JPH10324712A - Production of modified polypropylene and polypropylene resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce the subject compound modified in physical characteristics such as melt tension, etc., excellent in melt processability and having stable qualities by crosslinking a source polypropylene without melting using a specific peroxide compound. SOLUTION: This production of modified polypropylene is to put polypropylene (preferably a polypropylene homopolymer) particles (preferably <=5 mg/l piece in average particle weight), a peroxide (e.g. lauroyl peroxide, benzoyl peroxide, etc.) having a one minute half life temperature [preferably 100 deg.C to (melting point of the source polypropylene -10 deg.C)] equal to or less than that of source polypropylene used for the polypropylene particles and a main chain cleavage-protecting agent (divinylbenzene, etc.) in an aqueous medium and obtain the polypropylene particles having essentially no gel fraction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a modified polypropylene and a method for producing a polypropylene resin foam.

[0002]

2. Description of the Related Art Conventionally, polypropylene has been used as a raw material resin for various synthetic resin molded products. However, polypropylene has higher transparency, rigidity, surface gloss and heat resistance than other polyolefins. Although it is excellent in properties, it has a problem in melt processability, and has a drawback that it is inferior in moldability such as hollow molding, extrusion molding, foam molding and the like.

In particular, when melt-kneading a polypropylene and a foaming agent in an extruder and then extruding and foaming the melt-kneaded product to obtain a polypropylene resin foam, there are the following problems. That is, since the viscosity of polypropylene greatly changes with temperature, it is extremely difficult to maintain the viscosity at which a good foam having closed cells can be obtained.If the viscosity during extrusion foaming is too low, the foaming agent from the melt-kneaded material is Has a molding problem such that the foam quickly escapes and becomes a foam having an open-cell structure. On the contrary, if it is too high, uniform foaming is hindered, and the foam becomes a foam having an uneven surface.

For this reason, various proposals have conventionally been made to solve the above problems. For example, JP-A-62-2
No. 01942 discloses a method in which a peroxide having a specific MFI (melt flow index) is melt-kneaded with a peroxide, the polypropylene is crosslinked with the peroxide, and extrusion foaming is performed.

However, in this method, peroxide is mixed in the heated and molten polypropylene, so that the peroxide is decomposed as soon as it is mixed, and the polypropylene cannot be crosslinked or crosslinked. Even if it is possible, a reaction occurs before the peroxide and the polypropylene are not sufficiently mixed, and it is difficult to obtain a homogeneous product. In the above-mentioned publication, it is said that a uniform crosslinking reaction can be expected by using a peroxide having a high half-life temperature for 1 minute, but there is a limit, and a sufficiently satisfactory result has not been obtained. However, it is still insufficient in terms of improving the melt processability.

In addition, peroxide mixed under heating may cut the main chain of polypropylene and cause a decrease in viscosity due to a reduction in molecular weight. To prevent this, a large amount of a main chain cleavage inhibitor must be used. Must be added.

However, since the main chain scission inhibitor usually used is not sufficiently compatible with the polypropylene, the main chain scission inhibitor added in a large amount not only causes non-uniform physical properties due to poor dispersion, The main chain scission inhibitor sometimes reacts with peroxide and polymerizes itself, which also leads to non-uniformity of physical properties and inhibits uniform crosslinking of polypropylene. was there.

On the other hand, according to JP-A-62-121704, linear polypropylene is irradiated with high-energy ionizing radiation such as an electron beam or a gamma ray in the presence of active oxygen to cause long-chain branching. It is said that the melt processability of polypropylene can be improved.

However, in such a method, the reaction is performed by irradiating with high-energy ionizing radiation in an atmosphere in which a specific concentration of active oxygen exists, and after irradiating the radiation, free radicals generated by the irradiation are deactivated. Operation must be complicated, and equipment for irradiating high-energy ionizing radiation is required.
There was a disadvantage that it was disadvantageous in terms of cost.

The present inventors have conducted intensive studies in view of the above-mentioned problems of the prior art, and as a result, using a peroxide having a one-minute half-life temperature equal to or lower than the melting point of polypropylene, the peroxide was dissolved in an aqueous medium. After impregnating the polypropylene particles with
By decomposing the peroxide and slightly cross-linking the polypropylene to obtain polypropylene particles with a substantial gel fraction of 0%, the physical properties such as melt tension are modified, and homogeneous polypropylene with excellent melt processability can be easily obtained. Thus, the present invention has been completed.

