JP4129951B2 - Polypropylene surface modified resin particles - Google Patents

Description

【００７７】
実施例２〜４、比較例１
ポリプロピレン単独重合体（ガラス転移点：−２１℃、ビカット軟化点：１４８℃、融点：１６３℃、結晶化温度は１１８℃、ＭＦＲ：８ｇ／１０分）１００重量部当り、ホウ酸亜鉛粉末（気泡調整剤）０．０５重量部を添加して押出機内で溶融混練した後、押出機からストランド状に押出し、押出し後Ｘ秒後（表２中ではＸと表示）に、そのストランドを水槽中の冷却媒体（表２に示す温度に調節された水）中に沈めて冷却しながら引き取り、表２に示す時間（表２中では冷却時間と表示）冷却した後、冷却媒体中から引き上げ、長さ／直径比が略１．０になるようにストランドを切断して、１粒子当りの平均重量が２ｍｇの樹脂粒子を得た。尚、上記水槽中の冷却媒体の収容量は１７０リットルであった。得られた樹脂粒子に対し、ΔＨ_a及びΔＨ_bを測定した。その結果を表２に示す。
【００７８】
次いで４００リットルのオートクレーブに、上記樹脂粒子１００重量部、分散媒体として２３℃のイオン交換水２２０重量部、ドデシルベンゼンスルホン酸ナトリウム（界面活性剤）０．００５重量部とカオリン粉末（分散剤）０．３重量部と硫酸アルミニウム粉末（分散強化剤）０．０１重量部、有機過酸化物としてビス（４−ｔ−ブチルシクロヘキシル）パーオキシジカーボネート（1時間半減期温度：５８℃、1分間半減期温度：９２℃）及び表２に示す量の炭酸ガス（発泡剤）を仕込み、密閉状態で攪拌しながら表２に示す発泡温度よりも５℃低い温度まで昇温して（平均昇温速度３℃／分）からその温度で１５分間保持した。次いで、発泡温度まで昇温して（平均昇温速度３℃／分）同温度で１５分間保持した。次いで、オートクレーブの一端を開放してオートクレーブ内容物を大気圧下に放出して発泡粒子を得た。尚、樹脂粒子をオートクレーブから放出する間のオートクレーブ内圧力が、放出直前のオートクレーブ内圧力に保たれるように、オートクレーブ内に高圧の炭酸ガスを供給しながら放出を行った。得られた発泡粒子を水洗し遠心分離機にかけたのち、得られた発泡粒子を水洗し遠心分離機にかけたのち、室温２３℃の大気圧下に４８時間放置して養生した後、実施例１と同様にして発泡粒子の全体の高温ピーク熱量、発泡粒子の見かけ密度を測定した。それらの結果等を表２に示した。
【００７９】
尚、実施例２〜４及び比較例１で得られた発泡粒子は、いずれも無架橋であった（前記沸騰キシレン不溶分はいずれも０であった）。次いで、この発泡粒子を、耐圧容器内の加圧空気下に置いて発泡粒子に高められた気泡内圧を付与した後、表２に示す気泡内圧（表中では発泡粒子内圧と表示）の時に、２５０ｍｍ×２００ｍｍ×５０ｍｍの成形空間を持つ金型内に、金型を完全に閉鎖せずに僅かな隙間（約１ｍｍ）を開けた状態で（成形空間５０ｍｍの方向が５１ｍｍの状態で）充填した後、完全に型締めしてから、排気後、実施例１と同様にして表２に示す最低融着温度（最低飽和スチーム圧力）で成形した。
【００８０】
【表２】

【００８１】
以上の結果は、有機過酸化物が存在する水性媒体中にポリプロピレン系樹脂粒子を分散させると共に、該ポリプロピレン系樹脂粒子の基材樹脂融点よりも低温であって且つ該有機過酸化物が分解する温度下で該有機過酸化物を分解させることによって該ポリプロピレン系樹脂粒子の表面を改質して無架橋の表面改質粒子を得る工程を行なうと、それから得られた発泡粒子は、ポリプロピレン系樹脂のリサイクル性を維持しながら成形温度が低減されることを示している。より具体的には次の通りである。
【００８２】
実施例２、３、４と比較例１は、発泡粒子の見かけ密度がほぼ同じでありしかも、発泡粒子の全体の高温ピーク熱量及び内圧がほぼ同等であり、得られた成形体の見かけ密度が同じであるから対比するのに好都合である。実施例２、３、４と比較例１の対比より、比較例１における最低融着温度は０．４８ＭＰａ（Ｇ）であるのに対し、実施例２、３、４における最低融着温度は、それぞれ、０．４１ＭＰａ（Ｇ）、０．４３ＭＰａ（Ｇ）、０．４５ＭＰａ（Ｇ）となっている。
以上のことから、実施例４は比較例１に比べて最低融着温度が約２℃低下されていることが分り、実施例３は比較例１に比べて最低融着温度が約３．５℃低下されていることが分り、実施例２は比較例１に比べて最低融着温度が約５℃低下されていることが分る。
実施例２〜４及び比較例１の結果より、表面改質の条件が同じ場合には、ΔＨ_a／ΔＨ_bの比が小さいほど、最低融着温度の低減に寄与していることが分る。
【００８３】
【発明の効果】
本発明は、ΔＨ_a／ΔＨ_b比が０．９５以下のポリプロピレン系樹脂粒子であるから、この樹脂粒子に対して前記表面改質を行なった際に、効率よく表面改質を行なうことができる。そして、そのように表面改質された樹脂粒子（表面改質粒子）から得られる発泡粒子は、無架橋であって、成形温度が従来よりも低減されているので、より少ないエネルギーで成形が可能である。従来は、ＥＰＰ成形体の高剛性等の高物性化のためには融点の高いポリプロピレン系樹脂を使用して得られた、高温ピーク熱量の高い発泡粒子を使用しなければならないため必然的に成形温度が汎用の成形機の耐圧を超えてしまうという問題があったが、前記表面改質粒子から得られる発泡粒子では、融点の高いポリプロピレン系樹脂を使用して得られた、高温ピーク熱量の高い発泡粒子であっても、得られるＥＰＰ成形体の高剛性を維持したまま、従来よりも低温度のスチームで成形が可能となり、表面改質が充分であれば汎用の成形機の耐圧以内での成形も可能となる。従って、本発明の方法により得られた発泡粒子を使用すれば、従来よりも安価に高物性（高剛性）又は／及び軽量のＥＰＰ成形体を提供することが可能となる。また、表面改質された樹脂粒子、その発泡粒子、その成形体はいずれも無架橋であるから、ポリプロピレン系樹脂の環境適性及びリサイクル性を阻害しないので好ましい。
【図面の簡単な説明】
【図１】図１は、高温ピークをもつポリプロピレン系樹脂発泡粒子の、第１回目のＤＳＣ曲線のチャートの一例を示す図である。
【図２】図２は、ポリプロピレン系樹脂粒子の第２回目のＤＳＣ曲線のチャートの一例を示す図である。
【図３】図３は、実施例１と参考例１に基づく各例で得られた発泡粒子表面に対するマイクロ熱機械分析に基づくμＤＴＡ曲線の一例を示す図である。
【図４】図４は、他の実施例で得られた発泡粒子表面に対するマイクロ熱機械分析に基づくμＤＴＡ曲線の一例を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention is a polypropylene type suitable for producing polypropylene resin expanded particles. Surface modification Resin grain For child Related.
[0002]
[Prior art]
In recent years, due to the movement of integration of plastic materials, polypropylene resin in particular has excellent mechanical strength, heat resistance, processability, price balance, and excellent properties such as easy incineration and easy recyclability. Since then, the field of use is expanding.
Similarly, an uncrosslinked polypropylene resin-in-mold foam molded product (hereinafter sometimes referred to as “EPP molded product”, “foamed particle molded product”, or simply “molded product”) exhibits the excellent properties of the polypropylene resin. Without loss, characteristics such as buffering properties and heat insulating properties can be added, and therefore, they are widely used as packaging materials, building materials, heat insulating materials and the like.
[0003]
Recently, however, there are more opportunities for higher functionality than ever before. For example, for automotive applications, focusing on the excellent properties of EPP molded products, there have been a wide range of uses such as bumper cores, door pads, pillars, tool boxes, floor mats, etc. There has been a demand for weight reduction of vehicles, and at the same time, there has been a strong demand for weight reduction of parts constituting the vehicles. Even if it is an EPP molded object, it is not an exception, and the lighter weight EPP molded object has been calculated | required, maintaining conventional rigidity, shock absorbing property, and impact energy absorption. Further, for example, as a shipping box such as a fish box, a polystyrene resin in-mold foam molded product (hereinafter referred to as “EPS molded product”) is often used because of its high rigidity and low cost. It was. However, since the EPS molded body is inferior in impact resistance and heat resistance compared to the EPP molded body, it is difficult to repeatedly use it. In recent years, there have been many requests to use an EPP molded product that can be used repeatedly and with excellent environmental compatibility due to the growing awareness of environmental issues in public opinion. It has been desired.
