JP5037212B2 - Polypropylene resin pre-expanded particles, and in-mold foam moldings - Google Patents

Description

  The present invention relates to a polypropylene resin pre-expanded particle used for a buffer packaging material, a return box, an automobile interior member, an automobile bumper core, a heat insulating material, and the like, and an in-mold foam-molded article obtained by using the pre-expanded particle It is.

  The in-mold foam molded article obtained by using the polypropylene resin pre-expanded particles has characteristics such as shape flexibility, light weight, and heat insulation, which are advantages of the in-mold foam molded article. Compared to similar in-mold foam moldings, it is superior in chemical resistance, heat resistance and strain recovery after compression compared to in-mold foam moldings obtained using polystyrene resin pre-expanded particles. In addition, the dimensional accuracy, heat resistance, and compressive strength are excellent as compared with the in-mold foam molded body obtained using the polyethylene resin pre-expanded particles. Due to these characteristics, in-mold foam molded articles obtained using polypropylene resin pre-expanded particles are used in various applications such as automotive interior members, automotive bumper core materials, heat insulating materials, and cushioning packaging materials. .

  In general, in an in-mold foam molded product, a phenomenon called “inside-down” is observed after heat molding with steam or the like, particularly when a cushioning packaging material is obtained as a molded product. “Inclined” means that the center dimension is smaller than the end dimension of the box-shaped molded body, resulting in a difference. The absolute value of this difference varies depending on the size of each designed product. If is large, it becomes a defective product that cannot be used as a product. Most of the internal collapse may be recovered by drying at a high temperature of 60 ° C. or more and 80 ° C. or less, but if the time required for the high temperature drying is long, the productivity is remarkably deteriorated.

  With respect to the inversion phenomenon due to shrinkage of the molded body after heat molding, a polypropylene resin having a high resin rigidity is used to impart a molded body rigidity that acts as a reaction force, and deformation can be suppressed.

  However, polypropylene resin with high rigidity that can suppress the internal falling phenomenon is generally a resin with a low comonomer content and a high melting point, but it is necessary to obtain a good molded product as the melting point of the resin increases. The pressure of the formed heating steam tends to increase. For this reason, when a higher rigidity is required, a large amount of heating steam is consumed, resulting in an increase in utility cost, resulting in an increase in molding processing cost. Further, when a highly rigid resin is used, the heat molding pressure becomes high, so that it is necessary to use a molding machine or a mold having a high pressure resistance specification, which increases the equipment cost in addition to the utility cost. At present, most of the molding machines for in-mold foam molding of polypropylene resin pre-expanded particles occupy a specification with a pressure resistance of 0.4 MPa, and the molding heating steam pressure normally produced by using the molding machine is approximately. Up to about 0.36 MPa. The polypropylene-based resin pre-expanded particles used for in-mold foam molding use a resin having such a characteristic as to be compatible with this, and generally, ethylene-random polypropylene having a melting point of about 140 to 150 ° C. is used.

Up to now, various techniques have been studied for improving the rigidity of the in-mold foam molded article. In order to obtain high rigidity with a polypropylene resin, it is conceivable to simply use homopolypropylene. For example, Patent Document 1 discloses a DSC obtained by a differential scanning calorimeter with a tensile elastic modulus of 15,000 to 25000 kg / cm ^2. The technique regarding the homopolypropylene-type resin pre-expanded particle | grains whose calorie | heat amount of the high temperature side peak of a curve is 30-60 J / g is disclosed. Patent Document 1 also discloses that pre-foamed particles capable of obtaining an in-mold foam-molded product at a relatively low molding temperature can be produced using a homopropylene resin having an MFR in the range of 20 to 100 g / 10 min. Technology is disclosed.

  However, in the technique described in Patent Document 1, it is described that the pressure of the heating steam at the time of molding necessary for obtaining a good foamed molded product is 0.4 to 0.6 MPa. It cannot be molded with a molding machine of 4 MPa pressure resistance specification. Further, by using a homopolypropylene resin, “flexibility”, which is an important performance as a cushioning packaging material, is lowered.

  Although high rigidity cannot be obtained as compared with homopolypropylene, a technique using a polypropylene random copolymer has been studied with emphasis on moldability. For example, Patent Document 3 discloses a technique in which a propylene-based random copolymer having a melting point of 149 to 157 ° C., an MFR of 1 to 20 g / 10 minutes, and a half crystallization time of a certain value or less is used as the base resin. Is disclosed.

