JP2010077359A - Pre-foamed particle of polypropylene-based resin with reduced frictional noise - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide pre-foamed particles of a polypropylene-based resin and a foamed molded article of the polypropylene-based resin, which cause no unpleasant frictional noise (squeaking sound) of high frequency when friction occurs between the pre-foamed particles, between the foamed molded articles, or between the foamed molded article and another plastic product, metal product, and the like. <P>SOLUTION: The pre-foamed particles of a polypropylene-based resin include a butene copolymer polyethylene wax. The pre-foamed particles of the polypropylene-based resin preferably include the butene copolymer polyethylene wax in an amount of 2-12 pts.wt based on 100 pts.wt of the polypropylene-based resin. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polypropylene resin pre-expanded particle that can be suitably used for the production of a polypropylene resin foam molded article used for buffer packaging materials, boxes, heat insulating materials, automobile members and the like. More specifically, the present invention relates to a pre-expanded polypropylene resin particle that does not substantially generate a high-frequency friction sound.

  As a use of polypropylene resin foam moldings, it is widely used for automobile parts such as cushioning packaging materials and bumper core materials. However, these polypropylene resin foam molded products and polypropylene resin pre-expanded particles are harsh when the friction occurs between the pre-expanded particles, between the foam molded products, or other plastic products, metal products, and the like. May generate a squeaking noise.

As a method for preventing frictional noise, Patent Document 1 and Patent Document 2 disclose a method of attaching a specific substance to the surface of a polypropylene resin foam molded article, and low molecular weight polyethylene is disclosed as the specific substance. Patent Document 3 discloses pre-expanded particles whose surfaces are coated or impregnated with wax, polyethylene wax is disclosed as the wax, and pre-expanded particles made of expanded polypropylene resin are also disclosed as the pre-expanded particles.
JP 59-2010954 A JP 61-023632 A JP 2005-187715 A

  An object of the present invention is to provide a pre-expanded particle of polypropylene resin that uses a polyethylene wax to prevent frictional noise and generates less frictional sound. Specifically, the problem of the present invention is that when the friction occurs between the pre-foamed particles, the foam-molded bodies, or between the foam-molded body and other plastic products, metal products, etc. An object of the present invention is to provide a polypropylene resin pre-expanded particle and a polypropylene resin foamed molded article in which the generation of frictional noise (cushing sound) is further suppressed.

  The present inventors have found that, among polyethylene waxes, a polypropylene resin foam molded article made of polypropylene resin pre-expanded particles containing a butene-containing polyethylene wax is less likely to generate annoying frictional noise having a high frequency.

  That is, the first of the present invention relates to a polypropylene resin pre-expanded particle containing a butene copolymer polyethylene wax.

As a preferred embodiment,
(1) 2 parts by weight or more and 12 parts by weight or less of a butene-copolymerized polyethylene wax is contained with respect to 100 parts by weight of the polypropylene resin.
(2) The butene-copolymerized polyethylene wax has a viscosity average molecular weight of 1,000 to 5,000,
(3) The melting point of the butene-copolymerized polyethylene wax is 40 ° C. or higher and 130 ° C. or lower.
The present invention relates to the above-mentioned polypropylene resin pre-expanded particles.

  The second aspect of the present invention relates to a polypropylene resin foam molded article obtained by filling the polypropylene resin pre-expanded particles described above in a mold and heating, and the third aspect of the present invention is a copolymer of polypropylene resin and butene. The present invention relates to a method for producing polypropylene resin pre-expanded particles including a step of melt-kneading polyethylene wax using an extruder.

  When the polypropylene resin pre-expanded particles of the present invention are formed into a polypropylene resin foam molded product by in-mold foam molding, friction between foam molded products or between the foam molded product and other plastic products, metal products, etc. When this occurs, it is possible to obtain a polypropylene-based resin foam molded body that hardly generates an harsh frictional sound with a high frequency. Further, even when the polypropylene resin pre-expanded particles are rubbed with each other, a reduction in frictional sound can be expected.

