JPH054416B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a masterbatch containing a blowing agent, and in particular to a masterbatch suitable for producing extrusion molded products of polyolefin foam, particularly foam insulated cables. [Prior Art] Extrusion molding methods for synthetic resin foams are widely used in various fields, and are also applied, for example, to the manufacture of foam insulated cables and high frequency cables. In the production of synthetic resin foams by conventional extrusion, a foamable composition containing a blowing agent in a small amount of several parts by weight or less per 100 parts by weight of synthetic resin is used. Uniformly mixing such a small amount of blowing agent into a large amount of synthetic resin is disadvantageous in terms of mixing time and power consumption, so the inventors of the present invention have previously proposed the method disclosed in Japanese Patent Application Laid-Open No. 55-62935. In the publication, we proposed a method using a composition containing a synthetic resin and a blowing agent at a high concentration, that is, a masterbatch. This master batch only needs to be fed to the extruder hottuber at a predetermined ratio with the biosynthetic resin that does not contain a foaming agent, and is kneaded with the biosynthetic resin by the kneading action of the extruder, making it the target of extrusion foaming. It has the advantage that it is not necessary to mix the entire amount of the synthetic resin with the blowing agent. However, according to the inventors' continued research, it was found that the dimensions and shape of the masterbatch containing the foaming agent are extremely important in order to stably produce high-quality foamed molded products, especially foamed polyolefin insulated wires. did. In other words, if the master batch pellets are too large, they will not mix sufficiently with the biosynthetic resin pellets in the extruder, making it difficult to obtain a uniformly foamed molded product.Especially when manufacturing insulated cables, the capacitance of the foamed insulation layer will increase. and the outer diameter fluctuates greatly.
On the other hand, if the master batch pellets are too small, it is difficult to obtain pellets with uniform dimensions, and due to the irregular dimensions, there is a problem that the falling speed of each pellet in the hopper, that is, the feeding speed becomes non-uniform. If the feeding rate is uneven, it is natural that a product with a constant degree of foaming cannot be obtained. When mass producing foamed synthetic resin molded products, the masterbatch is usually transported close to the extruder by pneumatic transportation, but if the masterbatch pellets are square pellets obtained by shredding a sheet of the masterbatch composition, the air During transportation, pellets collide with each other or with the wall of the pellet transport pipe, which tends to cause the pellets to come off and form masterbatch powder. Pellet containing powder suffers from the same problems as irregularly sized pellets discussed above. Although spherical pellets are most preferable in terms of difficulty in forming powder, it is extremely difficult to mass-produce spherical pellets at low cost. [Problems to be Solved by the Invention] The problems to be solved by the present invention are to solve the above-mentioned difficulties of the conventional masterbatch. The object of the present invention is to develop a masterbatch that can be easily manufactured with uniform dimensions and that can be uniformly mixed with biosynthetic resin pellets in an extruder. [Means for Solving the Problems] The above problems can be solved by using a polyolefin masterbatch containing a blowing agent that has specific dimensions and shapes. That is, the present invention is a cut extrudate of a composition comprising a polyolefin and a blowing agent of 10 to 100 parts by weight per 100 parts by weight of the polyolefin, and has a maximum outer diameter of 1.0 to 2.5 mm and a length of 1.0 mm. This relates to a masterbatch characterized by a diameter of ~3.0 mm. [Structure and operation of the invention] Commercially available polyolefine pellets (hereinafter referred to as raw polyolefine pellets) have an average diameter of about 2 to 5 mm, although they vary somewhat depending on the manufacturer. If so, even if it is mixed with the raw polyolefin impellets and charged into the extruder hopper, no problematic separation will occur between the two while falling in the hopper. In addition, since the size of the masterbatch is smaller than that of conventional products, it is extruded after being extremely uniformly kneaded with the raw polyolefin pellets by the kneading action provided by a normal extruder. Therefore, by using the master batch pellets of the present invention, it is possible to produce high quality foam insulated wires with little variation in capacitance and outer diameter. Furthermore, the masterbatch of the present invention is easy to manufacture because it is made by extruding a composition consisting of polyolefin and a blowing agent into strands and then cutting them, and although the cut surfaces have some edges, the overall shape of the extrudate is It has a characteristic roundness. Therefore, compared to conventional square pellets, there are fewer corners that are easily removed, so powder is less likely to be generated even when the pellets are transported by air, and even if powder is generated, the amount is small and does not pose a problem in practice. A wide variety of blowing agents are used as the blowing agent constituting the masterbatch of the present invention, such as azodicarbonamide, 4,4'-oxybis(benzenesulfonyl hydrazide), azobisisobutyronitrile, dinitrosopentamethylenetetramine,
