JPH09249763A - Polypropylene resin foam particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low density, abundant in independent foams, and low shrinkage foam particle, without using a peroxide which requires caution in handling. SOLUTION: This polypropylene resin foam particle is obtd. by melting and kneading a base resin mainly comprising a polypropylene resin which has a Z average mol.wt. Mz of at least not less than 2.0×10<6> , a Mz/Mw(weight average mol.wt.) of not less than 3.0, and a mol.wt. curve (by gel permeation chromatograph) having a camel type bump showing the content of a branched polymer in the polymer region, a crosslinking additive, and a foaming agent, in an extruder, then by being foamed by pushed out of the extruder, and being cut.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel expanded polypropylene resin particle. More specifically, the present invention relates to expanded polypropylene resin particles used for producing various packaging materials and various product members.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of obtaining a foamed particle by melting a polypropylene resin by using an extruder, mixing a foaming agent, and extruding and cutting it from an extrusion die. (For example, Japanese Patent Publication No. 2-39367). However, according to this publication, only 20 times or less expanded polypropylene particles can be obtained. for that reason,
It is necessary to press the expanded beads several times and then expand the expanded beads to obtain a highly expanded expanded particle. It is considered that the reason why highly expanded foamed particles cannot be obtained is that the melt tension of the polypropylene resin during extrusion foaming is low.

Recently, a method of using a resin having a high melt tension in order to obtain highly expanded foamed particles has been proposed (JP-A-6-234878). However, even with this method, there is a problem that the foamed particles of 0.35 g / cm ³ or less are likely to be open cells and shrink. Furthermore, foamed particles of 0.23 g / cm ³ or less cannot be obtained by this method.

It has been conventionally known to chemically crosslink polypropylene resins, that is, to adjust the melt tension at the time of extrusion by using a peroxide and a crosslinking aid. However, since this method carries out a crosslinking reaction in an extruder, it is impossible to extrude due to a slight difference in the amount of peroxide depending on the extrusion conditions, which makes extrusion impossible. Is extremely difficult. Further, since peroxide is dangerous, there is a problem in that it requires careful handling.

[0005]

The inventors of the present invention have conducted various studies to solve the above-mentioned problems, and as a result, have found that a base resin containing a specific type of resin as a main component may contain a peroxide. The present inventors have found that the addition of a cross-linking aid in the absence of the compound can increase the melt tension at the time of extrusion foaming to obtain expanded particles having a low density, rich in closed cells, and less shrinkage, and the present invention has been completed.

Thus, according to the invention, the Z-average molecular weight M
A camel-type molecular weight distribution in which z is at least 2.0 × 10 ⁶ or more, Mz / Mw (weight average molecular weight) is 3.0 or more, and a curve is projected to indicate that the polymer contains a branched polymer. A base resin containing a polypropylene resin having a curve (according to gel permeation chromatograph) as a main component, a cross-linking aid and a foaming agent are melt-kneaded in an extruder, extrusion-foamed from the extruder, and cut. The resulting polypropylene-based resin expanded particles are provided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A Z-average molecular weight Mz is at least 2.0 × 10 ⁶ or more, Mz / Mw is 3.0 or more, and there is an extension of a curve indicating that a branched polymer is contained in the high molecular region. The reason why highly expanded foamed particles can be obtained by adding a crosslinking aid to a polypropylene resin having a camel-type molecular weight distribution curve in the absence of peroxide is as follows. This is probably due to the reason.

Compared with general polypropylene resins, camel polypropylene is, for example, JP-A-2-29.
As disclosed in Japanese Patent No. 8536, it is a resin having long chain branching manufactured by a very complicated process. Therefore, although it is excellent in foamability, it is considered that molecular cutting easily occurs. For example, as symbolized by an increase in melt flow index (hereinafter referred to as MI) due to an extrusion process, a camel-type polypropylene resin is extremely susceptible to deterioration due to heat or shear. From these facts, it is considered that the camel-type polypropylene resin has unstable radicals in the molecule due to its complicated manufacturing process, and thus is more deteriorated than general polypropylene resins.

The inventors of the present invention have developed a foaming property by mixing a crosslinking assistant with a base resin in the absence of a peroxide.
It has been found that a foam having excellent stability can be obtained. In the present invention, the crosslinking aid is considered to have a function of partially crosslinking the base resin or having a function of adjusting viscosity to prevent the MI from increasing. The method of measuring the gel permeation chromatograph (hereinafter referred to as GPC) performed in the present invention is as follows.