  Patent Document 4 describes the high-temperature-side crystal amount of a melting crystal curve obtained by using differential scanning calorimetry (hereinafter abbreviated as DSC) for the crystalline state of polypropylene resin pre-expanded particles used for in-mold foam molding. A technique for improving the compressive strength of the obtained in-mold foam molded article by setting the relationship between the low-temperature side crystal amount within a certain range is disclosed.

  However, regarding these technologies, the pressure of the heating steam required for in-mold foam molding is as high as 0.4 to 0.5 MPa, and in the same manner as the technologies described in Patent Documents 2 to 3, molding with particularly high pressure resistance performance. This technology is made possible by using a machine.

  Further, in Patent Document 4, when a polypropylene resin containing 1-butene as a comonomer is used, a resin having a high tensile elastic modulus, that is, a rigidity is obtained with respect to the resin melting point. By using this, a mold having a high rigidity is obtained. A technique is disclosed in which an inner foamed molded product can be obtained.

  However, even with this technique, the pressure of the heating steam required for in-mold foam molding is around 0.4 MPa, which is a relatively low molding heating steam pressure compared to other techniques, but in the example being implemented. The lowest is 0.36 MPa, which is the lower limit level of the molding machine performance of the 0.4 MPa pressure resistance specification that is often used at present.

  Furthermore, Patent Document 5 discloses a polypropylene-based resin having high rigidity by using polypropylene-based resin pre-expanded particles whose base resin is a propylene / 1-butene random copolymer containing 3 to 12% by weight of 1-butene component. A technique for obtaining a resin foam molded article is disclosed. It is described that when this technique is used, molding can be performed even with a molding machine having a pressure resistance of 0.4 MPa, which is often used at present, with the pressure of the molding heating steam being around 0.3 MPa. However, the 1-butene homopolypropylene resin random copolymer that does not contain an ethylene component described in the publication has a hard and brittle property compared to a polypropylene resin random copolymer that contains an ethylene component. When used as a base resin, especially in the case of buffer packaging applications, it repeatedly adversely affects the buffer performance, and in the case of automotive member applications, buffer characteristics, dimensional recovery after compression, It has the property that impact characteristics are inferior. Polypropylene resin foam molded products are superior to polystyrene resin foam molded products, which are the same in-mold foam molded products, in terms of rigidity, but have superior resistance to repeated impacts and flexibility. Some aspects are used for such purposes. For this reason, the technique described in the technology also has a drawback that it is not suitable for general cushioning packaging applications other than those intended only for rigidity.

As described above, as a method of suppressing the “inside-down” phenomenon, in order to apply pre-expanded particles based on a polypropylene resin having high rigidity, a special molding machine that can generally withstand high molding heating steam pressure. -Use of special molding dies or molding at high pressure is necessary, which causes cost increase.
JP-A-8-277340 Japanese Patent Laid-Open No. 10-316791 JP-A-11-156879 JP 7-258455 A JP-A-1-242638

  The object of the present invention is to mold polypropylene resin foamed particles in-mold, which can eliminate inversion by low heating conditions and drying in a short time, has excellent surface beauty, and is flexible and suitable for cushioning packaging Since a body can be obtained, it is providing the polypropylene resin pre-expanded particle which can obtain an in-mold molded object easily at low cost.

  As a result of diligent research in view of the above problems, the present invention has a low resin melting point, that is, even a polypropylene resin having low rigidity, and is stored in a region having a low angular frequency in the measurement of dynamic viscoelasticity at the time of melting. When tan δ, which is the loss tangent, which is the ratio of elastic modulus and loss elastic modulus, is in a specific region and has a specific melting behavior by differential scanning calorimetry, it is finally possible to reduce the internal tilt after thermoforming / drying. The headline, the present invention has been completed.

That is, in the first aspect of the present invention, the raw material polypropylene resin is modified by a reaction with an isoprene monomer and a radical polymerization initiator, and an angular frequency of 1 rad / s in dynamic viscoelasticity measurement at 180 ° C. The melting tangent (tan δ), which is the ratio between the storage elastic modulus and the loss elastic modulus, is a melting polypropylene that has two melting points as measured by differential scanning calorimetry using a modified polypropylene resin having a base resin of 1.0 or more and 3.0 or less. The present invention relates to a polypropylene resin pre-expanded particle having a peak and having a ratio of a melting peak calorie based on a high temperature side melting point to a total melting peak calorie of 10 to 70% of the two melting peaks.

