JP3514046B2 - Pre-expanded particles of polypropylene resin - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to polypropylene resin pre-expanded particles applicable to a method of in-molding pre-expanded particles to obtain a polypropylene resin foam-molded article having a desired shape. More specifically, polypropylene-based resin pre-expanded particles capable of being molded with a relatively low molding water vapor pressure and capable of obtaining a foamed molded product excellent in impact energy absorption, and a polypropylene-based resin foamed molded product using the same. Regarding manufacturing method.

[0002]

2. Description of the Related Art In-mold expanded molded articles obtained from polypropylene resin pre-expanded particles have excellent chemical resistance, impact resistance, compressive strain recovery, etc., as compared with molded articles obtained from polystyrene resin pre-expanded particles. Further, it has excellent heat resistance as compared with a molded product obtained from polyethylene resin pre-expanded particles, and has been conventionally used as a bumper core material for automobiles, various packaging materials and the like.

Conventionally, as a base resin for polypropylene-based resin foamed particles for producing the foamed molded product as described above, due to restrictions of foaming characteristics and in-mold molding with steam,
Melt flow rate (melt index) is 0.1
A propylene-α-olefin (mainly propylene-ethylene) random copolymer having an α-olefin content of 1% by weight or more at 25 g / 10 minutes was mainly used (for example, Japanese Examined Patent Publication No. 59-43492, Japanese Examined Patent Publication). 2-504
No. 95). The reason for setting the melt index (MI) within the above range is, for example, the above-mentioned Japanese Patent Publication No. 59-434.
In Japanese Patent Laid-Open No. 92, it is described that when the MI value exceeds 25, continuous foaming is likely to occur during pre-foaming, shrinkage may occur, and the mechanical strength of the molded body deteriorates. In Japanese Patent Publication No. 2-50945, MI is 2
It is described that when it exceeds 0, the fluidity becomes too large, the expansion ratio is difficult to increase, and the shrinkage easily occurs after foaming. However, as described above, conventional propylene having an α-olefin content of 1% by weight or more and a small MI value is used.
When a foamed molded product is produced by in-mold molding using pre-expanded particles having an α-olefin random copolymer as a base resin,
Since the rigidity of the resin is lower than that of the propylene homopolymer, the impact energy absorption of the molded product is not always satisfactory depending on the application.

On the other hand, propylene homopolymer is
The rigidity of the resin is higher than that of the above-mentioned conventionally used random copolymer, and the impact energy absorbability when formed into a foamed molded product is excellent, but the melting point is 160 to 165 ° C.
The molding water vapor pressure exceeds 5 kgf / cm ² (G) (indicating a gauge pressure), and there are problems with the mold clamping pressure of the molding machine, the pressure resistance of the mold, the amount of steam used, etc. There wasn't.

[0005]

The object of the present invention is to produce a molded article having a high rigidity and an excellent impact energy absorption, but it is difficult to mold the molded article, a propylene homopolymer and an α-olefin. In the polypropylene resin pre-expanded particles having a base resin of a random copolymer of propylene-α olefin having a low content and exhibiting physical properties close to those of the propylene homopolymer, lower molding at the time of in-mold molding of these pre-expanded particles By enabling molding with water vapor pressure, a foamed molded article having excellent impact energy absorption is obtained, as compared with the case of using conventional pre-expanded particles using a polypropylene-α-olefin random copolymer as a base resin. It is intended to provide polypropylene resin pre-expanded particles that can be obtained.

[0006]

Means for Solving the Problems As a result of earnest studies, the inventors of the present invention have carried out in-mold molding of pre-expanded particles to obtain polypropylene-based resin pre-expanded particles for use in producing desired polypropylene-based resin pre-expanded particles. As the propylene homopolymer having high resin rigidity and excellent impact energy absorption when formed into a foamed molded product, or polypropylene-α olefin having a physical property close to that of the propylene homopolymer with an α-olefin content of less than 1% by weight. We have succeeded in achieving the above object by using a polypropylene resin which is a random copolymer and has good resin fluidity when melted. That is, the present invention uses a polypropylene resin as a base resin and has a cell diameter of 50 to 1000 μm.
The open cell rate is 0 to 35% and the expansion ratio is 5 to 100.
In the polypropylene resin pre-expanded particles that are double,
The base resin is a propylene homopolymer or a random copolymer of propylene and α-olefin having an α-olefin content of less than 1% by weight, and ASTM D12
Melt flow rate (230
The polypropylene-based resin pre-expanded particles are characterized by having a temperature of 2.16 kg under a condition of 20 to 100 g / 10 minutes.