[0011]

That is, the present invention provides (1) polypropylene particles, a peroxide having a one-minute half-life temperature equal to or lower than the melting point of the raw polypropylene used for the polypropylene particles, Was added to an aqueous medium and stirred to impregnate the polypropylene particles with the peroxide and the main chain scission inhibitor. Then, the peroxide was decomposed to slightly crosslink the raw material polypropylene, and a substantial gel fraction of 0 was obtained. % Polypropylene particles containing a main chain breaking inhibitor in advance, and a raw polypropylene having a half-life temperature of 1 minute for the polypropylene particles. And a peroxide having a melting point of not more than the melting point of the aqueous medium and stirred,
After impregnating polypropylene particles with the peroxide, the peroxide is decomposed to slightly crosslink the raw material polypropylene to obtain polypropylene particles having a substantial gel fraction of 0%. Production method,
(3) The method for producing a modified polypropylene according to the above (1) or (2), wherein the one-minute half-life temperature of the peroxide is 100 ° C. to [the melting point of the raw material polypropylene−10 ° C.]
(4) The method for producing a modified polypropylene according to the above (1), (2) or (3), wherein the average weight of the polypropylene particles is 5 mg / 1 or less, (5) the above (1),
A gist of the present invention is a method for producing a polypropylene resin foam, which comprises extruding and foaming the polypropylene particles obtained by the method according to (2), (3) or (4).

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The raw material polypropylene used in the present invention is particularly preferably a propylene homopolymer, but may be a copolymer obtained by copolymerizing propylene with another monomer component.

In the present invention, when a copolymer of propylene and another monomer component is used as a raw material polypropylene, the other monomer component is contained in the copolymer, and in the case of a random copolymer, it is not more than 5.0% by weight. In the case of a block copolymer, the content is preferably 20.0% by weight or less. If the amount of other monomer components contained in the copolymer is larger than this, characteristics such as transparency, rigidity, surface gloss, and heat resistance inherent to polypropylene are undesirably impaired.

Other monomer components copolymerizable with propylene include ethylene, 1-butene, isobutylene,
-Pentene, 3-methyl-1-butene, 1-hexene,
Examples include 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene and the like. These copolymers may be a random copolymer or a block copolymer,
Further, not only binary but also ternary copolymers may be used.

The raw material polypropylene can be used alone or in combination of two or more. Further, the raw material polypropylene may be a high-density polyethylene, a low-density polyethylene, a linear low-density polyethylene, a linear ultra-low-density polyethylene, an ethylene-butene copolymer as long as the above-mentioned properties inherent to polypropylene are not impaired. If necessary, an ethylene resin such as a copolymer, an ethylene-maleic anhydride copolymer, a butene resin, polyvinyl chloride, a vinyl chloride resin such as a vinyl chloride-vinyl acetate copolymer, and a styrene resin are mixed as necessary. You can also.

The raw material polypropylene used in the present invention has a melt flow index (JIS K7210).
Is preferably 1 to 20 g / 10 min. Further, the melting point of the raw material polypropylene is preferably 135 ° C. or higher, preferably 145 ° C., and more preferably 155 ° C. or higher.

The polypropylene particles in the present invention are formed into particles using the above-mentioned raw material polypropylene. The specific shape of the polypropylene particles is not particularly limited, and any shape such as a spherical shape, an elliptical spherical shape, a columnar shape, and an irregular shape can be adopted. In order to efficiently perform the reaction in a short time, it is preferable to reduce the volume of the polypropylene particles and increase the specific surface area. For this purpose, the average weight per polypropylene particle is preferably 5 mg / 1 or less, more preferably 4 mg / 1 or less.

In the above case, the average weight of the polypropylene particles is determined by measuring the total weight of 20 randomly selected polypropylene particles and arithmetically averaging them. There is no need to have less than one.

The peroxide used in the present invention can crosslink the raw material polypropylene used for the polypropylene particles, and has a half-life temperature of 1 minute, that is, a decomposition temperature at which the half-life of the peroxide is 1 minute. Those having a melting point of the raw material polypropylene or lower are used. When a peroxide having a one-minute half-life temperature higher than the melting point of the raw material polypropylene is used, the raw material polypropylene is decomposed and the effect of the present invention cannot be obtained, and conversely, the melt processability is reduced.