As a preferred embodiment,
(1) The polypropylene resin having a melt flow rate (MFR) of the modified polypropylene resin of 3 g / 10 min or more and 30 g / 10 min or less,
The above-mentioned polypropylene resin pre-expanded particles are characterized by the following.

The second of the present invention relates to an in-mold foam molded article having a density of 10 kg / m ³ or more and 300 kg / m ³ or less, obtained by using the polypropylene resin pre-foamed particles described above.

  The polypropylene resin pre-expanded particles of the present invention are less deformed after heat molding when performing in-mold molding. Therefore, it is possible to obtain a polypropylene resin-in-mold foam-molded product that has sufficient flexibility as a buffer wrapping material and has little inward tilting at a low molding processing temperature.

The polypropylene resin used as the base resin for the pre-expanded polypropylene resin particles of the present invention is a resin mainly composed of propylene as a monomer, and propylene is preferably 80% by weight or more as a monomer, more preferably 85% by weight. % Or more, more preferably 90% by weight or more. As long as it contains propylene in the above range, it may contain other copolymerizable monomer components. Examples of copolymerizable monomer components include ethylene, 1-butene, isobutene, and 1-pentene. , 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene Α-olefins having 2 or 4 to 12 carbon atoms such as, cyclopentene, norbornene, cyclic olefins such as tetracyclo [6,2,1 ^1,8 , 1 ^3,6 ] -4-dodecene, 5-methylene-2-norbornene , Dienes such as 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, vinyl chloride, vinyl chloride Vinyl monomers such as den, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methylstyrene, vinyltoluene, divinylbenzene, etc. Can be mentioned. Among these, it is preferable to use ethylene and 1-butene in terms of improving cold brittleness resistance, low cost, and the like.

  The loss tangent tan δ (the ratio of the storage elastic modulus and the loss elastic modulus at an angular frequency of 1 rad / s in the dynamic viscoelasticity measurement at 180 ° C. of the polypropylene-based resin that is the base resin of the pre-expanded particles in the present invention. Hereinafter, it may be simply referred to as tan δ) is 1.0 or more and 3.0 or less. The tan δ in the polypropylene-based resin before the pre-foaming is in the above range, but when the pre-foamed particles and the in-mold molded product thereof are resinized, the tan δ may be 3.0 or more.

  In the present invention, the reason why the tan δ at the angular frequency of 1 rad / s in the dynamic viscoelasticity measurement at 180 ° C. is preferably 1.0 or more and 3.0 or less is not clear, but is considered as follows. When tan δ is less than 1.0, the viscosity effect of the resin is lowered and the elastic effect is very high, and there is also an effect of suppressing deformation after heat molding, but the elongation at the time of heat molding becomes worse, and at the time of heat molding There is a case where the fusion property between the pre-expanded particles is deteriorated and the surface elongation of the thermoformed article is deteriorated. On the other hand, when tan δ is larger than 3.0, the elastic effect is lowered and the deformation suppressing effect after the heat forming is not exhibited.

  The preferable range of the melting point of the polypropylene resin used in the present invention is 130 ° C. or higher and 155 ° C. or lower, more preferably 135 ° C. or higher and 150 ° C. or lower. When the melting point is within the above range, a good in-mold foamed product can be obtained even with a molding machine of 0.4 MPa pressure resistance specification that is often used at present.

  The melt flow rate (MFR) (hereinafter sometimes referred to as MFR) of the polypropylene resin in the present invention is preferably 3 g / 10 min to 30 g / 10 min, and more preferably 5 g / 10 min to 20 g / 10 min. preferable. Although there is no primary correlation between MFR and tan δ, when MFR is less than 3 g / 10 min, the tan δ tends to be less than 1.0, and the surface elongation may be significantly reduced. When the MFR exceeds 30 g / 10 min, the tan δ tends to exceed 3.0, and the deformation suppressing effect after heat molding may not be exhibited.

