JP4274463B2 - Polypropylene resin foam particles - Google Patents

Description

  The present invention relates to expanded polypropylene resin particles.

  In recent years, there has been a trend toward integration of plastic materials. Among them, polypropylene resins have excellent mechanical strength, heat resistance, processability, price balance, and excellent properties such as easy incineration and easy recyclability. Because it has, the field of use is expanding. One of the fields of use of the polypropylene resin is sometimes referred to as an in-mold foam molded body (hereinafter referred to as “EPP molded body” or “foamed particle molded body” or simply “molded body”) of non-crosslinked polypropylene resin expanded particles. ) The EPP molded body is widely used as a packaging material, a building material, a heat insulating material, and the like because it can add properties such as buffering properties and heat insulating properties without losing the excellent properties of the polypropylene resin.

  However, recently, there is an increasing demand for an EPP molded body using a resin with higher functionality than the polypropylene resin that has been used so far. Examples of fields in which higher functionality is desired include car use boxes for transportation such as automobile applications and fish boxes. In automotive applications, focusing on the excellent properties of EPP molded bodies, bumper core materials, door pads, pillars, tool boxes, floor mats and the like have been widely used. However, in recent years, there has been a demand for weight reduction of vehicles due to environmental and energy problems, and thus there has been a strong demand for weight reduction of parts constituting the vehicle. Even an EPP molded body is not an exception, and a lighter EPP molded body has been demanded while maintaining the conventional rigidity, shock absorbing property and impact energy absorption.

  On the other hand, in-mold foam molded bodies of polystyrene resin foam particles (hereinafter referred to as “EPS molded bodies”) have been widely used as shipping boxes for transporting fish boxes and the like because of their high rigidity and low cost. It was. However, the EPS molded body has a problem that it is not suitable for repeated use because it is inferior in impact resistance and heat resistance to the EPS molded body. However, in recent years, due to the increasing awareness of environmental issues in public opinion, there have been many requests to use an EPP molded body that is excellent in environmental compatibility and can be used repeatedly as a shipping box. Higher rigidity of the molded body has been desired.

  Incidentally, in order to obtain a highly rigid EPP molded body, several improvements have been made so far. As one of them, the use of a highly rigid polypropylene resin as a raw material has been developed. As the high-rigidity polypropylene resin, a propylene copolymer or a propylene homopolymer having a low comonomer composition ratio such as ethylene or butene as a copolymer component is generally known, and these raw materials are used. This makes it possible to obtain a highly rigid EPP molded body. A technique related to this is described in, for example, [Patent Document 1]. However, generally a high-rigidity polypropylene-based resin has a melting point that increases simultaneously with rigidity. Therefore, when these high-rigidity raw materials are used, the processing temperature for obtaining the EPP molded body is increased, particularly the molding temperature is increased. Originally, a molding machine for producing an EPP molded body has a structure that can withstand a high molding temperature, that is, a structure that can withstand high-pressure steam as compared with a molding machine for an EPS molded body. However, high-rigidity EPP molding using high-rigidity non-crosslinked polypropylene-based resin expanded particles (hereinafter sometimes referred to as “EPP particles” or simply “expanded particles”) obtained from the above-described rigid polypropylene-based resins. In order to obtain a body, steam having a pressure higher than the pressure resistance required for a molding machine for producing a conventional EPP molded body is required. Nevertheless, even if high-rigidity EPP particles are intentionally molded with a conventional EPP molding machine, there is a problem that the fusion rate between the foamed particles in the obtained molded product is insufficient. Under such circumstances, molding machines that can obtain an EPP molded body that maintains a sufficient fusion rate and can be used for production have been limited to special machines among molding machines for EPP molded bodies. Therefore, there has been a demand for a method of obtaining EPP particles that can be molded with a steam pressure within the pressure resistance of a molding machine for producing a conventional EPP molded body.

  On the other hand, as another method for obtaining a highly rigid EPP molded product, a method for obtaining a highly rigid EPP molded product using a polypropylene copolymer resin composed of propylene and a comonomer such as ethylene or butene has been developed. I came. In this method, the endothermic curve peak (hereinafter referred to as “high temperature”) is higher than the endothermic curve peak (hereinafter sometimes referred to as “inherent peak”) derived from the heat of fusion of the base resin in the DSC curve by differential scanning calorimetry of the expanded particles. In this method, the amount of heat of the high temperature peak is increased more than the value that has been conventionally managed. Techniques relating to this are described in, for example, [Patent Document 2] and [Patent Document 3]. When the expanded particles obtained by these methods are used, as in the case of obtaining a highly rigid EPP molded body using the highly rigid EPP particles obtained from the highly rigid polypropylene resin as described above, The steam of the pressure exceeding the pressure | voltage resistance of the molding machine for inducing the raise of molding temperature and manufacturing the conventional EPP molded object was required. Therefore, even in the case of the expanded particles described in [Patent Document 2] and [Patent Document 3], a molded body having a sufficient fusion rate between the expanded particles cannot be obtained when molded with a conventional EPP molding machine. However, the molding machine that can obtain an EPP molded body maintaining a sufficient fusion rate and can be used for production has been limited to a special one. Thus, even in the case of the method of controlling the amount of heat at the high temperature peak, a method of obtaining EPP particles that can be molded with a steam pressure within the pressure resistance of a conventional molding machine for producing an EPP molded body has been desired.

  The above-described problem is that a dispersion formed by dispersing resin particles having a polypropylene resin as a base resin in a dispersion medium in which an organic peroxide exists is obtained from the melting point of the base resin of the polypropylene resin particles. A surface modification step of obtaining substantially uncrosslinked surface-modified resin particles by decomposing the organic peroxide while maintaining the temperature at a low temperature and at a temperature at which the organic peroxide is substantially decomposed; This problem has been solved by using foamed particles obtained by foaming the surface-modified resin particles with a foaming agent to obtain substantially uncrosslinked foamed particles [Patent Document 4]. However, with the foamed particles described in Patent Document 4, the secondary foamability at the time of molding tends to be insufficient, leaving room for improvement.

International Publication No. 96/31558 Pamphlet Japanese Patent No. 2886248 JP-A-11-156879 JP 2002-167460 A

  The present invention relates to a surface-modified foamed particle having improved secondary foaming properties at the time of molding, and capable of fusing the particles with steam at a lower temperature, and the surface-modified uncrosslinked polypropylene resin It is an object of the present invention to provide expanded particles.

As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.
That is, according to the present invention, the following polypropylene resin expanded particles are provided.
[1] Polypropylene resin particles are dispersed in a dispersion medium containing an organic peroxide, and the dispersion medium is at a temperature lower than the melting point of the base resin of the polypropylene resin particles and the organic peroxide is substantially Surface modification step of obtaining substantially uncrosslinked surface modified resin particles by decomposing the organic peroxide while maintaining the temperature at which it is decomposed, and the surface modified resin particles using a foaming agent In the foamed polypropylene resin particles obtained by the foaming step of foaming to obtain substantially uncrosslinked foamed particles,
The base resin contains 0.01 to 0.9 parts by weight of one or more selected from the group consisting of fatty acids having 10 to 22 carbon atoms, amides of the fatty acids, esters of the fatty acids, and metal salts of the fatty acids. A polypropylene resin expanded particle characterized by the above.
[2] Substantially non-crosslinked foamed particles having a polypropylene resin as a base resin, and endotherm higher than the endothermic curve peak derived from the heat of fusion of the base resin in the DSC curve by differential scanning calorimetry. The amount of heat of the endothermic curve peak existing on the high temperature side of the surface layer portion of the expanded particle (ΔHs) and the amount of heat of the endothermic curve peak existing on the high temperature side of the inner expanded layer portion of the expanded particle (ΔHi) In the polypropylene resin expanded particles in which ΔHs <ΔHi × 0.86,
0.01 to 0.9 parts by weight of one or more selected from the group consisting of fatty acids having 10 to 22 carbon atoms, amides of the fatty acids, esters of the fatty acids, and metal salts of the fatty acids. Polypropylene-based resin expanded particles characterized by containing.

  The polypropylene resin expanded particles of the present invention are surface-modified, and the base resin is selected from the group consisting of fatty acids having 10 to 22 carbon atoms, amides of the fatty acids, esters of the fatty acids, and metal salts of the fatty acids. By including 0.01 to 0.9 parts by weight of one or more of the above, the secondary foamability at the time of molding is improved as compared with the conventional surface-modified polypropylene resin foamed particles. In addition, it is possible to easily obtain a molded article having an excellent appearance.

