JP4004321B2 - Polypropylene resin foam sheet and container - Google Patents

Description

【００３２】
（Ａ）高溶融張力ＰＰ：ＭＦＲ＝４．０ｇ／１０分（チッソ社製、ＦＨ３５００）
（Ｂ）直鎖状の結晶性ＰＰ：ＭＦＲ＝３．４ｇ／１０分（チッソ社製、Ａ５０１４）
（Ｃ）ＳＥＢＳ＝スチレン−エチレン・ブチレン−スチレンブロック共重合体
スチレン含有量１８％（旭化成社製、タフテックＨ１０６２）
発泡剤種：ＣＦ＝化学発泡剤（クラリアント社、ＣＦ４０Ｅ−Ｊ）
炭酸ガス＝物理発泡剤
ＭＦＲ：２３０℃測定値（ＪＩＳ−Ｋ６７５８法）
【００３３】
表１に得られた発泡シートのシート密度、シート厚み、シート外観、シート押出性、デュポン衝撃強度、及び実用落下試験の測定結果を示す。
【００３４】
各実施例のシートは、シート表面外観、シート押出性に優れると共に、実用落下試験における発泡シート成形体である容器の破損がみられないことから、耐衝撃性に優れ、電子部品の包装材料として優れた性能を有している。また、比較例１および２においては耐衝撃性のレベルが低く、実使用に耐えない。比較例３はシート外観や耐衝撃性は良好であるが、連続運転時の目ヤニの発生があり押出性に劣るものであった。比較例４および５は耐衝撃性は高いものの、シート外観が劣り表面破泡のために成形性および商品性に劣る。
【００３５】
【発明の効果】
本発明によれば、比較的低発泡倍率で表面平滑性が良好で寸法精度が良好であり、且つ優れた耐衝撃性を合わせ持った発泡シート及び発泡成形体である容器が得られ、大型の電子部品等の搬送用等に有用である。
【図面の簡単な説明】
【図１】 本発明の容器（一例）の断面図である。
【図２】 本発明の容器（一例）の平面図である。[0001]
BACKGROUND OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention can be applied to uses that require absorption and relaxation with respect to impact, and is particularly suitable as a packaging material for electronic parts. It is excellent in impact resistance, has good dimensional accuracy, and has a high surface smoothness. The present invention relates to a foamed sheet and a thermoplastic resin foamed molded article obtained by thermoforming the sheet. In the present invention, “%”, “part” and the blending ratio representing the composition of the resin composition are values based on mass, and unless otherwise specified, are represented by values when the total of the resin components is 100.
[0002]
[Prior art]
Conventionally, as a cushioning material that protects contents and deposits from impacts, etc., a thermoplastic foam sheet (hereinafter simply referred to as “foam sheet”) that is excellent in heat insulation, heat retention, cushioning, etc. and lightweight. Abbreviated) is a thermoplastic resin foam molded body (hereinafter abbreviated as “foam molded body”) such as a container that is thermoformed into a specific shape. As a specific example of the foam sheet having excellent properties, the polypropylene resin foam sheet has excellent performance in heat resistance. By utilizing the properties, automobile interior materials, household goods, food packaging materials, and electronic packaging are used. It is a material that is being developed for various uses in the field of materials.
[0003]
Among these applications, especially in packaging materials for electronic parts and precision machine parts, in order to protect the contents from impacts during transfer and storage, they have high cushioning performance and foam sheets. The foamed molding obtained by thermoforming is required to have a high dimensional accuracy, to have no irregularities due to surface bubble breakage, etc., to have high surface smoothness and excellent appearance. That is, the contents are firmly fixed, and the contents are protected from impacts such as vibration during transportation, and at the same time, the foam molded body and the contents are rubbed to minimize generation of fine wear powder from the foam molded body. It is necessary to keep it to the limit.
[0004]
As a method for obtaining a foamed molded product having high buffering properties, it is generally performed to reduce the apparent density (specific gravity) of the foamed sheet and to obtain a highly foamed molded product having a relatively large thickness. Therefore, when the foamed sheet is thermoformed into a foamed molded product containing a packaged body, the foamable sheet has poor formability, making it difficult to obtain a foamed molded product having a desired shape, and high dimensional accuracy is required. It is not suitable for packaging electronic parts. In addition, a plurality of cushioning foam sheets are often stacked for transportation, storage, etc., and in such a case, the highly foamed and thick material is bulky, so that it is sufficient to accommodate a large number of contents. There are problems such as inability to secure space.
