JP5161409B2 - Polypropylene resin extruded foam sheet and thermoformed product of the extruded foam sheet - Google Patents

Description

【００５２】
【表２】

【００５３】
得られた発泡シートの１ｍ^２当たりの重量（坪量）、シート幅、平均厚み、見掛け密度、独立気泡率、１４０℃における引張降伏点強度、及びＮｇ値を表３に示す。
【００５４】
【表３】

【００５５】
実施例１〜１２では、結晶化物が発生することなく押出温度を１７７℃まで（実施例６では１７６．５℃まで、比較例５と実施例１２では１７９℃まで、実施例８と比較例６では１７６℃まで、実施例１１では１７４℃まで）低下させることができたので、表３に示す独立気泡率の発泡シートが得られた。これは、樹脂（Ｂ）が樹脂（Ａ）に対し、メルトフローレートが充分に大きかったことと、融点が高く且つ結晶化温度が充分に低かったことが寄与しているものと思われる。一方、比較例１〜３では、押出温度を１８４℃に低下させたところ、得られる発泡シートに結晶化物が発生してしまったため、１８５℃が冷却の限界と判断した。その結果、比較例１〜３で得られた発泡シートは、独立気泡率が極端に低いものとなってしまった。また、比較例４では、樹脂（Ｂ）の結晶化温度が高く、押出温度を充分に低下させることができず、結果として、押出直後のチューブ状の発泡体を広げた際に裂けが発生してしまった。
【００５６】
次に、実施例１〜１２で得られた発泡シートのそれぞれに対し、両面をヒーターで加熱して軟化させた後、プラグアシスト真空成形法によって、開口部直径１７０ｍｍ、底部直径１５０ｍｍ、深さ３０ｍｍの円形収納部を有するトレーを目標に成形したところ、型の出のしっかりとした良好な成形品（トレー）が得られた。
【００５７】
次に、比較例１〜３で得られた発泡シートのそれぞれに対し、実施例１〜３と同様に、両面をヒーターで加熱して軟化させた後、プラグアシスト真空成形法によって、開口部直径１７０ｍｍ、底部直径１５０ｍｍ、深さ３０ｍｍの円形収納部を有するトレーを目標に成形したところ、型に沿わず、成形品とは言い難いものしか得られなかった。
【００５８】
【発明の効果】
以上説明したように、本発明のポリプロピレン系樹脂押出発泡シートは、２３０℃におけるメルトテンションが１０ｃＮ以上のポリプロピレン系樹脂（Ａ）１５〜７０重量％と、２３０℃におけるメルトテンションが０．４ｃＮ以下のポリプロピレン系樹脂（Ｂ）８５〜３０重量％（ただし、ポリプロピレン系樹脂（Ａ）＋ポリプロピレン系樹脂（Ｂ）＝１００重量％）との混合物が基材樹脂となっており、高価な樹脂（Ａ）の使用量が少なく抑えられているためコストの低減が可能である。また、本発明のポリプロピレン系樹脂押出発泡シートは、発泡性に劣る樹脂（Ｂ）が３０重量％以上含まれており、１５０〜７５０ｇ／Ｌという見掛け密度に発泡されているにもかかわらず、独立気泡率が７７％以上であり、Ｎｇ値が発泡シートの押出方向および幅方向において１６０×１０ ^−４ Ｎ／ｇ以上であるため、型の出に優れた熱成形品を得ることが出来るという効果を奏する。
【図面の簡単な説明】
【図１】メルトテンションテスターのオリフィスから樹脂を紐状に押出して、捲取り速度一定として紐状の樹脂を捲取りローラーで捲取った時のメルトテンション：ＭＴの経時変化を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention is a polypropylene resin extruded foam sheet,as well asThe present invention relates to a thermoformed product of the extruded foam sheet.
[0002]
[Prior art]
Conventionally, food packaging containers and the like obtained by thermoforming polystyrene resin foam sheets have been widely used. These containers are excellent in light weight, appearance, rigidity, and heat insulation and are suitable as packaging materials. However, with the recent spread of microwave ovens, heat resistance and the like have been further required.
