JPH11349718A - Crystalline polypropylene-based resin foam and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a crystalline polypropylene-based resin foam excellent in mechanical strength and impact resistance. SOLUTION: This crystalline polypropylene-based resin foam has a cross- shaped molecular orientation in the plane direction measured by a microwave molecular orientation analyzer. Furthermore, the method for producing the crystalline polypropylene-based resin foam comprises carrying out the extrusion expansion of a crystalline polypropylene-based resin containing a foaming agent, orienting the resultant extruded foam 4 in a state of the softened resin in the interior while cooling and thereby providing the cross-shaped molecular orientation in the plane direction measured with the microwave molecular orientation analyzer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a crystalline polypropylene resin foam and a method for producing the same. More specifically, the present invention relates to a crystalline polypropylene resin foam having low density and high mechanical strength, and a method for producing the same.

[0002]

2. Description of the Related Art
Polystyrene-based resin foams and crystalline polypropylene-based resin foams are often used as the foams that can be secondary-molded. However, polystyrene resin foams have not always been satisfactory in properties such as heat resistance, chemical resistance, and oil resistance. In addition, crystalline polypropylene resin foam is a resin excellent in various physical properties such as heat resistance, chemical resistance, and oil resistance, and is widely used for industrial members, food containers, and the like. In the system resin foam, crystals are generated in a process of cooling from a molten state, and the crystal state is a state in which large spherulites are unevenly distributed. Therefore, a crystalline polypropylene-based resin foam having stable properties cannot be obtained unless crystallization is controlled.

Therefore, in order to control the crystallization of the crystalline polypropylene resin, it is conceivable to add a crystal nucleating agent as an additive. When the crystal of the crystalline polypropylene resin is actually made uniform and fine, This has the effect of improving the mechanical properties of the foam obtained. However, if a crystal nucleating agent is present in the crystalline polypropylene-based resin, the crystallization rate is significantly increased, and a good foam cannot be obtained. Specifically, in the extrusion foam molding of a crystalline polypropylene resin, it is necessary to foam the extruded resin in a short period of time from uncrystallization in a molten state to crystallization, and perform molding. . Therefore, when the crystallization speed is high, the foam molding time becomes very short, and as a result, the molding conditions are narrowed, and a good foam cannot be obtained. On the other hand, when the crystallization rate is reduced by other known means, the crystallinity of the obtained foam decreases, and thus the mechanical strength is deteriorated.

[0004]

In view of the above problem, the present inventors have surprisingly found that a crystalline polypropylene resin foam having a cross-shaped molecular orientation is unexpectedly resistant to heat, chemical, and oil. The present invention has been found to be excellent in properties and the like, and furthermore to show good mechanical strength and impact resistance.

Thus, according to the present invention, there is provided a crystalline polypropylene-based resin foam characterized in that the molecular orientation in the plane direction measured by a microwave molecular orientation meter is cross-shaped. Furthermore, according to the present invention, a crystalline polypropylene-based resin containing a foaming agent is extruded and foamed, and the extruded foam is stretched while being cooled while the resin inside the foamed resin is softened, whereby the microwave molecule is expanded. A method for producing a crystalline polypropylene-based resin foam, characterized in that a crystalline polypropylene-based resin foam having a crosswise molecular orientation measured by an orientation meter is obtained.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The crystalline polypropylene resin used in the present invention is not particularly limited, and any commercially available crystalline polypropylene resin can be used. In addition, a polypropylene homopolymer composed of propylene or an olefin mainly composed of propylene (for example,
Olefin-propylene copolymer comprising a copolymer with ethylene, α-olefin or the like. This copolymer is a random or block copolymer containing an olefin component, and has the effect of improving the brittleness of polypropylene. Particularly, an ethylene-propylene copolymer is preferred.

[0007] In particular, as the crystalline polypropylene resin used in the present invention, a method of irradiating a low-level radiation or a method of mixing a small amount of peroxide described in Japanese Patent Publication No. 7-45551. It is preferable to use a polypropylene-based resin having a branched structure imparted to the polypropylene-based resin to increase the proportion of the ultrahigh molecular weight component. In the present invention, not only the above-mentioned crystalline polypropylene-based resin can be used alone, but also a non-crystalline polypropylene-based resin, another kind of resin or an elastomer can be mixed and used according to the purpose.

For example, it is preferable to mix a polyethylene resin as another type of resin for further improving the brittleness of the crystalline polypropylene resin. Examples of the polyethylene resin include a homopolymer of ethylene, a copolymer of ethylene-α-olefin, and a copolymer of ethylene with a non-olefin monomer having a carbon, oxygen, or hydrogen atom in a functional group.

