JP2001347522A - Polypropylene resin particles for foaming and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain polypropylene resin particles for foaming capable of shortening a heat treating time for modifying a storage period up to a crystal stability of a resin or crystallinity of the resin to suitability for foaming with stable crystallinity. SOLUTION: In a method for manufacturing the polypropylene resin particles, a cooling step of the resin obtained by heating to melt a polypropylene resin made of a copolymer of an ethylene and (or) an α-olefin and propylene containing 0.5 to 60 wt.% of the ethylene and (or) α-olefin component by an extruder and extruding the resin by the extruder has a first step of cooling the resin to a crystallizing temperature ±20 deg.C of the polypropylene resin, and a second step of cooling the resin to a temperature lower than the crystallizing temperature -40 deg.C in such a manner that the time required for the first step is longer by 1 to three times as long as the time required for the second step.

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 polypropylene resin particles for foaming. More particularly, the present invention relates to a method for producing polypropylene resin particles for foaming, which can shorten a storage period until the crystallinity of the resin is stabilized or a heat treatment time for obtaining crystallinity suitable for foaming.

[0002]

2. Description of the Related Art A polystyrene resin, a polyethylene resin or a polypropylene resin has been widely used as a base resin for a foamed molded article by in-mold molding. However, when a polystyrene-based resin is used as the base resin, there is a problem that the obtained foamed molded article is very brittle and has poor chemical resistance. As a solution to this problem, a foam molded article using a polyethylene resin as a base resin has been proposed. However, when a polyethylene resin is used as a base resin, a flexible and tough foam molded article is obtained. However, a cross-linking step is essential for lowering the density. As a result, there is a disadvantage that recyclability is poor.

[0003] It has also been proposed to use a polypropylene resin as a base resin (Japanese Patent Publication No. 56-1344).
Publication), the obtained foamed molded article is substantially non-crosslinked and can be made to have a low density. On the other hand, a generally known production method, that is, resin particles containing a foaming agent are subjected to a low-pressure atmosphere. In a method such as the docan method (Japanese Patent Publication No. 59-23731), the resin particles are impregnated with a blowing agent at a temperature equal to or higher than the Vicat softening temperature of the resin particles.
There is a problem that impregnation equipment that can withstand high pressure is required, and the equipment cost is high. Further, as another method for producing polypropylene-based resin particles, a method for producing propylene-based random copolymer resin particles for producing non-crosslinked pre-expanded particles (Japanese Patent Publication No. 61-215631) has been proposed. However, in this method, since the resin extruded from the extruder is rapidly cooled, the obtained resin is not stable in crystallinity, and the crystallinity stabilization period until the next step (impregnation with a foaming agent) is extended. . As a result, a place for storing the obtained resin is required, and there is a problem that the inventory cost increases and the cost increases.

On the other hand, various proposals have been made as a method for producing expandable polyolefin resin particles, including a method for producing spherical expandable polyolefin resin particles (Japanese Patent Publication No. 2-59171). When impregnating, to heat both the resin particles and gas above the Vicat softening temperature of the resin particles, impregnating equipment that can withstand high temperature and high pressure is required, which not only increases the equipment cost but also lowers the density. There is a problem that it is difficult to obtain a foam. further,
When the obtained expandable resin particles are heated with a heat medium to obtain expandable resin particles, the density distribution of the obtained expandable particles is large, so-called expansion variation is large, and molding is performed in a mold using such expandable particles. However, it is difficult to obtain a desired buffering property.

[0005] As a solution to such a problem, Japanese Patent Application No. 11-279662 discloses a method in which a polypropylene-based resin particle containing a copolymer of propylene and ethylene and / or α-olefin as a main component is scanned with a differential scanning calorimeter. It was obtained by impregnating foamed modified polypropylene-based resin particles obtained by heat treatment within a range from the endothermic peak temperature of the resin particles before the heat treatment in the DSC curve obtained by the measurement to a temperature 15 ° C. higher than the endothermic peak temperature. It has been proposed that foamed particles have a low density and uniform foamed particles can be obtained. However, even in this case, reduction of production time and energy saving by shortening the heat treatment process time are further required for cost reduction.