[0004]
By the way, in order to obtain a highly rigid EPP molded product, some improvements have been made so far, for example, using a highly rigid polypropylene resin as a raw material. As a 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. By using these raw materials, It was 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 rises at the same time as rigidity. When these high-rigidity raw materials are used, an increase in processing temperature for obtaining an EPP molded body, It was a rise. Conventionally, a molding machine for producing an EPP molded body has a structure corresponding to a high molding temperature, that is, a structure that can withstand high-pressure steam. In order to produce a highly rigid EPP molded product using rigid non-crosslinked polypropylene resin expanded particles (hereinafter sometimes referred to as “EPP particles” or simply “expanded particles”), In many cases, steam having a pressure higher than the pressure resistance of the molding machine is required, and it is difficult to obtain a sufficient fusion rate between the expanded particles. Actually, since there are limited molding machines that can obtain an EPP molded body that maintains a sufficient fusion rate and can support production, EPP particles that can be molded with steam at a lower temperature (low pressure) are obtained. A method was desired.
[0005]
Conventionally, a method for obtaining a highly rigid EPP molded body using a propylene-based copolymer resin composed of propylene and a comonomer such as ethylene or butene has been devised. 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. This is a method in which 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 foamed particles obtained by these methods are used, as in the case of trying to obtain a highly rigid EPP molded body using the highly rigid EPP particles obtained from the highly rigid polypropylene resin as described above, In particular, it causes an increase in molding temperature, often requires steam at a pressure exceeding the pressure resistance of a molding machine for producing an EPP molded body, and a sufficient value is obtained for the fusion rate between the expanded particles. There is a problem that it is difficult. In reality, since there are a limited number of molding machines that can obtain an EPP molded body that maintains a sufficient fusion rate and can support production, a method of obtaining EPP particles that can be molded with lower temperature steam is desirable. It had been. The present applicant disperses the polypropylene resin particles in a dispersion medium in which an organic peroxide is present, and the dispersion liquid has a temperature lower than the base resin melting point of the polypropylene resin particles and the organic peroxide. A substantially non-crosslinked surface modification formed by decomposing the organic peroxide while maintaining the temperature at which the product is substantially decomposed resin It has been found that the expanded particles obtained from the particles can achieve fusion between the expanded particles with low-temperature steam and give an EPP molded body having excellent rigidity, and the application has been completed earlier (Patent Document 4). reference).
[0006]
[Patent Document 1]
International Publication No. 96/31558 Pamphlet
[Patent Document 2]
Japanese Patent No. 2886248
[Patent Document 3]
JP-A-11-156879
[Patent Document 4]
JP 2002-167460 A
[0007]
[Problems to be solved by the invention]
INDUSTRIAL APPLICABILITY The present invention is a polypropylene suitable for the production of non-crosslinked polypropylene-based resin expanded particles that can achieve fusion between expanded particles with low-temperature steam and give a highly rigid (high compression strength) expanded particle molded body. system Surface modification Resin grain Child The issue is to provide.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, according to this invention, the manufacturing method of the polypropylene resin particle and polypropylene resin particle shown below is provided.
(1) In the dispersion medium in which the organic peroxide is present, Polypropylene resin particles whose base resin is a polypropylene resin having a melting point of 158 ° C. or higher Obtained by dispersing the organic peroxide by maintaining the dispersion medium at a temperature lower than the melting point of the base resin of the polypropylene resin particles and at a temperature at which the peroxide decomposes. , Surface-modified resin particles for producing expanded particles And the Surface modification Immediately after heating the resin particles from 30 ° C. to 200 ° C. at a rate of 10 ° C./min (first heating) with a differential scanning calorimeter, the resin particles are cooled from 200 ° C. to 30 ° C. at a rate of −10 ° C./min. Immediately after that, when heating again from 30 ° C. to 200 ° C. at a rate of 10 ° C./min (second heating), the amount of heat of the endothermic curve peak appearing in the DSC curve during the first heating (ΔHa ) And the calorific value (ΔHb) of the endothermic curve peak appearing in the DSC curve at the time of the second heating (ΔHa / ΔHb) is 0.95 or less. Surface modification Resin particles.
( 2 ) ΔHa / ΔHb is 0.85 or less (1) Polypropylene described Surface modification Resin particles.
( 3 ) The resin particles are columnar particles having a ratio (L / D) of length (L) to average diameter (D) of 0.5 to 2, and the average weight per particle is 0.1 to 2 20 mg, characterized in that (1) or (2) Polypropylene as described in Surface modification Resin particles.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Polypropylene system of the present invention Surface modification The polypropylene resin which is a base resin of resin particles (hereinafter sometimes referred to as “the base resin”) contains a polypropylene homopolymer or a propylene component in an amount of 60 mol% or more (preferably 80 mol of the propylene component). %) Or a copolymer of propylene and another comonomer, or a mixture of two or more selected from these resins.
[0010]
Examples of the copolymer of propylene containing 60 mol% or more of a propylene component with another comonomer include, for example, ethylene-propylene random copolymer, ethylene-propylene block copolymer, propylene-butene random copolymer, ethylene-propylene-butene random copolymer, etc. Is exemplified.
[0011]
The melting point of the base resin must be 158 ° C. or higher in order to increase mechanical properties such as compressive strength of the final EPP molded product, but is preferably 158 ° C. to 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).
[0012]
In the present invention, polypropylene Surface modification A synthetic resin other than polypropylene resin and / or an elastomer can be added to the resin particles 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, and most preferably at most 10 parts by weight.
[0013]
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.
[0014]
Examples of the elastomer include ethylene-propylene rubber, ethylene-1-butene rubber, propylene-1-butene rubber, styrene-butadiene rubber and hydrogenated products thereof, isoprene rubber, neoprene rubber, nitrile rubber, or styrene-butadiene block copolymer. Elastomers such as elastomers and hydrogenated products thereof are exemplified.
[0015]
In addition, various additives can be contained in this base resin in the range which does not impair the desired effect of this invention. 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. In addition, these additives may be used in the polypropylene system of the present invention, for example, by cutting a strand extruded by an extruder. Surface modification When producing resin particles (hereinafter sometimes referred to as “present resin particles”), they can be contained in the present resin particles by adding and kneading them to the present base resin melted in an extruder.
[0016]
Polypropylene system of the present invention Surface modification The main feature of the resin particles is that foamed particles that can achieve fusion between the foamed particles with low-temperature steam can be easily produced during molding. That is, the polypropylene resin particles of the present invention are under a nitrogen atmosphere, Surface modification Immediately after heating the resin particles from 30 ° C. to 200 ° C. at a rate of 10 ° C./min (first heating) with a differential scanning calorimeter, the resin particles are cooled from 200 ° C. to 30 ° C. at a rate of −10 ° C./min. Immediately after that, when the heating is again performed from 30 ° C. to 200 ° C. at the rate of 10 ° C./min (second heating), the calorific value (ΔHa) of the endothermic curve peak appearing in the DSC curve during the first heating. And the ratio (ΔHa / ΔHb) of the endothermic curve peak appearing in the DSC curve during the second heating (ΔHb) is 0.95 or less, preferably ΔHa / ΔHb is 0.85 or less. . Although the endothermic curve appearing in the DSC curve during the first heating and the endothermic curve appearing in the DSC curve during the second heating are slightly different, both are shown in FIG. An endothermic curve close to the DSC curve). ΔHa is the area surrounded by the DSC curve and the straight line connecting the melting end temperature (β in FIG. 2) of the endothermic curve appearing in the DSC curve during the first heating and the 80 ° C. point on the curve. ΔHb is surrounded by a DSC curve and a straight line connecting the melting end temperature (β in FIG. 2) of the endothermic curve appearing in the DSC curve during the second heating and the 80 ° C. point on the curve. This corresponds to the area of the portion. These heat quantities all mean the endothermic amount (J / g), and the endothermic value is expressed as an absolute value. The value of ΔHa / ΔHb will be described later as the numerical value is smaller. Surface modification The surface modification effect of the resin particles is great. Specifically, surface modification was performed using resin particles having a smaller value of ΔHa / ΔHb. Surface modification The foamed particles obtained from the resin particles can be molded with lower temperature steam, and / or can be molded with a lower foaming ability imparted to the foamed particles prior to molding. However, the lower limit of the value of ΔHa / ΔHb usually does not fall below 0.70. On the contrary, when the value of ΔHa / ΔHb exceeds 0.95, the effect is very small.