The homopolymers of ethylene include low-density polyethylene (LDPE) and high-density polyethylene (HDP).
E) and the like. As the ethylene-α-olefin copolymer, linear low-density polyethylene (L-LDP)
E), linear very low density polyethylene (VLDPE) and the like, and the α-olefin includes 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene and the like. Examples of the copolymer of ethylene and a non-olefin monomer having a carbon, oxygen, or hydrogen atom as a functional group include ethylene ionomer resin, ethylene-vinyl acetate copolymer resin, ethylene-vinyl alcohol copolymer resin, and ethylene. -Acrylic acid copolymer resin, ethylene-methyl methacrylate copolymer resin and the like. These polyethylene resins may be one kind or a mixture of a plurality of kinds.

The mixing ratio of the other resin is 5 to 10 parts by weight based on 100 parts by weight of the crystalline polypropylene resin.
It is preferable to mix 0 parts by weight, and it is particularly preferable to mix 10 to 50 parts by weight. A bubble regulator may be added to the crystalline polypropylene resin used in the present invention as appropriate. Examples of the foam adjuster include fine powder talc,
Bubble nucleating agents such as silica, a mixture of sodium bicarbonate and citric acid can be used conventionally. Furthermore,
Additives such as a stabilizer, a colorant, a flame retardant, an antistatic agent, an antibacterial agent, and a filler may be added as needed within a range that does not affect the extrusion foaming property.

In the method of the present invention, a molten resin is obtained by melting a raw material resin optionally containing an additive with a known extruder. Next, a foaming agent is added to the molten resin in the extruder. As the foaming agent, any of known foaming agents can be used. The foaming agent is roughly classified into a physical foaming agent and a chemical foaming agent, and both can be used in the present invention, but the physical foaming agent is preferable. Physical blowing agents are classified into inert gases, saturated aliphatic hydrocarbons, saturated alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, ethers, ketones, etc., and any of them is used in the present invention. can do. Specifically, carbon dioxide gas, an inert gas such as nitrogen,
Methane, ethane, propane, normal butane, isobutane, normal pentane, isopentane, neopentane,
Saturated aliphatic hydrocarbons such as normal hexane, 2-methylpentane, 3-methylpentane and 2,2-dimethylbutane; methylcyclopropane; cyclopentane;
Saturated alicyclic hydrocarbons such as dimethylcyclopropane, cyclohexane, methylcyclopentane, ethylcyclobutane, 1,1,2-trimethylcyclopropane, aromatic hydrocarbons such as benzene, methyl chloride, various fluorocarbons (for example, trichloromonofluoro Methane, dichlorodifluoromethane, monochlorodifluoromethane, 1,1,2-
Trichlorotrifluoroethane, 1,2-dichlorotetrafluoroethane, 1,1-dichloro-2,2,2-trifluoroethane, monochloro-1,2,2,2-tetrafluoroethane, 1,1,1, Halogenated hydrocarbons of 2-tetrafluoroethane, 1,1-dichloro-1-fluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, etc.), dimethyl ether,
Examples thereof include ethers such as 2-ethoxyethanol and methyl tert-butyl ether, and ketones such as acetone, ethyl methyl ketone and acetylacetone. These foaming agents may be used alone or as a mixture.

Next, the molten resin to which the foaming agent has been added is extruded from an extruder into a low-pressure zone, whereby the foamed resin is obtained. Here, the extrusion is performed via a mold from an extruder, but it is preferable to rapidly expand the molten resin in the width direction in the mold. The deployment angle in rapid deployment is preferably 90 ° or more, and particularly preferably 120 ° or more. The obtained foam is preferably formed into an arbitrary shape such as a sheet or a plate while being cooled by a cooling roll whose surface temperature is adjusted to 100 ° C. or lower.