  The polypropylene resin foamed molded article of the present invention has almost no harsh frictional sound with high frequency.

  The polypropylene resin used for the pre-expanded particles of the polypropylene resin of the present invention is a polymer comprising propylene monomer units, preferably 50% by weight or more, more preferably 80% by weight or more, and most preferably 90% by weight or more. Those having high stereoregularity polymerized with a type titanium chloride catalyst or a metallocene catalyst are preferred. Further, these polypropylene resins are preferably non-crosslinked, but crosslinked resins can also be used. The components copolymerizable with propylene include ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, and 3,4-dimethyl-1- Α-olefin having 2 or 4 to 12 carbon atoms such as butene, 1-heptene, 3-methyl-1-hexene, 1-octene and 1-decene, cyclic olefin such as cyclopentene and norbornene, 5-methylene-2-norbornene Diene such as 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, Methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride Acid, styrene, methyl styrene, vinyl toluene, and vinyl monomers such as divinylbenzene.

  The polypropylene resin preferably has a melt index (hereinafter referred to as MI) of 5 g / 10 min or more and 20 g / 10 min or less, measured at a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210. Is 6 g / 10 min or more and 12 g / 10 min or less. When MI is less than 5 g / 10 min, the foaming power when producing polypropylene resin pre-expanded particles is low, and it may be difficult to obtain polypropylene resin pre-expanded particles having a high expansion ratio. Moreover, it may become difficult to ensure the fusion strength between the polypropylene resin pre-expanded particles when a polypropylene resin foam molded article is formed. On the other hand, when MI exceeds 20 g / 10 minutes, the cell may break when producing the polypropylene resin pre-expanded particles.

  The melting point of the polypropylene resin is preferably 120 ° C. or higher and 160 ° C. or lower, more preferably 130 ° C. or higher and 160 ° C. or lower, and particularly preferably 135 ° C. or higher and 155 ° C. or lower. When the melting point is within this range, it becomes easy to balance the molding vapor pressure during molding in the mold with the mechanical strength and heat resistance of the molded body. That is, there is a tendency that molding can be performed without increasing the molding vapor pressure at the time of molding in the mold, and the necessary mechanical strength and heat resistance of the foamed molded product can be obtained.

  The butene-copolymerized polyethylene wax used in the present invention refers to a wax comprising ethylene and butene as monomer components, and the butene content in the butene-copolymerized polyethylene wax is preferably 2 wt% or more and 12 wt% or less, 5 to 10% by weight is more preferable, and 7 to 9% by weight is more preferable. If the butene content is less than 2% by weight, it may be difficult to obtain the effect of suppressing frictional noise. When the content of butene is more than 12% by weight, mechanical strength tends to be lowered when a polypropylene resin composition is prepared by adding butene-copolymerized polyethylene wax to a polypropylene resin.

  The melting point of the butene copolymer polyethylene wax used in the present invention is preferably 40 ° C. or higher and 130 ° C. or lower, more preferably 80 ° C. or higher and 110 ° C. or lower, and particularly preferably 85 ° C. or higher and 110 ° C. or lower. If the melting point of the butene-copolymerized polyethylene wax is lower than 40 ° C., the dispersion of the resin particles in the pressure vessel tends to become unstable when producing the polypropylene resin pre-expanded particles. Furthermore, it tends to cause a decrease in mechanical strength of the polypropylene resin composition. On the other hand, if the melting point is higher than 130 ° C., the effect of suppressing frictional noise may not be obtained.

  The butene copolymer polyethylene wax used in the present invention preferably has a viscosity average molecular weight of 1000 or more and 5000 or less. If the viscosity average molecular weight is less than 1000, the butene-copolymerized polyethylene wax tends to be sticky, which may cause a problem in workability when melt-kneading with a polypropylene resin. When the viscosity average molecular weight exceeds 5,000, the butene copolymer polyethylene wax hardly appears on the surface when melt-kneaded with the butene copolymer polyethylene wax and the polypropylene resin, and the effect of suppressing the frictional noise may not be obtained.