  The polypropylene resin as the base resin (hereinafter also referred to as “the base resin”) of the polypropylene resin particles used in the present invention is a polymer of propylene, but is a copolymer of propylene and an olefin other than propylene. They can be combined. The composition is composed of a copolymer of propylene and an olefin other than propylene, and the proportion of the olefin component other than propylene in the copolymer is 0.1% by weight or less (excluding 0), or propylene alone It is a mixture of a polymer, a copolymer of propylene and an olefin other than propylene, and the ratio of olefin components other than propylene in the mixture is 0.1% by weight or less (excluding 0). . As the olefin other than propylene, ethylene and α-olefins such as 1-butene, 1-pentene and 1-hexene are suitable. Among these, ethylene and / or 1-butene are preferable.

  The melting point of the base resin is preferably 130 ° C. or higher, more preferably 135 ° C. or higher, in order to increase mechanical properties such as compressive strength of the final EPP molded product. More preferably, the temperature is more preferably 155 ° C. or more, particularly preferably 155 ° C. or more, and most effective when the temperature is 158 ° C. or more. The upper limit of the melting point is usually 170 ° C. Furthermore, the base resin preferably has a melt flow rate (MFR) of 0.3 to 100 g / 10 min, particularly 1 to 90 g, considering the heat resistance of the foamed molded product and the foaming efficiency at the time of producing foamed particles. / 10 minutes are preferred. The MFR is a value measured under test condition 14 of JIS K7210 (1976).

  In the present invention, the base resin contains one or more selected from the group consisting of fatty acids having 10 to 22 carbon atoms, amides of the fatty acids, esters of the fatty acids, and metal salts of the fatty acids. When surface-modified foam particles containing these compounds are used, molding can be performed at a lower temperature than the foam particles whose surface is modified as described in Patent Document 4.

The fatty acid having 10 to 22 carbon atoms used in the present invention may be a linear saturated fatty acid such as lauric acid, myristic acid, palmitic acid, stearic acid or behenic acid, or may be a branched type. Also, unsaturated fatty acids such as oleic acid and erucic acid can be used. As the metal salt of the fatty acid, sodium, potassium, calcium, magnesium, zinc, aluminum salt of the above fatty acid and the like are used. The fatty acid amide may be ethylene bis fatty acid amide in addition to the fatty acid amide.
Examples of the fatty acid ester include alcohols or polyhydric alcohol esters of the above fatty acids, and examples include stearic acid monoglyceride, stearyl stearate, stearic acid diglyceride, propylene glycol monostearate, stearyl stearate and the like.

The compound selected from the group such as the fatty acid is contained in an amount of 0.01 to 0.9 parts by weight per 100 parts by weight of the polypropylene resin as the base resin. If it exceeds 0.9 parts by weight, the physical properties of the resulting molded article will be lowered, and if it is less than 0.01 parts by weight, the effect of further lowering the molding temperature cannot be obtained.
The compounding method of these compounds can be directly mixed with a screw feeder or the like when the raw material is melted and granulated with an extruder, or a predetermined amount can be added in advance as a high concentration master batch. Furthermore, it can also be put into a foaming container in the foaming step and impregnated into resin grains.

  In the present invention, a synthetic resin or / and an elastomer other than the polypropylene resin can be added to the base resin within a range that does not impair the intended effect of the present invention. The amount of the synthetic resin or / and elastomer added other than the polypropylene resin is preferably at most 35 parts by weight, more preferably at most 25 parts by weight per 100 parts by weight of the polypropylene resin. More preferably, it is at most 15 parts by weight, particularly preferably at most 10 parts by weight, most preferably at most 5 parts by weight.

  Synthetic resins other than polypropylene resins include high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, linear ultra-low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic. Examples thereof include ethylene resins such as acid copolymers and ethylene-methacrylic acid copolymers, and styrene resins such as polystyrene and styrene-maleic anhydride copolymers.

  Examples of the elastomer include ethylene-propylene rubber, ethylene-1-butene rubber, propylene-2-butene rubber, styrene-butadiene rubber and hydrogenated products thereof, isoprene rubber, neoprene rubber, nitrile rubber, and styrene-butadiene block copolymer. Elastomers such as elastomers and hydrogenated products thereof are exemplified.

  In the present invention, various additives can be added to the base resin as long as the desired effects of the present invention are not impaired. Examples of such additives include antioxidants, ultraviolet light inhibitors, antistatic agents, flame retardants, metal deactivators, pigments, dyes, nucleating agents, and bubble regulators. Examples of the air conditioner include inorganic powders such as zinc borate, talc, calcium carbonate, borax, and aluminum hydroxide. These additives are preferably used in a total amount of 20 parts by weight or less, particularly 5 parts by weight or less per 100 parts by weight of the base resin. These additives are used in the extruder when, for example, the polypropylene resin particles (hereinafter sometimes referred to as “the present resin particles”) used in the present invention are produced by cutting the strands extruded by the extruder. It can be contained in the resin particles by adding and kneading to the base resin melted in (1).

  The present resin particles for obtaining surface-modified resin particles (the surface-modified resin particles will be described later) are obtained by cutting the strands obtained by melting and extruding the base resin in an extruder. What was obtained by quenching the strand immediately after extrusion when manufacturing a resin particle is preferable. When the resin particles are so cooled, the surface modification described later can be performed efficiently. The quenching of the strand immediately after the extrusion is adjusted immediately after extruding the strand, preferably in water adjusted to 50 ° C. or lower, more preferably in water adjusted to 40 ° C. or lower, most preferably 30 ° C. or lower. This can be done by placing it in water. Then, the sufficiently cooled strand is pulled up from the water and cut into an appropriate length to obtain the resin particles having a desired size. The resin particles are usually adjusted to have a length / diameter ratio of 0.5 to 2.0, preferably 0.8 to 1.3, and the average weight per particle (chosen at random). The average value of 200 weights measured simultaneously is adjusted to be 0.1 to 20 mg, preferably 0.2 to 10 mg.

The polypropylene resin expanded particles (EPP particles) obtained in the present invention are produced by a method including a surface modification step and a foaming step (hereinafter also referred to as method A). In the surface modification step, the resin particles are dispersed in a dispersion medium in which an organic peroxide is present, and the obtained dispersion (hereinafter also referred to as a dispersion) is cooled at a temperature lower than the melting point of the base resin of the resin particles. And maintaining the temperature at which the organic peroxide is substantially decomposed to decompose the organic peroxide to modify the surface of the resin particles to thereby substantially non-crosslinked surface-modified resin. Get particles.
The surface-modified resin particles thus obtained are foamed with a foaming agent in the subsequent foaming step to be converted into substantially uncrosslinked foamed particles. The foamed particles obtained in this way are excellent in heat-fusibility and can be fused between the foamed particles with low-temperature steam. Further, the foamed particles can be made into an EPP molded article having excellent rigidity by filling the mold into a mold, introducing steam and heating.

  The dispersion medium used in the surface modification step is generally an aqueous medium, preferably water, and more preferably ion-exchanged water, but is not limited to water and does not dissolve the base resin. Any solvent or liquid that can disperse the resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol, and the like. The aqueous medium includes a mixed solution of water and an organic solvent such as the alcohol.