[0003]
On the other hand, a polypropylene resin foam sheet has recently attracted attention as a material for a thermoforming foam sheet that replaces a polystyrene resin foam sheet. This foamed sheet is produced by an extrusion foaming method using a high melt tension type polypropylene resin having a long chain branch as a raw material, developed by Highmont, USA.
[0004]
[Problems to be solved by the invention]
However, this polypropylene-based resin foam sheet is superior to the conventional polystyrene-based resin foam sheet in terms of heat resistance, but becomes expensive because it requires a step of forming a long-chain branch in the raw material polypropylene-based resin. There is a problem that the polypropylene resin foam sheet is inevitably expensive.
[0005]
In this regard, a low-cost low-tension type polypropylene resin (hereinafter referred to as “LMS-PP”) that does not have long chain branching to a high-melt tension type polypropylene resin (hereinafter referred to as “HMS-PP”). It is obvious that the cost of the foamed sheet can be reduced if the amount of expensive HMS-PP used can be reduced by mixing the above.
[0006]
However, if an attempt is made to obtain a polypropylene resin foamed sheet mixed with LMS-PP and having an apparent density of 150 to 750 g / L suitable for obtaining a thermoformed article having high shape-retaining properties, closed cells are inevitably produced. Since the rate is extremely lowered, it is difficult to use the foamed sheet mixed with LMS-PP for thermoforming.
[0007]
The present invention has been made in view of the above points, and an object thereof is to provide a polypropylene resin foam sheet having an apparent density of 150 to 750 g / L excellent in thermoformability at low cost.
[0008]
As a result of intensive studies on LMS-PP mixed with HMS-PP, the present inventors have selected a specific LMS-PP, so that even if it is a polypropylene resin foam sheet having an apparent density of 150 to 750 g / L. The present inventors have found that a polypropylene resin foam sheet having a high closed cell ratio and excellent thermoformability can be obtained, thereby completing the present invention.
[0009]
[Means for Solving the Problems]
That is, the present invention is (1) a polypropylene resin extruded foam sheet obtained by extrusion foaming a polypropylene resin containing one or more physical foaming agents selected from inorganic foaming agents and volatile foaming agents. ,
15 to 70% by weight of a polypropylene resin (A) having a melt tension at 230 ° C. of 10 cN or more, and 85 to 30% by weight of a polypropylene resin (B) having a melt tension at 230 ° C. of 0.4 cN or less (exceeding 0). % (However, the apparent density is 150 to 750 g / L and the closed cell ratio is a base resin of a mixture of polypropylene resin (A) + polypropylene resin (B) = 100 wt%).77% Or moreIn addition, the width of the foam sheet is 600 mm or more, and the tensile yield point strength (N) in the extrusion direction and the width direction of the polypropylene resin extruded foam sheet at 140 ° C. is 1 m of the foam sheet. ² The value divided by per weight (g) is 160 × 10 ^-4 N / g or more(2) 1 m of polypropylene resin extruded foam sheet, characterized in that²The polypropylene resin extruded foam sheet according to the above (1), wherein the weight per hit is 240 to 600 g, (3)30 to 60% by weight of a polypropylene resin (A) having a melt tension at 230 ° C. of 10 cN or more, and 70 to 40% by weight of a polypropylene resin (B) having a melt tension at 230 ° C. of 0.4 cN or less (exceeding 0). % (However, polypropylene resin (A) + polypropylene resin (B) = 100 wt%) as a base resin, the polypropylene resin as described in (1) or (2) above Extruded foam sheet,(4) The difference between the melting point of the polypropylene resin (B) and the melting point of the polypropylene resin (A) (the melting point of the resin (B) −the melting point of the resin (A)) is −2 to 8 ° C. AboveFrom (1) to (3)The polypropylene resin extruded foam sheet described,(5) The melt flow rate of the polypropylene resin (B) is 1.3 to 5.0 times the melt flow rate of the polypropylene resin (A).From (1) to (4)The polypropylene resin extruded foam sheet described,(6) Above (1)From(5The polypropylene resin extruded foam sheet according to any one of (1) and (2) is heat-softened and then thermoformed into a desired shape. .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The base resin used in the present invention comprises the following polypropylene resin (A) and polypropylene resin (B).