Measuring device: Waters, GPC 150-C type Measuring condition: Column KF-80M 2 bottles (SHODEX: Showa Denko KK) Column temperature 145 ° C. Injection temperature 145 ° C. Pump temperature 60 ° C. Solvent o-dichlorobenzene ( 1.0 ml / min) Scanning time 50 minutes Injection volume 400 μl The information obtained by this GPC is as follows. (1) Mn (number average molecular weight): The most basic average molecular weight obtained by measuring a physical property value directly related to the number of molecules of a polymer, and depends on the total number of molecules. (2) Mw (weight average molecular weight): The average molecular weight obtained when the measured physical properties are directly related to the weight of the polymer, which is the root-mean-square of the molecular weight, and depends on the higher polymerization degree molecule than Mn. (3) Mz (Z average molecular weight): The highest average molecular weight, which is the cube of the molecular weights.

The polypropylene resin contained as the main component in the base resin used in the present invention is a polymer having Mz of at least 2.0 × 10 ⁶ and Mz / Mw of 3.0 or more. The molecular weight distribution curve by GPC of this polypropylene resin is always a shape with an overhang in the high molecular weight region. When this is illustrated, as shown by curve A in FIG.
It does not show a monotonically decreasing curve on the polymer side from the peak of the molecular weight, and has a curve with three or more inflection points on the whole curve, and has a camel-back shape. A polypropylene resin having such a molecular weight distribution curve is referred to as a camel polypropylene resin in the present invention. On the other hand, the molecular weight distribution curve of the polypropylene-based resin that gives insufficient foamability is a simple chevron shape, which is a monotonically decreasing curve in the high molecular weight region as shown by the curve B. That is,
The camel-type molecular weight distribution shows that most of the polypropylene resin is linear, but a component with a high molecular weight has many branches. The camel-type polypropylene-based resin may be a camel-type homopolypropylene resin (for example, PF-814 manufactured by Highmont), or a block or random copolymer with ethylene (for example, SD-632 manufactured by Highmont).

The base resin used in the present invention contains the camel-type polypropylene resin as a main component. In the present invention, the main component is at least 60 with respect to the base resin.
It is meant to include at least wt. Therefore, the base resin may consist of a camel-type polypropylene resin alone or may further contain another resin, for example, an olefin resin.

As the olefin resin, general polypropylene resin (non-camel type polymer), ethylene-propylene block copolymer, ethylene-propylene random copolymer, high density polyethylene, low density polyethylene, linear chain resin Examples thereof include low-density polyethylene, linear ultra-low-density polyethylene, and ethylene-α-olefin copolymer.

Next, a crosslinking aid is added to the base resin in order to increase the melt tension and obtain good expanded particles having a high closed cell ratio. Specific examples of the crosslinking aid include polyfunctional monomers such as divinylbenzene, triallyl isocyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, tetramethylolmethane triacrylate, ethylene glycol dimethacrylate, zinc diacrylate; quinone. Oxime-based compounds such as dioxime, benzoquinone dioxime, p, p'-dibenzoylquinone dioxime;
Examples include maleimide compounds such as N, N-m-phenylene bismaleimide. Particularly preferred crosslinking aids are oxime compounds.

The crosslinking aid is preferably mixed in the range of 0.01 to 5 parts by weight with respect to 100 parts by weight of the base resin. If it is less than 0.01 parts by weight, it will not be effective as a cross-linking aid, and if it exceeds 5 parts by weight, it will exceed the necessary amount, and defective dispersion will occur, resulting in defects such as impairing the appearance of the molded product. As the foaming agent that can be used in the present invention, heat-decomposable solid compounds, volatile liquids or gases, inert gases, etc. can be used alone or in combination.

Specific examples of the heat-decomposable solid compound include azodicarbonamide, dinitrosopentamethylenetetramine and the like. Examples of the volatile liquid or gas include saturated aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane and neopentane, saturated aliphatic hydrocarbons such as cyclopentane and cyclohexane, trichlorofluoromethane. , Halogenated hydrocarbons such as dichlorotetrafluoroethane, ethers such as dimethyl ether, ketones such as acetone, alcohols such as methanol and ethanol, water and the like. In addition, examples of the inert gas include carbon dioxide and nitrogen.

