JP2003313348A - Polypropylene resin single-layer extrusion-foamed sheet and foamed forming formed therefrom - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene resin single-layer extrusion-foamed sheet, wherein the sheet itself and a forming formed therefrom have each a beautiful appearance, good formability, and the forming can be widely used as a cushioning material, a food container, a heat insulation material, an automotive component, or the like. <P>SOLUTION: The foamed sheet is one having a thickness of 1-5 mm, an expansion ratio of 3-20, and a closed-cell rate of 50% or higher and comprising a 200 μm deep surface layer which covers at least either surface and in which, in a cross section in the thickness direction, the number of cell walls in the thickness direction is 2-10 and a core layer which is formed between the 200 μm deep position and the center and in which the number of cell walls in the thickness direction is 10 or smaller per mm. The formed forming is one obtained by forming the sheet. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene resin single layer extruded foam sheet and a foam molded article formed from the foam sheet. More specifically, a polypropylene resin single-layer extruded foam sheet itself, and further, a molded product thermoformed from the foam sheet has a beautiful appearance and good moldability, and therefore, a cushioning material, a food container, a heat insulating material. The present invention relates to a polypropylene resin single-layer extruded foamed sheet that can be widely and suitably used in applications such as automobile members, and a foamed molded product formed by heating from the foamed sheet.

[0002]

2. Description of the Related Art A foamed sheet made of a thermoplastic resin is generally light in weight, has good heat insulating properties and cushioning properties, and can be molded by heat molding. , Mainly polystyrene-based resins and polyethylene-based resins, are widely used in applications such as cushioning materials, food containers, heat insulating materials, and automobile parts. Also,
In recent years, polypropylene-based 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.

Japanese Patent No. 2521388 proposes a method for producing a foamed sheet using a polypropylene resin having a specific molecular weight and equilibrium compliance. However, the produced foamed sheet has a foamed sheet appearance. Since it is made beautiful only by the surface layer without bubbles, it cannot be said that the appearance is satisfactory when a more rigorous appearance such as a food container is required. Further, if the cell density of the foam is increased in order to improve the heat insulating property, the closed cell ratio is lowered, so it is difficult to control so as to produce a well-balanced foam sheet including the appearance.

In JP-A-2002-46164, in a method of obtaining a foamed sheet by coextrusion, a foamed sheet having a finer cell diameter than the core portion is extruded and foamed in the surface layer to obtain a foamed sheet having a good appearance. Although a method for obtaining the foamed sheet is shown, it is desired to obtain a foamed sheet having a beautiful appearance by a simpler method, because the apparatus becomes complicated and high technology is required.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a polypropylene resin single-layer extruded foam sheet, which has a cut surface in the thickness direction from the surface layer A core layer in which a surface layer having a number of cell walls in the thickness direction up to 200 μm within a predetermined range is provided on one or both sides, and the number of cell walls per 1 mm from the surface layer in the thickness direction from 200 μm to the center is within a predetermined range. Consisting of, thickness,
By using a polypropylene resin single-layer extruded foam sheet with the expansion ratio and the closed cell ratio within the predetermined ranges, the foam sheet has a beautiful appearance and good moldability, and the appearance of the thermoformed molded article is It has been found that a foamed sheet can be obtained which can be suitably used for food containers, cushioning materials and the like because it is beautiful, and has completed the present invention.

That is, in the present invention, the number of cell walls in the thickness direction from the surface layer to 200 μm is 2 to 10 on the cut surface in the thickness direction of the polypropylene resin single layer extruded foam sheet.
A surface layer on one or both sides, and a core layer having a cell wall number of 10 or less per 1 mm from the surface layer to 200 μm in the thickness direction from the surface layer to a central portion, a thickness of 1 to 5 mm, A polypropylene resin single layer extruded foam sheet having a foaming ratio of 3 to 20 times and a closed cell ratio of 50% or more (claim 1), and having 10 or more cell walls in the total thickness direction.
The present invention relates to the polypropylene-based resin single-layer extruded foamed sheet (Claim 2) and the foam-molded article (Claim 3) obtained by thermoforming the polypropylene-based resin single-layered extruded foamed sheet of Claim 1 or 2.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The polypropylene resin single layer extruded foam sheet of the present invention has a thickness of 1 to 5 mm and an expansion ratio of 3 to 2.
It is a polypropylene resin single layer extruded foam sheet having 0 times the closed cell rate of 50% or more.