[0017]
Such ΔH _a / ΔH _b In order to obtain the present resin particles having a small value, the following operation (1), (2) or (3) may be performed after the polypropylene resin is heated and melted.
(1) The molten polypropylene resin is cooled in a cooling medium at least 30 ° C. lower than the crystallization temperature of the polypropylene resin, and then cut into particles.
(2) The molten polypropylene resin is cooled in a cooling medium that is at least 30 ° C. lower than the crystallization temperature of the polypropylene resin immediately after being cut into particles in the molten state.
(3) The molten polypropylene resin is cooled in a cooling medium that is at least 30 ° C. lower than the crystallization temperature of the polypropylene resin while being cut into particles in the molten state.
The cooling medium is not necessarily implemented with a gas such as air, but a liquid is more efficient and reliable. As such a liquid cooling medium, an aqueous medium is generally used, and water is preferably used. There is no particular limitation as long as it is not limited to water and does not dissolve the base resin. Examples of such include ethylene glycol, glycerin, methanol, ethanol, a mixture of water and the alcohol, and the like.
[0018]
Regarding the cooling in the above (1) to (3), the lower the temperature of the cooling medium (the more rapid the degree of cooling), and the longer the cooling time, ΔH _a / ΔH _b This resin particle with a small value can be obtained. From such a viewpoint, the temperature of the cooling medium needs to be at least 30 ° C. lower than the crystallization temperature of the polypropylene resin, but is preferably at least 35 ° C. lower than the crystallization temperature of the polypropylene resin. More preferably, it is at least 45 ° C. lower than the crystallization temperature of the polypropylene resin, more preferably at least 55 ° C. lower than the crystallization temperature of the polypropylene resin, and at least 65 lower than the crystallization temperature of the polypropylene resin. It is particularly preferable that the temperature is lower by 0 ° C., and most preferably lower by at least 80 ° C. than the crystallization temperature of the polypropylene resin. However, if the temperature of the cooling medium is too low, the cost for preparing the cooling medium increases more than necessary, so the temperature of the cooling medium is preferably 5 ° C. or higher. The cooling time by the cooling medium is preferably 1 second or longer, more preferably 5 seconds or longer, still more preferably 9 seconds or longer, and most preferably 12 to 20 seconds. The longer the cooling time is, the more effective, but if the cooling is performed for a sufficient time, the above-described effect will reach its peak.
[0019]
Note that ΔH _a / ΔH _b This resin particle with a small value can be obtained. ΔH _b The value is almost constant when the raw resin is determined, but ΔH _a Tends to show a smaller value as the degree of cooling from the molten state increases. For this reason, ΔH _a / ΔH _b The smaller the value, the higher the degree of cooling. And ΔH _a Indicates a small value (ie ΔH _a / ΔH _b (A small value) means that the crystallization of the resin particles is suppressed, and it is speculated that the suppression of the crystallization enhances the effect of surface modification on the resin particles described later. The
[0020]
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.
If the length / diameter ratio is too small or too large, filling of the foamed particles obtained therefrom into the mold may be hindered. On the other hand, if the average weight per particle becomes too heavy, the cooling efficiency may be deteriorated at the time of cooling. Conversely, if the average weight becomes too light, it becomes difficult to obtain expanded particles.
[0021]
A method for producing low-temperature fusible foamed particles (EPP particles) using the polypropylene resin particles of the present invention (hereinafter also referred to as method A) comprises a surface modification step and a foaming step. In the surface modification step, the resin particles are dispersed in a dispersion medium in which the organic peroxide is present, and the dispersion medium is at a temperature lower than the melting point of the base resin of the resin particles and the organic peroxide. But The surface of the resin particles is modified by decomposing the organic peroxide while maintaining the decomposition temperature. do it Uncrosslinked surface modification resin particle (Hereafter, it may be referred to as surface modified particles) Get. The surface-modified particles thus obtained are foamed using a foaming agent in the next foaming step. The Convert to uncrosslinked foam 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 filled in a mold and heated with steam to obtain an EPP molded body having excellent rigidity.
[0022]
The dispersion medium used in the surface modification step in the method A is generally an aqueous medium, preferably water, more preferably ion-exchanged water, but is not limited to water and dissolves the base resin. Any solvent or liquid that does not disperse and 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.
[0023]
Examples of the organic peroxide include various conventionally known ones such as isobutyl peroxide [50 ° C./85° C.], cumyl peroxyneodecanoate [55 ° C./94° C.], α, α′-bis ( Neodecanoyl peroxy) diisopropylbenzene [54 ° C./82° C.], di-n-propyl peroxydicarbonate [58 ° C./94° C.], diisopropyl peroxydicarbonate [56 ° C./88° C.], 1-cyclohexyl- 1-methylethylperoxyneodecanoate [59 ° C / 94 ° C], 1,1,3,3-tetramethylbutylperoxyneodecanoate [58 ° C / 92 ° C], bis (4-t-butyl Cyclohexyl) peroxydicarbonate [58 ° C./92° C.], di-2-ethoxyethyl peroxydicarbonate [59 ° C./92° C.], di (2- Tylhexylperoxy) dicarbonate [59 ° C./91° C.], t-hexyl peroxyneodecanoate [63 ° C./101° C.], dimethoxybutyl peroxydicarbonate [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-hexylperoxypivalate [71 ° C / 109 ° C], t-butylperoxypivalate [73 ° C / 110 ° C], 3,5,5-trimethylhexanoyl peroxide [77 ° C / 113 ° C], Octanoyl peroxide [80 ° C / 117 ° C], Lauroyl peroxide [80 ° C / 116 ° 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-toluoylbenzoyl peroxide [ 92 ° C / 131 ° C], benzoyl peroxide [92 ° C / 130 ° C], t-butyl peroxyisobutyrate [96 ° C / 136 ° C], 1,1-bis (t-butyl) Peroxy) -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-butylperoxy Maleic 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] Etc. are exemplified. 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 may be used alone or in combination of two or more, and 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.
[0024]
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.
[0025]
Conventionally, the use of organic peroxide for polypropylene is as follows: <1> ~ The usage method <4> is known.
<1> Polypropylene particles are homogeneously impregnated with an organic peroxide and a crosslinking aid, and the organic peroxide is decomposed at a temperature exceeding the melting point of the polypropylene to crosslink the polypropylene.
<2> A composition containing polypropylene and an organic peroxide is uniformly melt-kneaded in an extruder at a temperature exceeding the melting point of the polypropylene to uniformly decompose the organic peroxide, thereby narrowing the molecular weight distribution. Polypropylene is obtained (Japanese Patent Laid-Open No. 3-152136).
<3> Polypropylene particles are homogeneously impregnated with an organic peroxide and a crosslinking aid, and the organic peroxide is decomposed at a temperature below the melting point of the polypropylene to introduce a long-chain branched or crosslinked structure into the polypropylene. The melt tension is increased (Japanese Patent Laid-Open No. 11-80262). The polypropylene having an increased melt tension is then melt-kneaded with a foaming agent in an extruder and used for extrusion foaming.
<4> A composition containing polypropylene, an organic peroxide, and maleic anhydride is uniformly melt-kneaded in an extruder at a temperature exceeding the melting point of polypropylene and graft polymerization is performed.
Prior to the production of the EPP particles, all of the conventional methods for using the organic peroxide are polypropylene-based in a dispersion medium in which the organic peroxide is present in order to obtain EPP particles having excellent heat-fusibility. The resin particles are dispersed, and the dispersion medium has a temperature lower than the melting point of the base resin of the polypropylene resin particles and the organic peroxide. But The surface of the polypropylene resin particles is modified by decomposing the organic peroxide while maintaining the decomposition temperature. Nothing This is different from the method of use of the present invention for obtaining crosslinked surface-modified particles.
[0026]
In the surface modification step, the organic peroxide is at a lower temperature than the melting point of the base resin. In minutes Let me understand. Therefore, the one-hour half-life temperature of the organic peroxide is preferably not higher than the Vicat softening point (JIS K 6747-1981, the same shall apply hereinafter) of the base resin. 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. This is not preferable, and in some cases, the temperature is lower than the melting point of the base resin. so This is not preferable because it cannot be decomposed. The peroxide is heated to a temperature higher than the melting point of the base resin. In minutes When it is understood, since the peroxide decomposes in a state where it penetrates deep into the resin particles, the base resin constituting the resin particles is largely decomposed regardless of the surface and the inside. In some cases, only EPP particles that cannot be used for molding may be obtained, and even if molding can be performed, the mechanical properties of the finally obtained EPP molded body may be greatly reduced.
