JP2003292663A - Extruded polypropylene resin foam sheet and molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foamed polypropylene resin sheet having excellent heat insulating properties and rigidity, and a molded article made of the foamed sheet. SOLUTION: This is an extruded polypropylene resin sheet having an expansion ratio of 2 times or more and 30 times or less, and has a closed cell ratio of 5 or more.
0% or more and a cell density of 25 cells / mm ² or more; foamed polypropylene resin sheet; sheet containing carbon dioxide as a foaming agent; melt tension of polypropylene resin at 230 ° C. Is 5 g or more, and a molded article obtained by heat-forming the sheet.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polypropylene resin foam sheet. More specifically, since it has excellent heat insulating properties and rigidity, it can be widely and suitably used in applications such as cushioning materials, food containers, heat insulating materials, automobile members, etc., and molding formed by the foamed sheet. Regarding the body

[0002]

2. Description of the Related Art A foamed sheet made of a thermoplastic resin is generally lightweight, has good heat insulating properties and cushioning properties, and a molded product can be obtained by heat molding. Therefore, a polystyrene resin or a polyethylene resin is used. It is widely used for various purposes such as cushioning materials, food containers, heat insulating materials, and automobile parts. Further, in recent years, polypropylene resins having excellent heat resistance and solvent resistance have also been used.

However, polypropylene resins have low viscosity and tensile strength when melted, the strength of the cell wall during foaming is not sufficiently maintained, and it is difficult to obtain a foamed sheet having a high closed cell rate. In Japanese Patent No. 2521388, a method of using a polypropylene resin having a specific molecular weight and equilibrium compliance is proposed, but it is difficult to control under a wider range of extrusion conditions, and a foam is used to improve heat insulation. If the cell density is increased, the closed cell rate will decrease, and it is not possible to obtain a well-balanced foam sheet including the appearance.

As a method for improving the heat insulating property, a method of reducing the diameter of foam cells is generally used. JP 200
In 1-348453, a thermoplastic resin sheet having a thermoplastic resin foam layer having a cell wall density of 8 cells / mm or more in the thickness direction of the thermoplastic resin foam sheet and a cell wall density ratio of 2 or more and less than 6 is It is reported that by providing not only the cell wall but also the bubble structure as described above, the heat insulating property is further excellent. However, reducing the cell diameter corresponds to reducing the cell film thickness, and as a result, lowering the rigidity of the entire foam sheet.

When the foamed sheet is used for a food container or the like, there is a problem that if the rigidity of the foamed sheet itself is not satisfied, the container is likely to be deformed due to impact or stress during transportation or cooking.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polypropylene resin foam sheet having excellent heat insulating properties and rigidity, and a molded product formed from the foam sheet.

[0007]

The present inventors have arrived at the present invention as a result of intensive studies to solve the above problems. That is, the present invention is: A polypropylene resin extruded foam sheet having an expansion ratio of 2 times or more and 30 times or less, a closed cell ratio of 50% or more, and a cell density defined by the following formula (1) is 25 cells.
/ mm ² or more polypropylene resin foam sheet (claim 1), N _HDTD (pieces / mm ² ) = N _HD (pieces / mm) × N _TD (pieces / mm) ・ ・ ・ ( 1) N _HDTD : foam cross section perpendicular to extrusion direction Cell density in foam cross section N _HD : number of cells per 1 mm in foam cross section thickness direction N _TD : cells per 1 mm in width direction of extruded foam sheet Number 2. 2. The polypropylene resin foam sheet according to claim 1 containing carbon dioxide as a foaming agent (claim 2); The polypropylene-based resin foam sheet according to claim 1 or 2, wherein the polypropylene-based resin has a melt tension at 230 ° C. of 5 g or more ((claim 3), and 4. any one of claims 1 to 3). The present invention relates to a polypropylene-based resin foam-molded article obtained by heat-molding the above-mentioned foam sheet.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A polypropylene-based resin foam sheet having an expansion ratio of 2 times or more and 30 times or less according to the present invention has a closed cell ratio of 50% or more and a cell density defined by the following formula (1). It is characterized in that the number is 30 pieces / mm ² or more.