Since the foamed sheet is made of polypropylene resin, it can be used even at a high temperature of, for example, 120 ° C. and can be used for applications such as soup food containers. Further, it can be preferably used for food containers because of its excellent oil resistance.

Further, since the foamed sheet is a single-layer extruded foamed sheet, the manufacturing equipment can be simplified and the manufacturing can be carried out with inexpensive equipment.

Further, the foam sheet has a thickness of 1 to 5 m.
m, and further 1 to 3 mm, the heat molding cycle can be shortened, and the expansion ratio is 3 to 20 times, further 3 to 10 times, so that it can be made lightweight and highly heat insulating. Since the closed cell ratio is 50% or more, and further 60% or more, the heat insulating property is good, and the foamed sheet and the heating condition when heat-molding the foamed sheet are not narrowed and molded by molding. Does not deteriorate the appearance of the body. The width of the foamed sheet is not particularly limited,
It is preferably 50 to 2000 mm, more preferably 500 to 2000 mm from the viewpoint of economy and workability.

The polypropylene-based resin single-layer extruded foamed sheet has one or both surface layers in which the number of cell walls in the thickness direction from the surface layer (surface) to 200 μm is 2 to 10 in the thickness-wise cut surface. (200 from the surface in the thickness direction
up to 200 μm in the thickness direction from the surface layer to the center, and the core layer having 10 or less cell walls per 1 mm from the surface layer.

Whether or not the surface layer is present can be distinguished by observing the cross section of the foamed sheet. The thickness of the surface layer is defined as 200 μm because it is the necessary thickness of the surface layer to make the appearance beautiful.

When the surface layer is formed on one side,
It is preferable in that the thickness can be easily increased, and when formed on both sides, it is preferable in terms of excellent rigidity. Whether the surface layer is formed on one side or on both sides can be arbitrarily selected by appropriately adjusting the stretching and cooling when forming the foamed sheet.

The central portion is a position obtained by observing the cut surface.

When the number of cell walls of the surface layer is 2 to 10, more preferably 2 to 7, the smoothness of the surface of the foamed sheet is easily obtained, and the thickness adjustment of the foamed sheet is easy. When the number of the cell walls is too small, the smoothness of the surface layer is often impaired, and when the number is too large, surface streaks occur and it is difficult to obtain a foamed sheet having a large thickness. The cell walls forming the surface layer are included in the number of cell walls.

As described above, the number of cell walls per 1 mm of the core layer is 10 or less, but it is 6 to 9 from the viewpoint that it can be easily molded into a foamed sheet and that the foamed sheet can be easily heat-molded. Preferably. When the number of cell walls per 1 mm of the core layer is too large, it becomes difficult to obtain a foamed sheet having a large thickness, and the moldability often deteriorates.

When the core portion is less than 1 mm, it may be calculated by dividing the number of cell walls of the core portion by the thickness of the core portion.

The number of cell walls in the total thickness direction of the foamed sheet of the present invention as described above is preferably 10 or more, more preferably 13 or more, from the viewpoint of excellent heat insulating property.

The polypropylene-based resin used in the present invention has a melt tension measured at 230 ° C. of 5 g or more, and further 7 g or more. It is easy to control the expansion ratio, the cell diameter, and the closed cell ratio, and is manufactured. It is preferable because it is easy to do. If the melt tension measured at 230 ° C. is too low, there is not sufficient melt tension at the time of cell formation during foaming, so that it is not easy to form a cell membrane and the cells are likely to break.

