (JP-A-5-17
No. 9049), melting point (X _T ) [° C.], tensile modulus (X
_TM) [kg / cm ^2], butene component content (W _B) [wt%], when the ethylene component content (W _E) [wt%], 205X _T -X _TM ≦ 17800 and 355x _T -
X _TM ≦ 39000 and _{1 ≦ W B + W E ≦} 12 and W _E ≦
Mold expansion molded body 2 and the propylene random copolymer base resin which satisfies W _B ≧ 1 (JP-A-7-258
455) has been proposed. However, in the above cases, the effect of improving the compressive strength is not yet sufficient.

[0005]

Therefore, according to the present invention, the heat-sealing of the pre-expanded particles can be carried out by a conventional mold and a molding machine (both withstand pressure of 5.0 kg / cm ² -G) and obtained. It is an object of the present invention to provide a polypropylene resin pre-expanded particle and an in-mold foam molded article having high compressive strength without impairing the lightness of the in-mold foam molded article.

[0006]

Means for Solving the Problems In view of the above circumstances, the present inventors have conducted intensive studies and as a result, have found that a propylene-based random having a specific melting point and MI range and a half-crystallization time of not more than a specific value. It has been found that the above problems can be solved by using a copolymer, and the present invention has been completed. That is, the present invention has a melting point of 149 to 157 ° C, M
I is 1 to 20 g / 10 min and the half-crystallization time is 4
Pre-expanded polypropylene-based resin particles characterized by using an ethylene-propylene random copolymer having a duration of 5 seconds or less as a base resin, wherein the melting point is 149 to 157.
A polypropylene-based resin reserve characterized by using, as a base resin, an ethylene-propylene-1-butene random copolymer having a temperature of 1 ° C. and an MI of 1 to 20 g / 10 minutes and a half-crystallization time of 55 seconds or less. Expanded particles (Claim 2), propylene having a melting point of 149 to 157 ° C, an MI of 1 to 20 g / 10 min, and a half-crystallization time of 60 seconds or less.
Pre-expanded polypropylene resin particles characterized by using a 1-butene random copolymer as a base resin (Claim 3), and the temperature is raised from 40 ° C to 200 ° C at a rate of 10 ° C / min by a differential scanning calorimeter. Of the endothermic peak (α) [J / g] based on the crystal state originally possessed by the base resin, and the heat of fusion (β) of the endothermic peak appearing higher than this peak in the DSC curve obtained when [J / g]
Satisfies the following conditional expression (1): pre-expanded polypropylene resin particles according to any one of claims 1 to 3 (claim 4);

(Equation 2)And the polyp according to any one of claims 1 to 4.
Using at least one kind of pre-expanded particles of propylene-based resin
Density of 0.012 to 0.090 g / cm
^ThreeThe gist of the in-mold foam molded article (Claim 5).

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, in the present invention, the base resin of the polypropylene resin pre-expanded particles has a melting point of 149 to 157 ° C, preferably 150 to 155 ° C, and MI =
1 to 20 g / 10 min, preferably 3 to 15 g / 10 min, and an ethylene-propylene random copolymer having a half-crystallization time of 45 seconds or less, preferably 40 seconds or less; 150-155 ° C, M
I = 1-20 g / 10 min, preferably 3-15 g / 10 min, and the half-crystallization time is 55 seconds or less, preferably 5
An ethylene-propylene-1-butene random copolymer having a melting point of 0 second or less, a melting point of 149 to 157 ° C, preferably 150 to 155 ° C, and MI of 1 to 20 g / 10 minutes, preferably 3 to 15 g / 10 minutes. Ethylene-1 having a half-crystallization time of 60 seconds or less, preferably 55 seconds or less.
-Butene random copolymer may be used. These propylene-based resins are preferably those polymerized with a catalyst that gives highly stereoregular isotactic polypropylene.
For example, those polymerized with a catalyst comprising an organic metal compound such as titanium trioxide, magnesium chloride, ethylaluminum sesquichloride and trimethylaluminum, and an electron donor such as pyridine and methyl benzoate are preferable. These propylene resins may be used alone or in combination of two or more.