[0027]
In view of the above, the organic peroxide used in the surface modification step has a one-hour half-life temperature (when the organic oxide is decomposed at a constant temperature, the amount of active oxygen is one hour after the initial period. The temperature at which the base resin is halved is preferably 20 ° C. or more lower than the Vicat softening point of the base resin, and more preferably 30 ° C. or lower than the Vicat softening point of the base resin. 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 measured in accordance with JIS K 7121-1987 in the case of adjusting the state of the test piece "when measuring the glass transition temperature after performing a certain heat treatment". It means the midpoint glass transition temperature determined by bundle DSC. The peroxide is not higher than the Vicat softening point of the base resin in the dispersion medium in which the resin particles are present. In minutes Preferably, the temperature is 20 ° C. or more lower than the Vicat softening point of the base resin. In minutes More preferably, the temperature is 30 ° C. or more lower than the Vicat softening point of the base resin. so It is more preferable to decompose. 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 oxide is decomposed at a constant temperature) ± Hold in the temperature range of 30 ℃ for more than 10 minutes Minutes It is particularly preferable to solve the problem. 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 surface modification efficiency may be deteriorated. In addition, if it is kept for 10 minutes or more in the range of 1 minute half-life temperature ± 30 ° C, organic peroxide The It is easy to disassemble. The longer the holding time in the range of 1 minute half-life temperature ± 30 ° C., the more reliably the organic peroxide can be decomposed, but it is no longer necessary for a certain time or longer. 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.
[0028]
In order 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. That's fine. At this time, the rate of temperature rise may be selected so that the temperature is maintained in the range of 1 minute half-life temperature ± 30 ° C. for 10 minutes or more, but it is stopped at any temperature within the range of 1 minute half-life temperature ± 30 ° C. It is more preferable to hold the temperature 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. Note that the peroxide is equal to or higher than the glass transition temperature of the base resin. so It is preferable to decompose, considering the handleability of the peroxide, etc., the range of 40-100 ℃ In minutes More preferably, the range of 50-90 ° C In minutes More preferably, it is understood. In this specification, organic peroxide Decomposing means decomposing until the amount of active oxygen of the peroxide used is 50% or less of the original, but it is preferable to decompose until the amount of active oxygen is 30% or less of the initial, It is more preferable to decompose until the amount of active oxygen is 20% or less of the original, and it is further preferable to decompose until the amount of active oxygen is 5% or less of the initial. 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, and pyrolyzed to measure.
[0029]
Surface modified particles No Cross-linking. In the method A, a crosslinking aid or the like is not used in combination. Rack The bridge does not progress. still ,Nothing Crosslinking is defined as follows. That is, each of the base resin, the present resin particle, the treated particle, the EPP particle, and the EPP molded product was used as a sample (1 g of sample per 100 g of xylene) was immersed in boiling xylene for 8 hours, and then a standard mesh fluid was used. Is quickly filtered through a wire mesh having a mesh size of 74 μm as defined in JISZ 8801 (1966), and the weight of the boiling xylene-insoluble matter remaining on the wire mesh is measured. When the insoluble content is 10% by weight or less of the sample The Although it is called non-crosslinked, the insoluble content is preferably 5% by weight or less, more preferably 3% by weight or less, and 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.
P (%) = (M ÷ L) × 100
However, M is the weight (g) of insoluble matter, and L is the weight (g) of the sample.
[0030]
As described above, the present resin particles are subjected to the modification treatment of the surface of the present resin particles by decomposing the organic peroxide and then used for the production of foamed particles. The expanded particles are heated while being dispersed in a dispersion medium in a closed container in the presence of the foaming agent so that the surface modified particles are impregnated with the foaming agent, and then the expanded particles are decompressed. Is preferably produced by a method of releasing the surface-modified particles and the dispersion medium under a low pressure (hereinafter referred to as “dispersion medium releasing foaming method”) at a temperature at which the water is generated.
The surface modification step for forming the surface modified particles and the foaming step for obtaining expanded particles from the surface modified particles can be carried out at different times with different apparatuses, but the dispersion medium is released. When the foaming method is adopted, the surface modification is carried out during the heating process by simply adding a predetermined amount of the above-mentioned organic peroxide having an appropriate decomposition temperature to the aqueous medium in the sealed container and carrying out the usual dispersion medium releasing foaming method. This is efficient because the surface-modified particles are automatically obtained after the process is completed.
[0031]
The surface-modified resin particles, and thus the EPP particles and EPP moldings obtained therefrom, may contain about several hundred ppm to several thousand ppm of alcohol having a molecular weight of 50 or more produced by the decomposition of the peroxide. . As such an alcohol, when bis (4-t-butylcyclohexyl) peroxydicarbonate shown in Examples described later is used, Pt-butylcyclohexanol is a 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.
[0032]
In the dispersion medium releasing foaming method, it is preferable to add a dispersant to the dispersion medium so that the surface-modified particles under heating in the container are not fused to each other in the container. Such a dispersant is not limited as long as it prevents fusion of the surface-modified particles in the container, and can be used regardless of whether it is organic or inorganic. Inorganic substances are 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.
[0033]
Furthermore, in the above dispersion medium releasing foaming method, a dispersion strengthening agent that strengthens the dispersing power of the dispersing agent (prevents fusion of surface-modified particles within the container even if the amount of the dispersing agent added is small) is dispersed. It is preferable to add to the 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 a divalent or trivalent inorganic substance. . 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.
[0034]
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.
[0035]
Examples of the foaming agent used in the method for producing expanded polypropylene resin particles include aliphatic hydrocarbons such as propane, butane, hexane, and heptane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, and trifluoromethane. , 1,2-difluoroethane, 1,2,2,2-tetrafluoroethane, organic physical foaming agents such as halogenated hydrocarbons such as methyl chloride, ethyl chloride, methylene chloride, nitrogen, oxygen, air, carbon dioxide And so-called inorganic physical foaming agents such as water. An organic physical foaming agent and an inorganic physical foaming agent can be used in combination. A material mainly composed of one or more inorganic physical foaming agents selected from the group of nitrogen, oxygen, air, carbon dioxide, and water is particularly preferably used. Among these, nitrogen and air are preferable in consideration of the stability of the apparent density of the expanded particles, the environmental load and the cost. 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 particles in the sealed container.
[0036]
In the dispersion medium releasing foaming method, the filling amount of the physical foaming agent in 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 to increase the pressure in the space in the container as the apparent density of the target foamed particles is small, and it is desirable to decrease the pressure in the space as the apparent density of the target foamed particles is large. There is a tendency.
[0037]
In the above method A, the above-mentioned dispersion medium releasing foaming method is adopted, the apparent density is 10 g / L to 500 g / L, and the endotherm derived from the heat of fusion of the base resin in the DSC curve by differential scanning calorimetry of the foamed particles It is preferable to produce expanded particles having an endothermic curve peak (high temperature peak) on the higher temperature side than the curve peak (inherent peak). Such foamed particles are foamed particles having a high closed cell ratio and suitable for molding. In the case of the present invention, in the obtained expanded particles, it is particularly preferable that the amount of heat at the high temperature peak is 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 the present invention, the calorific value 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 calorific value of the high temperature peak and the calorific value of the intrinsic peak. It is preferable that it is 10 to 60%, and it is more preferable that it is 20 to 50%. The total amount of heat at the high temperature peak and the heat at the intrinsic peak is preferably 40 J / g to 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.
[0038]
The amount of heat at the high temperature peak of the expanded particles is shown in FIG. 1 obtained when 2 to 4 mg of expanded particles are heated at a rate of 10 ° C./minute from room temperature (30 ° C.) to 200 ° C. by a differential scanning calorimeter in a nitrogen atmosphere. The amount of heat (absorption of endothermic curve peak (high temperature peak) b that appears 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. The amount of heat) 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 T 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 (endothermic amount) at the high temperature peak. The melting end temperature T is the intersection of the DSC curve on the high temperature side of the high temperature peak b and the high temperature side baseline.
The total amount of heat at the high temperature peak and the heat at the intrinsic peak corresponds to the area of the portion surrounded by the straight line (α-β) and the DSC curve.
[0039]
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 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 part and the amount of heat at the high temperature peak for the internal foam layer are different.
[0040]
This high temperature peak b is observed in the first DSC curve measured as described above, but after obtaining the first DSC curve, it was once around 30 ° C. at 200 ° C. to 10 ° C./min. 2 is not recognized in the second DSC curve obtained when the temperature is increased again to 200 ° C. at 10 ° C./min, and is inherent to the endotherm during melting of the base resin as shown in FIG. Only peak a is observed.
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 determined based on the melting point (Tm) of the base resin. Tm-2 ° C.] to [Tm + 2 ° C.].
[0041]
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 become 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.