  Examples of polymerization methods for producing butene-copolymerized polyethylene wax include the Ziegler catalyst method and the metallocene catalyst method. Among them, butene-copolymerized polyethylene wax polymerized by the metallocene catalyst method has a narrow molecular weight distribution and suppresses friction noise. This is particularly preferable because the effect can be easily obtained.

  The melting point of polypropylene resin and butene-copolymerized polyethylene wax (hereinafter sometimes referred to as Tm) is 10 from 40 ° C. to 220 ° C. from 1 to 10 mg of polypropylene resin or polyethylene wax by a differential scanning calorimeter. The peak temperature of the endothermic curve in the DSC curve obtained when the temperature was raised at a rate of 10 ° C./min, then cooled to 40 ° C. at a rate of 10 ° C./min, and again raised to 220 ° C. at a rate of 10 ° C./min. Say.

  The amount of the butene-copolymerized polyethylene wax added to the polypropylene resin is preferably 2 to 12 parts by weight, more preferably 4 to 10 parts by weight, based on 100 parts by weight of the polypropylene resin. It is preferably 5 parts by weight or more and 8 parts by weight or less. When the addition amount of butene-copolymerized polyethylene wax is less than 2 parts by weight, the effect of suppressing frictional noise tends to be hardly exhibited. When the addition amount of butene-copolymerized polyethylene wax exceeds 12 parts by weight, when a butene-copolymerized polyethylene wax is added to form a polypropylene resin composition, the mechanical strength tends to be lowered.

  In the present invention, in order to obtain a polypropylene resin pre-expanded particle containing a butene-containing polyethylene wax, for example, a polypropylene resin composition is prepared by melt-kneading butene-copolymerized polyethylene wax in a polypropylene resin. The method of producing a polypropylene resin pre-expanded particle using a resin composition is mentioned.

  As a method of melt-kneading butene copolymer polyethylene wax to polypropylene resin, a method of dry blending polypropylene resin and butene copolymer polyethylene wax and then melt-kneading using an extruder, a large amount of butene copolymer polyethylene wax in advance. There is a method in which the resin pellets contained and the polypropylene resin pellets not containing waxes are dry blended and then melt-kneaded using an extruder.

  In addition, as a method of adding butene copolymer polyethylene wax to other polypropylene resin pre-expanded particles, a method of applying a solution or dispersion of butene copolymer polyethylene wax on the surface of polypropylene resin pre-expanded particles, polypropylene resin particles and Examples thereof include a method in which butene-copolymerized polyethylene wax is supplied to a heating tank, heated with stirring, coated, and pre-foamed.

  Since the butene-copolymerized polyethylene wax is less likely to peel off and the effect of preventing frictional noise is easily obtained and the process is simple, it is preferable to go through a step of melt-kneading the polypropylene resin and the butene-copolymerized polyethylene wax using an extruder. .

  In addition, as described in JP-A-3-86737, when a wax such as polyethylene wax is melt-kneaded and an inorganic gas is used as a foaming agent, good expanded polypropylene resin pre-expanded particles having a large cell diameter Tend to be able to get

  Next, the manufacturing method of the polypropylene resin pre-expanded particles of the present invention will be described. The polypropylene resin is added with additives as necessary, and melt-kneaded using an extruder, and the weight of one grain is preferably 0.2 to 10 mg, more preferably 0.5 to 6 mg. Processed into particles. At this time, it is preferable to melt-knead the polypropylene resin and the butene-copolymerized polyethylene wax together using an extruder. In general, the polypropylene resin particles are preferably produced by a strand cut method. For example, polypropylene resin particles having a desired shape can be obtained by cutting and solidifying polypropylene resin extruded in a strand form from a circular die with water, air, or the like.