A melt tension tester manufactured by Toyo Seiki Co., Ltd. was used to measure the melt tension.
Polypropylene resin heated to ℃, 1m / mi from an orifice with a diameter of 1mm, a length of 10mm and an inflow angle of 45 °
The strand is extruded at a speed of n, the extrudate is passed through a tension detecting pulley and is wound while being accelerated from a speed of 1 m / min, and the tension value when the extrudate is cut is measured.

Examples of the polypropylene resin as described above include those containing propylene units in an amount of 90% by weight (hereinafter referred to as%) or more, preferably 95% or more.

Examples of the units that can be contained in the polypropylene resin together with the propylene units include ethylene units and 1-butene. In order to obtain a clear effect by containing these copolymerized units, it is usually preferable to contain them in the range of 0.1 to 10%. For example, with propylene units, ethylene units or 1
-When the butene unit is contained in an amount of 1 to 10%, a highly flexible foamed sheet can be obtained.

Specific examples of the polypropylene resin include ethylene-propylene random copolymer,
Examples thereof include ethylene-propylene block copolymers. These may be used alone or in combination of two or more.

The polypropylene resin may be used as a mixture with other resin and / or rubber (hereinafter referred to as other resin etc.).

When the polypropylene resin is mixed with other resins, the polypropylene resin 1
It is 1 to 50 parts by weight of other resin, etc. with respect to 00 parts by weight (hereinafter referred to as "parts"), so that the characteristics of the polypropylene resin such as heat resistance and solvent resistance are not impaired and a desired cell structure can be easily obtained. It is preferable because it is easily obtained.

Examples of the other resins include polyethylene, poly-1-butene, poly-4-methyl-1-
Pentene, polyolefin resin such as ethylene-cyclic olefin copolymer, polystyrene, polystyrene resin such as styrene-butadiene copolymer, polyethylene terephthalate or polybutylene terephthalate, polyester resin such as polycarbonate, ethylene / α-
Examples thereof include rubber such as olefin copolymer. These may be used alone or in combination of two or more.

When the polypropylene resin is used in combination with another resin, a compatibilizer may be used in combination.

When the compatibilizing agent is used in combination, the amount of the compatibilizing agent used is 100 parts or less per 100 parts of polypropylene resin and other resins. It is preferable because heat resistance and solvent resistance are not easily impaired. From the viewpoint of obtaining a clear effect by using the compatibilizer together, it is preferable to use 0.5 part or more.

A cross-sectional photograph of an example of the polypropylene resin single layer extruded foam sheet of the present invention is shown in FIG.

In FIG. 1, the surface layer 1a on one side (upper side of FIG. 1)
The surface layer 2 is formed on.

In the figure, 1b is a surface layer on which no surface layer is formed, 3 is a core layer, and 4 is a central portion in the thickness direction.

As a method for producing the polypropylene resin single layer extruded foamed sheet, for example, a base resin such as the polypropylene resin and an additive used as necessary are mixed in a blender and then supplied to an extruder, After the resin has melted, the foaming agent is pressed in at high temperature and high pressure, mixed, cooled to an appropriate foaming temperature, extruded and foamed from a mold having an annular slit under atmospheric pressure, and this tubular foam is a cooling cylinder. A method of drawing and cooling the sheet, cutting it open, and then taking it into a sheet form can be mentioned.

By using the cooling cylinder, it is possible to easily obtain the desired cell structure and the desired thickness of the foamed sheet in the present invention.