[0011]
Examples of the polypropylene resin (A) (hereinafter sometimes simply referred to as resin (A)) include polypropylene, ethylene-propylene block copolymer, ethylene-propylene random copolymer, and propylene-butene block copolymer. And propylene-based copolymers such as propylene-butene random copolymer and ethylene-propylene-butene terpolymer. The propylene-based copolymer usually has a propylene component content of 50% by weight or more, and particularly preferably 80% by weight or more.
[0012]
Resin (A) exhibits a high melt tension with a melt tension at 230 ° C. of 10 cN or more. When the melt tension of the resin (A) is less than 10 cN, it is a polypropylene resin extruded foam sheet with an apparent density of 150 to 750 g / L, and a foam sheet having an excellent closed cell ratio of 50% or more is obtained. I can't. In order to obtain a polypropylene resin extruded foam sheet having a higher closed cell ratio, the melt tension of the resin (A) is preferably 11 cN or more, more preferably 13 cN or more, and more preferably 15 cN or more. Further preferred. On the contrary, if the melt tension of the resin (A) becomes too large, the elongation of the foamed sheet to be obtained at the time of thermoforming may be reduced and the thermoformability may be lowered. The melt tension is preferably 60 cN or less, more preferably 50 cN or less, and still more preferably 40 cN or less.
[0013]
Moreover, as resin (A), it is preferable that melt flow rate (The value measured by the condition M of Appendix A Table 1 of JISK7210: 1999) is 0.3-12 g / 10min, 0.5 More preferably, it is ˜8 g / 10 minutes.
[0014]
Further, the melting point of the resin (A) is preferably 156 ° C. or higher in consideration of the heat resistance of the foamed sheet to be obtained.
[0015]
The resin (A) is usually made to form a long chain branch or slightly crosslink by applying an electron beam or a peroxide to a polypropylene resin having a low melt tension at 230 ° C. and a melt tension of 5 cN or less. Is obtained. Examples of such resin (A) include commercially available “PF814” and “SD632” manufactured by Montel.
[0016]
For the polypropylene resin (A) is excellent in extrusion foaming, it is possible to obtain a high extruded foam of closed cell content by using only the resin (A) as a base resin. However, the foam obtained using only the resin (A) has a high raw material cost. Therefore, in the present invention, in order to reduce the raw material cost, the following polypropylene resin (B) (hereinafter sometimes simply referred to as resin (B)) is mixed with resin (A) as the base resin. Use.
[0017]
Examples of the resin (B) include polypropylene, ethylene-propylene block copolymer, ethylene-propylene random copolymer, propylene-butene block copolymer, propylene-butene random copolymer, ethylene-propylene-butene ternary copolymer. Examples include propylene-based copolymers such as polymers. The propylene-based copolymer usually has a propylene component content of 50% by weight or more, and particularly preferably 80% by weight or more.
[0018]
Resin (B) has a melt tension at 230 ° C.0.4 cN or less (exceeding 0)Of low melt tension. Resin (B) has a melt tension at 230 ° C.Said upper limitUse of a polypropylene-based resin exceeding the range is not preferable because the raw material cost increases. The resin (B) usually corresponds to a normal polypropylene resin which has not been subjected to an operation of forming a long chain branch by slightly acting an electron beam or a peroxide or slightly crosslinking. Usually, melt tension at 230 ° C. of resin (B)Lower bound ofIs 0.05 cNsoThere is 0.1 cNButpreferable.
[0019]
Moreover, even if it is resin (A), the melt tension in 230 degreeC will fall to 5 cN or less in the thing which applied the strong shearing by the extruder etc. in the molten state. For example, a foamed sheet obtained by subjecting resin (A) or resin (A) and resin (B) to strong shearing in an extruder and then extrusion foaming can be used for thermoforming, etc. a melt tension at 230 ° C. Some of the pellets obtained a scrap or the like to melt again when it has that decreases below 5 cN, such pellets,When the melt tension is 0.4 cN or less,It can be used as the resin (B).