  Examples of the organic peroxide used in the surface modification step include various conventionally known ones such as isobutyl peroxide [50 ° C./85° C.], cumyl peroxyneodecanoate [55 ° C./94° C.]. , Α, α′-bis (neodecanoylperoxy) diisopropylbenzene [54 ° C./82° C.], di-n-propyl peroxycarbonate [58 ° C./94° C.], diisopropyl peroxycarbonate [56 ° C. / 88 ° C], 1-cyclohexyl-1-methylethylperoxyneodecanoate [59 ° C / 94 ° C], 1,1,3,3-tetramethylbutylperoxyneodecanoate [58 ° C / 92 ° C] Bis (4-t-butylcyclohexyl) peroxydicarbonate [58 ° C / 92 ° C], di-2-ethoxyethylperoxydicarbonate [59 ° C / 92 ° C], di (2-ethylhexylperoxy) dicarbonate [59 ° C / 91 ° C], t-hexylperoxyneodecanoate [63 ° C / 101 ° C], dimethoxybutylperoxycarbonate [64 ° C / 102 ° C], di (3-methyl-3-methoxybutylperoxy) dicarbonate [65 ° C / 103 ° C], t-butylperoxyneodecanoate [65 ° C / 104 ° C], 2, 4-dichlorobenzoyl peroxide [74 ° C./119° C.], t-hexyl peroxypiparate [71 ° C./109° C.], t-butyl peroxypivalate [73 ° C./110° C.], 3, 5, 5- Trimethylhexanoyl peroxide [77 ° C / 113 ° C], Otanoyl peroxide [80 ° C / 117 ° C], Lauroyl peroxide [80 ° C / 1 6 ° C], stearoyl peroxide [80 ° C / 117 ° C], 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate [84 ° C / 124 ° C], succinic peroxide [87 ° C / 132 ° C], 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy) hexane [83 ° C / 119 ° C], 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate [90 ° C / 138 ° C], t-hexylperoxy-2-ethylhexanoate [90 ° C / 133 ° C], t-butylperoxy-2-ethylhexanoate [92 ° C / 134 ° C], m- Toluoyl benzoyl peroxide [92 ° C / 131 ° C], benzoyl peroxide [92 ° C / 130 ° C], t-butylperoxyisobutyrate [96 ° C / 1 6 ° C], 1,1-bis (t-butylperoxy) -2-methylcyclohexane [102 ° C / 142 ° C], 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane [106 ° C / 147 ° C], 1,1-bis (t-hexylperoxy) cyclohexane [107 ° C / 149 ° C], 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane [109 ° C / 149 ° C], 1,1-bis (t-butylperoxy) cyclohexane [111 ° C / 154 ° C], 2,2-bis (4,4-dibutylperoxycyclohexyl) propane [114 ° C / 154 ° C], 1,1-bis (t-butylperoxy) cyclododecane [114 ° C / 153 ° C], t-hexylperoxyisopropyl monocarbonate [115 ° C / 155 ° C], t-butylperoxymaleic acid [119 ° C / 168 ° C], t-butylperoxy-3,5,5-trimethylhexanoate [119 ° C / 166 ° C], t-butylperoxylaurate [118 ° C / 159 ° C], 2,5-dimethyl-2,5-di (m-toluoylperoxy) hexane [117 ° C / 156 ° C], t-butylperoxyisopropyl monocarbonate [118 ° C / 159 ° C ], T-butylperoxy-2-ethylhexyl monocarbonate [119 ° C / 161 ° C], t-hexylperoxybenzoate [119 ° C / 160 ° C], 2,5-dimethyl-2,5-di (benzoylperoxy) ) Hexane [119 ° C./158° C.] and the like. In addition, the temperature on the left side in [] immediately behind each organic peroxide is a 1-hour half-life temperature described later, and the temperature on the right side is a 1-minute half-life temperature described later. The organic peroxide is used alone or in combination of two or more, and is usually 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, per 100 parts by weight of the resin particles in the dispersion medium. Used by adding.

  In general, radicals generated by organic peroxides have three types of chain transfer actions: hydrogen abstraction, addition, and β decay. In the present invention, among these three actions, those having a particularly large addition action, that is, those generating oxygen radicals during decomposition are particularly preferred, and among them, a peroxide having a carbonate structure is most preferred. In addition, when using the organic peroxide, it is possible to use a chain transfer agent or the like as necessary (previously contained in the resin particles or / and added to the dispersion medium and used in combination). It is. The oxygen radical means an oxygen radical in which an organic group generated by decomposition of an organic peroxide is bonded in addition to a radical of oxygen alone.

In the method A, the organic peroxide is substantially decomposed at a temperature lower than the melting point of the base resin. Accordingly, the one-hour half-life temperature of the organic peroxide (the constant temperature when the amount of active oxygen is half of the initial value in one hour when the organic peroxide is decomposed at a constant temperature) It is preferable that it is below Vicat softening point of resin (JISK 6747-1981 and the same). When the 1-hour half-life temperature of the organic peroxide used exceeds the Vicat softening point of the base resin, a high temperature higher than the melting point of the base resin is required to rapidly decompose the peroxide. Therefore, it is not preferable. In some cases, it is not preferable because it cannot be substantially decomposed at a temperature lower than the melting point of the base resin. When the peroxide is substantially decomposed at a temperature higher than the melting point of the base resin, the peroxide is decomposed in a state where it penetrates deep into the resin particles. Since the resin material is greatly decomposed as a whole regardless of the surface or the inside, in some cases, there is a possibility that only EPP particles that cannot be used for molding may be obtained, and even if it can be molded, it is finally obtained. There exists a possibility that the mechanical physical property of an EPP molded object may fall large.
In consideration of the above, the organic peroxide used in Method A preferably has a one-hour half-life temperature of 20 ° C. or more lower than the Vicat softening point of the base resin. It is more preferable that the temperature is 30 ° C. or more lower than the Vicat softening point. The one-hour half-life temperature is preferably equal to or higher than the glass transition temperature of the base resin, more preferably 40 to 100 ° C., and 50 to 90 ° C. in view of handling properties. Is more preferable. The glass transition temperature is determined in accordance with JIS K 7121-1987, in which the state of the test piece is adjusted to “when measuring the glass transition temperature after performing a certain heat treatment”, and the midpoint glass transition temperature obtained by heat flux DSC is used. means.

  The peroxide is preferably substantially decomposed below the Vicat softening point of the base resin in the dispersion medium in which the resin particles are present, and is 20 ° C. higher than the Vicat softening point of the base resin. More preferably, it is substantially decomposed at a low temperature, and more preferably, it is substantially decomposed at a temperature 30 ° C. or more lower than the Vicat softening point of the base resin. The organic peroxide has a one-minute half-life temperature of the organic peroxide (the temperature at which the amount of active oxygen is half of the original in one minute when the organic peroxide is decomposed at a constant temperature). It is particularly preferable to keep the temperature in the temperature range of ± 30 ° C. for 10 minutes or more and substantially decompose. If it is attempted to decompose at a temperature lower than [one minute half-life temperature −30 ° C.], it takes a long time to decompose, resulting in poor efficiency. On the other hand, when the decomposition is attempted at a temperature higher than [one minute half-life temperature + 30 ° C.], the decomposition may be abrupt and the efficiency of the surface modification may be deteriorated. In addition, if the 1 minute half-life temperature is maintained within a range of ± 30 ° C. for 10 minutes or more, it becomes easy to substantially decompose the organic peroxide. The longer the retention time in the range of [one minute half-life temperature ± 30 ° C.], the more reliably the organic peroxide can be decomposed, but a longer time is no longer necessary. Longer times than necessary will lead to a decrease in production efficiency. The holding time in the above temperature range should normally be 60 minutes at the longest. To decompose the organic peroxide, first prepare the dispersion adjusted to a temperature at which the organic peroxide is difficult to decompose, and then heat the dispersion to the decomposition temperature of the organic peroxide. Good. At this time, the rate of temperature rise may be selected so as to be maintained in the range of [1 minute half-life temperature ± 30 ° C.] for 10 minutes or longer. However, any rate within the range of [1 minute half-life temperature ± 30 ° C.] More preferably, the temperature is stopped and the temperature is maintained for 5 minutes or more. As an arbitrary temperature at that time, a temperature within [1 minute half-life temperature ± 5 ° C.] is most preferable. The peroxide is preferably substantially decomposed at a temperature equal to or higher than the glass transition temperature of the base resin. Considering handling properties of the peroxide, the peroxide is substantially decomposed in the range of 40 to 100 ° C. It is more preferable to make it decompose, and it is still more preferable to make it decompose substantially in the range of 50-90 degreeC. Decomposing substantially means decomposing until the active oxygen content of the used peroxide is 50% or less of the original, but decomposing until the active oxygen content is 30% or less of the initial. It is more preferable to decompose until the amount of active oxygen becomes 20% or less of the initial amount, and further preferable to decompose until the amount of active oxygen becomes 5% or less of the initial amount. The above-mentioned half-life temperature of the organic peroxide is adjusted to a 0.1 mol / L concentration organic peroxide solution using a solution that is relatively inert to radicals (for example, benzene, mineral spirit, etc.) It is sealed in a glass tube subjected to nitrogen substitution, immersed in a thermostat set at a predetermined temperature, pyrolyzed and measured.