[0005]
On the other hand, in the foam having a low expansion ratio, the dimensional accuracy is relatively good, but the buffering performance may not be sufficient. To improve the problem, for example, as an improvement in impact resistance, for example, JP-A-6-212007 The publication proposes a method of adding an ethylene / α-olefin copolymer and high-density polyethylene to a polypropylene block copolymer. However, even these foamed molded products have insufficient impact resistance. For example, a large liquid crystal panel with a large shape to be packaged has a large weight and when it is accidentally dropped during transportation. As described above, when a large impact is applied from the outside, the foamed molded body may crack and damage the packaged product or affect its function, and there has been a need for improvement.
[0006]
As a means to further improve the impact resistance of foams with a low expansion ratio, a polypropylene resin having a high melt tension as a main component is used to increase the closed cell ratio, and a thermoplastic elastomer is added to improve the impact resistance. Although such a method can improve the properties such as impact resistance of the obtained foam sheet, in the foam sheet manufacturing process, during the continuous operation of the extruder, There is a problem in that productivity is low because the lip portion of the die, which is the die opening, is prone to eye cracks and requires maintenance.
[0007]
[Problems to be solved by the invention]
The present invention solves the above problems, a foam sheet having a relatively low foaming ratio, good surface smoothness, good dimensional accuracy, and excellent impact resistance, and a molded article thereof In particular, the present invention provides a foamed container that is suitably used for packaging electronic parts and the like that are particularly demanding.
[0008]
[Means for Solving the Problems]
The present invention has reached the present invention as a result of intensive studies on the above-mentioned problems. That is, it contains a high melt tension polypropylene resin (A), a linear crystalline polypropylene resin (B) and a styrene-ethylene-butylene-styrene block copolymer (C), and the following requirements 1 to 3 It is a polypropylene resin foam sheet that satisfies the above.
1. The component (A) is a high melt tension polypropylene resin having a melt tension at 200 ° C. of 4.0 g or more.
2. (C) Content of a component is 10 to 30%.
3. The density of the foam sheet is 180 kgm ⁻³ or more and less than 850 kgm ⁻³ .
The styrene content of the styrene-ethylene / butylene-styrene block copolymer (C) is preferably 10 to 40%. In addition, as the high melt tension polypropylene resin (A) and the linear crystalline polypropylene resin (B), a resin having an MFR at 230 ° C. of 2.0 to 5.0 g / 10 min is used (A The composition ratio (A) / (B) is preferably 50/50 to 90/10 when the total of the component (B) and the component (B) is 100. Furthermore, this invention includes the container which consists of said polypropylene resin foam sheet.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. The present invention mainly comprises a polypropylene resin comprising a high melt tension polypropylene resin and a linear crystalline polypropylene resin and a specific amount of styrene-ethylene-butylene-styrene block copolymer as described above. It is a foam sheet obtained by foaming a resin composition in a specific density range with a relatively low expansion ratio.
[0010]
In the present invention, the polypropylene resin is a homopolymer or copolymer obtained by polymerizing a propylene monomer as a main component, for example, a propylene homopolymer, a propylene-ethylene copolymer, a propylene-ethylene-diene copolymer. It is a polymer mainly composed of polypropylene such as coalescence.
[0011]
The (A) high melt tension polypropylene resin referred to in the present invention is the above polypropylene resin having a melt tension at 200 ° C. of 4.0 g or more. When the melt tension is less than 4.0 g, it is difficult to maintain air bubbles in the sheet during extrusion foaming, and it is difficult to obtain a good foamed sheet with high surface smoothness. In addition, surface foaming tends to occur during heating of the sheet during thermoforming, and irregularities are formed on the surface, which tends to reduce the appearance of the foamed molded article after molding. Here, the melt tension described in the present invention is obtained by using a capilograph manufactured by Toyo Seiki Seisakusho Co., Ltd. to melt the polypropylene by heating it at 200 ° C. for 5 minutes in the barrel of the apparatus. A value obtained by measuring the tension when a strand of 095 mm, length 8 mm, L / D = 3.8 is extruded into the atmosphere at a speed of 15 mm / min and taken up at a speed of 2.0 m / min. is there.
[0012]
The linear crystalline polypropylene resin (B) referred to in the present invention is the polypropylene resin described above, and includes those having units of monomers such as ethylene and butene other than propylene. It is a resin having a substantially linear molecular structure and crystallinity.