[0020]
The melt flow rate of the resin (B) (value measured under the condition M in Table 1 of Appendix A of JIS K7210: 1999) (hereinafter referred to as “MFR-B”) is the melt flow rate of the resin (A). (Hereinafter referred to as “MFR-A”) is preferably 1.2 times or more, and MFR-B is more preferably 1.3 to 5.0 times of MFR-A, and 1 of MFR-A. More preferably, it is 5 to 4.0 times. When MFR-B is 1.2 times or more of MFR-A, the foaming temperature can be sufficiently lowered, and a foam sheet having a high closed cell ratio can be easily obtained.
[0021]
In addition, when the resin (A) is melt-kneaded in an extruder or the like and then extruded, it increases to 2 to 4 times the melt flow rate before melt-kneading, but the resin (B) is melted before melt-kneading. Almost the same as the flow rate, or just a slight increase. Therefore, MFR-B is a melt of preferably 1.3 to 5.0 times the MFR-A, more preferably a resin in an extruder When it is 1.5 to 4.0 times (A) and the resin (B) Since the flow rates are almost the same, as a result, the mixing of the two becomes more uniform, and even if the foaming temperature is lowered sufficiently, the generation of crystallized products is suppressed, so a foam sheet with a higher closed cell ratio can be obtained. Can be obtained.
[0022]
Further, the resin (B) is selected so that the difference between the melting point of the resin (B) and the melting point of the resin (A) (melting point of the resin (B) −melting point of the resin (A)) is −2 to 8 ° C. The resin (B) is more preferably selected so that the difference is 1 to 7 ° C. As the difference becomes smaller than −2 ° C., if the foaming temperature is lowered to obtain a foam sheet having a high closed cell ratio, the resin (B) starts to crystallize and crystals are easily generated in the foam sheet. The value is reduced. Conversely, as the difference becomes larger than 8 ° C., it becomes difficult to obtain a foam sheet having a high closed cell ratio.
[0023]
In the present invention, as the resin (B), a polypropylene homopolymer, a propylene-ethylene block copolymer, or an impact-resistant polypropylene obtained by mixing a rubber component with a polypropylene homopolymer is preferably used. The melting point of the resin (B) is preferably 155 ° C. or higher, and more preferably 157 ° C. or higher.
[0024]
Moreover, it is preferable that the difference of the crystallization temperature of resin (A) and the crystallization temperature of resin (B) is 12 degreeC or more. If the difference is less than 12 ° C., crystallized products are likely to be generated during the production of the foamed sheet, which is not preferable. The difference is more preferably 13 to 35 ° C.
[0025]
In the present invention, the resin (A) and the resin (B), the resin (A) 15 to 70 wt%, the resin (B) 85 to 30 were mixed at a ratio of weight percent is used (however, the resin (A ) + Resin (B) = 100 wt%). At that time, if the mixing ratio of the resin (A) is too large, the contribution to cost reduction is reduced. Conversely, if the mixing ratio of the resin (A) is too small, it becomes difficult to obtain a foam sheet having a large closed cell ratio, or even if a foam sheet having a high closed cell ratio is obtained, the bubbles are broken during thermoforming. It is easy to foam and it becomes difficult to obtain a good thermoformed product. From this point of view, the resin (A) and the resin (B), the resin (A) 30 to 60 wt%, the resin (B) 70 to 40 are used in a ratio by weight% (where the resin (A) + resin (B) = 100 wt%) is preferable.
[0026]
In the present invention, the base resin is basically a mixture of the resin (A) and the resin (B). However, in the range not impairing the intended purpose of the present invention, the ionomer or In addition, an elastomer such as ethylene-propylene rubber may be contained and used. These amounts are at most 30 parts by weight per 100 parts by weight of the mixture of the resin (A) and the resin (B), but are preferably 20 parts by weight or less.
[0027]
The melt tension of the resin (A) or the resin (B) can be measured with a melt tension tester type II manufactured by Toyo Seiki Seisakusho Co., Ltd. Specifically, using a melt tension tester having an orifice with an inner diameter of 2.095 mm and a length of 8 mm, the orifice is heated to 230 ° C. in advance, and resin (A) or resin (B) is placed therein. After putting 4 g and leaving it for 5 minutes, the extrusion speed of the piston was set to 10 mm / min, 230 ° C. molten resin was extruded into a string from the orifice, and this string was put on a tension detection pulley having a diameter of 45 mm, and then 5 rpm / Sec. (Strike speed of string-like object: 1.3 × 10^-2m / sec²) While gradually increasing the scraping speed at a ratio of), scraping is performed with a scraping roller having a diameter of 50 mm.