In the present invention, the extruded foam is stretched while cooling while the resin inside is softened, so that the molecular orientation in the plane direction measured by a microwave molecular orientation meter is cross-shaped. A crystalline polypropylene-based resin foam can be obtained. Measurement of the molecular orientation in the plane direction using a microwave molecular orientation meter is described in, for example,
The measurement can be performed using a microwave molecular orientation meter (MOA-2001A manufactured by KS System Co., Ltd.) described in Japanese Patent Publication No. 25 by the method described in the same publication. That is, in the range of 3.5 to 4.2 GHz, a microwave having a frequency at which the microwave transmission intensity is about 1/2 of the maximum value is set as a measurement wavelength, and the microwave is irradiated perpendicularly to the surface of the sample. The molecular orientation in the plane direction (the VD direction, that is, the direction perpendicular to the MD direction and the TD direction) can be measured. However, since the microwave molecular orientation meter described in this publication can measure only a sample thickness of up to 3.0 mm, a sample exceeding 3.0 mm is reduced to a thickness of about 2.0 mm (for example, a method of removing with a ham slicer). Use a sample of the sliced surface.

The measurement results are output as a graph. In the present invention, the inclination of the axis of the cross-shaped molecular orientation graph of the crystalline polypropylene-based resin foam may be any angle. Foam with such orientation is stretched
Due to the orientation, it has high strength and improved brittleness. Here, the cross-shaped shape does not indicate a strict meaning, but includes a shape in which the vertical axis and the horizontal axis intersect at an arbitrary angle. In addition, when the shape of the obtained graph is circular,
It indicates that the molecules are oriented uniformly in each direction or not at all. In addition, commercially available uniaxially stretched sheets and films become gourd-shaped graphs,
The biaxially stretched one is a gourd-shaped graph in which the axis of the stretched portion is inclined by 45 °.

The crystalline polypropylene resin foam of the present invention obtained by the above method preferably has a thickness of 1.0 to 30 mm, particularly preferably 1.5 to 20 mm. The density is preferably in the range of 0.025 to 0.7 g / cc, particularly preferably in the range of 0.05 to 0.5 g / cc.

[0016]

The present invention will be described below in more detail with reference to Examples and Comparative Examples.

Example 1 Hydrocerol HK (a mixture of citric acid and sodium hydrogen carbonate as a cell nucleating agent) was added to 100 parts by weight of a crystalline polypropylene resin: SD632 (propylene-ethylene block copolymer, manufactured by Montell). Boehringer
(Ingelheim Co., Ltd.) 0.2 parts by weight were previously mixed with a blender, and the mixture was fed to a foam extruder 1 (FIG. 1) in which a 90 mm first extruder and a 115 mm second extruder were connected. The mixture was supplied and melt-kneaded in a first extruder adjusted to a temperature of 150 to 230 ° C. Then the first
Normal butane as a foaming agent was pressed into the base resin at a ratio of 2.0 parts by weight from the tip of the second extruder.
Thereafter, the mixture was supplied to a second extruder adjusted to a temperature of 145 to 180 ° C, and the temperature of the mixture (resin) was adjusted to a temperature (165 ° C) suitable for foaming. The molten mixture containing the foaming agent was moved from the cylindrical mold 2 having an inner diameter of 16 mmφ to the mold 3 and rapidly developed in the mold 3 to a width of 600 mm (development angle 170 °). Then, by extruding from the mold 3 having a width of 600 mm and a slit of 0.5 mm into the atmosphere,
The molten mixture was foamed. Extruded foam 4
The surface was cooled and formed into a plate shape with a cooling roll 5 having a diameter of 40 mm (peripheral speed of 3.3 m / min) through which cooling water at 0 ° C. was passed.

The obtained foam has a thickness of 2.5 mm and a density of 2.5 mm.
0.18 g / cc, basis weight 450 g / m ^Two, Crystallinity 40
%, Puncture impact value 64 kgf · cm, bending strength 4.4 Mp
a and the 10% compressive strength was 0.44 Mpa. Note that
The crystallinity, puncture impact value, flexural strength and compressive strength are as follows:
Measured under conditions.

[Crystallinity] According to JIS K7122, the heat of crystallization is calculated from the result of the heat of crystallization measured by a differential scanning calorimeter (DSC), and the heat of crystallization is calculated by substituting the heat of crystallization into the following equation. Was.

PP crystallinity (%) = (heat of crystallization (mJ / m
g) /209.5) × 100 Measuring apparatus: Differential scanning calorimeter DSC200 type (manufactured by Seiko Instruments Inc.) Measurement start / end temperature: −40 ° C. to 220 ° C.−40 ° C.
220 ° C

[Punch Impact Value] Measured according to JIS P8134. Equipment: Impact piercing strength tester (Toyo Tester Co., Ltd.)
Test piece: (width) 150 x (length) 150 W x original thickness (m
m)

[Bending strength] Measured according to JIS K7203. Apparatus: Tensilon universal tester UCT-10T
(Orientec Co., Ltd.) Specimen: (width) 25 x (length) 100 x original thickness (mm) Test speed: 1.5 mm / min Distance between supports: 45 mm

[Compressive strength] Measured according to JIS K6767. Apparatus: Tensilon universal tester UCT-10T
(Made by Orientec Co., Ltd.) Test piece: (width) 50 x (length) 50 x (stack) 25 (m
m) Test speed: 10 mm / min

Further, as shown in FIG. 2, the molecular orientation of the obtained foam was measured with a device and a method described in JP-A-2-265725 by taking four samples in the TD direction. FIG. 3 shows the measurement results. As is clear from FIG. 3, the molecular orientation in the plane direction was a cross shape.