In the present invention, in order to more reliably prevent the raw material polypropylene from being decomposed, it is necessary to use one of peroxides.
It is desired that the minute half-life temperature is lower by at least 10 ° C. than the melting point of the raw material polypropylene used. In addition, if the one-minute half-life temperature of the peroxide is too low, there is a storage problem such that the peroxide must be stored at a low temperature. It is desirable that the one-minute half-life temperature of the object be 100 ° C. or higher. Therefore, it is desirable that the peroxide used in the present invention has a one-minute half-life temperature of 100 ° C. to [the melting point of raw polypropylene—10 ° C.].

Here, the melting point of the raw material polypropylene was determined by raising the temperature of 3 to 5 mg of the raw material polypropylene from room temperature to 220 ° C. at a heating rate of 10 ° C./min with a differential scanning calorimeter to obtain a first DSC curve. Immediately after cooling down
The temperature at the peak of the peak appearing at the highest temperature on the second DSC curve obtained when the temperature is lowered to 40 ° C. at 0 ° C./min and then raised again to 220 ° C. at a rate of 10 ° C./min. Shall be.

Examples of such peroxides include lauroyl peroxide, m-toluoyl-benzoyl peroxide, benzoyl peroxide, bis (4
-Butylcyclohexyl) peroxydicarbonate. As the peroxide used in the present invention, lauroyl peroxide, m-toluoyl-benzoyl peroxide, and benzoyl peroxide are preferable among the above-mentioned compounds because they are easy to handle.

Further, in the present invention, the main chain cleavage inhibitor comprises:
It is used to prevent the main chain of the raw material polypropylene from being cut by the peroxide. Examples of such a main chain scission inhibitor include methyl methacrylate, divinylbenzene, triallyl cyanurate and the like. Among these, highly reactive divinyl having two vinyl bonds in one molecule is preferable. Preferably, benzene is used.

In the present invention, first, the above-mentioned polypropylene particles, peroxide and main chain scission inhibitor are charged into an aqueous medium and stirred to minimize decomposition of the peroxide. The polypropylene particles are impregnated with a peroxide or a main chain scission inhibitor at a temperature and for a time such that at least half of the total amount of the added peroxide remains.

Specifically, heating to a decomposition temperature at which the peroxide has a half-life of 10 hours, ie, a half-life of 10 hours, is performed for 1 to 6 hours, preferably 1.5 to 4.5. By holding for a period of time, the polypropylene particles are impregnated with a peroxide or a backbone chain breaker.

As the aqueous medium used in the present invention, water containing a surfactant is usually used. Since such an aqueous medium is a good heating medium having good thermal conductivity, it is possible to uniformly heat the supplied polypropylene particles and the like,
In addition, since the temperature control is also easy, it is possible to easily impregnate the polypropylene particles with the peroxide or the main chain scission inhibitor easily.

In the present invention, the aqueous medium is preferably 150 to 500 parts by weight based on 100 parts by weight of the polypropylene particles.
Use parts by weight.

The amount of the peroxide used is preferably 0.1 to 3.0 parts by weight, more preferably 0.2 to 1.5 parts by weight, based on 100 parts by weight of the polypropylene particles. . If the amount exceeds 3.0 parts by weight, the raw material polypropylene used for the polypropylene particles is easily decomposed, which is not preferable. In addition, in this case, in order to prevent the raw material polypropylene from being decomposed, a large amount of a main chain breaking inhibitor is added. Therefore, the addition of a large amount of the main chain scission inhibitor causes a problem that a gel is easily generated in polypropylene. On the other hand, if the amount of the peroxide is less than 0.1 part by weight, it becomes impossible to sufficiently impart melt processability suitable for producing an extruded polypropylene foam having a foaming ratio of 5 to 30 times to polypropylene. It is not preferable because there is a possibility that it may be caused.

The amount of the main chain scission inhibitor varies depending on the type thereof, but it is usually preferably 0.01 to 5.0 parts by weight, more preferably 0.03 to 5.0 parts by weight, per 100 parts by weight of polypropylene. 1.0 part by weight. If the amount exceeds 5.0 parts by weight, a gel is easily formed in the polypropylene, which is not preferable. If the amount is less than 0.01 part by weight, the polypropylene is easily decomposed, which is not preferable.