[0013]
The polypropylene resin foam sheet of the present invention uses the high melt tension polypropylene resin (A) and the linear crystalline polypropylene resin (B) as the polypropylene resin. Further, if it is a small amount within the range not affecting the effect of the present invention, it may be a mixture of polypropylene resins other than the above (A) and (B) and / or other resins having good miscibility. Examples of such resins include polyethylene resins, ethylene vinyl acetate copolymer resins, ethylene propylene random copolymer resins, ethylene / butene / propylene copolymer resins and ethylene / propylene rubbers.
[0014]
In the present invention, the styrene-ethylene / butylene-styrene block copolymer (C) is a resin obtained by hydrogenating a butadiene block portion of a copolymer comprising a styrene polymer block and a butadiene polymer block. In general, these are commercially available as SEBS resins. In this copolymer, those having a styrene content of 10 to 40% are preferably used. If the styrene content is less than 10%, the dispersed particle diameter of the styrene component in the styrene-ethylene / butylene-styrene block copolymer becomes fine, and the impact resistance improving effect becomes insufficient. On the other hand, if the styrene content exceeds 40%, the compatibility with the polypropylene resin decreases due to an increase in the styrene component, and the effect of improving the impact resistance becomes insufficient.
[0015]
In the present invention, the content of the styrene-ethylene-butylene-styrene block copolymer (C) in the foamed sheet is 10 to 30%. When the component (C) is less than 10%, the impact strength is not improved sufficiently. On the other hand, when the component is more than 30%, the proportion of the polypropylene resin as the main component as the foam decreases, so the melt tension of the resin component And the appearance of the sheet is impaired due to bubble breakage on the sheet surface.
[0016]
It is preferable to use a resin whose MFR at 230 ° C. of the high melt tension polypropylene resin (A) and the linear crystalline polypropylene resin (B) is 2.0 to 5.0 g / 10 min. If the MFR is less than 2.0 g / 10 min, the extrudability becomes unstable due to the effect of decreasing fluidity, and if it exceeds 5.0 g / 10 min, the extrudability becomes stable but the viscosity decreases. Therefore, it is difficult to uniformly form the bubbles, the growth of the bubbles cannot be suppressed, the bubble wall is easily broken, irregularities are generated on the sheet surface, and the surface appearance is deteriorated.
[0017]
The blending ratio of the polypropylene resin component composed of the high melt tension polypropylene resin (A) and the linear crystalline polypropylene resin (B) is the sum of the component (A) and the component (B) as 100. The composition ratio (A) / (B) is preferably 50/50 to 90/10. When the blending ratio of the high melt tension polypropylene resin (A) is less than 50, it is not preferable that bubbles are connected and the foam gas is dissipated during the formation of the foam sheet. If the blending ratio of the linear crystalline polypropylene resin (B) is less than 10, the extrusion stability at the time of forming the foamed sheet is lowered, and the mouthpiece provided at the tip of the extruder during continuous operation of the extruder This is not preferable because the lip portion of the die is likely to be damaged.
[0018]
The mixing method of the high melt tension polypropylene resin (A), the linear crystalline polypropylene resin (B) and the styrene-ethylene-butylene-styrene block copolymer (C) is not particularly limited. A method of directly feeding the raw material stirred and mixed into the extruder, or a method of melting and mixing the raw material after stirring and mixing with a single-screw or twin-screw extruder to form pellets, and the like can be used.
[0019]
Carbon dioxide gas is used as the foaming agent in the present invention as a chemical foaming agent or a physical foaming agent. As the chemical foaming agent, a mixture of sodium bicarbonate and citric acid is preferably used, and the generated foaming gas is carbon dioxide. The method of adding the chemical foaming agent is not particularly limited, but a method of dry blending to a resin composition of a polypropylene resin, a method of adding using a quantitative feeder in a hopper of an extruder, a polypropylene resin, Any method of creating and adding a masterbatch based on a polyolefin resin such as a polyethylene resin may be used. The amount of chemical foaming agent added is within a range where a desired foaming ratio can be obtained, and the specific amount varies depending on the type of foaming agent, but when the total resin composition component is 100%, 0.1 to 3.0 parts are added. It is preferable to do. If the addition amount is less than 0.1 part, the desired foaming ratio cannot be obtained, and if added over 3.0 parts, the uniform dispersion and sufficient decomposition of the foaming agent in the extruder does not proceed, A good foam sheet may not be obtained.