  A cell nucleating agent can be illustrated as an additive which can be added when producing polypropylene resin particles. The cell nucleating agent can adjust the cell diameter of the polypropylene resin pre-expanded particles to a desired value. As the cell nucleating agent, inorganic nucleating agents such as talc, calcium carbonate, silica, kaolin, titanium oxide, bentonite and barium sulfate are generally used. The amount of cell nucleating agent added varies depending on the type of polypropylene resin used and the type of cell nucleating agent, and cannot be specified unconditionally, but is generally 0.001 part by weight or more with respect to 100 parts by weight of polypropylene resin particles. The amount is preferably 2 parts by weight or less. In addition to the cell nucleating agent, the following additives can be exemplified.

  An antistatic agent comprising a nonionic surfactant such as alkyldiethanolamide, alkyldiethanolamine, hydroxyalkylethanolamine, fatty acid monoglyceride, fatty acid diglyceride;

  IRGANOX (registered trademark) 1010 (Ciba), IRGANOX (registered trademark) 1076 (Ciba), IRGANOX (registered trademark) 1330 (Ciba), IRGANOX (registered trademark) 1425 WL (Ciba), IRGANOX (registered trademark) 3114 (Ciba), etc. Hindered phenolic antioxidants;

  Phosphorus processing stabilizers such as IRGAFOS (registered trademark) 168 (Ciba), IRGAFOS (registered trademark) P-EPQ (Ciba), IRGAFOS (registered trademark) 126 (Ciba); lactone processing stabilizers; hydroxylamine processing stabilizers Agents; metal deactivators such as IRGANOX (registered trademark) MD1024 (Ciba);

  Benzotriazole ultraviolet absorbers such as TINUVIN (registered trademark) 326 (Ciba) and TINUVIN (registered trademark) 327 (Ciba); Benzoate light stabilizers such as TINUVIN (registered trademark) 120 (Ciba); CHIMASSORB (registered trademark) Hindered amine light stabilizers such as 119 (Ciba), CHIMASSORB (registered trademark) 944 (Ciba), TINUVIN (registered trademark) 622 (Ciba), TINUVIN (registered trademark) 770 (Ciba);

  Flame retardants such as halogen flame retardants and antimony trioxide; non-halogen flame retardants such as FLAMESTAB (registered trademark) NOR116 (Ciba), MELAPUR (registered trademark) MC25 (Ciba); hydrotalcite, calcium stearate, etc. Examples include acid neutralizers; IRGASTAB (registered trademark) NA11 (Ciba) crystal nucleating agents; triazine compounds such as melamine; polyethers such as polyethylene glycol; and polyhydric alcohols such as glycerin.

  The polypropylene resin pre-expanded particles in the present invention are prepared by charging a water-based dispersion containing polypropylene resin particles and water, a dispersant and a foaming agent into a pressure vessel, heating to a predetermined temperature, and then under pressure. The resin particles and water are obtained by discharging the mixture of the resin particles and water into an atmosphere at a lower pressure than in the pressure vessel. Specifically, an aqueous dispersion containing the resin particles, a foaming agent, a dispersing agent and a dispersion aid is charged in a pressure vessel, and the temperature is raised to a predetermined temperature (hereinafter sometimes referred to as a foaming temperature) while stirring. After impregnating the resin particles with a foaming agent, adding a foaming agent as necessary, holding the inside of the pressure vessel at a constant pressure (hereinafter sometimes referred to as foaming pressure), and then adding the water dispersion from the bottom of the pressure vessel An example is a method of discharging in an atmosphere lower than the pressure inside the pressure vessel. The pressure vessel to be used is not particularly limited, and any pressure vessel can be used as long as it can withstand the pressure in the vessel and the temperature in the vessel at the time of producing the polypropylene resin pre-expanded particles. For example, an autoclave type pressure vessel can be mentioned.

  Examples of the blowing agent include aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, and normal pentane; inorganic gases such as air, nitrogen, and carbon dioxide, and mixtures thereof.