N _HDTD (units / mm ² ) = N _HD (units / mm) × N _TD (units / mm) (1) The thickness and width of the polypropylene-based resin foam sheet of the present invention are not particularly limited. No thickness, but 0.2-10
mm and width of 50 to 2000 mm are preferable in terms of economy and workability.

The polypropylene resin used in the present invention is not particularly limited, but the fact that the melt tension measured at 230 ° C. is 5 g or more makes it easy to control the expansion ratio, cell diameter and closed cell diameter. It is preferable because it is easy to do. When the melt tension measured at 230 ° C. is less than 5 g, there is not sufficient melt tension in cell formation during foaming, so that it is not easy to form a cell film and the cells are likely to break. A melt tension tester manufactured by Toyo Seiki was used to measure the melt tension.
Polypropylene resin heated to 30 ° C, caliber 1m
m, 10 mm in length, 1 m from an orifice with an inflow angle of 45 °
It was extruded at a speed of / min, the extrudate was passed through a tension detection pulley, and was wound while being accelerated from a speed of 1 m / min, and the tension value when the extrudate was cut was measured.

As the polypropylene resin, a polyolefin resin such as polypropylene, polyethylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-cyclic olefin copolymer, or polystyrene is used as the polypropylene resin. Polystyrene resin such as styrene-butadiene copolymer, polyester resin such as polyethylene terephthalate or polybutylene terephthalate, polycarbonate, rubber such as ethylene / α-olefin copolymer, etc. They may be used, and in that case, it is preferable to mix them so as to add less than 50 parts by weight. 50 added
If it is more than the weight part, the characteristics of the polypropylene resin such as heat resistance and solvent resistance may be impaired.

When a polypropylene resin and another resin are mixed and used, a compatibilizer may be used together. When a compatibilizer is used in combination, if it exceeds 10 parts by weight, the advantage of extrusion foaming, that is, economical efficiency, may be impaired, and heat resistance and solvent resistance may be impaired.

Next, the method for producing the polypropylene resin foamed sheet in the present invention includes, for example, mixing the base resin such as the polypropylene resin and the additive with a blender, and then supplying the mixture to an extruder to melt the resin. Then, a method in which a foaming agent is press-fitted at high temperature and high pressure, mixed, cooled to an appropriate foaming temperature, and extruded and foamed under atmospheric pressure can be mentioned.

In the present invention, the preferred foaming agent is
Aliphatic hydrocarbons such as propane, butane, isobutane, pentane, hexane, heptane, alicyclic hydrocarbons such as cyclobutane, cyclopentane, cyclohexane, chlorodifluoromethane, dichloromethane, dichlorofluoromethane, trichlorofluoromethane, chloroethane , Halogenated hydrocarbons such as dichlorotrifluoroethane, trichlorotetrafluoroethane and tetrachlorodifluoroethane, inorganic gases such as carbon dioxide, nitrogen and air, and one or more volatile blowing agents such as water are preferable. Further, it is more preferable to contain carbon dioxide because a foamed sheet having fine foam cells can be easily manufactured and a foamed sheet excellent in heat insulation and rigidity can be easily manufactured.

The amount of the foaming agent added is selected according to the type of the foaming agent and the target expansion ratio, but generally 100% of the base resin is used.
0.1 to 10 parts by weight is preferable with respect to parts by weight.

Further, in order to adjust the cell density of the foamed sheet to an appropriate size, a mixture of sodium bicarbonate and citric acid or a foaming nucleating agent such as talc or mica may be used in combination, if necessary. The amount of the foam nucleating agent used, if necessary, is generally 0.0 with respect to 100 parts by weight of the resin composition.
It is preferably 1 to 3 parts by weight.

Further, the foamed sheet of the present invention is within a range that does not impair physical properties such as heat insulation, rigidity, heat resistance and solvent resistance.
It may contain additives such as a flame retardant, an ultraviolet absorber, an antioxidant, a copper damage inhibitor, a filler, a lubricant and a pigment.