Specific examples include paratoluenesulfonyl hydrazide and sodium bicarbonate, and preferred examples include azodicarponamide, 4,4'-oxybis(benzenesulfonylhydrazide), and mixtures thereof. As the base polyolefin used in the masterbatch of the present invention, any of those conventionally used in this field can be used, such as various polyolefins and various copolymers of olefin and other monomers. . Preferred specific examples include various polyethylenes of extremely low density to high density, polypropylene, polybutene-1, poly-4-
Homopolymers or substantially homopolymers of olefins such as methylpentene-1, or copolymers of olefins and vinyl acetate, ethyl acrylate, etc., such as ethylene-propylene copolymers, poly-4-methylpentene -1 copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, and the like. Among these, various polyethylenes having extremely low density to high density are particularly preferred. As polyolefin in masterbatch,
Usually, the same polyolefin as the constituent material of the desired polyolefin foam is used, but a different type of polyolefin may be used if necessary. The blending ratio of the blowing agent in the masterbatch is 10 to 100 parts by weight per 100 parts by weight of the polyolefin. If it is less than 10 parts by weight, the original function as a masterbatch will be poor, while if it is more than 100 parts by weight, the kneading properties of the polyolefin and the blowing agent will be poor, and the resulting kneaded composition will be brittle, so that its extrudates There are problems in that powder is easily generated when shredding, or it is easy to break or become powder during air transportation.
Therefore, the blending ratio of the blowing agent is preferably 15 to 50 parts by weight. The master batch of the present invention has a maximum outer diameter of 1.0 to 2.5
mm, extruded and cut pellets with a length of 1.0 to 3.0 mm are essential. Square pellets have the problem of easily generating powder as mentioned above, but even if they are extruded or cut pellets, pellets with a maximum outer diameter larger than 2.5 mm and a length longer than 3.0 mm may have excessive pellet dimensions. Therefore, it is difficult to mix uniformly with raw polyolefin impellets in an extruder, making it difficult to produce high-quality foam molded products. On the other hand, pellets with a maximum outer diameter smaller than 1.0 mm and a length shorter than 1.0 mm have a difference in falling speed in the hopper compared to commercially available raw polyolefin pellets due to the small pellet size, and pellet separation is difficult. In addition to the problems that arise, such undersized pellets are difficult to manufacture because masterbatch compositions generally do not have good extrudability. That is, to produce undersized pellets, the masterbatch composition is
Although it is necessary to extrude at an outer diameter of less than 1.0 mm, the extrusion processability of the composition is poor, so continuous extrusion is not possible and the composition is often cut. Therefore, the preferred dimensions of the masterbatch of the invention are a maximum outer diameter of 1.5 to 2.5 mm and a length of 1.5 to 2.5 mm, particularly a maximum outer diameter of 1.5 to 2.0 mm and a length of 1.9 to 2.5 mm. The masterbatch of the present invention may contain various conventional additives such as pigments, flame retardants, anti-aging agents, fillers, etc., if necessary. When the pigment is blended into the masterbatch, the amount thereof is about 5 to 200 parts by weight, preferably about 10 to 100 parts by weight, per 100 parts by weight of the polyolefin. Alternatively, the amount of the blowing agent is about 40 to 400 parts by weight, preferably about 70 to 200 parts by weight, per 100 parts by weight of the pigment, and the amount of polyolefin is about 40 to 300 parts by weight, per 100 parts by weight of the total amount of the pigment and the blowing agent. The masterbatch of the present invention can be easily manufactured by extruding the above-described composition into strands having a circular or oval cross section and cutting the strands in water or in air. Even if an extruded product of a polyolefin composition has some corners on its surface, the corners will become rounded within a short time after extrusion. It may be extruded into triangles or the