With respect to the size of the cooling cylinder, it is preferable that the diameter of the cooling cylinder is 2 to 4 times the diameter of the annular portion of the mold, and the length of the cooling cylinder is in close contact with the foamed sheet. It is preferable that the length is 50 mm or more. If the diameter of the cooling cylinder is less than 2 times, the corrugate is likely to remain in the obtained foamed sheet, and if it is more than 4 times, it is unfavorable because the foamed sheet is stretched so as to reduce the closed cell rate. Further, if the portion of the cooling cylinder that is in close contact with the foamed sheet is less than 50 mm, the cooling is insufficient and it becomes difficult to obtain a desired cell structure.
Moreover, it is preferable that the cooling cylinder is cooled to 30 ° C. or lower by a coolant such as circulating water. By cooling to 30 ° C or lower, it becomes easy to obtain a desired cell structure. The contact time between the cooling cylinder and the foamed sheet depends on the thickness of the foamed sheet, but is preferably 0.5 to 5 seconds. When the contact time is 0.5 seconds or less, the cooling effect for obtaining the desired bubble structure cannot be obtained, and the cell diameter of the surface layer portion is enlarged. Further, if the contact time exceeds 6 seconds, the efficiency of the manufacturing process may be reduced.

Examples of the foaming agent include propane,
Aliphatic hydrocarbons such as butane, isobutane, pentane, hexane, heptane, alicyclic hydrocarbons such as cyclobutane, cyclopentane, cyclohexane, chlorodifluoromethane, dichloromethane, dichlorofluoromethane, trichlorofluoromethane, chloroethane, dichlorotrimethane Fluoroethane, trichlorotetrafluoroethane, tetrachlorodifluoroethane and other halogenated hydrocarbons, carbon dioxide, nitrogen, air and other inorganic gases,
Volatile foaming agents such as water are included. These may be used alone or in combination of two or more,
It is preferable to use at least carbon dioxide because a foamed sheet having a desired cell structure can be easily manufactured, and a foamed sheet excellent in appearance, moldability and heat insulating property can be easily manufactured.

The amount of the foaming agent used may be appropriately determined depending on the type of the foaming agent and the target expansion ratio, but it is generally preferably 0.1 to 10 parts with respect to 100 parts of the base resin.

If necessary, in order to adjust the cell density of the foamed sheet to a desired value, a mixture of sodium bicarbonate and citric acid or a foaming nucleating agent such as talc or mica may be used in combination.

Generally, the amount of the foam nucleating agent added is preferably 0.01 to 3 parts with respect to 100 parts of the base resin.

Examples of the additives other than the foam nucleating agent include flame retardants, ultraviolet absorbers, antioxidants, copper damage inhibitors,
Examples include fillers, lubricants and pigments. These additives are added to the foamed sheet of the present invention within a range that does not impair physical properties such as appearance, moldability, heat insulation, rigidity, heat resistance, and solvent resistance.

Since the foamed sheet of the present invention as described above has excellent 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.・ Smooth surface, heat resistance, solvent resistance, rigidity, etc. by reverse draw molding, air slip molding, snap back molding, reverse draw molding, free drawing molding, plug and ridge molding, ridge molding, etc.
It is possible to obtain a molded product having excellent heat insulating properties.

The heat molding method is a method in which the foamed sheet is preheated and then molded. However, due to secondary foaming of the foamed sheet during preheating, the density, thickness, cell structure,
The closed cell ratio may change.

In the foamed sheet of the present invention, a non-foamed layer made of a thermoplastic resin may be formed on one surface or both surfaces of the foamed sheet in order to obtain printability and rigidity.

As the thermoplastic resin forming the non-foamed layer, polystyrene resin, modified polyphenylene ether resin, polyethylene resin, polypropylene resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyamide resin, poly Arylate resin, polyimide resin, polyether sulfonic acid resin, polysulfone resin, polyester resin,
Examples thereof include acrylic resin, polyvinyl chloride resin, polycarbonate resin and the like. These may be used alone or in combination of two or more. Among these, polypropylene resin is preferable from the viewpoint of adhesiveness to the foamed sheet.

[0045]

EXAMPLES Next, the present invention will be explained based on Examples and Comparative Examples, but the present invention is not limited to these Examples.