[0007]

The base resin of the propylene-based resin pre-expanded particles of the present invention has a melting point of 130 to 150 ° C. as compared with the melting point of the random copolymer of propylene and α-olefin which has been mainly used in the past. High, 160-165 ° C. for propylene homopolymer and 150-160 ° C. for random copolymer of propylene and α-olefin having an α-olefin content of less than 1% by weight, When a resin with good flowability during melting is not used, the molding steam pressure is 1 to 4 kg compared to conventional random copolymers.
f / cm ² increases. On the other hand, in the case of using the propylene-based resin pre-expanded particles of the present invention made of a base resin having a good fluidity at the time of melting, the molding steam pressure is 1 to 2 k.
Since gf / cm ^{2 is} lowered, molding can be performed using a conventionally used molding machine and mold. The reason for this is not necessarily clear, but the propylene-based resin with good fluidity used as the base resin in the present invention is a resin that is filled with pre-expanded particles in a molding die and expanded / pressed by being heated by steam. It is presumed that melting may occur even at a temperature that does not reach the melting point of, and particles may be fused to each other. The melting point of the polypropylene resin is measured by using a differential scanning calorimeter (DSC), and the sample is heated at 200 ° C. at a rate of 10 ° C./min.
After melting by heating up to 40 ° C. at a rate of 10 ° C./min, crystallization was performed at 10 ° C./min, and the temperature was raised again at 10 ° C./min to measure the endothermic curve, the peak temperature of the endothermic peak was taken as the melting point. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the melt flow rate of polypropylene-based resin means ASTM Standards (Standard) which is a standard test method in the United States.
s of American Society for
According to Testing and Materials), it was measured by applying a load of 2.16 kg at 230 ° C. The polypropylene resin used as the base resin of the pre-expanded particles in the present invention is a propylene homopolymer or a random copolymer of propylene and α-olefin having an α-olefin content of less than 1% by weight and having a melt flow rate of 20. -100 g / 10 minutes, more preferably 25-80 g / 10 minutes. If the melt flow rate is less than 20, the particles will not fuse to each other unless the molding pressure is increased, and if it exceeds 100, the foamed particles will be too brittle, and the cells constituting the foam will break during foaming or molding. Further, in the case of a random copolymer of propylene and α-olefin, if the α-olefin content is 1% by weight or more, the rigidity of the resin becomes too low, and the impact energy absorbency when formed into a molded product is impaired. Be done.

Examples of the α-olefin to be copolymerized with propylene include ethylene, butene-1, isobutene, pentene-1, hexene-1, 4-methylpentene-1, octene-1, etc. Therefore, ethylene and butene-1 are preferable. These can be used alone or in combination of two or more.

The polypropylene resin used as the base resin for the expanded beads of the present invention may contain, if necessary, a nucleating agent, a stabilizer, an antioxidant, a neutralizing agent, an ultraviolet absorber, a lubricant, an antiblocking agent, and a filler. A lacquer additive such as an agent, a colorant, an antistatic agent, etc. can be used together within a range that does not impair the effects of the present invention.

The cell diameter of the polypropylene resin pre-expanded particles according to the present invention is 50 to 1000 μm, preferably 80.
To 800 μm, more preferably 100 to 500 μm. In the present invention, if the cell diameter is less than 50 μm, foaming and shrinkage occur during molding, and a good molded product cannot be obtained.
If it exceeds 0 μm, a uniform cell cannot be obtained. The cell diameter of the polypropylene resin pre-expanded particles means random sampling of 10 pre-expanded particles, cutting each sample particle from the center with a razor, and observing the cut surface with a loupe with a scale, and measuring 2 mm on the scale. The number of cells traversing the length was counted, the average chord length was obtained from the following formula, and the average value of the average chord length of 10 particles was taken as the cell diameter. Average chord length (μm) = number of cells crossing a length of 2 mm / 2 mm

The polypropylene resin pre-expanded particles according to the present invention have an open cell rate of 0 to 35% and an expansion ratio of 5 to 10.
It is 0 times. In the present invention, the open cell ratio is the ratio of open cells to total cells, and the expansion ratio refers to how many times the volume of expanded particles is larger than the volume of resin particles before expansion. These values are obtained from the following equations (1) and (2).

Open cell ratio (%) = (V−v) / V × 100 (1) Foaming ratio = V / (W / d) (2) V: Submerge the foamed particle sample in water Measured volume v: true volume of the expanded particle sample [value measured using an air-comparison hydrometer (eg, Toshiba Beckman, air-comparison hydrometer 930)] W: weight of the expanded particle sample d: resin Density (g / cm ³ )

When the open cell ratio exceeds 35%, the expansion pressure of the foamed particles in the mold during molding is not sufficient, so that a molded product in which the particles are fused well cannot be obtained. The open cell rate is preferably 25% or less, more preferably 15% or less.