[0042]
However, when obtaining an EPP molded article using EPP particles having a small high-temperature peak heat quantity, the minimum fusing temperature tends to be relatively low, but the strength physical properties such as compression strength (rigidity) of the EPP molded article are relatively high. There is a tendency to decrease. On the other hand, when obtaining an EPP molded product using expanded particles having a high high temperature peak heat, strength properties such as compressive strength of the EPP molded product tend to be relatively high, but the minimum fusion temperature is relatively high. Therefore, as described above, there is a problem in that high pressure steam may be required when manufacturing an EPP compact. 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 expanded particles obtained by Method A are those in which the minimum fusing temperature is effectively reduced. 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.
[0043]
When the foamed particles having a high temperature peak in the DSC curve are heated by dispersing the surface-modified particles in the dispersion medium in a closed container, the foamed particles have a melting end temperature (Te) or higher of the base resin constituting the surface-modified particles. Without increasing the temperature, stop at an arbitrary temperature (Ta) within a range of 20 ° C. lower than the melting point (Tm) of the base resin and lower than the melting end temperature (Te), and a sufficient time at that temperature (Ta). , Preferably 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 melting end temperature (Te) + 10 ° C., and stopped at that temperature, necessary Thus, the surface-modified particles can be obtained by foaming by releasing the surface-modified particles from the inside of the sealed container under a low pressure after holding at the temperature for a sufficient time, preferably about 10 to 60 minutes.
The melting point (Tm) is a value obtained by performing differential scanning calorimetry on 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. It is the temperature at the top of the endothermic curve peak a unique to the base resin found in the obtained second DSC curve (an example of which is shown in FIG. 2), and the melting end temperature (Te) is the intrinsic endothermic curve. DSC curve on the high temperature side of peak a and high temperature side baseline (B _L ) And the intersection (β).
[0044]
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, there are rarely two or more endothermic peaks. In that case, a straight line that passes through the vertex of each peak and is parallel to the vertical axis of the graph (perpendicular to the horizontal axis) is drawn. _L And the peak apex on the straight line having the longest length is defined as Tm. However, when two or more longest straight lines exist, the peak apex on the highest temperature side is defined as Tm.
[0045]
The amount of heat at the high-temperature peak in the expanded particles mainly depends on the temperature Ta, the holding time at the temperature, the temperature Tb, the holding time at the temperature, and the rate of temperature increase with respect to the resin particles when the expanded particles are produced. Dependent. The amount of heat at the high temperature peak of the expanded particles tends to increase as the temperature Ta or Tb decreases 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.
[0046]
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.
[0047]
The apparent density (g / L) of the expanded particles is calculated by dividing the weight (g) of the expanded particles by the apparent volume (L) of the expanded particles. The apparent volume of the expanded particles was 23 ° C., and about 5 g of the expanded particles left at atmospheric pressure for 48 hours or more was converted to 100 cm of water at 23 ° C. ³ From the excluded volume when submerged in the water in the graduated cylinder in which the particle is contained, the apparent volume (cm ^Three ) And converted into liters. For this measurement, the weight of the expanded particles is 0.5000 to 10.0000 g, and the apparent volume of the expanded particles is 50 to 90 cm. ^Three An amount of a plurality of expanded particles is used.
[0048]
As described above, the EPP particles obtained from the surface-modified particles obtained by modifying the surface of the resin particles by decomposing the organic peroxide can be molded with low-temperature steam. It is found from the measurement results that
[0049]
As a result of DSC measurement of the expanded particles, the expanded particles obtained by the method A tend to be different from the expanded particles obtained by the conventional method. When the melting point was measured by dividing into a surface layer portion of the expanded particle and an internal expanded layer not including the surface layer portion, the conventional expanded particle had a melting point (Tm _s ) Is the melting point (Tm) of the internal foam layer _i ), The expanded particles obtained by the method A have a melting point (Tm) of the surface layer portion. _s ) Is the melting point (Tm) of the internal foam layer _i ) Was observed to be lower. In expanded particles that can be molded with low temperature steam, its Tm _s Is Tm _i It is preferably lower by 0.05 ° C. or more, more preferably by 0.1 ° C. or more, and further preferably by 0.3 ° C. or more.
[0050]
Melting point (Tm) of the surface layer portion of the expanded particle _s ) Is a characteristic peak a of the second DSC curve obtained by performing the same operation as the measurement of the high temperature peak calorific value of the foamed particles except that 2-4 mg of the foamed particles are cut out and collected as a sample. Means the temperature at the apex of Further, the melting point (Tm) of the inner foam layer of the foam particles _i ) Is the second DSC obtained by cutting out from the inside of the expanded particles so as not to include the surface layer portion, collecting 2 to 4 mg and using this as a sample, and performing the same operation as the measurement of the high temperature peak heat quantity of the expanded particles described above. It means the temperature at the apex of the intrinsic peak a of the curve.
[0051]
In addition, when the high temperature peak calorific value was measured by dividing the foamed particle into a surface layer portion and an internal foam layer not including the surface layer portion, the conventional foamed particles were found to have a high temperature peak calorific value (ΔH _s ) And the amount of heat at the high temperature peak of the internal foam layer (ΔH _i ) _s ≧ ΔH _i In contrast to the property of × 0.87, in the expanded particles obtained by Method A, ΔH _s <ΔH _i It was observed to be x0.86. For expanded particles that can be molded with low temperature steam, ΔH _s <ΔH _i X0.86, but ΔH _s <ΔH _i × 0.83 is preferable, ΔH _s <ΔH _i X0.80 is more preferable, and ΔH _s <ΔH _i X0.75 is more preferable, and ΔH _s <ΔH _i X0.70 is particularly preferable, and ΔH _s <ΔH _i It is most preferable that it is x0.60. ΔH _s Is ΔH _s ≧ ΔH _i It is preferable that it is x0.25. ΔH _s <ΔH _i × 0.86 enables in-mold molding at a lower temperature than expanded particles that are not surface-modified, and ΔH _s The smaller the value, the greater the effect. ΔH _s Is preferably 1.7 J / g to 60 J / g, more preferably 2 J / g to 50 J / g, still more preferably 3 J / g to 45 J / g, and 4 J / g to 40 J. Most preferred is / g.
[0052]
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 of the foamed particles is cut out from the inside of the foamed particles so as not to include the surface layer portion, and 2 to 4 mg are collected and used as a sample to measure the high temperature peak calorific value of the foamed particles described above. The same operation can be performed.
[0053]
A method of measuring the melting point and the high temperature peak by dividing the foamed particles into a surface layer portion and an internal foam layer not including the surface layer portion is as follows.
The surface layer portion of the foamed particles may be measured by collecting the surface layer portion by slicing the surface layer portion using a cutter knife, a microtome, or the like. 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 the foamed particle. In other words, it is sliced from one or a plurality of randomly selected locations on the surface of the expanded particles so that a portion exceeding 200 μm is not included. When a portion exceeding 200 μm from the surface of the foamed particle toward the center of gravity of the foamed particle is included on the back surface of the surface layer part of the sliced foamed particle, the internal foamed layer is contained in a large amount, and the melting point of the surface layer part and There is a possibility that the high temperature peak 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.
[0054]
On the other hand, the internal foam layer that does not include the surface layer portion of the foam particle is the entire surface of the foam particle so that the surface of the foam particle and the portion between the surface of the foam particle and 200 μm from the surface of the foam particle toward the center of gravity of the foam particle are not included. What is necessary is just to use for the measurement of melting | fusing point and a high temperature peak using what excised the surface layer part from. However, if the size of the expanded particles is too small and the internal foam layer disappears when the 200 μm portion is cut off from the above surface, the surface of the expanded particles and the surface of the expanded particles are directed toward the center of gravity of the expanded particles. If the surface of the foamed particle is cut out from the entire surface of the foamed particle so that the portion between 100 μm is not included, and the inner foamed layer still disappears, the surface of the foamed particle The surface of the foamed particle is cut off from the entire surface of the foamed particle so as not to include a part between the surface of the foamed particle and the center of gravity of the foamed particle. When the internal foamed layer obtained from one foamed particle is less than 2 to 4 mg, the above operation is repeated using a plurality of foamed particles to collect the required amount of the internal foamed layer.
[0055]
In addition, for each foamed particle surface of the surface-modified foamed particles obtained by Method A and the foamed particles that have not been surface-modified obtained by the conventional method, Micro Heat of TI Instruments Japan Co., Ltd. Using the analysis system “2990 type micro thermal analyzer”, micro differential thermal analysis (μDTA) was performed under the condition of a heating rate of 10 ° C./second from 25 ° C. to 200 ° C. The melting start temperature of the surface of the formed expanded particles (the melting start temperature referred to in claim 4) is a temperature lower than the melting point of the base resin, whereas the surface modification obtained by the conventional method is performed. It was found that the melting start temperature of the surface of the expanded foam particles is 5 ° C. or more higher than the melting point of the base resin. The melting start temperature here means a temperature at which the μDTA curve starts to change downward (specific heat per hour starts to change) from the baseline (BL) in the μDTA curve based on the μDTA.