  In Method A, the surface-modified resin particles are substantially non-crosslinked. In Method A, since a crosslinking aid or the like is not used together, crosslinking does not proceed substantially. The term “substantially non-crosslinked” is defined as follows. That is, regardless of the base resin, the present resin particles, the surface-modified resin particles, the EPP particles, and the EPP molded body, each sample was used (1 g of sample per 100 g of xylene), and this was immersed in boiling xylene for 8 hours. The mixture is quickly filtered through a wire mesh having a mesh size of 74 μm as defined in JIS Z 8801 (1966), which defines a standard mesh screen, and the weight of the boiling xylene-insoluble matter remaining on the wire mesh is measured. A case where the insoluble content is 10% by weight or less of the sample is called substantially non-crosslinked, but the insoluble content is preferably 5% by weight or less and preferably 3% by weight or less. More preferably, it is most preferably 1% by weight or less. The smaller the insoluble content, the easier it is to reuse. The insoluble content P (%) is expressed by the following formula (1).

P (%) = (M ÷ L) × 100 (1)
However, M is the weight (g) of insoluble matter, and L is the weight (g) of the sample.

  As described above, the resin particles are subjected to the production of foamed particles after decomposing the organic peroxide to modify the surface of the resin particles. The foamed particles are heated when the surface modified resin particles are impregnated with the foaming agent by heating while being dispersed in a dispersion medium in a closed container in the presence of the foaming agent, and then the pressure is released. It is preferable to produce the surface modified resin particles and the dispersion medium at a temperature at which the expanded particles are generated under a low pressure (hereinafter referred to as “dispersion medium releasing foaming method”).

  In Method A, the surface modification step for forming the surface-modified resin particles and the foaming step for obtaining foamed particles from the surface-modified resin particles can be carried out at different times using different apparatuses. However, when the dispersion medium releasing foaming method is adopted, the organic peroxide having an appropriate decomposition temperature is simply added to the aqueous medium in the sealed container and the ordinary dispersion medium releasing foaming method is performed. Since the surface modification is completed in the middle of heating and the surface-modified resin particles are automatically obtained, it is efficient.

  In the dispersion medium releasing foaming method, it is preferable to add a dispersant to the dispersion medium so that the surface-modified resin particles under heating in the container do not fuse with each other in the container. As such a dispersant, any agent that prevents fusion of the surface-modified resin particles in the container may be used, and any organic or inorganic material can be used, but it is easy to handle. A finely divided inorganic substance is preferred. For example, natural or synthetic clay minerals such as amusnite, kaolin, mica, clay, aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, iron oxide and the like in one kind or a combination of several kinds Can be used.

  In the dispersion medium releasing foaming method, the filling amount of the physical foaming agent into the container is appropriately selected according to the type of foaming agent used, the foaming temperature, and the apparent density of the intended foamed particles. For example, when nitrogen is used as the dispersion medium and water is used as the dispersion medium, the pressure in the sealed container in a stable state immediately before the start of foaming, that is, the pressure (gauge pressure) in the space in the sealed container is 0. It is preferable to select so as to be 6 to 6 MPa. Usually, it is desirable that the pressure in the space in the container be higher as the apparent density of the desired expanded particles is smaller, and the pressure in the space is desirably lower as the apparent density of the desired expanded particles is larger. There is a tendency.

  Furthermore, in the dispersion medium releasing foaming method, a dispersion strengthening agent that strengthens the dispersing power of the dispersing agent (prevents fusion of the surface-modified resin particles within the container even if the amount of the dispersing agent added is small). It is preferable to add to the dispersion medium. Such a dispersion strengthening agent is an inorganic compound that can be dissolved in at least 1 mg or more in 100 cc of water at 40 ° C., and at least one of the anion or cation of the compound is divalent or trivalent. is there. Examples of such inorganic substances include magnesium chloride, magnesium nitrate, magnesium sulfate, aluminum chloride, aluminum nitrate, aluminum sulfate, iron chloride, iron sulfate, and iron nitrate.

  Usually, the dispersant is used in an amount of about 0.001 to 5 parts by weight and the dispersion strengthener is used in an amount of about 0.0001 to 1 part by weight per 100 parts by weight of the resin particles.

  Examples of the blowing agent used in Method A include aliphatic hydrocarbons such as propane, butane, hexane, and heptane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, trifluoromethane, and 1,2-difluoroethane. , 1,2,2,2-tetrafluoroethane, organic physical foaming agents such as halogenated hydrocarbons such as methyl chlorite, ethyl chlorite, methylene chlorite, nitrogen, oxygen, air, carbon dioxide, water, etc. So-called inorganic physical foaming agents are exemplified. An organic physical foaming agent and an inorganic physical foaming agent can be used in combination. In the present invention, those mainly composed of one or more inorganic physical foaming agents selected from the group of nitrogen, oxygen, air, carbon dioxide and water are particularly preferably used. Among these, nitrogen and air are preferable in view of the stability of the apparent density of the expanded particles, environmental load, cost, and the like. Water used as a foaming agent may be water (including ion-exchanged water) used as a dispersion medium in order to disperse the surface-modified resin particles in the closed container.

  In the surface-modified resin particles obtained by the method A, and thus the EPP particles and EPP moldings obtained therefrom, an alcohol having a molecular weight of 50 or more produced by the decomposition of the peroxide is several hundred ppm to several thousand. About ppm can be contained. As such an alcohol, when bis (4-tert-butylcyclohexyl) peroxycarbonate shown in Examples described later is used, pt-butylcyclohexanol is the surface modification of the present invention. It can be contained in the fine resin particles. Other alcohols can be included if other peroxides are used. Examples of such alcohol include isopropanol, S-butanol, 3-methoxybutanol, 2-ethylhexylbutanol, and t-butanol.

  Method A employs the above dispersion medium releasing foaming method, has an apparent density of 10 g / L to 500 g / L, and an endothermic curve peak derived from the heat of fusion of the base resin in the DSC curve by differential scanning calorimetry of the expanded particles. It is preferable to produce expanded particles having an endothermic curve peak (high temperature peak) on the higher temperature side than (inherent peak). Such foamed particles are foamed particles having a high closed cell ratio and suitable for molding. In the case of the method A, it is particularly preferable that the foamed particles obtained have a high-temperature peak heat quantity of 2 J / g to 70 J / g. If the amount of heat at the high temperature peak is less than 2 J / g, the compression strength, energy absorption amount, etc. of the EPP molded product may be reduced. On the other hand, if it exceeds 70 J / g, the air pressure required in the step of increasing the air pressure in the foamed particles prior to molding the foamed particles may become too high, or the molding cycle may be prolonged, which is not preferable. In Method A, the heat quantity of the high temperature peak is particularly 3 J / g to 65 J / g (more preferably 12 J / g to 58 J / g), and the sum of the heat quantity of the high temperature peak and the heat quantity of the intrinsic peak. It is preferable that it is 10 to 60%, and it is more preferable that it is 20 to 50%. Moreover, it is preferable that the sum total of the calorie | heat amount of a high temperature peak and the calorie | heat amount of an intrinsic peak is 40 J / g-150 J / g. In the present invention and the present specification, the calorific value of the high temperature peak and the calorific value of the intrinsic peak both mean endothermic amounts, and the numerical values are expressed in absolute values.

The amount of heat at the high temperature peak of the expanded particles is obtained when 2 to 4 mg of expanded particles are heated at a rate of 10 ° C./minute from room temperature (10 to 40 ° C.) to 220 ° C. with a differential scanning calorimeter in a nitrogen atmosphere. The amount of heat of the endothermic curve peak (high temperature peak) b appearing on the higher temperature side than the temperature at which the intrinsic endothermic curve peak (intrinsic peak) a derived from the heat of fusion of the base resin found in the first DSC curve shown in FIG. It corresponds to the area of the high temperature peak b, and can be specifically obtained as follows.
First, a straight line (α−β) connecting a point α corresponding to 80 ° C. on the DSC curve and a point β on the DSC curve corresponding to the melting end temperature of the expanded particles is drawn. Next, a straight line parallel to the vertical axis of the graph is drawn from the point γ on the DSC curve corresponding to the valley between the intrinsic peak a and the high temperature peak b, and the point intersecting with the straight line (α−β) is defined as σ. . The area of the high temperature peak b is that of the portion surrounded by the curve of the high temperature peak b portion of the DSC curve, the line segment (σ-β), and the line segment (γ-σ) (the portion hatched in FIG. 1). This is the area, which corresponds to the amount of heat at the high temperature peak. The melting end temperature is the intersection of the DSC curve on the high temperature side of the high temperature peak b and the high temperature side baseline.
Moreover, the sum total of the heat amount of the high temperature peak and the heat amount of the intrinsic peak corresponds to the area of the portion surrounded by the straight line (α-β) and the DSC curve.