[0028]
In the present invention, in order to obtain the melt tension, first, the scooping speed is increased until the string-like material hung on the tension detecting pulley is cut, and the scooping speed when the cord-like material is cut: R (rpm) Ask. Next, the string-like material is removed at a constant tearing speed of R × 0.7 (rpm), and the melt tension of the string-like material detected by the detector connected to the tension detection pulley is measured over time. Then, when the melt tension is plotted on the vertical axis and the time is plotted on the horizontal axis, a graph having an amplitude as shown in FIG. 1 is obtained.
[0029]
As the melt tension in the present invention, the median value (X) of the amplitude of the stable portion in FIG. 1 is adopted. However, if the string-like material does not break even when the reeling speed reaches 500 rpm, the melt tension of the string-like material is obtained from the graph obtained by winding the string-like material with the stringing speed set to 500 rpm. At the time of time measurement of the melt tension, but sometimes rarely peculiar amplitude values are detected, it is assumed to ignore such peculiar amplitude values.
[0030]
The melting points of the resin (A) and the resin (B) are 3 to 5 mg of the raw material resin from a room temperature (15 to 30 ° C.) at a temperature rising rate of 10 ° C./min in a nitrogen gas atmosphere using a differential scanning calorimeter. Obtained when the temperature was raised to 210 ° C. and the first DSC curve was obtained, then immediately lowered to 40 ° C. at a temperature lowering rate of 10 ° C./min, and then again raised to 210 ° C. at a temperature raising rate of 10 ° C./min. The temperature at the top of the main melting peak appearing on the highest temperature side on the second DSC curve. The crystallization temperature is the temperature at the top of the main exothermic peak appearing on the highest temperature side on the DSC curve obtained when the temperature is lowered to 40 ° C. immediately after the first DSC curve is obtained. .
[0031]
In the polypropylene resin extruded foam sheet of the present invention, the resin (A) and the resin (B) are put into the extruder from the hopper in the extruder at the above ratio, and the resin (A) and the resin (B) are melted in the extruder. At the same time, after kneading with a foaming agent, this melt-kneaded product is extruded under low pressure through a die attached to the tip of the extruder and foamed. In order to obtain a sheet-like foam in the present invention, a circular die having an annular lip is used, and extrusion foaming is performed from the die lip to obtain a tubular foam, and then the tube is cut open to form a sheet. The method is preferably adopted. In addition, it can manufacture also by the method of extruding from a T die instead of a circular die.
[0032]
As the foaming agent, an inorganic foaming agentWhenVolatile blowing agentOne or more physical foaming agents selected fromIs used. Carbon dioxide, air, nitrogen, etc. can be used as the inorganic foaming agent. Volatile blowing agents include aliphatic hydrocarbons such as propane, n-butane, i-butane, pentane and hexane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, dichlorotetra Halogenated hydrocarbons such as fluoroethane, methyl chloride, ethyl chloride, and methylene chloride can be used..These foaming agents can be appropriately mixed and used.
[0033]
The amount of foaming agent used varies depending on the type of foaming agent, desired foaming ratio, etc., but the guideline of the amount of foaming agent used to obtain a polypropylene resin extruded foam sheet with an apparent density of 150 to 750 g / L is as follows: The amount is about 0.1 to 5 parts by weight per 100 parts by weight of the resin.
[0034]
When the base resin and the foaming agent are melt-kneaded in the extruder, various additives can be added as necessary. Additives include inorganic powders such as talc and silica, acidic salts of polycarboxylic acids, bubble regulators such as a reaction mixture of polycarboxylic acid and sodium carbonate or sodium bicarbonate, talc, silica, calcium carbonate, clay Inorganic fillers such as zeolite, alumina and barium sulfate (talc and silica also have a function as a bubble regulator), heat stabilizers, ultraviolet absorbers, antioxidants, colorants and the like. The bubble regulator can be added in an amount of about 13 parts by weight or less per 100 parts by weight of the base resin (except when the resin contains a large amount of the inorganic filler).