[0006]

Means for Solving the Problems In view of the above situation, the present inventors have conducted intensive studies and found that the crystallinity was stabilized,
The present inventors have found a method for producing polypropylene-based resin particles for foaming, which can significantly shorten the storage period until the resin crystal stability or the heat treatment time for modifying the crystallinity of the resin to one suitable for foaming. Thus, according to the present invention,
0.5 ethylene and / or α-olefin component
ポ リ プ ロ ピ レ ン 60% by weight of a polypropylene resin composed of a copolymer of ethylene and / or α-olefin and propylene, which is heated and melted, and the step of cooling the resin extruded from the extruder is carried out by crystallization of the polypropylene resin. Temperature ± 20
C. and a second step of cooling to a temperature lower than the crystallization temperature −40 ° C., wherein the time required for the first step is 1 to 3 times longer than the time required for the second step. A method for producing polypropylene resin particles for foaming, and polypropylene resin particles for foaming produced by this method are provided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The polypropylene resin used in the method of the present invention comprises a copolymer of ethylene and / or an α-olefin with propylene (hereinafter referred to as a propylene copolymer) as a main component. The proportion of the ethylene and / or α-olefin component in the coalescence is 0.1%.
It is 5 to 60% by weight, preferably 1.0 to 40% by weight. If the proportion of the ethylene and / or α-olefin component is less than 0.5% by weight, it is close to a homopolypropylene resin, and the effect of the present invention cannot be utilized. On the other hand, if the proportion exceeds 60% by weight, the softening point of the resin is lowered, and the resin particles are likely to be thermally coalesced. When such resin particles are pre-foamed, foamed particles, so-called twin or triple particles, are likely to be generated, which causes trouble during molding.

[0008] The propylene-based copolymer is a binary copolymer,
Either a terpolymer or a multipolymer may be used. Further, any of a random copolymer and a block copolymer may be used, but a random copolymer is preferred. Specifically, random copolymerization of ethylene or butene-1 with propylene is particularly preferred. Examples of the α-olefin in the propylene-based copolymer include those having 4 to 12 carbon atoms such as butene-1, isobutene, pentene-1, 3-methyl-butene-1, octene-1, and decane-1. .

The propylene-based copolymer may be used in accordance with the purpose of modifying propylene or other monomers copolymerizable with ethylene and / or α-olefin within a range not to impair the effects of the present invention. It may be copolymerized. Examples of such a monomer include one or more selected from a cyclic olefin monomer, a diene-based monomer, and other monomers. Examples of the cyclic olefin include cyclopentene and cyclohexene, and examples of the diene-based monomer include butadiene, norbornene, 5-methylene-2-norbornene, 1,4-hexadiene, and methyl-1,4-hexadiene. And
Examples of the other monomers include vinyl monomers such as vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, and maleic acid. One or more thermoplastic resins can be melt-kneaded with the polypropylene resin in the present invention as long as the recyclability and the like are not impaired.

The thermoplastic resin that can be melt-kneaded includes, for example, propylene homopolymer; propylene, ethylene, α-
Olefins, cyclic olefins, binary copolymers with one or more monomers selected from diene-based monomers and vinyl-based monomers, terpolymers or multi-component copolymers, Random copolymer or block copolymer, for example, ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-propylene-butene random terpolymer, etc .; low density polyethylene, high density polyethylene, linear Α-polyolefin having 4 to 12 carbon atoms such as low density polyethylene, polybutene-1, polyisobutene, polypentene-1, polymethylpentene-1; cyclic polyolefin such as cyclopentene; 1,2-polybutadiene, 1,3-polybutadiene , Norbornene, 5-methylene-2-norbornene, , 4
A homodiene-based polymer such as hexadiene, methyl-1,4-hexadiene; a block copolymer of butadiene and styrene and a hydrogenated product thereof; vinyl chloride, vinylidene chloride, styrene, acrylonitrile, vinyl acetate, acrylic acid, methacrylic Examples thereof include vinyl-based homo- or copolymers such as acid and maleic acid.

[0011] The above-mentioned thermoplastic resin is heated to 180 to 250 ° C by a kneader such as a co-kneader, a Banbury mixer, a Brabender, a single screw extruder, or a twin screw extruder.
And uniformly melt-kneaded with the polypropylene resin.
Among these kneaders, a single-shaft or two-shaft type
A screw extruder is preferred. Melt kneading may be performed a plurality of times in order to sufficiently uniformly mix the components. The method of the present invention comprises:
The polypropylene resin obtained as described above is heated and melted by an extruder, and the cooling step of the resin extruded from the extruder is a first step of cooling to a crystallization temperature of the polypropylene resin ± 20 ° C., A second step of cooling to a temperature lower than the crystallization temperature of −40 ° C., wherein the time required for the first step is 1 to 3 times longer than the time required for the second step.