If the melting point of the base resin is less than 149 ° C., an in-mold foam molded article having a sufficiently high compressive strength cannot be obtained even if other conditions are satisfied. When the melting point is higher than 157 ° C., the conventional mold and molding machine (both withstand pressure 5.0 kg)
/ Cm ² -G), a sufficiently fused in-mold foam molded article cannot be obtained.

If the MI of the base resin is less than 1 g / 10 minutes, the foaming efficiency in the pre-foaming step of converting the resin particles into pre-foamed particles is unpreferably low. In addition, MI is 20 g
If the time exceeds / 10 minutes, the pre-expanded particles are not easily cracked, which is not preferable.

When the half-crystallization time of the base resin is 45 seconds or more for the ethylene-propylene random copolymer, the half-crystallization time for the ethylene-propylene-1-butene random copolymer is 55 seconds. When the time exceeds 2 seconds, and when the half-crystallization time of the ethylene-1-butene random copolymer exceeds 60 seconds, an in-mold foam molded article having a sufficiently high compressive strength cannot be obtained.

Usually, as a method for evaluating the compressive strength of a foamed molded article, a compressive stress at 50% compression is used.
At the time of% compression, the resin portion in the in-mold foam molded body has undergone deformation beyond the elastic deformation range. It is said that when subjected to deformation beyond the elastic deformation range, deformation or destruction occurs not only in the amorphous region but also in the crystalline region. In addition to the degree, the difficulty of deformation of the crystal, in other words, the rigidity of the crystal can be considered to have a large effect. When the stereoregularity of the base resin molecular chains is high and the distribution of the comonomer components is uniform, the crystallization time is shortened. Therefore, when the half-crystallization time is short, not only the degree of crystallinity is increased, but also defects in the crystal are reduced, and a crystal having higher rigidity is generated. For this reason, when the half-crystallization time is short, it is assumed that high compressive strength is provided. Further, when the melting point of the base resin is lowered, the compressive strength of the in-mold foam molded article is reduced even if the resin has the same crystallinity. This is presumed to be because when the melting point of the base resin is low, the crystal has many defects and the rigidity of the crystal is low, so that the compressive strength is low.

Here, the melting point of the base resin is defined as the temperature of a sample of 4 to 10 mg raised from 40 ° C. to 200 ° C. at a rate of 10 ° C./min.
The temperature at the endothermic peak in the DSC curve obtained when cooling at a rate of 10 minutes per minute and cooling to 200 ° C. again at a rate of 10 ° C./min.

The MI value of the base resin is defined by JIS K7
This is a value measured at a temperature of 230 ° C., a load of 2.16 kg, and a die diameter of 2.095 ± 0.005 mm in accordance with No. 210.

Further, the half-crystallization time of the base resin is defined as 0.1 to 0.2 mm of the base resin substantially containing no nucleating agent.
230 ° C with thick film sandwiched between cover glasses
After heating for 10 minutes and dropping it in silicone oil kept at 115.0 ± 0.1 ° C. and measuring the time change of the transmitted light amount, the transmitted light amount (time = 0) immediately after the dropping and crystallization It means the time (unit: second) until the transmitted light amount becomes の of the difference of the transmitted light amount after completion, and can be measured using, for example, a semi-crystallization time measuring device MK-801 type manufactured by Kotaki Seisakusho.