[0056]
In addition, for each foamed particle surface of the surface-modified foamed particles obtained by Method A and the foamed particles that have not been surface-modified obtained by the conventional method, Micro Heat of TI Instruments Japan Co., Ltd. Using the analysis system “2990 type micro thermal analyzer”, micro differential thermal analysis (μDTA) was performed under the condition of a heating rate of 10 ° C./second from 25 ° C. to 200 ° C. The extrapolated melting start temperature (the extrapolated melting start temperature referred to in claim 5) of the surface of the foamed particles thus obtained is lower than the melting point + 4 ° C. of the base resin, whereas the conventional method It was found that the extrapolated melting start temperature of the surface of the foam particles not surface-modified obtained in (5) was higher by 8 ° C. or more than the melting point of the base resin. The extrapolated melting start temperature here is a straight line obtained by extending the baseline (BL) of the μDTA curve to the high temperature side, and a tangent line drawn from each point on the μDTA curve on the high temperature side from the melting start temperature. The temperature at the intersection of the tangent line (TL) with the maximum angle between the tangent line and the straight line obtained by extending the base line (BL) to the high temperature side.
[0057]
One example of the above-mentioned μDTA curve for each of the expanded particles (surface-modified expanded particles) obtained in Example 1 described later and the expanded particles obtained in Reference Example 1 (expanded particles not surface-modified). 3 shows. In FIG. 3, the curve Cm is based on the expanded particles obtained in Example 1, the Pm point on the curve Cm is the melting start temperature, and the Pme point is the baseline (BL) and the tangent (TL). ) Is the extrapolated melting start temperature that is the intersection point with). On the other hand, the curve Cnm is based on the expanded particles obtained in Reference Example 1, the Pnm point on the curve Cnm is the melting start temperature, and the Pnme point is the baseline (BL) and the tangent (TL). Is the extrapolated melting start temperature that is the intersection of Pm, Pme, Pnm, and Pnm in FIG. 3 are 131 ° C., 135 ° C., 168 ° C., and 171 ° C., respectively.
FIG. 4 shows an example of a μDTA curve for a surface-modified EPP foam particle surface based on another example using a propylene homopolymer having a melting point of 162 ° C. and an MFR of 18 g / 10 min as a base resin. In FIG. 4, the curve Cm is a μDTA curve, the Pm point on the curve Cm is the melting start temperature, and the Pme point is the intersection of the baseline (BL) and the tangent (TL). Temperature. Pm and Pme in FIG. 4 are 140 ° C. and 142 ° C., respectively.
[0058]
In the micro differential thermal analysis, the expanded particles are fixed to the sample stage of the apparatus (if one expanded particle is too large as it is, it is fixed to an appropriate size, for example, by cutting in half) Next, the probe tip (the portion to be in contact with the surface of the foamed particle has a tip portion of 0.2 μm in length and width) was lowered to contact with the surface of the foamed particle toward a randomly selected portion on the surface of the foamed particle. Implemented in the state.
As the melting start temperature and extrapolation melting start temperature of the surface of the expanded particles by the micro differential thermal analysis, an arithmetic average value of 8 points excluding the maximum value and the minimum value is adopted from the measurement results of 10 different measurement points. In addition, when there are a plurality of maximum values and minimum values, an arithmetic average value of several points excluding them is adopted. In addition, when all 10 measured values on the average are the same, or when only the maximum and minimum values are obtained and the difference between the maximum and minimum values is within 10 ° C., the 10-point phase An arithmetic mean value is adopted. When only the maximum and minimum values were obtained, and the difference between the maximum and minimum values exceeded 10 ° C, measurements were made on 10 points on different surfaces and the same procedure as described above. What is necessary is just to obtain | require an arithmetic mean value and to employ | adopt it. If the condition is still not met, repeat the same operation.
[0059]
The above μDTA results indicate that the decrease in the melting start temperature on the surface of the expanded particles and / or the decrease in the extrapolated melting start temperature on the surface of the expanded particles contributes to the decrease in the minimum fusion temperature required during molding. ing. The foamed particles that can be molded with low-temperature steam have a melting start temperature on the surface of the foamed particles based on the above measurement of not more than the melting point (Tm) of the base resin, preferably [Tm-5 ° C.] or less. Tm−10 ° C. or less, more preferably [Tm−15 ° C.] or less, particularly preferably [Tm−16 ° C.] to [Tm−50 ° C.], and [Tm− Most preferably, it is 17 [deg.] C. to [Tm-35 [deg.] C.]. The foamed particles that can be molded with low-temperature steam have an extrapolated melting start temperature of the foamed particle surface based on the above measurement of [Tm + 4 ° C.] or lower, preferably [Tm-1 ° C.] or lower, Tm−6 ° C.] or less, more preferably [Tm−17 ° C.] to [Tm−50 ° C.], and [Tm−18 ° C.] to [Tm−35 ° C.]. Most preferred. Such a decrease in the minimum fusion temperature is particularly effective in the case of EPP particles having a melting point of the base resin of 158 ° C. or higher and a high temperature peak. The lower the melting start temperature of the foam particle surface, the greater the contribution to the lowering of the minimum fusing temperature required at the time of molding, but if the melting start temperature is too low, the compression strength of the resulting molded product, etc. There is a possibility that mechanical properties and the like are reduced.
[0060]
Further, when the MFR was measured, it was observed that the MFR value of the expanded particles obtained by the method A was the same as the MFR value of the present resin particles before the surface modification but a larger value than that. . 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 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.
[0061]
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. When measuring the MFR of the expanded particles, it is necessary to avoid the inclusion of bubbles or the like in the sample in order to obtain an accurate measurement value. 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.
[0062]
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 A and the surface of the EPP molded body 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 product by ATR measurement (total reflection absorption measurement method), the surface of the EPP molded product produced from the expanded particles obtained by Method A was newly added to 1033 cm. ^-1 It was confirmed that there was a difference in absorption in the vicinity, and it was recognized that there was a change such as addition or insertion of oxygen alone or a functional group containing oxygen. Specifically, 1166cm ^-1 When both peak heights in absorption of the same (the absorption peak height for the molded product from the foamed particles obtained by Method A and the absorption peak height for the conventional molded product) are the same, from the foamed particles obtained by Method A 1033cm of the surface of the molded body ^-1 The height of the nearby absorption peak is 1033 cm of the surface of the conventional molded body. ^-1 It is higher than the height of the nearby absorption peak. 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 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 considered to increase the permeability of steam during molding and enable molding with low temperature steam. From such a viewpoint, it is preferable that the expanded particles that can be molded with low-temperature steam have a ratio of oxygen to carbon of 0.15 or more by the EDS on the surface of the expanded particles.
Expanded particles that can be molded with low-temperature steam are obtained by modifying the oxygen-containing modified surface or / and reversing the melting point or / and reducing the high-temperature peak heat quantity of the surface layer of the expanded particles or / and the surface of the expanded particles. It is presumed that the minimum fusing temperature is greatly reduced by lowering the melting start temperature or / and lowering the extrapolated melting start temperature on the surface of the expanded particles.
[0063]
The EPP particles obtained by the above-described method are aged at atmospheric pressure, and after increasing the bubble internal pressure as necessary, are heated with water vapor or hot air to obtain expanded particles with a higher expansion ratio. It is possible.
[0064]
In the EPP molded body, 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 bubbles as necessary. They can be manufactured by adopting a batch molding method in which they are heated and expanded to be 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, the EPP molded body continuously supplies the EPP particles between the belts that continuously move along the upper and lower sides in the passage after increasing the bubble internal pressure as necessary, and a saturated steam supply region (heating region). ), The EPP particles are expanded and fused together, then cooled by passing through a cooling region, and then the obtained molded body is taken out from the passage and sequentially cut to an appropriate length ( For example, it can also be produced by a molding method described in JP-A-9-104026, JP-A-9-104027 and JP-A-10-180888. 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 placed in a sealed container, and the pressurized air is allowed to permeate into the foamed particles by leaving the container in a state where the pressurized air is supplied. That's fine. 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.
[0065]
Further, a surface decoration material can be laminated and integrated on at least a part of the surface of the EPP molded body. Such a laminated composite type in-mold foam molded body and a method for producing the same are disclosed in US Pat. No. 5,928,776, US Pat. No. 6,096,417, US Pat. No. 6,033,770, US Pat. No., WO 98/00287, Japanese Patent No. 3092227, and the like.
Further, the insert material can be combined and integrated so that all or part of the insert material is embedded in the molded body. Such insert composite type in-mold foam moldings and methods for producing the same are described in detail in various publications such as US Pat. No. 6,033,770, US Pat. No. 5,474,841, Japanese Patent Publication No. 59-1277714, and Japanese Patent No. 3092227. It is described in.