According to this method, in the first step, the polypropylene-based resin in a molten state is gradually cooled to a temperature close to the crystallization temperature of the resin, that is, to a crystallization temperature of ± 20 ° C. Can be encouraged to proceed regularly. However, when the heated and melted resin is rapidly cooled, the crystallization of the resin becomes irregular, and such a resin is heated at a rate of 10 ° C./min at a rate of 10 ° C./min using a scanning differential calorimeter.
DSC curve (1) obtained when heating from 0 ° C. to 220 ° C., and 220 ° C. at a cooling rate of 10 ° C./min.
From 30 ° C to 30 ° C and then at a rate of 10 ° C / min.
DS obtained when heated again from 0 ° C to 220 ° C
C-curve (2) does not show the same shape. This means
When pre-expanded using such resin particles means that crystallization is not stable, not only does the production efficiency of the obtained expanded particles decrease, but also the expansion of the finally obtained expanded molded article Multiple is not stable.

The average cooling rate in the first step is not particularly limited, and varies depending on the processing capability of the equipment used, the characteristics of the raw material resin, and the like, but is preferably, for example, about 5 to 20 ° C./sec. The polypropylene-based resin cooled in the first step is then further cooled in a second step to a temperature lower than a crystallization temperature of −40 ° C. The cooling temperature in the second step may be a temperature lower than the crystallization temperature −40 ° C.,
It is preferable to cool at around normal temperature. In the method of the present invention, the time required for the first step is 1-3 times longer than the time required for the second step. If the time of the first step is shorter than the time of the second step, the crystallization of the polypropylene-based resin tends to be irregular, resulting in the same undesired result as in the case of the above-mentioned rapid cooling.

In the case where the time of the first step is longer than three times the time of the second step, if the first step is unnecessarily long, the space required for cooling and the amount of the cooling medium become large and the If the second step is made shorter than necessary, the resulting resin is likely to be charged with static electricity, and the risk of occurrence of troubles such as ignition of static electricity during transportation increases, which is not preferable. In addition, once cut resin adheres to the vicinity of the cutter due to static electricity and cuts the resin twice, so that fine powder particles are generated or strands are cut,
It is not preferable because the production efficiency is reduced. Here, the “production efficiency” means a value obtained by dividing the product yield by the amount of resin charged into the extruder. If the time of the first step and the time of the second step cannot be measured accurately,
For example, when the resin melted by heating is extruded by the strand method, the time ratio between the two steps may be calculated by replacing the length (distance) between the resin and the cooling medium.

In the method of the present invention, after the polypropylene resin is heated and melted, it is preferable in mass industrial production that the resin is extruded into a strand from an extruder and subjected to a cooling step. The first step of cooling the heat-melted polypropylene resin to its crystallization temperature ± 20 ° C. may be performed by passing through an air layer having a temperature lower than the crystallization temperature ± 20 ° C., but hot water, ethylene glycol, It is preferable to use methanol or the like as a cooling medium in terms of a heat transfer effect,
Among them, it is more preferable to use hot water. Next, the second step of cooling the resin from the crystallization temperature to a temperature lower than 40 ° C. is the same as in the first step.
Although it may be performed through an air layer at a temperature lower than 40 ° C.,
It is preferable to use water, ethylene glycol, methanol, or the like as a cooling medium from the viewpoint of the heat transfer effect, and it is more preferable to use water.

In the polypropylene resin particles for foaming of the present invention, since the resin extruded from the holes of the extruder is cooled in the above-described steps, the obtained resin particles have stable crystallinity, and The crystal stability period before use for (impregnation) can be shortened. In addition, the polypropylene resin particles for foaming of the present invention have a density distribution of the foamed particles obtained narrow, so as to be used as a raw material for producing foamable resin particles with uniform foaming, a DSC obtained by a scanning differential calorimeter. From the main endothermic peak temperature in the curve, 1
Heat treatment is performed within a temperature range of 5 ° C. higher, and then the obtained heat-treated polypropylene resin particles for foaming are impregnated with a foaming agent at a temperature not higher than the Vicat softening temperature of the polypropylene resin to obtain uniform foaming. It is possible to obtain foamable resin particles and foam particles having a uniform foam.