[0020]
On the other hand, as the physical foaming agent, an explosion-proof facility is not required in the extrusion facility, and an inert gas and carbon dioxide gas excellent in safety are preferably used. As a method for adding a physical foaming agent, a method of directly injecting carbon dioxide gas from a position set to lower the pressure of the molten resin of the first stage extruder of the tandem extruder, or the same pressure of the twin screw extruder is lowered. A method of supplying to a set position is exemplified. The addition amount of the physical foaming agent is within a range where a desired expansion ratio can be obtained, and is preferably 0.1 to 3.0 parts. When the addition amount is less than 0.1 part, the desired foaming ratio cannot be obtained, and when the addition amount exceeds 3.0 parts, the closed cell ratio may decrease. Moreover, in order to control the cell diameter of the foamed sheet to an appropriate size, if necessary, a foam nucleating agent such as a mixture of sodium bicarbonate and citric acid or talc may be used in combination.
[0021]
The density of the polypropylene resin foam sheet of the present invention is 180 kgm ⁻³ or more and less than 850 kgm ⁻³ , and more preferably 300 kgm ⁻³ or more and less than 600 kgm ⁻³ . When the density is lower than 180 kgm ⁻³ , the closed cell ratio of the foam cell is lowered, and when the container is molded, the surface appearance of the molded product is lowered. Further, if the density is 850 kgm ⁻³ or more, sufficient buffering properties and light weight cannot be obtained. The closed cell ratio is preferably 40% or more. When the closed cell ratio is lower than 40%, the sag increases when the sheet is heated during thermoforming, and surface foaming tends to occur, and the appearance of the container, which is a molded product, tends to decrease.
[0022]
The polypropylene resin foam sheet of the present invention can be kneaded with an antistatic agent generally used for suppressing the generation of static electricity due to charging on the surface, or can be applied to the surface. Moreover, it can also be used by performing antistatic or conductive printing on the surface. Furthermore, it can also be used as a laminated sheet in which a non-foamed layer is laminated on one side or both sides by a general method such as film lamination for the purpose of surface protection or decoration.
[0023]
As a method for producing the polypropylene resin foam sheet of the present invention, the high melt tension polypropylene resin (A), the linear crystalline polypropylene resin (B), and the styrene-ethylene-butylene-styrene block copolymer are used. A known extrusion foaming method using a carbon dioxide gas which is a chemical foaming agent or a physical foaming agent is used as a foaming agent for the mixture with the coalesced (C). For example, a resin melted and softened in an extruder such as a single screw extruder, a twin screw extruder, or a tandem extruder is extruded from a die having a straight die (T-type die), and then a cooling medium is placed inside. A method of cooling by contacting with a metal cooling roll that has been circulated, or by extruding from an annular extruder die (circular die) and then cooling by contacting with a cylindrical annular cooling device, and cutting the sheet in a certain line Although the method to make a thing is mentioned, It does not specifically limit to this.
[0024]
When producing polypropylene resin foam sheets, suitable foam regulators, crosslinking agents, foaming aids, fillers, stabilizers, antioxidants, facials, as long as the physical properties of the polypropylene resin foam layer are not impaired. The amount etc. can be mixed.
[0025]
The polypropylene resin foam sheet of the present invention is molded and used as a container. As the forming method, thermoforming is preferable. As a method for heating the sheet during thermoforming, there are an indirect heating method using a heater, a direct heating method in which a sheet is brought into contact with a hot plate and a heating method using hot air, and the forming method includes vacuum forming and compressed air. There are moldings, more specifically, straight vacuum forming, straight pressure forming, drape vacuum forming, drape pressure forming, plug assist forming, drape and plug assist forming, plug assist pressure forming, plug assist reverse draw forming, action forming, Plug assist air strip molding, match mold (press) molding and the like can be mentioned, and any of these can be used in the present invention.
[0026]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
[0027]
The measurement methods used in the following examples and comparative examples were as follows.
(Sheet density) Measured with an electronic hydrometer (MD-200S) manufactured by Mirage Trading Co., Ltd.
(Sheet appearance) The appearance of the sheet was evaluated according to the following criteria.
○: Good sheet appearance is shown.
X: Roughness due to surface bubble breakage is observed.
(Sheet extrudability)
○: No problem in extrudability due to continuous operation for 24 hours.