like and then cut. However, those extruded and cut into strands with a circular cross section are particularly preferred. When extrusion molding is performed using the masterbatch of the present invention, the masterbatch and raw polyolefin impellets are mixed at a predetermined mixing ratio (for example, the foamed polyolefin contained in the mixture of the masterbatch and raw polyolefin impellets is The composition can be extruded and foamed by a conventional method by blending the agent in an amount of about 0.25 to 5 parts by weight, preferably about 0.5 to 3.0 parts by weight, per 100 parts by weight of the polyolefin. In the present invention, it is preferable to use the following means during this extrusion foaming. That is, as a weighing means for weighing the masterbatch, a gravimetric scale is used in place of the volumetric scale that has been commonly used in the past. This effectively prevents fluctuations in the blending ratio with the raw polyolefin pellets due to fluctuations in the apparent specific gravity of the masterbatch pellets, allowing stable extrusion over a long period of time. In addition, the hopper used to feed the extruder should preferably have a smaller capacity than conventional hoppers, and should preferably have a cylindrical shape close to the diameter of the extruder. By using such a hopper, it is possible to further reduce the difference in falling speed between the masterbatch and the raw polyolefin impellets on the way to the extruder. [Example] The present invention will be described below with reference to Examples. However, parts indicate parts by weight. Examples 1 to 8, Comparative Examples 1 to 3 100 parts of polyethylene with a density of 0.95 and 25 parts of azodicarbonamide were thoroughly mixed for 20 minutes using two rolls kept at 130°C, and then heated to 140°C to form a thin string. Extrusion Cylindrical masterbatch pellets of Examples and Comparative Examples shown in Table 1 were produced by cutting in water. Each masterbatch pellet and raw polyethylene pellets with a density of 0.96 (average particle size: 3.5mm) were weighed at a ratio of 20 parts of raw polyethylene pellets to 1 part of masterbatch pellets, and the pellets were heated to a barrel temperature of 200.
℃, L/D 24 extruder hopper at a rate such that the residence time in the hopper is approximately 5 minutes, and extruded onto a conductor with an outer diameter of 0.65 mm to foam, with a foaming degree of 25% and a thickness of
A 0.15mm foam insulated wire was manufactured. However, the size of the lower outlet of the hopper used at this time was almost the same as the diameter of the extruder. The following evaluation was performed for each Example and Comparative Example, and the results are shown in Table 1. Ease of manufacturing masterbatch pellets: When manufacturing the masterbatch pellets described above, continuous extrusion of thin string-like extrudates and cutting in water were extremely easy. Those that were able to be continuously extruded and cut fairly well were evaluated as good, those where the thin string-like extrudates sometimes broke and continuous extrusion could not be performed were evaluated as acceptable, and those where the thin string-like extrudates frequently broke were judged as unacceptable. Separability of pellets in the extruder hopper: Separation of masterbatch pellets and raw polyethylene pellets in the hopper changes the amount of blowing agent supplied, and the degree of foaming of the extrudate therefore increases. Capacity changes over time. Therefore, the smaller the variation in capacitance over time is, the lower the pellet separation property is, so the foam insulating layer with a capacitance variation of less than 1% over 180 minutes is excellent, and those with a capacitance variation of 1% or more and less than 2% are excellent. Excellent, 2% or more and less than 3% is good, 3% or more and less than 5% is acceptable, and 5% or more is bad. Uniform kneading of pellets in the extruder: When the masterbatch pellets and raw polyethylene pellets are kneaded uniformly in the extruder, the capacitance and outer diameter of the foamed insulating layer become stable, and conversely, the kneading becomes more stable. Inadequacy causes their properties to constantly fluctuate. Therefore, the foam insulating layer should have a capacitance variation of less than 1% and an outer diameter variation of less than 0.005 mm for 10 minutes, and a capacitance variation of 1% or more and less than 1.5% and an outer diameter variation of less than 0.005 mm. Good if the capacitance fluctuation is 1.5% or more and less than 2%, and outer diameter fluctuation is 0.01mm or more and less than 0.015mm, and capacitance fluctuation is 2% or more. Those with a capacitance variation of 2.5% or more and an outer diameter variation of 0.015 mm or more and less than 0.02 mm were considered acceptable, and those with a capacitance variation of 2.5% or more and an outer diameter variation of 0.02 mm or more were unacceptable. In the table below, master batch pellets are indicated as MBP.