Further, in the method for producing a foamed sheet of the present invention, for the purpose of obtaining a desired width of the foamed sheet or a desired cell structure, for example, extrusion foaming is followed by drawing by drawing into a mandrel, air drawing. Cooling may be promoted by spraying.

The polypropylene resin foamed sheet of the present invention obtained by the above-mentioned production method preferably has a closed cell rate of 50% or more, more preferably 60% or more. When the closed cell ratio is less than 50%, the rigidity of the foamed sheet and a molded body obtained by heat molding the foamed sheet is deteriorated and the appearance of the molded body is deteriorated, which is not preferable. In addition, it is preferable that the cell density defined by the following formula (1) is 25 cells / mm ² or more.

N _HDTD (pieces / mm2) = N _HD (pieces / mm) × N _TD (pieces / mm) (1) N _HDTD : foam cross section perpendicular to extrusion direction Cell density in foam cross section N _HD : Number of cells per 1 mm in the thickness direction of the foam cross section N _TD : Number of cells per 1 mm in the width direction of the extruded foam sheet If the cell density is less than 25 cells / mm ² , the heat insulation of the foam sheet will decrease. Therefore, it is not preferable. The number of cells per 1 mm in the direction parallel to the foamed sheet to be extruded can be appropriately adjusted by adjusting the speed at which the extruded foamed sheet is taken in order to adjust the weight per unit area or the productivity. Is preferably adjusted to 2 to 10 pieces / mm, and more preferably adjusted to 3 to 7 pieces / mm. When it is less than 2 pieces / mm, stress is generated in the sheet during the foaming process in order to increase the take-up speed,
In some cases, the open cells of the foamed cells may be caused and the closed cell rate may be reduced. Further, when the number of cells is more than 10 cells / mm, productivity may be impaired because an operation of extremely slowing down the take-up speed is required.

Further, since the foamed sheet in the present invention is excellent in heat moldability such as plug molding, vacuum molding, and pressure molding, plug molding, matched mold molding, straight molding, drape molding, plug assist molding, plug assist molding. Reverse draw molding, air slip molding, snap back molding, reverse draw molding, free drawing molding, plug and ridge molding, ridge molding, etc. for smooth surface, heat resistance, solvent resistance, rigidity and heat insulation. An excellent molded product can be obtained. In the heat molding, the foamed sheet is molded after being nominally heated, but the density, thickness, cell structure, and closed cell ratio may change due to secondary foaming of the foamed sheet during preheating.

The foamed sheet of the present invention has a non-foamed layer made of a thermoplastic resin on one or both sides for the purpose of improving surface properties, heat moldability, etc., and obtaining further rigidity. You may form in. The thermoplastic resin, polystyrene resin, modified polyphenylene ether resin, polyethylene resin, polypropylene resin, polyethylene terephthalate resin,
Polybutylene terephthalate resin, polyamide resin, polyarylate resin, polyimide resin, polyether sulfonic acid resin, polysulfone resin, polyester resin, acrylic resin, polyvinyl chloride resin, polycarbonate resin etc. Alternatively, two or more kinds can be used in combination, but polypropylene resin is preferable from the viewpoint of adhesiveness to the foamed sheet. The method of molding the non-foamed layer is not particularly limited,
After forming the foamed sheet, a separately prepared non-foamed film may be laminated by heating or using an adhesive to be molded, or may be separately extruded and laminated on the foamed sheet.

[0023]

EXAMPLES Next, the foamed sheet relating to the present invention will be explained based on Examples and Comparative Examples, but the present invention is not limited to such Examples. (Foam cross section perpendicular to extrusion direction Cell density measurement in foam cross section) The cross section perpendicular to the extrusion direction of the foamed sheet of the present invention was observed with a scanning electron microscope (SEM) magnified 25 to 100 times, The number of cells contained per 1 mm in the thickness direction of the bubbles observed in the visual field and the number of cells contained per 1 mm in the width direction were measured and averaged at 15 points respectively, and N _HD and N _TD were respectively taken as N _HD by the following formula. _HDTD was calculated.