X: Generation | occurrence | production of eye crack becomes remarkable in the lip | rip part of die | dye by continuous operation for 24 hours.
[0028]
(DuPont impact strength) The DuPont impact strength of the foam sheet was measured with a DuPont impact tester manufactured by Toyo Seiki Co., Ltd. at a 1/2 inch hemispherical impact core, a load of 200 g, and an environmental temperature of 23 ° C. The results were calculated according to JIS-K7211, and indicated as 50% impact fracture energy values (unit: J).
[0029]
(Practical drop test) The foamed sheet was molded into a container (length 400 mm, width 300 mm, depth 45 mm) as shown in FIGS. 1 and 2 with a vacuum forming machine, and 300 mm × 200 mm × thickness 10 mm, weight inside 700 g of a metal plate was put, and it was put in a corrugated cardboard in a state where it was stacked 10 steps. A corrugated cardboard box packed with 10 trays was dropped once from 900 mm on one corner and three ridge corners of the corrugated board, and then 6 sides were evaluated each time, and the damaged state of the container was evaluated. Evaluation criteria: ○ = no damage, x damage.
[0030]
(Examples 1-5, Comparative Examples 1-5)
Tandem extruder in which a 90 mm first extruder (L / D = 28) manufactured by Toshiba Machine and a 115 mm second extruder (L / D = 20) are connected by a single pipe using the composition shown in Table 1. And a cylinder temperature of 230 to 150 ° C., foam extrusion was performed with a 165 M / M circular die (set temperature of 180 ° C.) to form each sheet, which was subjected to the evaluation test.
[0031]
[Table 1]

[0032]
(A) High melt tension PP: MFR = 4.0 g / 10 min (CHISSO, FH3500)
(B) Linear crystalline PP: MFR = 3.4 g / 10 min (manufactured by Chisso Corporation, A5014)
(C) SEBS = styrene-ethylene / butylene-styrene block copolymer styrene content 18% (Asahi Kasei Co., Ltd., Tuftec H1062)
Foaming agent type: CF = chemical blowing agent (Clariant, CF40E-J)
Carbon dioxide gas = physical foaming agent MFR: 230 ° C. measured value (JIS-K6758 method)
[0033]
Table 1 shows the measurement results of sheet density, sheet thickness, sheet appearance, sheet extrudability, DuPont impact strength, and practical drop test of the obtained foamed sheet.
[0034]
The sheet of each example is excellent in sheet surface appearance and sheet extrudability, and has no impact on the container, which is a foamed sheet molded body in a practical drop test, so it has excellent impact resistance and is used as a packaging material for electronic components. Has excellent performance. Further, Comparative Examples 1 and 2 have a low level of impact resistance and cannot withstand actual use. In Comparative Example 3, the sheet appearance and impact resistance were good, but the appearance of the eyes during continuous operation was poor and the extrudability was poor. Although Comparative Examples 4 and 5 have high impact resistance, the sheet appearance is inferior and surface moldability is inferior to moldability and commercial property.
[0035]
【The invention's effect】
According to the present invention, a foam sheet and a foamed molded body container having a relatively low foaming ratio, good surface smoothness, good dimensional accuracy, and excellent impact resistance can be obtained. This is useful for transporting electronic parts and the like.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a container (one example) of the present invention.
FIG. 2 is a plan view of a container (one example) of the present invention.

Claims (3)

Contains high melt tension polypropylene resin (A), linear crystalline polypropylene resin (B) and styrene-ethylene-butylene-styrene block copolymer (C), and satisfies the following requirements 1 to 3 In the case where both the (A) component and the (B) component have a MFR at 230 ° C. of 2.0 to 5.0 g / 10 minutes, and the total of the (A) component and the (B) component is 100 A polypropylene resin foam sheet having a composition ratio (A) / (B) of 50/50 to 90/10 .
1. The component (A) is a high melt tension polypropylene resin having a melt tension at 200 ° C. of 4.0 g or more.
2. (C) Content of a component is 10 to 30%.
3. The density of the foam sheet is 180 kgm ⁻³ or more and less than 850 kg m ⁻³ .  2. The polypropylene resin foam sheet according to claim 1, wherein the styrene content of the styrene-ethylene / butylene-styrene block copolymer (C) is 10 to 40%. A container comprising the polypropylene resin foam sheet according to claim 1 or 2 .

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