[Table] Comparative Example 4 100 parts of polyethylene with a density of 0.95 and 25 parts of azodicarbonamide were thoroughly mixed for 20 minutes using two rolls kept at 130°C, then sheeted out at 3.0 mm, and this sheet was pelletized at room temperature. do
Approximately square masterbatch pellets of 3.0 mm square were manufactured. Using this pellet, a foamed insulated wire having a foam thickness of 0.15 mm was manufactured in the same manner as in Example 1. The separation of the pellets in the extruder hopper of this comparative example was excellent, and the pellets could not be uniformly kneaded in the extruder. Example 9 A product with an outer diameter of 1.8 mm and a length of
A 2.2 mm cylindrical master batch pellet was obtained. These pellets and raw polyethylene pellets with a density of 0.92 (average particle size: 4.5 mm) were weighed at a ratio of 20 parts of raw polyethylene pellets to 1 part of masterbatch pellets, and the barrel temperature was 160°C. D24
The mixture was fed into the hopper of an extruder at a rate such that the residence time in the hopper was about 5 minutes, and the foam was extruded onto a conductor with an outer diameter of 0.65 mm to produce a foamed insulated wire with a foaming degree of 25% and a thickness of 0.15 mm. The ease of producing the masterbatch pellets of this example was excellent, the separability of the pellets in the extruder hopper was excellent, and the uniform kneading of the pellets in the extruder was also excellent. Comparative Example 5 Using the masterbatch composition used in Example 9, the outer diameter was 3.5 mm and the length was prepared in the same manner as in Example 9.
Obtain 3.0 mm cylindrical master batch pellets,
A foam insulated wire with a foam thickness of 0.15 mm was produced in the same manner as in Example 9. The masterbatch pellets of this comparative example were easy to manufacture, the pellets had excellent separability in the extruder hopper, and the pellets were not uniformly kneaded in the extruder. Example 10 A ratio of 16 parts of raw polyethylene pellets (average particle size: 2 to 5 mm) having a density of 0.96 to 1 part of the masterbatch pellets of Example 4 was measured by weight, and the barrel temperature was 205°C. ／Feed it to the hopper of the D24 extruder, extrude it onto a 0.5φmm conductor, and foam it.
At the same time, colored polyethylene was coated on the foam layer using another extruder to produce a two-layer foam electric wire having a foam layer-colored solid layer (foam layer 0.15 mm, solid layer 0.03 mm). The obtained wire has no pinholes, no fluctuations in capacity or outside diameter during wire manufacturing, has a good appearance, and has excellent electrical properties.

Claims (1)

[Scope of Claims] 1. Cylindrical pellets obtained by cutting an extrudate of a composition comprising a polyolefin and 10 to 100 parts by weight of a blowing agent per 100 parts by weight of the polyolefin,
A master batch characterized by a maximum outer diameter of 1.0 to 2.5 mm and a length of 1.0 to 3.0 mm. 2. The masterbatch according to claim 1, wherein the polyolefin is polyethylene and is a cylindrical pellet having an outer diameter of 1.5 to 2.0 mm and a length of 1.9 to 2.5 mm.