  MFR is measured using the MFR measuring instrument described in JIS-K7210 under the conditions of orifice 2.0959 ± 0.005 mmφ, orifice length 8.000 ± 0.025 mm, load 2160 g, 230 ± 0.2 ° C. This is the value when

  The pre-expanded polypropylene resin particles of the present invention have two melting peaks in the differential scanning calorimetry measurement, and are calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side among the melting peaks. The ratio Qh / (Ql + Qh) × 100 (hereinafter sometimes abbreviated as DSC ratio) of the melting peak on the high temperature side is 10% or more and 70% or less. More preferably, it is in the range of 15% or more and 50% or less. When the DSC peak ratio is less than 10%, wrinkles due to shrinkage occur on the surface of the molded body, and deformation after heat molding becomes large. If it exceeds 70%, even if it has a heating pressure upper limit that can be molded by a normal molding machine, it becomes an in-mold foam molded product with poor surface aesthetics, such as a loss of fusion property and a large number of intergranularity. .

  The DSC ratio is measured using a DSC6200 differential scanning calorimeter manufactured by Seiko Instruments Inc., and 5-6 mg of polypropylene resin pre-expanded particles are heated from 40 ° C. to 220 ° C. at a rate of 10 ° C./min. The melting curve (illustrated in FIG. 1) obtained at the time of the calculation has two peaks, and calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side of the melting peak, The parameter represented by the melting peak ratio Qh / (Ql + Qh) × 100 was defined as the DSC ratio.

  A polypropylene resin having a tan δ at an angular frequency of 1 rad / s in a dynamic viscoelasticity measurement at 180 ° C. of 1.0 or more and 3.0 or less is, for example, a raw material polypropylene resin obtained by crosslinking and decomposing radical polymerization. A method obtained by a reaction with an initiator (for example, a method described in JP-A No. 2002-80610) or a method in which a raw material polypropylene resin is obtained by a reaction with a radical polymerizable monomer and a radical polymerization initiator. Can be used. Among these, a method of obtaining a raw material polypropylene resin by reaction with a radical polymerizable monomer and a radical polymerization initiator is more easily achieved by tan δ at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement at 180 ° C. Is preferable because it is possible to obtain a polypropylene-based resin having 1.0 to 3.0. The polypropylene resin thus obtained is hereinafter referred to as a modified polypropylene resin.

  The radical polymerizable monomer is preferably one that can be graft copolymerized with the raw material polypropylene resin and does not cause a significant decrease in melt viscosity due to the main chain breakage of the raw material polypropylene resin during melt kneading.

  Specific examples of preferable radical polymerizable monomers include aromatic vinyl compounds such as styrene, methylstyrene, chlorostyrene, bromostyrene, fluorostyrene, hydroxystyrene, divinylbenzene; diisopropenylbenzene; isoprene, 1,3- Conjugated diene compounds such as butadiene and chloroprene; ester compounds composed of polyhydric alcohols and two or more acrylic acids, such as diethylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane diacrylate, trimethylolpropane triacrylate Can be used alone or in combination of two or more. Of these, isoprene is most preferable because it is inexpensive and easy to handle, and the reaction easily proceeds uniformly.

  The addition amount of the radical polymerizable monomer is preferably 0.1 part by weight or more and 20 parts by weight or less, and more preferably 0.2 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the raw material polypropylene resin. When the amount of the radical polymerizable monomer is less than 0.01 part by weight, a sufficient deformation suppressing effect may not be obtained. When the amount exceeds 20 parts by weight, the surface beauty at the time of heat molding may be impaired. .

  Examples of the radical polymerization initiator used in the present invention include so-called hydrogen peroxide-extracting organic peroxides, such as ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxydioxide. Examples include carbonates and peroxyesters.

  More specifically, ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide; 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t Peroxyketals such as -butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, 2,2-bis (t-butylperoxy) butane; permethane hydroperoxide, Hydroperoxides such as 1,1,3,3-tetramethylbutyl hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2,5-di (t- Butylperoxy) hexane, α, α'-bis ( t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, etc. Dialkyl peroxides; diacyl peroxides such as benzoyl peroxide; peroxydicarbonates such as di (3-methyl-3-methoxybutyl) peroxydicarbonate and di-2-methoxybutylperoxydicarbonate; t-butylperoxide Oxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxyisopropyl carbonate, 2,5- Dimethyl-2,5-di (benzoylperoxy) hexa , T- butyl peroxy acetate, t- butyl peroxybenzoate, etc. peroxy esters such as di -t- butyl peroxy isophthalate and the like.