  The amount of the foaming agent used varies depending on the type of polypropylene resin to be used, the type of foaming agent, the target foaming ratio, etc., and cannot be specified unconditionally. However, the amount used is generally 2 with respect to 100 parts by weight of the polypropylene resin particles. It is preferably ˜60 parts by weight.

  Further, there is a case where a method of using water used as a dispersion medium as a foaming agent instead of the foaming agent or together with the foaming agent may be used.

  As the dispersant, for example, it is preferable to use a poorly water-soluble inorganic compound such as basic tricalcium phosphate, basic magnesium carbonate, calcium carbonate, magnesium phosphate, barium sulfate, aluminum oxide, and kaolin. As the dispersion aid, for example, an anionic surfactant such as sodium dodecylbenzene sulfonate or sodium linear alkyl fin sulfonate is preferably used. Among these, the use of basic tricalcium phosphate and linear alkyl fin sulfonic acid soda is preferable for obtaining good dispersibility. The amount of these dispersants and dispersion aids used varies depending on the type, the type and amount of the polypropylene resin used, the type of foaming agent, etc., but usually 0.1 to 3 dispersants per 100 parts by weight of water. It is preferable that the amount is 0.0001 to 0.1 part by weight of a dispersion aid. In some cases, the aqueous dispersion medium is made acidic by mixing an acid with the aqueous dispersion medium in order to reduce the amount of the dispersant adhering to the polypropylene resin pre-expanded particles.

  The aqueous dispersion of polypropylene resin particles prepared in the pressure vessel in this way is heated to a predetermined foaming temperature with stirring, and is maintained for a certain period of time, usually 5 to 180 minutes, preferably 10 to 60 minutes. At the same time, the pressure in the pressure vessel rises and the foaming agent is impregnated into the polypropylene resin particles. Thereafter, the foaming agent is additionally supplied until a predetermined foaming pressure is reached, and is maintained for a certain time, usually 5 to 180 minutes, preferably 10 to 60 minutes. Thus, an aqueous dispersion of polypropylene resin particles held at the foaming temperature and the foaming pressure is released by releasing the valve provided at the lower part of the pressure vessel under a low pressure atmosphere (usually atmospheric pressure). Resin pre-expanded particles can be produced.

  When the aqueous dispersion of polypropylene resin particles is discharged into a low-pressure atmosphere, it can also be discharged through an opening orifice of 2 to 10 mmφ for the purpose of adjusting the flow rate and reducing magnification variation. In some cases, the low-pressure atmosphere is filled with saturated steam for the purpose of increasing the expansion ratio.

  The foaming temperature varies depending on the melting point [Tm (° C.)] of the polypropylene resin used, the type of foaming agent, etc., and cannot be specified unconditionally, but is generally determined from the range of Tm−30 (° C.) to Tm + 10 (° C.). . The foaming pressure varies depending on the type of polypropylene resin used, the type of foaming agent, and the expansion ratio of the desired polypropylene resin pre-foamed particles, and cannot be specified unconditionally, but generally ranges from 1 to 8 MPa (gauge pressure). It is determined.

  The polypropylene resin pre-expanded particles obtained as described above can be made into a polypropylene resin expanded foam by a conventionally known molding method. For example, a) a method in which pre-expanded particles are pressurized with an inorganic gas, impregnated with the inorganic gas in the pre-expanded particles to give a predetermined internal pressure of the pre-expanded particles, filled in a mold, and heated and fused with water vapor. B) A method in which the pre-expanded particles are compressed by gas pressure and filled in a mold, and the recovery power of the pre-expanded particles is used for heat fusion with water vapor. C) The pre-expanded particles are not subjected to any pretreatment. A method such as a method of filling a mold and heat-sealing with water vapor can be used.

  As the inorganic gas, air, nitrogen, oxygen, helium, neon, argon, carbon dioxide, or the like can be used. These may be used alone or in combination of two or more. Among these, highly versatile air and nitrogen are preferable.