In the present invention, besides impregnating the polypropylene particles with the main chain scission inhibitor using an aqueous medium as described above, the main chain scission inhibitor is previously contained in the polypropylene particles. The particles can then be impregnated with peroxide using an aqueous medium. In order to contain the main chain breaking inhibitor in advance in the polypropylene particles, for example, after melt-kneading the raw resin and the main chain breaking inhibitor in an extruder, if the melt-kneaded product is molded into particles good. However, in this case, since a part of the main chain breaking inhibitor may vaporize and dissipate from the polypropylene particles with the elapse of time and the content thereof may be reduced, the polypropylene containing the main chain breaking inhibitor may be used. After granulation of the particles, it is desired that the polypropylene particles be impregnated with peroxide at a relatively early stage and undergo a crosslinking step described below.

Next, in the present invention, preferably 10
The polypropylene particles are kept at a temperature of 0 ° C. to [the melting point of the raw material polypropylene −10 ° C.] and a half-life temperature of 1 minute of the peroxide used for 5 to 120 minutes, preferably 15 to 60 minutes. The raw material polypropylene is decomposed and slightly crosslinked without melting to obtain polypropylene particles having a substantial gel fraction of 0%.

The gel fraction was determined by placing about 1 g of a sample in 100 g of xylene, boiling the mixture for 8 hours, quickly filtering the resulting mixture through a 100-mesh wire gauze, and removing the boiling xylene-insoluble component remaining on the wire gauze by 20 g. After drying at 24 ° C. for 24 hours, the weight: G (g) was measured and determined by the following equation.
In the present invention, a substantial gel fraction of 0% means that the gel fraction of polypropylene obtained by the following equation is less than 0.5%.

## EQU1 ## Gel fraction (% by weight) = [G (g) / sample weight (g)] × 100

In the present invention, by using a peroxide having a one-minute half-life temperature equal to or lower than the melting point of the raw material polypropylene,
Since the raw polypropylene can be cross-linked at a temperature lower than the melting point of the raw polypropylene without melting it, unlike the case where peroxide is mixed into the raw polypropylene in the heated and molten state as in the conventional method, it is added immediately. Since the peroxide is not decomposed to the above, and since the polypropylene particles are impregnated with the peroxide before the crosslinking reaction is started, the crosslinking reaction can be made uniform, so that the quality can be improved. A stable product can be obtained.

Further, in the present invention, the raw material polypropylene is impregnated with the peroxide without being heated and melted, so that the main chain of the raw material polypropylene is hardly cut by the peroxide, and the use of the main chain breaking inhibitor is not required. Since the amount can be relatively small, there is no possibility that the mixing of a large amount of the main chain scission inhibitor causes non-uniformity of physical properties.

The polypropylene modified according to the present invention has a high melt tension, is excellent in moldability, and has a stable quality. In particular, the expansion ratio is 5 to 30 times (in terms of foam density, it is 0%). (0.030 to 0.18 g / cm ³ ), which is suitable for producing a polypropylene foam by extrusion foaming.

Next, a method for producing the polypropylene foam of the present invention will be described.

The method for producing a polypropylene foam of the present invention comprises extruding and foaming the polypropylene particles obtained as described above. As a specific extrusion foaming method in the present invention, for example, after melt-kneading polypropylene particles and a foaming agent in an extruder, the melt-kneaded product is extruded under a low pressure through a die attached to the tip of the extruder to foam. The known method can be adopted. The foam obtained by the present invention may be a sheet-like foam or a plate-like thick foam.

As the foaming agent used in the present invention, an inorganic foaming agent, a volatile foaming agent, a decomposition-type foaming agent and the like can be used. As the inorganic foaming agent, carbon dioxide, air, nitrogen and the like can be used. Propane as a volatile blowing agent,
Aliphatic hydrocarbons such as n-butane, i-butane, pentane and hexane, cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride And halogenated hydrocarbons such as methylene chloride. In addition, azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate, and the like can be used as the decomposition-type foaming agent.

In the present invention, the amount of the foaming agent used varies depending on the type of the foaming agent, the desired expansion ratio, and the like. For example, foaming for obtaining a foam having a density of about 0.2 to 0.013 g / cm ³ is used. The standard of the use amount of the agent is about 0.5 to 25 parts by weight (in terms of butane) of the volatile blowing agent per 100 parts by weight of the polypropylene particles. In addition, the density is 0.09 g / c.
The standard of the amount of the foaming agent used to obtain a foam exceeding m ³ is 0.1 wt.
About 10 to 10 parts by weight, and about 0.1 to 5 parts by weight in the case of a decomposable foaming agent.