  When the intrinsic peak and the high temperature peak of the expanded particles are measured by the differential scanning calorimeter as described above, when the weight per expanded particle is less than 2 mg, a plurality of expanded foams having a total weight of 2 mg to 10 mg. The particles may be used for the measurement as they are, and when the weight per foamed particle is 2 mg to 10 mg, the foamed particles may be used for the measurement as it is, and the weight per foamed particle. Is more than 10 mg, one cut sample having a weight of 2 mg to 10 mg obtained by cutting one expanded particle into a plurality of particles may be used for the measurement. However, this cut sample is obtained by cutting one foamed particle using a cutter or the like, but at the time of cutting, the surface of the foamed particle that is originally provided is left without being cut, and each cut sample It is preferable that the foamed particles are cut so as to have the same shape as much as possible, and in each cut sample, the area of the surface of the expanded particles remaining without being cut is as much as possible. For example, when the weight per expanded particle is 18 mg, if the expanded particle oriented in an arbitrary direction is cut horizontally from the middle of the vertical direction, two approximately 9 mg cut samples having substantially the same shape are obtained. In each cut sample, the surface of the expanded particles from the beginning is left as it is, and the area of the surface is almost the same in each cut sample. One of the two cut samples thus obtained may be used for the measurement of the intrinsic peak and the high temperature peak as described above. In the present specification, when simply expressed as “high temperature peak of foamed particles”, the heat quantity of the high temperature peak obtained by the above measurement is referred to, and this is the surface layer of the foamed particles described later. The amount of heat at the high temperature peak for the portion and the amount of heat at the high temperature peak for the inner foam layer portion are different.

This high temperature peak b is observed in the first DSC curve measured as described above, but after obtaining the first DSC curve, it is once around 40 ° C. at 220 ° C. to 10 ° C./min. It is not recognized in the second DSC curve obtained when the temperature is lowered to (40 to 50 ° C.) and again raised to 220 ° C. at 10 ° C./min. In the second DSC curve, only the intrinsic peak a corresponding to the endotherm when the base resin is melted as shown in FIG. 2 is recognized.
The temperature at the peak of the intrinsic peak a appearing in the first DSC curve of the expanded particles is usually in the range of [Tm−5 ° C.] to [Tm + 5 ° C.] based on the melting point (Tm) of the base resin. (Most commonly appears in the range of [Tm−4 ° C.] to [Tm + 4 ° C.]). Further, the temperature at the apex of the high temperature peak b appearing in the first DSC curve of the expanded particles usually appears in the range of [Tm + 5 ° C.] to [Tm + 15 ° C.] based on the melting point (Tm) of the base resin. (Most commonly appears in the range of [Tm + 6 ° C.] to [Tm + 14 ° C.]). In addition, the temperature at the top of the intrinsic peak a observed in the second DSC curve of the expanded particles (temperature corresponding to the melting point of the base resin) is usually [ Tm-2 ° C.] to [Tm + 2 ° C.].

As described above, the EPP particles preferably have a crystal structure in which a high temperature peak appears in the first DSC curve in DSC measurement. However, the amount of heat of the high temperature peak is strongly influenced by the difference between the melting point and the foaming temperature of the resin. The
The high temperature peak heat quantity of the EPP particles acts as a factor that determines the minimum fusion temperature, particularly with respect to the fusion between the EPP particles. The minimum fusion temperature here means a temperature that gives the lowest saturated steam pressure necessary for the EPP particles to fuse together in the mold. The high temperature peak calorific value is closely related to this minimum fusing temperature, and when the same base resin is used, the minimum fusing temperature is lower when the high temperature peak calorific value is larger than when the high temperature peak calorific value is large. There is a tendency to be lower. The value of the high temperature peak heat quantity is strongly influenced by the foaming temperature applied to the resin in the production stage of the EPP particles. When the same base resin is used, the high temperature peak heat quantity is lower than when the foaming temperature is lower. The value tends to be smaller.
However, when obtaining an EPP molded product using EPP particles having a small high-temperature peak heat amount, the minimum fusing temperature tends to be relatively low, but the strength physical properties such as compression strength (rigidity) of the EPP molded product are relatively high. Tend to decline. On the other hand, when an EPP molded product is obtained using expanded particles having a high high-temperature peak heat quantity, the strength properties such as the compression strength of the EPP molded product tend to be relatively high, but the minimum fusion temperature is relatively high. As described above, there is a problem in that steam with high pressure may be required when manufacturing an EPP compact as described above. That is, the most preferred foamed particles are foamed particles having the opposite properties such that the minimum fusing temperature is low and the strength properties such as compressive strength of the EPP molded article are relatively high.

  The foamed particles obtained by Method A are those in which the minimum fusing temperature is effectively reduced even when the high-temperature peak heat quantity is large. When a foamed particle molded body is produced using the foamed particles, a molded body having practical strength in mechanical properties such as compressive strength can be obtained.

  Foamed particles having a high temperature peak in the DSC curve are the melting end temperature (Te) of the base resin constituting the surface-modified resin particles when the surface-modified resin particles are dispersed in a dispersion medium and heated in a closed container. Without increasing the temperature above, stop at an arbitrary temperature (Ta) that is 20 ° C. lower than the melting point (Tm) of the base resin and lower than the melting end temperature (Te), and that temperature (Ta) is sufficient Held for about 10 to 60 minutes, and then adjusted to an arbitrary temperature (Tb) in the range of 15 ° C. lower than the melting point (Tm) to the end of melting temperature [(Te) + 10 ° C.] The surface-modified resin particles can be obtained by foaming by releasing the surface-modified resin particles from the inside of the sealed container under a low pressure after holding at this temperature for a further sufficient time, preferably about 10 to 60 minutes, if necessary.

The melting point (Tm) is a differential scanning calorimetry of the resin particles in the same manner as the DSC curve of the expanded particles as described above using 2 to 4 mg of the resin particles as a sample. This is the temperature at the apex of the endothermic curve peak a unique to the base resin found in the second DSC curve (an example of which is shown in FIG. 2), and the melting end temperature (Te) is the inherent temperature. This is the intersection (β) between the DSC curve on the high temperature side of the endothermic curve peak a and the high temperature side base line (BL).
The endothermic curve peak appearing in the second DSC curve for the resin particles usually appears as one endothermic curve peak on the premise that it is a peak based on melting of the polypropylene resin. However, when it consists of a mixture of two or more polypropylene resins, two or more endothermic peaks are rarely observed. In that case, a straight line that passes through the apex of each peak and is parallel to the vertical axis of the graph (perpendicular to the horizontal axis) is drawn, and the length from the peak apex to the baseline BL is measured on each straight line. The peak apex on the straight line having the longest length is defined as Tm. However, when there are two or more straight lines of the same degree and the longest straight line cannot be specified, the peak apex on the highest temperature side is defined as Tm.

  The amount of heat of the high temperature peak in the expanded particles is mainly determined by the temperature (Ta), the retention time at the temperature, the temperature (Tb), the retention time at the temperature, and the retention time for the resin particles when the expanded particles are produced. Depends on the heating rate. The amount of heat at the high temperature peak of the expanded particles tends to increase as the temperature (Ta) or (Tb) falls within the above temperature range or as the holding time increases. Usually, 0.5 to 5 ° C./min is employed as the rate of temperature rise during heating (average rate of temperature rise from the start of heating to the start of temperature holding). By repeating the preliminary experiment in consideration of these points, it is possible to easily know the production conditions for the expanded particles exhibiting a desired high-temperature peak heat quantity.

  In addition, the temperature range demonstrated above is a suitable temperature range at the time of using an inorganic type physical foaming agent as a foaming agent. When an organic physical foaming agent is used in combination, the appropriate temperature range shifts to a lower temperature side than the above temperature range depending on the type and amount of use.

  As described above, the EPP particles, which are obtained from the surface modified resin particles obtained by modifying the surface of the present resin particles by decomposing the organic peroxide and can be molded with low-temperature steam, have the following structural uniqueness. It has been found from the measurement results that it has the property.