[0066]
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.
[0067]
【Example】
The present invention will be described below with reference to examples and comparative examples.
[0068]
Example 1, Reference Example 1
Zinc borate powder (bubbles) per 100 parts by weight of polypropylene homopolymer (glass transition point: −21 ° C., Vicat softening point: 147 ° C., melting point: 162 ° C., crystallization temperature: 123 ° C., MFR: 18 g / 10 min) Adjusting agent) After adding 0.05 part by weight and melt-kneading in an extruder, it is extruded into a strand form from the extruder, and 1 second after the extrusion, the strand is cooled in a cooling medium (water adjusted to 18 ° C. in a water bath). 1) After being submerged and taken out while being cooled and sufficiently cooled (cooling time 13 seconds), the strand was pulled up from the cooling medium and the strand was cut so that the length / diameter ratio was approximately 1.0. Resin particles having an average weight per unit of 2 mg were obtained. In addition, the accommodation amount of the cooling medium in the water tank was 170 liters. With respect to the obtained resin particles, ΔH _a And ΔH _b Was measured. The results are shown in Table 1.
[0069]
Next, in a 400 liter autoclave, 100 parts by weight of the resin particles, 220 parts by weight of ion exchange water at 23 ° C. as dispersion medium, 0.005 parts by weight of sodium dodecylbenzenesulfonate (surfactant) and 0 kaolin powder (dispersant) .3 parts by weight and 0.01 parts by weight of aluminum sulfate powder (dispersion strengthening agent), bis (4-tert-butylcyclohexyl) peroxydicarbonate as an organic peroxide (1-hour half-life temperature: 58 ° C., halved for 1 minute) (Initial temperature: 92 ° C.) (In Example 1, no organic peroxide is used) and the amount of carbon dioxide gas (foaming agent) shown in Table 1 is charged, and the foaming temperature (165.5 ° C.) is stirred in a sealed state. Then, the temperature was raised to a temperature 5 ° C. lower than that (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. The release was performed while supplying high-pressure carbon dioxide gas into the autoclave so that the pressure inside the autoclave during the release of the resin particles from the autoclave was maintained at the pressure inside the autoclave immediately before the release. The obtained foamed particles are washed with water, centrifuged, and allowed to stand for 48 hours under atmospheric pressure at room temperature of 23 ° C. for 48 hours, and then the high temperature peak heat of the foam particles, the high temperature peak heat of each of the surface layer portion and the internal foam layer. And each melting | fusing point, MFR of an expanded particle, the apparent density of an expanded particle, etc. were measured. The results are shown in Table 1. The expanded particles obtained in Example 1 and Reference Example 1 were Nothing It was cross-linked (the boiling xylene insolubles were all 0).
[0070]
Next, after placing the foamed particles under pressurized air in a pressure-resistant container to give the foamed particles an increased bubble internal pressure, at the time of the bubble internal pressure shown in Table 1 (indicated as foamed particle internal pressure in the table), Fill a mold with a molding space of 250 mm x 200 mm x 50 mm with a slight gap (about 1 mm) without completely closing the mold (with the direction of the molding space 50 mm being 51 mm) Thereafter, the mold was completely clamped, and after the air in the mold was evacuated with steam, the mold was molded at the lowest fusion temperature (minimum saturation steam pressure) shown in Table 1. After molding, the product was cooled in water until the surface pressure of the molded product in the mold reached 0.059 MPa (G), then the molded product was removed from the mold, dried at 60 ° C. for 24 hours, and then cooled to room temperature (23 ° C.). . Subsequently, after curing in the room for 14 days, the apparent density, compressive strength, and b / n ratio were measured for the molded body. The minimum fusing temperature (minimum saturation steam pressure) means that a molded body is repeatedly produced by increasing the saturation steam pressure in increments of 0.01 MPa from 0.15 MPa (G) to 0.55 MPa (G), and molding after curing. A test in which about 10 mm incision is made in the thickness direction of the molded body so that the length of the 250 mm × 200 mm surface of the body is divided into two parts with a cutter knife in about 2 mm, and then the molded body is bent and broken from the cut portion. Saturation required for molding when the ratio (b / n) of the number (b) of the foamed particles existing on the fracture surface to the number (b) of the material-broken foamed particles is 0.50 or more for the first time. It means steam pressure.
[0071]
However, in Reference Example 1, the value of (b / n) is 0.30 at a saturated steam pressure of 0.55 MPa (G), which is the pressure resistance of the molding machine used in this test, and 0.50 It did not reach. In order to obtain a (b / n) value of 0.50 or more, a higher saturated steam pressure is required. The number (n) of the expanded particles is the sum of the number of expanded particles peeled between the expanded particles and the number (b) of expanded particles whose material is destroyed in the expanded particles. A larger value of (b / n) is preferable because the bending strength and tensile strength of the molded body are increased.
[0072]
The compressive strength in Table 1 is a test piece obtained by cutting a molded body after curing obtained at the lowest fusing temperature so as to have a length of 50 mm, a width of 50 mm, and a thickness of 25 mm. ), And a compression test was performed until the strain reached 55% under conditions of a test piece temperature of 23 ° C. and a load speed of 10 mm / min according to JIS Z 0234 (1976) A method. -The stress at the time of 50% strain was read from the strain diagram, and this was taken as the compressive strength. The apparent density (g / L) of the expanded particles in Table 1 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 water at 100C at 23 ° C was measured. ^Three From the excluded volume when submerged in the water in the graduated cylinder in which the particle is contained, the apparent volume (cm ^Three ) And convert this to liters. From this measured value, the apparent density (g / L) of the expanded particles is calculated. In this measurement, the weight of the expanded particles is 0.5000 to 10.0000 g, and the apparent volume of the expanded particles is 50 to 90 cm. ³ The expanded particles are used. Since the internal pressure of the expanded particles in Table 1 is expressed by the gauge pressure as described above, (G) is appended to the numerical value. Further, in Example 1 and Reference Example 1, and in Examples 2 to 4 and Comparative Example 1 described later, the glass transition temperature, the melting point of the base resin, the melting point of the expanded particles, and the heat amount of the high temperature peak are Shimadzu Corporation. This was measured using a Shimadzu heat flux differential scanning calorimeter “DSC-50” manufactured by Seisakusho.
[0073]
The above results indicate that ΔH is present in the dispersion medium in which the organic peroxide is present. _a / ΔH _b A dispersion formed by dispersing polypropylene resin particles having a particle size of 0.95 or less is lower than the melting point of the base resin of the polypropylene resin particles, and the organic peroxide Is The surface of the polypropylene resin particles is modified by decomposing the organic peroxide while maintaining the temperature Nothing When the process of obtaining the surface-modified particles for crosslinking is employed, the foamed particles obtained therefrom are shown to reduce the molding temperature while maintaining the recyclability of the polypropylene resin. More specifically, it is as follows.
[0074]
In Example 1 that passed through the surface modification step and Reference Example 1 that did not go through the surface modification step, the apparent density of the expanded particles was close and the high-temperature peak heat amount of the entire expanded particles was almost the same. Although the apparent density and the apparent density of the cut sample of the sample for measuring the compressive strength are somewhat different, a comparison is possible. From comparison between Example 1 and Reference Example 1, although both expanded particles have almost the same high-temperature peak heat, the expanded particles of Example 1 that have undergone the surface modification step have a high-temperature peak heat at the surface layer. It can be seen that the temperature is lower than the high-temperature peak heat quantity of the surface layer portion of the expanded particles of Reference Example 1 that has not undergone the quality process. The minimum fusing temperature required in Example 1 is 0.36 MPa (G), whereas the minimum fusing temperature required in Reference Example 1 is that the internal pressure of the expanded particles is more than twice that of Example 1. Nevertheless, it exceeds 0.55 MPa (G), and it can be seen that the minimum fusing temperature of Example 1 is lower by 13 ° C. or more than that of Reference Example 1. Moreover, the compression strength of the molded body obtained in Example 1 is commensurate with the high temperature peak of the entire foamed particles and the apparent density of the cut sample, and is not particularly reduced.
It is considered that the decrease in the high-temperature peak heat quantity at the surface layer portion of the expanded particles contributes to the decrease in the minimum fusing temperature necessary at the time of molding.
[0075]
Furthermore, with respect to the foamed particles obtained in Example 1 and the foamed particles obtained in Reference Example 1, a micro thermal analysis system “2990 type micro thermal of TI Instruments Japan Co., Ltd. was applied to the surface of each foamed particle. Using the “analyzer”, micro differential thermal analysis (μDTA) was performed from 25 ° C. to 200 ° C. at a temperature increase rate of 10 ° C./second. As a result, the surface of the expanded particles obtained in Example 1 started to melt. While the temperature is 131 ° C. and the extrapolation melting start temperature is 135 ° C., the surface of the expanded particles obtained in Reference Example 1 has a melting start temperature of 168 ° C. and the extrapolation melting start temperature is 171 ° C. Met.