N _HDTD (units / mm ² ) = N _HD (units / mm) × N _TD (units / mm) (1) N _HDTD : foam cross section perpendicular to extrusion direction Cell density in foam cross section N _HD : Number of cells per 1 mm in the thickness direction of foam cross section N _TD : Number of cells per 1 mm in width direction of extruded foam sheet (measurement of foaming ratio of foam sheet) Specific gravity calculated according to JIS-K6767 And the specific gravity (0.91) of the polypropylene resin. (Measurement of closed cell rate of foam sheet) ASTM D-28
According to the method described in 56, it was measured by an air pycnometer. (Evaluation of heat insulation property of foamed sheet) According to JIS A-1412 using a thermal conductivity measuring device (HC-074) manufactured by Hidehiro Seiki Co., Ltd.
The thermal conductivity at an average temperature of 20 ° C. was measured according to the method described in 1.

Regarding Examples 1 to 3 and Comparative Examples 1 to 3,
When the thermal conductivity was less than 0.049 W / m · K, the heat insulating property was good (◯), and when it was 0.049 W / m · K or more, the heat insulating property was insufficient (×). Further, in Example 4 and Comparative Example 4, the threshold value was 0.045 W / m · K. (Evaluation of Rigidity of Foamed Sheet) According to the method described in JIS K6767, the tensile elastic modulus in the width direction of the extruded foamed sheet was measured. In the following, the magnitude of rigidity will be represented by the magnitude of the tensile elastic modulus. Examples 1 to 3, Comparative Example 1
For 3 to 3, if the tensile modulus of the test piece is 10.0 MPa or more, the rigidity is good (◯), 10.0 MPa
If it is less than, it is judged that the rigidity is insufficient (x). Further, in Example 4 and Comparative Example 4, the threshold value is set to 8.3
It was set to MPa. (Evaluation of Formability of Foamed Sheet) The clamped foamed sheet was put in an oven set at 350 ° C., preheated for 30 seconds, and then the opening 1 was opened using a mold adjusted to 25 ° C.
A tray-shaped molded body having a size of 10 mm × 110 mm and a depth of 35 mm is prepared. A molded product obtained from a foamed sheet with excellent secondary moldability has a good appearance (○), but a foamed sheet with poor secondary moldability has many irregularities and streaks on the surface, and in some cases, uneven thickness causes unusable molding. It becomes a body (x).

The following polypropylene resins were used in Examples and Comparative Examples.

PP-1: 100 parts by weight of polypropylene homopolymer (J103WB manufactured by Grand Polymer Co., melt index 3 g / 10 minutes) as a radical generator, t-butylperoxyisopropyl monocarbonate (1 minute half-life temperature) (159 ° C.) 0.325 part by weight was blended and stirred for 5 minutes using a ribbon blender.

This mixture was fed from a hopper of a twin-screw extruder (TEX44, manufactured by Japan Steel Works, Ltd.) at a feed rate of 50 kg / h, and an isoprene monomer was fed from a feeding portion provided on the way using a metering pump. A modified polypropylene resin obtained by supplying strands at a rate of 25 kg / h, cooling the strands with water, and cutting.

PP-2: Commercially available high melt tension polypropylene (Profax PF-814 manufactured by Montel Co.) PP-3: Polypropylene homopolymer (J103WB manufactured by Grand Polymer Co.) PP-1, PP-2 and PP-3 melt Table 1 shows the index and the melt tension at 230 ° C.