In the present invention, a foam regulator may be further added to the melt-kneaded product of the polypropylene particles and the foaming agent. Examples of the foam control agent include inorganic powders such as talc and silica, acidic salts such as polycarboxylic acids, and reaction mixtures of polycarboxylic acids with sodium carbonate or sodium bicarbonate. It is preferable to add the foam control agent in an amount of about 13 parts by weight or less per 100 parts by weight of the polypropylene particles.
Further, if necessary, additives such as a heat stabilizer, an ultraviolet absorber, an antioxidant, and a coloring agent can be further added.

[0042]

Hereinafter, the present invention will be described in more detail with reference to specific examples.

Examples 1 to 7 and Comparative Examples 1 to 4 An aqueous medium obtained by adding 0.01 part by weight of sodium dodecylbenzenesulfonate to 250 parts by weight of water was placed in a 5-liter autoclave. The polypropylene particles, peroxide and main chain scission inhibitor shown in 1 were added, and the lid of the autoclave was closed. Next, nitrogen gas was introduced into the upper space in the autoclave, and nitrogen replacement was performed so that the oxygen concentration in the space became 0.2% by volume or less.

In the above operation, the amount of the polypropylene particles used was 100 parts by weight, and the amounts of the peroxide and the main chain scission inhibitor were also shown in Table 1. Example 3
Operations of Examples 4 and 7 and Comparative Examples 1 and 3 were different from those of the other Examples and Comparative Examples in the following points, and the other operations were performed in the same manner as the other Examples and Comparative Examples.

In Examples 3 and 4, polypropylene particles containing a main chain scission inhibitor in advance were used, so that the main chain scission inhibitor was not added to the aqueous medium. Example 7
In this case, the nitrogen substitution performed after closing the lid of the autoclave was omitted. In Comparative Example 1, only the polypropylene particles shown in Table 1 and the peroxide and the main chain scission inhibitor were introduced into the autoclave without using the aqueous medium, and the subsequent operation was performed. In Comparative Example 3, no backbone cleavage inhibitor was used.

Next, while stirring the inside of the autoclave,
The peroxide used was heated to the 10 hour half-life temperature of the peroxide used at a rate of 2 ° C./min and held at that temperature for 2 hours. Thereafter, the peroxide used was heated at a heating rate of 2 ° C./min to a half-life temperature of 1 minute, kept at that temperature for 20 minutes, and then cooled to take out the polypropylene particles from the autoclave.

[0047]

[Table 1]

The details of the polypropylene particles used in the examples and comparative examples are as follows. X: polypropylene particles having an average weight of 18.0 mg / piece [E250G manufactured by Idemitsu Petrochemical; melting point: 163.7 ° C.] Y: polypropylene particles having an average weight of 18.0 mg / piece [M7500 made by Nippon Polyolefin; melting point: 162.8]
° C] MX: The above particles X were melt-kneaded in an extruder, extruded into strands, and cut to an average weight of 2.5 mg / piece. MY: The above-mentioned particles Y are melt-kneaded in an extruder, extruded into strands, and cut so as to have an average weight of 2.5 mg / 1. XY1: The particles X and the particles Y are blended at a weight ratio of 2: 8, melt-kneaded in an extruder, extruded into strands, and cut to an average weight of 2.5 mg / 1 [melting point 162] .7 ° C]. XY2: The particles X and the particles Y are blended at a weight ratio of 4: 6, melt-kneaded in an extruder, extruded into strands, and cut to an average weight of 2.5 mg / 1 [melting point 162] 0.9 ° C]. XMMA: 0.25 parts by weight of methyl methacrylate (MMA) per 100 parts by weight of the particles X is blended as a main chain breaking inhibitor, and these are melt-kneaded in an extruder and extruded into strands, and the average weight is 2.5 mg / Cut into one piece. YDVB: 0.1 parts by weight of divinylbenzene (DVB) per 100 parts by weight of the above-mentioned particle Y is compounded as a main chain breaking inhibitor, and these are melt-kneaded in an extruder and extruded into strands, and the average weight is 2.5 mg / 1. What was cut into individual pieces.