  The polypropylene resin foam molded article obtained as described above is less likely to generate annoying frictional noise having a high frequency.

  Next, the present invention will be described with reference to examples and comparative examples. The present invention is not limited to the following examples. The polypropylene resin foam molded article was evaluated by the following method.

<Friction noise prevention effect in foamed molding>
On the polypropylene resin foam molded body cut into a 300 × 150 × 20 mm rectangular parallelepiped shape, the polypropylene resin foam molded body cut into a 30 × 10 × 20 mm rectangular parallelepiped shape is placed so that the skin layer is in contact with the upper and lower sides. Furthermore, in a state where a load was applied by placing a weight of 2 kg thereon, the polypropylene resin foam molded bodies were rubbed together by reciprocating a distance of 15 mm at 50 mm / second.

Frictional sound is collected with a microphone installed at a distance of 5 cm from the rubbed place, and the collected sound is analyzed using the real-time analyzer DSSF3 Light manufactured by Yoshimasa Electronics Co., Ltd. The sound pressure level (A sound) at a frequency of 8000 Hz after 60 seconds from the first time and the sound pressure level (B sound) at a frequency of 8000 Hz before rubbing were obtained, and the value obtained by the following calculation formula was taken as the friction sound pressure.
Frictional sound pressure (dB) = A sound (dB)-B sound (dB)

At the same time, we listened to the generation of noise when rubbed together and observed the presence or absence of generation of frictional noise. Evaluation criteria are as follows.
A: No frictional noise is generated.
○: Friction noise hardly occurs.
Δ: A small frictional noise is generated.
X: A loud friction noise is generated.
XX: A large frictional sound close to noise is generated.

<Compressive strength>
A test piece having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm was cut out from the polypropylene resin foamed molded article so as not to have a skin layer, and compressed at a speed of 10 mm / min in accordance with NDZ-Z0504. Compressive stress (MPa) was measured. It is a measure of the rigidity of a foamed molded product.

Example 1
MI = 9 g / 10 min as base resin, melting point 147 ° C., butene content is 7.5% by weight with respect to 100 parts by weight of polypropylene random copolymer containing 4% by weight of 1-butene and 0.5% by weight of ethylene as comonomer. Dry blend of the above polypropylene random copolymer, butene copolymer polyethylene wax and talc using 6 parts by weight of butene copolymer polyethylene wax having a viscosity average molecular weight of 2900 and a melting point of 102 ° C. and 0.03 part by weight of talc as a cell nucleating agent. did. The dry blended mixture was melt-kneaded in an extruder, extruded into a strand from a circular die, cooled with water, and cut with a cutter to obtain resin particles having a weight of 1.2 mg / grain.

100 parts by weight (50 kg) of the obtained resin particles, 200 parts by weight of water, 1.0 part by weight of basic tribasic calcium phosphate and 0.03 part by weight of sodium alkyl sulfonate were charged into a pressure-resistant autoclave having a capacity of 0.35 m ³ . Under stirring, 15 parts by weight of isobutane was added as a foaming agent, and then the contents of the autoclave were heated to a foaming temperature of 140 ° C. Thereafter, isobutane was additionally injected and the pressure was increased to a foaming pressure of 2.0 MPa (gauge pressure). After maintaining at the foaming temperature and the foaming pressure for 30 minutes, the valve at the bottom of the autoclave was opened, and through a 4.0 mmφ opening orifice, The contents of the autoclave were released under atmospheric pressure to obtain polypropylene resin pre-expanded particles.

  After impregnating the obtained polypropylene resin pre-expanded particles with air by an air pressure treatment to give an internal pressure of 0.18 to 0.22 MPa, it is filled in a 320 × 320 × 60 mm mold, and 0.30 MPa. It was heated and fused with steam at a molding temperature of (gauge pressure) to obtain a polypropylene resin foam molded article. The evaluation results are shown in Table 1. A polypropylene resin foamed molded product without frictional noise could be produced.