The time required for the heat treatment varies depending on the size (volume), shape, etc. of the resin particles. For example, when the volume of the particles is about 3.0 mm ³ , the cooling step of the present invention is excluded. For example, in the case of quenching all at once, it took 0.5 hours or more after reaching a required temperature. In the processing less than the required time, unevenness of the heat treatment occurs between the central part and the surface part of the polypropylene resin particles,
In the obtained foamed particles, the cell diameter varies within one foamed particle, and as a result, the density of the foamed particles varies. Further, the foamed molded article obtained from such foamed particles has poor buffering properties.

On the other hand, in order to cool the polypropylene resin particles for foaming of the present invention in the above step, the resin particles in a molten state are once cooled to a temperature near the crystallization temperature of the resin, and then the resin is cooled. Crystallization progresses regularly,
The time required for heat treatment can be greatly reduced. In addition, DSC
The endothermic peak of the polypropylene resin in the curve is obtained by scanning 3 to 7 mg of the polypropylene resin with a scanning differential calorimeter (SE).
IKO DSC 200) at a rate of 10 ° C / min.
DSC curve (1) obtained by heating from 220 ° C. to 220 ° C., then from 220 ° C. to 3
The temperature can be determined from a DSC curve (2) obtained when the temperature is lowered from 0 ° C. and then heated again from 30 ° C. to 220 ° C. at a rate of 10 ° C./min. The main endothermic peak temperature of the polypropylene-based resin means the endothermic peak temperature in the DSC curve (2), and when the DSC curve (2) has only one endothermic peak, it is the temperature of the peak.
When there are a plurality of endothermic peaks, the temperature is the highest peak temperature.

The DSC curves (1) and (2) show that the polypropylene resin has a stable crystallinity.
The curves have almost the same shape, and the difference between the peak temperatures in both DSC curves usually falls within ± 2 ° C. The crystallization temperature of the polypropylene-based resin is 3 to 7 mg of resin particles.
Using a differential scanning calorimeter (SEIKO DSC 200 type)
Heating from -30 ° C to 220 ° C at a heating rate of ° C / min,
Next, it is determined from a DSC curve obtained when the temperature is lowered from 220 ° C. to −30 ° C. at a temperature lowering rate of 10 ° C./min. That is, when there is only one crystallization peak obtained from the DSC curve, the temperature of that peak is the crystallization temperature, and when there are multiple crystallization peaks, the highest peak temperature is the crystallization temperature. Note that the endothermic peak temperature and the crystallization temperature are respectively defined by DISC STATION (SEIKO SSC-5200H
Ver.2.9). Further, as the temperature of the resin particles,
The surface temperature of the resin particles at the end of the first step and the second step was measured with a non-contact type thermometer (TRD506C, manufactured by Minolta), and the average value of n = 10 was defined as the average resin temperature of each step.

[0020]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Example 1 In an extruder, polypropylene-based resin particles comprising an ethylene-propylene random copolymer (ethylene component: 5% by weight, main endothermic peak temperature in a DSC curve obtained by a scanning differential calorimeter: 135 ° C, Vicat softening temperature: 125
C., crystallization temperature: 95 ° C.), and after heating and melting at 220 ° C., the resin was extruded in a strand form from an extruder.
Next, the polypropylene resin was passed through a 2 m water tank containing hot water at 90 ° C. heated by an electric heater to cool the strands to 95 ° C. (first step). Further, the strand was passed through a 1 m water tank containing water at 30 ° C. to cool the strand to 40 ° C. (second step), and then cut with a cutter to an average volume of 3 mm ³ to have a diameter of 1.4.
Thus, pelletized polypropylene resin particles having a diameter of 1.95 mm and a length of 1.95 mm were obtained. One day after cutting, the modified polypropylene resin was transferred to a scanning differential calorimeter (SEIKO DS
DSC model (1) obtained by heating from 30 ° C. to 220 ° C. at a rate of 10 ° C./min using a C200 type), and then 3 ° C. to 3 ° C. at a rate of 10 ° C./min.
FIG. 1 shows DSC curves (2) obtained when the temperature was lowered to 0 ° C. and then heated again from 30 ° C. to 220 ° C. at a rate of 10 ° C./min.