The following peroxides were used.
In addition, the 1-minute half-life temperature and the 10-hour half-life temperature of the peroxide used in Examples and Comparative Examples are also shown in Table 1. A: Lauroyl peroxide [Perloyl L manufactured by NOF] B: m-toluoyl-benzoyl peroxide [Nipper BMT-K40 manufactured by NOF] C: Benzoyl peroxide [NIPER F manufactured by NOF
F] D: Dicumenyl peroxide [Parkmill D manufactured by NOF] E: 2,5-dimethyl-2,5-di (t-butylperoxy) hexene-3 [Perhexin 25B manufactured by NOF] F: Bis (4 -Butylcyclohexyl) peroxydicarbonate [Perloyl TCP manufactured by NOF Corporation]

Further, methyl methacrylate, divinylbenzene, and triallyl cyanurate were used as the main chain scission inhibitor, and in Table 1, MMA, DVB, and TAC were abbreviated.

The melt tension and the melt viscosity at a shear rate of 100 sec ^-1 of the modified polypropylene particles were measured by the following measuring methods. Table 2 shows the measurement results and the melt tension per unit melt viscosity. The melting characteristics of the polypropylene particles X and Y are also shown in Table 2 as reference data 1 and 2 for reference.

[Measurement Method of Melt Tension]
Melt tension tester I manufactured by Toyo Seiki Seisaku-sho, Ltd.
Using an I-type nozzle having a nozzle diameter of 2.0 mm and an L / D of 5, the measurement was performed at a resin temperature of 230 ° C. and an extrusion speed of 10 mm / min.

[Measurement Method of Melt Viscosity] The melt viscosity was measured by using a Reobis 2100 manufactured by Chiast Co., Ltd. as a melt viscosity measuring device, and using a tip nozzle attached to the device to measure a melt of particles to be measured at a resin temperature of 230 ° C. Shearing speed 100 sec
It was measured by extruding and flowing under the condition of ^-1 . In this case, the hole diameter D of the nozzle was set to 1.0 mm, and the ratio L / D of the length L of the nozzle to the hole diameter D of the nozzle was set to 10.

[0054]

[Table 2]

Examples 8 to 14 and Comparative Examples 5 to 9 Next, the polypropylene particles obtained as described above were
After mixing with butane in the ratio shown in Table 3 into an extruder (L / D: 46) equipped with a single screw of 50 mmφ and melt-kneading, a lip with a diameter of 75 mmφ and a gap of 0.3 mm attached to the extruder tip was mixed. It was extruded and foamed through a circular die to obtain a tubular foam, which was then cut open to obtain a foam sheet. Table 3 also shows the foaming state and foam density of the foam sheet.

[0056]

[Table 3]

The foamed sheets obtained in this example were all foamed well and had stable quality.

[0058]

As described above, according to the method for producing the modified polypropylene of the present invention, a peroxide having a one-minute half-life temperature equal to or lower than the melting point of the polypropylene is used to convert the peroxide into an aqueous medium. After impregnating the polypropylene particles in the medium, the peroxide is decomposed and the polypropylene is slightly crosslinked to obtain polypropylene particles having a substantial gel fraction of 0%. A homogeneous polypropylene having excellent properties can be easily obtained.

Further, according to the method for producing a polypropylene resin foam of the present invention, a foam having a relatively low density can be favorably produced, and the quality of the foam obtained is very stable.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI // B29K 23:00 105: 04

Claims (5)

[Claims] 1. A method in which a polypropylene particle, a peroxide having a one-minute half-life temperature not higher than the melting point of the raw polypropylene used for the polypropylene particle, and a main chain scission inhibitor are charged into an aqueous medium and stirred. After impregnating the polypropylene particles with a peroxide and a main chain scission inhibitor, the peroxide is decomposed to slightly crosslink the raw material polypropylene to obtain polypropylene particles having a substantial gel fraction of 0%. Production method of quality polypropylene. 2. A polypropylene particle containing a main chain scission inhibitor in advance and a peroxide having a one-minute half-life temperature not higher than the melting point of the raw polypropylene used for the polypropylene particles are charged into an aqueous medium and stirred. Then, after the polypropylene particles are impregnated with the peroxide, the peroxide is decomposed to slightly crosslink the raw material polypropylene, thereby obtaining polypropylene particles having a substantial gel fraction of 0%. Method for producing polypropylene. 3. The peroxide has a one-minute half-life temperature of 100 ° C.
2. The melting point of the raw material polypropylene is −10 ° C.
Or a method for producing a modified polypropylene according to item 2. 4. An average weight of the polypropylene particles is 5 mg /
4. The method for producing a modified polypropylene according to claim 1, wherein the number is one or less. 5. A method for producing a polypropylene resin foam, comprising extruding and foaming the polypropylene particles obtained by the method according to claim 1, 2, 3 or 4.