  When the high temperature peak heat quantity was measured by dividing the surface layer portion of the expanded particles and the internal expanded layer portion not including the surface layer portion, the high temperature peak heat amount (ΔHs) of the surface layer portion of the expanded particles not surface-modified and the internal expanded layer Whereas the relationship with the amount of heat (ΔHi) of the high-temperature peak of the part was such that ΔHs ≧ ΔHi × 0.87, the expanded particles obtained by Method A had ΔHs <ΔHi. It was observed to be x0.86. Expanded particles that can be molded with low-temperature steam have a relationship of ΔHs <ΔHi × 0.86, preferably ΔHs <ΔHi × 0.83, and ΔHs <ΔHi × 0.80. Is more preferable, ΔHs <ΔHi × 0.75 is further preferable, ΔHs <ΔHi × 0.70 is particularly preferable, and ΔHs <ΔHi × 0.60 is satisfied. Most preferred. ΔHs is preferably ΔHs ≧ ΔHi × 0.25. When ΔHs <ΔHi × 0.86, in-mold molding can be performed at a lower temperature than expanded particles that are not surface-modified. ΔHs is preferably 1.7 J / g to 60 J / g, more preferably 2 J / g to 50 J / g, and particularly preferably 3 J / 9 to 45 J / g. It is most preferable that it is / 9-40J / 9.

  The high temperature peak calorific value of the surface layer portion of the expanded particle can be obtained by performing the same operation as the measurement of the high temperature peak heat amount of the expanded particle described above except that the surface layer portion of the expanded particle is cut out and 2 to 4 mg is collected and used as a sample. . In addition, the high temperature peak calorific value of the internal foamed layer portion of the foamed particle is cut out from the inside of the foamed particle so as not to include the surface layer portion, and 2 to 4 mg is collected and used as a sample to measure the high temperature peak calorific value of the foamed particle described above The same operation can be performed.

A method for preparing a sample when the high temperature peak calorific value is measured by dividing the foamed particle into a surface layer portion and an internal foam layer portion not including the surface layer portion is as follows.
The surface layer portion of the expanded particle may be sliced using a cutter knife, a microtome, etc., and the surface layer portion may be collected and used for measurement. However, the surface of the foamed particle always exists on the entire surface of the surface layer portion of the sliced foamed particle, but on the back surface of the surface layer portion of the sliced foamed particle, the surface of the foamed particle faces the center of gravity of the foamed particle. In other words, the surface of the expanded particle is sliced from one or a plurality of points selected at random so that a part exceeding 200 μm is not included. If the back surface of the surface layer portion of the sliced foamed particle includes a part exceeding 200 μm from the surface of the foamed particle toward the center of gravity of the foamed particle, it will contain a large amount of the internal foamed layer part and the melting point of the surface layer part. In addition, there is a possibility that the high temperature peak heat quantity cannot be measured accurately. In addition, when the surface layer part obtained from one expanded particle is less than 2-4 mg, what is necessary is just to collect the required amount surface layer part by repeating the said operation using several expanded particle.

  On the other hand, the inner foamed layer portion that does not include the surface layer portion of the foamed particle is such that the surface of the foamed particle and the portion between the surface of the foamed particle and 200 μm from the surface of the foamed particle toward the center of gravity of the foamed particle are not included. What is necessary is just to use for the melting | fusing point and high temperature peak calorie | heat amount measurement using what cut off the surface layer part from the whole surface. However, if the size of the expanded particles is too small and the 200 μm portion is removed from the above surface, the internal expanded layer portion disappears. From the expanded particle surface to the center of gravity of the expanded particle from the expanded particle surface When the surface layer portion is cut from the entire surface of the expanded particle so that the portion between 100 μm is not included, and the inner expanded layer portion is still lost, the expanded particle The surface of the foamed particle is cut out from the entire surface of the foamed particle so that the portion between the surface of the foamed particle and the portion between the surface of the foamed particle and the center of gravity of the foamed particle is 50 μm is not used. In addition, what is necessary is just to collect a required amount of internal foamed layer parts by repeating the said operation using several foamed particles, when the internal foamed layer part obtained from two foamed particles is less than 2-4 mg.

  Further, when MFR was measured, it was observed that the MFR value was the same as or larger than the MFR value of the resin particles before surface modification. In the present invention, the MFR value of the expanded particles is preferably 1.2 times or more, more preferably 1.5 times or more of the MFR value of the resin particles before surface modification. Most preferably, it is 8 to 3.5 times. The MFR value of the expanded particles is preferably 0.5 to 150 g / 10 minutes considering the heat resistance of the EPP molded product and the expansion efficiency at the time of manufacturing the expanded particles, and preferably 1 to 100 g / 10. It is more preferable to make the minute, more preferably 10 to 80 g / 10 minutes.

  The MFR of the above-mentioned expanded particles is a press sheet having a thickness of 0.2 mm to 1 mm prepared on a heated press machine in which the temperature of the expanded particles is adjusted to 200 ° C., and a sample is cut out from the sheet in a pellet shape or a rod shape. It is the value which measured by the method similar to the measurement of MFR of the said uncrosslinked propylene-type resin using. Incidentally, in order to obtain an accurate MFR measurement value of the expanded particles, it is necessary to avoid mixing of bubbles and the like into the sample. If air bubbles are unavoidably mixed, a press sheet can be prepared for the purpose of defoaming with a hot press machine within the range of repeating the same sample up to 3 times.

Further, the foamed particles obtained by the method A form a modified surface containing a slight amount of oxygen due to the addition action of the organic peroxide, particularly when an organic peroxide that generates oxygen radicals is used. This is clear from the analysis of the surface of the expanded particles obtained by the method of the present invention and the surface of the EPP molded product produced therefrom. Specifically, the surface of the EPP molded body produced from the foamed particles obtained by the method A (ie, substantially the same as the surface of the foamed particles) and the EPP produced from the conventional non-surface-modified foamed particles. As a result of comparing each surface of the molded body by ATR measurement (total reflection absorption measurement method), the surface of the EPP molded body produced from the expanded particles obtained by Method A newly has a difference in absorption around 1033 cm ^−1. It was confirmed that there was a change such as addition or insertion of oxygen alone or a functional group containing oxygen. Specifically, when both peak heights in absorption at 1166 cm ⁻¹ (the absorption peak height for the molded body from the foamed particles obtained by Method A and the absorption peak height for the conventional molded body) are made the same, The height of the absorption peak near 1033 cm ^{−1 on the} surface of the molded body from the expanded particles obtained in A is higher than the height of the absorption peak near 1033 cm ^{−1 on the} surface of the conventional molded body. Furthermore, as a result of elemental analysis using an EDS (energy dispersive analyzer) as a surface observation of the expanded particles, the ratio of oxygen to carbon was 0.2 (mol / mol) in the case of expanded particles obtained by Method A. On the other hand, in the case of the conventional expanded particle, it was 0.09 (mol / mol). From such a viewpoint, in the present invention, the ratio of oxygen to carbon on the surface of the expanded particles is preferably 0.15 or more.
From the above, it is clear that a modified surface containing a slight amount of oxygen is formed by the addition action of the organic peroxide. The formation of such a modified surface is believed to favor steam permeability during molding. The EPP particles obtained by the method A described above have a reduced high-temperature peak heat amount on the modified surface containing oxygen and / or a surface layer portion of the expanded particles or / and a decreased extrapolated melting start temperature on the expanded particle surfaces. Therefore, it is estimated that the minimum fusing temperature is greatly reduced.

The EPP particles obtained by the above-mentioned method A are aged under atmospheric pressure, and after increasing the bubble internal pressure as necessary, by heating with steam or hot air, Is possible.
In the method for producing an EPP molded body according to the present invention, the EPP particles are filled in a mold that can be heated and cooled and that can be opened and closed and sealed, after increasing the internal pressure of the bubble, and supplying saturated steam. It is possible to carry out by adopting a batch molding method in which the EPP particles are heated and expanded in the mold to be expanded and fused, and then cooled and taken out from the mold. As a molding machine used in the batch molding method, a number of molding machines already exist all over the world, and the pressure resistance is 0.41 MPa (G) or 0.45 MPa (G) although it varies slightly depending on the country. There are many things. Therefore, the pressure of the saturated steam when the EPP particles are expanded and fused is preferably 0.45 MPa (G) or less, and more preferably 0.41 MPa (G) or less. .