It is considered that the decrease in the melting start temperature or / and the extrapolation melting start temperature on the surface of the expanded particles due to the above-described μDTA contributes to the decrease in the minimum fusion temperature required at the time of molding.
[0076]
[Table 1]

[0077]
Examples 2-4, Comparative Example 1
Zinc borate powder (bubbles) per 100 parts by weight of polypropylene homopolymer (glass transition point: −21 ° C., Vicat softening point: 148 ° C., melting point: 163 ° C., crystallization temperature: 118 ° C., MFR: 8 g / 10 min) Adjusting agent) After adding 0.05 part by weight and melt-kneading in the extruder, it is extruded into a strand from the extruder, and X seconds after the extrusion (indicated as X in Table 2), the strand is placed in a water tank. Taken while cooling in a cooling medium (water adjusted to the temperature shown in Table 2), cooled, then cooled for the time shown in Table 2 (indicated as cooling time in Table 2), then pulled up from the cooling medium, length The strand was cut so that the / diameter ratio was approximately 1.0 to obtain resin particles having an average weight per particle of 2 mg. In addition, the accommodation amount of the cooling medium in the water tank was 170 liters. With respect to the obtained resin particles, ΔH _a And ΔH _b Was measured. The results are shown in Table 2.
[0078]
Next, in a 400 liter autoclave, 100 parts by weight of the resin particles, 220 parts by weight of ion exchange water at 23 ° C. as dispersion medium, 0.005 parts by weight of sodium dodecylbenzenesulfonate (surfactant) and 0 kaolin powder (dispersant) .3 parts by weight and 0.01 parts by weight of aluminum sulfate powder (dispersion strengthening agent), bis (4-tert-butylcyclohexyl) peroxydicarbonate as an organic peroxide (1-hour half-life temperature: 58 ° C., halved for 1 minute) (Phase temperature: 92 ° C.) and carbon dioxide gas (foaming agent) in the amount shown in Table 2 were charged, and the temperature was raised to a temperature 5 ° C. lower than the foaming temperature shown in Table 2 while stirring in an airtight state (average rate of temperature increase) From 3 ° C./min) 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. The release was performed while supplying high-pressure carbon dioxide gas into the autoclave so that the pressure inside the autoclave during the release of the resin particles from the autoclave was maintained at the pressure inside the autoclave immediately before the release. The obtained foamed particles were washed with water and subjected to a centrifuge. The obtained foamed particles were washed with water and subjected to a centrifuge, and then left to stand at atmospheric pressure at room temperature of 23 ° C. for 48 hours. In the same manner as above, the high-temperature peak heat amount of the entire foamed particles and the apparent density of the foamed particles were measured. The results are shown in Table 2.
[0079]
The expanded particles obtained in Examples 2 to 4 and Comparative Example 1 Nothing It was cross-linked (the boiling xylene insolubles were all 0). Next, after placing the foamed particles under pressurized air in a pressure-resistant container to give the foamed particles an increased bubble internal pressure, at the time of the bubble internal pressure shown in Table 2 (indicated as foamed particle internal pressure in the table), A mold having a molding space of 250 mm × 200 mm × 50 mm was filled in a state where a slight gap (about 1 mm) was opened without completely closing the mold (the direction of the molding space 50 mm was 51 mm). Thereafter, the mold was completely clamped, and after evacuation, it was molded at the lowest fusion temperature (minimum saturation steam pressure) shown in Table 2 in the same manner as in Example 1.
[0080]
[Table 2]

[0081]
As a result of the above, the polypropylene resin particles are dispersed in an aqueous medium in which the organic peroxide is present, the temperature is lower than the melting point of the base resin of the polypropylene resin particles, and the organic peroxide is present. Is The surface of the polypropylene resin particles is modified by decomposing the organic peroxide at a temperature to be dissolved. Nothing When the step of obtaining the surface modified particles for cross-linking is performed, the foamed particles obtained therefrom are shown to reduce the molding temperature while maintaining the recyclability of the polypropylene resin. More specifically, it is as follows.
[0082]
In Examples 2, 3, and 4 and Comparative Example 1, the apparent density of the expanded particles is substantially the same, and the entire high temperature peak heat amount and the internal pressure of the expanded particles are approximately the same, and the apparent density of the obtained molded body is Since it is the same, it is convenient to compare. From the comparison between Examples 2, 3, and 4 and Comparative Example 1, the minimum fusion temperature in Comparative Example 1 is 0.48 MPa (G), whereas the minimum fusion temperature in Examples 2, 3, and 4 is These are 0.41 MPa (G), 0.43 MPa (G), and 0.45 MPa (G), respectively.
From the above, it can be seen that the minimum fusing temperature of Example 4 is about 2 ° C. lower than that of Comparative Example 1, and that of Example 3 is about 3.5% lower than that of Comparative Example 1. It can be seen that the temperature is lowered, and in Example 2, the minimum fusing temperature is lowered by about 5 ° C. compared to Comparative Example 1.
From the results of Examples 2 to 4 and Comparative Example 1, when the surface modification conditions are the same, ΔH _a / ΔH _b It can be seen that the smaller the ratio is, the lower the minimum fusing temperature is.
[0083]
【The invention's effect】
The present invention provides ΔH _a / ΔH _b Since the ratio is 0.95 or less polypropylene resin particles, when the surface modification is performed on the resin particles, the surface modification can be efficiently performed. And the expanded particles obtained from the surface-modified resin particles (surface-modified particles) are ,Nothing Since it is cross-linking and the molding temperature is reduced as compared with the prior art, molding is possible with less energy. Conventionally, in order to achieve high physical properties such as high rigidity of an EPP molded body, it has been necessary to use expanded particles having a high high temperature peak heat quantity obtained by using a polypropylene resin having a high melting point. Although there was a problem that the temperature exceeded the pressure resistance of a general-purpose molding machine, the foamed particles obtained from the surface-modified particles had a high high-temperature peak heat obtained by using a polypropylene resin having a high melting point. Even foamed particles can be molded with steam at a lower temperature than before while maintaining the high rigidity of the resulting EPP molded body, and within the pressure resistance of a general-purpose molding machine if the surface modification is sufficient. Molding is also possible. Therefore, by using the expanded particles obtained by the method of the present invention, it is possible to provide an EPP molded body having higher physical properties (high rigidity) and / or lighter weight than conventional ones. Also, the surface-modified resin particles, the foamed particles, and the molded products Nothing Since it is cross-linking, it is preferable because it does not hinder the environmental suitability and recyclability of the polypropylene resin.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a first DSC curve chart of polypropylene resin expanded particles having a high temperature peak.
FIG. 2 is a diagram showing an example of a second DSC curve chart of polypropylene resin particles.
FIG. 3 is a diagram showing an example of a μDTA curve based on micro thermomechanical analysis on the surface of expanded particles obtained in each example based on Example 1 and Reference Example 1. FIG.
FIG. 4 is a diagram showing an example of a μDTA curve based on micro thermomechanical analysis on the surface of expanded particles obtained in another example.

Claims (3)

In a dispersion medium in which an organic peroxide is present, polypropylene resin particles having a polypropylene resin having a melting point of 158 ° C. or higher as a base resin are dispersed, and the dispersion medium is used as a base resin melting point of the polypropylene resin particles. and peroxide to a lower temperature than is held in decomposing temperature was obtained by decomposing the organic peroxide, a surface-modified resin particles for the production of expanded particles, the surface Immediately after the modified resin particles were heated by a differential scanning calorimeter from 30 ° C. to 200 ° C. at a rate of 10 ° C./min (first heating), 200 ° C. to 30 ° C. at a rate of −10 ° C./min. The amount of heat of the endothermic curve peak appearing in the DSC curve at the time of the first heating when heated from 30 ° C. to 200 ° C. at a rate of 10 ° C./min immediately after that (second heating). (ΔHa) and the second Polypropylene surface modified resin particles the ratio of the heat quantity (.DELTA.Hb) of the endothermic curve peaks appearing in the DSC curve at the time of eye heating (ΔHa / ΔHb) is characterized in that it is 0.95 or less. 2. The polypropylene-based surface-modified resin particles according to claim 1, wherein ΔHa / ΔHb is 0.85 or less. The resin particles are columnar particles having a ratio (L / D) of length (L) to average diameter (D) of 0.5 to 2, and the average weight per particle is 0.1 to 20 mg. The polypropylene-based surface-modified resin particles according to claim 1 or 2 , wherein:

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