[0035]
The foamed sheet of the present invention has an apparent density of 150 to 750 g / L and a closed cell ratio obtained by the method described above.77% Of a polypropylene resin extruded foam sheet. When the apparent density is less than 150 g / L, it becomes difficult to maintain the closed cell ratio of the obtained foamed sheet at 50% or more, and the thermoformability deteriorates. On the other hand, when the apparent density is higher than 750 g / L, the heat insulating performance of the foam sheet and the thermoformed product obtained therefrom is extremely deteriorated, which is not preferable. From such a viewpoint, the apparent density of the foamed sheet of the present invention is preferably 160 to 450 g / L, and more preferably 170 to 400 g / L. Moreover, if the closed cell ratio of the foam sheet is smaller than 50%, the thermoformability is deteriorated..
[0036]
The foam sheet of the present invention isThe width is 600 mm or more,The width is preferably 600 to 1200 mm. A foam sheet having such a width is preferable because a normal thermoforming machine can be used. The foam sheet of the present invention is 1 m²The per weight (basis weight) is preferably 240 to 600 g. The larger the basis weight, the easier it is to produce a foam sheet having a higher closed cell ratio. However, if the basis weight becomes too large, the apparent density of the foam sheet cannot be maintained at 750 g / L or less. The thickness of the foam sheet is usually 0.5 to 2.5 mm, but preferably 0.7 to 2.0 mm.
[0037]
The thickness of the foam sheet can be adjusted by, for example, the size of the die slit gap, and the width can be adjusted by the size of the die slit width (or the die lip diameter and blow-up ratio in the case of a circular die). it can. The apparent density can generally be adjusted by the amount of foaming agent added.
[0038]
The foam sheet of the present invention has a tensile yield point strength (N) at 140 ° C. of 1 m of the foam sheet.²The value divided by the weight per gram (g) (hereinafter referred to as “Ng value”) is not only in the extrusion direction of the foam sheet but also in the so-called width direction orthogonal to the extrusion direction,160x10^-4N / g or more.As the Ng value increases, cracks are less likely to occur when the sheet is stretched during thermoforming. However, if it is too large, sharp thermoforming may be difficult. From this point of view, the Ng value is 220 × 10^-4N / g or less is preferredNew.
[0039]
The tensile yield point strength at 140 ° C. was adjusted to 140 ° C. in accordance with JIS K6767: 1999 Annex 1 2 with the distance between chucks set to 50 mm and the temperature chamber surrounding the measurement site of the tensile tester. (Temperature control continues until the tensile test is completed.) Open the thermostatic chamber door, quickly load the measurement sample in the thermostatic chamber, and then close the thermostatic chamber door. 4 seconds) and then left for 1 minute before starting the tensile test. At this time, measurement is performed three times for each direction, and the arithmetic average value of the three times is adopted.
[0040]
The tensile yield point strength at 140 ° C. of the foamed sheet shows a larger value as the closed cell ratio is higher, the basis weight is heavier, and the degree of tension in the extrusion direction and the width direction immediately after extrusion is larger to a certain extent. By conducting preliminary experiments in consideration of these points, a foam sheet having a target tensile yield strength can be obtained.
[0041]
The closed cell ratio (%) of the foamed sheet is based on the procedure C described in ASTM D2856-70, and is measured using an air comparison type hydrometer 930 type manufactured by Toshiba Beckman Co., Ltd. It is calculated from the true volume: Vx by the following formula (1), and is obtained as an average value of three measured values.
[0042]
[Expression 1]
S (%) = (Vx−W / ρ) × 100 / (Va−W / ρ) (1)
[0043]
However, in the above equation (1), Vx is the true volume (cm^Three) Corresponds to the sum of the volume of the resin constituting the foam and the total volume of bubbles in the closed cell portion in the foam. In addition, Va, W, and ρ in the above formula (1) are as follows.
[0044]
Va: Apparent volume of the foam (cm) calculated from the outer dimensions of the foam used for the measurement^Three)
W: Total weight of the foam used for measurement (g)
ρ: Density of base resin constituting the foam (g / cm^Three)
[0045]
In addition, since the test piece must be stored in a non-compressed state in the sample cup attached to the air comparison type hydrometer, cut the length and width to 2.5 cm each (thickness is left as it is) Apparent volume is 15cm^ThreeA plurality of sheets are used so as to be closest to each other.