  Further, in the method for producing an EPP molded body according to the present invention, the EPP particles are continuously supplied between the belts that continuously move along the upper and lower sides in the passage after increasing the bubble internal pressure as necessary. When passing through the steam supply region (heating region), the EPP particles are expanded and fused together, then cooled by passing through the cooling region, and then the resulting molded product is taken out from the passage and sequentially cut to an appropriate length. Can be produced by a continuous molding method (for example, molding methods described in JP-A-9-104026, JP-A-9-104027, JP-A-10-180888, etc.). In this method, the inside of the passage is in the mold.

  In order to increase the bubble internal pressure of the EPP particles, the foamed particles are put in a sealed container, and the pressurized gas is allowed to permeate into the foamed particles by leaving the container in a state where the pressurized gas is supplied. That's fine. The gas supplied under pressure can be used without any problem as long as the main component is an inorganic gas that does not liquefy or solidify under the required pressure, but is further selected from the group consisting of nitrogen, oxygen, air, carbon dioxide, and argon. Alternatively, those mainly composed of two or more inorganic gases are particularly preferably used, and among them, nitrogen and air are preferable in consideration of environmental load and cost.

The internal pressure P (MPa) of the expanded particles whose internal pressure is increased is measured by the following operation. Here, an example is shown in which the internal pressure of EPP particles is increased using air.
First, EPP particles used for molding are placed in a closed container, and pressurized air is supplied into the container (usually, the air pressure in the container is maintained within a range of 0.98 to 9.8 MPa as a gauge pressure). ) The internal pressure of the EPP particles can be increased by allowing the air to permeate into the EPP particles by leaving the supplied state for an appropriate time. The EPP particles whose internal pressure has been sufficiently increased are supplied into a mold of a molding machine. The internal pressure of the EPP particles is determined by performing the following operation using a part of the EPP particles immediately before in-mold molding (hereinafter referred to as the expanded particle group).

  70 mm × with a large number of needle holes of a size that allows foam particles to pass through, but allows air to pass freely within 60 seconds after taking out the foam particles just before in-mold molding with increased internal pressure from the pressurized tank It is housed in a polyethylene bag of about 100 mm and moved to a temperature-controlled room under an atmospheric pressure with an air temperature of 23 ° C. and a relative humidity of 50%. Subsequently, the weight is read on a balance in the temperature-controlled room. The weight is measured 120 seconds after the above expanded particle group is taken out from the pressurized tank. The weight at this time is defined as Q (g). The bag is then left in the same greenhouse for 48 hours. Since the pressurized air in the expanded particles permeates through the cell membrane and escapes to the outside as time passes, the weight of the expanded particles decreases accordingly, and after 48 hours, the weight has reached equilibrium. Stabilize. After 48 hours, the weight of the bag is measured again, and the weight at this time is defined as U (g). Then, immediately, take out all the foam particles from the bag in the same temperature chamber and read the weight of the bag alone. Let the weight be Z (g). Any of the above weights shall be read up to 0.0001 g. The difference between Q (g) and U (g) is the increased air amount W (g), and the internal pressure P (MPa) of the expanded particles is calculated by the following equation (2). The internal pressure P corresponds to a gauge pressure.

P = (W ÷ M) × R × T ÷ V (2)
However, in the formula (2), M is the molecular weight of air, and here, a constant of 28.8 (g / mol) is adopted. R is a gas constant, and here, a constant of 0.0083 (MPa · L / (K · mo1)) is adopted. T means an absolute temperature, and since an atmosphere of 23 ° C. is adopted, it is a constant of 296 (K) here. V means a volume (L) obtained by subtracting the volume of the base resin in the expanded particle group from the apparent volume of the expanded particle group.

The apparent volume (L) of the expanded particle group was determined by submerging the entire amount of the expanded particle group taken out of the bag after 48 hours into water in a measuring cylinder containing 100 cm ^{3 of} 23 ° C. water in the same constant temperature room. The volume V (cm ³ ) of the expanded particle group is calculated from the scale at the time of making it, and this is obtained by converting this to liter (L) units. The apparent expansion ratio of the expanded particle group is determined by dividing the base resin density (g / cm ³ ) by the apparent density (g / cm ³ ) of the expanded particle group. The apparent density (g / cm ³ ) of the expanded particle group is obtained by dividing the weight of the expanded particle group (difference between U (g) and Z (g)) by the volume V (cm ³ ).
In the above measurement, the foamed particle group weight (difference between U (g) and Z (g)) is 0.5000 to 10.0000 g and the volume V is 50 to 90 cm ^3. A group of expanded particles is used.

The internal pressure in the bubbles of the EPP particles is preferably 0 to 0.5 MPa, more preferably 0 to 0.3 MPa, and most preferably 0 to 0.1 MPa.
If the bubble internal pressure becomes too high, the secondary foaming force at the time of molding becomes excessive, impeding the penetration of saturated steam into the molded body, resulting in insufficient temperature at the center of the molded body, and mutual melting of EPP particles. Wearing tends to be bad.
The apparent density of the EPP molded body produced by the above method can be arbitrarily selected depending on the purpose, but is usually in the range of 9 g / L to 600 g / L. The apparent density of the EPP compact is the apparent overall density as defined in JIS K 7222 (1999). However, the volume of the molded body used for calculating the apparent overall density is the volume calculated from the outer dimensions, but if the shape is complex and calculation from the outer dimensions is difficult, the molded body is submerged. Excluded volume is adopted.

Further, a surface decoration material can be laminated and integrated on at least a part of the surface of the EPP molded body. US Pat. No. 5,928,776, US Pat. No. 6,096,417, US Pat. No. 6,033,770, US Pat. No. 5,474,841, European Patent No. 477476, WO 98/34770 No., WO 98/00287, Japanese Patent No. 3092227, and the like.
Further, the insert material can be combined and integrated in the EPP molded body so that all or part of the insert material is embedded. Such insert composite type in-mold foam moldings are described in detail in US Pat. No. 6,033,770, US Pat. No. 5,474,841, Japanese Patent Publication No. 59-127714, Japanese Patent No. 3092227, etc. Are listed.

  The EPP molded article produced as described above preferably has an open cell ratio based on ASTM-D2856-70 Procedure C of 40% or less, more preferably 30% or less, and 25% or less. Most preferably it is. The smaller the open cell ratio, the better the mechanical strength.

  The present invention will be described below with reference to examples and comparative examples.

Examples 1-4, Comparative Examples 1-5
Bubbles containing a foam regulator masterbatch (0.01 parts by weight of zinc borate powder (bubble regulator) per 99 parts by weight of “Resin 1” shown in Table 1 per 99 parts by weight of “Resin 1” shown in Table 1. Conditioner masterbatch) 1.01 parts by weight, and the amounts shown in Tables 2 and 3 for the types of additives shown in Tables 2 and 3 (content per 100 parts by weight of “resin 1” which is the base resin ( The same as in parts by weight)) was added by dry blending, and these were supplied to an extruder, heated, melted and kneaded, and then extruded as a strand from the extruder. The strand is immediately put in water adjusted to 18 ° C. and taken up while being rapidly cooled. After sufficiently cooled, the strand is pulled up from the water and cut to have a length / diameter ratio of about 1.2. Resin particles having an average weight per particle of 2 mg were obtained.

  Next, 100 parts by weight of the resin particles, 300 parts by weight of ion-exchanged water at 18 ° C., 0.005 parts by weight of sodium dodecylbenzenesulfonate (surfactant), 0.3 parts by weight of kaolin powder (dispersant) are added to a 5-liter autoclave. Parts, aluminum sulfate powder (dispersion strengthening agent) 0.01 parts by weight, bis (4-t-butylcyclohexyl) peroxycarbonate (organic peroxide) 1 part by weight, and carbon dioxide in the amounts shown in Tables 2 and 3 (Foaming agent) was charged, and the temperature was raised to 5 ° C. lower than the foaming temperatures shown in Tables 2 and 3 while stirring (average heating rate 3 ° C./min) and held at that temperature for 15 minutes. Next, the temperature was raised to the foaming temperature (average rate of temperature increase of 3 ° C./min) and held at that temperature for 15 minutes. Next, one end of the autoclave was opened, and the contents of the autoclave were released under atmospheric pressure to obtain expanded particles. In addition, it discharged | emitted, supplying nitrogen gas in an autoclave so that the internal pressure of an autoclave during discharge | release of a resin particle from an autoclave might be maintained at the autoclave internal pressure just before discharge | release.

  The obtained foamed particles were cured and dried in an oven at 60 ° C. for 12 hours, and then the high temperature peak heat quantity of the foam particles, the high temperature peak heat quantity of the surface layer portion and the internal foam layer portion, the apparent density of the foam particles, and the like were measured. The results are shown in Tables 2 and 3.