  Among these, it is preferable to use a radical polymerization initiator having a particularly high hydrogen abstraction ability. For example, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis Peroxyketals such as (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, 2,2-bis (t-butylperoxy) butane; dicumyl peroxide 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t Dialkyl peroxides such as butyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3; Diacyl peroxides such as oxides; t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t -Butyl peroxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butyl peroxyacetate, t-butyl peroxybenzoate, di-t-butyl peroxyisophthalate, etc. Examples include peroxyesters. These may be used alone or in combination of two or more.

  The amount of radical polymerization initiator added is 0.01% by weight based on 100 parts by weight of the raw material polypropylene resin, although the appropriate amount range varies depending on the hydrogen abstraction ability of the radical polymerization initiator and the amount of radical polymerizable monomer added. Part to 5 parts by weight, preferably 0.03 part to 3 parts by weight. When the addition amount of the radical polymerization initiator is less than 0.01 parts by weight, tan δ is difficult to be 3.0 or less, that is, it is difficult to obtain a deformation suppressing effect after thermoforming, and when it exceeds 5 parts by weight, tan δ is It may not be 1.0 or more, and it is difficult to obtain good surface beauty.

  When producing the modified polypropylene, the order of mixing and melt-kneading of other materials such as a raw material polypropylene resin, a radical polymerizable monomer, a radical polymerization initiator and an additive added as necessary The method and method are not particularly limited. For example, the raw material polypropylene resin, radical polymerizable monomer, radical polymerization initiator and other materials may be mixed and then melt kneaded, or the raw material polypropylene resin, radical polymerization initiator and other materials may be mixed. After mixing, radically polymerizable monomers may be added using a pump or the like when melt kneading them.

  In addition, after obtaining the modified polypropylene-based resin, melt kneading may be repeated for the purpose of adding an additive or other resin, and a part of the raw material polypropylene and the additive or other resin may be melt kneaded in advance. Then, after forming a master batch, a modified polypropylene resin may be obtained by using a mixture of this and the remaining raw material polypropylene resin.

  The apparatus used for the melt kneading includes a kneader, a Banbury mixer, a Brabender, a kneader such as a single-screw extruder, a twin-screw extruder, a horizontal agitator such as a twin-screw surface renewal machine, a twin-screw multi-disk device, or the like. Examples thereof include an apparatus capable of heating a polymer material such as a vertical stirrer such as a double helical ribbon stirrer to an appropriate temperature and kneading while applying an appropriate shear stress.

  Among them, as a method for producing the modified polypropylene resin, a mixture of a raw material polypropylene resin, a radical polymerization initiator and other materials added as needed is supplied from a hopper to a twin-screw extruder, and a pump A method in which radically polymerizable monomers are supplied to a twin-screw extruder using, for example, melt kneading in the extruder is particularly preferable.

  The polypropylene-based resin used in the present invention is usually extruded into a strand shape to be easily used for pre-foaming, pelletized, or cut immediately after being discharged from a die, etc. In a desired particle shape such as a cubic shape or a rectangular parallelepiped shape, the weight per particle is preferably 0.3 mg or more and 3.5 mg or less, more preferably 0.5 mg or more and 1.8 mg or less. To be processed.

  Surfactant-type or polymer-type antistatic agents, pigments, flame retardant improvers, conductivity improvers, etc., used as needed for polypropylene resins, are usually melted in the resin particle manufacturing process. It is preferable to add to the obtained resin.

  As a method of foaming polypropylene resin particles to obtain pre-foamed particles, for example, a propylene resin dispersion is obtained by dispersing in water in a pressure vessel together with a foaming agent, and the dispersion is preferably the polypropylene resin particles. The polypropylene resin particles are impregnated with a foaming agent by heating to a temperature in the range of −25 ° C. to + 10 ° C., more preferably −20 ° C. to + 5 ° C., and the pressure is higher than the vapor pressure indicated by the foaming agent. And a method for obtaining polypropylene-based pre-expanded particles by releasing a dispersion of the polypropylene-based resin particles and water in a lower-pressure atmosphere than in the container while keeping the temperature and pressure in the container constant. It is done.