As is apparent from FIG. 1, the DSC curves (1) and (2) are curves having almost the same shape, and it can be seen that the crystallinity is stable. In addition, regarding the polypropylene resin particles for foaming obtained above, the production efficiency was determined, and as the number of days required for the crystals to stabilize,
The number of days until the DSC curves (1) and (2) showed almost the same shape was measured. Table 1 shows the results. Next, 50 L of water, 600 g of tertiary calcium phosphate as a dispersant, and 30 g of sodium dodecylbenzenesulfonate as an activator were added to an autoclave having an internal volume of 100 L to prepare an aqueous medium. 30 kg of a foaming polypropylene resin was suspended in the above aqueous medium and stirred. Next, the mixture was heated to 145 ° C., kept at that temperature for 20 minutes, cooled, dehydrated, and the product was taken out to obtain a heat-treated polypropylene resin for foaming. The time required for the heat treatment step is the time when heating from 30 ° C. to 220 ° C. at a rate of 10 ° C./min using a scanning differential calorimeter of the polypropylene resin particles treated at the same temperature for different times. The time until the peak temperature of the obtained DSC curve stably showed a constant value was measured.
Table 1 shows the results.

Next, in an autoclave having an inner volume of 5 L,
Water, 30 g of tertiary calcium phosphate as a dispersant, and 1 g of sodium dodecylbenzenesulfonate as an activator were added to form an aqueous medium, and the heat-treated polypropylene resin for foaming obtained above was added to the aqueous medium. Suspended and stirred. Then isobutane was injected using nitrogen pressure, the mixture was heated to 80 ° C., kept at that temperature for more than 4 hours and then cooled to 25 ° C. Subsequently, dehydration was performed to obtain expandable polypropylene resin particles. The foamable polypropylene-based resin particles thus obtained were steam-heated for about 30 seconds by a prefoaming machine to obtain polypropylene-based foamed particles having a density of 0.045 g / cc. Table 1 shows the results.

Example 2 Example 2 was repeated except that the cooling medium used in the first step was changed to ethylene glycol, and the resin temperature at the end of the first and second steps was changed as shown in Table 1. In the same manner as in Example 1, polypropylene-based expanded particles were obtained.
Table 1 shows the results. Example 3 Except having changed the resin temperature at the time of completion | finish of a 1st process and a 2nd process respectively as shown in Table 1, it carried out similarly to Example 1, and obtained the polypropylene expanded particle. Table 1 shows the results. Examples 4 and 5 Except that the length of the water tank in the first step and the second step was changed as shown in Table 1, the same procedure as in Example 1 was performed to obtain expanded polypropylene particles. Table 1 shows the results.

Comparative Example 1 Example 1 was repeated except that the cooling medium used in the first step was changed to ethylene glycol, and the resin temperature at the end of the first and second steps was changed as shown in Table 1. In the same manner as in Example 1, polypropylene-based expanded particles were obtained.
Table 1 shows the results. Comparative Example 2 Polypropylene expanded particles were obtained in the same manner as in Example 1 except that the resin temperature at the time when the first step and the second step were completed was changed as shown in Table 1. Table 1 shows the results.

Comparative Examples 3.4 Except that the length of the water tank in the first step and the second step was changed as shown in Table 1, the same procedure as in Example 1 was carried out to obtain expanded polypropylene particles. Table 1 shows the results. Comparative Example 5 Polypropylene foam particles were obtained in the same manner as in Example 1 except that the resin was quenched instead of the first step and the second step. Table 1 shows the results. FIG. 2 shows a DSC curve (1) and a DSC curve (2) of the obtained modified polypropylene resin.

[0026]

[Table 1]

As is clear from Table 1, the resin obtained by the method of the present invention has stable crystallinity, and the processing time required for foam molding can be greatly reduced.

[0028]

According to the method of the present invention, a resin having stable crystallinity can be obtained. By using this resin, the processing time required for foam molding can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a DSC curve (1) and a DSC curve (2) of the modified polypropylene resin obtained in Example 1.

2 is a DSC curve (1) and a DSC curve (2) of the modified polypropylene resin obtained in Comparative Example 5. FIG.

Claims (4)

[Claims] 1. An extruder is used to extrude a polypropylene resin comprising a copolymer of ethylene and / or α-olefin and propylene, wherein the ethylene and / or α-olefin component is 0.5 to 60% by weight. Heat and melt,
The step of cooling the resin extruded from the extruder includes a first step of cooling to a crystallization temperature of the polypropylene-based resin ± 20 ° C., and a second step of cooling to a temperature lower than the crystallization temperature of −40 ° C. A method for producing polypropylene resin particles for foaming, wherein the time required for the first step is 1 to 3 times longer than the time required for the second step. 2. The method according to claim 1, wherein the heat-melted polypropylene resin is extruded from an extruder into a strand. 3. The method according to claim 1, wherein the polypropylene resin is a random copolymer of ethylene and / or α-olefin and propylene. 4. Polypropylene resin particles for foaming produced by the method according to claim 1.