The nucleating agent is a compound which promotes heterogeneous nucleation and raises the crystallization temperature of the resin. Examples thereof include kaolin, talc, calcium carbonate, adipic acid, polycyclopentene, and benzoic acid which is an organic acid aluminum salt. Aluminum, aluminum hydroxy-di (t-butylbenzoate), bis (p-methylbenzylidene) sorbitol and bis (p-ethylbenzylidene) sorbitol, which are sorbitol derivatives, and 2,2′-methylenebisphosphate, which is an organic phosphate Examples thereof include (4,6-di-t-butylphenyl) sodium and sodium bis (4-t-butylphenyl) phosphate. These nucleating agents increase the crystallization rate (reduce the crystallization time), but have little effect on improving the compressive strength of the in-mold foam molded article.
Generally, these nucleating agents generate heterogeneous nuclei and increase the rate of crystallization. In other words, by increasing the amount of crystal nuclei or eliminating the induction period in which the base resin molecular chains are folded to generate crystal nuclei (uniform nucleation), apparently,
Increase the crystallization rate (decrease the half-crystallization time) and increase the degree of crystallinity. However, there is no difference in the primary structure of the molecular chain of the base resin, and improvement in the rigidity of the crystal itself cannot be expected. Also,
The resulting crystals are finer than when no nucleating agent is added. Therefore, when the half-crystallization time is shortened by the addition of a crystal nucleating agent, the tensile elastic modulus and the bending elastic modulus, which are the resin physical properties in the elastic deformation region which is almost proportional to the crystallinity, are improved. It is assumed that the effect of improving the compressive strength of the in-mold foam molded article is small.

Further, the pre-expanded particles of the present invention have a DSC curve obtained by differential scanning calorimetry (however, sample 4
In a DSC curve when 10 to 10 mg was heated at a rate of 10 ° C./min from 40 ° C. to 200 ° C.), an endothermic peak (hereinafter, referred to as a low-temperature peak) based on a crystal state originally possessed by the base resin. Heat of fusion α (J / g), and the heat of fusion β (J / g) of an endothermic peak (hereinafter referred to as a high-temperature peak) that appears on the higher temperature side than the low-temperature peak is 0.25 ≦ β / (α +
β) ≦ 0.60, preferably 0.30 ≦ β /
It is preferable to satisfy (α + β) ≦ 0.50. β /
If (α + β) is less than 0.25, the ability of the base resin cannot be sufficiently brought out, and an in-mold foam molded article having sufficiently high compressive strength may not be obtained. Also, β
// (α + β) exceeds 0.60, the molding pressure increases, and the conventional mold and molding machine (both withstand pressure of 5.0 kg / cm)
^{In the case of 2-} G), a sufficiently in-mold foam molded article which is sufficiently heat-sealed may not be obtained. The compression strength tends to increase as β / (α + β) increases. The high-temperature peak crystal is generated by thickening the low-temperature peak crystal by the heat treatment until foaming. In general, thickening of a crystal involves rearrangement of molecular chains in the crystal, and the number of defects in the crystal after the thickening is smaller, so that more high-temperature peak crystals having higher rigidity are obtained, that is, β / (α + β) It is presumed that the compression strength increases as the value increases.

Here, how to determine α and β will be described with reference to FIG. The point of contact between the DSC curve and the tangent drawn from the minimum point A closest to the low temperature peak to the beginning of the low temperature peak is B, and the point of contact of the DSC curve with the tangent drawn from the minimum point A to the end of the high temperature peak is C. . Low temperature peak heat of fusion α
Is the area surrounding the line segment AB and the DSC curve, and the high temperature peak heat of fusion β is determined from the area surrounding the line segment AC and the DSC curve.

In the polypropylene resin as the base resin of the pre-expanded particles of the present invention, inorganic fillers such as silica, talc, kaolin and zeolite, heat stabilizers, weathering agents,
Lubricants, antistatic agents and pigments can be added. The amount of these additives is preferably 3% by weight or less, and more preferably 1% by weight or less, so that the cell diameter of the foamed particles does not become fine and nonuniform.

These polypropylene resins are melted in advance using an extruder, a kneader, a Banbury mixer, a roll, or the like, and are formed into a columnar shape, an elliptical columnar shape, a spherical shape, a cubic shape,
The particles are formed into a desired particle shape such as a rectangular parallelepiped or the like so that the particle weight of the particles is 0.2 to 10 mg, preferably 0.5 to 6 mg.

The method for producing the polypropylene resin pre-expanded particles is not particularly limited and may be carried out by a known method.
For example, a polypropylene resin as a base resin is dispersed in water while stirring in a pressure vessel, and then a volatile foaming agent is supplied and heated to a predetermined foaming temperature under pressure. Under low pressure atmosphere (usually under atmospheric pressure)
A method of releasing into the air may be used.