In the preparation of the dispersion, as a dispersant, for example, inorganic dispersants such as tribasic calcium phosphate, basic magnesium carbonate, calcium carbonate, kaolin, magnesium sulfate, titanium dioxide, and so on, for example, sodium dodecylbenzenesulfonate, n- It is preferable to use a dispersion aid such as paraffin sulfonic acid soda and α-olefin sulfonic acid soda. Among these, combined use of tricalcium phosphate and sodium dodecylbenzenesulfonate is more preferable. The amount of the dispersant and the dispersion aid varies depending on the type and the type and amount of the polypropylene resin used, but usually 0.2 parts by weight or more and 3 parts by weight or less of the dispersant with respect to 100 parts by weight of water. It is preferable to mix, and it is preferable to mix 0.001 part by weight or more and 0.1 part by weight or less of the dispersion aid. Moreover, in order to make the polypropylene resin particles have good dispersibility in water, it is usually preferable to use 20 to 100 parts by weight with respect to 100 parts by weight of water.

  Examples of the blowing agent include hydrocarbons such as propane, butane, pentane, and hexane, and inorganic gases such as air, nitrogen, and carbon dioxide, and these can be used alone or in combination of two or more. There is no limit to the amount of these foaming agents used, and it may be set in consideration of the type of foaming agent, the ratio between the resin amount in the container and the space volume in the container, and the desired foaming ratio. Preferably they are 5 weight part or more and 50 weight part or less with respect to 100 weight part of polypropylene resin particles.

  In addition to using the foaming agent, as a method for economically producing the polypropylene resin pre-expanded particles, the water used for the dispersion medium can be expanded by adding, for example, a hydrophilic compound in the polypropylene resin. (For example, JP-A-10-306179, JP-A-11-106576, etc.) can also be used.

  Furthermore, when the polypropylene resin pre-expanded particles do not reach a desired expansion ratio, a method of increasing the expansion ratio by pressurizing the inside of the pre-expanded particles with an inert gas and heating the mixture (for example, Japanese Patent Laid-Open No. 10-237212). Gazette) is also available.

  As a method for molding an in-mold foam molded body from the polypropylene resin pre-expanded particles of the present invention, for example, the polypropylene resin pre-expanded particles are pre-air-pressed in a pressure-resistant container, and air is introduced into the polypropylene resin pre-expanded particles. The foaming ability is imparted by press-fitting, and this is filled in a mold that can be closed but cannot be sealed, and the steam is heated at a steam pressure of about 0.20 to 0.4 MPa for 3 to 30 seconds. To the extent that the polypropylene resin pre-expanded particles can be fused together by heating for about a heating time, and then the after-expansion of the in-mold foam molding after taking out the in-mold foam molding by water cooling can be suppressed. Examples of the method include a method of opening a mold after cooling and obtaining an in-mold foam molded article.

The density of the in-mold foam molded body obtained using the polypropylene resin pre-expanded particles obtained as described above is preferably 10 kg / m ³ or more and 300 kg / m ³ or less, more preferably 15 kg / m ^3. It is 250 kg / m ³ or less.

  Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited only to these examples. “Parts” and “%” are based on weight unless otherwise specified.

  Moreover, the evaluation in an Example and a comparative example was performed with the following method.

[Measurement of loss tangent tan δ, which is the ratio of storage elastic modulus to loss elastic modulus]
A polypropylene resin was hot-pressed at 190 ° C. for 5 minutes using a 1.5 mm-thick spacer to produce a 1.5 mm-thick press plate, which was punched out using a φ25 mm punch to obtain a test piece. As a measuring device, a viscoelasticity measuring device manufactured by TA Instruments, ARES was used, and a parallel plate jig having a diameter of 25 mm was attached. Set up a thermostat to surround the jig and keep it at 180 ° C. After the jig is preheated, open the thermostat, insert a test piece with a diameter of 25 mm between the parallel plates, close the thermostat and preheat for 5 minutes before paralleling The plate interval was compressed to 1 mm. After compression, the thermostat was opened again, the resin protruding from the parallel plate was scraped off with a brass spatula, the thermostat was closed and the temperature was kept again for 5 minutes, and then dynamic viscoelasticity measurement was started. The measurement was performed in the range of angular frequency from 0.1 rad / s to 100 rad / s, and the loss tangent tan δ was obtained as the storage elastic modulus and loss elastic modulus at each angular frequency and the calculated value. Among these results, the value of loss tangent tan δ at an angular frequency of 1 rad / s was adopted. The amount of strain was 5%, and the measurement was performed in a nitrogen atmosphere.