[0046]
The extruded foam sheet can be heat-softened and thermoformed into a desired shape. Examples of the foam molding method include a method in which the foam is heat-softened and bent to form a box-like body, and a method in which the foam is heat-softened and then closely adhered to the mold and molded into a desired shape. It is done. The latter method includes, for example, vacuum forming, pressure forming, and applications such as free drawing forming, plug-and-ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, and air slip forming. Further, plug assist molding, plug assist reverse draw molding, or a combination of these can be employed.
[0047]
For the extruded foam sheet of the present invention, a substantially non-foamed thermoplastic resin film or sheet can be laminated on one side or both sides of the extruded foam sheet, if necessary. The substantially non-foamed thermoplastic resin film or sheet (hereinafter referred to as “non-foamed resin layer”) may have a single-layer structure or a multi-layer structure. In any case, the thickness on one side of the non-foamed resin layer is preferably 5 to 500 μm, more preferably 10 to 300 μm, and more preferably 15 to 100 μm.
[0048]
Moreover, as a non-foaming resin layer, what consists of polypropylene resin is preferable. If the non-foamed resin layer is made of polypropylene resin, it can be easily adhered to the foamed sheet by extrusion lamination, lamination by passing between the hot roll and the nip, or coextrusion lamination. Can do.
[0049]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0050]
Examples 1-12Comparative Examples 1 to6
Resin (A) and resin (B) shown in Table 1 are dry blended in advance at the ratio shown in Table 2, and this is put into a hopper of an extruder, and a bubble regulator master batch (Nippon Boehringer Ingelheim Co., Ltd.) The company's “H-CF20E”) was charged into the hopper of the extruder at the ratio shown in Table 2 (weight ratio per 100 parts by weight of the dry blend of resin (A) and resin (B)), and the resin ( After melting A) and resin (B) and kneading with H-CF20E, a foaming agent (in Examples 1-6 and Comparative Examples 1-4 uses isobutane in the extruder)Comparative Example 5Then, carbon dioxide was used. ) At a ratio shown in Table 2 (weight ratio per 100 parts by weight of the dry blend of the resin (A) and the resin (B)), and the molten resin and the foaming agent are sufficiently kneaded, and then gradually The temperature of the melt-kneaded product is lowered and extruded and foamed through a circular die having a lip with a diameter of 78 mm and a gap of 0.3 mm to obtain a tubular foam, and then the inside of the tubeTheWhile cooling along the surface of the cylindrical cooling drum, cooling was performed by blowing air onto the outer surface of the tube, and then the cooled tube was cut open to obtain a sheet-like foam. The extrusion temperature, die pressure, and extrusion amount at this time are shown together in Table 2.
[0051]
[Table 1]

[0052]
[Table 2]

[0053]
1m of the obtained foam sheet²Table 3 shows the per weight (basis weight), sheet width, average thickness, apparent density, closed cell ratio, tensile yield point strength at 140 ° C., and Ng value.
[0054]
[Table 3]

[0055]
Example 112Then, the extrusion temperature up to 177 ° C. without generating crystallized (up to 176.5 ° C. in Example 6,Comparative Example 5And examples12In the examples up to 179 ° C8WhenComparative Example 6In the examples up to 176 ° C11So it could be reduced to 174 ° C)Shown in Table 3Closed cell ratioofA foam sheet was obtained. This is probably because the resin (B) had a sufficiently high melt flow rate as compared to the resin (A), and the melting point was high and the crystallization temperature was sufficiently low. On the other hand, in Comparative Examples 1 to 3, the extrusion temperature was lowered to 184 ° C.LetAs a result, since a crystallized product was generated in the obtained foamed sheet, 185 ° C. was judged to be the limit of cooling. As a result, the foam sheets obtained in Comparative Examples 1 to 3 had extremely low closed cell ratios. Further, in Comparative Example 4, the crystallization temperature of the resin (B) is high, and the extrusion temperature cannot be lowered sufficiently. As a result, tearing occurs when the tubular foam immediately after extrusion is expanded. I have.