If the expansion ratio is less than 5, the expansion ratio is large and uniform pre-expanded particles cannot be obtained.
If it exceeds twice, the pre-expanded particles are more likely to be broken and shrunk, so that satisfactory pre-expanded particles cannot be obtained. The expansion ratio of the pre-expanded particles is preferably 5 to 80 times, more preferably 7 to 7 times.
It is 0 times.

The method for producing pre-expanded polypropylene resin particles of the present invention is as follows: 1) a method of impregnating resin particles with a volatile foaming agent in a liquid phase or a gas phase, and heating with a heating medium such as water vapor to foam (for example, JP-A-58-65734),
2) A method in which resin particles and a volatile foaming agent are dispersed in water in a pressure-resistant container, the resin particles are impregnated with the foaming agent at a high temperature, and then the contents are discharged into a low-pressure atmosphere to foam (for example, a special method). (Kaisho 58-197027) 3) A method in which a resin is heated and melted in an extruder, kneaded with a volatile foaming agent, and then extruded in a strand form to be foamed and cut into foamed particles (Japanese Patent Laid-Open No. H8-8187). No. 76230) can be used. Among these foaming methods, the method 2) is preferable. The reason for this is presumed to be that when the melting behavior of the expanded particles is measured by a differential scanning calorimeter (DSC), the crystal peaks are separated into two and the molding process width is wide.

The volatile foaming agent used in the method for producing pre-expanded polypropylene resin particles of the present invention includes aliphatic hydrocarbons such as propane, butane, pentane and hexane, and alicyclic hydrocarbons such as cyclopentane and cyclohexane. , Halogenated hydrocarbons such as dichlorodifluoromethane and dichlorotetrafluoroethane. These may be used alone or in combination of two or more. The amount of the foaming agent is selected depending on the type of the foaming agent and the desired expansion ratio, but generally 1 to 50 parts by weight is used with respect to 100 parts by weight of the resin.

The polypropylene resin pre-expanded particles according to the present invention are prepared by subjecting the expanded particles obtained as described above immediately after the production without any post-treatment, or after curing and drying for an appropriate time after the production. The internal pressure is kept at atmospheric pressure, or after the expanded particles are impregnated with air or the like to increase the internal pressure inside the particles to give the foaming ability, they are subjected to molding. Then, the method for producing a polypropylene resin foam molded article according to the present invention,
Using the pre-expanded particles as described above, by a normal in-mold molding, a mold equipped with a molding machine and having a large number of steam holes, which is closed but not sealed, is filled with a molding steam pressure of 5 kgf / c.
The heating is performed at m ² or less.

[0019]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 Melt flow rate = 40 g
/ 10 minutes, density 0.91 g / cm ³ , 100 parts by weight of propylene homopolymer pellets (about 1.8 mg / grain) having a melting point of 165 ° C. by DSC (differential scanning calorimeter), 2 parts by weight of basic tribasic calcium phosphate Parts, 0.05 parts by weight of sodium dodecyl sulfonate, 300 parts by weight of pure water, and 9 parts by weight of isobutane are placed in a pressure-resistant container of 10 L, heated to 164 ° C. with stirring, and the pressure in the container is 19 kgf /
Isobutane was added until it became stable at cm ² (G). After the internal pressure has stabilized, the diameter of the orifice plate attached to the ball valve attached to the bottom of the pressure vessel via a flange is 4 mm.
A mixture of resin particles and water was discharged to the atmospheric pressure through the openings of the above to foam. The foamed particles were placed in an atmosphere of 80 ° C. for 20 minutes.
After drying for an hour, foamed particles having an expansion ratio of 15 times, an open cell ratio of 4%, and a cell diameter of 120 μm were obtained. Next, the foamed particles were placed in a pressure resistant container and pressurized at 80 ° C. with an air pressure of 7 kgf / cm ² (G) for 1 hour to impregnate air to impart a foaming ability. Subsequently, a small mold (290 mm x 270 mm x 60 mm) mounted on a molding machine (P-110 made by Toyo Kikai Metal).
And the heated steam pressure is 4 to 5 kgf.
/ Cm ² was subjected to molding varied in the range of (G), good molded body between the particles were well fused with heating lowest vapor pressure 4.2kgf / cm ² (G) was obtained.