[Measurement of melting peak by differential scanning calorimetry]
The DSC ratio is measured using a DSC6200 type differential scanning calorimeter manufactured by Seiko Instruments Inc., and 5-6 mg of polypropylene resin pre-expanded particles are heated from 40 ° C. to 220 ° C. at a rate of 10 ° C./min. The melting curve (illustrated in FIG. 1) obtained at this time has two peaks, and the melting on the high temperature side calculated from the melting peak calorie Ql on the low temperature side and the melting peak calorie Qh on the high temperature side of the melting peaks. This is a parameter represented by the peak ratio Qh / (Ql + Qh) × 100.

[Measurement of melting point]
Using a DSC6200 type differential scanning calorimeter manufactured by Seiko Instruments Inc., 5-6 mg of polypropylene resin was heated from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min, and the temperature was held for 3 minutes. Then, after cooling to 40 ° C. at a temperature decrease rate of −10 ° C./min, holding the temperature for 3 minutes, the melting obtained when the temperature is increased again from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min. In the curve, the peak temperature obtained was taken as the melting point.

[Expansion ratio of pre-expanded particles]
Seeking bulk volume weight w of the pre-expanded polypropylene resin particles of about 50 cm ³ (g) and ethanol submerged volume v (cm ^3), calculated by the following equation from the density d of before foaming of the resin particles (g / cm ^3).
Foaming ratio = d × v / w

[Molded body density]
After drying the molded body, the molded body weight w (g) and the submerged volume v (L) were determined, and the molded body density (g / L) was calculated from the following formula.
Compact density = w / v

[Minimum molding heating steam pressure]
Polypropylene based on polyolefin foam molding machine Pearlstar P-150N manufactured by Toyo Machine Metal Co., Ltd., adjusted in advance so that the air pressure inside the particles becomes 2.0 atm in a block mold of 270 mm long x 290 mm wide x 40 mm thick The resin pre-expanded particles are filled, the air in the mold is first expelled with water vapor of 0.1 MPa, and then heat-molded for 10 seconds using heated steam at an arbitrary pressure to obtain a polypropylene-based resin foam molded article. The foamed molded product was divided by hand to confirm the fused state of the internal foamed particles. The lowest molding heating steam pressure in a state where 60% or more of the foamed particles were visually destroyed by fusion between the foamed particles was examined. The standard was a pressure capable of continuous production of 0.34 MPa or less when a generally used 0.4 MPa pressure-resistant molding machine was used.

[Molding evaluation in box-shaped compacts]
After molding by 0.28MPa steam heating using a polyolefin foam molding machine Pearlstar P-150N manufactured by Toyo Machine Metal Co., Ltd., left at 25 ° C for 2 hours, and then kept in a temperature-controlled room at 65 ° C for 5 hours. After leaving still, it took out and it stood to cool at 25 degreeC, and the molded object of the shape shown in FIG. 2 was obtained.

  The amount of inward tilt is the product required quality, which is obtained by measuring and averaging the value obtained by subtracting the dimension b of the center part from the average value of the dimensions c1 and c2 of the end part in the longitudinal direction of the molded body 2 specimen. It was set as the pass ((circle)) that it was -10-10 mm.

  Further, in the evaluation of the surface property of the thin-walled portion, it was determined that there was almost no intergranularity or wrinkles, and the case where intergranularity or wrinkles were observed (×).

(Manufacture of resin 1)
100 parts by weight of raw material polypropylene (resin melting point 142 ° C., MFR 6.5 g / 10 min) and a radical initiator t-butyl peroxy-isopropyl monocarbonate (Nippon Yushi Co., Ltd., Perbutyl I) in the ratio of Table 1 The blend stirred and mixed is supplied to a twin screw extruder (manufactured by Nippon Steel Works, Ltd., TEX44XCT-38) using a metering feeder, and isoprene is fed from the middle of the extruder using a liquid addition pump to a raw material polypropylene. Various pellets were obtained by supplying at a ratio of Table 1 to 100 parts by weight, and melt-kneading.

  The biaxial extruder was of the same direction biaxial type, the screw diameter was 44 mmφ, and the maximum screw effective length (L / D) was 38. The set temperature of the cylinder part of the twin screw extruder was 180 ° C. until the isoprene monomer injection, 200 ° C. after the isoprene injection, and the screw rotation speed was set to 120 rpm.