  Next, a slight gap (about 10 mm) was opened in the mold having a molding space of 250 mm × 200 mm × 50 mm without completely closing the mold without applying internal pressure to the foamed particles. After filling in a state (with the direction of the molding space 50 mm being 60 mm), the mold is completely clamped, and after the air in the mold is evacuated with steam, a saturated steam pressure of 0.41 MPa (G) is introduced. Molded. After molding, the molded body in the mold was cooled with water until the temperature reached 100 ° C., then the molded body was taken out of the mold, cured at 60 ° C. for 12 hours, and then cooled to room temperature (23 ° C.). Subsequently, after curing in the room for 14 days, the apparent density, compressive strength, and number of voids on the surface of the molded body were measured. The results are shown in Tables 2 and 3.

The apparent density (g / L) of the expanded particles in Tables 2 and 3 is calculated by dividing the weight of the expanded particles by the apparent volume of the expanded particles. Specifically, after curing, the weight (g) of a plurality of randomly selected expanded particles was measured, and then submerged in water in a measuring cylinder containing 100 cm ³ of water at 23 ° C. From the excluded volume, the apparent volume (cm ³ ) of the expanded particles was read and converted into liters. From this measured value, the apparent density (g / L) of the expanded particles was calculated. For this measurement, expanded particles having a weight of expanded particles of 0.5000 to 10.0000 g and an apparent volume of expanded particles of 50 to 90 cm ³ were used.

Moreover, the compressive strength in Table 2 and Table 3 was measured as follows.
Using a test piece obtained by cutting the molded body to have a length of 50 mm, a width of 50 mm, and a thickness of 25 mm (with the entire surface cut), the test piece temperature in accordance with method A of JIS Z 0234-1976 A compression test was performed until the strain reached 75% under the conditions of 23 ° C. and a load speed of 10 mm / min. The stress at the time of 50% strain was read from the obtained stress-strain diagram, and this was defined as the compressive strength.

Further, the number of voids on the surface of the molded body was measured as follows.
On the surface of the obtained molded body (surface on the side of 250 mm × 200 mm), at a randomly selected location (however, a continuous surface free from defects due to steam holes, filling devices, release pins, and other mold structures) 100 mm × Write a 10 mm ruled line, and count the number of voids whose width in the plane direction exceeds 0.5 mm and the depth in the thickness direction exceeds 0.5 mm within that range (one void). In the case of having these two conditions, it is counted as one), and the number of voids per 10 cm ² was used.

  Further, the glass transition temperature, the melting point of the base resin, the melting point of the foamed particles, and the high temperature peak heat amount in Table 1 were measured using a Shimadzu Shimadzu Corporation Shimadzu heat flux differential scanning calorimeter “DSC-50”. .

The above results indicate the following. Each of Examples 1 to 4 and Comparative Examples 1 to 5 is formed by using surface-modified low temperature moldable polypropylene resin expanded particles. Example 1 and Comparative Example 1 are different from Example 1 in that 0.5 parts by weight of stearic acid, which is an additive targeted in the present invention, is added, whereas Comparative Example 1 is the present invention. The target additive was not added. In Example 1 and Comparative Example 1, except for the presence or absence of additives, other production conditions, the properties of the obtained expanded particles, the apparent density of the molded body, the apparent density of the cut sample for measuring the compressive strength, the compressive strength, etc. Although it is substantially the same, the number of voids on the surface of the molded body is greatly different. In Example 1, as a result of addition of 0.5 part by weight of stearic acid, which is an additive targeted in the present invention, the number of voids on the surface of the molded body was smaller than that of the molded body of Comparative Example 1 that was not added. It can be seen that there is a significant decrease.
In Example 2 and Comparative Example 2, 0.5 parts by weight of magnesium stearate, which is an additive targeted in the present invention, is added in Example 2, whereas in Comparative Example 2, the present invention is added. The additive which is the target in (1) was not added. In Example 2 and Comparative Example 2, except for the presence or absence of additives, other production conditions, the properties of the obtained expanded particles, the apparent density of the molded product, the apparent density of the cut sample for measuring the compressive strength, the compressive strength, etc. Although it is substantially the same, the number of voids on the surface of the molded body is greatly different. In Example 2, as a result of adding 0.5 part by weight of magnesium stearate, which is an additive targeted in the present invention, the number of voids on the surface of the molded body was compared with that of the molded body of Comparative Example 2 that was not added. It can be seen that is significantly reduced.
In Example 3 and Comparative Example 3, 0.5 parts by weight of behenic acid, which is an additive targeted in the present invention, was added in Example 3, whereas Comparative Example 3 was used in the present invention. The target additive was not added. In Example 3 and Comparative Example 3, except for the presence or absence of additives, other production conditions, the properties of the obtained expanded particles, the apparent density of the molded product, the apparent density of the cut sample for measuring the compressive strength, the compressive strength, etc. Although it is substantially the same, the number of voids on the surface of the molded body is greatly different. In Example 3, 0.5 parts by weight of behenic acid, which is an additive targeted in the present invention, was added. As a result, the number of voids on the surface of the molded body was smaller than that of the molded body of Comparative Example 3 that was not added. It can be seen that there is a significant decrease.
In Example 4 and Comparative Example 4, 0.5 parts by weight of stearamide, which is an additive targeted in the present invention, is added in Example 4, whereas in Comparative Example 4, the present invention is added. The additive which is the target in (1) was not added. In Example 4 and Comparative Example 4, except for the presence or absence of additives, other production conditions, the properties of the obtained expanded particles, the apparent density of the molded product, the apparent density of the cut sample for measuring the compressive strength, the compressive strength, etc. Although it is substantially the same, the number of voids on the surface of the molded body is greatly different. In Example 4, as a result of addition of 0.5 part by weight of stearic acid, which is an additive targeted in the present invention, the number of voids on the surface of the molded body was smaller than that of the molded body of Comparative Example 4 that was not added. It can be seen that there is a significant decrease.
The comparative example 5 shows the example which used the usage-amount of stearic acid in Example 1 exceeding 0.9 weight part which is the upper limit of this invention (1.0 weight part). As a result, in Comparative Example 5, in comparison with Example 1, a reduction in the expansion ratio (increase in apparent density) of the expanded particles was observed, and a decrease in the compression strength of the molded article was observed.

FIG. 1 is a drawing showing an example of a first DSC curve chart of polypropylene resin expanded particles having a high temperature peak. FIG. 2 is a drawing showing an example of a second DSC curve chart of polypropylene resin particles.

Explanation of symbols

a Inherent endothermic curve peak derived from the heat of fusion of the base resin found in the first DSC curve (inherent peak)
b Endothermic curve peak that appears on the higher temperature side than the temperature at which the intrinsic peak a appears (high temperature peak)

Claims (2)

The polypropylene resin particles are dispersed in a dispersion medium in which an organic peroxide is present, and the dispersion medium is at a temperature lower than the melting point of the base resin of the polypropylene resin particles and the organic peroxide is substantially decomposed. A surface modification step of obtaining substantially non-crosslinked surface-modified resin particles by decomposing the organic peroxide while maintaining the temperature, and foaming the surface-modified resin particles using a foaming agent In the polypropylene resin foamed particles obtained by the foaming step to obtain substantially uncrosslinked foamed particles,
The base resin contains 0.01 to 0.9 parts by weight of one or more selected from the group consisting of fatty acids having 10 to 22 carbon atoms, amides of the fatty acids, esters of the fatty acids, and metal salts of the fatty acids. A polypropylene resin expanded particle characterized by the above. It is a substantially non-crosslinked foamed particle having a polypropylene resin as a base resin, and has an endothermic curve peak on the higher temperature side than the endothermic curve peak derived from the heat of fusion of the base resin in the DSC curve by differential scanning calorimetry. The amount of heat (ΔHs) of the endothermic curve peak existing on the high temperature side of the surface layer portion of the expanded particle and the amount of heat (ΔHi) of the endothermic curve peak existing on the high temperature side of the inner expanded layer portion of the expanded particle are ΔHs. In the polypropylene resin expanded particles of <ΔHi × 0.86,
0.01 to 0.9 parts by weight of one or more selected from the group consisting of fatty acids having 10 to 22 carbon atoms, amides of the fatty acids, esters of the fatty acids, and metal salts of the fatty acids. Polypropylene-based resin expanded particles characterized by containing.

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