(Number of Cell Walls in Thickness Direction of Foam Section) A scanning electron microscope (S
It is observed by magnifying 25 to 100 times by EM), and the number of cell walls observed from the surface layer to 200 μm of the foamed sheet in the visual field is measured including the surface layer cell walls. Similarly, the cell wall between the surface layer of 200 μm and the center of the foamed sheet is also measured, and the number of cell walls per 1 mm is calculated.

The cross section of the foamed sheet to be observed was selected so that 15 locations perpendicular to the extrusion direction of the obtained foamed sheet would cover the entire width direction, and the number of cell walls was measured and averaged for each cross section. To do.

(Expansion Ratio of Foamed Sheet) JIS-K67
It is calculated from the specific gravity calculated according to No. 67 and the specific gravity (0.91) of the polypropylene resin.

(Closed Cell Rate of Foamed Sheet) ASTM D
It measures with an air pycnometer according to the method described in -2856.

(Thickness of Foamed Sheet) Five points of the cross section perpendicular to the extrusion direction of the foamed sheet are selected so as to substantially cover the entire width direction, and the thickness is measured and averaged for each cross section.

(Appearance of Foamed Sheet) Judgment is made based on the following criteria by observing the surface of the foamed sheet visually and by touch. ◯: Excellent surface smoothness and good appearance X: Poor appearance due to many irregularities, corrugated lines, uneven thickness, and roughness on the surface

(Formability of Foamed Sheet) The clamped foamed sheet was placed in an oven set at 350 ° C.
After preheating for 2 seconds, a tray-shaped molded body having an opening of 110 mm × 110 mm and a depth of 35 mm was prepared using a mold adjusted to 25 ° C., and judgment was made based on the following criteria. ◯: Good appearance ×: Many irregularities and streaks on the surface, and in some cases uneven thickness is not acceptable for use

In Examples and Comparative Examples, the following polypropylene resins were used. PP-1: polypropylene homopolymer (J103WB manufactured by Grand Polymer Co., melt index 3 g / 10
Min) 100 parts, and 0.325 parts of t-butylperoxyisopropylmonocarbonate (1 minute half-life temperature 159 ° C.) as a radical generator was mixed and stirred for 5 minutes using a ribbon blender. This mixture was fed at a feed rate of 50 kg / h from a hopper of a twin-screw extruder (manufactured by Nippon Steel Works, Ltd., TEX44), and wasoprene monomer was fed from a hopper provided in the middle at a rate of 0.25 using a metering pump.
Modified polypropylene resin obtained by supplying at a rate of kg / h, cooling the strand with water and cutting (melt index 0.5 g / 10 min, melt tension 13
g). PP-2: Commercially available high melt tension polypropylene (manufactured by Montel Corporation, Profax PF-814) (melt index 3.0 g / 10 minutes, melt tension 9.8 g).

Example 1 100 parts of polypropylene resin PP-1 and 0.1 part of a foam nucleating agent (sodium bicarbonate-citric acid) were mixed by stirring with a ribbon blender, and the mixture was fed to a Φ65-90 mm tandem extruder. After melting in a first-stage extruder (φ65 mm) set to 200 ° C., 1.5 parts of liquid carbon dioxide as a foaming agent was press-mixed with 100 parts of PP-1, and the temperature was set to 161 ° C. 2nd stage extruder (φ90m
m), cooled, and discharged from a circular die (φ75 mm) under atmospheric pressure at 50 kg / h, outer diameter 200 mm,
While molding with a cooling cylinder whose main body length is 200 mm and whose temperature is regulated to 15 ° C by circulating water, while taking it at 4.1 m / min, blow atmospheric air inside to stretch and cool to obtain a cylindrical foam. Then, this was cut open with a cutter to obtain a foamed sheet 1 having a width of 630 mm. The properties of the obtained foamed sheet are shown in Table 1.

Example 2 A foamed sheet 2 was obtained in the same manner as in Example 1 except that PP-2 was used instead of the polypropylene resin PP-1 used in Example 1.