(Production of resins 2 to 7)
Resin 2 to Resin 7 pellets were obtained by the same operation as Resin 1 except that the type of raw material polypropylene, the amount of radical initiator, and the amount of isoprene shown in Table 1 were changed.

表１に示すポリプロピレン系樹脂を用い、ポリプロピレン系樹脂１００部に対し、造核剤としてタルクを０．０３部添加・混合し、５０ｍｍφ単軸押出機で混練したのち造粒し、ポリプロピレン系樹脂粒子（１．３ｍｇ／粒）を製造した。

Using polypropylene resin shown in Table 1, 0.03 part of talc as a nucleating agent is added to and mixed with 100 parts of polypropylene resin, kneaded with a 50 mmφ single screw extruder, granulated, and polypropylene resin particles (1.3 mg / grain) was produced.

  100 parts of the polypropylene resin particles, 2 parts of powdery basic tricalcium phosphate as a dispersing agent, 0.05 part of n-paraffin sulfonic acid sodium as a dispersing aid, and 300 parts of water are charged into a pressure-resistant container having an internal volume of 10 L. While stirring, 15 parts by weight of isobutane was added, the temperature was raised to the temperature shown in Table 2, and isobutane was further injected to adjust the pressure as shown in Table 2 and maintained for 30 minutes. Then, while maintaining the internal temperature and pressure of the vessel as shown in Table 2 while injecting nitrogen, the valve at the bottom of the pressure vessel is opened, and the aqueous dispersion medium is released under atmospheric pressure through an orifice plate having an aperture diameter of 4.0 mmφ. As a result, pre-expanded polypropylene resin particles were obtained.

次に得られた発泡粒子を用いて最低成形加熱蒸気圧力、および箱型成形体における成形評価（内倒れ量、薄肉部表面性）を行った。

Next, using the obtained foamed particles, the minimum molding heating steam pressure and the molding evaluation (inside-down amount, thin-wall surface property) in a box-shaped molded body were performed.

  When the evaluation results of the polypropylene resin pre-expanded particles using the resins shown in Examples 1 to 4 and the polypropylene resin pre-expanded particles shown in Comparative Examples 1 to 5 are compared, implementation using the technique described in the present invention is performed. In the example, excellent results were obtained for all of the minimum forming steam superheating pressure, the amount of inclining and the surface property of the thin wall portion, while in the comparative example, the minimum forming steam superheating pressure, the amount of inclining and the surface property of the thin portion It was inferior in one or more points.

  As described above, in the pre-expanded polypropylene resin particles, when the technique described in the present invention is used, there is little inversion and the surface is beautiful and dry using a molding machine of 0.4 MPa pressure resistance specification which is often used at present. Since a molded article having a short time can be obtained, the molded article can be efficiently produced.

It is an example of a DSC curve obtained when a differential scanning calorimeter is used to measure polypropylene resin pre-expanded particles according to the present invention. The horizontal axis is the temperature, and the vertical axis is the endothermic amount. The shaded portion on the low temperature side is Ql, and the shaded portion on the high temperature side is Qh. It is a perspective view which shows the shape of the box-shaped molded object used for shaping | molding evaluation.

Explanation of symbols

a Thin-walled part b Location where the center dimension was measured c Location where the end dimension was measured

Claims (3)

Ratio of storage elastic modulus and loss elastic modulus at an angular frequency of 1 rad / s in dynamic viscoelasticity measurement at 180 ° C., in which raw material polypropylene resin was modified by reaction with isoprene monomer and radical polymerization initiator in a loss tangent tanδ are, the modified polypropylene resin is 1.0 to 3.0 as a base resin has two melting peaks as measured by differential scanning calorimetry, of the two melting peaks Of these, the ratio of the melting peak heat quantity based on the high temperature side melting point to the total melting peak heat quantity is 10% or more and 70% or less, and the polypropylene resin pre-expanded particles are characterized in that: Modified polypropylene resin of melt flow rate (MFR), characterized in that it is a polypropylene resin is 3 g / 10 min or more 30 g / 10 min or less, the pre-expanded polypropylene resin particles according to claim 1. Obtained using the pre-expanded polypropylene resin particles according to claim 1 or 2, density of 10 kg / ^{m 3} or more 300 kg / ^{m 3} or less in-mold expansion molded article.

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