Example 2 A foam was produced in the same manner as in Example 1 except that the amount of normal butane injected was 3.0% by weight and the peripheral speed of the cooling roll was 2.5 m / min. The resulting foam has a thickness of 5.
0 mm, density 0.12 g / cc, basis weight 590 g / m ² ,
The crystallinity was 41%, the puncture impact value was 122 kgf · cm, the bending strength was 2.8 Mpa, and the 10% compression strength was 0.43 Mpa. FIG. 4 shows the molecular orientation in the plane direction measured in the same manner as in Example 1. As is clear from FIG. 4, the molecular orientations in the plane direction were all cross-shaped.

Comparative Example 1 The same molten mixture as in Example 1 was extruded into the atmosphere from a circular mold having a diameter of 80 mm and a slit of 0.5 mm, and the resulting tubular foam was placed along a cylindrical mandrel having an outer diameter of 380 mm. The plate was cut out at one point on the circumference with a cutter to obtain a foam. The obtained product has a thickness of 2.5 mm, a density of 0.18 g / cc and a basis weight of 4
50 g / m ² , crystallinity 43%, puncture impact value 16 kgf
・ Cm, bending strength 4.3 Mpa, 10% compression strength 0.3
It was 0 Mpa. FIG. 5 shows the molecular orientation in the plane direction measured by the same method as in Example 1. As is clear from FIG. 5, the molecular orientations in the plane direction were all elliptical.

Comparative Example 2 A foam was prepared in the same manner as in Comparative Example 1 except that the amount of normal butane was 3.0% by weight.

The obtained foam had a thickness of 5.0 mm, a density of 0.11 g / cc, a basis weight of 570 g / m ² , and a crystallinity of 39.
%, Puncture impact value 90 kgf · cm, bending strength 1.6 Mp
a, 10% compressive strength was 0.22 Mpa. FIG. 6 shows the molecular orientation in the plane direction measured in the same manner as in Example 1. As is clear from FIG. 6, the molecular orientations in the plane direction were all elliptical.

Table 1 summarizes the thickness, density, basis weight, crystallinity, puncture impact value, bending strength and 10% compressive strength of the products of Examples 1 and 2 and Comparative Examples 1 and 2.

[0030]

[Table 1]

As is clear from Examples 1 and 2 and Comparative Examples 1 and 2, if the molecular orientation in the plane direction is a cross shape, the polypropylene-based resin foam has excellent mechanical strength.

[0032]

The crystalline polypropylene resin foam having a cross-shaped molecular orientation according to the present invention is excellent in heat resistance, chemical resistance, oil resistance, etc., and furthermore has good mechanical strength and impact resistance. Has the property.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for producing a foam of Example 1.

FIG. 2 is a schematic view showing a measurement site of a molecular orientation in a plane direction.

FIG. 3 is a graph showing the molecular orientation in the plane direction of Example 1.

FIG. 4 is a graph showing the molecular orientation in the plane direction of Example 2.

5 is a graph showing the molecular orientation in the plane direction of Comparative Example 1. FIG.

FIG. 6 is a graph showing the molecular orientation in the plane direction of Comparative Example 2.

[Explanation of symbols]

 1. Extruder 2. Cylindrical type 3. Mold 4. Foam 5. Cooling roll 6. Pickup roll

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 105: 04 B29L 7:00 C08L 23:10

Claims (2)

[Claims] 1. A crystalline polypropylene-based resin foam characterized in that the molecular orientation in the plane direction measured by a microwave molecular orientation meter is cross-shaped. 2. Extrusion and foaming of a crystalline polypropylene resin containing a foaming agent, and stretching of the extruded foam while cooling it while the resin inside the foamed resin is softened. A method for producing a crystalline polypropylene-based resin foam, characterized in that a crystalline polypropylene-based resin foam having a cross-shaped measured molecular orientation is obtained.