The minimum steam pressure for heating is
The molded body is left in an atmosphere of 80 ° C. for 24 hours and then taken out,
After cooling to room temperature, a cut is made in the molded body to break it, and the fracture surface is visually observed, and the area broken at the inside, not at the interface of the particles, is 60% or more, and the result is 60% of the melting point. The forming water vapor pressure for obtaining the coating was the minimum water vapor pressure.

Example 2 Melt flow rate = 22 g
/ 10 minutes, using a propylene homopolymer with a melting point of 164 ° C
Expanded particles were obtained in the same manner as in Example 1 except that the above was used. Foaming
The particles have an expansion ratio of 12 times, an open cell rate of 2%, and a cell diameter of 18
It was 0 μm. Using the foamed particles, the same as in Example 1
The minimum water vapor pressure when molded in this way is 4.5k
gf / cm ²(G).

[Comparative Examples 1 to 3] Melt flow rate and melting point were 3 g / 10 minutes at 162 ° C. and 10 g / minute, respectively.
Expanded particles were obtained and molded in the same manner as in Example 1 except that three propylene homopolymers of 164 ° C. for 10 minutes and 165 ° C. for 18 g / 10 minutes were used. Table 1 shows, together with Examples 1 and 2, the expansion ratio, the open cell ratio, the cell system of these expanded particles, and the heated steam pressure necessary for fusing the particles with each other by 60% or more.

[0024]

[Table 1]

As is clear from the results shown in Table 1, the pre-expanded particles of the present invention in which the base resin has a melt flow rate of 20 or more were compared with Comparative Examples in which the base resin had a melt flow rate of less than 20. Molding steam pressure is low by 1 kgf / cm ² or more, and molding can be performed with a molding steam pressure of 5 kgf / cm ² or less, even though propylene homopolymer is used as the base resin.

[Examples 3 and 4, Comparative Examples 4 and 5] Various random propylene and ethylene having different melt flow rates and ethylene contents and having an ethylene content of less than 1% by weight shown in Table 2 below. Using the copolymer, pre-expanded particles were obtained in the same manner as in Example 1, and the results of molding were shown in Table 2.

[0027]

[Table 2]

As is clear from the results shown in Table 2, the pre-expanded particles of the present invention are a base resin containing a random copolymer of propylene and ethylene, which has an ethylene content of less than 1% by weight and shows physical properties close to those of a propylene homopolymer. Even when used as, the molding can be performed with a molding steam pressure lower by about 1 kgf / cm ^{2 as} compared with the comparative example using a resin having a melt flow rate of less than 20.

[0029]

EFFECTS OF THE INVENTION The polypropylene resin pre-expanded particles of the present invention have a propylene homopolymer having a high resin rigidity and capable of producing a molded article excellent in impact energy absorption, or an α-olefin content of less than 1% by weight. Pre-expanded polypropylene resin particles with a high melting point, which are based on a random copolymer of propylene and α-olefin, can be molded with a significantly lower heating steam pressure, and a molding machine equipped with heavy equipment and a mold are used. Without using a conventional polypropylene resin molding machine.

Claims (6)

(57) [Claims] 1. A polypropylene resin as a base resin,
Cell diameter is 50 ~ 1000μm, open cell rate is 0 ~ 35%
In the polypropylene resin pre-expanded particles having an expansion ratio of 5 to 100 times, the base resin is a propylene homopolymer, or a random copolymerization weight of propylene and α-olefin having an α-olefin content of less than 1% by weight. A polypropylene resin pre-expanded particle which is a coalesced product and has a melt flow rate (230 ° C., 2.16 kg load) measured according to ASTM D1238 in the range of 20 to 100 g / 10 minutes. 2. The polypropylene resin pre-expanded particles according to claim 1, wherein the base resin is a propylene homopolymer, and the molding steam pressure during in-mold molding is 5 kgf / cm ² or less. 3. The melting point of the propylene homopolymer is 1.
The polypropylene resin pre-expanded particles according to claim 2, which have a temperature of 60 ° C or higher. 4. The polypropylene resin pre-expanded particles according to claim 1, wherein the base resin is a random copolymer of propylene and α-olefin, and the α-olefin is ethylene and / or butene-1. 5. The polypropylene resin pre-expanded particles according to claim 4, wherein the random copolymer of propylene and α-olefin has a melting point of 150 ° C. or higher. 6. A polypropylene resin pre-expanded particle according to claim 1 is filled in a mold which has a large number of steam holes and is closed but not hermetically sealed, and has a molding water vapor pressure of 5 kgf. / cm preparation of the polypropylene resin foamed molded, characterized by mold molding by heating at ² or less.