As the volatile foaming agent, for example, propane,
Examples include aliphatic hydrocarbons such as butane, pentane, and hexane; and halogenated hydrocarbons such as dichlorodifluoromethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, methyl chloride, methylene chloride, and ethyl chloride. These foaming agents may be used alone or in combination of two or more. The amount is not limited, and may be appropriately used depending on the desired expansion ratio of the expanded particles. Usually, the amount is 5 to 50 parts by weight based on 100 parts by weight of the polypropylene resin.

In preparing the aqueous dispersion, an inorganic suspending agent such as tribasic calcium phosphate, basic magnesium carbonate, calcium carbonate and the like, and a sodium dodecylbenzenesulfonate and a sodium n-paraffinsulfonate may be used. And a suspending aid such as sodium α-olefin sulfonate. Among them, the combination use of tribasic calcium phosphate and sodium dodecylbenzenesulfonate is preferable. The amount of the suspending agent and suspending aid used depends on the type,
Depending on the type and amount of the polypropylene resin used, the suspending agent is usually 0.2 to 100 parts by weight of water.
3 parts by weight, 0.001 to 0.1 parts by weight of a suspension aid.
In order to improve the dispersibility in water, the polypropylene resin is usually used in an amount of 2 parts per 100 parts by weight of water.
It is preferable to use 0 to 100 parts by weight.

A gaseous or liquid foaming agent is supplied to an aqueous dispersion of a polypropylene resin prepared in a pressure vessel, heated to a predetermined foaming temperature, and usually for a period of 5 to 1 hour.
The pressure is maintained for 80 minutes, preferably 10 to 60 minutes, and the pressure in the pressure vessel rises, so that the foaming agent is impregnated in the polypropylene resin. Thereafter, a foaming agent is additionally supplied until the foaming pressure reaches a predetermined foaming pressure.
Minutes, preferably 10-60 minutes. Thus, the expanded polypropylene resin particles can be produced by discharging the aqueous dispersion of the polypropylene resin heated under pressure through an opening orifice of 2 to 10 mmφ under a low-pressure atmosphere (usually under atmospheric pressure).

The foaming temperature depends on the polypropylene resin used.
Melting point T_m° C, almost (T _m−20) ° C. to (T
_m+5) Determined from the range of ° C. Also, the foaming pressure
It is selected according to the desired foaming ratio, but generally 10 to 50 kg
/ Cm^Two-G.

The expansion ratio of the polypropylene resin pre-expanded particles is usually 3 to 60 times, preferably 5 to 40 times.
Range of double. The method for measuring the expansion ratio of the pre-expanded particles is as follows. Weight (W) [g] of fully dried foamed particles, ethanol immersion volume (V) [cm ³ ]
Is measured. These and the base resin density (d) [g / c
m ³ ] according to the following equation. Expansion ratio = (V / W) × d

The foam molded article of the present invention is obtained by in-mold foam molding using the foam particles obtained as described above. In order to make the foamed particles into an in-mold foam molded article, for example, a) the foamed particles are subjected to a pressure treatment with an inorganic gas to impregnate the particles with the inorganic gas, apply a predetermined internal pressure, and then fill the mold. , Steam and the like (Japanese Patent Publication No. Sho 51-22951)
), B) a method of compressing the foamed particles at a gas pressure, filling the mold and heating and fusing the particles with steam or the like utilizing the recovery force of the particles (Japanese Patent Publication No. 53-33996). sell.
The density of the in-mold foam molded article is 0.012 to 0.090 g /
cm ³ range. When trying to obtain an in-mold foam molded article having a density of less than 0.012 g / cm ³ ,
It is not preferable because deformation is likely to occur, the percentage of defective products increases, and productivity decreases. If the density of the in-mold foam molded article exceeds 0.090 g / cm ³ , the lightness characteristic of the in-mold foam molded article is impaired, which is not preferable.

[0027]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but these do not limit the present invention at all.