Further, a foaming aid and a nucleating agent may be added. Examples of the foaming aid include fine powder talc, silica,
A foam nucleating agent such as a mixture of sodium hydrogen carbonate and citric acid can be used. In addition, pigments, antistatic agents, flame retardants, ultraviolet absorbers, antioxidants and the like may be mixed. In the present invention, known techniques can be used as they are for melt-kneading and extrusion foaming. For example, as the extruder, a tandem extruder of a type in which two extruders are connected in series is used, and a foaming agent is pressed into a base resin containing a crosslinking aid by the first extruder to form a foamable melt. And in a second extruder, cool the melt to a temperature suitable for foaming, then
The resin is extruded and foamed from a nozzle die having holes formed therein. Then, the foamed resin is cut into an arbitrary size (for example, by a pelletizer) to obtain polypropylene-based resin foamed particles.

The expanded polypropylene resin particles of the present invention may have a shape such as a sphere, an ellipse or a pellet. Further, the expanded particles are preferably 0.010 to
0.050 g / cm ³ , more preferably 0.015
It has a density of 0.028 g / cm ³ . Density 0.01
If less than 0 g / cm ^3, unpreferably poor formability, higher than 0.050 g / cm ^3, since the high magnification of a molded article can not be obtained undesirably.

Further, the expanded particles preferably have a maximum particle size of 20 mm or less. When the maximum particle size is larger than 20 mm, it is not preferable because the foamed particles are blocked when being filled in the molding die, and it becomes difficult to reproduce the shape of the molding die. At present, the minimum diameter of expanded particles is about 1 mm. Further, the expanded beads preferably have a closed cell ratio of 50 to 100%.

The expanded polypropylene resin particles of the present invention can be produced, for example, by filling a molding die having a desired shape and heating with steam or the like. The molded body can be manufactured by using a known method.

[0021]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 70 parts by weight of a homopolypropylene resin (PF-814, manufactured by Highmont Co.) having a camel-type molecular weight distribution curve, and an ethylene-propylene random copolymer (S-13).
1, manufactured by Sumitomo Chemical Co., Ltd.), 2.0 parts by weight of trimethylolpropane trimethacrylate as a cross-linking aid and 0.5 parts by weight of talc as a nucleating agent are premixed with 30 parts by weight, and a caliber of φ50-φ65 mm Was fed to the extruder.

From the center of the first extruder, 20 parts by weight of butane gas as a foaming agent was injected and melt-kneaded. The resin was transferred from the first extruder to the second extruder, extruded and foamed in a strand shape from a mold kept at a temperature (158 ° C.) most suitable for foaming in the second extruder, and cut with a pelletizer. . The mold has a diameter of 0.7 mm, a hole interval of 10 mm, and the number of holes is 6.
The one having 0 was used.

The obtained expanded particles have an average diameter of 3.0 mm,
The average length was 2.5 mm, the density was 0.028 g / cm ³ , and the closed cell rate was 83%. The maximum particle size is 3.0 mm
Met. The foamed particles were placed in 3 Kg / cm ² of nitrogen for 5 times.
After leaving for an hour, the inside is immediately 300 x 300 x 60 m
It was filled in a metal mold having a size of m and molded with water vapor of 2.5 kg / cm ² . The obtained molded product was a completely fused molded product and had a density of 0.022 g / cm ³ .

Example 2 80 parts by weight of an ethylene-propylene block copolymer (SD-632, manufactured by Highmont) having a camel-type molecular weight distribution curve, and an ethylene-propylene block copolymer (AH585A, manufactured by Sumitomo Chemical Co., Ltd.) Cross-linking aid, zinc diacrylate 0.5 part by weight, hydrocerol HK (made by Boehringer) as a nucleating agent, relative to 20 parts by weight
0.05 parts by weight are mixed in advance and the diameter is φ50-φ65 mm.
Was fed to the extruder.

From the center of the first extruder, 20 parts by weight of butane gas as a foaming agent was injected and melt-kneaded. The resin was transferred from the first extruder to the second extruder, and extruded and foamed in a strand shape from a mold kept at a temperature (158 ° C.) most suitable for foaming in the second extruder, and then exited from the mold. Cut with a cutter blade that has a rotating mechanism in place. The mold used had a diameter of 0.7 mm, a hole interval of 10 mm, and a number of holes of 60.