(Example 2)
Polypropylene resin pre-expanded particles and polypropylene resin in the same manner as in Example 1 except that a butene copolymer polyethylene wax having a butene content of 8.5% by weight, a viscosity average molecular weight of 4600, and a melting point of 90 ° C. was used. A foamed molded product was obtained. The evaluation results are shown in Table 1. A polypropylene resin foamed molded product without frictional noise could be produced.

(Example 3)
A polypropylene resin pre-expanded particle and a polypropylene resin foam molded article were obtained in the same manner as in Example 1 except that the amount of butene-copolymerized polyethylene wax added was 3 parts by weight. The evaluation results are shown in Table 1. A polypropylene resin foamed molded article with almost no frictional sound could be produced.

Example 4
A polypropylene resin pre-expanded particle and a polypropylene resin foam molded article were obtained in the same manner as in Example 2 except that the amount of butene-copolymerized polyethylene wax added was 3 parts by weight. The evaluation results are shown in Table 1. A polypropylene resin foamed molded article with almost no frictional sound could be produced.

(Example 5)
A polypropylene resin pre-expanded particle and a polypropylene resin foam molded article were obtained in the same manner as in Example 1 except that the amount of butene-copolymerized polyethylene wax added was 11 parts by weight. The evaluation results are shown in Table 1. A polypropylene resin foamed molded product without frictional noise could be produced.

(Example 6)
A polypropylene resin pre-expanded particle and a polypropylene resin foam molded article were obtained in the same manner as in Example 2 except that the amount of butene-copolymerized polyethylene wax added was 3 parts by weight. The evaluation results are shown in Table 1. A polypropylene resin foamed molded product without frictional noise could be produced.

(Comparative Example 1)
A polypropylene resin pre-expanded particle and a polypropylene resin foam molded article were obtained in the same manner as in Example 1 except that the butene-copolymerized polyethylene wax was not added. The evaluation results are shown in Table 1. The resulting polypropylene resin foamed molded article produced a large frictional sound.

(Comparative Example 2)
Polypropylene resin pre-expanded particles and polypropylene in the same manner as in Example 1 except that a polyethylene wax having no butene (butene content: 0% by weight), a viscosity average molecular weight of 1000, and a melting point of 110 ° C. was used as a monomer. -Based resin foam molding was obtained. The evaluation results are shown in Table 1. The resulting polypropylene resin foamed molded article produced a small frictional sound.

(Comparative Example 3)
In the same manner as in Example 1, except that polyethylene monomer having no butene (butene content: 0% by weight), a viscosity average molecular weight of 4000, and a melting point of 124 ° C. was used as the monomer component, A polypropylene resin foam molded article was obtained. The evaluation results are shown in Table 1. The resulting polypropylene resin foamed molded article produced a large frictional sound.

  From the above results, it is apparent that the polypropylene resin pre-expanded particles containing butene as the monomer component contain butene copolymer polyethylene wax have the effect of preventing the frictional noise of the polypropylene resin foam molded article.

Claims (6)

  Polypropylene resin pre-expanded particles containing butene-copolymerized polyethylene wax.   The polypropylene resin pre-expanded particles according to claim 1, comprising 2 parts by weight or more and 12 parts by weight or less of butene copolymer polyethylene wax with respect to 100 parts by weight of the polypropylene resin.   The polypropylene resin pre-expanded particles according to claim 1 or 2, wherein the butene-copolymerized polyethylene wax has a viscosity average molecular weight of 1,000 to 5,000.   The polypropylene resin pre-expanded particles according to any one of claims 1 to 3, wherein a melting point of the butene-copolymerized polyethylene wax is 40 ° C or higher and 130 ° C or lower.   A polypropylene resin foam molded article obtained by filling the polypropylene resin prefoamed particles according to any one of claims 1 to 4 in a mold and heating.   A method for producing pre-expanded polypropylene resin particles, comprising a step of melt-kneading a polypropylene resin and a butene-copolymerized polyethylene wax using an extruder.