Examples 1 to 9 and Comparative Examples 1 to 8 Pellets of a propylene-based random copolymer having a melting point, MI, and half-crystallization time shown in Table 1 (each particle having a weight of about 1.8)
mg) 100 parts by weight, 300 parts by weight of water, 2.0 parts by weight of tricalcium phosphate, 0.05 parts by weight of sodium n-paraffin sulfonate, and 9 to 12 parts by weight of isobutane are charged into a pressure-resistant container and stirred. While the temperature was raised to the foaming temperature shown in Table 1 and maintained for 20 minutes, isobutane was additionally injected to adjust the internal pressure of the container to the foaming pressure shown in Table 1, and held for 10 minutes. Thereafter, while maintaining the temperature and the pressure in the container constant while injecting isobutane, the bubble at the bottom of the pressure-resistant container was opened, and the aqueous dispersion was discharged under atmospheric pressure through an orifice plate having an opening diameter of 4 mm to obtain foamed particles. . Table 1 shows the expansion ratio of the obtained expanded particles. Next, after impregnating the obtained foamed particles with air, 270 × 290 × 6
A molded body was obtained by filling a 0 mm block mold and heating at a steam pressure (molding pressure) shown in Table 1. As physical properties of the obtained molded body, the fusion rate of the molded body, surface appearance,
The rigidity (compression strength) was evaluated by the following method. Table 1 shows the results.

Fusion rate: about 5 mm with a knife on the surface of the molded body
, A molded body was divided along the cracks, the fracture surface was observed, and the ratio of the number of particles in which the material was broken to the total number of particles was determined. ◎: fusion rate of 80% or more ○: fusion rate of less than 60 to less than 80% △: fusion rate of less than 30 to less than 60% ×: fusion rate of less than 30% Usually, the level of fusion rate that is satisfactory as a molded article is: 60% or more.

Surface appearance: The molded product surface was evaluated according to the following scale. ：: There are no irregularities on the surface and there is almost no gap between the particles. Δ: There are no irregularities on the surface, but the gaps between the particles are somewhat noticeable. ×: The surface has irregularities, and the gap between the particles is extremely large.

Rigidity (compressive strength): A test piece sample of 50 mm × 50 mm × 25 mm was compressed at 10 mm / min according to NDS-Z0504, and the compressive stress at 50% compression (20 ° C.) was determined.

[0032]

[Table 1]

[Brief description of the drawings]

FIG. 1. Differential scanning calorimetry D for expanded particles.
An SC curve showing an endothermic peak (low-temperature peak) based on the crystal state originally possessed by the base resin, the heat of fusion α (J /
g) and the heat of fusion β (J / g) of the endothermic peak (high-temperature peak) appearing on the higher temperature side than the low-temperature peak.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI B29K 105: 04

Claims (5)

[Claims] 1. Melting point: 149 to 157 ° C., MI: 1 to 2
Pre-expanded polypropylene resin particles characterized by using, as a base resin, an ethylene-propylene random copolymer having 0 g / 10 min and a half-crystallization time of 45 seconds or less. 2. Melting point: 149 to 157 ° C., MI: 1 to 2
Pre-expanded polypropylene resin particles, characterized by using an ethylene-propylene-1-butene random copolymer having a base crystallization time of 0 g / 10 min and a half-crystallization time of 55 seconds or less. 3. Melting point: 149 to 157 ° C., MI: 1 to 2
Pre-expanded polypropylene resin particles, characterized by using a propylene-1-butene random copolymer having a base crystallization time of 0 g / 10 min and a half-crystallization time of 60 seconds or less. 4. From 40 ° C. to 20 by differential scanning calorimetry.
DS obtained when the temperature is raised to 0 ° C at a rate of 10 ° C / min.
In the C curve, the heat of fusion (α) [J / g] of the endothermic peak based on the crystal state originally possessed by the base resin, and the heat of fusion (β) of the endothermic peak appearing on the higher temperature side than this peak
The polypropylene resin pre-expanded particles according to any one of claims 1 to 3, wherein [J / g] satisfies the following conditional expression (1). (Equation 1) 5. A density of 0.012 to 0.090 g formed by using at least one kind of the pre-expanded polypropylene resin particles according to claim 1. Description:
/ Cm ³ in-mold foam molded article.