[0030]

[Table 1] (Example 1) 100 parts by weight of polypropylene resin PP-1, a foaming nucleating agent (sodium bicarbonate-citric acid mixture: a chemical foaming agent manufactured by Dainichiseika Kogyo Co., Ltd., trade name Diebrow PE-)
MD20 (AL) N, foaming component concentration 20%, base resin: polyethylene) 0.1 part by weight of the mixture was mixed by stirring with a ribbon blender, supplied to a φ65-90 mm tandem extruder and set to 200 ° C. Stage extruder (φ65
mm), liquid carbon dioxide as a foaming agent was press-mixed with PP-1 in an amount of 1.5 parts by weight.
Cool in a second-stage extruder (φ90 mm) set at 61 ° C., and apply 5 at atmospheric pressure from a circular die (φ75 mm).
Discharge at 0 kg / h, outer diameter 200 mm, body length 20
While molding with a 0 mm cooling cylinder, while drawing at 3.8 m / min, air is blown inside to stretch and cool to obtain a cylindrical foam, which is cut with a cutter to open 63
A foamed sheet having a width of 5 mm was obtained. Table 2 shows the physical properties of the obtained foamed sheet. (Example 2) Polypropylene resin PP-1 in Example 1
Foamed sheet 2 was obtained by the same operation except that PP-2 was used instead of. Table 2 shows the physical properties of the obtained foamed sheet. (Example 3) In Example 1, carbon dioxide was added as a foaming agent to 1.
A foamed sheet 3 was obtained by the same operation except that 1 part by weight of carbon dioxide and 0.5 part by weight of isobutane were used instead of using 5 parts by weight. Table 2 shows the physical properties of the obtained foamed sheet. (Example 4) In Example 1, carbon dioxide was added as a foaming agent to 1.
A foamed sheet 4 was obtained by the same operation except that 1.7 parts by weight of carbon dioxide was used instead of using 5 parts by weight. Table 2 shows the physical properties of the obtained foamed sheet. (Comparative Example 1) A foamed sheet 5 was obtained by the same operation except that the temperature of the second-stage extruder, which was set to 161 ° C in Example 1, was set to 165 ° C. Table 2 shows the physical properties of the obtained foamed sheet. (Comparative Example 2) The take-up speed in Example 1 was 3.8 m / min.
On the other hand, the foam sheet 6 was obtained by performing the same operation except that the flow rate was 4.5 m / min. Table 2 shows the physical properties of the obtained foamed sheet. Comparative Example 3 Polypropylene resin PP-1 in Example 1
A foamed sheet 7 was obtained by the same operation except that PP-3 was used instead of. Table 2 shows the physical properties of the obtained foamed sheet. (Comparative Example 4) In Example 1, carbon dioxide of 1.
A foamed sheet 8 was obtained by the same operation except that 1.6 parts by weight of isobutane was used instead of using 5 parts by weight. Table 2 shows the physical properties of the obtained foamed sheet.

[0031]

[Table 2]

[0032]

EFFECTS OF THE INVENTION According to the present invention, in addition to heat resistance and solvent resistance, it has excellent heat insulating properties and rigidity, and thus can be widely and suitably used in applications such as cushioning materials, food containers, heat insulating materials, and automobile parts. It is possible to provide a polypropylene-based resin foamed sheet and a molded body molded from the foamed sheet.

Claims (4)

[Claims] 1. A polypropylene resin extruded foam sheet having a foaming ratio of 2 times or more and 30 times or less, and a closed cell ratio of 5.
A polypropylene-based resin foam sheet having a cell density of 0% or more and a cell density defined by the following formula (1) of 25 cells / mm ² or more. N _HDTD (pieces / mm ² ) = N _HD (pieces / mm) × N _TD (pieces / mm) (1) N _HDTD : foam cross section perpendicular to extrusion direction Cell density in foam cross section N _HD : Number of cells per 1 mm in thickness direction of foam cross section N _TD : Number of cells per 1 mm in width direction of extruded foam sheet 2. The polypropylene resin foam sheet according to claim 1, which contains carbon dioxide as a foaming agent. 3. The polypropylene resin foam sheet according to claim 1, wherein the polypropylene resin is a polypropylene resin having a melt tension of 5 g or more at 230 ° C. 4. A polypropylene-based resin foam-molded article obtained by heat-molding the foam sheet according to claim 1.