The obtained expanded particles have an average diameter of 3.0 mm,
The average length was 2.5 mm, the density was 0.021 g / cm ³ , and the closed cell rate was 72%. The maximum particle size is 3.5 mm
Met. The inside of the foamed particles is 500 × 500 × 50
It was placed in a metal mold having a size of mm, compression-filled with 4.2 Kg / cm ² of nitrogen, and then molded with 3.5 Kg / cm ² of steam. The obtained molded product was a completely fused molded product and had a density of 0.028 g / cm ³ .

Examples 3 to 6 The same conditions as in Example 2 were carried out except that the base resin and the crosslinking aid shown in Table 1 were used. Comparative Example 1 The procedure was carried out under the same conditions as in Example 5, except that the base resin shown in Table 1 was used and no crosslinking aid was used. Comparative Example 2 The procedure was carried out under the same conditions as in Example 3 except that the base resin shown in Table 1 was used and no crosslinking aid was used. Comparative Example 3 It was carried out under the same conditions as in Example 3 except that the base resin, the crosslinking aid and the peroxide described in Table 1 were used.

Tables 1 and 2 show the densities of the particles of Examples 1 to 6 and Comparative Examples 1 to 3, the closed cell ratio, the maximum particle size, and the appearance of the obtained molded products.

[0029]

[Table 1]

[0030]

[Table 2]

In the table, PF-814 and SD-632 are manufactured by Highmont Co., S-131 (propylene-ethylene random copolymer), AH-585A and Esprene NO4.
16 (ethylene-butene copolymer) is a product of Sumitomo Chemical Co., Ltd., M
H-8 (homopolypropylene resin) is manufactured by Mitsubishi Chemical Corporation. Further, “part” means part by weight. Further, the appearance ∘ means that there is no shrinkage and there is sticking on the surface, Δ means that the surface has wrinkles due to shrinkage, and × means that the shrinkage is severe.

From Tables 1 and 2, in the absence of peroxide,
It can be seen that the use of the crosslinking aid makes it possible to obtain expanded particles capable of imparting a good appearance.

[0033]

Industrial Applicability The expanded polypropylene resin particles of the present invention have a Z-average molecular weight Mz of at least 2.0 × 10 ⁶ and a Mz / Mw (weight average molecular weight) of 3.0 or more, and have a high molecular weight range. A base resin mainly composed of a polypropylene resin having a camel-type molecular weight distribution curve (by gel permeation chromatograph) with a curve showing that it contains a branched polymer, a crosslinking aid and a foaming agent. It is obtained by melt-kneading in an extruder, extrusion foaming from the extruder, and cutting. Therefore, it is possible to obtain expanded particles having a low density, rich in closed cells, and less shrinkage.

Further, melt kneading in the absence of peroxide,
It is not necessary to use a peroxide, which is problematic in that it must be handled with care because it is extruded and foamed. Therefore, the expanded particles can be easily obtained. Furthermore, since the expanded beads have a density of 0.010 to 0.050 g / cm ³ , expanded beads capable of providing a molded product having excellent heat insulating properties and cushioning properties can be obtained.

Further, since the expanded particles have the maximum particle size of 20 mm or less, blocking is less likely to occur when the expanded particles are filled in the molding die, and the shape of the molding die can be reproducibly molded.

[Brief description of drawings]

FIG. 1 is a diagram showing the molecular weight distributions of a camel polypropylene resin and other polypropylene resins.

Claims (4)

[Claims] 1. The method of claim 1, wherein the Z-average molecular weight Mz is at least 2.0 ×
Mz / Mw (weight average molecular weight) of 10 ⁶ or more and 3.0
Above, and a base resin containing a polypropylene resin as a main component, which has a camel-type molecular weight distribution curve (by gel permeation chromatograph) with a curve protrusion indicating that the polymer contains a branched polymer, Expanded polypropylene resin particles obtained by melt-kneading a crosslinking aid and a foaming agent in an extruder, extrusion-foaming from the extruder, and cutting. 2. The particles according to claim 1, wherein the melt-kneading in the extruder is carried out in the absence of peroxide. 3. Expanded particles are from 0.010 to 0.050 g
Particles according to claim 1 or 2 having a density of / cm ³ . 4. The particle according to claim 1, wherein the expanded particle has a maximum particle size of 20 mm or less.