[0056]
Next, Examples 1 to12Each of the foam sheets obtained in the above was heated and softened on both sides with a heater, and then a tray having a circular storage portion with an opening diameter of 170 mm, a bottom diameter of 150 mm, and a depth of 30 mm was obtained by a plug-assisted vacuum forming method. When molded to the target, a good molded product (tray) with a solid mold was obtained.
[0057]
Next, for each of the foamed sheets obtained in Comparative Examples 1 to 3, after both surfaces were heated with a heater and softened in the same manner as in Examples 1 to 3, the opening diameter was measured by a plug-assisted vacuum forming method. When a tray having a circular storage portion having a diameter of 170 mm, a bottom diameter of 150 mm, and a depth of 30 mm was formed as a target, only a molded product that could not be said to be a molded product was obtained.
[0058]
【Effect of the invention】
  As described above, the polypropylene resin extruded foam sheet of the present invention has 15 to 70% by weight of a polypropylene resin (A) having a melt tension of 10 cN or more at 230 ° C. and a melt tension of 0.4 cN or less at 230 ° C. A mixture of polypropylene resin (B) 85-30 wt% (however, polypropylene resin (A) + polypropylene resin (B) = 100 wt%) is the base resin, and expensive resin (A) Since the amount of use is reduced, the cost can be reduced. In addition, the polypropylene resin extruded foam sheet of the present invention contains 30% by weight or more of the resin (B) that is inferior in foamability, and is independent even though it is foamed to an apparent density of 150 to 750 g / L. Bubble rate is77%AboveYes, Ng value is 160 × 10 in the extrusion direction and width direction of the foam sheet ^-4 N / g or moreTherefore, there is an effect that it is possible to obtain a thermoformed product that is excellent in mold release.
[Brief description of the drawings]
FIG. 1 is a graph showing the change over time in melt tension: MT when resin is extruded into a string from an orifice of a melt tension tester and the string-like resin is scraped with a scraping roller at a constant scooping speed.

Claims (6)

A polypropylene resin extruded foam sheet obtained by extrusion foaming a polypropylene resin containing one or more physical foaming agents selected from an inorganic foaming agent and a volatile foaming agent,
15 to 70% by weight of a polypropylene resin (A) having a melt tension at 230 ° C. of 10 cN or more, and 85 to 30% by weight of a polypropylene resin (B) having a melt tension at 230 ° C. of 0.4 cN or less (exceeding 0). % (Provided that the base resin is a mixture of polypropylene resin (A) + polypropylene resin (B) = 100 wt%), the apparent density is 150 to 750 g / L, and the closed cell ratio is 77 % or more. The width of the foam sheet is 600 mm or more, and the tensile yield point strength (N) in the extrusion direction and the width direction at 140 ° C. of the polypropylene resin extruded foam sheet is divided by the weight (g) per 1 m ^{2 of} the foam sheet. value is a polypropylene resin extruded foam sea, characterized in that at both 160 × 10 -4 ^{N / g} or more . The polypropylene resin extruded foam sheet according to claim 1, wherein the weight of the polypropylene resin extruded foam sheet is 240 to 600 g per 1 m ² . 30 to 60% by weight of a polypropylene resin (A) having a melt tension at 230 ° C. of 10 cN or more and 70 to 40% by weight of a polypropylene resin (B) having a melt tension at 230 ° C. of 0.4 cN or less (exceeding 0). % (Provided that polypropylene resin (A) + polypropylene resin (B) = 100% by weight) is a base resin, and is a polypropylene resin extruded foam sheet according to claim 1 or 2 . The difference between the melting point of the polypropylene resin (B) and the melting point of the polypropylene resin (A) (the melting point of the resin (B)-the melting point of the resin (A)) is -2 to 8 ° C. The polypropylene resin extruded foam sheet according to any one of 1 to 3 . The polypropylene resin extruded foam sheet according to any one of claims 1 to 4, wherein the melt flow rate of the polypropylene resin (B) is 1.3 to 5.0 times the melt flow rate of the polypropylene resin (A). . A thermoformed article of a polypropylene resin extruded foam sheet, which is obtained by heat-softening the polypropylene resin extruded foam sheet according to any one of claims 1 to 5 and then thermoforming it into a desired shape.

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