The characteristics of the foamed sheet thus obtained are shown in Table 1.

Embodiment 3 In addition to the cooling by the cooling cylinder in Embodiment 1, air is blown from the outer peripheral side of the extruded cylindrical foamed sheet to promote cooling of the outside of the foamed sheet.
A foamed sheet 3 was obtained in the same manner as in.

The characteristics of the foamed sheet obtained are shown in Table 1.

Example 4 1.7 parts of carbon dioxide was used in place of 1.5 parts of carbon dioxide used in Example 1, and a cooling cylinder having an outer diameter of 254 mm was used instead of a cooling cylinder having an outer diameter of 200 mm. A foamed sheet 4 was obtained in the same manner as in Example 1 except that a foamed sheet having a width of 750 mm was obtained. The properties of the obtained foamed sheet are shown in Table 1.

Comparative Example 1 A foamed sheet 5 was obtained in the same manner as in Example 1 except that cooling with circulating water was not performed in place of the cooling cylinder cooled to 15 ° C. used in Example 1.

The characteristics of the foamed sheet 5 thus obtained are shown in Table 1.

Comparative Example 2 A foamed sheet 6 was obtained in the same manner as in Example 1 except that a cooling cylinder having a main body length of 40 mm was used instead of the cooling cylinder having a main body length of 200 mm used in Example 1.

The characteristics of the foamed sheet obtained are shown in Table 1.

Comparative Example 3 The temperature of 161 ° C. of the second-stage extruder in Example 1 was changed to 16
A foamed sheet 7 was obtained in the same manner as in Example 1 except that the temperature was changed to 7 ° C.

The characteristics of the foamed sheet thus obtained are shown in Table 1.

Comparative Example 4 Instead of the cooling cylinder having an outer diameter of 200 mm used in Example 1,
Foamed sheet 8 in the same manner as in Example 1 except that a 750 mm wide foamed sheet was obtained using a cooling cylinder having an outer diameter of 254 mm.
Got

The characteristics of the foamed sheet thus obtained are shown in Table 1.

[0068]

[Table 1]

[0069]

The polypropylene resin single layer foam sheet of the present invention is lightweight, has good heat resistance and solvent resistance, has a beautiful appearance, and has good thermoformability. The foam molded from the foamed sheet can be widely and suitably used for applications such as cushioning materials, food containers and automobile members.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an example of a polypropylene-based resin single-layer extruded foam sheet of the present invention, showing a scanning electron microscope (SE
It is a photograph taken by enlarging and observing with M).

[Explanation of symbols]

1a, 1b surface 2 surface layer 3 core layers 4 center

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4F074 AA24 AA25 BA32 BA33 BA34                       BA35 BA36 BA37 BA38 BA39                       BA40 BA45 BA47 BA53 BA95                       BC12 CA22 DA02 DA03 DA12                       DA14 DA23 DA24 DA34                 4F207 AA11 AB02 AB05 AB06 AB07                       AB14 AG01 AG20 AR15 KA01                       KA11 KF04 KW41

Claims (3)

[Claims] 1. A single-sided or double-sided surface layer in which the number of cell walls in the thickness direction from the surface layer to 200 μm is 2 to 10 on the cut surface in the thickness direction of a polypropylene resin single layer extruded foam sheet, and a surface layer. A thickness of 1 to 5 mm, a foaming ratio of 3 to 20 and a closed cell ratio of 50%, which is characterized by comprising a core layer having 10 or less cell walls per 1 mm from 200 μm to the central portion in the thickness direction. The above polypropylene resin single layer extruded foam sheet. 2. The polypropylene resin single layer extruded foam sheet according to claim 1, wherein the number of cell walls in the entire thickness direction is 10 or more. 3. A foam-molded article obtained by heat-molding the polypropylene-based resin single-layer extruded foam sheet according to claim 1 or 2.